What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
Use performance self-tapping screws for self-tapping screws with a diameter of 0.8mm to 12mm. For this type of screw, it generally has a high hardness. Self-tapping screws must be screwed into the test, that is, screw the screw into a test plate to check whether the hardness of the screw meets the standard. The shape of the drill tail, the hardness of this kind of screw is very strong. Compared with ordinary screws, it not only has better maintenance ability, but also has a very strong effect in connecting objects. For screws with this performance, it is generally not necessary. Auxiliary processing can directly drill a hole on the object and lock it into the object, which is not only very convenient to use, but also greatly improves work efficiency. This kind of drill screw can be said to be the first choice of the staff in various fields.
The heating bolt pre-stretching method makes the bolt pre-stretch to the required deformation amount by heating, and then tighten the nut. After cooling, the bolt is shortened and the connection is pre-tightened. This is a commonly used fastening method in infrastructure installations. However, it is not suitable for devices that often need to be disassembled and adjusted, because during the disassembly process, the connected parts will be heated and elongated together with the bolts, and the use of open flame heating will be limited in some occasions; the use of electric heating will make the structure of the screw It becomes complicated and increases the investment, and even if it is difficult to disassemble, such as the propeller shaft of the ship, etc., the heating method is not suitable.
Several concepts about high-strength bolts 1. According to the specified performance level of bolts above 8.8, they are called high-strength bolts. The current national standard only lists M39. For large-size specifications, especially those with a length greater than 10 to 15 times High-strength bolts, domestic production is still short-term. The difference between high-strength bolts and ordinary bolts: High-strength bolts can withstand larger loads than ordinary bolts of the same specification. High-strength outer hexagon bolts High-strength outer hexagon bolts are made of Q235 (ie A3). The material of high-strength bolts is 35# steel or other high-quality materials, which are heat-treated after being made to improve the strength. The difference between the two is the difference in material strength. From raw materials: High-strength bolts are made of high-strength materials. The screws, nuts and washers of high-strength bolts are all made of high-strength steel, such as No. 45 steel, 40 boron steel, 20 manganese titanium boron steel, 35CrMoA, etc. Ordinary bolts are usually made of Q235 (equivalent to A3 in the past) steel. In terms of strength grades: high-strength bolts are increasingly used. Two strength grades are commonly used, 8.8s and 10.9s, of which 10.9 is the majority. The strength level of ordinary bolts is lower, generally 4.4, 4.8, 5.6 and 8.8. High-strength bolts High-strength bolts are viewed from the force characteristics: high-strength bolts apply pretension and transmit external forces by friction. Ordinary bolt connection relies on the shear resistance of the bolt and the bearing of the hole wall to transmit the shear force. When the nut is tightened, the pre-pressure is very small, and its influence can be ignored. In addition to its high material strength, high-strength bolts also exert a large amount of pressure on the bolts. The pre-pressure generates extrusion force between the connecting components, so that there is a large friction force perpendicular to the direction of the screw, and the pre-pressure, anti-slip coefficient and steel type directly affect the bearing capacity of high-strength bolts. According to the force characteristics, it is divided into pressure type and friction type. The calculation methods of the two are different. The minimum specification of high-strength bolts is M12, and M16~M30 are commonly used. The performance of super-large bolts is unstable and should be used with caution in design.
The front wall sound insulation pad is used to absorb the heat and noise transmitted by the firewall, and also plays the role of heat insulation and vibration isolation, ensuring a relatively quiet and comfortable environment in the car and improving ride comfort. As shown in FIGS. 1 and 2 , the front wall sound insulation and heat insulation pad 101 is generally fixed to the vehicle body by means of screw buckles 102 . The screws 100 are clamped by the clamping feet 103 in the screw The limiting rib 104 clamps the screw 100. After the screw 100 is clamped into the screw buckle 102, the tail end of the screw 100 is exposed, which is easy to scratch the operator when assembling other components, and the exposed screw 100 is easy to cause corrosion, thereby affecting the connection strength of the screw 100, and also The service life of the screw 110 is reduced.
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