3 Cases of Surface Removal Treatment of Metal Materials

Pre-processing and auxiliary processing are processing procedures other than sheet metal blanking and forming, which mainly include surface cleaning, deburring, correction, drilling, tapping, threading, and material modification treatment of metal materials. Pre-processing and auxiliary processing are processing procedures other than sheet metal blanking and forming, which mainly include surface cleaning, deburring, correction, drilling, tapping, threading, and material modification treatment of metal materials.

The surface cleaning of metal materials is one of the important auxiliary processing procedures for sheet metal processing. It runs through the processing of sheet metal parts. It includes the removal of oil, rust, and oxide scale on the surface of raw materials and blanks, as well as sheet metal processing. Work such as removal of rust, burrs, flash, oxide layer, and other dirt on parts blanks, process processed parts, and cleaning of the processed surface or welding spatter, welding slag, rust, etc. before painting the surface of the parts. Doing a good job of cleaning the surface of the material is an important measure to maintain or improve the corrosion resistance of the equipment and ensure the quality of the product.

Surface oil removal

Surface oil removal mainly includes electric degreasing, hot alkali degreasing, and cleaning fluid degreasing. Among them: electric degreasing is to use the chemical cleaning function of the degreasing agent and the mechanical cleaning function of cathode hydrogen evolution bubbling to remove the oil on the surface of the workpiece; hot alkali degreasing is to use the alkaline solution composed of soda ash additives and additives to dissolve in the higher Soaking at temperature will remove the oil through various effects of adsorption, entrainment, wetting, dissolution, emulsification, dispersion, and chemical corrosion on the dirt, both of which consume a large amount of electric energy and heat energy, and the cost is relatively high.

To reduce costs, homemade lye degreasing is commonly used in production. The following table shows several commonly used chemical degreasing lye formulations and methods of use.

No.	Caustic soda	Trisodium Phosphate	Sodium carbonate	Sodium silicate	Other	Process parameters, temperature and time	Scope of application
1	50-55	25-30	25-30	10~15	/	90-95°C Dip, spray 10min	Copper and iron heavy oil
2	40-60	50-70	20-30	5~10	/	80-90°CDip and spray until clean
3	60-80	20-40	20-40	5~10	/	70-90°C Soak until clean
4	70-100	20-30	20-30	10~50	/	70-90°C Dip, spray 2-10min	Nickel-chromium alloy steel
5	/	/	20-30	/	Potassium dichromate1-2	60-90°C Dip, spray 5-10min	Black, non-ferrous metal light oil
6	750	/	/	/	Sodium Nitrite225	250-300°C spray 15min	Titanium alloy
7	5~10	50-70	20-30	10~15	/	80-90°C spray 5-8min	Copper, copper alloy
8	/	70-100	/	5~10	OP-1 Emulsifier 1~3	70-80°C Soak until clean
9	/	20-40	50-60	/	Soap powder 1-2	70-80°C Soak until clean	Brass, zinc, etc.
10	5~10	50	30	/	/	70-80°C Dip, spray 10min	Aluminum and its alloy heavy oil
11	/	40-60	40-50	2~5	Wetting agent 3~5ml/L	70-80°C spray 5-10min
12	/	20-25	25-30	5~10	/	60-80°CDip and spray until clean	Aluminum magnesium zinc tin and its alloys

Commonly used metal cleaning fluids are: gasoline, kerosene, benzene, xylene, and other organic solvents, which have strong cleaning ability against oil-soluble dirt and are suitable for various metal materials, but the price is relatively expensive. In addition, it can also be cleaned with multifunctional metal cleaning liquids on the market. Commercial metal cleaning liquids are often supplied as powders, pastes or glues, and can be used by adding more than 95% of water during use. It can clean both water-soluble and oil-soluble dirt, is safe to work, and has low environmental pollution. The cost is less than 1/3 of gasoline. It has been widely used at home and abroad. The following table shows the formula and use of several metal cleaning fluids.

Component		Main process parameters	Scope of application
Name	content/%
XH-16	3~7	Room temperature, impregnated	Steel
SL9502	0.1-0.3	Room temperature, dip, rub, spray
664 detergent	2~3	75°C soak 3-4min	Steel degreasing, not suitable for copper and zinc
Detergent	1~3	60-80°C soak 5min	Aluminum copper and its alloys
8201	2~5	Room temperature Rinse until clean	Copper and its alloys
XT-10 detergent	0.2	4-6min	Aluminum and its alloys

Rust removal

There are two main methods for removing rust and oxide scale on the surface of metal materials: mechanical rust removal and chemical rust removal.

1. Mechanical derusting

Mechanical rust removal is a processing method that directly uses appropriate tools or media to perform mechanical processing such as grinding, friction, rolling, and spraying on the surface of the material through mechanical equipment to achieve the purpose of rust removal and polishing. Commonly used mainly include: sandblasting, projectile and shot blasting, rust removal, roller polishing, grinding wheel polishing, etc.

Sandblasting is a method widely used in steel plates, steel pipes, section steels, and various steel equipment. It can remove various dirt such as rust and oxide scale on the surface of the workpiece and produce a uniformly rough surface. The sandblasting method is of good quality and high efficiency, but the dust is large, so it must be carried out in a closed sandblasting room.

The projectile method uses the high-speed airflow in the compressed air duct to make the iron shot impact the rust layer on the metal surface to achieve the purpose of rust removal. The diameter of the iron shot is generally 0.8~1.5mm, and the compressed air pressure is generally 0.4~0.5MPa. The projectile derusting method is used for the overall derusting of parts or components, and the productivity of this derusting method is not high.

The shot blasting method uses a special shot blasting machine to project iron shots or other abrasives onto the surface of the raw material at a high speed to remove oxide scale, rust, and dirt on the surface.

In addition, the rust removal of the pipe end can be carried out by the wire wheel rust removal method shown in Figure (a). The wire wheel has a good rust removal effect, but the effect of removing the oxide scale is not obvious. The use of the abrasive belt derusting method shown in Figure (b) can not only achieve the ideal derusting effect but also can completely remove the oxide scale. The dedusting effect is more thorough than the wire wheel method, and the efficiency is higher. For stainless steel, titanium and other materials that are sensitive to iron ions, only stainless steel wire wheels can be used instead of carbon steel wire wheels.

Derusting of pipe ends

For other parts of the surface that need to be trusted, generally, the method of grinding wheel or wire brush is used for treatment, and tools and materials such as a scraper, sandpaper, and other tools and materials can also be used to remove or grind the rust manually. Manual dedusting does not require professional equipment and is simple to use, so it is widely used, especially for extra-large steel parts, which can only be manually deducted and blackened. However, the labor intensity is high, the work efficiency is low, the quality is poor, and the rust in the rust hole is difficult. Removal; while the use of special equipment for mechanical rust removal can remove oxide scales thoroughly and has high quality, but special equipment requires a large amount of energy, high cost, high noise, large dust, and environmental pollution, and it is not suitable for complex shapes The application of workpieces and thin-walled plates is limited.

The metal materials after derusting should be prevented from being rusted again after derusting. Therefore, after the raw materials and parts are trusted by sandblasting, shot blasting, etc., generally within the range of 10 to 20 minutes, protective treatment should be carried out immediately dedusting.

2. Chemical derusting

Chemical rust removal generally uses the action of inorganic acid and rust to produce chemical dissolution and mechanical peeling to achieve rust removal. Chemical dusting has simple methods and low cost and can be used for dusting parts with complex shapes and different degrees of corrosion.

Burr removal

1. Manual chiseling

Burrs are often produced on the edges of the sheet metal blanks obtained by cutting or shearing, or the surface after other processing. Spatter and welding slag produced by welding are also burrs. All burrs should be removed. The most commonly used method of deburring is mechanical deburring. The commonly used mechanical deburring methods and operating points are as follows.

The chisel is made of T7, T8 tool steel, and the heat-treated head is 58~62HRC. Used for trimming, chopping, cutting, and deburring of various materials. The sharp chisel β1 is generally used at 45°~50°. When processing soft materials, use a flat chisel with a β of 30°~50°; when processing medium materials, use a flat chisel with a β of 50°~60°; the processing is harder When feeding, use a flat chisel with β of 60°~70°. During operation, keep the chisel and the workpiece at an angle of 50°~60°.

2. Mechanical chiseling

Used for deburring, trimming, and beveling of weldments for materials below medium-hardness.

3. Scrape

Remove all kinds of burrs, trim edges, and scrape solid dirt.

4. File

Single tooth file with aluminum and soft material; double tooth file with hard material; coarse tooth file with large allowance, rough surface, or soft material; fine tooth file with a small allowance and smooth surface. Diamond-coated files are suitable for filing glass, ceramics, non-ferrous metals, and hardened steel. Other files are only suitable for materials below medium hardness.

5. Hand polished

Emery cloth, grinding wheel, whetstone, sticky (coated) abrasive cloth.

Trimming, removing thorns, removing rust, removing solid oil stains.

6. Removal

Brush wire includes metal wire, including high-strength steel wire, stainless steel wire, copper wire, aluminum wire; non-metallic wire, such as nylon wire, chemical fiber wire, animal and plant wire, etc. Various abrasives (silicon carbide, aluminum oxide, boron nitride, diamond, etc.) can be adhered (coated) on the wire.

Used for rust removal, small burr removal, trimming, polishing of various materials, and degreasing with cleaning fluid.

7. Mechanical grinding and cutting

There are mainly two kinds of portable pneumatic or electric. There are three types of grinding wheels:

Grinding wheels, suitable for various materials except for non-ferrous metals, plastics, and rubber; brush wheels, wire brushes are the same as manual brushes, suitable for various materials; cloth wheels, suitable for polishing various materials (with polishing paste), except for micro glitch.

Deburring, trimming, polishing, and cleaning fluid can remove oil.

8. Abrasive belt mill

Suitable for rust removal, deburring, and polishing of various materials.

The belt grinder can grind flat surfaces, outer circles, inner circles, and profiles. Abrasive belt linear speed (m/s): non-ferrous metals 22~30; steel 10~25; glass fiber 30~50, to prevent sand belt clogging, dry abrasive or grinding fluid can be added, and its production efficiency is ordinary grinding Five times, high precision (such as flatness up to 1μm), surface up to Ra0.8~0.2μm, low cost.

9. Rolling or vibration polishing

Derusting, deburring, and polishing of small parts of various materials.

Working medium: various abrasive blocks, sand metal pellets, glass balls, dried fruit shells, water drum speed is 10~50r/min, high value for rough grinding and low value for fine grinding.