What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
Thread Code Broadcast Coarse Thread Series UNC Fine Thread Series UNF Extra Fine Thread Series UNEF Fixed Pitch Series UN Marking Method Broadcast Marking Method: Thread Diameter - Number of Threads per Inch Serial Code - Accuracy Grade Example: Coarse Thread Series 3/8—16 UNC— 2A Fine pitch series 3/8—24 UNF—2A Extra fine pitch series 3/8—32 UNEF—2A Fixed pitch series 3/8—20 UN—2A The first digit 3/8 indicates the outer diameter of the thread, in inches , to convert to metric unit mm, multiply by 25.4, that is, 3/8×25.4=9.525mm; the second and third digits 16, 24, 32, 20 are the number of teeth per inch (the number of teeth on the 25.4mm length); The text code UNC, UNF, UNEF, UN after the third digit is the series code, and the last two digits 2A are the precision grade. UNC: Unified Coarse Thread.
Today's advanced manufacturing represented by large aircraft, large power generation equipment, automobiles, high-speed trains, large ships, and large complete sets of equipment has entered an important development direction. As a result, fasteners will enter an important stage of development. High-strength bolts are used for the connection of important machinery, and repeated disassembly or various installation torque methods require extremely high-strength bolts. Therefore, the quality of its surface condition and thread accuracy will directly affect the service life and safety of the host. In order to improve the friction coefficient and avoid corrosion, seizure or sticking during use, the technical requirements stipulate that the surface should be treated with nickel phosphorus plating. The thickness of the coating is guaranteed to be within the range of 0.02 to 0.03 mm, and the coating is uniform, dense, and free of pinholes.
Some heavy equipment such as large motors, large reducers, etc., in order to facilitate the installation and adjustment of equipment and the need for maintenance space, a certain position needs to be moved during equipment installation and maintenance. Usually, a steel base or platform is set under the equipment, and the base or The platform is provided with an oblong bolt installation slot, commonly known as an oblong slot, as shown in Figure 1--Figure 4. When using common hexagon head bolts or common T-bolts with the long circular groove in Figures 1 and 2, auxiliary fixing bolts or welding stoppers are required on the back of the long circular groove to prevent the bolt from rotating when the nut is tightened. In Fig. 3 and Fig. 4, the long circular groove itself has a clamping groove to prevent the rotation of the bolt, but this structure greatly increases the processing cost of the long circular groove.
Ordinary T-bolts, the bolt head is rectangular, the screw part and the bolt head are T-shaped, and the width of the head is smaller than the width of the opening part of the T-slot, so that the head of the T-bolt can extend from the length of the T-slot. Insert the T-slot into the T-slot at any position in the direction. When the workpiece needs to be fixed, turn the T-bolt 90 degrees so that the length of the head is perpendicular to the T-slot, hook the inside of the opening of the T-slot, and screw it by tightening The nut on the T-bolt threaded rod holds the workpiece in place. The T-bolt of this structure can easily connect the bolt and the base piece quickly, and is widely used, but there are also some shortcomings, due to the contact area between the head of the T-bolt and the inner side of the opening of the T-slot. If it is too small, the frictional resistance is correspondingly small. On the one hand, the bolts are easy to follow the rotation during the process of tightening the nut. Unreliable.
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