Common misunderstandings and selection principles of fasteners

Common misunderstandings and selection principles of fasteners

Selection principle of fasteners

1. Determine category

Standard fasteners are divided into ten categories, and the selection should be determined according to the application occasions and functions of standard fasteners.

① Bolt: the bolt is generally matched with the nut (usually with one washer or two washers), which is used for connection and fastening.

② Nut: the nut is matched with the bolt.

③ Screws: screws are usually used alone (sometimes with washers) and generally play a fastening or tightening role.

④ Studs: studs are generally threaded at both ends (single head studs are threaded at one end). Usually, one end of the thread is firmly screwed into the body of the component, and the other end is matched with the nut, which plays the role of connection and fastening, but also has the role of spacing to a large extent.

⑤ Washer: the washer is used between the bearing surface of bolts, screws and nuts and the process bearing surface to prevent looseness and reduce the stress of the bearing surface.

⑥ Self 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.

⑦ Rivet: one end of the rivet has a head, and the rod has no thread. When in use, insert the rod into the hole of the connected part, and then rivet the end of the rod to connect or fasten.

⑧ Pin: when in use, the pin is inserted into the workpiece and usually plays the role of connection or positioning.

⑨ Retaining ring: the retaining ring is usually on the shaft or in the hole to limit the axial direction of the workpiece.

⑩ Wood screw: wood screw is used to screw into wood for connection or fastening.

2. Determine standards and varieties

1. Selection principle of varieties:

(1) considering the working efficiency of processing and assembly, the variety of standard parts should be minimized in the same machinery or project.

(2) from the perspective of economy, the varieties of commodity standard parts should be preferred.

(3) according to the expected use requirements of standard parts, the varieties shall be selected according to the type, mechanical performance, accuracy, thread and other aspects.

2. Type:

(1) bolt:

① General purpose bolts: there are many varieties, including hexagon head and square head. See the national standard gb5780-gb5790, etc.

② Bolt for reaming hole: when in use, insert the bolt tightly into the reamed hole to prevent workpiece dislocation, see GB27, etc.

③ Anti rotation bolt: it can be divided into square neck and vertebral body, see gb12-15, etc.

④ Bolts for special purposes: for example, bolts for T-groove, see GB37; Union bolt, see gb798; Foundation bolts, see gb799, etc.

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 hoisting machinery, see gb3632, etc.

⑵ nut:

① General purpose nuts: mainly refer to hexagonal nuts, and square nuts. There are many varieties, see gb41, gb6170-6177, etc.

② Slotted nut: it mainly refers to hexagon slotted nut, that is, the screw is processed above the hexagon nut. It is used in conjunction with threaded bolts with holes and cotter pins to prevent the relative rotation of bolts and nuts. See gb6178-6181, etc.

③ Lock nut: refers to the nut with locking function, including nylon insert hexagon lock nut, see gb889, gb6182, gb6183 and all metal hexagon lock nut, see gb6184-6187.

④ Nuts for special purposes: such as dished nuts, see gb62; Ring nut, see gb63; Cap Nut, see gb802, gb923; Knurled nuts, see gb806, gb807 and embedded nuts, see gb809, etc.

(3) screw:

① Machine Screw: it is divided into many varieties due to different head types and groove types. The head types include cylindrical head, pan head, countersunk head and semi countersunk head. The head shape is slotted (slotted) and cross recessed. See gb65, gb67-69, gb818-820, etc.

② Set screw: the set screw uses its tail end to prevent mutual displacement between workpieces and transmit less torque. See gb71, gb73-75, gb77, gb78, etc.

③ Socket head cap screws: socket head cap screws are suitable for occasions where the installation space is small or the screw head needs to be embedded., See gb70, gb6190, gb6191 and gb2672-2674, etc.

④ Special purpose screws: such as Set Screws, see gb72, gb828, gb829; See gb827-839, gb948, gb948 and eyebolt, see gb825, etc. for screws that do not come out.

(4) studs:

① Unequal length double head studs: applicable to the occasion where one end is screwed into the body of the component for connection or fastening. See gb897-900, etc.

② Equal length double head stud: it is suitable for matching the connecting end with the nut, and plays the role of connection or spacing. See gb901, gb953, etc.

(5) washer:

① Flat Washer: used to overcome the uneven supporting surface of the workpiece and increase the stress area of the supporting surface. See gb848, gb95-97 and gb5287.

② Spring (elastic) washer: see gb93, gb859, etc. for Spring Washer, see gb860, gb955, etc.

③ Non return washer: with internal tooth lock washer, see GB861; External tooth lock washer, see gb862; Single lug lock washer, see gb854; Double lug lock washer, see gb855; Round nut lock washer, see gb858, etc.

④ Inclined washer: in order to adapt to the inclination of the supporting surface of the workpiece, inclined washer can be used. Square bevel washer with I-steel, see gb852; Refer to gb853 for square and oblique washers for channel steel.

(6) self tapping screw:

① Ordinary self tapping screw: the thread conforms to gb5280 (thread for self tapping screw), and the pitch is large, which is suitable for use on steel sheet, copper, aluminum and plastic. See gb845-847, gb5282-5284, etc.

② Self tapping locking screw: the thread conforms to ordinary metric coarse thread, which is suitable for use in vibration resistant occasions. See gb6560-6564.

(7) rivet:

① Hot forged rivet: generally larger in size, it is mostly used in locomotives, ships, boilers, etc., and the head is usually formed by hot forging. See gb863-866.

② Cold heading forming rivet: generally, the 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 rivet, see gb873-875, etc.

④ Special purpose rivets: headless rivets, see gb1016; Tubular rivet, see gb975; Label rivet, see gb827, etc.

⑤ Blind rivets: they are single-sided rivets. They are a new type of rivets widely used in recent years. They are fast, safe and convenient, and have the advantages of waterproof and leakage proof.

(8) pin:

① Cylindrical pin: whether there is threaded cylindrical pin, see gb119; Internal thread cylindrical pin, see gb120; External thread cylindrical pin, see gb878; Elastic cylindrical pin, see gb879; Cylindrical pin with hole, see gb880, etc.

② Taper pin: with or without threaded cylindrical pin, see gb117; Internal thread cylindrical pin, see GB118; Screw tail taper pin, see gb881; Split taper pin, see gb877.

③ Cotter pin: generally, it matches with the threaded bolt with hole and slotted nut to prevent the bolt and nut from loosening. See gb91.

(9) retaining ring:

① Circlip: circlip with holes. See GB893; Circlip for shaft. See gb894 and split ring for shaft gb896.

② Steel wire retainer: steel wire retainer for holes, see gb895.1; See gb895.2 for steel wire retaining ring for shaft and gb921 for steel wire locking ring.

③ Locking ring for shaft parts: see gb883 for the ring locked with taper pin; See gb884, gb885, etc. for the retaining ring locked with screws.

④ Shaft end retaining ring: see gb891 for shaft end retaining ring fastened with screws and gb892 for shaft end retaining ring fastened with bolts.

(10) wood screw:

It is divided into many varieties due to different head types and groove types. The head types include round head, countersunk head, semi countersunk head, etc. the head groove shape is slotted (slotted groove) and cross groove. See gb99-101, gb950-952, etc.