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Eight surface treatment methods for fasteners, screws and nuts

2019-10-09

For fastening screw nut production, surface treatment is a process with the inevitable, many vendors in inquiring about the screw fasteners, way of surface treatment, hebei xin yu metal products co., LTD. According to the summarized information about the surface of the screw fasteners common processing ways there are eight kinds of forms, such as: black (blue), phosphating, hot dip zinc, dacromet, electric galvanized, chrome plating, nickel and zinc impregnation.The surface treatment of the fastener screws is a process of forming a covering layer on the surface of the workpiece through certain methods.

Eight surface treatment methods of fasteners, screws and nuts:

1. Black (blue)

The fasteners prepared for black treatment were heated and oxidized in the solution tank (145±5℃) with NaOH and NaNO2 oxidant, and a layer of magnetic Fe3O4 film was generated on the surface of the metal fasteners, with a thickness of 0.6 -- 0.8 microns in black or blue-black.Both HG/20613-2009 and HG/ t20634-2009 fasteners for pressure vessels require blue treatment.

2, phosphating

Phosphating is a process of chemical and electrochemical reaction to form phosphate chemical conversion film, which is called phosphating film.The purpose of phosphating is to protect the base metal from corrosion to some extent.It is used as the base before painting to improve the adhesion and anti-corrosion ability of paint film.It is used for anti-friction lubrication in cold metal processing.Phosphating treatment is required as standard for large diameter twin - end studs for pressure vessels.

3. Hot dip zinc

Hot dip zinc is to dip the steel member after derusting into the zinc solution melted at about 600℃ to make the steel member surface adhere to the zinc layer. The thickness of the zinc layer shall not be less than 65 microns for the sheet below 5mm, and the thickness of 5mm and above shall not be less than 86 microns.So as to play the purpose of anti-corrosion.

4. Dacro

DACROMET is the translation and abbreviation of DACROMET, DACROMET, DACROMET, and dicron.Domestic named zinc chromium coating, is a zinc powder, aluminum powder, chromic acid and deionized water as the main components of the new anticorrosive coating.There is no hydrogen embrittlement problem and the torque-preload consistency is good.If the environmental protection of hexavalent chromium is not considered, it is actually most suitable for high strength fasteners with high anticorrosive requirements.

5, electric galvanized

Electrogalvanization, also known as cold galvanization in the industry, is the use of electrolysis, forming uniform, dense, good combination of metal or alloy deposits on the surface of the workpiece process.Compared with other metals, zinc is relatively cheap and easy to plating a kind of metal, belongs to the low value anti-corrosion coating, is widely used to protect iron and steel parts, especially to prevent atmospheric corrosion, and used for decoration.Plating technology includes trough plating (or hang plating), roll plating (suitable for small parts), blue plating, automatic plating and continuous plating (suitable for wire, strip).

Galvanization is the most commonly used coating for commercial fasteners.It's cheaper and looks better. It can be black or army green.However, its anti-corrosion performance is generally, its anti-corrosion performance is the lowest zinc coating.General electric galvanized neutral salt spray test in 72 hours, there are also the use of special sealant, so that the neutral salt spray test up to more than 200 hours, but the price is expensive, is the general galvanized 5~8 times.

Fasteners for structural parts are usually colored zinc and white zinc, such as 8.8 and other commercial grade bolts.

6, chrome plated

Chromium plating is mainly to improve the surface hardness, beautiful, anti - rust.Chromium coating has good chemical stability, in alkali, sulfide, nitric acid and most organic acids do not occur, but can be dissolved in halogen acid (such as hydrochloric acid) and hot sulfuric acid.Because chromium does not discolor, it can maintain its reflection ability for a long time when used, which is superior to silver and nickel.

7, nickel plating

Nickel plating is mainly wear - resistant, corrosion - resistant, rust - resistant, general thickness of thin process divided into electroplating and chemical two categories.

8, zinc impregnation

The principle of powder zincizing technology is that the zincizing agent and steel products are placed in the zincizing furnace and heated to about 400 ℃.At the same time, iron atoms spread inward and outward, forming an intermetallic compound of zinc and iron on the surface of a steel piece, known as a zinc-iron coating.


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