Hardware painting knowledge

One, bottom wood

Hardware paint substrate: cold-rolled steel sheet stamping parts or sheet galvanized steel sheet stamping parts or sheet magnesium alloy stamping parts or sheet aluminum alloy stamping parts or sheet metal but the paint process is very different


Two, hardware baking process

Pretreatment, drying, primer painting, baking, topcoat painting, baking, inspection, packaging

Three. Surface pretreatment

(1) 1 degreasing; 2 washing; 3 rusting; 4 washing; 5 table adjustment; 6 washing; 7 phosphating; 8 washing; 9 washing; 10 drying;

(2) Purpose and importance of pretreatment: – The purpose of pretreatment is to obtain a good coating, because the above stamping parts will have grease, oxide rust skin, dust, rust and corrosive substances on the surface during manufacturing, processing, handling and storage, if not removed, will directly affect the performance of the coating, appearance, etc. Pretreatment plays a very important role in painting process.

(3) Significance of pretreatment: – Pretreatment and coating, drying are the three main processes of coating process, of which coating pretreatment is the basic process, it has an important impact on the whole coating quality, coating life, coating appearance and so on – through degreasing, rust removal, phosphating and other processes after the surface of the workpiece clean, uniform No fat.

1. Oil removal: mineral oil, grease, animal and vegetable oils, such as hand-touched oils during operation and transportation, greatly reduce the adhesion of most coatings, and affect their drying, but also reduce the hardness and gloss of the coating. The main alkali is NaOH, NaHCO3 and so on. Special degreasing powder can be purchased and then mixed into water solution. The saponification of soap.

2, rinse with water, so as not to contaminate the solution in the previous process to the next process. Clear water must be alive.


3. Removal of rust and yellow rust can promote the spread of corrosion products under the coating and make the coating lose shielding and impermeability. Under high temperature and humidity conditions can lead to early damage of coatings and metals, loose yellow rust, poor adhesion, and can fall off with the coating. There are many methods of rust removal, such as alkali method, acid method, mechanical method, electrolysis, etc., the common is alkali method. Remove the oxide scale and rust from the surface of the workpiece by chemical solution, usually with sulfuric acid and oxalic acid. It can also be supplemented by ultrasonic cleaning.

4. The abbreviation of surface adjustment (neutralization): remove the excess alkali (or acid) from the rust removal process by acid (or alkali) solution, adjust the pH value as neutral as possible, that is, PH = 7; function: accelerate the phosphating speed, refine the phosphating crystallization, increase the crystallization point of phosphating;

5. Phosphating is the central link of pretreatment before coating. Phosphoric acid manganese, zinc, cadmium orthophosphate solution is used to treat metal workpiece, so that an insoluble phosphate protective film is formed on the surface of the workpiece. The phosphating film has a compact structure of fine pores, enlarges the surface area of the workpiece, and enlarges the contact surface of the coating. As a result, a favorable mutual penetration between the phosphating film and the coating is created, and the adhesion of the organic coating to the workpiece is greatly improved. The phosphating film formed by phosphating is a stable and non-conductive isolation layer, which makes the metal surface from good conductor to bad conductor, inhibits the formation of micro-battery and effectively prevents the corrosion of coating. The commonly used phosphating methods are divided into high-temperature phosphating (70-90 C), medium-temperature phosphating (50-70 C) and room-temperature phosphating (20-30 C). Phosphating film is usually black.

6, drying process is basically carried out in the water tank. And each process has time limit. Dry the water and prepare the paint.

Four. Inspection before hanging.

Check the appearance of the unpainted workpiece before going on line; a large part of the unpainted defective products should be inspected for direct spraying or removal of the old paint; remove the old paint method, solvent soaking cleaning or removal with a special paint remover.

Five, grinding

Non-essential process, remove surface granular impurities and increase a certain degree of roughness to increase paint adhesion; first pass: 400 # sandpaper second pass; 800 # sandpaper or finer.

6. The hanging device hooks the product on the hanging device, the hanging device conducts electricity and moves along with the pipeline; the hanging device should be conductive and grounded (for electrostatic coating); the hanging device is generally customized according to the different characteristics of the product; a large number of the whole pipeline turnover use.

Seven, dust removal, surface dust, hair and so on; compressed air; electrostatic precipitator gun; flame combustion;

8. Pre-spraying of low potential (such as shadows, concave parts, etc.) before automatic spraying is necessary, but it is also the choice when there is no automatic spraying equipment. The efficiency is not high, the productivity is limited, there are many unstable factors, the bad rate is high, and the thickness of the film is uneven manual spraying equipment mainly includes air compressor. Gas pipeline, air oil and water separator, spray gun, paint container, spray booth and so on. The types of spray guns are:


1, gravity type;

2, suction type;

3. Press delivery.

9. Disk spraying automatic spraying belongs to the category of electrostatic spraying. The high voltage difference between spraying device and grounding workpiece produces electrostatic force. The coating is thrown out by the centrifugal force produced by Disk at a fixed speed. After spraying the electrostatic spraying coating on the workpiece, the Disk moves up and down to cover the whole workpiece. It is a rotating disk electrostatic spraying equipment, also known as centrifugal electrostatic atomizing equipment, rotating speed of the rotating disk is 5 000 ~ 60 000 R / min, working voltage is: 70 ~ 120 KV, using air motor drive, electrostatic coating used electrostatic coating, coating.