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SAND CABINET BASICS

THE BASICS

Media Blast manufactures a complete line of Light Duty, General Purpose and an array of Siphon and Pressure Production abrasive blast machinery. In addition to the common dry type blast machinery Media Blast also manufactures the Hurricane line of “Wet” abrasive blast machinery. The following basic information about blasting machinery will help you select the right machine for your application. Click on highlighted term for blasting definitions. Use the Buying Guide located on the home page to help decide which machine is correct for your application.

CLEANING SPEED:
Cleaning speed varies with the amount of compressed air used. Always allow for existing needs when establishing the amount of compressed air required. Compressed air is measured in Cubic Feet per Minute. Because of quality differences in the construction of air compressors, CFM can vary within the same horsepower rating, still the following rule generally holds true: What takes a 5 HP compressor 1 hour to process, will take a 10HP compressor 20 minutes, and take a 20 HP compressor 7 minutes. When you double the cubic feet per minute of compressed air, you triple the production capacity or reduce the blasting time by two-thirds. This is the single most important factor permitting production type machinery to make up for the additional cost of the machinery by saving labor time.

Each abrasive gun size operates at a temperature that increases in frictional heat as the abrasive gun size increases in CFM usage. Larger guns generate more heat during the blast and greatly reduce the processing time. The increase in frictional heat is added to the increase of abrasive flow to create surprisingly faster blasting times. The faster the blast cleaning rate the more machine features required to maintain normal operation of the equipment. Production machinery doesn’t just cost more, it does more!

Light Duty machines are not capable of operating with abrasive guns larger than 20 CFM, or 5 HP because they lack the support features to operate with the larger blast guns. Light duty machines are excellent choices when the parts are small and continuous operation is not required on a daily basis. Production machines, using larger guns, can compress 8 hours of blasting into less than 1 hour. If unlimited compressed air is available, a production machine can pay for its increased cost by saving labor at an almost geometric rate.

CABINET SIZE:
Never choose a blasting cabinet based on part size alone. Better operator visibility and more room for moving the part within the cabinet result in faster cleaning. Larger cabinets produce better visibility by allowing the abrasive to expand to a lower particle density inside the cabinet. A larger cabinet size also increases part mobility, allowing for movement and rotation when blasting 100% of the part surface. Visualize painting the part: if you need to flip or turn the part to paint it, you will need to do the same inside the cabinet when blasting. The more three-dimensional the part the more rotation required. Regardless of the part’s shape, however, picture it inside a box, and then flip it visually in your mind to determine the required cabinet size. Look to the Shop Standard line for larger cabinets with smaller, non-production dust collectors when you require a large cabinet for non-production blasting.

DUST COLLECTOR FILTRATION:
What makes a production cabinet suitable for production work is the dust collector. Negative pressure dust collectors are the cleanest and most efficient to operate. In a negative pressure dust collector the exhaust blower is located downstream of the dust collector filter. This creates longer blower service because the air drawn through the blower has already been filtered. Media Blast’s negative pressure dust collectors offer larger filter areas for maximum use between filter cleanings. As dust and worn abrasive collect on the filter surface, blower performance is decreased. Therefore, the more filter surface you have the longer a machine will operate before filter cleaning is required.

Media Blast’s production machines are easy to service and offer self-cleaning filter assemblies. If cleaning is easy, the operator will clean the collector faster and more frequently. If cleaning is difficult and time consuming the operator often neglects this important duty. Media Blast’s hopper bottom dust collectors are the easiest to drain and allow for environmentally safe dust removal.

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 1 hour or more. Even small 5 HP abrasive guns will discharge almost 3000 pounds of abrasive in 8 hours! Light Duty machines are great tools for applications not on a daily basis and if your compressed air is limited to 20 CFM. Production machines will also operate with the smaller abrasive guns creating the most maintenance free operation when used.

SIPHON OR DIRECT PRESSURE MACHINES:
All blast machines – whether siphon or direct pressure – use compressed air to force the abrasive against the part being cleaned. Siphon machines use suction to pull the abrasive into he blast gun, while pressure machines use a pressurized pot to pneumatically push the abrasive to the blast nozzle. Siphon machines operate with an abrasive gun with two hoses, one for compressed air and one for abrasive. Pressure machines use a single hose with a mixture of compressed air and abrasive.

Siphon machines are the most common type of abrasive machinery. A siphon machine can run for very long periods of time, while direct pressure machines must be stopped about every five to seven minutes to allow the pressure pot to recharge. Siphon machines never have to stop unless the cabinet runs completely out of abrasive media. Siphon machines also have an advantage over pressure machines in that they operate with a much wider range of abrasive sizes. The only abrasive a siphon machine will not operate with is large or heavy type represented by steel shot and steel grit.

Pressure machines are appropriate if the blasting process requires a heavy abrasive or “blind hole” cleaning. A pressure machine works with heavy abrasive in the same way a pressurized paint pot works with thick paints. A pressure machine will blast into “blind holes” or deep pockets because it concentrates the abrasive and compressed air into a smaller nozzle area and pneumatically pushes the media into the pocket. A pressure machine creates a higher abrasive particle velocity than a siphon machine at any given blasting pressure. Pressure machines also increase the blasting temperature of the abrasive by creating a higher abrasive particle density on the part. While direct pressure machines create higher abrasive particle velocity and greater blasting temperatures, their efficiency is significantly reduced by the interruptions required to recharge the pressure pot. In addition most abrasives can be destroyed using both types of machines with normal air compressor line pressures. The information above is general in nature and it must be mentioned that features are available that eliminate some of these conditions. Cost of the direct pressure machine is greater than the siphon type, and the direct pressure machinery should be used when the application requires the direct pressure delivery advantages.

The last basic information explains the wet blasting machinery. Because of the water used a wet machine has the ability to eliminate frictional heat that can damage certain materials. In addition, the wet machine can operate with ultra fine abrasives i.e. 4000 mesh creating new possibilities not available using dry type machinery. A chemically clean part surfaces can be achieved using the wet machine.

Usually the wet process is a known application and Media Blast offers the Hurricane stainless steel line to fill the need for this type of application using a slurry pumped system not to be confused with simple air agitation.