History of Blast Cleaning dates back to 1870 when Mr.B.C.Tilghmaan of Philadelphia obtained the first patent for sand blasting. In this process a jet of sand propelled at high velocity by a steam or air blast, is employed as a tool for cutting stone and other materials, and at lower velocity of jet it is employed for grinding and ornamenting the surface of the glass. In the same year Mr.B.CTilghman obtained the patent for abrasive throwing wheels but it took almost 60 more years for the first operational machine to be produced.
Blast cleaning is mainly of two types depending on the method of propelling of abrasives:
Airless Blast Cleaning uses motor driven bladed wheel rotating at high speed. The abrasive is propelled by this bladed wheel, which employs the combination of radial and tangential forces to impart the necessary velocity to the abrasive. The position of the wheel from which the shot is projected is controlled to concentrate the blast in the desired direction. Among the advantages of the wheel method of propulsion are easy control of shot velocity, high production capacity, and freedom from the moisture problem encountered with compressed air.
As has been explained in the section Setting the Blast Pattern that to achieve the best cleaning efficiency the abrasive quality plays a very important role. However it is one of the most neglected areas and is a major area of concern. The following are the findings of the speakers during visit to the users of blast cleaning process:
No regular interval specified for addition of abrasives. Abrasives added when the blasting time increases the specified time limit.
Sizes of abrasives changed on the availability & cost. No incoming abrasive inspection for quality. No records maintained. The above factors play a very vital role in blast cleaning process.
One way of reducing media consumption is to reduce the media flow rate. You may have been told to run "full motor amps" to get the most work out of the media. And, that is a true statement, it will get the most work out of your media. Unfortunately some of the "full work of the media will only eat up your machine and not do any beneficial cleaning of your parts. If the parts surface is flooded with media it will affect the cleaning rate.
The media flow rate has to be optimized without sacrificing the cleaning effectiveness. Once the value is determined (usually based upon motor amps) one should strive to maintain that setting .If you can reduce your "Working Amps" (Ammeter reading - No Load Amps = Working Amps) by 10% you are throwing 10% less shot and you automatically cut your media costs by 10%. Some blast cleaning operations need different flow rate; light cleaning for some parts and heavy cleaning for others. Again, you should determine the minimum amount of media for each blast cleaning condition. Throwing media is the same as throwing money, don't throw more than you absolutely need.
Wheel parts life is a big concern for almost all the users of shot blasting & shot peening machines. Read More