Process Flow Diagram
The first process is the Preparation process. In this process, the vehicle is driven into the spray booths. The vehicle is then sanded over the entire body surface so as to ensure that all the irregularities are removed and to also remove all uneven surfaces on the vehicle’s body so as to ensure that as the vehicle is being sprayed with a new coat of paint, it spreads evenly over the entire surface of the vehicle. This also done so as to ensure that adhesion of the coat of paint of the vehicle surface is improved so that a good finishing paint coat is done on the surface of the vehicle which is durable and has superior surface finish.
Secondly, the air spray guns are prepared. This is done by pressurizing the paint in the hoses. This paint, is pushed at the nozzle throat where it is pressurized to an air pressure of about 30 to 90 pounds per square inch. This is done to ensure that the paint comes out as a spray at the nozzle. The spray in this form ensures that minimal paint is used and also a good surface finish is done on the vehicle. Minimal paint usage also means reduction in paint emissions to the atmosphere and thus pollution is also reduced.
In the spraying process, an electrostatic spraying mechanism is utilised. After the paint is pressurized to about 30-90 psi, it is converted into a spray at the nozzles these paint particles are charged electrostatically as these particles come out through the nozzle opening the body surface also acquires an opposite charge to these particles by induction. Borrowing from the principle of charges that unlike charges attract, these particles fall on the vehicle’s body resulting in a good and permanent spray finish.
The other process is the face. Face is the area through which the intake airflows in the spray painting booths. In the booth, there exists a painting cycle. To aid this, the booth is equipped with supply air fans and exhaust air fans. The supply air fans, move air from outside the shop through a heat exchanger and then through a system of filters and then into the spraying
Booths. The exhaust air fans on the other hand, exhaust air moves through filters and then out of the booths (Heitbrink, 1995). This ensures that air emissions are reduced and also that the health of the personnel working in the booth is well taken care of. In this case there are many types of face locations depending on type of booth. Several designs may be adopted that is Cross draft spray booths, Downdraft spray booths, Semi-Downdraft booths.
In the case of my design I adopt a cross draft spray booth. This because they provide a clean working environment and efficiently remove over sprays from the booth. In this method, air enters through filters at the front of booth and exhausted through filters at the back of the booth (Heitbrink). It blows horizontally over the vehicle to be painted. Exhaust filters efficiently remove and collect paint particles as they are exhausted up through the exhaust stack.
Also a good Stack Designs was adopted for the spray booths. These stacks offer rain protection without obstructing air flow this is in line with maintaining air quality emissions regulatory compliance for the facility. Spray particles emissions in the spray booth should flow through this stacks. Since some of the emissions may react with atmospheric moisture and lead to the production of acidic rainfall such as Sulphur dioxide and Nitrogen dioxide.
The last process is the Drying process. In this case, the facility uses heaters to speed up the rate of drying of the paint coating on the vehicle this is in line with Texas Regulations that the process of drying the paint on vehicles should be accelerated so as to minimise emissions into the environment and in the long run protect it. After this the vehicle is driven out of the booth. The booth is then given a wash-down so as to remove any excessive paint that may have remained after the completion of the painting process.
REFERENCES
– Texas Administrative Code on Environmental Quality, Texas Commission on Environmental Quality.(TCEQ)
– The Michigan Department of Environmental Quality (MDEQ) report on VOC and ES emissions
– TCEQ Regulatory Guidance – surface coating facilities – February 2011.
– Guidance on Emission to Atmosphere Guidance note of 2004.
