1 phosphate coating treatment

When metal parts are treated with acid phosphate, a phosphate coating is obtained on the surface, which is called phosphating. Phosphated film has abrasion resistance and can reduce the friction coefficient and can also improve the electrical insulation performance.

1.1 Purpose: Prevent metal corrosion.

1.2 Defects and causes in the phosphating process

Defect Status Cause

No phosphate film on the metal surface The surface is unchanged or blackened The oil rust is not cleaned

Hoarfrost on the phosphating film

Even and fine white powder

High temperature

Spots on the phosphate film

Flowering and uneven color Phosphate solution becomes soy sauce color Poor oil removal before treatment

Surface rust and oxide film have not been removed

Corrosion resistance of phosphating film

Poor or yellowish surface with rusty yellow surface with residual acid

xx Phosphating process requirements: The color of the phosphating film should be gray to light dark gray. The film layer must be continuous, uniform, and the crystals should be fine, and there should be no loose film.

1.3 metal passivation

The passivation of the metal surface is to use chemical methods to form a passivation film on the metal surface.This passivation film can resist corrosion in the general atmosphere to prevent the metal from rusting before anti-corrosion construction.This method of improving the metal surface is called Passivation. (Aluminum is generally chemically oxidized before passivation)

Common passivation agents: nitrate, nitrite, chromate, dichromate, etc.

1.4 Defects:

Phosphate treatment has little effect on the part itself, but it has a corrosive effect on hardware parts of ordinary materials, so the riveting process arrangement of hardware parts must be considered.

2 oxidation

Role: Generally used to improve the corrosion resistance of the surface of the part and get a beautiful appearance, such as oxidation blackening of hardware parts, springs, aluminum materials, etc. (no significant impact on the size and accuracy of the part)

Anodizing of aluminum: Can significantly improve the corrosion resistance and abrasion resistance of aluminum and its alloy products, and also has a strong ability to adsorb coatings and pigments

3 sandblasting

3.1 Dry blasting treatment: Use compressed gas or high-speed rotating impeller to accelerate the abrasive to the surface of the substrate, remove oil, rust and residues, make the surface of the substrate clean and rough, and also cause internal stress on the surface. Fatigue strength is favorable.

3.2 Types and main ingredients of grit:

Type Chilled steel grit Pure alumina Emery standard grit

Main ingredients: Fe Al2O3, iron quartz, quartz

Note: Apply non-stick coating to the non-spray area so that the coating can be removed quickly after spraying.

4 drawing processing

4.1 Drawing process:

(1) The pattern formed by different types of sandpaper is not the same. The larger the model of the sandpaper, the shallower the pattern formed by the finer sand particles, and conversely, the smaller the model of the sandpaper, the larger the pattern formed by the coarser sand particles. The deeper the sandpaper type must be indicated on the engineering drawing.

(2) The drawing is directional: it must be marked on the engineering drawing as straight or horizontal drawing (indicated by double arrows).

(3) The drawing surface of the drawing workpiece must not have any raised parts, otherwise the raised parts will be flattened.

Note: Generally, the wire must be treated with electroplating, oxidation, etc. after drawing the wire. For example: iron plating, aluminum oxidation. Due to the defects of the wire drawing machine, when there are large holes in small workpieces and workpieces, consideration should be given to designing wire drawing fixtures To avoid the poor quality of the workpiece after drawing.

4.2 Wire drawing machine functions and precautions:

Before drawing, the drawing machine must be adjusted to the appropriate height according to the thickness of the material.

The slower the speed of the conveyor belt, the finer the grinding, and the thicker it becomes. The feed depth is too large, the surface of the workpiece will burn, so it should not be too much for each feed, it should be about 0.05mm.

The pressure of the pressure cylinder is too small, which will not compress the workpiece, and the workpiece will be thrown out by the centrifugal force of the roller. Too much pressure will increase the grinding resistance and affect the grinding effect.

The wire drawing machine’s effective wire drawing width does not exceed 600mm. If the length direction is greater than 600mm and the width direction is less than 600mm, you must pay attention to the wire drawing direction, because the wire drawing direction is along the material feed direction.

5 electroplating

5.1 Plate a metal film on the surface of the workpiece to make it anti-corrosive, wear-resistant, lubricating, and electrically conductive. Such as: white zinc plating, color zinc plating, copper plating, etc.

5.3 Coating specifications for different materials

Bottom Metal Material Part Type Coating Type Coating Thickness (μm)

carbon steel

General structure

Parts Copper / Chromium / Ni 12 ~ 15

Zinc 12 ~ 15

Cadmium 9 ~ 12

Fasten

Parts Zinc 9 ~ 12

Cadmium 12 ~ 15

Elastic parts Zinc 12 ~ 15

Cadmium 9 ~ 12

Copper and copper Alloy general junction

Structural parts Chrome / Nickel 9 ~ 11

Nickel or high tin bronze 9 ~ 12

Fastening parts Nickel or high tin bronze 6 ~ 9

Elastic parts Nickel 6 ~ 9

Note: The reasons for the plating fall off are: 1. The workpiece is not cleaned thoroughly before plating 2. The plating solution is defective and has impurities.

6 spraying

6.1 Paint

6.1 Surface treatment before baking: derusting, degreasing, phosphating.

General requirements and processing of baking paint for workpieces:

(1) The surface of the workpiece is required to be baked, and the unevenness affects the appearance.

(2) If there is a through hole on the required baking paint surface, the hole must be treated with 0.1mm on one side during the process arrangement to avoid the hole from being reduced due to baking paint.

(3) If there are through-hole studs, nuts and direct tapping threads on the painted surface, special instructions must be noted and special attention should be paid to avoid the paint from adhering to the threads and causing defects.

(4) The workpiece after painting is generally not subject to external impact forces, such as bending, stamping, etc. to avoid the paint layer from falling off.

(5) The surface of the paintwork

(6) Inspection method for baking paint: Use a single-sided blade to cut the puncture paint film, four horizontally and vertically, and a line spacing of 1mm to form small squares with a side length of 1mm. Then, use adhesive tape to compact and then suddenly force upward Pull away and observe the paint film.

6.2 Introduction to Huawei Surface Treatment Code

7 silk screen

7.1 Silk screen process requirements and precautions:

(1) The screen printing process is usually the last processing process (the next process is assembly), and it is surface-treated before screen printing, such as surface treatment such as plating, baking paint, oxidation.

(2) Although the surface of the screen printing workpiece may have raised parts, the area of the screen printing required must not be uneven, and there must be no sharp edges near the screen printing area to avoid screen rupture during screen printing.

(3) The silk screen of the workpiece must be positioned, and it must be considered whether the silk screen can be positioned during the process arrangement. If necessary, positioning fixtures can be added.

(4) The workpiece after silk screen must be baked in an oven, so there must not be any objects damaged by high temperature on the workpiece.

polishing

1 Superiority: After ordinary stainless steel polishing, a bright surface similar to a mirror can be obtained.

Slag appearing on the workpiece after spot welding can be removed with a polishing machine.If a grinder is used, it is easy to grind into uneven surfaces.