Metal Fixing Screws

Metal Fixing Screws are one of the most widely used connectors in mechanical assembly. Their heads are usually designed in the form of pan heads, countersunk heads or hexagonal flanges. The threaded part can be coarse or fine in accordance with ISO 965 standards to adapt to different connection thickness and strength requirements. The material is mostly made of medium carbon steel or alloy steel, which has been quenched and tempered. According to ISO 898-1's regulations on strength levels, the tensile strength of grade 8.8 M6 screws is not less than 800 MPa, and the non-proportional elongation strength is not less than 640 MPa, so that it has sufficient strength reserves when bearing shear and tensile composite loads. At the same time, the screw head groove type is verified for torsional strength in accordance with the ISO 7049 standard. Taking cross-recessed pan head screws as an example, its breaking torque is not less than 3.0 Nm, which is far more than the 2.0 Nm tightening torque required for normal installation. This ensures that the slot will not slip or deform during the automatic tightening process. It is widely used in the assembly of household appliance casings and the fixation of electronic equipment racks.

In terms of anti-corrosion and installation reliability, the surface of metal fixing screws is usually treated with galvanized or zinc-aluminum coating to extend its service life in humid or mildly corrosive environments. According to the ASTM B117 neutral salt spray test, when the thickness of the galvanized layer is not less than eight microns, the screws can withstand 480 hours in a five percent sodium chloride salt spray environment without red rust, meeting the life cycle requirements of general indoor and outdoor equipment. During installation, according to the VDI 2230 systematic calculation guideline, the recommended torque applied to the M8 grade 8.8 screws is about 25 Nm, and the corresponding pre-tightening force is about 18,000 N. This value is based on the actual measurement calibration of the friction coefficient of 0.14 to ensure that the connection will not loosen under vibration conditions. This type of screws are therefore widely used for base fixation of mechanical equipment, installation of internal components of distribution boxes and secondary connection nodes of building steel structures, taking into account fastening strength and long-term stability.

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