Coating Technology of Slew Ring Bearing | CHG Bearing

Sep 13, 2022

First. Electro-galvanizing (also known as cold galvanizing)

Electro-galvanizing, also known as cold galvanizing in the industry, is the process of forming a uniform, dense, well-bonded deposit of metal or alloy on the surface of a part using electrolysis.

Compared to other metals, zinc is a relatively inexpensive and easy to coat metal, and is a low-value anti-corrosion plating that is widely used to protect steel parts, especially from atmospheric corrosion, and for decorative purposes. Plating techniques include bath plating (or hanging plating), barrel plating (suitable for small parts), blue plating, automatic plating and continuous plating (suitable for wire and strip).

Domestic classification by plating solution can be divided into four major categories.

1. Cyanide galvanizing

Since (CN) is highly toxic, environmental protection has imposed strict restrictions on the use of cyanide in zinc plating, and has continued to promote the development of zinc plating systems that reduce and replace cyanide plating, requiring the use of low-cyanide (microcyanide) plating solutions.

After using this process, the quality of the product is good, especially color plating, after passivation to maintain good color.

2、Zincate galvanizing

This process is the evolution of cyanide galvanizing. Two major schools of thought have been formed in China: a) Wuhan Material Protection Institute's "DPE" series; b) GuangDian Institute's "DE" series. Both of them are alkaline additive zincate galvanizing with a pH value of 12.5~13.

With this process, the plating lattice structure is columnar, with good corrosion resistance, and suitable for color galvanizing.

Note: After the product comes out of the tank ->; Washing ->; Light out (nitric acid + hydrochloric acid) ->; Washing ->; Passivation ->; Washing ->; Washing- >; scalding dry->; drying->; aging treatment (80~90℃ in oven.)

3. Chloride galvanizing

This process is widely used in the electroplating industry, accounting for up to 40% of the total.

After passivation (orchid white), zinc can replace chromium (comparable to chromium plating), especially after the addition of water-soluble varnish, it is difficult for the layman to distinguish whether it is galvanized or chromium plated.

This process is suitable for white passivation (orchid white, silver white).
Triple-row Roller Slewing Bearings

4. Sulfate galvanizing

This process is suitable for continuous plating (wire, strip, simple, large parts and components) at low cost.

The purpose of zinc plating is to prevent corrosion of steel objects, to improve the corrosion resistance and service life of steel, and also to increase the decorative appearance of products. Since almost one tenth of the steel in the country is corroded every year, zinc plating is generally used to protect the steel or its parts from corrosion.

Since zinc is not easy to change in dry air and can produce an alkaline zinc carbonate film in a humid environment, this film can protect the internal parts from corrosion damage, even if the zinc layer is damaged by some factors, zinc and steel will form a microcell after a period of time combined, and the steel substrate becomes the cathode and is protected. To summarize, zinc plating has the following characteristics:

1.Good corrosion resistance, meticulous and uniform bonding, not easy for corrosive gases or liquids to enter the interior.

2. Since the zinc layer is pure, it is not easy to be corroded under acid or alkali environment. Long-term effective protection of the steel body.

3. After passivation by chromic acid to form a variety of colors to use, can be selected according to customer's favorite, galvanized beautiful and decorative.

4. zinc plating has good ductility, in a variety of bending, handling impact, etc. will not easily fall off.

Second, hot dipped galvanizing

(Inexpensive, easy to cover the dead ends, mostly used for steel plates, steel pipes, steel wires and strips, etc.)

Hot dipped galvanizing is the reaction between molten metal and iron substrate to produce an alloy layer, thus combining both the substrate and the coating. Hot-dip galvanizing is done by pickling the steel parts first, in order to remove the iron oxide from the surface of the steel parts. After pickling, the parts are cleaned by ammonium chloride or zinc chloride aqueous solution or ammonium chloride and zinc chloride mixed aqueous solution bath, and then sent to the hot dip plating bath. Hot dip galvanizing has the advantages of uniform plating, strong adhesion and long service life.

Third, thermal spraying (usually with zinc)

The coating material is heated and melted, atomized into very fine particles by a high-speed airflow, and sprayed onto the surface of the workpiece at a very high speed to form the coating. Different coating materials can be used to achieve different properties such as wear resistance/corrosion resistance/oxidation resistance/heat resistance according to the needs.

Heat source: electric arc; plasma spraying (slightly more advanced), combustion flame, etc. Powdered or filamentary metal (usually zinc), in a molten or semi-molten state, is deposited onto the surface of the substrate.

It is sprayed onto the surface of the treated workpiece at a very high flight speed to form a solid covering layer so that the surface of the workpiece acquires different hardness/abrasion/corrosion/heat/conductivity/insulation/heat/seal/anti-microwave radiation and other physicochemical properties.

Thermal spraying materials: alloy powder - nickel-based, iron-based, cobalt-based alloy powder, according to different coating hardness, applied to the repair and protection of mechanical parts.

Advantages: high economic efficiency

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