The most common type of dry blast cabinet is a siphon blast (aka suction blast) cabinet.
This blast cabinet comes with a line to supply compressed air and another line to siphon abrasive media into the blasting gun. The blast nozzle expels the mixture of compressed air and abrasive.
Siphon blast cabinets differ from pressure blast cabinets, where the abrasive media and air are compressed in a pressure pot, then expelled through a single hose through the blast nozzle.
Today we are talking strictly about troubleshooting abrasive flow issues in siphon blast cabinets.
If you have not found the problem, here are some things to look at.
Check the Air pressure
If your abrasive media flow seems off, check the air gun to see if the correct air pressure is being produced by the air compressor. The compressor output pressure gauge can be checked to ensure that the compressor is operating at the right pressure. The compressor could be defective if there is not enough air.
Particles may be clogging the line
If your blast gun is not drawing any abrasive, turn off the compressed air supply. The blast gun’s nozzle should be removed and the passageway checked for obstructions. Most commonly, debris such as paint chips, burrs, and rust fragments block the pickup line at the gun end or at the gun’s other end.
The abrasive pickup lines are likely to be clogged if there is no airflow at the gun but there is some abrasive.
You might need to add more abrasive
Another possibility if you have air flow, but no media, is that you need to add more abrasive to the tank. If there is still plenty of abrasive in the tank, check the valves. They could be blocked or defective.
Your abrasive media may be spent
Abrasive doesn’t last forever. If the abrasive has passed its maximum number of recycles, it needs to be disposed of and the abrasive in the tank replenished. Each type of abrasive has a limit to how many times it can be used before it becomes too small to strip or clean a surface. Your blast media may be at this point and the blasting power won’t work even if it is picked up by the intake hose.
The blast nozzle may be worn out
Blast nozzles also wear out over time. The accelerated abrasive eats away at the nozzles, widening the passageway through which the media and compressed air are propelled. The larger the nozzle aperture, the more pressure is needed to accelerate media with the same force.
If your blasting gun seems to be lacking the force it did in the past, it may be time to get a fresh blast nozzle. Drain the water trap (airfilter) from your air compressor.
Water traps remove already condensed water in the air compressor line. Air flows from one side to the other, and then condensed water builds up at the bottom. You can drain this out. Air usually exits through a filter that removes small particles from the air.
The water trap of the compressor can become full and condensed liquid water may evaporate.
Under normal use, the water trap will fill up approximately once per week. If you live in an especially humid location, it may fill up even faster. You should drain the water trap every time you use the compressor in blasting to prevent rust.
This is an important part of sandblasting cabinet maintenance. Excessive moisture in the air and abrasive lines can be the root cause of many problems with abrasive flow in sandblasters.
Removing unwanted moisture from hot, compressed air
If you have too much moisture in your air or abrasive lines, this can cause abrasive flow issues. This can be caused most often by an air compressor that’s slightly smaller than the blast cabinet volume. Excessive condensation can occur if your air compressor is not able to stop, start, cool down and cool off during your blasting process.
To understand why this happens, let’s look at the steps in the abrasive blasting process.
Because compressed air is under pressure, the molecules of air become slightly warmer than normal due to friction. This eventually warms the tank above ambient temperature. This pressurized air is then introduced to the blast cabinet, which is cooler than the air in the tank and compressor. Because the dust collector blower circulates air, the blast cabinet is cooler that the air coming from the supply line.
Condensation is often caused by warm air coming from the supply. If you are blasting continually, and the air compressor has no time to cool down, the condensation may cause jamming in the lines. How can you resolve this problem?
Upgrading the air compressor system
For industrial blasting applications, you may need to add a multi-stage air drying system. A compressor that can supply 20 liters per second of air also provides 24 liters per day of water.
That water needs to be removed, done in multiple stages. Aftercoolers can take 15 liters out of the initial 24 liters. A refrigerated dry air dryer would remove another 7 liter. For heavy duty blasting setups, you may et up a dessicant air cooler in a subsequent stage to remove the most amount of water vapor possible.
These are some of the most common issues with abrasive flow in siphon blast cabinets. You can contact us here or by calling (916) 409-2458 if you are experiencing any problems or have general questions about abrasive blasting.