Button head semicircular head American machine screw is a fastener that combines aesthetics and functionality. Its surface treatment needs to choose the appropriate process according to the application scenario. It is widely used in mechanical assembly, electronic equipment, automobiles, and other fields.
1. Electroplating
Galvanizing
Conventional galvanizing: low cost, salt spray test time is 24-72h, rust resistance is general, the surface is silvery white, and passivation treatment is required.
Hot dip galvanizing: coating thickness 50-100μm, salt spray performance is improved to more than 200h, but the surface is rough, suitable for heavy industry.
Nickel plating: high gloss, good corrosion resistance, suitable for electronic and decorative purposes, high cost.
Chrome plating: high hardness, wear resistance, salt spray for more than 120h, divided into decorative chrome and hard chrome; the latter is used in a mechanical wear environment.
2. Chemical treatment
Phosphating: a gray-black matte surface that improves lubricity and paint adhesion, but has weak salt spray performance, and is often used in conjunction with oiling.
Blackening: Beautiful black appearance, low anti-rust ability requires re-applying of anti-rust oil, suitable for indoor equipment.
3. Coatings
Dacromet: No risk of hydrogen embrittlement, salt spray test can reach 500-1000h, can withstand high temperature of 300℃, but the color is limited to silver gray and gray green.
Powder spraying; various colors, thickness 40-80μm, strong weather resistance, but the thread needs to be masked to avoid affecting the matching accuracy.
4. Stainless steel material
Passivation treatment: For stainless steel 304 or 316, nitric acid or citric acid passivation is used to enhance the oxide film, improve corrosion resistance, and maintain the original color of the metal.
Key selection factors
Environmental requirements: Nickel plating or Dacromet is preferred in a marine environment; chrome plating or stainless steel is considered in high-temperature environments.
Matching accuracy: The thickness of the electroplating layer needs to be controlled to avoid affecting the thread engagement.
Cost: Galvanizing is economical, and nickel or chromium plating costs 30-50% higher.
Balance performance and cost according to actual needs, and ask suppliers to provide salt spray test reports when necessary.
The two screws can be partially replaced in function, but the choice needs to be weighed according to specific working conditions.
Through reasonable selection and standardized operation and application, button head semicircular head American machine screws can balance aesthetics and structural strength, and are an ideal choice for precision assembly.
