Application of powder coating in construction machinery cab

Powder coating features

The successful implementation of the powder coating process is a major breakthrough in the coating process of the construction machinery industry, which has been greatly improved in terms of production cost, construction technology, environmental protection and automation in terms of traditional solvent-based coatings to powder coatings.

The powder coating process offers the following advantages:

1) Powder coating does not contain organic solvents, does not emit harmful gases in production, can prevent air pollution, and improves the working conditions of workers, belongs to environmental protection coatings, while the solvent content of traditional paints is more than 40%, and contains a large number of toxic substances such as toluene and xylene; 

2) Powder coating can be recycled, the utilization rate is more than 95%, or even up to 99%, and the paint utilization rate is generally 35%~50%;

3) It is easy to get a thicker coating (50~300μm) at one time, so it can reduce the construction process, save energy and improve efficiency;

4) reduced risk of fire due to the absence of solvent volatilization;

5) Powder coating has excellent mechanical and chemical properties;

6) The yield of powder spraying is higher than that of spray painting, generally speaking, the rejection rate of spray painted parts is about 10%, while the powder spraying parts are about 1%, and the repair rate is low, which is conducive to reducing costs;

7) The construction is simple, does not require very skilled operation technology, is easy to master, there will be no sagging problem when the film is thickly coated, and it is easy to implement automatic assembly line coating;

8) Since the powder coating is solid, it is easy to manage in storage.

Cab powder coating process

1. Process flow

Upper part→ pre-degreasing→ degreasing → washing → washing→ surface tone → phosphating → washing → washing → pure water washing→ cathode electrophoresis → ultrafiltration one → ultrafiltration two → pure water washing→ draining → drying → strong cold → (grinding) → gluing→ powder spraying → drying→ strong cold → shielding → color painting → shielding→ leveling→ drying→ cooling → the next piece.

2. The requirements of powder coating for the white parts of the cab

Construction machinery products are limited by steel, welding process and mold, resulting in many defects on the surface of finished white parts, such as solder joint defects, mold forming defects, grinding defects, etc. Therefore, most of the company's products need to scrape putty, dry, polish, and then spray topcoat after electrophoretic primer to ensure the best appearance. However, the powder coating needs to be in the baking environment of 180~200 °C for a long time in the film-forming process, so the bottom coating is required to have high temperature baking resistance. In addition, due to the electrostatic adsorption principle used in the coating process of the powder, the base coating is required to be electrically conductive. Therefore, the putty putty and sealant used to make up for the defects of the finished white parts are required to have conductivity and high temperature resistance. In order to solve the problem of white parts defects, a large number of process tests were carried out without changing the previous process, and various brands of putty and sealants were selected at home and abroad for testing, and the test results were:

1) putty is not suitable for large-scale and thick scraping, and the coating is prone to defects such as bulging, pinholes, and orange peel

2) The ratio of putty requires high requirements, otherwise the powder coating is prone to pinholes;

3) The sealant can be used as a process to compensate for weld defects, but a white body needs to be used, otherwise the powder coating is prone to color difference;

4) The sealant cannot be scraped as a compensatory material for the defects of the plate

3. The design of the powder spraying process

3.1 Layout of the powder electrostatic spray gun

Most of the construction machinery products are flat or pipe fittings, so they are suitable for high-voltage electrostatic spraying. The characteristics of powder electrostatic spraying technology are that the workpiece can be coated at room temperature, and the utilization rate of powder is high, up to more than 95%; The coating film is thin and uniform, smooth, and has no sagging, and can form a continuous, flat and smooth coating film even on the sharp edges and rough surfaces of the workpiece.

The existence of the inner cavity or some dead angles can be carried out in the back of the manual repair station, and the quality of automatic powder spraying can be checked at the same time, and the uneven parts of the existing powder spit and powder can be dealt with in time to ensure the excellent coating appearance.

3.2 Design of the powder room

The design of the powder room mainly focuses on two aspects: first, the size of the opening of the chamber, mainly including the import and export of the workpiece, the telescopic port of the reciprocating machine, and the chain through the mouth, the opening is as small as possible, which can reduce the power of the recovery system, reduce the procurement cost and use cost;
Second, the selection of wall plate materials, the wall plate of different materials has different adsorption properties for powder, in order to facilitate the operator to clean the powder room after the end of each shift, the material with poor powder adsorption should be selected.
Of course, it is necessary to consider the use conditions at the same time, and it is generally recommended to use stainless steel at the bottom, and PP board or PVC board for the surrounding and ceiling

Generally speaking, construction machinery products are composed of two colors, and the output is balanced, and at the same time can not be rotated for mass production, so 2 powder spraying booths can be designed to produce at the same time, so as to avoid color change operations.

3.3 Design of the recycling system

The recovery system of powder coating equipment is generally divided into two types, namely single-stage filter type recovery device and large cyclone filter type secondary recovery device. The appearance coating color of construction machinery products is generally relatively simple, and most of them are 2 colors.

Therefore, the selection of single-stage filter type recovery device is conducive to reducing investment and operating costs, and reducing the amount of powder room cleaning at the end of each shift. The single-stage filter cartridge recovery unit consists of the following components: powder filling device, rotary screen (or vibrating screen), powder supply drum, filter element, fan, ultimate filter element, etc

Because the stable air flow blows smoothly into the inside of the powder booth from the various openings around the powder booth, the oversprayed powder is finally brought into the recovery assembly, which prevents the overflow of the powder and improves the recovery efficiency of the powder. In addition, the powder concentration in the powder booth must be below the explosion limit of the powder. Therefore, the design of the actual air volume of the powder room is as follows.

1) Calculation formula of exhaust air volume of powder room

Q1＝3600K· S· V

Where: Q1 is the exhaust air volume of the powder room, m3/h; S is the total area of all openings in the powder room, m2; K is the efficiency coefficient of the powder room, taking 1.8~3.6, V is the air flow rate of the powder room, m/s, and the speed of inhaling air at the opening is 0.4~0.7m/s.

2) The formula for calculating the exhaust air volume of the recovery device

Q2＝D/n·p

where: Q2 is the exhaust air volume of the recovery device, m3/h; D is the total amount of powder discharged, g/min; n is the powder coating efficiency; p is the lower limit concentration of powder explosion, 30g/m3.

Therefore, the actual air volume of the powder room Q≥Q1, Q2. The wind speed at the opening of the automatic powder spraying chamber is higher than that of the manual powder spraying chamber, so as to adapt to the spraying of multiple guns and large powder supply, to ensure that the powder does not overflow and the powder concentration is about 50% lower than the explosive concentration, and the speed is not more than 0.3m/s near the spraying workpiece, so as to reduce the damage of the air flow to the spray shape and ensure a high deposition rate.

epilogue

For the construction machinery industry, powder coating technology, as a new type of environmental protection technology, is one of the important manifestations of green production technology, and has high promotion value.

Some large domestic construction machinery manufacturers not only use powder coating technology in a wide range of OEMs, but also have required most of the outsourcing partners to promote the use of powder coating technology, and its good economic value has been recognized by everyone.