What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
1) Scope This standard specifies the lock nut (referred to as nut), the size of the locking device, technical requirements, acceptance rules and measurement methods. This standard applies to the design, production, inspection and user acceptance of nuts and locking devices for tapered bushings. 2) Terminology The terms used in this standard conform to the provisions of GB/T 6930. This standard specifies the marking system, index, test method and marking of the mechanical and working performance of the effective torque section steel hexagonal lock nut. This standard is applicable to coarse thread 6H class nuts made of carbon steel or alloy steel, the width across the sides conforming to the provisions of GB 3104, the nominal height is ≥ 0.8D, and the guaranteed load and effective torque need to be specified, and the thread diameter is 3 ~ 39mm. Except for the effective torque part, the thread size and tolerance are specified in GB 193, GB 196 and GB 197. The working temperature range of the nut should be in accordance with: All-metal nut without electroplating treatment: -50℃～+300℃. All-metal nuts with electroplating treatment: -50℃～+230℃; nuts embedded with non-metallic elements: -50℃～+120℃. This standard does not apply to nuts with special performance requirements (such as weldability and corrosion resistance). For stainless steel and non-ferrous metals with fine pitch lock nuts or thin nuts made of carbon steel or alloy steel, the performance indicators and test methods of effective torque specified in this standard may be adopted by mutual agreement.
The working principle of the nut is to use the friction between the nut and the bolt for self-locking. However, the reliability of this self-locking is reduced under dynamic loads. In some important occasions, we will take some anti-loosening measures to ensure the reliability of the nut locking. Among them, the use of lock nuts is one of the anti-loosening measures. There are also two types of locking nuts. One is to use two identical nuts to screw on the same bolt, and a tightening torque is added between the two nuts to make the bolt connection reliable. The other is a special lock nut, which needs to be used together with a lock washer. As shown in FIG. 1, a plastic gasket 2 is arranged in the center of the nut 1 to play a locking effect, but the process is complicated and the production is inconvenient. One is to drill through threaded holes from the outer surface of the nut to the inner thread surface (usually 2, distributed at 90 on the outer surface), which are used to screw in small-diameter countersunk head screws. The purpose is to apply a thread to the thread. A centripetal force prevents the lock nut from loosening. At present, the lock nut with better quality on the market is inlaid with small copper pieces that are consistent with the thread of the lock nut on the inner surface of the nut, which is used to prevent the radial jacking screw from directly contacting the locked thread and being damaged. By. 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 process is equally complex.
Rivets are mostly used for fixed riveting and movable riveting between parts. The rivets used for movable riveting are mostly cylindrical, and there is no size limit for riveted parts, which is easy to cause parts to be squeezed and deformed during riveting. For example, The parts are inserted into the parts for active riveting. When riveting, the riveting force can easily cause the parts to clamp the parts, which in turn causes difficulty in the movement of the parts and the parts, high operating force and noise problems, and the parts are easily damaged.
At present, in the field of building curtain wall, factory building support structure, shelf structure and other fields of steel structure connection, if closed profiles (such as rectangular steel pipes) are used as the connection structure, welding connection is generally used, and bolt connection cannot be realized. The reason why a bolted connection is not possible is that the profile is a closed structure and it is not possible to place the bolt at the connection location because the size of the bolt head is larger than the thread hole diameter on the profile. Welded connections affect the structural quality of outdoor projects, with poor corrosion resistance, reduced structural strength, and frequent fire accidents. However, the existing non-welded steel structure and the fastening connection of the bracket have complicated T-bolt structure, troublesome processing technology and high production cost.
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