What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
Nuts and bolts are one of the most widely used fasteners in modern mechanical structures. At present, the common metric bolts and nuts are generally trapezoidal in cross-section. The connection between the bolt and the nut is prone to loosening under severe vibration, or even falls off by itself, and the tightening force of the bolt and nut thread is mainly concentrated in the bolt thread and Between the teeth of the first few threads where the threads of the nut are in contact, resulting in loosening of the fastener and sliding pressure of the threads
For the detection of the shear force of the elastic cylindrical pin, the method and the tooling are marked, but the tooling is only a means to be used on the test bench, and the process of embedding the cylindrical pin into the tooling is a more difficult process. Generally, it is used to place the tooling on a plane, a vise, a simple V-shaped, and a simple U-shaped fixture. Originally, the elastic cylindrical pin was detected by hand or pliers to hold the cylindrical pin and align the pin with the outer cylinder of the tooling. Use a hammer to smash the shear holes, and adjust the concentricity of the inner and outer cylinders of the shear holes of the tooling from time to time. The limitations, dangers and difficulties of this assembly method are relatively large, often testing a set of cylindrical pins, which takes a lot of time and is difficult for lesbians to complete.
The performance grade 8.8 of stainless steel bolts refers to the material's tensile strength limit of 800MPa and yield limit of 640MPa. The performance grades of stainless steel bolts, studs and studs are divided into 10 grades: from 3.6 to 12.9. The number before the decimal point represents 1/100 of the tensile strength limit of the material, and the number after the decimal point represents 10 times the ratio of the material's yield limit to the tensile strength limit. There are 7 grades of performance grades for nuts, from 4 to 12. The numbers roughly represent 1/100 of the minimum stress that the stainless steel nut is guaranteed to withstand. For unified inch threads, there are three thread grades for external threads: grades 1A, 2A and 3A, and three grades for internal threads: grades 1B, 2B and 3B, all of which are clearance fits. The higher the rating number, the tighter the fit. Classes 1, 1A and 1B, very loose tolerance classes, which are suitable for tolerance fits of internal and external threads. Grades 2, 2A and 2B are the most common thread tolerance grades specified for inch series mechanical stainless steel fasteners. Grades 3, 3A and 3B, screwed together to form the tightest fit, suitable for tight tolerance stainless steel standard parts, for safety critical designs. Metric threads, there are three thread grades for external threads: 4h, 6h and 6g, and three thread grades for internal threads: 5H, 6H, 7H. Thread fit is best combined into H/g, H/h or G/h. For bolts, stainless steel nuts and other refined fastener threads, the standard recommends 6H/6g fit. Carbon steel: The strength grade is marked by ? It consists of two separated numbers. The meaning of the number part before the ? in the marking code represents the nominal tensile strength, for example, 4 in grade 4.8 represents 1/100 of the nominal tensile strength of 400N/MM2. The meaning of the ? and the number part after the point in the marking code represents the yield-strength ratio, that is, the ratio of the nominal yield point or the nominal yield strength to the nominal tensile strength. For example, the yield point of grade 4.8 products is 320N/mm2. The strength grade mark of stainless steel products consists of two parts separated by —. The symbol before — in the sign code indicates the material. Such as: A2, A4 and other signs — indicate strength, such as: A2-70 Carbon steel: The mechanical properties of bolts can be divided into: 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9, 12.9 in total 10 performance levels
Therefore, there is a need to design a bearing retaining ring disassembly and installation device that facilitates the installation and disassembly of the bearing retaining ring, and is safe and reliable.
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