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Troubleshooting: Sandblasting

Overview

The following will allow you to troubleshoot issues that may arise during the blasting process, including clean up and machine operation.

The Abrasive flow keeps flowing even when my foot is not on the foot pedal.

  1. Check that the foot pedal pressure is higher than the abrasive flow. On a pressure pot system the foot pedal should be regulated to at least 80psi whilst the abrasive flow pressure should be set at between 20 - 30 psi.
  2. Check that the regulator on your compressor is fully open so as not to restrict the air pressure on the regulators on your pressure pot system.
  3. Check the diaphragm on your foot pedal valve. It may have worn a hole through the rubber and need replacing.

Too much abrasive flows out when I blast.

  1. Check that your flow valves are set correctly. The starting point for the setting of the abrasive valve and the air flow valve should be 50% open. A fine adjustment can be made on the air flow valve, moving it open or closed by 1 millimetre intervals to get the right consistency.
  2. If you are getting too much sand flow you need more air flow to balance the mix. Adjust in 1 millimetre increments until you get the desired effect.
  3. Check to make sure the sand flow valve is not too far open.

When I press the foot switch I get a burst of abrasive and I can blast but in about 30 seconds I seem to be getting nothing but air. I have to release it and step on it again. 

  1. Your air valve setting is open too wide, your abrasive flow will begin shooting well but after a few seconds the air will over power the sand and you will lose consistency. Re-adjust your valve settings. Even if you haven’t changed anything, the simple wear of the nozzle will affect the pressure settings, and making a slight adjustment is necessary. Humidity may also affect the settings.

I can’t seem to get a consistent sand flow, I get plenty of air but I just can’t get the sand to flow.

  1. You have probably got a blockage in the system.
  2. First check the nozzle -- is there anything stuck in it?
  3. Second check the hose -- is it coiled up. The hose should always be laid out straight without coils so that the abrasive gets a clear passage without delayed build ups on the curves. This will also wear out the hose faster.
  4. The blockage may also be in the sand flow valve. You will need to pull the valve section apart and check for any foreign particles causing the blockage. It is very important to sift the abrasive every time you pour it into the pressure pot. This will keep foreign particles out of your system.
  5. Other causes for sand not flowing correctly may be humidity in the air causing moisture in the sand making it stick. The only way to fix this problem is to dry out the abrasive.

It seems to take a long time to blast a product.

  1. The blasting action should be almost instant. Your air flow is probably too lean making a softer blasting action. Increase your air mix.

I get an uneven etched image when I blast.

  1. Don’t spray in one place for prolonged times. Always keep moving slowly over the area. Start blasting at one side of the resist and work your way evenly across the area.

Some areas are harder to blast than others and this results in different depths of blasting.

  1. You have probably applied an uneven coating of adhesive. Where the adhesive has a build-up it will take longer to blast than the thinner areas. You will get deep ridges along the built up adhesive areas where the thinner adhesive layer has been blasted away.

When I blast the item the resist lifts off the surface, ruining the item.

  1. The surface of the item may not have been cleaned properly before applying the resist.
  2. The resist may not have been properly dried before adhering to your item surface. Moist resists will not adhere properly. Make sure the resist is completely dry.
  3. The adhesive may not have been given enough time to dry. Make sure that the adhesive has gone clear and all the milky looking areas have disappeared before you apply the resist.
  4. The resist may not have been burnished well enough. In general you don’t have to burnish the resist very hard but you must make sure you burnish all areas to ensure there are no air bubbles under centre of letters like o, e, etc.
  5. You may be blasting at an angle to the surface of the blasting item. Make sure you are blasting at 90 degrees to the blasting surface.
  6. You may be blasting too close to the surface. Stay about 6-10 cm away.
  7. You may be blasting at too high a pressure.

Small areas of the resist blast away (such as the middle of an “a”).

  1. Ensure you have cleaned the surface prior to applying the resist.
  2. Check to see if you have adhered the resist properly (see above).
  3. You may be blasting too close or at an angle.
  4. Check the quality of your wash out process.

When I take my foot off the foot pedal the Sand flow keeps going.

  1. Check that you have enough psi coming out of your compressor. A 100lb Pressure Pot will need at least 80psi-compressor output to operate the foot pedal properly.
  2. Check the diaphragm gasket in the sand flow valve. It may have worn a hole in itself. You will need to replace it.
  3. Check the foot pedal valve. It may be worn out and need replacing.

I try to pressurise the Pot but it does not pressurise.

  1. Ensure the compressor is outputting 80psi to operate the foot pedal properly.
  2. Check that the O ring on the pressure pot is not worn.

REMOVING THE RESIST

The resist is really stuck to the job and won’t come off easily.

  1. The job may be coated with a clear protective layer that sticks strongly to the resist. Try soaking in clean water for a long time. Even overnight soak if necessary. This rarely happens but certain kinds of coatings on some pre-coated metals may cause excessive sticking.