What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
The machinery industry is one of the main users of fasteners. Due to China's late understanding of the important position of mechanical basic parts in the machinery industry and a long-term lack of investment, the entire industry has a poor foundation, weak foundation and weak strength. Especially with the improvement of the level of the main engine in China, the bottleneck phenomenon that the mechanical basic parts lag behind the main engine has become increasingly apparent. Today, although the state has given certain support in technology introduction, technological transformation, scientific research and development, etc., there is still a big gap compared with the current market demand and foreign levels. Unstable quality, high early failure rate and poor reliability. Fasteners are the main basic products in the machinery industry, and the development of the machinery industry also puts forward higher requirements for fastener products. Domestic ordinary standard fasteners have always been in oversupply, while high-end fasteners (high temperature, special-shaped, titanium-plastic composite, special performance and other fasteners) are in short supply, and they also rely on imports. The State Machinery Bureau lists ordinary standard fasteners as restricted development products, and high-strength special-shaped fasteners as currently encouraged development products. With the improvement of the country's industrialization level and technological progress, the use of high-strength fasteners has gradually increased.
The lifting ring screw should be made of 20 or 25 steel (GB699). The lifting ring screw must be forged as a whole. The forgings should be normalized and the oxide scale should be removed. The grain size of the finished product should not be lower than grade 5 (YB27-77). There must be over-burning, crack defects.
The first is to use two identical nuts to screw on the same bolt, and add a tightening torque between the two nuts to make the bolt connection reliable. The second is a special anti-loosening nut, which needs to be used together with a kind of anti-loosening washer. The special lock nut is not a hexagonal nut, but a medium round nut. There are 3, 4, 6 or 8 notches on the circumference of the nut (depending on the size of the nut and the product series of the manufacturer). Several notches are both the focal point of the tightening tool and the snap-in of the lock washer bayonet. The third type is to drill through threaded holes from the outer surface of the nut to the inner thread surface (usually 2, which are distributed at 90 on the outer surface), which are used to screw in small-diameter countersunk head screws. The purpose is to give the thread Apply a centripetal force to prevent the locknut from loosening. The better quality lock nut sold on the market is inlaid with a small copper block that is consistent with the thread of the lock nut on the inner surface of the nut to prevent the radial jacking screw from directly contacting the locked thread and damaging the latter. . This kind of lock nut is gradually applied in the shaft end locking of rotating motion parts, such as the anti-looseness of the bearing at the mounting end of the ball screw. The fourth type of lock nut is composed of two parts, each part has staggered cams. Since the slope angle of the internal wedge design is greater than the nut angle of the bolt, this combination is tightly integrated into a whole. When vibration occurs When the lock nut is moved, the raised parts of the lock nut move with each other to generate lifting tension, so as to achieve a perfect anti-loosening effect. The fifth is structural anti-loosening. Through the design and improvement of the threaded structure, a self-locking function is obtained without the help of other external factors. Therefore, its applicability is wider than the above methods, and the requirements for the environment are also relatively high. Low. There are many types of lock nuts, such as nylon nuts and flange nuts. In short, this kind of lock nuts plays a role in preventing loosening. Twist the nut onto the screw, screw, bolt, etc., so that it will not come loose. So that they can be actively connected together, so that it is firm, and the stability can reach a high degree.
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.
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