1. Dry ice cleaning principle

1) Physical principle: freezing through the polar temperature of dry ice (-78.5 degrees Celsius), so that the oil on the surface of the workpiece loses viscosity, so that the oil is easy to handle;

2) Power principle: when the dry ice is blown out by the high-speed compressed air of the system, it leaves the nozzle and shoots to the workpiece surface, producing a certain impact force, so as to play the role of cleaning dirt;

3) Expansion principle: When fine granular dry ice is hit on the surface of the workpiece, it will expand rapidly, and the volume will expand about 800 times. Through this expansion force, the residue will be cleaned up.

Dry ice cleaning schematic

2. Composition of dry ice cleaning system

The complete automotive plastic parts (including bumper) dry ice cleaning system is composed of liquid carbon dioxide storage system, dry ice manufacturing system, compressed air supply system and jet cleaning system, as shown in the figure:

3. Difference between dry ice cleaning technology and traditional pre-treatment process route

Traditional automobile bumper coating process:

Injection molding → upper part → cleaning (degreasing cleaning and washing) → blow water → moisture drying →

Check → flame treatment → electrostatic dust removal → paint spraying → drying the next part

Dry ice cleaning bumper coating process:

Injection molding → upper part → dry ice cleaning → flame treatment → electrostatic dust removal → paint spraying →

Drying small pieces

To sum up, it can be seen that the traditional pretreatment process is mainly divided into: pre-degreasing cleaning → degreasing cleaning → water washing 1 cleaning → water washing 2 cleaning → pure water washing → blowing water → drying → inspection and other procedures. Compared with the dry ice treatment process, its process route is long and there are more procedures. In the early investment, production efficiency, operating costs and other convenience at a disadvantage.

4. Application advantages of dry ice technology

4.1 Small floor area and flexible space

The cleaning equipment in the workshop covers only about 3*3m space, and the other is the conveying pipeline. Compared with the traditional process, it requires the construction of multiple washing tank, degreasing tank, water drying furnace and manual cleaning, which greatly reduces the floor area.

4.2 Energy Saving and Environmental Protection

Traditional pretreatment process, not only need to add chemical agents, but also need to heat cleaning water, after cleaning also need to dry; This process not only consumes a lot of energy, but also causes pollution of water quality and environment.

Dry ice pretreatment does not require drying heating and chemical treatment; Its dry ice is carbon dioxide, in the process of use will not produce secondary pollution (no "three wastes" pollution); And carbon dioxide from waste gas recycling, in energy conservation and environmental protection advantages are very obvious.

4.3 Low investment and low cost

Equipment one-time investment is low, infrastructure cost is almost zero; The integrated operating cost of the late production line is also greatly reduced.

5. Key points of dry ice technology planning and design

1) Air supply volume of the station room: according to the standard of dry ice consumption and carbon dioxide concentration, the recommended air supply volume is greater than or equal to 6000m3/h; At the same time, considering the dust removal and guidance of the cleaning station, so as not to cause secondary pollution after cleaning dust roundabout in the cleaning station, it is recommended that the wind speed of the section is greater than 0.8m/s;

2) Noise: The dry ice equipment will make noise during cleaning, which is about 110 decibels. This noise is always present when starting up. In addition, the ice maker has a purge action before starting up, and the noise during the purge is about 110-150 decibels, which is expected to take about 10 minutes. Noise problems can be made sound insulation treatment, a separate build a smaller soundproof room; It can also not be processed, because if the dry ice technology is used, the whole line can be basically automated, no manual operation state, and the impact will be reduced.

3) Equipment safety interlocking: Since robots are used for dry ice pretreatment, safety is very important, especially personal safety. The pre-planning scheme should reflect the safety interlock signal processing of dry ice equipment and peripheral equipment to meet the needs of production safety.