How to pick the best blast cabinet

Before selecting a blasting cabinet, you will first need to size up your air compressor. For what takes a 20 CFM (cubic feet per minute) compressor one hour to process will take a 40 CFM compressor 15 minutes to complete and an 80 CFM compressor five minutes to complete.

Light-duty machines will never be capable of operating with abrasive guns larger than 20 CFM. They lack the support equipment to operate with the larger blast guns. Machines, costing more, can compress 8 hours of processing into less than one hour by using a larger blast gun. If unlimited compressed air is available, the production type of machinery can pay for the increased cost by saving labor at an almost geometric rate. Light-duty machines are excellent choices when the parts are small and continuous operation is not required.

Cabinet size:

Never choose a blasting cabinet based on part size alone. Larger cabinets always produce better visibility allowing the abrasive to expand to a lower particle density inside the cabinet. A larger cabinet size increases mobility allowing part movement and rotations required when blasting 100% of the part surface. Always picture yourself painting the part, and if you need to flip and turn the part to paint the surface, usually you will need to do the same when blasting inside a cabinet. The fastest blasting rates occur when the blast gun is almost 90 degrees to the part surface. Regardless of the shape of the part, picture the longest dimension inside a square box and this will allow maximum mobility and part rotation when selecting the cabinet size. When a large cabinet is required, but production style isn't, look to the cabinets with a large work area but smaller non-production dust collectors.

Machine Style - Light-Duty or Production:

What makes a production cabinet suitable for production work is the dust collector. If the collector is negative pressure it will be one of the cleanest to operate. Negative pressure dust collectors usually have the exhaust blower after the dust filter. This creates longer blower life, less service, and a cleaner operation. Large filter area allows maximum operational time prior to filter cleaning. Dust collector filters decrease blower performance as dust and worn abrasive collect on the filter surface. The more filter surface you have, the longer a machine can operate before service. Ease of service is another important factor when choosing a production machine. Production machines usually include self-cleaning filter assemblies. If cleaning is easy, the operator will clean the collector. If cleaning is difficult and time-consuming, the operator, during production work, often neglects this important requirement. Hopper bottom dust collectors are the easiest to drain and allow the collected material to exit into a plastic bag preventing escape into the surrounding area. Please remember that production is a word that describes many things, and when blasting is involved you should think of production type machinery when the blasting is daily, for periods of one hour or more. Even small 20 CFM abrasive guns will discharge almost 3000 pounds of abrasive in eight hours! Light-duty machines are great tools for applications not on a daily basis and if your compressed air is limited to 20 CFM. Please remember that all production machines will also operate with the smaller abrasive guns and create the most maintenance-free operation when used.

Type of cabinet:

When you think about machine type, the often misunderstood terms "siphon" and "pressure" appear. All machine types use compressed air to pressure the abrasive against the part to be cleaned. But not all blast machines are pressure types. Pressure-type machines use a pressure vessel to allow the abrasive to be pushed to the blast nozzle. Pressure machines work with heavy abrasives in the same way a pressurized paint pot works with thick paints. Using more than one atmosphere to push the abrasive, via a pressure pot, to the blast nozzle creates faster particle velocities at any given blasting pressure. Pressure-pot machines also increase the blasting temperature of the abrasive by creating a higher abrasive density pattern. The information outlined above does not mean pressure-pot machines are faster, but it does mean that pot machines will operate with some abrasives that siphon machines will not operate with.

Siphon-type machines are the most common type of abrasive cabinet. Unlike a pressure pot machine, a siphon machine can run for as long as abrasive is inside the system. Pressure-pot machines must be stopped about every four to five minutes, allowing the pot to recharge. Siphon machines never have to stop unless the cabinet runs completely out of abrasive media. Siphon-blast machines and pressure-pot machines both use pressure to clean the part, but the industry makes a distinction between pressure and siphon-type cabinets. Siphon machines also have an advantage over pressure-pot machines in that siphon machines operate with a much wider range of abrasive types and sizes. The only abrasive a siphon machine will not operate well with is large steel shot and large steel grits.

Finishing Equipment also offers an outstanding guide to abrasive performance, pressure calculations, and blasting facts at www.sandblasters.com/guide.htm.