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030 Wet blasting powder coated parts

From One Extreme to the Other

Let's see what happens when you use different media on a powder coated surface

The great thing about the Dana-Ridge wetblast machines is the amazing versatility and range of applications. The biggest determining factor when blasting is the media choice followed by the blast pressure.

The experiment

We took a piece of square hollow section steel with black powder coating and divided it into sections.We then used a COMET wetblast machine to blast the powder coat off and timed the process 

The test piece

A piece of steel square bar coated with black powder coat and sectioned off into 105x42mm rectangles

The machine

 This test was done in a 42 year old COMET machine with a 1.5kW pump-set. 

Larger machines such as the MARS and above have higher volume pumps and generally larger nozzles and air-jets. This means even more media flow and hence an even more efficient blast. We will compare the difference in power in future articles.

It is also possible to remove the coating even quicker by increasing the air pressure, however we don’t recommend going higher than 90psi as you just end up wearing the media out much faster as you obliterate the water cushion.

The Results

46 Grit Aluminium Oxide 297-420 microns @ 80PSI

46 grit aluminium oxide – A tough, angular shaped media that is great for removing surface coatings. It gives a matte finish and is the second largest media trialed in this instance.

43 seconds to process.

Crushed Glass 500-1000 microns @ 80PSI

0.5-1mm crushed glass – Angular in shape it is good for removing coatings and providing a matte finish. It’s softer than aluminium oxide or garnet however and its edges will round the more it is used

47 seconds to process

AB Glass Bead 177-297 microns @80psi

VS25AB Glass bead – A mid-sized glass bead that gives the best of all worlds. Large enough to remove coating but small enough to give a high-quality finish that wetblast machines are renowned for.

01:30 minutes to process

AD Glass Bead 105-210 microns @80psi

V25AD Glass bead – A very fine glass bead. Although technically can be used to remove coatings such as powder coat, it is better suited to uncoated alloys, soft metals and plastics to clean or brighten. However for the sake of this demonstration it took:

8:20 minutes to process.

AH Glass Bead 44-88 microns @80psi

VS25AH Glass bead – An extremely fine glass bead- best suited to uncoated alloys, soft metals and plastics. Not ideal for powder coat removal but in this case took

10:35 minutes to process

AH Glass Bead (contaminated) @ 80 PSI

We had done a pretty ordinary job of swapping from a large angular grit to the fine powdery AH bead. This meant very fine AH bead was contaminated with grains of aluminium oxide. For interest sake we have included the results here. The processing time was quicker but the finish was not as bright as it should have been. In this particular situation it would be like combining the longer processing time with a pretty ordinary finish. Worst of all worlds. Not to say that there aren’t instances where mixing media is actually beneficial.

5:35 minutes to process

Conclusion

Unsurprisingly, large angular media is much faster than tiny spherical beads when removing a tough  powder coating (43 seconds vs more than 10 minutes). However, it does demonstrate both the ability of the machine to process a wide range of surfaces and the role that media choice can play when optimising efficiency.

One extreme to the other

Frequent questions and answers

Probably not as it will take longer and the final finish doesn’t provide a nice keyed surface for new coatings to cling to. Check out the comparisons done in our test  to see just how much difference there is.

You will tend to get more of a matte finish when using angular media. Great for getting a keyed surface for new coatings to stick to.

Not necessarily. All media has different sizes and properties so comparing a large bead with a very fine oxide for example, the bead should be quicker.

No. Most people end up using one or two types of media that suits them best. Even a mid-sized glass bead and a larger oxide will likely cover many of the general jobs you’ll encounter.

Crushed glass is the cheapest option and certainly does a good job. However, compared to media such as aluminium oxide or garnet, for example, it is quite soft. When it wears it tends to round as it repeatedly impacts during processing. Oxide will break into smaller pieces that also retain hard edges and lasts longer. Either way the wet unit will still allow much longer media life than a dry unit.

Large angular grit will tend to give a slightly more profiled finish and if reprocessed with a glass bead, that surface will be brightened. If you looked at the surface under a microscope you would see the angular grit give pointed peaks and troughs while the bead afterward would round those peaks.

Yes you can clean plastic and rubber. We recommend using a fine glass bead.

The paints and oils usually sit on top of the water inside the sump and make their way out of the overflow. If any does make it through, it just becomes part of the blast stream

Yes you can etch glass, stone metals etc etc. You can use tape to make sure areas you don’t want blasted are protected.

Glass bead will have a mild peening effect. The larger the bead the more pronounced it will be. Thin metal (under 1mm thick for example) will try to curl as one surface is blasted compared to the other. This effect can be mitigated by equally blasting the other side of the piece. 

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