Standard summary of threads in the pneumatic industry

Standard summary of threads in the pneumatic industry

Threads are used to deal with machinery every day, especially hydraulic and pneumatic. For a long time, domestic and foreign, metric and imperial, straight cone, sealed and unsealed, inner and outer, 55 degrees and 60 degrees . In short, I often get messed up. I use it to check it from beginning to end. I can summarize it here. I hope it helps.

　　My method is to print out the frequently used ones and put them on the side of the table, and use them to check them at any time. After a long time, they will naturally be remembered.

One

　　NPT is a general-purpose American standard taper pipe thread with a tooth profile angle of 60°

　　 PT thread is an inch taper thread with a profile angle of 55°, which is most commonly used in sealing. The inch pipe thread is a fine thread, because the coarse thread has a large tooth depth, which will seriously reduce the strength of the pipe with the outer diameter of the thread.

　　PF thread is a parallel thread for pipe.

　　G is a 55-degree non-thread sealing pipe thread, which belongs to the Wyeth thread family. Marked as G stands for cylindrical thread, G is the general term for pipe thread (Guan), the division of 55 and 60 degrees is functional

　　ZG is commonly known as pipe cone, that is, the thread is processed by a conical surface. The general water pipe joints are like this. The old national standard is marked as Rc

Metric thread is expressed by pitch, American and British thread is expressed by the number of threads per inch. This is the biggest difference between them. Metric thread is 60 degree equilateral thread, inch thread is isosceles 55 degree thread, and American thread 60 degrees. Metric units are used for metric threads, and inch units are used for American and British threads.

　　Pipe thread is mainly used to connect pipes. The internal and external threads are closely matched. There are two types of straight pipes and tapered pipes. The nominal diameter refers to the diameter of the connected pipe, obviously the larger diameter of the thread is larger than the nominal diameter.

　　1/4, 1/2, 1/8 are the nominal diameters of inch threads, and the unit is inches. 　　二

　　1, inch unified thread

　　 is widely used in inch system countries, this type of thread is divided into three series: coarse thread series UNC, fine thread series UNF, extra fine thread series UNFF, plus a fixed pitch series UN.

　　Marking method: thread diameter—number of teeth per inch series code—precision grade

　　 Example: Coarse tooth series 3/8—16UNC—2A

　　Fine tooth series 3/8—24UNF—2A

　　 Special fine tooth series 3/8—32UNFF—2A

　　 fixed pitch series 3/8—20UN—2A

The first digit 3/8 represents the outer diameter of the thread, the unit is inches, and the conversion to the metric unit mm must be multiplied by 25.4, that is, 3/8×25.4=9.525mm; the second and third digits 16, 24, 32, and 20 are The number of teeth per inch (the number of teeth on a length of 25.4mm); the text code UNC, UNF, UNFF, UN after the third digit is the serial code, and the last two digits 2A are the accuracy grade.

　　2, 55°Cylindrical pipe thread conversion

The 55° cylindrical pipe thread comes from the inch series, but it is widely used in metric and inch countries. It is used to connect pipe joints and pipes for conveying liquids, gases, and installing wires. However, the codes in different countries are different, so you should press The foreign codes in the table (contrast table) are transformed into Chinese codes. Now the codes of 55° cylindrical pipe threads in various countries are listed in the table below.

　　 country code

　　 China G

　　 Japan G, PF

　　 UK BSP, BSPP

　　 France G

　　 Germany R (internal thread), K (external thread)

　　 Former Soviet Union G, TPУБ

　　ISO Rp

　　3, 55° tapered pipe thread conversion

　　 55° tapered pipe thread means that the thread profile angle is 55° and the thread has a taper of 1:16. This series of threads are widely used in the world, and its code names are different in different countries. See the table below. According to the foreign code in the table below, it will be converted into our country code.

　　 country code

　　 China ZG, R (external thread)

　　 British BSPT, R (external thread), Rc (internal thread)

　　 France G (external thread), R (external thread)

　　 Germany R (external thread) 　　Japan PT, R

　　ISO R (external thread), Rc (internal thread)

　　4、60°Conical pipe thread conversion

　　 60° tapered pipe thread refers to a pipe thread with a tooth profile angle of 60° and a thread taper of 1:16. This series of threads are used in the machine tool industry in my country, the United States and the former Soviet Union. Its code name, our country used to be K, then Z, and now it is NPT. See the table below for the thread code comparison table.

　　 country code

　　 China Z (old) NPT (new)

　　 US NPT

　　 Soviet Union B

　　5, 55° trapezoidal thread conversion

　　 Trapezoidal thread refers to a metric trapezoidal thread with a profile angle of 30°. This series of thread is relatively uniform at home and abroad, and its code is quite consistent. See below for the thread code

　　 country code

　　 China T (old) Tr (new)

　　ISO Tr

　　 Germany Tr

　　Former Soviet Union Tr

　　 Three, thread classification

　　 can be divided into:

　　1, International Metric Thread System

　　The thread used by the Chinese National Standard CNS. The tooth top is flat, which is easy to turn, and the tooth bottom is arc-shaped to increase the thread strength. The thread angle is 60 degrees, and the specification is represented by M. Metric thread can be divided into two types: coarse thread and fine thread. The notation is M8x1.25. (M: code, 8: nominal diameter, 1.25: pitch).

　　2, American Standard Thread (American StandardThread)

　　 The top and root of the thread are both flat, and the strength is better. The thread angle is also 60 degrees, and the specification is expressed by a few teeth per inch. This kind of thread can be divided into three grades: coarse thread (NC); fine thread (NF); extra fine thread (NEF). The notation is like 1/2-10NC. (1/2: outer diameter; 10: number of teeth per inch; NC code).

　　3, unified standard thread (UnifiedThread)

　　 is jointly formulated by the United States, the United Kingdom, and Canada, and is currently the commonly used inch thread.

　　 The thread angle is also 60 degrees, and the specification is expressed in terms of a few teeth per inch. This kind of thread can be divided into coarse thread (UNC); fine thread (UNF); extra fine thread (UNEF). The notation is like 1/2-10UNC. (1/2: outer diameter; 10: number of teeth per inch; UNC code)

　　4, V-shaped thread (Sharp VThread)

　　 The top and roots are both pointed, weak in strength, and not often used. The thread angle is 60 degrees.

　　5, WhitworthThread (WhitworthThread)

　　The thread adopted by the British National Standard. The thread angle is 55 degrees, and the symbol is "W". Suitable for rolling method manufacturing. The notation is like W1/2-10. (1/2: outer diameter; 10: number of teeth per inch; W code).

　　6, round thread (KnuckleThread)

　　 is the standard thread specified by German DIN. Suitable for the connection of bulbs and rubber tubes. The symbol is "Rd".

　　7, pipe thread (PipeThread)

　　To prevent leakage, it is often used to connect gas or liquid pipes. The thread angle is 55 degrees, which can be divided into straight pipe thread code "P.S., N.P.S." and oblique pipe thread code "N.P.T.", the taper is 1:16, that is, 3/4 inch per foot.

　　8, square thread (SquareThread)

　　The transmission efficiency is high, second only to the ball thread, and it cannot be adjusted with a nut after wear, which is a disadvantage. Generally used for the screw of the vise and the screw of the crane.

　　9, trapezoidal thread (TrapezoidalThread)

　　 is also known as Akem thread. The transmission efficiency is slightly lower than that of the square thread, but it can be adjusted with a nut after wear. The metric thread angle is 30 degrees, and the inch thread angle is 29 degrees. Generally used for lead screw of lathe. The symbol is "Tr".

　　10, buttress thread (ButtressThread)

　　 is also called oblique thread, which is only suitable for unidirectional transmission. Such as screw jacks, presses, etc. The symbol is "Bu".

　　11, ball thread

　　 is the thread with the best transmission efficiency. It is difficult to manufacture and the cost is extremely high. It is used in precision machinery. Such as the lead screw of a CNC machine tool.

　　 The representation of inch bolts:

　　LH 2N 5/8 × 3-13UNC-2A

　　(1) LH is left-hand thread (RH is right-hand thread, which can be omitted).

　　(2) 2N double thread thread.

　　(3) 5/8 inch thread, outer diameter 5/8".

　　(4)3 Bolt length is 3".

　　(5)13 The thread counts 13 teeth per inch.

　　 (6) UNC unified standard thread coarse pitch.

　　(7) Level 2 fit, external thread (3: tight fit; 2: middle fit; 1: loose fit) A: external thread (can be omitted) B: internal thread

　　Inch thread:

　　The size of inch thread is usually expressed by the number of threads per inch of length, referred to as "number of threads per inch", which is exactly equal to the reciprocal of the thread pitch. For example, a thread with 8 teeth per inch has a pitch of 1/8 inch.