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5 Ways to Control VOCs in the Home Appliance and Hardware Industry!

Time：

2024-09-24

The Ecological Environment Bureau of Foshan City has released the "Clean Production Guidelines for Metal Coating Enterprises in Foshan City (VOCs Special)", proposing clean production methods for reducing VOCs in the coating process of home appliances and hardware industry, including green product design, improvement of raw and auxiliary materials, improvement of production processes and equipment, cleaning of production environment, and strengthening VOCs governance.

To reduce the generation and emissions of VOCs and fight the battle to protect the blue sky. The Ecological Environment Bureau of Foshan City has organized the compilation of the "Clean Production Guidelines for Metal Coating Enterprises in Foshan City (VOCs Special)", which analyzes the basic situation of metal coating in Foshan and proposes clean production methods to reduce VOCs in metal coating production based on the characteristics of Foshan enterprise production.

In this issue, we will take you to learn about the painting process in the home appliance and hardware industry, as well as how companies can reduce the generation and emissions of VOCs in various production processes.

Home appliance hardware industry

Household appliances use plastic and hardware (steel, copper, aluminum, aluminum alloys, etc.) as the main raw materials, and the production and coating process will generate a certain amount of VOCs.

Production process

01. Paint spraying process

Paint spraying includes oil-based paint spraying and water-based paint spraying, and VOCs are released during the spraying, leveling, and drying processes.

02. Powder spraying process

In the coating of home appliance hardware, powder coating products have better quality than paint coating. The processing cost of powder coating is also higher than that of paint coating. The exhaust gas generated in the powder spraying process is mainly particulate matter, and there is a small amount of VOCs in the solidification process.

03. Insulation paint coating process

In motor production, insulation paint seals the surface of the stator or rotor to achieve insulation. There are two methods for sealing the surface of stator or rotor with insulating paint: paint soaking process and paint dripping process. In the insulation paint soaking process, the VOCs emissions from the two processes of paint soaking and drying are relatively high.

At present, the insulation paint immersion process is commonly used in the sealing of stator or rotor insulation paint. Another part is the use of insulation paint dripping process.

In the insulation paint dripping process, insulation paint is dripped onto the surface of the stator or rotor by a dripping machine, and fully covers the surface of the stator or rotor.

In the process of dripping paint, the processes that generate and emit a large amount of VOCs are insulation paint dripping and drying. Comparing the two painting processes, the drip painting process produces less VOCs and emits less than the immersion painting process.

Raw and auxiliary materials

01. Raw and auxiliary materials for paint spraying

The types of paint spraying used for home appliance hardware include water-based paint, oil-based paint, water-based fluorocarbon paint, oil-based fluorocarbon paint, and silicone paint.

Oil paints have a high VOC content. In oil-based paints, there are also significant differences in VOCs content. For example, oil-based paints used for fans have the highest VOCs content, while oil-based paints used for other products have lower VOCs content.

During paint spraying, the generation and emission of VOCs not only come from the composition of the paint, but also from auxiliary materials such as solvents and curing agents.

Using different paints requires the use of different solvents. The VOCs content varies greatly among different solvents. When using raw materials from different manufacturers, the solvents used are also different, and the amount of VOCs contained is also different.

In raw materials with high VOC content, the production of VOCs is not only related to the content of organic volatiles, but also to the boiling point of organic volatiles. Organic compounds with high boiling points evaporate less at low temperatures, while organic compounds with low boiling points evaporate more under the same conditions.

02. Powder coating raw materials

The raw material for powder coating is powder coating. Powder is a solid with a content of 100% and does not contain VOCs. No solvents or curing agents need to be added during use. Due to the powder spraying process, particles are generated, and a small amount of organic matter or odor is released during solidification due to high temperature.

03. Insulation paint

Insulation paint is the raw material for coating the stator and rotor of a motor. Insulation paint is an insulation protective material used to form a high impedance insulation layer between the iron core and coil of a motor, in order to prevent current leakage and ensure the normal operation of the motor.

VOCs control status

01. Waterborne paint spraying and powder spraying

Waste gas treatment

From the composition of water-based paint, powder coating, and auxiliary materials, it can be seen that the amount of VOCs generated by the use of water-based paint and powder spraying processes is relatively small. At the same time, most of them use automated spraying production lines, which can achieve fully enclosed collection.

The temperature of the exhaust gas collected during painting and powder spraying is relatively low, so there is no need to cool it down. But the exhaust gas contains a lot of particulate matter or paint mist, and it needs to be sprayed with water to remove the particulate matter and paint mist. After water spraying, dehydration or drying treatment should be carried out, and finally treated by adsorption with secondary activated carbon or multi-stage activated carbon.

The exhaust gas generated during drying or solidification has a high temperature and contains a small amount of particulate matter and VOCs. When the temperature of the drying exhaust gas and solidification exhaust gas is greater than or equal to 40 ℃, it must be cooled down. Water spray can be used to cool down while removing some particulate matter or VOCs. After being sprayed with water, the exhaust gas needs to be dehydrated or dried, and finally treated with activated carbon adsorption. When using activated carbon adsorption treatment for exhaust gas, attention should be paid to the type and filling amount of activated carbon, and timely replacement of activated carbon to ensure the treatment effect.

02. Oil paint spraying exhaust gas treatment

When spraying oil-based paint on household appliance hardware, a continuous automatic spray painting production line is often used. The exhaust gas generated by oil-based paint spraying is also divided into spray painting exhaust gas and drying exhaust gas. The temperature difference between spray painting exhaust gas and drying exhaust gas is significant, and they need to be pretreated separately.

Oil paint contains a large amount of VOCs, and the pre treated exhaust gas should not be adsorbed by activated carbon. The process of combining zeolite molecular sieve adsorption with catalytic combustion/thermal storage combustion is better.

03. Spraying of Fluorocarbon Paint and Organosilicon Paint

Waste gas treatment

Fluorocarbon paint and silicone paint produce low temperature paint exhaust gas during spraying, mostly at room temperature, with the main pollutants being particulate matter or paint mist. The concentration of pollutants varies greatly depending on the product and process. The pre-treatment of paint exhaust gas includes water spraying and dehydration or drying. In practical work, pre treated spray paint exhaust gas can be treated with zeolite molecular sieve adsorption+catalytic combustion treatment or thermal storage combustion treatment, as well as secondary or multi-stage activated carbon adsorption treatment. The key is to observe the concentration of VOCs in the pre treated paint exhaust gas.

The temperature of the drying exhaust gas is high and needs to be cooled down. It can be cooled by spraying water. The exhaust gas after water spraying needs to be dehydrated. After pre-treatment, the dried exhaust gas can be treated with activated carbon adsorption, zeolite molecular sieve adsorption+catalytic combustion treatment, or thermal storage combustion treatment according to the actual situation of the enterprise.

04. Exhaust gas treatment for insulation paint coating

When insulating paint is applied to the stator or rotor of a motor, the following situations may occur:

① When using water-based insulation paint, whether it is soaking or dripping process, if the concentration of VOCs in the pre treated exhaust gas is low, activated carbon secondary or multi-stage adsorption treatment can be used; When the concentration of VOCs in the pre treated exhaust gas is high, zeolite molecular sieve adsorption+catalytic combustion treatment or thermal storage combustion treatment should be used. It should be noted that the temperature of the exhaust gas entering the activated carbon adsorption layer should be below 40 ℃. When the exhaust gas temperature is too high, it cannot directly enter the activated carbon adsorption layer and the temperature must be lowered.

② When using oil-based insulation paint, especially with immersion process, the concentration of VOCs in exhaust gas is relatively high. Therefore, zeolite molecular sieve adsorption+catalytic combustion or thermal storage combustion treatment process should be applied.

05. Other waste gas treatment

When manually painting or powder coating household appliance hardware, the difficulty of collecting exhaust gas increases, and at the same time, the concentration of VOCs in the collected exhaust gas is relatively low. In this case, it is necessary to strengthen the collection of exhaust gas.

Clean production methods for household appliance coating

1、 Green Product Design

01. Replace metal with plastic

With the improvement of the quality of engineering plastics and the decrease in product prices, there are various processing methods available, and some plastics can be reused, which increases the possibility of using plastics instead of metals as raw materials for home appliance hardware. In the process of replacing metal with plastic, the use of plastic masterbatch eliminates the need for coating or coloring of processed plastic parts, significantly reducing VOC emissions.

02. Replace with other materials

Using materials such as stainless steel, alumina, or ceramics instead of metals to prepare household appliance accessories can eliminate or eliminate the process of surface coating, reducing the consumption of VOCs containing raw materials in the production process.

03. Surface treatment using electrochemical methods

Using electrochemical methods for surface treatment of household appliance hardware and changing the coating method is also aimed at reducing the use and emissions of VOCs through product design.

04. Stick with plastic or paper

With the development of adhesive technology, for some home appliance hardware parts with low coating quality requirements, plastic film or paper with printed graphics can be used to stick on the surface of the home appliance hardware parts, replacing the coating process.

05. Replace oil-based paint spraying products with powder spraying products

Replacing oil-based paint spraying products with powder spraying products has significant benefits in reducing VOCs emissions. In practical work, factors such as production equipment, production processes, and costs need to be considered. If the cost requirements can be met and the equipment and process are feasible, powder coating products should be used instead of oil-based paint coating products.

2、 Improvement and selection of raw and auxiliary materials

01. Replace oil-based paint with water-based paint

Replacing oil-based paint with water-based paint can not only reduce the VOCs content in the paint, but also decrease the amount of VOCs generated by solvents and related additives. The biggest difference between oil-based paint and water-based paint is in the solvent. Water based paint uses water as the solvent, while oil-based paint uses organic compounds as the solvent. There is a significant difference in the VOCs content between water and organic matter. Water based paint should be given priority when meeting product performance requirements.

02. Use raw materials containing organic compounds with high boiling points

In oil-based paint spraying, various raw materials containing organic substances may be used, such as oil-based paint, solvents, etc. The use of raw materials containing high boiling point organic compounds will be beneficial in reducing the generation and emissions of VOCs, especially during low-temperature curing and drying.

3、 Improve production processes and equipment

01. Low consumption process research and development

Low consumption process refers to a process that consumes less raw and auxiliary materials in production. The main directions of research and development are:

① Minimize the thickness of the sprayed film as much as possible while ensuring product performance. Reducing the thickness of the sprayed film is to reduce the consumption of raw and auxiliary materials, which is beneficial for reducing the generation and emission of VOCs.

② Reduce the rework rate of spraying and baking, and improve the one-time success rate of the spraying process. Reducing the amount of rework will decrease the consumption of raw materials and also reduce the emissions and production of VOCs.

③ Reasonably set process parameters based on workpiece size and coating requirements, including spraying distance, nozzle type, spraying speed, coating flow rate, nozzle angle, etc.

④ According to the product situation, a combination of automatic spraying and manual spraying will be adopted.

02. Improve the automation level of spray painting or powder coating

Manual painting or powder spraying can increase raw material consumption and easily generate unorganized emissions of VOCs. For products that are not suitable for using automated spray painting or powder coating production lines, mechanical arms can be used to operate and build easily adjustable and adaptable intermittent production automated spray painting or powder coating sections, improving production efficiency and reducing VOC emissions.

03. Determine and control the production parameters for spraying well

Due to the small size and thin coating of household appliance hardware components. The process parameters of spraying and the control of process parameters directly affect the spraying quality of household appliance hardware. It is necessary to carefully determine the process parameters and strictly control them, otherwise, it will not only affect product quality and production efficiency, increase VOCs emissions, but also lead to an increase in production costs.

4、 Clean production environment

01. Improve the automation level of weighing, batching, and conveying of raw and auxiliary materials

Improving the automation level of raw and auxiliary material weighing, batching, and transportation can reduce human errors, improve weighing accuracy, reduce unorganized emissions during batching and transportation processes, and help reduce the generation and emission of VOCs, thereby improving production efficiency.

02. Improve the sealing of automated spraying production lines

Improving the airtightness of automated spraying production lines can reduce the unorganized emissions of VOCs, which is beneficial for the treatment of exhaust gases. The automated production line that has been in production for many years needs to be repaired, well maintained, and loopholes plugged. If necessary, modifications should be made to further improve the airtightness of the production line.

03. Optimize the storage environment for raw and auxiliary materials

The room for storing household appliance hardware containing VOCs coating raw and auxiliary materials must be fully enclosed, and the temperature of the warehouse must be strictly controlled. The storage environment of some raw and auxiliary materials, such as solvents used in oil-based paints, especially solvents with high VOC content, high concentration, or low boiling point, should be well controlled.

5、 Strengthen VOCs management

01. Strengthen the management of activated carbon usage

In the coating production of home appliance hardware, a part is treated with activated carbon adsorption technology. The effectiveness of activated carbon adsorption treatment process is closely related to the management of activated carbon. Activated carbon management includes the selection of activated carbon, replacement of activated carbon, and control of moisture content and temperature before entering activated carbon adsorption. At present, the management of activated carbon mainly relies on manual labor. Therefore, it is necessary to strengthen the training and management of employees.

02. Collect and pre treat exhaust gas effectively

In the painting of home appliance hardware, there are significant differences in the properties of exhaust gases generated in each process. In order to improve the effectiveness of waste gas treatment and reduce the cost of waste gas treatment, it is necessary to do a good job in the quality collection and pretreatment of waste gas. The pre treated exhaust gas can be combined and treated uniformly.

03. Recovery and utilization of thermal energy

When using catalytic combustion/regenerative combustion exhaust gas treatment processes, the heat generated during combustion is an energy source. When designing exhaust gas treatment processes, it is necessary to consider the recovery and utilization of combustion heat. The recycling and utilization of combustion heat can not only improve the environment, but also reduce production costs and enhance the economic benefits of enterprises.

Classic case

The case enterprise belongs to the production enterprise of small or micro motors, and the small or micro motors produced are matched with well-known domestic and international home appliance production enterprises.

In the production of stator immersion paint, 17 production lines of the enterprise have switched to using water-based insulation paint, leaving only one production line using oil-based insulation paint.

After water-based paint replaced oil-based paint, the amount of VOCs brought in by raw materials decreased by 80.52%, and the effect was significant.

The motor manufacturing enterprise should control the production environment from the following aspects:

① The enterprise has an independent paint storage area, where unused and unused paint is stored in a sealed manner.

② The enterprise has a paint mixing room, which is fully enclosed and equipped with a waste gas collection and treatment system, connected to environmental protection treatment facilities. The waste gas from the paint mixing room is treated by environmental protection equipment, and after the paint is mixed, it is transported to each dipping production line through a centralized paint supply system and a sealed pipeline.

③ The material feeding and unloading on the dipping line are open, and the feeding port is kept in a negative pressure state. The dipping, dripping, and drying processes are fully enclosed and automated continuous operations. Dripping paint flows back to the immersion tank through the collection channel, and the exhaust gas is discharged to the VOCs exhaust gas collection and treatment system.

④ Hazardous waste containing VOCs, such as waste paint buckets and cleaning cloths, should be classified and placed in labeled containers, kept sealed, and promptly transported and disposed of.

The enterprise optimizes the exhaust gas treatment process, and after pre-treatment, the exhaust gas is treated using a zeolite concentration drum+RTO treatment process.

Before the implementation of this plan, the efficiency of exhaust gas treatment was 70%; After the implementation of the plan, the efficiency of exhaust gas treatment has increased to 95%. The implementation of this plan has increased the efficiency of exhaust gas treatment by 25%.