What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
There are two typical pin shearing fixture tooling, among which the traditional fixture shown in Fig. 1 is more complicated and consists of fixture, spacer, washer and shearing block guide post, hardened bushing, shearing block and so on. The cylindrical pin is installed in the hardened bushing, and the axial load is applied through the shear block to complete the shear test. The fixture is complicated in manufacture and has many consumables, because the size of the hardened bushing is similar to that of the cylindrical pin. , and to keep the notch of the cylindrical pin upward, it is difficult to install before the test, and the broken cylindrical pin after the test remains in the hardened bushing and is difficult to remove.
Inch Screws C-1: Thread Code: The denominator is marked as 8, and then the numerator is directly called the number. Ex: 1/8 x 0.50 –PPB: 1 Thread screw x 0.50” long, PPB Ex: 5/16 x 0.50 –PPB = 2.5/8 x 0.50-PPB : 2 ½ inch screw x 0.50” long, PPB Ex: 5/32 x 0.50 –PPB =1.25/8 x 0.50-PPB: 1 ½ ½ inch screw x 0.50” long , PPB Ex: 1/4 x 0.50-PPB= 2/8 x 0.50-PPB: 2-point screw x 0.50” long, PPB Note: Coarse or fine pitch is sometimes indicated. UNF: Fine pitch: more commonly used in the electronics industry UNC: Coarse Thread: More commonly used for heavy machinery construction. Ex: 3/8 x 0.50, UNF –PPB: 3 point fine thread screw x 0.50” long, PPB. C-2: Length Code: In inches, must be multiplied by 25.40 is converted to mm. Measured with a buckle gauge, it is a metric thread when it matches the metric thread, and an inch thread when it matches the inch thread. You can also use a caliper to measure the outer diameter and pitch of the thread. The outer diameter of the metric thread is in millimeters, Such as 6, 8, 10, 12, 18, 20 mm, etc., the pitch is also in millimeters, such as 0.5, 0.75, 1, 1.5, 2, 3, etc. The outer diameter of the imperial thread is in inches, (per inch Equal to 25.4 mm) such as 3/16, 5/8, 1/4, 1/2, etc. Therefore, the reading of the outer diameter with a metric caliper often has irregular decimals. The inch pitch is expressed by how many teeth per inch. Set the caliper at 25.4 mm, align one caliper tip with the thread cusp, and the other caliper tip, if aligned with the thread cusp, is an inch thread, and if the thread cusp is not aligned, it should be a metric thread. The tip is printed on the white chalk. The chalk is clear and easy to measure. To measure the metric pitch, you should measure a length, such as 10, 15, 20, millimeters, etc., count how many teeth are included, and calculate the pitch in inches. The specified thread specification is inch thread, such as: G1. Metric threads are specified in metric units of millimeters. Such as: M30. The imperial system is determined by how many teeth there are in one inch (2.54 cm), generally a 55-degree angle. The metric system is the pitch determined by the distance between the two tooth tips, usually a 60-degree angle anchor screw: tighten the machine, etc. Screws for use on the ground. Also called anchor bolts. The difference between British and American screws is difficult to distinguish visually. The difference between British and American screws is that the rolling angle of British screws is 55 degrees, while the rolling angle of American screws is 60 degrees. These two standard screws are used in most screws. It can be used in general, but 1/2 size screws are not allowed, because the standard thread of inch 1/2 is 1/2-12 teeth, while the American system is 1/2-13 teeth.
When the countersunk head screws and hexagon socket head bolts are produced by the cold heading process, the original structure of the steel will directly affect the forming ability of the cold heading process. In the process of cold heading, the plastic deformation of the local area can reach 60%-80%, so the steel must have good plasticity. When the chemical composition of the steel is constant, the metallographic structure is the key factor to determine the plasticity. It is generally believed that the coarse flaky pearlite is not conducive to cold heading forming, while the fine spherical pearlite can significantly improve the plastic deformation ability of the steel. For medium carbon steel and medium carbon alloy steel with a large amount of high-strength bolts, spheroidizing (softening) annealing is performed before cold heading, so as to obtain uniform and fine spheroidized pearlite to better meet the actual production needs. For the softening annealing of medium carbon steel wire rods, the heating temperature should be kept above and below the critical point of the steel, and the heating temperature should not be too high, otherwise tertiary cementite will precipitate along the grain boundary, resulting in cold heading cracking. The wire rod of medium carbon alloy steel is annealed by isothermal spheroidization. After heating at AC1+ (20-30%), the furnace is cooled to slightly lower than Ar1, the temperature is about 700 degrees Celsius for an isothermal period, and then the furnace is cooled to about 500 degrees Celsius and air-cooled. The metallographic structure of the steel changes from coarse to fine, from flake to spherical, and the cracking rate of cold heading will be greatly reduced. The general area of softening annealing temperature for 35\45\ML35\SWRCH35K steel is 715-735 degrees Celsius; while the general heating temperature for spheroidizing annealing of SCM435\40Cr\SCR435 steel is 740-770 degrees Celsius, and the isothermal temperature is 680-700 degrees Celsius.
Usually, a tight fit is used between the cylindrical pin and the pin hole, such as the cooperation between the cylindrical pin and the pin hole on the rotating shaft of the motor. Due to the tight fitting structure between the cylindrical pin and the pin hole, the shaft with the pin hole needs to be well positioned during assembly, and then the cylindrical pin is aligned with the pin hole, and then knocked or pressed to fit. The cylindrical pin is pressed into the pin hole. There is no device specially used for the installation of cylindrical pins in the prior art, and two or more people are required to cooperate to install the cylindrical pins into the pin holes. installation quality.
The above content is uploaded by Yueluo or the Internet. If there is any copyright issue, please contact [email protected].
