What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
Countersunk head screws are mostly used after installation, and the surface of the parts cannot be raised, and the parts to be fastened have two thicknesses. Thickness, after the screw is tightened, there is still a part of the screw thread that does not enter the threaded hole. In this case, the countersunk head screw can definitely be tightened. There is usually a situation where the thickness of the fastened part is less than the height of the head of the countersunk head screw, which is commonly seen in sheet metal parts in mechanical equipment, such as the connection between the hinge of the chassis and the door and the box; the sheet metal of the equipment The connection of the cover to the equipment, etc. Due to the small thickness of the part, the tightened sheet metal part, the screw through hole completely becomes a conical hole, in this case, when the countersunk head screw is tightened, the screw head is not a tapered surface to press the sheet metal part , but the bottom of the screw head and the top of the threaded hole are squeezed. Although it feels that the screw is tightened, the sheet metal part is stuck instead of being pressed. In this case, although it feels that the screw is tightened, the sheet metal The gold pieces were indeed not tightened. This is a very common situation. Let’s talk about the reasons for the processing: the head cone of the countersunk screw has a 90° conical angle, and the apex angle of the newly bought drill is usually 118°-120°. Some workers who lack training do not know this angle is poor. It is often used to ream the hole with a 120° drill bit, which results in that when the countersunk head screw is tightened, it is not the conical surface of the head, but a line at the bottom of the screw head, which is one of the reasons why the so-called countersunk head screw cannot be tightened. , it's not the screw's fault.
An automatic circlip device discloses an automatic circlip device capable of realizing automatic assembly of the circlip to improve production efficiency and reduce labor costs. However, there are problems of low degree of automation and low work efficiency.
Most of the existing screws use an integral metal structure, and there are still some problems, such as large weight, high cost of materials, wear resistance, hardness, rust resistance, corrosion resistance, high and low temperature resistance, brittleness, toughness, etc. Many occasions cannot meet the needs of production, and further improvements are needed to improve production efficiency, reduce costs, improve safety, and prolong the service life of screws.
There is a standard for the outer hexagon bolt standard, which is a grade standard, which is divided into grade 4.8 and grade 8.8. These two levels are used a lot in the market. Especially grade 4.8 hex head bolts. Because it is much cheaper than 8.8 hex bolts. Of course it is more widely used. But for demanding products. Because of its high requirements in various aspects such as hardness. This requires the use of 8.8 hex bolts. Grade 8.8 hex bolts are harder in terms of hardness and screw torque. It is safer to use the product. Tighter and more stable.
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