Fasteners - Fundamentals of Screws
2022-09-30
Fasteners - Fundamentals of Screws 1. Terminology Relating to Screws ● Difference of screws, screws, bolts and fasteners. ● Common English expression: screw/screw - Screw; Bolt; Fastener. ● Definition of thread: the thread is a shape with uniform spiral bulge on the external or internal surface of a solid. 2. Function of thread ● Fastening and connection functions: applicable to most screw products at this stage. ● Driving action (displacement action): such as micrometer used by QC to check dimensions. ● Sealing function: such as connection and sealing of pipes. 3. The history of thread development Machine Screw → Self Tapping Screw → Self Drilling Tapping Screw. ● Machine thread: during assembly, drill and tap the thread on the assembly first. The specification of the tapped internal thread is consistent with that of the external thread of the screw. Use a small torque for assembly. ● Self tapping thread: during assembly, drill holes on the assembly first, without tapping the internal teeth, and use a large torque for assembly. ● Self drilling thread: it is directly used on the assembly, and the screw drilling and tapping are formed at one time. 4. Screw processing method ● Turning: make the material reach the expected shape by removing the material. Advantages: high processing precision, no mold limitation. Deficiency: high production cost and slow processing speed. ● Forging: extrude the material with external force to deform it to achieve the desired shape. Advantages: fast production speed, low cost, suitable for mass production. Inadequate: The forming is limited by the mold, and the mold cost of complex products is high. 5. Cold heading process ● Cold heading: It refers to the process of extruding and deforming the metal wire with the help of external force by using the die under the condition that the metal wire is not heated. ● Cold heading process is only one kind of forging process. 6. Common raw materials for manufacturing screws ● Metal and nonmetal. ● Metals: Fe, Cu, Al. ● Iron: carbon steel, alloy steel, stainless steel. ● Form of raw materials (wire and bar). ● Processing technology of raw materials. ● Current sources of metal materials: Japan/South Korea, Taiwan, mainland China. 7. Screw standard ● National standards: GB National Standards, BS British Standards. ● Industry standards: SAE American Society of Automotive Engineers, AISI American Iron and Steel Institute, JCIS Japanese camera industry standard, DIN German industry standard JIS Japanese industry standard. ● Enterprise standards: GE American General Motors Standard, IBM Standard, SONY Standard
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