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Is Powder Coating for you?
The powder coating process is nearing a half century of use but retains some of its early image of mystery and technical discomfort among the metal fabrication industry. We are comfortable with cutting, forming, and welding, but painting and its attendant issues of chemistry, electrostatic fields, cure rates and the like become intellectual hurdles for us. Need not be. The fact is that powder coating is a mature process with the unknowns wrung out.
Additionally, integrating powder coating into your manufacturing base may:
• Be an excellent, low risk, cost reduction
• Improve apparent and real quality
• Reduce lead times and working capital
• Be a platform for increased sales
Powder Coating Process
Here are the key ingredients of a functioning powder system:
- Pretreatment Washer - Get the surface clean. Really clean. Parts are likely to have both organic (oil, forming waxes) and inorganic (rust, laser scale) contaminants on them. These need to be removed. Pretreatment washers are usually stainless steel enclosures through which parts pass on an overhead conveyor. 3 to 9 stages are most common. For most applications/parts a 5 stage washer is adequate. First, an alkaline cleaning stage (90-125 degrees F) followed by a city water rinse, then phosphate pretreatment or one of the new alternative non-phosphate pretreatments now available (90-125 degrees) and 2 final rinses takes care of the organics. The chemical suppliers can look at the inorganic contaminants and come up with specific solutions for them.
- Dry-Off Oven - Dry off the parts in a gas convection oven (capable of drying off complicated parts) at about 250-300 degrees F. 6-8 minutes is usually enough.
- Powder Booth - Apply the powder coating in a contained space with proper collection of over-spray. All powder booth manufacturers live by the NFPA guide lines for construction, so a modern booth will confidently contain the powder process. Depending on your part volume and number of colors, you may want to recover over-spray and recycle powder to the application guns.
- Cure Oven - Cure the parts for about 20-25 minutes at metal temperature of about 350- 400 degrees F. A gas fired oven is most common. It is easy to operate and able to cure complex shapes. Simple, basically 2 dimensional, parts can be cured with infrared heat (gas or electric) but the heat source does not do well on complex geometries.
- Conveyor – moving product through each of the steps is straight forward. Most powder systems use overhead monorail or power and free conveyor. The key questions are how heavy and long are the parts and how fast do they have to move to meet your output targets.
How Do I Choose The Right Equipment
- What are your quality goals? Surface quality and corrosion performance are the leading issues. The powder process is well known for quality surface appearance. No sags, uniform coating, limited or no “orange peel”. The surfaced will also be hard, scratch resistant and well attached to the substrate. Corrosion performance is another matter. Here you need to decide/forecast what environment your product will live in. Inside a building with no exposure to sunlight or corrosive elements? Maybe outside with full exposure to sunlight, salt spray and the like. Powder lines impart corrosion resistance through 2 basic processes. First, cleaning the parts and applying a barrier to corrosion we call a “conversion coating”. The conversion coating is a thin, amorphous or crystalline barrier. Second, applying the powder coating.
- How fast do you need to process parts? Now we need to crunch some numbers. The objective is to characterize the mix of products that will be processed. Today and into the realistic future. Length, width, height, weight. Once this information is collected, you or the equipment suppliers can look into how the parts can be racked to give good productivity and finish quality. It is important to keep the 80/20 rule in mind. Maybe 90/10. Don’t design a paint line around large, infrequently painted parts unless you have no alternative. Also, assume you will process parts for about 6.5 hours/shift. System part opening is next.
- What part opening or window will the system have? The part opening through which your product will move will drop out to the “how fast” study above. The bigger the part opening, the more parts get processed/foot/minute. A trade off. Line speed vs. part opening. Here it is important to remember that part length and line speed drive the foot print size of the system.
- What size powder booth is needed? Again, this drops out of the study done on line speed and part opening. Slower line speeds (about 6 fpm) can usually be serviced by 2 manual gun operators assuming the part opening is not too high. As line speed picks up to 8 fpm+, automatic guns will probably be needed. We normally have about 1 automatic gun/foot of part opening on both sides of the part opening + the 2 manual positions. When you use automatic guns, you will probably want to start recovering powder and recycling over-spray back to the automatics. Your powder booth supplier can help with this analysis.
- What foot print will be needed? Key drivers for foot print are line speed, product weight and product length. All the process steps are timed. Stage 1 of the pretreatment washer will usually take about 90 seconds to complete. 1.5 minutes times a typical line speed of 8 fpm yields a first stage length of 12’. Similarly, if it takes 25 minutes to cure your parts, it will take 8 fpm x 25 minutes or 200’ of conveyor in the cure oven. The faster the line speed, the larger the footprint. Also driving foot print are product length and weight. Longer parts require larger turn radii. Heavier parts may require more than 25 minutes to cure. Figure 3 offers up a curve that scopes the foot print required. If you have a tall building (25’+) it may be possible to stack the ovens and save some space.
- What’s this going to cost? Cost vary depending on your specific circumstances. Building interior obstructions, difficulty of installation, use of mild steel vs. stainless steel for washer sections, potential need for waste treatment equipment. The cost of the powder booth is not included in the curves. Booth costs range from $20,000 for a simple, all manual booth to $500,000 for a full up automatic booth with quick color change and many guns operating at fast line speed.
Additional Factors
- Permits – you will need to look into permits to install and operate a system. However, a powder system will not be a new adventure for your local or state permitting authority. Lots of people have gone through the process before you. It will probably take 3-6 months for approvals.
- Housekeeping – Most fabricators know that cleanliness and orderliness make them money. Same for powder coating. Keep the maintenance and materials flow disciplined and the paint line will be a source of pride to you and your staff.
- Training/labor – You will need one floor operator/leader that can track pretreatment chemistry and operating parameters. No chemistry degreed needed. The rest are normal, conscientious laborers.
- Financing – Working capital is always an important. Where do you place your money? Look at leasing the paint line. Many leasing companies are comfortable with powder systems. Leasing frees up money for other growth or cost reduction projects.
- What about used? Yes, a good used/reconditioned system will come in at about 60% of a new system. But it has to fit the description you came up with in your above evaluation.
How Can Slocum Equipment, Inc. Help?
Slocum Equipment, Inc. has over two decades of experience in providing new and used powder coating systems to companies providing industrial finishing services.
What differentiates SEI from the broad range of equipment dealers and on-line trading companies is our ability to deliver cutting edge powder coating solutions that focus on quality finish, production efficiencies and financial suitability.
The success of SEI is largely due to our experience in building powder coat systems for a broad range of clients. SEI has an extensive network of industry experts who play a major role in the design, installation and service of these systems.
Whether you are looking to build a Turnkey System for large production runs or building a Batch System to finish varying size parts, SEI has the knowledge and experience of powder coating systems that guarantees that you will get the right equipment at the right price!
Call us at: 888-310-2680 to review your powder coating needs or complete our System Design Requirements Form so we can help you find the best powder coating solution to meet your finishing requirements.
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