Plastic Sandwich Booths

Question:

I have worked on a powder coating line for 10 years. I am interested in reducing the color change times for our powder booths. Recently I heard about plastic sandwich booths. Please give me complete details of construction and basic design mechanism of these booths and how much it will cost. V. M.

Answer:

I have been looking for an excuse to talk about these plastic sandwich booths and "quick color change" systems for some time. Now I have one.

It has often been said that duplicate equipment shortens the time it takes to perform a color change in powder coating. Extra booths, collectors, hoppers, guns, and so on all dramatically shorten the time it takes to change color. Nothing is faster than having a second powder booth and recovery (including guns) ready to go online for color change, but many people do not have the room or the capital to purchase two powder booths. This is especially true when you want to spray and reuse many colors.

The plastic sandwich powder booth was designed as part of an overall system to reduce color change time using the same booth. The booth is constructed of a smooth white plastic corrugated "sandwich" that provides both strength and reflected light for a bright interior. This design inherently attracts less overspray powder since it is nonconductive. The smooth surface makes it very easy to clean using squeegees and compressed air guns. The plastic walls are scratch resistant and very durable. They can be made strong enough to support in-booth sprayers, if necessary. Often the booths are designed with hinged doors on the touch-up openings and at least one part opening. These doors are closed during cleaning operations to contain the powder displaced by blow-off guns.

The most important part of these fast color change systems is the powder feed and recovery system. How effective a particular system is on providing quick color change is based solely on whether the feed and recovery system is easy to clean. Guns are often mounted on retractable mounts that withdraw the guns from the booth while they are automatically cleaned with compressed air. The powder is pumped to the guns from a feed center that is designed to automatically purge the feed hoses and clean the pumps and pick-up tubes during color change. The hopper or powder box can then be changed for the new color.

The reclaim system uses cyclone technology to separate the powder coating from the containment airstream. These cyclones are often "break-apart" construction or have clean-out doors to aid in cleaning operations. An in-line sieve (typically vibratory type for quick cleaning) can be located under the cyclone or in the feed center. Powder is transferred to the feed center from the cyclone using standard powder pumps or dense phase pumps.

A cartridge collector is used as a final filtration device to ensure that the air is fit to be returned to the plant airstream. This device is not cleaned for color change purposes. Therefore, the powder collected here is scrapped, making cyclone efficiency in these systems very important.

These systems typically cost more than standard cartridge booth systems. However, if you buy a lot of cartridge modules for color change or another cartridge booth, a quick color change system that employs a plastic sandwich booth may be your best "low-cost" option. These systems are available from just about every powder application and recovery booth company. For a complete list refer to www.pfonline.com/suppliers.html.

Now we should take some time to discuss the value of recycling powder coatings versus the cost of purchasing a quick color change system. Before you can evaluate any color change system you first must put a value on the amount of reclaim you will generate. For instance, if you spray 100 lbs of powder per hour at 80% first pass transfer efficiency, then you will generate 20 lbs of reclaim per hour. If your powder coating costs $2.00 per pound, then you can save $40.00 per hour reclaiming your overspray powder. Obviously, your transfer efficiency, spray rate and your powder coating costs will affect this calculation one way or the other. However, powder costs are falling, making the value of reclaim less attractive. The next area of color change economics is determining how much labor time it takes to perform a color change. A cartridge booth system may take 30 minutes or more to perform a color change, depending upon how many guns are spraying and how long they were spraying. The same configuration of "quick color change" system may take 10 minutes or less. Depending upon your labor rate, this cost savings can be significant. Before purchasing any powder coating system, you should evaluate the cost of your reclaim and the cost to perform the color change. Take note that different system designs will provide different costs/savings. Lastly, compare any operational savings to the capital cost of the equipment to be purchased to determine the return on investment or payback. The answer for you will become clear.