Screw manufacturing process flow including

feed-in →material inspection→heading→threading→plating-baking→ QA→packaging→shipping

How to make the screw head?

Forging can be classified according to the processing

  1. Cold Heading:   High production efficiency, suitable for producing small screws
  2. Hot forging:  Low production efficiency, suitable for producing large screws >M16

Cold heading 

Hot forging

Thread rolling: High production efficiency, low cost, suitable for mass production

Heat Treatment:

Heat treatment is the process of heating or cooling material in order to obtain desired properties and other conditions.

Self-tapping screws need to be carburized to obtain a very hard surface for thread tapping and forming or cutting. Usually, the surface hardness of self-tapping screws is HV450Min.

Surface treatment:

The process of forming a cover layer on the surface of the workpiece by certain methods is called surface treatment, the purpose of which is to give the product surface aesthetic and anti-corrosion effect on the surface of the product.

  1. Plating: The part to be plated is immersed in an aqueous solution containing the metal compound to be deposited, and an electric current is passed through the plating solution to precipitate and deposit the plated metal on the part. Through the plating solution, the plated metal is precipitated and deposited on the part. General electroplating has galvanization, copper, nickel, chromium, copper-nickel alloy, and so on. Chromium, copper-nickel alloy, etc. Sometimes blackening (bluing), phosphating, etc. are also included. 
  2. Hot dip galvanizing: done by immersing carbon steel parts in a bath of dissolved zinc at a temperature of about 510°C. The result is that the iron-zinc alloy on the surface of the product gradually turns into passivated zinc on the surface of the product. The result is a gradual transformation of the iron-zinc alloy on the surface of the steel part into passivated zinc on the exterior surface of the product.
  1.  Mechanical plating: by plating the particles of metal to impact the surface of the product, and cold welding the coating to the surface of the product

 At present, there are three main materials of carbon steel, stainless steel, and brass in the market for standard parts. 

1. Carbon steel

a. Low carbon steel: domestic is usually called A3 steel. Foreign basically called 1008, 1015, 1018, 1022, etc. Mainly used for 4.8-grade bolts and 4-grade nuts, small screws, and other products without hardness requirements.

b. Medium carbon steel: domestic usually called No. 35, No. 45 steel, foreign basic called 1035, CH38F, 1039, 40ACR, etc. Mainly used for 8-grade nuts, 8.8-grade bolts, and 8.8-grade hexagonal products.

c. High carbon steel: basically not used in the market at present.

d. Alloy steel: add alloy elements to plain carbon steel to increase some special properties of steel

2. Stainless steel

By grade mainly SUS302, SUS304, SUS316. its good heat resistance, good corrosion resistance, good weldability

3. Brass

Commonly used materials for brass … zinc-copper alloy. The market mainly uses H62, H65, H68 brass as standard parts.

Hardness Grade:

The grade of bolts for steel structure connection is divided into more than 10 grades, such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9.    

Among them, 8.8 grade and above bolts are made of low carbon alloy steel or medium carbon steel and heat-treated (quenched and tempered), commonly known as high-strength bolts, and the rest are commonly known as ordinary bolts.