Complete Guide to Screw Manufacturing and Processes

1.Distinctions Between Screws, Nuts, Bolts, and Studs:

A Bolt generally has a hexagonal head and a shank with external threads. A Screw (or machine screw) is usually smaller, featuring heads like flat or cross-recessed types, with external threads on the shank. A Stud (technically a double-ended stud) has external threads on both ends, usually with a smooth unthreaded shank in the middle. The longer threaded end is designed to engage with a tapped hole, while the shorter end connects with a nut.

• Common English Terms:
  Screw / Bolt / Fastener.
• Definition of Thread:
  A thread is a uniform helical ridge structure found on the external or internal surface of a solid cylinder or cone.

• Fastening and Connection: This is the primary function for the vast majority of screw products currently in use.
• Power Transmission (Displacement): Converting rotary motion into linear movement, such as in micrometers used for QC dimensional inspection.
• Sealing: Preventing leakage in connections, commonly seen in pipe fittings and plumbing systems.

Machine Threads: Assembly requires pre-drilling and tapping a hole in the component. The internal thread matches the external thread specifications of the screw, allowing for assembly with lower torque.

Self-Tapping Threads: Assembly requires only a pre-drilled hole without tapping. A significantly higher torque is applied during installation to form the mating threads.

Self-Drilling Threads: These can be driven directly into the material, performing drilling and tapping in a single operation.

This refers to the raw wire coils purchased directly from material manufacturers. A standard wire coil typically includes the following specifications:

A. Manufacturer / Brand
B. Product Name
C. Specifications
D. Material Grade
E. Heat Number or Batch Number
F. Quantity or Weight

The primary chemical components of carbon steel wire rods include C, Mn, P, S, Si, Cu, and Al. Among these, lower content of Copper (Cu) and Aluminum (Al) is preferred for optimal quality.

To achieve the required wire diameter (e.g., drawing to 3.5mm).

Cold Heading Process

 

 

The material is formed through the interaction between molds. The wire is first cut and then upset into a screw blank, forming the head drive (such as a Phillips slot or other head types), thread blank diameter, shank length, underhead radius, etc.

Note: Designs can be customized according to customer requirements. Common head types include P-head, B-head, F-head, and T-head. Standard drive types feature Phillips, Slotted, Torx, and Hex Socket.

Changes Before and After Thread Rolling

Thread Rolling Machine

1.Purpose: To achieve higher hardness and strength for screws after cold heading.

2.Function: Enables self-tapping fastening, and improves mechanical properties such as torsional resistance, tensile strength, and wear resistance.

3.Classification:

A. Annealing: (700℃ x 4hr) Elongates the microstructure towards polygonization.

B.Carburizing Heat Treatment: Adds carbon elements to the metal components to increase surface hardness (specifically for low-carbon metals).

C.Quenching and Tempering: Alters the internal metal structure through temperature changes without adding elements, achieving superior mechanical properties.

The surface of the product after electroplating can achieve the desired color effect as well as an anti-oxidation coating.