Self drilling sms

The self-tapping screw features a sharp needle-shaped tip with an angle of 18 to 45 degrees depending on sheet thickness. These screws are manufactured according to DIN 7500 standards for various metal and plastic sheet applications. The DIN 7500 standard divides screws into four types where type C is for sheets up to 1 millimeter, type F for sheets up to 3 millimeters, and type D for plastic materials. The threads feature a coarse pitch with a 35-degree angle and sharp cutting edges for material displacement. The unthreaded section beneath the screw head is designed as the torque-bearing zone. The first thread is partially formed to facilitate tip guidance into the workpiece material. The threaded length covers at least 60 percent of the total shank length. Common sizes for these screws range from ST2.2 up to ST8 millimeters with corresponding pitch values.

Self-tapping screws are manufactured from 10B21 or 15B21 alloy steel with 0.18 to 0.23 percent carbon content and boron element for enhanced hardenability. Carburizing heat treatment is performed at 880 to 930 degrees Celsius for 60 to 120 minutes duration. Surface hardness after carburizing reaches 550 to 750 Vickers while core hardness reaches 250 to 350 Vickers. The case depth ranges from 0.1 to 0.25 millimeters for sizes up to ST5 and 0.15 to 0.35 millimeters for larger sizes. White or yellow galvanized zinc coating with 5 to 12 microns thickness provides basic corrosion resistance. Dacromet (Geomet) coating with 8 to 15 microns thickness is used for highly corrosive environments and high temperatures. Maximum installation torque varies between 1.5 to 18 Newton meters depending on screw size. Applications include automotive assemblies, household appliances, metal cabinets, and building sheet metal connections.

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