Short course in Engineering Graphics
Section 2. IMAGE OF PARTS CONNECTIONS
There are detachable and permanent connections of parts. Detachable connections include those that allow disassembly and reassembly of the connected parts without destruction or damage. These include, for example, connections made using a bolt and nut.
One-piece connections include connections of parts with a rigid mechanical connection that remains throughout their entire service life. Disassembly of such connections is impossible without destruction or damage to the parts themselves or the elements connecting them. One-piece connections include, for example, connections between parts by welding, rivets, and soldering.
In turn, detachable connections are divided into movable, allowing movement of one part relative to another, and stationary, in which parts cannot move one relative to another. An example of a movable connection of parts could be the connection of a movable nut with a support screw of a lathe, and a fixed connection would be the connection of parts with a screw.
There are also groups of special connections, which include connections of parts in machine transmissions, for example connections of gear wheels. This also includes connecting parts using springs, when after removing the load the parts must be returned to their original position.
When making connections of parts in drawings, their full, simplified or conditional images are used. Sometimes (for example, when denoting welding, soldering, etc.) additional symbols are used.
Currently, detachable connections have become widespread in mechanical engineering: threaded, gear (spline), keyed, pin, cotter pin, wedge, and articulation connections.
Detachable connections of machine parts made using threads have become widespread in modern mechanical engineering. A threaded connection can ensure relative immobility of parts or movement of one part relative to another. The main connecting element in a threaded connection is the thread.
carved is a surface formed by the helical movement of a flat contour along a cylindrical or conical surface. In this case, a helical protrusion of the corresponding profile is formed, limited by helical and cylindrical or conical surfaces (Fig. 2.2.1, a).
Threads are classified according to the shape of the surface on which it is cut (cylindrical, conical), according to the location of the thread on the surface of the rod or hole (external, internal), according to the shape of the profile (triangular, rectangular, trapezoidal, round), purpose (fastening, fastening and sealing , running, special, etc.), the direction of the helical surface (left and right) and the number of passes (single-start and multi-start).
All threads are divided into two groups: standard and non-standard; For standard threads, all their parameters are determined by standards.
The main thread parameters are determined by GOST 11708-82. The thread is characterized by three diameters: external d (D), internal d1 (D1) and middle d2 (D2).
The diameters of the external thread are designated d, d\, d2, and the diameters of the internal thread in the hole are D, D1 and D2.
The outer diameter of the thread d (D) is the diameter of an imaginary cylinder described around the tops of the external thread or the valleys of the internal thread. This diameter is decisive for most threads and is included in the thread designation.
Profile thread - the contour of the thread section with a plane passing through its axis (Fig. 2.2.1, 2.2.2).
Profile angle thread - the angle between the sides of the profile (Fig. 2.2.2).
Step thread P - the distance between adjacent sides of the same name of the profile in the direction parallel to the thread axis (Fig. 2.2.1).
Thread stroke t is the distance between the nearest identical sides of a profile belonging to the same screw surface in a direction parallel to the thread axis (Fig. 2.2.1). In a single-start thread (Fig. 2.2.1, a) the stroke is equal to the pitch, and in a multi-start thread (Fig. 2.2.1, b) - the product of the pitch P and the number of starts n(t = lP).
In Fig. 2.2.3, a - thread length l, thread length with full profile l1.
Escape thread - a section of an incomplete profile in the zone of transition of the thread into the main part of the object lз.
Falsehood thread l4 - the size of the unthreaded part of the surface between the ends of the rung and the supporting surface of the part.
Undercut thread /2 includes thread run-out and under-run. To eliminate runaway or undercut threads, perform groove b (Fig. 2.2.3, b).
To make it easier to screw in a threaded rod, a conical chamfer is made at the end of the thread at an angle of 45° (Fig. 2.2.3, b).
Let's look at standard general purpose threads.
Thread metric is the main fastening thread. This is a single-start thread, mostly right-handed, with large or small pitch. The metric thread profile is an equilateral triangle. The projections and valleys of the thread are blunted (Fig. 2.2.4) (GOST 9150-81).
Thread pipe cylindrical has a profile in the form of an isosceles triangle with an apex angle of 55° (Fig. 2.2.5), the peaks and valleys are rounded. This thread is used in pipelines and pipe connections (GOST 6351-81).
Thread trapezoidal serves to transmit movement and effort. The profile of a trapezoidal thread is an isosceles trapezoid with an angle between the sides of 30° (Fig. 2.2.6). For each diameter, the thread can be single-start or multi-start, right-handed or left-handed (GOST 9484-81).
Thread stubborn has a profile of an unequal trapezoid (Fig. 2.2.7). The profile depressions are rounded and there are three different pitches for each diameter. Serves to transmit movement with large axial loads (GOST. 10177-82).
Thread round for bases and sockets, for safety glasses and lamps, for sanitary fittings (GOST 13536-68) has a profile obtained by pairing two arcs of the same radius (Fig. 2.2.8) (GOST 13536-68).
Thread conical inch with profile angle 60° (GOST 6111-52) is used for hermetic connections in pipelines of machines and machines; cut on a conical surface with a taper of 1: 16 (Fig. 2.2.9).
Conical pipe thread has a profile similar to the profile of a cylindrical pipe thread; used in valves and gas cylinders. It is possible to connect pipes having a conical thread (taper 1: 16) with products having a cylindrical pipe thread (GOST 6211-81).
Special threads are threads with a standard profile, but different from the standard diameter or thread pitch, and threads with a non-standard profile.
Non-standard threads - square and rectangular(Fig. 2.2.10) - are manufactured according to individual drawings, on which all thread parameters are specified.
Thread image in the drawing is carried out in accordance with GOST 2.311-68. On the rod, the threads are depicted with solid main lines along the outer diameter and solid thin lines along the inner diameter. In Fig. 2.2.11, a shows the thread on the cylinder, and in Fig. 2.2.11, b - on a cone.
In the hole, the threads are depicted with solid main lines along the internal diameter and solid thin lines along the outer diameter. In Fig. 2.2.12, and the thread is shown in a cylindrical hole, and in Fig. 2.2.12, b - conical.
In images obtained by projecting a threaded surface onto a plane perpendicular to its axis, a continuous thin line is drawn with an arc 3/4 of the circumference, open anywhere, but not ending at the axes. When depicting a thread, a solid thin line is drawn at a distance of at least 0.8 mm from the main line and no more than the thread pitch. The visible thread boundary is drawn as a solid base line at the end of the full thread profile to the line of the outer diameter of the thread. The thread run-out is depicted as a solid thin line, as shown in Fig. 2.2.13.
Chamfers on a threaded rod or in a threaded hole that do not have a special structural purpose are not depicted in projection onto a plane perpendicular to the axis of the rod or hole. A solid thin line of the thread image should intersect the chamfer boundary line (Fig. 2.2.13, 2.2.14). Hatching in sections and sections is brought to a solid main line.
A thread with a non-standard profile is depicted as shown in Fig. 2.2.15, with all dimensions and additional data with the addition of the word “thread”.
In threaded connections, the thread is conventionally drawn on the rod, and in the hole - only that part of the thread that is not covered by the rod (Fig. 2.2.16).
The thread designation includes: thread type, size, thread pitch and stroke, tolerance range, accuracy class, thread direction, standard number.
The type of thread is conventionally designated:
M - metric thread (GOST 9150-81);
G - cylindrical pipe thread (GOST 6357-81);
Tg - trapezoidal thread (GOST 9484-81);
S - persistent thread (GOST 10177-82);
Rd - round thread (GOST 13536-68);
R - external conical pipe (GOST 6211-81);
Rr - internal conical (GOST 6211-81);
Rp - internal cylindrical (GOST 6211-81);
K - conical inch thread (GOST 6111-52).
Size conical threads and cylindrical pipe threads are conventionally designated in inches (1" = 25.4 mm); for all other threads, the outer diameter of the thread is indicated in millimeters.
Step threads are not indicated for metric threads with coarse pitch and for inch threads; in other cases it is indicated. For multi-start threads, the thread designation includes the thread lead, and the pitch is indicated in parentheses.
Direction threads are indicated for left-hand threads (LH) only.
The tolerance field and thread accuracy class may not be indicated on training drawings.
Examples of thread designations:
M 30 - metric thread with an outer diameter of 30 mm and a large thread pitch;
M 30 x 1.5 - metric thread with an outer diameter of 30 mm, fine pitch 1.5 mm;
G 1 1/2-A - cylindrical pipe thread with size 1 1/2", accuracy class A;
Tg 40x6 - single-start trapezoidal thread with an outer diameter of 40 mm and a pitch of 6 mm;
Tg 20 x 8 (P4) - double-start trapezoidal thread with an outer diameter of 20 mm, a stroke of 8 mm and a pitch of 4 mm;
S 80 x 10 - single-start thrust thread with an outer diameter of 80 mm and a pitch of 10 mm;
S 80 x 20 (P10) - double-start thrust thread with an outer diameter of 80 mm, a stroke of 20 mm and a pitch of 10 mm;
Rdl6 - circular thread with an outer diameter of 16 mm;
Rdil6LH - round thread with a diameter of 16 mm, left;
R 1 1/2 - conical pipe thread with a size of 1 1/2".
K 1 1/2 GOST 6111-52 - inch conical thread with a size of 1 1/2".
Thread designations according to GOST 2.311-68 refer to the outer diameter, as shown in Fig. 2.2.17.
The designation of conical threads and cylindrical pipe threads is applied as shown in Fig. 2.2.18, a, b, c.
The parts are connected using threaded products.
Standard threaded products include threaded fasteners (bolts, screws, nuts, studs). The technical requirements establish 12 accuracy classes for screws, bolts and studs and 7 accuracy classes for nuts. The types and symbols of coatings for fasteners have also been established.
The structure of fastener symbols includes:
1 - name of the product (bolt, screw, etc.);
2 - execution (version I is not indicated);
3 - designation of metric thread and its diameter;
4 - thread pitch (for small metric);
5 - designation of the thread tolerance field;
6 - length of bolt, screw, stud in mm;
7 - accuracy class;
8 - grade of steel or alloy;
9 - designation of the type of coating;
10 - coating thickness in mm;
11 - number of the standard for the design of the fastener and its dimensions.
In educational drawings, positions 5, 7, 8, 9, 10 in an engineering graphics course may not include the product designation in the condition, since it is impossible to assign these parameters justifiably without special knowledge.
Bolt It is a cylindrical rod with a head at one end and a thread at the other end. Bolts are used (together with nuts and washers) to fasten two or more parts. There are various types of bolts, differing from each other in the shape and size of the head and shaft, thread pitch, manufacturing accuracy and performance.
Bolts with hex heads have from three (Fig. 2.2.19) to five designs: version 1 - without holes (in the head and rod); version 2 - with a hole on the threaded part of the rod; version 3 - with two holes in the bolt head.
When depicting a bolt in a drawing, two types are performed (Fig. 2.2.20) according to the general rules and the dimensions of bolt length l, thread length /o, wrench size S and thread designation Md are indicated. The height H of the head in the length of the bolt is not included. Hyperbolas formed by the intersection of the conical chamfer of the bolt head with its faces are replaced by other circles.
Examples of bolt symbols:
Bolt Ml2 x 60 GOST 7798-70 - with a hex head, first design, with M12 thread, coarse thread pitch, bolt length 60 mm.
Bolt 2M12 x 1.25 x 60 GOST 7798-70 - with fine metric thread M12x1.25, second version, bolt length 60 mm.
Screw It is a cylindrical rod with a thread at one end and a head at the other end. According to their purpose, screws are divided into fastening and installation screws. Screw fasteners are used to connect parts by screwing the threaded part of the screw into one of the parts being connected.
Set screws are used to secure the parts together. Their rod is completely cut, they have a cylindrical or conical pressure end or a flat end (Fig. 2.2.21).
Mounting screws come in four designs; version 1 - the thread diameter is larger than the diameter of the smooth part of the rod (Fig. 2.2.22); version 2 - thread diameter is equal to the diameter of the smooth part; version 3 and the screw head has a Phillips slot for a screwdriver.
Depending on the operating conditions, screws are manufactured (Fig. 2.2.23) with a cylindrical head (GOST 1491-80), a semicircular head (GOST 17473-80), a semi-countersunk head (GOST 17474-80) or a countersunk head (GOST 17475-80) with a slot, as well as with a turnkey head and with corrugation.
The height of the head is not included in the length of the screw, with the exception of screws with a countersunk head (Fig. 2.2.23).
In the drawing, the shape of a slotted screw is completely conveyed by one image on a plane, parallel to the axis of the screw. In this case, indicate the thread size, screw length, length of the threaded part (lо = 2d + 6 mm) and the symbol of the screw according to the relevant standard.
Examples of screw symbols:
Screw M12x50 GOST 1491-80 - with a cylindrical head, first design, with M12 thread with a coarse pitch, 50 mm long;
Screw 2M12x1, 25x50 GOST 17475-80 - with countersunk head, second version, with fine metric thread with a diameter of 12 mm and a pitch of 1.25 mm, screw length 50 mm.
Hairpin It is a cylindrical rod with threads at both ends (Fig. 2.2.24). A pin is used to connect two or more parts. One end of the stud 1\ is screwed into the threaded hole of the part, and a nut is screwed onto the other end \o. Studs are produced with two threaded ends of equal length for parts with smooth through holes. The length of the smooth part of the stud rod must be at least 0.5d.
The design and dimensions of the studs are determined by standards depending on the length of the threaded end:
GOST 22032-76l1= 1.0d - the pin is screwed into steel, bronze, brass;
GOST 22034-76 l1, = 1.25d; GOST 22036-76l1 = 1.6d - the stud is screwed into cast iron;
GOST 22038-76 l1 = 2d; GOST 22040-76 l1 = 2.5d - the stud is screwed into light alloys.
When depicting a stud, only one view is drawn on a plane parallel to the axis of the stud, and the dimensions of the thread, the length of the stud and its symbol are indicated. Examples of stud symbols:
Stud M8 x 60 GOST 22038-76 - with a large metric thread with a diameter of 8 mm, stud length 60 mm, intended for screwing into light alloys, length of the screwed end 16 mm;
Stud M8 x 1.0 x 60 GOST 22038-76 - the same, but with a fine thread pitch of -1.0 mm.
screw- a fastener with a threaded hole in the center. It is used for screwing onto a bolt or stud until it stops in one of the parts to be connected. Depending on the name and operating conditions, the nuts are hexagonal, round, wing, shaped, etc. Hexagonal nuts are most widely used. They are manufactured in three versions: version l - with two conical chamfers (Fig. 2.2.25); version 2 - with one conical chamfer; version 3 - without chamfers, but with a conical protrusion at one end.
The shape of the nut in the drawing is fully conveyed by its two views: on the projection plane parallel to the nut axis, half of the view is combined with half of the frontal section, and on the plane perpendicular to the nut axis, from the chamfer side.
The drawing indicates the thread size, wrench size S and gives the designation of the nut according to the standard.
Examples of nut symbols:
Nut M12 GOST 5915-70 - first version, with a thread diameter of 12 mm, large thread pitch;
Nut 2M12 x 1.25 GOST 5915-70 - second version, with fine metric thread with a diameter of 12 mm and a pitch of 1.25 mm.
A washer is a turned or stamped ring that is placed under a nut, screw or bolt head in threaded connections. The flatness of the washer increases the supporting surface and protects the part from scuffing when screwing the nut with a wrench. In order to protect the threaded connection from spontaneous loosening under conditions of vibration and alternating loads, spring washers in accordance with GOST 6402-70 and lock washers with tabs are used.
Round washers according to GOST 11371-78 have two designs (Fig. 2.2.26): version 1 - without chamfer, version 2 - with chamfer. The shape of a round washer is fully conveyed by one image on a plane parallel to the axis of the washer.
The internal diameter of the washer is usually 0.5...2.0 mm larger than the diameter of the bolt rod on which the washer is placed. The symbol of the washer also includes the thread diameter of the rod, although the washer itself does not have a thread.
Examples of washer symbols:
Washer 20 GOST 11371-78 - round, first version, for bolt with M20 thread;
Washer 2.20 GOST 11371-78 - the same washer, but of a second design.
Pipeline connecting parts (couplings, elbows, tees, etc.) are threaded connections made of ductile iron and intended for connecting pipes in pipelines (Fig. 2.2.27). Pipes are used in communications transporting liquid or gas, as well as for laying cables.
The design and dimensions of pipeline connecting parts are determined by standards. The ends of the pipes have external threads, and the connecting parts have internal threads. The main parameter of the pipe connection parts is the nominal diameter Dy - the internal diameter of the pipes in millimeters. The connecting parts of the pipelines are coated mainly with zinc.
Examples of symbols for pipeline connecting parts:
Long coupling 20 GOST 8955-75 - straight, non-galvanized, for pipes with a nominal diameter of 20 mm;
Angle Ts-25 GOST 8946-75 - straight, galvanized, for pipes with a nominal bore of 25 mm.
Images of threaded connections in the drawings are made in accordance with the requirements of the standards. Threaded connections are fixed threaded connections. These include connecting parts using bolts, screws, studs, nuts and pipeline fittings.
The image of a threaded connection consists of the parts depicted and connected. There are constructive, simplified and conventional images of fasteners and their connections.
When depicting a constructive image, the dimensions of the parts and their elements exactly correspond to the standards. In a simplified representation, the dimensions of fasteners are determined by conventional relationships depending on the diameter of the thread and chamfers, splines, threads in blind holes, etc. are drawn in a simplified manner.
Symbols are used for fastener rod diameters of 2 mm or less. Simplified and conventional images of fasteners are established by GOST 2.315-68. This section provides simplified images of fasteners in threaded connections that are recommended in training drawings.
A bolted connection consists of a bolt, nut, washer and connected parts. Through holes with a diameter of d0 = (1.05...1.10)d, where d is the diameter of the bolt thread. Insert a bolt into the hole, put a washer on it and screw the nut until it stops (Fig. 2.2.28).
The length of the bolt is determined by the formula l = Н1+ Н2 + SШ + Н + К, where H1 and H2 are the thickness of the parts being connected; Sm - washer thickness, S Ш = 0.15d; H-nut height, H = 0.8d; K is the length of the protruding bolt rod, K = 0.35d.
The gauge bolt length is rounded to the nearest standard bolt length.
On the drawing of a bolted connection (Fig. 2.2.28), at least two images are made - on a projection plane parallel to the axis of the bolt, and on a projection plane perpendicular to its axis (from the nut side). When depicting a bolted connection in section, the bolt, nut and washer are shown uncut. The head of the bolt and the nut in the main view are depicted with three faces. Adjacent parts are hatched with an inclination in different directions. The drawing of a bolted connection indicates three dimensions: thread diameter, bolt length and bolt hole diameter.
The symbols of the bolt, nut and washer are written in the specifications of the assembly drawing.
Hairpin the connection consists of a stud, washer, nut and connected parts. Connecting parts with a pin is used when there is no room for a bolt head or when one of the parts being connected has a significant thickness. In this case, it is not economically feasible to drill a deep hole and install a long bolt. The pin connection reduces the weight of the structures. One of the parts connected by a pin has a recess with a thread - a socket for a pin, which is screwed into it with end l1 (see Fig. 2.2.24). The remaining parts to be connected have through holes with a diameter of d0 = (1.05...1.10)d, where d is the diameter of the stud thread. The socket is first drilled to a depth l2, which is 0.5d greater than the screwed end of the stud, and then a thread is cut into the socket. At the entrance to the socket, a chamfer is made with = 0.15d (Fig. 2.2.29, a). With a pin screwed into the socket, the parts are then connected as in the case of a bolted connection.
The length of the pin is determined by the formula l = H2 + SШ + H+ K, where H2 is the thickness of the attached part; SSh - thickness of the washer; H - nut height; K is the length of the protruding end above the nut. The estimated length of the stud is rounded to the standard value. In the drawing of a stud joint, the separation line of the parts to be connected must coincide with the thread boundary of the screwed-in threaded end of the stud (Fig. 2.2.29, b). The pin socket ends in a conical surface with an angle of 120°. It is almost impossible to cut a thread to the end of the socket, but on assembly drawings it is allowed to depict a thread for the entire depth of the socket.
The drawing of a stud connection shows the same dimensions as the drawing of a bolted connection. The hatching in the threaded connection of the stud with the part into which the stud is screwed, in the section, is brought to a continuous main thread line on the stud and in the socket.
Screw connection includes parts to be connected and screw and washer. In connections with countersunk screws and set screws, do not use a washer.
One of the parts to be connected should have a threaded socket for the end of the screw, and the other should have a smooth through hole with a diameter dо= =(1.05...1.10)d. If a screw with a countersunk or semi-countersunk head is used, then the corresponding side of the hole in the part must be countersunk for the screw head (Fig. 2.2.30).
The length of the screw is determined by the formula l = Н = SH + l1, where Н is the thickness of the attached part; SSh - thickness of the washer; l1 is the length of the screwed-in threaded end of the screw, which is assigned for the corresponding material, as for a stud.
The estimated screw length is rounded to the standard length value.
The depiction of a screw connection in the drawing is similar to a bolted connection in relative dimensions. The relative sizes of the screw heads are shown in Fig. 2.2.31.
On a screw connection, the thread boundary on the screw shaft must be inside a smooth hole; the thread margin not used when screwing in is approximately three thread pitches (Z.P). If the diameter of the screw head is less than 12 mm, then it is recommended to depict the slot as one thick line. In the top view, the slot in the head is shown rotated 45°. Three dimensions are indicated on the connection drawing: thread diameter, screw length, and hole diameter for the passage of the screw.
Pipe connection consists of connected pipes and pipeline connecting parts. When connecting two pipes with a coupling, in addition to the coupling, the connection includes a lock nut and a gasket (Fig. 2.2.32).
Drawings of pipe connections are made according to the dimensions of their parts as structural drawings, without simplifications. Before starting to draw a pipe connection, it is necessary to select the dimensions of the pipes and connecting parts based on the value of the nominal bore Dy from the tables of the relevant standards.
The rules for making drawings of pipes and pipelines are set out in more detail in GOST 2.411-72.
Screw(running) connections refer to movable detachable joints. In these connections, one part moves relative to another part along a thread. Typically, these connections use trapezoidal, thrust, rectangular and square threads. Drawings of screw connections are made according to general rules.
Serrated(slotted) compound is a multi-key connection in which the key is integral with the shaft and located parallel to its axis. Toothed joints, like keyed joints, are used to transmit torque, as well as in structures that require parts to move along the axis of the shaft, for example, in gearboxes.
Due to the large number of projections on the shaft, a gear connection can transmit more power than a key connection and provide better alignment of the shaft and wheel.
According to the cross-sectional shape, the teeth (splines) are straight-sided, involute and triangular (Fig. 2.2.33). GOST 2.409-74 establishes conventional images of gear shafts, holes and their connections.
The circles and forming surfaces of the protrusions (teeth) of the shafts and holes are shown along the entire length by main lines (Fig. 2.2.34). The circles and generatrices of the surfaces of the depressions are shown with solid thin lines, and in longitudinal sections - with solid main lines.
When depicting gear joints and their parts that have an involute or triangular profile, the pitch circles and generatrices of the pitch surfaces are shown with a dash-dotted thin line (Fig. 2.2.34, b).
On a plane perpendicular to the axis of the gear shaft or hole, the profile of one tooth (protrusion) and two cavities is shown, and the chamfers at the end of the spline shaft and in the hole are not shown.
The boundary of the toothed surface of the shaft, as well as the boundary between the teeth of the full profile and the run-out, is shown by a solid thin line (Fig. 2.2.34, a).
In longitudinal sections, the teeth are conventionally aligned with the plane of the drawing and are shown uncut, and in joints in the hole, only that part of the protrusions is shown that is not covered by the shaft (Fig. 2.2.34, b).
The symbol of the spline shaft or hole according to the relevant standard is placed in the table of parameters for the manufacture and control of connection elements. The symbol of the connection may be indicated in the drawing with a mandatory reference to the standard on a leader shelf drawn from the outer diameter of the shaft (Fig. 2.2.35).
Keyed connection consists of a shaft, wheel and key. A key (Fig. 2.2.36) is a part of a prismatic (prismatic or wedge keys) or segmental (segment keys) shape, the dimensions of which are determined by the standard. Keys are used to transmit torque.
A key is placed in a special groove on the shaft. The wheel is placed on the shaft so that the groove of the wheel hub hits the protruding part of the key. The dimensions of the grooves on the shaft and in the wheel hub must correspond to the cross-section of the key.
The dimensions of the parallel keys are determined by GOST 23360-78; dimensions of connections with wedge keys - GOST 24068-80; dimensions of connections with segment keys - GOST 24071-80.
Prismatic keys come in regular and guide types. The guide keys are attached to the shaft with screws; they are used when the wheel moves along a shaft.
Depending on the shape of the ends of the keys, there are three designs:
version 1 - both ends are rounded;
version 2 - one end is rounded, the second is flat;
version 3 - both ends are flat.
The working surfaces of prismatic and segment keys are the lateral edges, while for wedge keys the upper and lower edges are wide, one of which has a slope of 1:100.
The cross sections of all keys have the shape of rectangles with small chamfers or rounded. The cross-sectional dimensions of the keys are selected depending on the diameter of the shaft, and the length of the keys is selected depending on the transmitted forces.
The symbols of keys are determined by standards and include: name, design, dimensions, standard number. An example of a key designation:
Key 10 x 8 x 60 GOST 23360-78 - prismatic, first design, with cross-sectional dimensions 10x8 mm, length 60 mm.
Drawings of keyed connections are made according to general rules. The keyed connection is shown in a frontal section by the axial plane (Fig. 2.2.37). In this case, the key is shown uncut; a local cut is made on the shaft. The second image of a keyed connection is a section through a plane perpendicular to the shaft axis. The gap between the bases of the groove in the bushing (wheel hub) and the key is shown enlarged.
Pin connection(Fig. 2.2.38) - cylindrical or conical - used for precise mutual fixation of fastened parts. Cylindrical pins ensure repeated assembly and disassembly of parts.
Cotter pins used to limit the axial movement of parts (Fig. 2.2.39) to lock castle nuts.
Wedge connections(Fig. 2.2.40) provide easy disassembly of the connected parts. The edges of the wedges have a slope from 1/5 to 1/40
In articulation joints(Fig. 2.2.41) the protrusion of one part fits into the groove or hole of another part; the parts are rotated relative to each other, and this ensures their connection.
Permanent connections have become widespread in mechanical engineering. These include welded, riveted, soldered, and adhesive connections. This also includes connections obtained by crimping, pouring, flaring (or rolling), core punching, stitching, interference fit, etc.
Welded joints are produced by welding. Welding is the process of obtaining a permanent connection of solid objects consisting of metals, plastics or other materials by locally heating them to a molten or plastic state without or using mechanical forces.
Welded connection is a set of products connected by welding.
A weld is a material that has solidified after melting. A metal weld differs in its structure from the metal structure of the metal parts being welded.
According to the method of mutual arrangement of the welded parts, there are butt joints (Fig. 2.3.1, a), corner (Fig. 2.3.1, b), T-joints (Fig. 2.3.1, c) and lap joints (Fig. 2.3.1, d ). The type of connection determines the type of weld. Welds are divided into: butt, corner (for corner, T-joints and lap joints), spot (for lap joints, spot welding).
In terms of their length, welds can be: continuous along a closed contour (Fig. 2.3.2, a) and along an open contour (Fig. 2.3.2, b) and intermittent (Fig. 2.3.2, c). Intermittent seams have welded sections of equal length with equal intervals between them. In double-sided welding, if the welded sections are located opposite each other, such a seam is called a chain seam (Fig. 2.3.3, a), but if the sections alternate, then the seam is called a checkerboard seam (Fig. 2.3.3, b).
Thin-sheet structures can be welded without preliminary preparation of the welded edges. The form of edge preparation depends on the thickness of the parts being welded, the position of the seam in space and other data.
Terms and definitions related to welding are established by GOST 2.601-68. The most common type of welding is electric welding, which can be manual, semi-automatic and automatic.
Welding methods, types and structural elements of welds are determined by the relevant standards. Conventional images and designation of seams of welded joints are carried out in accordance with GOST 2.312-72. Welds are depicted with solid main lines if the seam is visible, and with dashed lines if the seam is invisible (Fig. 2.3.4). A one-way arrow with a leader line is drawn from the image of the seam. The symbol of the weld is written above the leader line flange if the seam is visible, i.e. the front side of the seam is shown (Fig. 2.3.5, a, 6), and under the leader line flange if the seam is invisible, i.e. the reverse side of the seam is shown (Fig. 2.3.5, c, d).
The structure of the weld symbol is shown in Fig. 2.3.6, where:
1 - auxiliary signs, O - seam along a closed contour, | - assembly seam;
2 - designation of the standard for the type and structural elements of the seam;
3 - alphanumeric designation of the seam according to this standard;
4 - symbol of the welding method according to the standard for a given seam;
5 - auxiliary sign A - triangle and seam leg size;
6 - dimensions in mm of an intermittent seam with signs: / - for a chain seam and Z - for a checkerboard seam or ] - sign of an open welding contour;
7 - auxiliary signs (Q or co) for seam processing;
8 - designation of the roughness of a machined seam;
9 - instructions on seam control.
Examples of weld symbols:
GOST 14806-80 = T5 - RiZ = 1 6-50 Z 100 - the seam is made by electric arc welding of aluminum, T-joint T5, manual welding in a shielding gas environment Ri3, weld leg 6 mm A6, checkerboard weld, length of the welded section 50 mm, pitch - 100 mm (50 Z 100).
GOST 5264-80-C18 - the seam is made by manual electric arc welding during installation 1, butt seam (C 18) along an open contour.
If there are several identical seams in the drawing, the designation is applied to only one seam, and therefore the seam is assigned a serial number indicating the number of these seams along the leader line. All other seams of this type are indicated on the shelf of the leader line with a designation of the serial number of the seam (Fig. 2.3.7), if the front side of the seam is indicated, and under the shelf of the leader line, if the back side of the seam is indicated. In Fig. 2.3.7 designation No. 1 two fillet welds made by manual electric arc welding; on the front side, the reinforcement of the seam must be removed Q by mechanical processing, after which the roughness of the seam must correspond to the sixth class (Ra = 2.5 µm).
Five seams No. 2 are made as single-sided Tic seams with a 5 mm A5 leg, manual electric arc welding.
If all the seams in the drawing are made according to the same standard, then its number is not entered into the seam designation, but is written in the technical requirements in the field of the drawing as “Welded seams according to GOST...”.
If all the seams in the drawing are the same, then the symbol of the seams can not be applied on the images, but one record of the symbol of the seam of the technical requirements can be made, for example: “Welds according to GOST 5264-80-U5-A4”.
Riveted joints used in structures exposed to high temperatures, corrosion, vibration, as well as in connections made of poorly weldable metals or in connections of metals with non-metallic parts. Such connections are widely used in boilers, railway bridges, some aircraft structures and in light industry.
At the same time, in a number of industries, with the improvement of welding technology, the volume of use of rivet joints is gradually decreasing.
The main fastening element of riveted joints is the rivet. It is a short cylindrical rod of round cross-section, at one end of which there is a head (Fig. 2.3.8). Rivet heads can be spherical, conical or conical-spherical in shape.
Depending on this, heads are distinguished as semicircular (Fig. 2.3.8, a), countersunk (Fig. 2.3.8, b), semi-concealed (Fig. 2.3.8, c), flat (Fig. 2.3.8, d).
In assembly drawings, rivet heads are shown not by their actual dimensions, but by relative sizes, depending on the diameter of the rivet shank d.
The technology for making a riveted connection is as follows. Holes are made in the parts to be joined by drilling or another method. The head rod of the rivet is inserted into the through hole of the parts to be joined until it stops. Moreover, the rivet can be hot or cold. The free end of the rivet extends approximately 1.5d beyond the part. It is riveted with blows or strong pressure and a second head is created (Fig. 2.3.9).
The diameter of the rivet rods is selected according to special tables. Approximately, it is assumed to be equal to the thickness of the parts being connected. The length of the rivet rod is also taken taking into account the thickness of the parts being connected and the allowance. Approximately it is 1.5d.
Rivet seams can be single-row or multi-row. The rivets are usually spaced equally apart in a row. The arrangement of rivets in the seam can be row or staggered. The parts to be connected in rivet joints can be overlapped or butted with overlays.
The drawings indicate all the structural dimensions of the riveted joint seams. In this case, all the rivets of the connection are not drawn out. Usually one or two of them are shown, and the location of the rest is indicated by the intersection of the axes (Fig. 2.3.10).
Rivet seams have their own designations, which are marked on the drawings. The designation indicates the diameter (d) and length (/) of the rivet shank, the metal group and the GOST number that determines the shape of the head and coating.
For example, a rivet with a semicircular head, length d = 25 mm, shaft diameter d = 10 mm, made of group OO metal, without coating, has the designation: Rivet 10x25 GOST 10299-80.
Connecting parts by soldering is widely used in instrument making and electrical engineering. When soldering, the parts being connected are heated to a temperature that does not lead to their melting. The gap between the parts to be joined is filled with molten solder. Solder has a lower melting point than the materials being joined by soldering. For soldering, soft solders POS - tin-lead according to GOST 21930-76 and GOST 21931-76 and hard solders Per - silver according to GOST 19738-74 are used.
Solder in views and sections is depicted as a solid line 2S thick. To indicate soldering, a symbol is used (Fig. 2.3.11, a) - an arc with a convexity towards the arrow, which is drawn on the leader line indicating the soldered seam. If the seam is made around the perimeter, then the leader line ends with a circle. The number of seams is indicated on the leader line (Fig. 2.3.11, b).
The brand of solder is recorded either in the technical requirements or in the specifications in the “Materials” section.
Adhesive joints allow you to join a variety of materials. The adhesive seam, like the solder seam, is depicted according to a solid line with a thickness of 25. A symbol is drawn on the leader line (Fig. 2.3.12, a), resembling the letter K. If the seam is made along the perimeter, then the leader line ends with a circle (Fig. 2.3.12, b). The brand of glue is recorded either in the technical requirements or in the specifications in the “Materials” section.
Crimping (reinforcement) protects the connected elements from corrosion and chemical exposure to a harmful environment, performs insulating functions, allows you to reduce the weight of the product (Fig. 2-3-13), and save materials.
Rolling and punching are carried out by deforming the parts being connected (Fig. 2.3.14, a, b). Stitching with threads and metal staples is used to join paper sheets, cardboard, and various fabrics.
GOST 2.313-82 establishes symbols and images of seams of permanent joints obtained by soldering, gluing, and stitching.
The connection of parts by interference fit is ensured by a system of tolerances and fits at a certain temperature before welding the parts.
Special connections include connecting parts with gears, springs, etc. Gears constitute the most common group of mechanical gears and are used to convert and transmit rotational motion between shafts with parallel (cylindrical gears), intersecting (bevel gears) and intersecting (worm gears) axes , as well as for converting rotational motion into translational motion and vice versa (rack and pinion gears).
In a gear drive, motion is transmitted through direct contact between the teeth of the wheel and the gear. A gear with a smaller number of teeth is called a gear, and a gear with a larger number is called a wheel. The main element of a gear wheel is the teeth. In Fig. 2.4.1 shows an image of a gear wheel indicating its elements, terms and designations.
The diameters of the circles of the depressions df, peaks d3 and pitch circle d depend on the number of teeth z and the engagement pitch Pt. The pitch of engagement is determined by the length of the arc of the pitch circle between identical points of two adjacent teeth. The length of the pitch circle is equal to ld = zP1, whence the diameter of the pitch circle is d = (P1/l) z. The ratio P1/l is called the gear module, denoted by the letter t and measured in millimeters, i.e. t = P1/l, then d = mz. The module is the main parameter of a gear; its values are established by ST SEV 310-76. Many gear sizes depend on the module size. Typically, the height h of the tooth is taken equal to 2.25t, while the height of the head ha of the tooth is taken equal to t, and the height of the tooth foot hf is 1.25t. The diameter of the circle of the peaks is da = m(z + 2), the diameter of the circle of the depressions is df = m(z + 2.5).
The symbols of gear wheels are determined by GOST 2.402-68.
The circles and generatrices of the surfaces of the teeth protrusions are shown with solid main lines, the dividing circles are shown with dash-dot thin lines, the circles and generatrices of the surfaces of the tooth cavities are not shown in the views or are depicted with a solid thin line.
In sections and sections, the generatrices of the surfaces along the entire length are depicted with solid main lines (Fig. 2.4.2, a, b).
The teeth of gear wheels are drawn only in axial sections, conditionally aligning them with the secant plane, and are shown uncut. If it is necessary to show the tooth profile, then it is shown in a limited area of the wheel image or an extension element is used (Fig. 2.4.3).
Working drawings of cylindrical gears are made in accordance with GOST 2.403-75. An image of a gear and a table of parameters are placed on the drawing. The data specified in the standard is applied to the image of the wheel. The image of a cylindrical gear (Fig. 2.4.4) indicates: the diameter of the circle of the tops of the teeth, the width of the rim, the dimensions of the chamfers and the radii of roundings, the roughness of the surfaces of the tops, valleys and side surfaces
Teeth, and also apply the dimensions of all structural elements of the part (rim, hub, wheel).
The table of parameters is placed in the upper right corner of the drawing (Figure 2.4.4 shows the dimensions of the table graphs and their location).
The parameter table in the spur gear drawing consists of three parts, separated from each other by solid main lines. The first (upper) part contains data for manufacturing, the second - for control, and the third - reference data for the gear. Working drawings of gear parts of other types are carried out in accordance with the requirements of GOST 2.405-75 - GOST 2.406-76.
At least two images are drawn on the gear drawing (Fig. 2.4.5). In the main view, the engagement can be shown in section. Then the drive wheel tooth appears in front of the driven wheel tooth. The outline of the visible tooth is drawn with solid main lines, and the outline of the invisible tooth is drawn with dashed lines. On the gear drawing, only one dimension is usually indicated - the value of the interaxial distance. The rules for the symbols of other data for transmissions of various types are determined by GOST 2402-68.
Springs serve to accumulate energy due to elastic deformation under the influence of external load. With the cessation of this load, the springs restore their original shape. According to their external shape (Fig. 2.4.6), springs can be screw (cylindrical and conical) and non-screw (spiral, plate, disc). Based on the type of deformation (or loading), compression, tension, torsion, and bending springs (flat springs) are distinguished.
In cross section, the coils of the spring have either a round (Fig. 2.4.6, a, b) or rectangular (Fig. 2.4.6, b, d, e) shape. Accurate imaging of springs is labor-intensive and impractical.
GOST 2.401-68 establishes conventional images and rules for making drawings of springs for all industries.
When depicting cylindrical springs (Fig. 2.4.6, a), the sections of the coils of the spring are conventionally depicted as circles, and the coils themselves as straight lines. The outer coils of the spring, which work in compression, are not working; they are preloaded and processed to ensure complete contact with the supporting surfaces. The remaining parts of the spring have a constant pitch, so the centers of the sections must be staggered. With a large number of turns, they are depicted only from the ends of the springs, skipping the central part. An axial dash-dotted line is drawn through the center of the sections of the turns. The image of helical springs in the drawing is positioned horizontally. Springs are drawn in a free (unloaded) state. Tension springs are shown without any space between the coils.
On the drawings of springs with controlled force parameters, test diagrams are placed - a graph of load versus deformation or deformation versus load (Fig. 2.4.7).
The working drawings show springs with right-hand winding only. The winding direction is indicated in the technical requirements, which are located under the image of the spring.
Technical requirements must comply with GOST 2.401-68. On the training drawings it is enough to indicate the following data:
length of the deployed spring L, mm;
number of working turns n;
total number of turns n1;
winding direction;
diameter of the control rod Ds, mm, or diameter of the control sleeve Dr, mm;
Dimensions for reference.
If the thickness of the section of the spring material in the drawing is 2 mm or less, then the spring is depicted as a solid main line with a thickness of 0.6...1.5 mm (see Fig. 2.4.6, d, e).
Among detachable connections, threaded ones are most common. These include bolted, stud and screw connections, shown in Figure 209. The parts of these connections - bolts, screws, studs, nuts and washers - have the shape, dimensions, etc. established by the standard. symbols. Using these designations, you can find the dimensions of fasteners in the corresponding standards tables. How to do this was shown using the example of a bolt drawing.
Images of fasteners can be found mainly in assembly drawings. In these drawings, bolted, stud and screw connections are drawn according to relative sizes. This means that the size of individual elements is determined depending on the outer diameter d of the thread. As a result, the work on completing the drawing is accelerated.
The dimensions of fasteners are not indicated on assembly drawings. But how, in this case, can you determine which bolt or stud is included in the connection?
The necessary data is recorded in specifications. We will get to know her later. Now let's look at the images of the main threaded connections.
32.1. Image of bolted connections. This connection is shown in Figure 216. In the parts that need to be connected (part 1 and part 2), holes are drilled with a slightly larger diameter than the diameter of the bolt.
It is recommended to draw drawings of fastening connections in a simplified manner (Fig. 217, d). This is as follows. Chamfers on hexagonal and square heads of bolts and nuts, as well as on the rod, are not shown. It is allowed not to show the gap between the bolt shaft and the hole in the parts being connected.
To make the drawing presented in Figure 217, d easier to understand, we will show the formation of a bolted connection in stages. First, a bolt is shown and above it are two parts to be connected (Fig. 217, a). Then the bolt is shown in the holes of these parts, and above it is a washer (Fig. 217, b). In Figure 217, a washer is put on a bolt, and a nut is shown above it. The completed drawing of the bolted connection is shown in Figure 217, d.
Please note that the parts to be connected (1 and 2) are shaded in different directions.
Rice. 216. Bolted connection
Rice. 217. Simplified image of a bolted connection
Bolts in the assembly drawing are shown uncut if the cutting plane is directed along their axis. Nuts and washers are also shown uncut.
The specifications for bolts indicate the diameter and type of thread, the length of the rod and the standard number1. Record Bolt M12 x 1.25 U-60 means: bolt with metric thread (diameter) 12 mm, pitch 1.25 mm (small), rod length 60 mm.
1 In the textbook, to simplify recording here and below, the standard number is not given for other fasteners.
For a nut, indicate the diameter and type of thread. Record screw M16 means: a nut with a metric thread, having a diameter of 16 mm, the thread pitch is large. For washers, indicate the diameter of the bolt. Record Washer 12 means: washer for a bolt with a diameter of 12 mm.
You will draw bolted connection elements using relative dimensions. They are determined depending on the outer diameter of the thread according to the relationships shown in Figure 217. Consider an example of determining the relative dimensions for a bolted connection with an M20 thread (d = 20 mm):
diameter of the circle circumscribed around the hexagon, D = 2d(2 x 20 = 40 mm);
bolt head height h = 0.7d(0.7 x 20 = 14 mm);
for the threaded part l0 ~ 2d + 6(2 x 20 + 6 = 46 mm);
nut height H = 0.8d(0.8 x 20 = 16 mm);
bolt hole diameter d = 1.1d(1.1 x 20 = 22 mm);
washer diameter Dsh = 2.2d (2.2 x 20 = 44 mm);
washer height S = 0.15d(0.15 x 20 = 3 mm).
Using these dimensions, you can draw a bolted connection.
1.
Depending on what value determine the relative dimensions of a bolted connection?
2.
When making a cut on the assembly drawing, the cutting plane passed along the axis of the bolt, nut and washer. Do they need to be hatched?
3.
Is it possible in Figure 217, d not to show the gap between the bolt shaft (part 5) and the holes in the connected parts 1 and 2?
4.
Decipher the designation: “Bolt M16 x 70” and “Nut M20”.
5.
What is the large circle depicted in the top view (Fig. 217, d)?
6.
Name the number of the part shown in the top view with a hexagon (Fig. 217, d).
59. Draw a sketch of the bolted connection, guided by the example in Figure 217, d Thread diameter d is 10 mm. The thickness of each of the connected parts is 15 mm. The length l of the bolt shaft is 45 mm.
32.2. Image of stud connections. A stud is a rod that has threads on both ends. With one end of the pin, the entire length of the thread is screwed into a blind (non-through) threaded hole in part 1 (Fig. 218). A nut is screwed onto the other end, under which a washer is placed. In this way, the parts to be fastened are pressed together (parts 1 and 2). The hole in part 2 has a slightly larger diameter than the pin (Fig. 218).
Rice. 218. Hairpin connection
Let us show step by step the formation of the hairpin connection shown in Figure 219, g.
First, the part shows a hole for the thread and a drill above it (Fig. 219, a), and then a hole with a thread and on top a tap with which the thread is cut (Fig. 219, b). Above the hole (Fig. 219, c) a pin is shown, which is screwed into the hole (Fig. 219, d), and the part being connected is shown above.
In Figure 219, e, the washer is put on a stud; the nut is shown above. And finally (Fig. 219, g), a drawing of a hairpin connection is shown.
The nut and washer, as in a bolted connection, are depicted in a simplified manner, i.e., without chamfers. The chamfers on the hairpin are also not shown.
The line defining the thread boundary at the lower end of the stud is always drawn at the level of the surface of the part into which the stud is screwed (detail 1, Fig. 219, g).
Look carefully at how a threaded rod is depicted screwed into a hole. The thread in the hole is shown only where it is not closed by the end of the rod (Fig. 220, a). The bottom of the blind hole is shown unfilled with a rod. For clarity, the lower part of the hole is highlighted in brown.
At the end of the hole there is a conical recess obtained from the drill (see Fig. 220, a). It is drawn with an angle of 120° at the apex, but the size of this angle is not indicated. Do not make the mistake shown in Figure 220, b, where the diameter of the recess turns out to be greater than the diameter of the hole, which cannot be the case.
Rice. 219. Simplified image of a hairpin connection
The shading is brought to a solid thick line (Fig. 221, a), and not to a thin one, as shown in Fig. 221, b.
You will calculate the relative dimensions for drawing the stud connection depending on the thread diameter according to the ratios shown in Figure 219.
Designation Hairpin M10 x 60 should be understood as follows: the stud has a metric thread, its diameter is 10 mm, length 60 mm (to the screwed end).
Bolt connection
Task 1. On a sheet of A3 format, draw a bolt according to actual dimensions, a connection - according to conditional dimensions.Take the bolt according to GOST 7798-70. Place a washer under the nut in accordance with GOST 11371-68. Take the initial data from Table 1.1. An example of task 1 is shown in Fig. 1.3.
Table 1.1
Initial data for constructing a bolt connection
|
Option |
d , mm bolt diameter |
p , mm thread pitch |
Thickness parts to be fastened |
Scale |
|
|
m |
n |
||||
1.1. Image of a bolted connection (Fig. 1.1)
On a sheet of A3 drawing paper, mark the locations for the image of the bolt, nut and connection.
At the location of the connection image, the location of the projections is determined, center lines are drawn and the diameter of the bolt is indicated with thin lines.
In the main view of the image, the base of the bolt head is outlined. The dimensions of the fastened parts are set off from it m And n, washer thickness S = 0,15d, nut height N = 0,8d and thread exit beyond the nut k = (0.25…0.5) d or (2…4) R. Then draw a line defining the height of the nut head.
In the top view, circles are drawn:
d– outer thread diameter (bolt diameter);
d 1 – 0,85d– symbol of the thread on the end of the bolt;
D = 2d– diameter of the circle for constructing the hexagon of the nut and bolt head;
D w = 2.2 d– diameter of the washer.
From the top view to the main view and the left view, the dimensions of the faces of the nut and bolt head and the diameter of the washer are projectively transferred D w, and thread symbol d 1.
Then determine the length of the threaded part of the bolt: l 0 = 2d + 2p. The obtained value is agreed upon with GOST and noted on the drawing. Determine the size of the chamfer C = 0,15d and apply it on images of the end of the bolt.
Determine the hole diameter d 0 = 1.1 d in detail m And n and put it on the drawing. The sequence of drawing chamfers on the hexagonal head of a bolt is set out in paragraphs. 1.2, and the nuts in paragraph 3.3.
Details m And n depicted in cross-section. The contours of these parts are determined in the drawing, and what is included in the cut is shaded (fasteners on assembly drawings are shown without a cut).
Apply dimensions. The following dimensions must be entered on this assembly drawing:
d– bolt thread diameter;
l– bolt length;
l 0 – bolt thread length;
S– turnkey size.
Dimensions l, l 0 , and S consistent with GOST.
Then the extra lines are removed from the drawing and outlined.
Rice. 1.1. Constructing a bolt connection using conditional relationships
1.2. Bolt drawing
It is performed in accordance with GOST 7798-70 in the following sequence (Fig. 1.2).
1.2.1. According to the specified values of the outer diameter of the thread d and calculated bolt length l from the tables of GOST 7798-70 (Table 1.2) determine the remaining dimensions of the bolt (head height N, circumscribed circle diameter D, radius headrest R, length of the threaded part of the rod l 0).
1.2.2. Draw the contours of the images of the bolt: the main view, the top view and the left view. N.B.!: Drawing the view must begin with the center lines.
1.2.3. In the view on the left, draw a circle with a diameter D 1 = 0,9s(Where S- turnkey size). This circle is the line of intersection of the end of the bolt head with the chamfer.
1.2.4. Mark the points IN""" 1 , IN""" 2 , IN""" 3 , IN""" 4 located on circle D 1 and determine their positions on the main view ( IN"" 1 and IN"" 3 ) and top view ( IN" 2 and IN" 4).
1.2.5. From points IN"" 1 IN" 3 and IN" 2 IN" 4 draw straight lines at an angle of 30° to the end of the bolt head, which, at the intersection with the corresponding edges of the bolt head, determine the points A"" 1 , A"" 4 and WITH 2 ," WITH" 5 .
Using a line passing through points A"" 1 , A"" 4 , find the points A"" 2 and A"" 3 .
1.2.6. Through dots A"" 2 , WITH"" 2 , A"" 3 draw a circular arc.
1.2.7. Arc of a circle A"" 2 WITH"" 2 A"" 3 allows you to define points M 0 and N 0 straight line on which the centers of K are located 0 arcs of circles passing through the points A"" 1 , A"" 2 and A"" 3 , A"" 4 .
In the top view, horizontal projections of these curves are drawn in the form of circular arcs passing through points A" 1 , WITH" 1 , A" 2 and A" 1 WITH" 6 A" 6. After this, indicate the threaded part of the bolt shaft, draw chamfers (with × 45°), draw a fillet r(smooth transition from the bolt shaft to its head).
At the final stage of drawing up the bolt, its dimensions are applied (according to GOST 7798-70).
Rice. 1.2. Sequence of drawing a standard bolt version 1
Table 1.2
Hex head bolts of normal accuracy (GOST 7798-70)
|
d |
S |
N |
D , no less |
R |
l |
l o |
|
|
0,25...0,6 | |||||||
|
0,40... 1 ,1 |
28...100 | ||||||
|
0,6...1,6 |
32...200 | ||||||
|
0,6...1,6 |
35...260 | ||||||
|
0,6...1,6 |
45...300 | ||||||
|
3 3, 3 |
0,8...2,2 |
55...300 | |||||
|
0,8...2,2 |
65...300 | ||||||
|
1,0 … 2,7 |
75...300 | ||||||
|
1,0...3,2 |
90...300 | ||||||
|
1,2. . .3,3 |
105...300 | ||||||
|
1,6...4,3 |
1 15...3 0 0 | ||||||
Notes: 1. Length 1 is selected within the specified limits from the range: 8, 10, 12, 14, 16, (18), 20, (22), 25, (28), 30, (32), 35, (38) , 40, 45, 50, 55, 60, 65 , 70, 75, 80, (85), 90, (95), 100, (105), 110, (115), 120, (125), 130, 140 , 150, 160, 170, 180, 190, 200, 220, 240, 260, 280, 300.
2. An example of a symbol for a bolt with a hex head, thread diameter 12 mm, length 60 mm in version 1, with a large thread pitch and dimensions in accordance with GOST 7798-70: Bolt M12x 60 GOST 7798-70. The same, with a fine thread pitch of 1.25 mm: Bolt M12 x 1.25 x 60 GOST 7798-70.
Rice. 1.3. Example of task 1
Bolts, nuts, studs and screws are usually produced by special factories that supply all enterprises with these parts. Therefore, images of fasteners are found mainly in assembly drawings, where they are shown in connection with other parts and with each other.
In this case, the following types of images of these parts and their connections may occur:
- constructive (detailed images), when the shape of parts or their connections is conveyed without significant deviations from the natural one (Fig. 9.15, a, c; rice. 9.16; rice. 9.17, c, e, rice. 9.18);
- simplified when the images do not retain many details of the shape of the parts and their connections (Fig. 9.15, G; rice. 9.18, and; rice. 9.19, a, c, d, g);
- conditional, when the concept of parts and their connections is conveyed schematically (Fig. 9.19, b, d, f, h).
GOST 2.315–68 establishes simplified and conventional images of fasteners on assembly drawings and general view drawings of all industries and construction, some of which are shown in Fig. 9.19. A simplified or conventional image is chosen depending on the purpose and scale of the drawing. In this case, fasteners whose rod diameters in the drawing are 2 mm or less are depicted conventionally. The size of the image should give a complete picture of the nature of the connection.
Threaded connections on assembly drawings are usually drawn according to relative sizes. The size of the individual connection elements is determined depending on the outer diameter of the thread.
The dimensions of fasteners are not indicated on assembly drawings.
The necessary data is contained in the designation, which is recorded in the specification.
Bolted connections
Simplifications consist in not depicting chamfers on hexagonal and square bolt heads and nuts I, and also on the rod II. This means that the lines that represent the chamfers disappear. Doesn't show gap III between the bolt shank and the hole in the parts to be joined 1 And 2. In Fig. 9.16 it is highlighted.
In addition, the thread is shown along the entire length of the bolt shaft (Fig. 9.15, d), and is not limited to its size l 0, as is the case in reality (Fig. 9.15, A – V) (IV). The image of the thread is also not shown in a view perpendicular to the axis of the rod, i.e. do not draw 3/4 of the circle with a thin line (see Fig. 9.15, G) (V). The same applies to simplified images of studs and screws.
To the drawing in Fig. 9.15, G easier to understand, its formation is shown in stages. First, a bolt is shown and above it are two parts to be connected. 1 And 2 (see Fig. 9.15, A), then the bolt is shown in the holes of these parts, and above them there is a washer 5 (see Fig. 9.15, b). In Fig. 9.15, the washer is put on the bolt 3, and above them there is a nut shown 4. At the same time, in Fig. 9.15, A chamfers are shown on the head and shaft of the bolt, and in Fig. 9.15, b they are no longer shown, but the gap between the bolt shank and the holes in the parts shown is shown. In Fig. 306, V this gap is no longer shown, but the chamfer on the nut is shown.
Rice. 9.15.
The completed simplified drawing of a bolted connection is shown in Fig. 9.15, G. It complies with GOST 2.315–68.
Please note that the lines of the invisible contour when depicting the nut and washer are not drawn (see Fig. 9.15, G).
When drawing a nut and a bolt head, take the side of the hexagon equal to the outer diameter of the thread. Therefore, in the main image, the vertical lines delimiting the middle edge of the nut and bolt head coincide with the lines of the outer diameter of the thread.
Examples of symbols for bolts, nuts and other fasteners are given in Chapter. 7 (see 7.3).
The dimensions by which the elements of a bolted connection are drawn are usually calculated depending on the outer diameter of the thread from the ratios shown in Fig. 9.15. They are called relative.
Examples of determining relative dimensions for a structural image of a bolted connection with M30 threads (d = 30 mm).
The diameter of a circle circumscribed around a hexagon is D=2d=(2 30) = 60 mm; bolt head height h= 0.7 = 0.7 30 = = 21 mm; cut length l 0 = 2d+ 6 = 2 30 + 6 = 66 mm; nut height N = 0,8d 30 = 24 mm; bolt hole diameter d 0 =1,1 d= 1.1 30 = 33 mm; washer diameter D m = 2.2 d= 2.2 30 = = 66 mm; washer height S = 0.1 d= 0.15 30 = 4.5 mm.
Relative sizes for the image of a simplified connection are calculated using the same ratios.
Hairpin connections
The formation of a drawing of a hairpin connection is shown in stages in Fig. 9.17.
First, a hole for the thread is drilled in the part and a chamfer is made (see Fig. 9.17, A), the thread is cut with a tap (see Fig. 9.17, b), pin shown 3 (see Fig. 9.17, V). The pin is screwed into the hole. Above it is the part to be connected, which has a smooth hole (see Fig. 9.17, G). A part is put on the free end of the pin 2, and on top there is a washer (see Fig. 9.17, d). Washer 4 put on a stud, nut 5 is shown above (see Fig. 9.17, e), which is screwed onto stud 3 (see Fig. 9.17, and).
Rice. 9.16.
Rice. 9.17.
Nut 5 and washer 4 are depicted in a simplified manner, as in a bolted connection, i.e. without chamfers.
The line defining the thread boundary at the lower end of the stud is drawn at the level of the surface of the part in the constructive image 1, into which the pin is screwed.
Notice how the threaded rod is depicted screwed into the hole (see Fig. 9.17, Where). This is discussed in Chap. 7, and the corresponding images are shown in Fig. 7.13.
In Fig. 9.17, g shows a simplified drawing of a hairpin connection. It does not show the chamfers, the gap between the stud rod and the hole in the part being connected, and the end of a blind threaded hole that is not filled with threads, shown in Fig. 9.17, b–f, where for clarity of the nature of the connections they are shown when they first appear.
The relative dimensions for drawing a stud connection are calculated depending on the thread diameter according to the ratios shown in Fig. 9.17.
Examples of symbols for studs are given in 8.1.
Screw connections
There is no nut in the screw connection. A blind hole with a thread and the threaded part of the screw are drawn in the same way as in a stud joint. Only in structural images the thread boundary on the rod is located above the parting line of the parts being connected.
Structural connections with screws are shown in Fig. 9.18. If the screws have a slot (slot) for gripping with a screwdriver, it is conventionally depicted as one solid thick line. In the top view, it is carried out at an angle of 45° (see Fig. 9.18).
Rice. 9.18.
Simplified images of screw connections are shown in Fig. 9.10 and 9.19, d, f.
This type of connection refers to fastening detachable connections. It is an assembly unit consisting of a bolt, nut, washer and connecting parts. Typically, bolts are used to connect parts to flanges and when frequent assembly and disassembly of the product is necessary.
Bolt- this is a threaded product, which is a rod that has a thread for a nut at one end, and a head of various shapes at the other. There are a significant number of types of bolts, differing from each other in the shape and size of the head and shank, thread pitch, design and manufacturing accuracy. The most common hex head bolts are made of normal, high and rough precision. Depending on the purpose, hex bolt heads have a normal height according to GOST 7798-70 and a reduced height according to GOST 7796-70 (Appendix A, table A.1, A.2). Each bolt diameter d correspond to certain dimensions of its head. With the same diameter, the bolt can be manufactured in different lengths l, which is standardized. The standard bolt length depends on the thickness of the parts being connected.
Standard bolt length The size is calculated from the threaded end of the rod to the supporting surface of the head. Bolt thread length l O also standardized and set depending on its diameter d and length l.
According to their design features, the following types of bolts are distinguished: 1 - without holes (in the head and shaft), 2 - with a hole for a cotter pin in the shaft, 3 - with two holes in the bolt head (for fastening the heads of a group of bolts with wire).
screw- this is a part with a threaded hole used for screwing a bolt, screw or stud onto the rod and is the closing part of the power circuit of a detachable threaded connection.
The standard provides nuts of various shapes: hexagonal, slotted, wing nuts, cap nuts, etc. Turnkey nuts can be round, square, hexagonal, etc. The most common hexagonal nuts are manufactured in three designs: 1 – with two conical chamfers on the outer surface; 2 – with one chamfer; 3 – without chamfers and with a cylindrical or conical projection at one end of the nut. For standard nuts, metric threads with coarse and fine pitch are used. According to the degree of accuracy, nuts are divided into nuts of normal, increased and rough accuracy. Nuts are divided according to their height into normal, low, high and extra high.
Washer- this is a product placed under a nut, bolt or screw head to increase their supporting surface. The washer is a flat ring of a certain thickness, without threads, with a hole slightly larger than the diameter of the rod.
The configuration of the washers is different. Round washers, manufactured according to GOST 11371-78, have two designs: 1 – without chamfer; 2 – with a chamfer (Appendix A, table A.5).
Spring washers, manufactured according to GOST 6402-70, are a steel ring with a slot and ends spread in different directions. Spring washers are divided into light, normal, heavy and extra heavy (Appendix A, Table A.6).
Simplified and conventional representation of a bolt connection
In assembly drawings of general types, bolt connections are depicted in accordance with GOST 2.315-68 in a simplified and conditional manner (depending on the scale) (Figure 8). The simplified image does not show the chamfers, the gap between the rod and the hole; the thread in the section is carried out to the end of the rod, but in the top view it is not shown. Fasteners whose rod diameters in the drawing are equal to or less than 2 mm are depicted conventionally.
a) simplified, b) conditional
Figure 8 – Images of a bolt connection
Symbols of standard products in bolted connections
For educational purposes, the designation of standard products can be written in a simplified manner.
The following parameters are indicated in the bolt designation: name, version (version 1 is not indicated), diameter, fine pitch, standard bolt length, standard number.
Bolt M 24×2.0×90 GOST 7798-70 - execution bolt 1 d=24mm, with fine thread pitch Р=2.0mm, length L= 90mm.
The nut symbol indicates the following parameters: name, version (version 1 is not indicated), diameter, fine pitch, standard number.
For educational purposes, the nut designation can be written in a simplified manner.
Nut 2M24×2.0 GOST 5915-70 – performance nut 2 , with outer diameter metric thread d=24mm, with fine thread pitch P=2.0mm.
The symbol of the washer includes: name, version (version 1 is not indicated), thread diameter of the fastener rod, standard number.
Washer 24 GOST 6402-70 – washer, with thread diameter of fastener rod 24mm.
Connecting parts with a pin.
A pin connection of parts consists of a stud, nut, washer and fastened parts.
Studs are used for detachable connections of parts in cases where one of the parts being fastened is thick or, due to its design, there is no room for a bolt head.
A stud connection is carried out as follows: in one of the parts to be connected there is a blind or through hole with a thread, and in the other there is a hole without a thread with a diameter of 1.1d, where d is the diameter of the stud.
The stud is screwed at one end into the first hole and passes freely through the second, then, as with a bolted connection, a washer is put on the protruding end of the stud and a nut is screwed on. The depth of the blind hole must be greater than the length of the screwed end of the stud, i.e. The end of the pin should not rest against the bottom of the hole.
The nut and washer are depicted in a simplified manner, as in a bolted connection.
The line defining the thread boundary at the lower end of the stud is always drawn at the level of the surface of the part into which the stud is screwed.
The dimensions of the parts of the simplified connection image are taken depending on the thread diameter of the stud - d, Figure 12.
The resulting stud length l (without the threaded screw-in end) is compared with standard values and the nearest larger standard value is selected.
Standard range of bolt lengths in mm according to GOST 22036-76: 14; 16; (18); 20; (22); 25; (28); thirty; (32); 35; (38); 40; 42; 45; (48); 50; 55; 60; 65; 70; 75; 80; 85; 90; (95); 100; (105); 110; (115); 120.
Magnitude l 1 depends on the material of the part into which the pin is screwed, and determines the standard of the pin:
l 1 = d – for steel, bronze, brass – GOST 22032–76;
l 1 = 1.25d – for malleable and gray cast iron – GOST 22034–76;
l 1 = 2d – for light metals – GOST 22038–76.
Figure 12 – Simplified illustration of connecting parts with a pin
Connecting parts with a screw
A screw connection consists of a screw and two parts to be connected, such as a cover and a housing.
This type of connection is performed as follows: a cover with unthreaded holes is placed on a part with threaded holes (body), and then screws are screwed into the body and the heads press the cover to the body.
The dimensions of the parts of the simplified image of the connection are taken depending on the diameter of the screw thread - d, Figure 13.
The length of the screwed-in (mounting) end of the screws - l1 depends on the material of the parts that have a threaded hole, and is calculated using the same formulas as for a stud connection.
When screws have a slot for gripping with a screwdriver, this slot is conventionally depicted as one solid thick line.
Sheet 2-3 includes 5-7 sketches of the main parts, made according to the assembly drawing. All sketches are done in pencil on squared paper or graph paper. The sequence of the sketch and the requirements for its implementation are set out in the description of sheet 2-1.
Each detail is drawn on a separate sheet. Sheet formats for sketches are chosen independently (in accordance with GOST 2.301-68, taking into account the number of images (types, sections, sections) and their size).
Sketching parts begins with reading the assembly drawing. Using the description of the drawing, you should determine what parts (and in what quantity) the assembly unit consists of, how the parts are connected to each other and their interaction. When analyzing the shape of each part, they focus on the projection connection and shading of the part. Having found the part in all the images, determine the number of views, the main view, the sections necessary to depict it in the drawing. After this, they begin to sketch the part.
You should not copy a part from an assembly drawing, since views and sections in an assembly drawing give an idea of the design of the product, and in a sketch - about the shape of the part. Therefore, when depicting parts, you must remember:
The number of images should be minimal, but quite sufficient to understand the design of the part;
If the design of the part is symmetrical, the full cut can be omitted by connecting half of the part's appearance to the cut;
It is advisable to place the image of the part as it is installed in the machine during processing or in the product;
The image should occupy 70% of the sketch area, according to this the size of the images on the sketch is selected;
When making a sketch of a part, they determine what dimensions need to be put in order to manufacture the depicted part.
Usually, dimensions for drawings of parts are taken from the contours of the assembly drawing, since there are only a few nominal dimensions in the drawing - these are overall, connecting, installation and some others, but we are interested in all the dimensions necessary for the manufacture of the part. In this manual, printed drawings do not have a specific (standard) scale.
In order to determine the true dimensions of the part, it is necessary to find out how many times the assembly drawing is reduced (or enlarged) during printing. For this purpose, find the largest size in the drawing (the larger the size, the smaller the error in the calculation). For example, size 120, when directly measured in the figure, turned out to be equal to 52 mm. Dividing 120 by 52 gives a reduction factor of approximately 2.307. Now, in order to find out the dimensions not indicated on the assembly drawing, you need to measure them on the drawing and multiply the resulting values by 2.307.
The main inscription is drawn up according to the description of the assembly drawings given in this manual. The designation of the drawing is entered in the frame located in the upper left corner (frame size 70×14). In this case, the designation is rotated 180°.
Simplifications of images allowed in the assembly drawing should not be mechanically transferred to sketches of parts. For example, grooves and chamfers that are not shown on the assembly drawing are drawn according to GOST 10549-80. Elements of parts that are not shown on the assembly drawing are drawn on the sketches: casting and stamping slopes, tapers, roundings, fillets, etc.
