Powder coating has lately emerged as one of the most efficient and highly valued means of achieving high quality surface finish for the metals. It has replaced liquid painting and various other methods like electroplating etc. While planning a powder coating system and installing the plant, the most convenient and highly desirable option is to get an ecologically acceptable and an extensively automated coating process. The choice of system - technology depends on a lot of factors. One of the most important of those being the object itself that needs to be coated. Other constraints may include space availability, material of the object, availability of technology, availability of expertise in the field etc. These are a few parameters, which define the choice among the various system concepts, system designs, plant layouts, booth designs and loading & unloading methods. In addition, the standards of automation must be defined specifically.
First and foremost the main parameters, which would influence the concept, design and layout of the system, need to be defined,. These are:
1. By object -
- The quantity of the material that is to be coated. This would define the technology to be used in the coating plant as well as the material used for cleaning and coating purpose.
- The geometry of the components. This information makes it easier to plan out the locations of loading, unloading, movement and coating position.
- The thickness of the coat that is required on the components.
- The quality of the coat that is required to be done
2. By System Technology-
- The conveyor system for efficient movement of the material.
- The construction of the hangers/hoist system
- The pretreatment technique that shall be used. This depends on the basic physical and chemical structure and properties of the material, of which the components to be coated, are made.
The chain conveyor serves the transportation of the work - components and thus becomes an important feature in the automation of the coating process. Depending on requirements, single leg or circular leg conveyors are installed. For an easy conveyance system a hanger construction suitable for the respective production is needed. Apart from the technological factors, the building circumstances are another important factor which, if not considered while planning and designing the layout of the plant, can bring all plans to a stop. This factor or parameters can be defined in the following manner -
- Space availability (if the minimum required are is available or not)
- Ground conditions and specifications
- Other factors (air currents etc.)
The ground must be electro-statically conductive and, no air turbulences or solvent vapors should exist in the surroundings of the planned location of the booth, as it might influence the quality of the coating. High room temperatures should also be avoided.
CONCEPTUAL POWDER COATING SYSTEM
Powder coating is a simple process which requires minimum skills as it is a fully automated system and human hands do not touch the components during the whole process. The components to be coated are initially cleaned of all the dust and foreign impurities on the surface. This is known as pretreatment. It is employed for improved bonding of the powder coat to the material being coated to provide a longer life to the coat. The method employed is a basically a dip in water and chemicals in various tanks. The pretreated components are jigged and hung into the coating booth on a fixed or rotatable hanger. The components are coated from all sides while being rotated. The components are then moved out directly into the oven. Oven trolleys might be used to facilitate the process. The trolley, if used, is rolled into the oven when full. In the oven, the powder melts at a temperature of 180° to 220°C, in 10-15 minutes, polymerizes, fuses and cures into the final, uniform and consistent powder coat that is high in aesthetic value. It is a permanent solution as compared to the normal painting procedure. At the end of the curing process, the product is brought out of the oven and allowed to cool down. The products are then removed from the paint - shop. Following is a step wise procedure and the sequence of activities that happen during the powder coating process –
Step 1 – The Components to be coated are loaded into the system after being thoroughly inspected.
Step 2 – The component enters the pre treatment plant and is first cleaned by rinsing with plain water.
Step 3 – The components are then cleaned further by recycled reverse osmosis water and then pure reverse osmosis water.
Step 4 – The cleaned components are treated with titanium and once again cleaned with pure reverse osmosis water.
Step 5 – After removing the water droplets the components are put into the drying oven for a complete dry off before it exits the pre treatment chamber.
Step 6 – The pre treated product is then unloaded from the pre treatment chamber and loaded into the powder coating booth. It coats the product using an automated spray technique from all sides.
Step 7 – In the final step the product is put into a curing oven, where the powder coat polymerizes and gives an even coat to the product.
The powder coating plant proposed here shall coat the sheet metal with the following specifications –
- Area Required – 20m L x 7m W x 5.5m H approx. for powder coating booth.
16m L x 4.5m W x 5.5m H approx. for pre treatment unit.
- Pre-treatment tanks – 7 nos. (size – 3m L x 1.5m W x 1.85m H)
- Electrical hoist of 1 ton capacity for material handling during pre treatment
- 1 powder coating booth of back to back type with size 3m L x 1.85m W x 2m H
- Powder spraying equipments – 2 nos.
- Powder curing oven of elevated type – 1 no. having size 4.5m L x 4.3m W x 2m H
- Over head conveyor – 4 wheel type – heavy duty with length 47.5m approx.
- Tentative conveyor speed to be 0.3 m/ minute
- Component type (object) – sheet metal heavy components for making electric control panels etc., with the maximum size of 2500 mm L x 1000 mm W x 1000 mm H
Following are the electrical Specifications for the system:
Paint Booth Cabin - Input Voltage: 200 - 230 Volts, 60HzPower Consumption : 35VA.Maximum Electrostatic Voltage: 85KV. Maximum Electrostatic Current: 50 uA.
Curing Oven – For baking temperature 250°, power required is 1 kW. 220V, 50Hz.
CONVEYORISED POWDER COATING PLANT WITH PRE TREATMENT UNIT
SOURCES
Powder coating systems – concept and layout. ITW Gema.
<http://www.itwfinishing.com.au/docs/document_4416073b5a6fe.pdf>
ADARSH™, Powder coating equipments. Thakur Dharma Chand & Sons (ISO 9001:2008 certified company). <http://www.adarshindia.com/powder_coating_plants_and_equipments.htm>
The Powder Coating Plant Process. Redline Industries limited.
< http://www.redlineltd.com/pdf/The%20Powder%20Coating%20Plant%20Process.pdf>
Powder Coating Technical Data. Digger Specialties Inc.
< http://www.sharonfence.com/pdf/regis-pc-sheet.pdf>
