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Selection principles of fasteners(1)

Date:2020-06-08

1. Determine the category
Standard fasteners are divided into ten categories, and the selection should be based on the use of the standard fastener and its use function to determine.
① Bolt: The bolt is generally matched with a nut (usually plus a washer or two washers), and is used for connection and fastening.
②Nuts: Nuts and bolts are used together.
③Screw: The screw is usually used alone (sometimes with a washer), and generally plays a role of tightening or tightening.
④Studs: studs are generally threaded at both ends (single-end studs are single-end threaded), usually one end of the screw is screwed into the body of the component, and the other end is matched with the nut to play the role of connection and fastening , But to a large extent also has a fixed distance effect.
⑤ Washer: The washer is used between the support surface of bolts, screws and nuts and the process support surface to prevent loosening and reduce the stress of the support surface.
⑥Self-tapping screw: The screw hole of the workpiece matched with the self-tapping screw does not need to be tapped in advance. While screwing in the self-tapping screw, the internal thread is formed.
⑦Rivet: The rivet has a head at one end, and the rod has no thread. When in use, the rod is inserted into the hole of the connected piece, and then the end of the rod is riveted to connect or fasten.
⑧ Pin: The pin is inserted into the workpiece when it is in use, and usually plays a role of connection or positioning.
⑨ Retaining ring: Retaining ring is usually on the shaft or in the hole, which plays a role in limiting the axial direction of the workpiece.
⑩Wood screws: Wood screws are used for screwing into wood for connection or fastening.
Second, determine the standards and varieties
1. The principle of variety selection:
(1) Considering the efficiency of processing and assembly, within the same machine or project, the variety of standard parts should be minimized.
⑵For economic considerations, priority should be given to the selection of commodity standard parts.
⑶According to the expected use requirements of standard parts, select the type according to the type, mechanical performance, precision and thread.
2. Type:
⑴ Bolt:
①General purpose bolts: there are many varieties, including hexagon head and square head, see national standard GB5780-GB5790, etc.
② Bolts for reaming holes: When using, bolts are tightly inserted into the holes made by the hinge to prevent the workpiece from being misaligned, see GB27, etc.
③ Anti-rotation bolt: There are square neck and vertebrae, see GB12-15, etc.
④Special purpose bolts: see GB37 for T-slot bolts; see GB798 for hinge bolts; see GB799 for anchor bolts.
⑤ High-strength bolt connection pair for steel structure: generally used for friction-type connection of steel structures such as buildings, bridges, towers, pipe supports and lifting machinery, see GB3632, etc.
⑵Nut:
①General-purpose nuts: mainly refers to hexagon nuts, and other square nuts, many varieties, see GB41, GB6170-6177 and so on.
②Slotted nut: mainly refers to the hexagonal slotted nut, that is, the process is processed above the hexagonal nut. It is used in conjunction with bolts with holes and cotter pins to prevent relative rotation of bolts and nuts, see GB6178-6181, etc.
③ Lock nut: refers to a nut with a locking function, with nylon insert hexagonal lock nut, see GB889, GB6182, GB6183 and all metal hexagonal lock nut, see GB6184-6187.
④Special purpose nuts: such as dish nuts, see GB62; ring nuts, see GB63; cap nuts, see GB802, GB923; knurled nuts, see GB806, GB807 and embedded nuts, see GB809, etc.
⑶Screw:
①Machine screw: Divided into many varieties due to different head shape and groove shape. The head type includes cylindrical head, pan head, countersunk head and semi countersunk head, and the head shape is slotted (a flat material) and cross groove. See GB65, GB67-69 and GB818-820 etc.
②Set screw: The set screw uses its tail end to prevent mutual displacement between the workpieces and transmit less torque. See GB71, GB73-75, GB77, GB78, etc.
③ Hexagon socket head cap screws: Hexagon socket head cap screws are suitable for occasions where the installation space is small or the head of the screw needs to be buried. , See GB70, GB6190, GB6191 and GB2672- 2674 etc.
④Special purpose screws: such as positioning screws, see GB72, GB828, GB829; do not take off the screws, see GB827-839, GB948, GB948 and eyebolts, see GB825, etc.
⑷ Stud:
①Dual-head studs of unequal length: suitable for occasions where one end is screwed into the component body to play a role of connection or tightening. See GB897-900 and so on.
②Equal-length double-headed studs: suitable for connecting the end with the nut, playing the role of connection or fixed distance. See GB901, GB953, etc.
⑸ Washer:
①Flat washer: It is used to overcome the uneven support surface of the workpiece and increase the stress area of ​​the support surface. See GB848, GB95-97 and GB5287.
②Spring (elastic) washers: see GB93, GB859, etc. for spring washers, and GB860, GB955, etc. for elastic washers.
③Backwash washer: with internal tooth lock washer, see GB861; external tooth lock washer, see GB862; single ear stop washer, see GB854; double ear stop washer, see GB855; round nut stop washer, see GB858 Wait.
④Diagonal washer: In order to adapt to the inclination of the workpiece support surface, oblique washers can be used. For square steel washers with I-beam, see GB852; for square steel washers with channel steel, see GB853.
⑹Self-tapping screws:
①Ordinary self-tapping screw: The thread conforms to GB5280 (thread for self-tapping screw), the pitch is large, suitable for use on thin steel plate or copper, aluminum, plastic. See GB845-847, GB5282-5284, etc.
②Self-tapping locking screw: The thread conforms to the common metric coarse thread, suitable for use in vibration-resistant occasions. See GB6560-6564.
⑺ Rivets:
①Hot forging rivets: The general specifications are large, and they are mostly used for locomotives, ships and boilers. The head is usually formed by hot forging. See GB863-866.
② Cold heading forming rivets: the general diameter specification is ≤16mm, and the head is usually formed by cold heading. See GB867-870, GB109, etc.
③ Hollow and semi-hollow rivets: hollow rivets, see GB976; semi-hollow rivets, see GB873-875, etc.
④Special purpose rivets: there are headless rivets, see GB1016; tubular rivets, see GB975; sign rivets, see GB827, etc.
⑤Bucket rivet: It is a kind of rivet that is riveted on one side. It is a new type of rivet that has been widely used in recent years. It has the characteristics of rapidity, safety, and convenience, and has the advantages of waterproof and leakage resistance.
⑻ Pin:
① Cylindrical pin: with or without threaded cylindrical pin, see GB119; internally threaded cylindrical pin, see GB120; externally threaded cylindrical pin, see GB878; elastic cylindrical pin, see GB879; perforated cylindrical pin, see GB880, etc.
②Conical pin: with or without threaded cylindrical pin, see GB117; internally threaded cylindrical pin, see GB118; screw-tailed conical pin, see GB881; open-ended conical pin, see GB877.
③ Cotter pin: It is generally matched with the bolt with screw hole and slotted nut to prevent the bolt and nut from loosening. See GB91.
⑼ Retaining ring:
① Elastic retaining ring: elastic retaining ring with holes. See GB893; elastic retaining ring for shaft. See GB894 and shaft stop ring GB896.
② Steel wire retaining ring: steel wire retaining ring with holes, see GB895.1; steel wire retaining ring for shafts, see GB895.2 and steel wire locking ring, see GB921.
③ Locking retaining ring for shaft parts: Retaining ring with conical pin lock, see GB883; Retaining ring with screw lock, see GB884, GB885, etc.
④ Shaft end retaining ring: shaft end retaining ring fastened with screws, see GB891 and shaft end retaining ring fastened with bolts, see GB892.
⑽Wood screws:
It is divided into many varieties because of the different head shape and groove shape. There are several types of heads, such as round head, countersunk head, and semi countersunk head. The head grooves are slotted (slotted) and cross grooved. See GB99-101, GB950-952, etc.

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