Abrading – Machine – Sandblast
Patent
1994-12-14
1996-12-31
El-Arini, Zeinab
Abrading
Machine
Sandblast
134 7, 134 6, 134 21, 134 38, 134 42, 451 39, 451101, B24C 100, B24C 302, B24C 700, B24C 900
Patent
active
055889018
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the art of cleaning contamination such as old paint, grease, rust and the like from surfaces by blast cleaning. In particular, the invention is concerned with blast cleaning wherein relatively soft abrasive particles such as sodium bicarbonate particles are transported into impact engagement with the contaminated surface by a stream of pressurized air or water, and, more particularly, is concerned with novel means and methods of uniformly dispersing the soft abrasive particles into the pressurized air or water stream.
2. Summary of Prior Art
In recent years, there has been an increase in the use of cleaning systems utilizing a blast of abrasive sodium bicarbonate particles suspended in a stream of pressured air or water. Sodium bicarbonate as an abrasive blast media has distinct advantages over sand particles used for many years as the abrasive media for blast cleaning. Because of the toxic nature of sand particles (crystalline silica) when inhaled, government regulations require the use of sophisticated fresh air breathing masks to insure the health of the operator by preventing the ingestion of the silica product into the lungs. Sand blasting, moreover, cannot be economically utilized to clean softer substrates such as aluminum, plastic laminates and the like or used to blast clean machines in food processing plants because of the difficulty of removing the silica particles such as from bearing surfaces.
On the other hand, sodium bicarbonate or other like relatively soft abrasives having a Mohs hardness of less than 4.0 can effectively clean softer substrates such as aluminum or plastic components without harming the underlying surface. Importantly, sodium bicarbonate particles are reasonably soluble in water and can be readily removed by hosing down the machine and substrate after the blast cleaning. Sodium bicarbonate is not toxic and does not require elaborate fresh air breathing masks for the operator. Only standard protective clothing and ear and eye protection may be utilized. This is not necessarily a requirement but depends primarily on the substrate and the coating being removed. Sodium bicarbonate can be utilized to remove surface corrosion, lime, scale, paint, grease and machine oil from any surface, without damaging the surface and can be washed away from bearing surfaces of machinery.
Standard sand blasting equipment consists of a pressure vessel or blast pot to hold particles of sand, connected to a source of compressed air by means of a hose and having a means of metering the blasting medium from the blast pot, which operates at a pressure that is the same or slightly higher than the conveying hose pressure. The sand/compressed air mixture is transported to a nozzle where the sand particles are accelerated and directed toward a workpiece. Flow rates of the sand or other blast media are determined by the size of the equipment. Commercially available sand blasting apparatus typically employ media flow rates of 10-30 pounds per minute. About 1.2 pounds of sand are used typically with about 1.0 pound of air, thus yielding a ratio of 1.20.
As discussed above, when it is required to remove coatings such as paint or to clean surfaces such as aluminum, magnesium, plastic composites and the like, less aggressive abrasives, including inorganic salts such as sodium chloride and sodium bicarbonate can be used in conventional sand blasting equipment. The media flow rates required for the less aggressive abrasives is substantially less than that used for sand blasting, and has been determined to be from about 0.5 to about 10.0 pounds per minute, using similar equipment. This requires much lower medium to air ratio, in the range of about 0.05 to 0.40.
The employment of less aggressive abrasives such as sodium bicarbonate as a blast cleaning medium does encounter problems in effecting the transfer of the abrasive particles from a supply hopper to the nozzle from which pressured water or air issues and where the abrasive is mi
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Rubey, III Arthur C.
Spears, Jr. William E.
Taylor Andrew M.
Corporation Yelapa
El-Arini Zeinab
Fishman Irving M.
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