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Powder Coating A Roaster

by | Mar 29, 2012 | 0 comments

Our latest build is taking shape and the welding is almost done.  The next step would be to send the machines off for powder coating.  My powder coater has really been a great help in the builds so far and he takes great pride in the machines.  But before I can deliver the 3 frames, 16 doors and hundreds of internal components to him, we first have to decide on the colour schemes!

To find out what colours we should paint the roasters, I set off to first find out how powder coatings are made.  I went to our country’s 3 largest manufacturers, one of which is the world’s largest manufacturer of powdered coatings, Interpon.  After meeting with all the engineers, I was taken through both the highly secretive production facilities and even had a look at the laboratories where the powder is measured for break strength, thickness and colour.  I even had a chance to look at their spectrometers to see how they measure the exact colour of the powders.  With these, they can also match any colour of an item sent to them by customers.

But the real treat was in seeing how the powder is made!  Unfortunately, no photos allowed.  The powder starts out as a series of secret dry ingredients that are all put into giant hoppers.  This dry substance is then sent to an extruder: a type of giant, long, continuous mixer where the ingredients are mixed and heated at the same time.  The resin component of the mixture melts in the extruder, and a continuous stream of molten paint oozes out the other end.  After extrusion, the paint is spread out on a conveyor belt with huge rollers.  The conveyor belt is cooled with water from underneath, although no water is added to the paint mixture itself.  After a few meters on the belt, the resin returns to a solid state and the whole slab of rolled-out paint is sent through a second roller that breaks it up into manageable little chunks.  Air is then used to transport the flakes to an enormous grinder, where the flakes are reduced to very specific particle sizes; each colour has its own optimum particle size.  In fact, the grinders work on exactly the same principle as coffee grinders, and they even use normal coffee grinders in the lab to grind up small quantities of sampled paints.

After all that processing, this is the end result:

To apply the powder, an electrically charged spray gun is used.  The roaster frames and other components are all suspended by wire hooks from giant rails.  The charged paint particles stick to the electrically grounded parts when sprayed.  Due to the nature of the electric charge, it is possible to get a very uniform layer of powder.  After spraying, the parts go into industrial ovens that use gas burners similar to those used in fluid bed roasters to bake the paint on at 200 degrees Celsius for about 20 minutes.  The paint then returns to almost the same state as when it exited the extruder and coats the parts uniformly.  After cooling, the paint hardens and creates a very durable coating that is much more scratch-resistant than wet-spray paints.  Thanks to international standards, we can also now use RAL colour charts to paint our frames exactly the same colour anywhere in the world.

But powder coating can also be tricky.  Lighter colours tend to darken or “brown” when subjected to heat.  In other words, white colours and coffee roasters don’t mix.  But Diedrich and Giesen have both used white in their colour schemes, so I am sure there has to be a way.  To find out, I commissioned 2 tests at both laboratories where a piece of steel similar to what our roasters are made of will be powder coated with a white paint.  The parts will then be subjected to 200 hours of continuous heat at 80 degrees Celsius in small specialized ovens.  After the test, we will examine the panels on the spectrometer to find out if any permanent discolouring occurred.  These tests should help us find out what paints we can apply, and where on the roasters they can be applied as some parts get hotter than others.

I will check back in 7 days to do a report on our findings.

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