What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
In the design of modern aviation and aerospace vehicles, in order to reduce weight and save space, the space of the fastening installation system is getting narrower and narrower, and blind hole installation is often required. In this case, single-sided riveting installation is usually used for fastening connection. At present, this kind of fastening connection products are mainly blind rivets. The riveting installation principle of blind rivets is to use the method of pulling, pulling the mandrel, and extruding the nail sleeve to deform it at the blind end to achieve the function of fastened connection. This kind of fastening connection method requires special riveting, generally imported riveting, the replacement of internal parts is expensive, the installation process is complicated, and the installation cost is high.
High-strength hexagon head bolt combination screws for steel structures, mainly used in railway and highway bridges, boiler steel structures, industrial plants, high-rise civil buildings, tower and mast structures, hoisting machinery and their steel structures need to use friction-type high-strength bolt combinations for screws. It is characterized by an extra dodecagon at the end of the bolt, also known as the bolt. When installing, a special electric wrench must be used, which has two socket heads up and down, one is set on the hexagonal body of the nut, and the other is set on the decagon body of the outer hexagon screw. When tightening, apply a clockwise force to the nut, and apply an equal counterclockwise force to the dodecagon body of the bolt, so that the connecting neck between the end of the outer hexagon screw and the dodecagon body is subjected to torsion shearing until the neck is sheared. So far, the installation has come to an end. This torsion shear type high-strength outer hexagon screw is a one-time-use screw and generally cannot be removed after installation.
The existing automobile fastener nut is a common nut. After the nut is matched with the bolt, during the tightening or disassembly process, there will be a phenomenon of sliding wire, and the safety factor is relatively low; It is difficult to guarantee, easy to rust, requires frequent inspection and replacement, and increases the cost of using the car, which can no longer meet the needs of the market.
Inspection method There are two types of screw surface inspection, one is the inspection before the screw is produced and not plated, and the other is the inspection after the screw is plated, that is to say, after the screw is hardened and the surface of the screw is treated. . After the screws are produced and before electroplating, we inspect the screws in various aspects such as size and tolerance. See if there are national standards or customer requirements. After the surface treatment of the screws, we will inspect the plated screws, mainly to check the color of the plating and whether there are any broken screws. In this way, when we deliver screw goods to customers, customers can successfully pass the customs when they receive the goods. Inspection of screws after treatment: 1. Appearance quality requirements The inspection of the appearance of screws is carried out from the aspects of appearance, electroplating layer and so on. Second, the inspection of the thickness of the screw coating 1. The measuring tool method uses a micrometer, a vernier caliper, a plug gauge, etc. 2. Magnetic method The magnetic method is used to measure the thickness of the coating layer, which is a non-destructive measurement of the non-magnetic coating layer on the magnetic substrate with a magnetic thickness gauge. 3. Microscopy Microscopy is called metallographic method, which is to magnify the etched fasteners on a metallographic microscope with a micrometer eyepiece to measure the thickness of the coating on the section. 4. Timing flow method The timing flow method uses a solution that can dissolve the coating to flow on the local surface of the coating, and calculates the thickness of the coating according to the time required for the local coating to dissolve. There are also coating drop method, anodic dissolution Coulomb method, etc. 3. Inspection of the adhesion strength of the screw coating There are many methods for evaluating the adhesion between the coating and the base metal, usually the following. 1. Friction polishing test; 2. File method test; 3. Scratch method; 4. Bending test; 5. Thermal shock test; 6. Extrusion method. 4. Inspection of corrosion resistance of screw coatings The corrosion resistance inspection methods of coatings include: atmospheric exposure test; neutral salt spray test (NSS test); acetate salt spray test (ASS test), copper accelerated acetate salt spray test (CASS) test); and corrosion paste corrosion test (CORR test) and solution spot corrosion test; immersion test, inter-dipping corrosion test, etc.
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