The surface treatment process of Custom Bolt is as follows:

1. Types of surface treatment:

  Surface treatment is the process of forming a covering layer on the surface of the workpiece through a certain method. Its purpose is to give the product surface beauty and anti-corrosion effects. The surface treatment methods carried out are attributed to the following methods:

1. Electroplating: Immerse the electroplated parts in an aqueous solution containing the deposited metal compound, and pass current through the plating solution to precipitate and deposit the electroplated metal on the parts. General electroplating includes zinc, copper, nickel, chromium, copper-nickel alloy, etc.

Sometimes boiled black (bluish), phosphating, etc. are also included.

2. Hot-dip galvanizing: It is completed by immersing the carbon steel parts in a molten zinc plating tank with a temperature of about 510℃. The result of standard parts manufacturers is that the iron-zinc alloy on the surface of the steel parts gradually becomes passivated zinc on the outer surface of the product. Hot-dip aluminum plating is a similar process.
3. Mechanical plating: impact the surface of the product through the particles of the coated metal, and cold weld the coating to the surface of the product.
4. Operation process

(1) Galvanized (blue and white, colorful, black)

1. Pre-treatment: thermal degreasing tank (5 tanks)-electrolytic degreasing tank (3 tanks)-derusting tank (4 tanks)
2. Electroplating: electroplating tank (20 tanks) (ammonium chloride, zinc oxide, gloss agent, softener solution).
3. Post-processing: melting tank (1 tank)-green medicine tank (1 tank)-(blue and white / colorful / black)

(2) Blackening:

1. Pre-treatment: thermal degreasing tank (4 tanks)-derusting tank (4 tanks)
2. Blackening: blackening (5 tanks) (caustic soda, sodium nitrite solution)
3. Post-processing: anti-rust oil (1 tank)

(3) Phosphating:

1. Pre-treatment: thermal degreasing tank (1 tank)-descaling tank (1 tank)-electrolytic degreasing tank (1 tank),

  — Surface treatment (1 slot)

2. Phosphating: Phosphating (forming a film)
3. Post-treatment: dip anti-rust oil (2 tanks)

(4) Hot-dip galvanizing:

1. Pre-treatment: Degreasing tank (1 tank)-Derusting tank (1 tank)-FLUX tank (1 tank)-drying
2. Hot dip galvanizing: hot dip galvanizing tank
3. Post-treatment: centrifugal treatment — ammonia chloride cooling — clean water cooling

Ningbo non-standard screws

2. Quality control:

  The quality of electroplating is mainly measured by its corrosion resistance, followed by appearance. Corrosion resistance is to imitate the working environment of the product, set it as the test condition, and conduct a corrosion test on it. The quality of electroplating products is controlled from the following aspects:

1. Coating thickness:

The operating life of a fastener in a corrosive atmosphere is proportional to the thickness of its coating. General recommended economical electroplating coating

The thickness is 0.00015in～0.0005in (4～12um).

Hot-dip galvanizing: The standard average thickness is 54 um (nominal diameter ≤ 3/8 is 43 um), and the minimum thickness is 43 um (nominal diameter ≤ 3/8 is 37 um).

2. Appearance:

The surface of the product is not allowed to have partial non-plating, scorching, roughness, dullness, peeling, skinning, and obvious streaks, and no pinhole pitting, black plating slag, loose passivation film, cracking, shedding and serious Passivation marks.

3. Coating distribution:

With different deposition methods, the way the plating layer gathers on the surface of the fastener is also different. During electroplating, the coating metal is not uniformly deposited on the outer peripheral edge, and a thicker coating is obtained at the corners. In the threaded part of the fastener, the thickest coating is located on the crest of the thread, gradually thinning along the side of the thread, and the thinnest deposit at the bottom of the thread, while hot-dip galvanizing is just the opposite. The thicker coating is deposited on the inner corners and At the bottom of the thread, the metal deposition tendency of the mechanical plating is the same as that of the hot-dip plating, but it is smoother and the thickness is much more uniform on the entire surface [3].

4. Hydrogen embrittlement:

During the processing and treatment of fasteners, especially in the pickling and alkali washing before plating and subsequent electroplating, the surface absorbs hydrogen atoms, and the deposited metal coating then traps hydrogen. When the fastener is tightened, hydrogen is transferred to the most stress-intensive part, causing the pressure to increase beyond the strength of the base metal and produce tiny surface cracks. Hydrogen is particularly active and quickly penetrates into the newly formed fissures. This pressure-break-infiltration cycle continues until the fastener breaks. It usually occurs within a few hours after the first stress application.

In order to eliminate the threat of hydrogen embrittlement, fasteners should be heated and baked as quickly as possible after plating to allow hydrogen to seep out of the coating. Baking is usually carried out at 375-4000F (176-190°C) for 3-24 hours.

Since mechanical galvanizing is non-electrolyte, this actually eliminates the threat of hydrogen embrittlement, while galvanizing uses electrochemical methods, which has hydrogen embrittlement. In addition, due to engineering standards, hot-dip galvanizing of fasteners with hardness higher than HRC35 (Gr8 in British system, and above 10.9 in metric system) is prohibited by engineering standards. Therefore, hydrogen embrittlement rarely occurs in hot-dipped fasteners.

5. Adhesion:

Stud Suppliers cut or pry off with a solid tip and considerable pressure. If the coating is peeled off in a flake or skin shape before the tip of the knife, so that the base metal is exposed, it should be considered that the adhesion is not enough.