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Screws: Cold Headed and Thread Rolled
Most screws are made in three steps: heading, thread rolling and coating. Wire from a coil is cut into blanks, and each blank is cold headed: a punch squeezes the end into a die shaped like the head, so a flat head comes from a flat die, with almost no waste. The thread is then rolled, not cut: the blank is rolled between hardened dies that press the thread into it. Rolling makes no swarf, needs a blank 15–20 % lighter than cutting would, gives a 10–20 % stronger thread, and runs at about one piece a second. Most screws are then zinc plated or blackened against rust.
Advanced
About one per second (industrial)
Instructions
1
1
Cut blanks
Cut blanks
Wire from a coil is fed in and cut to the length of the screw: each piece is a blank.
Materials for this step:
Steel Wire10 kgTools needed:
Cold Heading Machine2
2
Head
Head
A punch drives into the end of the blank and the metal flows into the head die. Complex heads take two blows; slotted heads get their slot cut afterwards.
Tools needed:
Cold Heading Machine3
3
Roll the thread
Roll the thread
The blank rolls between two flat dies, one fixed and one sliding, which press the thread into it cold.
Tools needed:
Thread Rolling Dies4
4
Coat
Coat
The screws are cleaned and given a coating against rust, such as zinc electroplating or black oxide.
5
5
Check
Check
Length, head and thread diameter are measured on samples.
Tools needed:
Digital Caliper 6-InchMaterials
1- 10 kgPlaceholder
Tools Required
3- Placeholder
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