1. Determination of categories
There are twelve categories of standard fasteners * * *, which are determined according to the use occasions and functions of fasteners.
(1) Bolts and bolts are widely used for detachable connection in remanufacturing, and are generally used together with nuts (usually with one washer or two washers).
(2) Nuts and bolts are used together.
(3) screws are usually used alone (sometimes with washers), and generally play a role in fastening or fastening, and should be screwed into the internal thread of the machine body.
(4) Studs are mostly used to connect places where one of the connected parts is thick, and it is necessary to use a compact structure or it is not suitable to use bolts because of frequent disassembly. Screw
columns are generally threaded at both ends (single-headed studs are threaded at one end). Usually, one thread is firmly screwed into the component body, and the other end is matched with nuts, which plays the role of connection and fastening, but it also plays the role of spacing to a great extent.
(5) Wood screws Wood screws are used to screw in wood and play a role in connection or fastening.
(6) The self-tapping screw and the working screw hole matched with the self-tapping screw need not be pre-tapped, and the internal thread is molded while screwing in the self-tapping screw.
(7) The washer is placed between the bearing surface of bolts, screws and nuts and the bearing surface of the workpiece to prevent looseness and reduce the stress on the bearing surface.
(8) Retaining ring Retaining ring is mainly used to position, lock or stop the parts on the shaft or hole.
(9) Pins are usually used for positioning, connecting or locking parts, and can also be used as overload shearing elements in safety devices.
(1) The rivet has a head at one end and the stem is unthreaded. When in use, the rod is inserted into the hole of the connected piece, and then the end of the rod is riveted tightly, which plays the role of connection or
fastening.
(11) the connecting pair is the combination of screw or bolt or tapping screw and washer. After the washer is installed on the screw, it must be able to rotate freely on the screw (or bolt) without falling off. Mainly plays the role of fastening or tightening.
(12) Others mainly include welding nails.
2. Determine varieties
(1) Selection principle of varieties
① Considering the working efficiency of processing and assembly, the varieties of fasteners should be reduced as much as possible in the same machinery or project;
② from the economic point of view, commercial fastener varieties should be preferred.
③ According to the expected use requirements of fasteners, the selection varieties are determined according to the types, mechanical properties, accuracy and threads.
(2) types
① bolts
a) general purpose bolts: there are many kinds, including hexagonal head and square head. Hexagon-head bolts are the most commonly used, and they are classified into A, B, C and other product grades according to manufacturing accuracy and product quality < P >, with Grade A and B being the most widely used, and they are mainly used in important places with high assembly accuracy and under large impact, vibration or variable load < P >. Hexagon head bolts can be divided into hexagon head and large hexagon head according to the size of their head supporting area and installation position.
varieties with holes in the head or screw are used when locking is needed. The square head of the square head bolt has a large size and stress surface, which is convenient for the wrench mouth to get stuck or lean against other parts to start and stop.
It is often used in rough structures and sometimes in T-shaped grooves, which is convenient for the bolt to loosen and adjust its position in the grooves. See GB8, GB578～579, etc.
b) Bolts for reaming holes: When in use, the bolts are tightly inserted into the reamed holes to prevent the workpiece from dislocation, as shown in GB27, etc.
c) anti-rotation bolt: it can be divided into square neck and tenon, see GB 12 ~ 15, etc.
d) special purpose bolts: including bolts for T-shaped groove, eye bolts and anchor bolts. Bolts for T-groove are mostly used in places where the connection needs to be disconnected frequently < P >; Anchor bolts are used to fix the frame or motor base in cement foundation. See GB798, GB799, etc.
e) High-strength bolt connection pairs for steel structures: generally used for friction
connection of steel structures such as buildings, bridges, towers, pipe supports and hoisting machinery, see GB3632, etc.
② Nuts
a) General purpose nuts: There are many kinds, such as hexagonal nuts and square nuts. Hexagon nut with hexagon bolt is the most widely used, which is divided into A, B, C and other product grades according to the manufacturing accuracy and product quality. Hexagon thin nuts are used as auxiliary nuts in locking devices, which play a locking role, or are used where the threaded connection pair < P > mainly bears shear force. Hexagon thick nuts is often used in connections that are often disassembled. The square nut is matched with the square head bolt, so the wrench is not easy to slip when stuck, and it is mostly used in rough and simple structures. See GB41, GB617～6177, etc.
b) slotted nut: it mainly refers to hexagonal slotted nut, that is, a groove is machined above the hexagonal nut. It is used with threaded bolt with hole and cotter pin
to prevent the bolt and nut from rotating relatively, see GB6178～6181, etc.
c) lock nut: refers to the nut with locking function, including nylon insert hexagon lock nut and all-metal hexagon lock nut. Hexagonal
lock nut has a very reliable anti-loosening ability, which has the advantages of no damage to bolts and connected parts
and frequent loading and unloading at the service temperature of-6 ~+1℃ and certain medium conditions. See GB889, GB6182～6187, etc.
d) special purpose nuts: such as butterfly nuts, cap nuts, knurled nuts and embedded nuts. Generally, butterfly nuts can be disassembled without tools
, and are usually used in places where they need to be disassembled frequently and the stress is not great; Cap nut is used where the end screw thread needs to be covered. See GB62, GB63, GB82,
GB923, GB86, GB87, GB89, etc.
③ screws
a) machine screws: they are divided into many varieties due to different head shapes and groove shapes. There are several types of head, including cylindrical head, pan head, countersunk head and semi-countersunk head. The groove shape of head
is generally slotted (slotted), crossed groove and hexagonal groove. Cross-groove screws have good alignment when being screwed, and the head strength is greater than that of one-groove screws, so it is not easy to be bald. Generally, they are mostly used in mass production. Hexagon socket head screws and hexagon socket head screws can exert a large tightening torque, and the connection strength is high, and the head can be buried in the machine body, which is used for the joints requiring compact structure and smooth appearance. See GB65, GB 67 ~ 69 and GB 818 ~ 82, etc.
b) set screws: set screws are used to fix the relative positions of parts, and the heads are of slotted, hexagonal and square head types. The square head
can exert a large tightening torque, and the jacking force is large, so it is not easy to be bald. However, the head size is large, which is inconvenient to be buried in the parts and unsafe, especially for the moving parts. The one with a slotted and hexagonal socket is easy to sink into the parts. According to the different use requirements, the end of the set screw is commonly used in three types: cone end, flat end and < P > cylindrical end. The cone end is suitable for parts with low hardness; When using taper-end screw without tip, a hole should be drilled on the top surface of the part, and the conical surface is pressed against the edge of the hole < P >. The screw with flat end has a large contact area and does not damage the surface of the part after being tightened. It is used to tighten the plane with high hardness or adjust the position frequently. Screws with cylindrical ends at the end
do not damage the surface of the parts, and are mostly used to fix the parts mounted on the pipe shaft (thin-walled parts). The cylindrical ends are pushed into the holes on the shaft, and a large load can be transmitted by the shear resistance of the cylindrical ends. See GB71, GB73 ~ 75, GB77 ~ 78, etc.
c) Hexagon socket head screws: Hexagon socket head screws are suitable for occasions where the installation space is small or the head of the screw needs to be buried, as shown in GB7, GB 619 ~
6191 and GB2672～2674;
d) special-purpose screws: such as set screws, non-slip screws and eyebolts. See GB72, GB 828 ~ 829, GB 837 ~ 839,
GB 948 ~ 949 and GB825, etc.
④ Studs
a) Unequal-length double-headed studs: suitable for the occasion where one end is screwed into the machine body of the component for connection or fastening, as shown in GB 897 ~ 9;
b) Equal-length double-headed stud: suitable for connecting or spacing with nuts at both ends. See GB91 and GB953, etc.
⑤ wood screws
are divided into many varieties due to different head shapes and groove shapes. There are several types of heads, such as round head, countersunk head, semi-countersunk head, etc., and the groove shape of the head is slotted (straight groove) and cross groove
, as shown in GB 99 ~ 11 and GB 95 ~ 952.
⑥ Self-tapping screws
a) Ordinary self-tapping screws: the thread conforms to GB528, with large pitch, which is suitable for use on thin steel plates or copper, aluminum and plastics, as shown in GB 845 ~ 847,
GB 5282 ~ 5284, etc.
b) Self-tapping locking screw: the thread conforms to the common metric coarse thread, and it is suitable for vibration-resistant occasions. See GB656～6564.
⑦ washer
a) flat washer: used to overcome the unevenness of the workpiece bearing surface and increase the stress area of the bearing surface, as shown in GB848, GB 95 ~ 97 and GB95～97;
b) spring (elastic) washer: the spring washer prevents the fastener from loosening by elasticity and bevel friction, and is widely used in the joints that are often disassembled
. There are many sharp elastic warping teeth on the circumference of the elastic washer with internal teeth and the elastic washer with external teeth, which are pressed on the supporting surface to prevent the fastener from loosening. The elastic washer with internal teeth is used under the screw head with small head size; External tooth elastic washer is mostly used under bolt head and nut. The elastic washer with teeth is smaller than the ordinary spring washer, and the fastener bears uniform force and is reliable in preventing loosening, but it is not suitable for frequent disassembly. See GB93, GB 859 ~ 86 and GB955；;
c) check washers: there are internal tooth lock washers, external tooth lock washers, single ear stop washers, double ear stop washers and stop washers for round nuts
. Single-ear and double-ear stop washers allow the nut to be tightened and locked at any position, but the fastener should be close to the edge, as shown in GB 861 ~ 862, GB 854 ~ < P > 855, GB858, etc.
d) Oblique washer: In order to adapt to the inclination of the working bearing surface, an oblique washer can be used. Square inclined washer is used to flatten inclined planes such as channel steel and I-beam flange, so that the bearing surface of the nut is perpendicular to the nail rod and the screw rod is prevented from being subjected to bending force when the nut is tightened. See GB 852 ~ 853, etc.
⑧ retaining ring
a) elastic retaining ring: the elastic retaining ring for shaft and hole is stuck in the shaft groove or hole groove for the rolling bearing to stop retreating after being installed, and there is also an open retaining ring for shaft
, which is mainly used for positioning parts in the shaft groove, but it cannot bear axial force. See GB 893 ~ 894 and GB896;
b) steel wire retaining ring: steel wire retaining ring with holes (for shaft) and steel wire locking ring. The steel wire retaining ring is installed in the shaft groove or hole groove for the positioning of parts, and can also bear certain axial force when it is the same as < P >. See GB 895.1 ~ .2 and GB921；;
c) Locking retaining rings for shaft parts: retaining rings locked with taper pins and retaining rings locked with screws are mainly used to prevent axial movement of shaft parts. See GB 883 ~ 892.
d) shaft end retaining ring: the shaft end retaining ring fastened with screws and the shaft end retaining ring fastened with bolts are mainly used to lock the parts fixed at the shaft end
. See GB 883 ~ 982.
⑨ pin
a) cylindrical pin: cylindrical pin is mostly used to fix parts on the shaft, transmit power or serve as a positioning element. Cylindrical pins have different diameter tolerances, which can be used for different matching requirements. Cylindrical pins are generally fixed in holes by interference, so it is not advisable to disassemble them more. See GB 119 ~ 12, GB 878 ~ 88, etc.
b) Conical pin: Conical pin has a taper of 1: 5, which is convenient for installation and alignment, and can also ensure self-locking. It is generally used as a positioning element and a connecting element
, and is often used in places requiring frequent disassembly. Tapered pin with internal thread and tapered pin with screw tail are used for holes that are not penetrated or holes where it is difficult to punch pins. Open-tailed circle
After the taper pin is driven into the hole, the end can be opened to prevent the pin itself from slipping out of the hole. See GB 117 ~ 118, GB881 and GB877, etc.
The pin holes of cylindrical pins and all kinds of conical pins are generally reamed, which will reduce the positioning accuracy and fastening of the connection after repeated assembly and disassembly, and can only transmit a small load
. The elastic cylindrical pin itself is elastic, and it can keep tension when installed in the hole, so it is not easy to loosen, and it is convenient to disassemble, and it does not affect the matching property. The pin hole does not need to be hinged. A pin with holes and a pin shaft are both used at the hinge joint;
c) cotter pin: cotter pin is an anti-loosening device for connecting parts. When in use, it is inserted into the pin holes of nuts, bolts with pin holes or other connectors
, and then the feet are separated. See GB91.
⑩ rivets
a) hot forging rivets: generally, they are large in specifications and are mostly used in locomotives, ships and boilers. Usually, the head is formed by hot forging, as shown in
GB 863 ~ 866;
b) cold heading rivet: generally, the diameter is 16mm, and the head is usually formed by cold heading, as shown in GB 867 ~ 87 and GB19.
c) hollow and semi-hollow rivets: hollow rivets are used in places where the shear force is not great, and are often used to connect nonmetallic parts such as plastic, leather, wood and canvas;