It is possible that the first sandblasters were fast-moving rivers or desert windstorms. Someone noticed the results and an idea was born.
The first blast cabinets utilized “wet blasting” with the abrasive media suspended in water. Wet blasting cabinets provided simple abrasive containment that eliminated dust and enabled the abrasive to be recycled. But without frictional heat the wet blasting process was slow and could not accommodate all different types of abrasives.
Next to be developed were dry blasting cabinets. Dry blasting cabinets eliminated the water mess and simplified changing abrasives. Importantly, dry blasting cabinets were much faster than wet machines — about 6 times faster for most normal applications. But much like the desert windstorm before it, the dry blasting process resulted in poor visibility.
The solution was the addition of exhaust blowers to remove the dusty air and replace it with clean air from outside the cabinet. Larger and larger exhaust blowers were developed to further improve visibility by quickly removing more dirty air from the cabinet. Larger exhaust blowers increased the airflow out of the cabinet but they also required more filter area and larger dust collectors to store the dust removed from the cabinet.
These new, more powerful dry blasting cabinets were only efficient if the abrasive could be recycled. The dust removed from the cabinet by the blower and filtration systems includes material blasted from the part surface, as well as re-usable abrasive. The separator reclaimer was developed to recycle abrasive and separate out the good abrasive to enable it to be used over and over again. The separator reclaimer can recycle some abrasives up to 100 times. This made it possible to use a wider range of abrasives and more expensive abrasives such as industrial diamonds.
Dry blasting cabinets utilize two abrasive delivery methods: either siphon or direct pressure delivery.
The first dry blasting machines relied on a siphon delivery method, using an injector gun to siphon or pull the abrasive to the blasting nozzle. Siphon type equipment is easy to make and simple to operate but does require higher blasting pressures. In sandcarving, dry blasting siphon equipment can be ideal for quick and simple surface etching. Because siphon delivery methods result in a wider fan pattern, it is useful for uniformly blending large open areas.
Dry blasting cabinets utilizing direct pressure abrasive delivery methods were a later development. These direct pressure machines use a pressure vessel or pot to pneumatically push the abrasive to the nozzle. With direct pressure, the abrasive has no delivery weight so it travels faster, creates more frictional heat and has a much tighter and smaller blast pattern.
Direct pressure methods deliver abrasive at about twice the speed of siphon delivery methods. Cabinets using direct pressure operate on less compressed air and produce more frictional heat. In sandcarving, direct pressure concentrates the abrasive into a smaller pattern area making it ideal for detailed masks or films. Because direct pressure provides a more focused pattern of abrasive delivery it keeps more abrasive off the mask, thereby extending the life of the mask. The more focused pattern also enables deeper carving.
The evolution of the sandcarving industry has created a seemingly limitless array of applications – different materials, unlimited sizes and shapes of the parts to be carved, varying details of design or depths of carving and the number of parts to be produced in a period of time – these are just the beginning of sandcarving requirements.
To address this range of sandcarving applications demands machinery designs offering a range of abrasive flow rates, abrasive types and sizes, blasting pressures, compressed air volume, frictional heat and machine duty cycles. Not surprisingly, there is no “one size fits all” machine that will address all the needs of the sandcarving industry.
With this wide array of applications and machinery how can the buyer choose the right sandcarving cabinet for any one application?
Again, the first choice must be the abrasive delivery method — either siphon or direct pressure delivery. Will the primary use call for surface etching or blending large open areas? If so, then the siphon machine is ideal. If a more focused pattern or deeper carving is required, then a direct pressure machine is preferred. Direct pressure also allows processing with lower blasting pressure using less compressed air and enabling more mask detail.
The next question in selecting the right sandcarving cabinet concerns the required volume or flow of abrasive through the nozzle. The size of the nozzle determines the volume or flow of abrasive. The industry refers to small nozzles as micro and large nozzles as macro. In direct pressure, micro nozzles are 1/8 inch I.D. or smaller and macro nozzles are 3/16th or larger. In siphon delivery cabinets, micro nozzles are 1/4 inch I.D. or smaller and macro nozzles are 5/16th or larger.
Why does the volume or flow of abrasive through the nozzle matter? Because the greater the flow of abrasive, the higher the frictional heat and the higher the frictional heat, the less design detail.
Macro nozzles with more frictional heat are used for high production with less design detail. Micro nozzles with less frictional heat are used for detailed design work – whether in high production runs or one-time-only part production.
After deciding the abrasive delivery method, siphon or direct pressure, and the volume or flow of abrasive, micro or macro, the buyer will next need to consider the machine duty cycle.
Machine duty cycle is the amount of time the machine is designed to operate on a daily basis. Duty cycle is determined by the size of the exhaust blower and the size of the dust collector filter. The right machine duty cycle will match the very highest anticipated daily usage.
To keep pace with the creativity and vision of the sandcarving industry, dry blasting manufacturers have evolved a full line of machinery — siphon or direct pressure, micro or macro and a wide range of duty cycles – machines shaped and modified to meet the special needs of the sandcarving industry. One size never fits all!
Robert Robinson – Biographical Sketch
Robert Robinson draws from four decades of experience in the sandblast machinery manufacturing industry. In 1977, Robinson founded Media Blast & Abrasive, Inc., manufacturer of the CrystalBlast line of sandcarving and etching machinery and manufacturer of the largest line of abrasive blasting cabinets available on the market today. Media Blast & Abrasive partners with IKONICS Imaging® to offer the sandcarving industry a complete line of machinery, mask, film and expertise. As a consultant to Media Blast, Robinson continues to design new machinery in response to the needs of the sandblast manufacturing industry.