Powder Coating Clinic
We are trying to expand our business and are interested in getting involved with powder coating. What do we need to know to get started?
Q. I have a question about getting started in powder coating. My family has been in the steel construction business for the last 30 years. We are trying to expand our business and are interested in getting involved with powder coating. What do we need to know to get started? B.M.
A. Every powder coating process has the same four components. First you must clean the part. Second you may have to dry the part if your cleaning system uses liquid cleaning/pretreatment chemistries. Third you must spray the part with powder. Finally you must cure the part.
These are the four basic steps in the powder coating process. As product performance and customer requirements expand so must the powder process expand beyond these four simple steps. Higher corrosion standards require more involved pretreatment systems. Stringent appearance standards may require an environmental room for the powder booth. Higher production volumes normally require conveyance systems. And so forth. For now we will discuss only the four basic steps.
Cleaning the part. Cleaning the part is one of the most important steps in the process. Remember, a paint job is only as good as the surface that you apply the paint to. This saying goes for painting a house to powder coating productions parts.
Which type of cleaning system you need depends upon the types of soils you are looking to remove and the number of parts you must produce per unit time (i.e. parts per hour, day, month, year, etc.). Soils are categorized into two basic types: inorganic soils and organic soils. Inorganic soils are heat scale, welding smut and rust/oxidation. These soils can be removed by grit blasting, sanding/grinding, vibratory finishing, or chemical etching. Organic soils are oils, waxes, fingerprints and so forth and can be removed by grit blasting or cleaning chemicals.
Selecting the right cleaning system is relatively simple. If your parts are predominantly oily, select a chemical based system sized for your production rate and product size. For instance, spray wands are very good at cleaning large parts in small quantities. Immersion tanks are great for handling small- to medium-size parts in moderate quantities. In-line spray washers are designed to handle any size parts in high volume production systems.
Similarly, if your parts are predominantly rusty and have a lot of scale and welding smut, then select a cleaning system that can handle your production volume. For instance, grit blasting and sanding/grinding operations are very effective at cleaning larger parts in relatively smaller production volumes. While immersion and in-line washers can handle any size products in mid- to high-production volumes.
Drying the part. If you selected a chemical based cleaning system then you will have to dry the parts before powder coating them. This is normally done in a dry-off oven using heat, high air circulation and exhaust to evaporate the moisture. Most dry-off ovens use convection heat systems operating around 250°F at 10 min dwell time, depending upon the mass of the product. Entrapped moisture needs to be displaced using compressed air or high static pressure fans and ductwork, before the parts enter the oven to ensure complete drying of the parts. Any moisture left on the parts will evaporate in the elevated temperatures of the cure oven, causing the powder to be pushed from the affected area exposing the raw substrate. Therefore, all parts must be dry before powder coating.
Coating the part. Powder coatings are normally applied using spray apparatus, although some systems use fluidized beds. Spray guns come in a variety of types and configurations. They can be automatic or manual, corona-charging or tribo-charging guns. Which one you select depends upon what you are coating and how many parts you are coating per unit time. Typically, low volume production systems use manual guns and high production volume systems use automatic guns.
The parts must be coated in an approved spray booth to meet all local and national fire code and safety standards and regulations. Powder booths have several varieties as well. They can be cyclone, cartridge or hybrid style booths using a wide range of construction materials (painted steel, galvanized, stainless steel, plastic and sandwich). Booths can be configured to be walk-in batch booths or in-line conveyorized booths, depending upon production requirements. They can be designed to reclaim the over-sprayed powder or used as a spray-to-waste system.
Selecting the right gun and powder booth takes some effort and serious consideration. Since this explanation will take too much time now, I will save that discussion for another column.
Curing the part. After the part has been coated with powder, the coating must be melted, fused and cured onto the part. This is always accomplished using a heat source to start, although some powders can be cured using UV light after the coating has been melted using heat first.
Cure ovens can be designed to employ direct-fired or indirect-fired convection, infrared or ultraviolet energy sources. The most common cure ovens use direct-fired convection heat energy to cure the powder coating, followed by indirect-fired convection heat energy, IR and UV.
Cure ovens can be operated by electricity, natural gas, propane or heating oil. I have not seen any wood-burning, coal-burning or nuclear ovens in my 25 years in this industry, so we can pretty much rule those systems out for now.
Convection ovens typically run at 300–450°F air temperature, depending upon the type of powder coating that is used. IR systems usually operate at higher part surface temperatures, to reduce their length and improve efficiency, although they do not heat the air. UV systems are only used to cure UV-curable powders and do not generate any heat. This is why these UV systems require either convection or IR heat systems to melt the powder before the UV light is used to cure the coating.
Ovens can be configured as walk-in batch systems or in-line conveyor systems, as production needs require.
How to be successful. This part of your question is the most difficult one to answer. If I knew the secret to success, I would be retired by now living in Tahiti. But since I am still working, that pretty much tells you how much I know about finding success.
The best advice I can give you is this:
1. Find out what the market is for powder coating on your customer’s products or for powder coating services in your area.
2. Determine how much competition there is in this market.
3. Determine how much it will cost to buy a powder coating process, designed to meet your particular quality and production needs (capital costs).
4. Determine how much it will cost to use powder coating on your parts (opera- tional costs).
5. Can you make money by offering these services or powder coated products? If so, how much money can you make? (Profit)
6. What is the return on your investment or payback for this process? If the return on investment is less than you can make keeping your money in the bank, don’t do it! (Capital costs divided by profit potential)
There are several sources that you can tap into when you proceed with this endeavor. The Powder Coating Institute has a handbook and operational costing software that can make your investigation very simple (www.powdercoating.org). There are trade shows and conferences that offer technical workshops on these subjects. Finally, there are suppliers and consultants that can assist you in your efforts, as well (www.pfonline.com/suppliers). I recommend that you use all these resources before you spend your money on a new or used powder coating system. It can save you a lot of money in the long run.
Infrared cure is gaining increased attention from coaters as a result of shorter cure cycles and the possibility of smaller floor space requirements when compared to convection oven curing.
How can you calculate the cost of powder coating a component if you only know its surface area? Powder coating expert Rodger Talbert has the answer.
Question: What methods are available for removing cured powder coatings, and what are the pros and cons of these methods?