Issue link: https://www.e-digitaleditions.com/i/954267
In my early days in the porcelain busi- ness, we used Nichrome steel rod for hangers that were subjected to more than 1,600°F. But that's expensive and probably cost prohibitive. Design a fix- ture that meets the standards of your principle hangers. Make the hangers from 3/8- or 1/2-inch rod stock, and go from there. Occasionally have a person test-fit a representative quantity of the racks to the fixture. You should be able to get a year or so of service before need- ing to replace a hanger. My qualifier here is that I have no idea what your racks look like or what types of parts you hang on them. —G.T. Repairing chips and scratches on oil-rubbed bronze powder- coated aluminum Q Is there any special paint I can u s e t o r e p a i r c h i p s a n d s c r a t c h e s o n o i l - r u b b e d bronze powder-coated aluminum in the field? R.B., Addison, Ill. A Touch-up coatings are avail- able for most powder coatings. These come in a variety of types (spray cans, liquid pens, small bot- tles with brushes, etc.). Selecting which touch-up device depends upon the amount of repair that is necessary. For instance, very small chips can be touched up by using the pens or small bottle/brushes, while larger areas re- quire spray cans. Having said all that, touch-up on rubbed bronze may be very difficult, de- pending upon how the look was first created. If it's a single-coat process, then any touch-up paint provided by the supplier will work. However, if it's a multi-step process, using a combination of plating or a different base and top- coats, performing touch-up will be near to impossible without having a notice- able repaired area. —N.L. Building a cooldown tunnel Q We run parts that are up to 1/2 inch in material thickness along with some solid cast- ings. We have about 120 feet of con- veyor from our cure oven to the washer that are available for loading and un- loading. This space does not allow enough cooldown time for safe han- dling. Has anyone built a cooling cham- ber that would be effective in bringing the temperature down on my parts? L.H., Carrington, N.Dak. A Actually, if your maintenance guys are pretty good, they can b u i l d y o u o n e . U s u a l l y , cooldown chambers are placed in a des- ignated enclosed area after the oven. They're similar to the oven with an ex- haust and a supply fan at a minimum. You may need auxiliary fans to move the air across the parts. The supply air should be filtered. You won't affect the air balance in the plant if you build a chamber specifically for cooldown. Considering where you are most of the time, the ambient air could be suffi- cient. Cooling 1/2-inch-thick material, however, depending on the conveyor speed, could require some time, which might eat into the unload area. I am aware of some very heavy steel products that are processed in what is considered a warm climate, using this method. A lot of fresh air is introduced across the parts, and they're warm at the unload station, but not too warm to cause a problem. Of course, if you have money, you can get a chilled air-cooling tunnel, but I assure you this will cost both in capital and in operating expen- ditures. It will take up a fair amount of space as well. —G.T. Burning off powder coatings from steel or aluminum parts Q Our powder coater has been having problems powder coating our parts and has been burning off the powder coating sometimes more than once for the same part. Our parts are chair frames and are made out of 1-inch, 14-gauge carbon steel tubing. Some of the parts on the chairs are cast aluminum unions that fit into the tubing. What is the process and temperatures of burn off? How do burn off and temperatures af- fect the metal and aluminum? D.J., White Bear Lake, Minn. A The metal is heated between 800°F to 1,000°F during the burn-off process. Normally, this temperature won't affect steel or aluminum, providing it's not heat- treated or tempered. If for instance you're using a tempered aluminum (6061 T6, with the T6 standing for the temper) the burn-off process will anneal (soften) the aluminum. However, if you're using mil-grade materials, not tempered aluminum or heat-treated steels, then you should be fine. Never burn-off powder from magnesium as a tremendous fire will occur. —N.L. Saving space in a powder coating system Q We're trying to save space a n d s h o r t e n c y c l e t i m e through our powder coating system. We're considering cutting out some of the conveyer between the dry- off oven and the coating booth. Right now, it's 225 feet at 15 feet per minute from a 360°F dry-off. The parts cur- rently go into the booth at no more than 165°F. How hot can the parts be before we encounter a problem? J.L., Crawfordsville, Ind. A By now you may have found out that parts going into the powder booth at 165°F are too hot. You lose film control because the heat attracts the powder particles, and different thermal conditions along the part attract different amounts of pow- der. Thus, you may have 3 mils in a broad area and 5 mils in a corner that tends to be hotter. You'll also see web- bing of the powder, which will give you a poor part appearance. And, depend- ing on the gel temperature of the pow- der you're using, you could see powder beginning to gel prematurely. Bad idea. What you need is a cooling area. The conveyor area between the dryoff stage and the powder spray booth should be sufficient for a cooling tunnel. This doesn't need to be forced chilled air. It can be outside air blowing across the parts, then exiting the plant. This should be sufficient, depending on the metal thickness. Be sure to filter this air because these are good clean parts. And exhausting the cooling tunnel air will maintain the air balance in the plant. —G.T. 38 POWDER COATING, March 2018