What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
The main technical problem solved by Guangdong Yueluo Hardware Industry Co., Ltd. is to provide a fixing screw for installation, so as to provide a PCB fixing method with convenient operation, reliable connection and low production cost. In order to solve the above-mentioned technical problems, a technical solution adopted by Guangdong Yueluo Hardware Industry Co., Ltd. is to provide a fixing screw for installation, which includes a screw body, the axial surface of the screw body is formed with extended screw teeth, and the screw body is The bottom has a hemispherical screw tail, the top of the screw body is provided with a screw head, and the upper surface of the screw head is provided with a slot. According to a preferred embodiment of Guangdong Yueluo Hardware Industry Co., Ltd., the screw body is composed of an upper tapered rod and a lower cylindrical screw rod, and the tapered rod is an inverted cone. According to a preferred embodiment of Guangdong Yueluo Hardware Industry Co., Ltd., the diameter of the circular upper surface of the inverted cone of the taper rod is equal to the diameter of the screw mounting hole. According to a preferred embodiment of Guangdong Yueluo Hardware Industry Co., Ltd., the screw further has a washer, the washer is arranged between the screw head and the screw body, and the washer is a cylinder. According to a preferred embodiment of Guangdong Yueluo Hardware Industry Co., Ltd., the lower surface of the cylindrical washer has a plurality of teeth, and the teeth are along the edge of the connection between the upper surface of the inverted cone of the tapered rod and the washer Ribs formed by extending outwards. According to a preferred embodiment of Guangdong Yueluo Hardware Industry Co., Ltd., the teeth of the washer are in contact with and pressed against the PCB board. According to a preferred embodiment of Guangdong Yueluo Hardware Industry Co., Ltd., the protruding strip is an arc-shaped or straight-shaped structure. According to a preferred embodiment of Guangdong Yueluo Hardware Industry Co., Ltd., the notch opened on the upper surface of the screw head is a slot. [0018] According to a preferred embodiment of Guangdong Yueluo Hardware Industry Co., Ltd., the notch provided on the upper surface of the screw head is a cross groove. According to a preferred embodiment of Guangdong Yueluo Hardware Industry Co., Ltd., the fixing screw is integrally formed with conductive material. Compared with the existing technology, the fixing screws for installation designed by Guangdong Yueluo Hardware Industry Co., Ltd. can not only ensure the accuracy of the PCB installation position, but also can be installed easily and reliably, which greatly reduces the manufacturing cost and waste of metal materials.
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.
Commonly used screw materials in my country are No. 45 steel, 40Cr, ammoniated steel, 38CrMOAl, superalloy, etc. 1) No. 45 steel is cheap and has good processing performance, but poor wear resistance and corrosion resistance. Heat treatment: quenched and tempered HB220-270, high-frequency quenched HRC45--48. 2) The performance of 40Cr is better than that of No. 45 steel, but it is often plated with a layer of chromium to improve its corrosion resistance and wear resistance. However, the requirements for the chrome plating layer are relatively high. If the plating layer is too thin, it is easy to wear, and if it is too thick, it is easy to peel off. After peeling off, it will accelerate the corrosion, and it has been rarely used. Heat treatment: quenched and tempered HB220—270, hard chrome plated HRC>553) nitrided steel, 38CrMoAl have excellent comprehensive properties and are widely used. Generally, the nitride layer reaches 0.4-0.6 mm. However, this material has low resistance to hydrogen chloride corrosion and is relatively expensive. 4) The superalloy material is superior to other materials. This material does not need coating, and is mainly used for the raw halogen-free screw of injection molding machine. The material has high oxidation resistance and corrosion resistance.
Cylindrical pins are widely used, and they are usually provided with matching pin holes. For the tails of cylindrical pins exposed outside the pin holes, they usually do not have a guiding function, which cannot meet the needs of quick installation of workpieces.
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