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【Professional knowledge】The principle of selection of commonly used fasteners can be used in mechanical design

【Professional knowledge】The principle of selection of commonly used fasteners can be used in mechanical design

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  • Time of issue:2022-04-16
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(Summary description)

【Professional knowledge】The principle of selection of commonly used fasteners can be used in mechanical design

(Summary description)

  • Categories:Company news
  • Author:
  • Origin:
  • Time of issue:2022-04-16
  • Views:0
Information

1. Determine the category

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

Bolts: Bolts are generally matched with nuts (usually plus a washer or two washers) for connection and fastening.

Nuts: Nuts are used in conjunction with bolts.

Screws: Screws are usually used alone (sometimes with washers), generally for tightening or tightening.

Stud: Studs are generally threaded at both ends (single-headed studs are threaded at one end), usually one end of the rib 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 to a large extent also has the role of distance.

Washers: Washers are used between the bearing surfaces of bolts, screws and nuts and the process bearing surface to prevent loosening and reduce the stress on the bearing surface.

Self-tapping screw: The screw hole of the workpiece matched with the self-tapping screw does not need to be tapped in advance, and the internal thread is formed at the same time as the self-tapping screw is screwed in.

Rivet: A rivet has a head on one end and an unthreaded stem. When in use, the rod is inserted into the hole of the connected piece, and then the end of the rod is riveted for connection or fastening.

Pin: The pin is inserted into the workpiece when in use, usually for connection or positioning.

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

Wood Screws: Wood screws are used to screw into wood for connection or fastening.


2. Determining standards and varieties

1. Principles of selection of varieties:

Considering the efficiency of processing and assembly, the variety of standard parts should be minimized within the same machinery or project.

From the economical consideration, the commodity standard parts varieties should be preferred.

According to the expected use requirements of the standard parts, the selected varieties are determined in terms of type, mechanical properties, precision and thread.

2. Type:

bolt:

General-purpose bolts: There are many varieties, including hexagonal head and square head, see national standards GB5780-GB5790, etc.

Bolts for reaming holes: When using, the bolts are tightly inserted into the reamed holes to prevent the workpiece from being dislocated, see GB27, etc.

Anti-rotation bolt: There are square neck and vertebra, see GB12-15 and so on.

Special purpose bolts: such as T-slot bolts, see GB37; joint bolts, see GB798; anchor bolts, see GB799, etc.

High-strength bolt connection pair for steel structure: generally used for friction-type connection of steel structures such as buildings, bridges, towers, pipeline supports and hoisting machinery, see GB3632, etc.


Nut:

General purpose nuts: mainly refer to hexagonal nuts, and there are also square nuts, which have many varieties, see GB41, GB6170-6177, etc.

Slotted nut: mainly refers to the hexagonal slotted nut, that is, the groove is processed above the hexagonal nut. It is used in conjunction with the screw hole bolt and cotter pin to prevent the relative rotation of the bolt and the nut, see GB6178-6181, etc.

Lock nut: refers to the nut with locking function, including nylon insert hexagonal lock nut, see GB889, GB6182, GB6183 and all-metal hexagonal lock nut, see GB6184-6187.

Special purpose nuts: such as disc nuts, see GB62; ring nuts, see GB63; cap nuts, see GB802, GB923; knurled nuts, see GB806, GB807 and embedded nuts, see GB809, etc.


Screw:

Machine screws: Divided into many varieties due to different head types and groove types. There are several types of head types: cylindrical head, pan head, countersunk head and semi-sink head. See GB65, GB67-69 and GB818-820, etc.

Set screw: Set screw uses its tail to prevent mutual displacement between workpieces and transmit less torque. See GB71, GB73-75, GB77, GB78, etc.

Hexagon socket head cap screws: The 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.

Special purpose screws: such as positioning screws, see GB72, GB828, GB829; non-prolapse screws, see GB827-839, GB948, GB948 and eyebolts, see GB825, etc.


Studs:

Unequal length studs: suitable for occasions where one end is screwed into the body of the component for connection or fastening. See GB897-900 and so on.

Equal length stud stud: suitable for matching the connecting end with the nut, which plays the role of connection or distance. See GB901, GB953, etc.


washer:

Flat washer: used to overcome the unevenness of the support surface of the workpiece and increase the stress area of ​​the support surface. See GB848, GB95-97 and GB5287.

Spring (elastic) washers: see GB93, GB859, etc. for spring washers, and GB860, GB955, etc. for elastic washers.

Backstop washers: lock washers with internal teeth, see GB861; lock washers with external teeth, see GB862; single-ear stop washers, see GB854; double-ear stop washers, see GB855; round nut stop washers, see GB858, etc. .

Diagonal washers: In order to adapt to the inclination of the workpiece support surface, inclined washers can be used. For square inclined washers with I-beam, see GB852; for channel steel, see GB853.


Self-tapping screws:

Ordinary self-tapping screw: the thread conforms to GB5280 (thread for self-tapping screw), the pitch is large, and it is suitable for use on thin steel plate or copper, aluminum, and plastic. See GB845-847, GB5282-5284, etc.

Self-tapping locking screw: The thread conforms to the ordinary metric coarse thread, which is suitable for use in applications requiring vibration resistance. See GB6560-6564.


rivet:

Hot forging rivets: generally larger in size, mostly used in locomotives, ships and boilers, etc., usually the head is formed by hot forging. See GB863-866.

Cold heading forming rivets: The general diameter specification is less than or equal to 16mm, and the head is usually formed by cold heading. See GB867-870, GB109, etc.

Hollow and semi-hollow rivets: hollow rivets, see GB976; semi-hollow rivets, see GB873-875, etc.

Special purpose rivets: with or without head rivets, see GB1016; tubular rivets, see GB975; sign rivets, see GB827, etc.

Blind rivet: It belongs to a single-sided riveting rivet. 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 anti-leakage.


pin:

Cylindrical pins: cylindrical pins with or without threads, see GB119; cylindrical pins with internal threads, see GB120; cylindrical pins with external threads, see GB878; elastic cylindrical pins, see GB879; cylindrical pins with holes, see GB880, etc.

Tapered pin: cylindrical pin with or without thread, see GB117; cylindrical pin with internal thread, see GB118; taper pin with screw tail, see GB881; taper pin with split end, see GB877.

Cotter pin: It is generally matched with screw bolts with holes and slotted nuts to prevent the bolts and nuts from loosening. See GB91.


retaining ring:

Retaining ring: Retaining ring with holes. See GB893; circlips for shafts. See GB894 and shaft retaining ring GB896.

Wire retaining ring: wire retaining ring with holes, see GB895.1; wire retaining ring for shaft, see GB895.2 and wire locking ring, see GB921.

Locking retaining rings for shaft parts: retaining rings locked with taper pins, see GB883; retaining rings locked by screws, see GB884, GB885, etc.

Shaft end retaining ring: shaft end retaining ring fastened with screws, see GB891 and shaft end retaining ring fastened with bolts, see GB892.


Wood screws:

It is divided into many varieties due to different head shapes and groove shapes. There are several types of head, such as round head, countersunk head, and semi-sink head. See GB99-101, GB950-952, etc.

3. Mechanical performance grade

Bolts, Screws, Studs and Nuts

Table 1-1: Bolt, Screw, Stud and Nut Property Classes


set screw

Table 1-2

Self-tapping screws and self-tapping locking screws

Ordinary self-tapping screws are not classified according to mechanical properties, as long as appropriate specifications are selected, see Article 3.6 and Table 3 in GB3098.5) to meet their general use requirements.

The mechanical properties of self-tapping locking screws are divided into two grades, A and B. A grade is a high-strength grade; B-grade is a low-intensity grade.

Stainless Steel Bolts, Screws, Studs and Nuts

Table 1-3


4. Accuracy

The accuracy of standard parts (fasteners) is determined by the product grade.

Table 1-4: Product grade and accuracy of standard parts (fasteners)


5. Thread

Thread tolerance class

Standard parts (fasteners) rib tolerance class

Table 1-5


Note: 1) Only the set screw with mechanical properties of class 45H and the thread tolerance of hexagon socket head cap screw of class 12.9 can adopt 5g class. (2) Selection of pitch

Comparison of Coarse and Fine Threads

Table 1-6

Determine the specification

The first series of values ​​should be selected as far as possible for diameter specifications, and the values ​​in parentheses in the product standard size table and the values ​​in the specification table should not be used as much as possible.

Length specifications generally do not use specifications other than those specified in product standards. Generally, when bolts or nuts are matched and connected, the length of (0.2-0.3) d exposed at the end of the thread is appropriate.

For specifications that match the diameter and length, the specifications within the product specification range should be preferred.

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