VOL. 10 November ISSUE YEAR 2009

MFN Trainer Column

in Vol. 10 - November Issue - Year 2009
What Can Go Wrong in Blast Cleaning
Ananda Talukdar

Ananda Talukdar

I have been associated with Blast Cleaning for almost 25 years. It took me almost 15 years to understand "What can go wrong in Blast Cleaning". Ever since then I have been assisting the industry to make the process of Blast Cleaning user friendly. I still remember way back in 2005 I visited a company and their Managing Director took me around his plant and finally to the Shot Blasting Machine Area. One thing which struck me was that the Shot Blasting Machine was in a remote place. On enquiring from him the reason for this Step Motherly treatment I was surprised when he said, "You see the Shot Blasting machine is a self destructive machine and as such frequently breaks down. This is also the reason why this particular Machine is not under TPM." I could not buy his statement and I said "Give me six months time and I will get this machine under the TPM Fold." Exactly 2 months later the machine came under the TPM Fold.
Today in this competitive scenario the necessity of cost cutting in every sphere of an industry is very common and Blast Cleaning cannot be an exception. Few of the underlying causes that can affect cost and productivity are given below:

Seven out ten users of Blast Cleaning Operations waste an average of 15-25% of usable abrasives because of improper separation systems.
When a work mix is either too coarse or too fine, it can increase cleaning time by as much as 30%. Longer cycle time means greater consumption and unnecessary wear & tear.
Wear of equipment parts increases by 50% or more if there is as little as 2% dust content in the work/operating mix.
Abrasive consumption increases by as much as 25% if the size of abrasive that the Separator takes out is increased by only one shot/grit size of about 0.127 mm.
The presence of free graphite in the abrasive increases the consumption.
The use of a worn out Blade/Vane will increase the length of the blast pattern particularly at the tail end resulting in a proportion of the available blast missing the target or work piece and a reduction in blast intensity in the target area.
A wear of 6 mm on the beveled edge of control cage lengthens the blast pattern often to the point that some abrasive misses the work piece.
When wear on the leading edge of the impellor segment exceeds 3 mm, the abrasive will hit the back of the blade rather than being delivered to the throwing face. This will result in a drop in velocity of the abrasive leaving the blades/vane thereby increasing the blasting time.

How these affect the blast cleaning operation can only be appreciated if we know the original quote of Mr. Benjamin Franklin who described the process as thus:

……..an impact cleaning operation that is neither cutting, grinding nor abrading. It is essentially a pounding, battering or bombarding of the work surface by successive impact of the flying abrasive.

Impact is the key to blast cleaning. Following are the factors that control the process:

Proper targeting of the abrasives on the work piece.
The proper size of abrasives.
Inadequate abrasives.

I am sure the readers can now correlate the underlying causes with the factors that control the process.

My assistance to the blast cleaning industry was moving at a snail’s pace and then one day Mr. Steven Baiker, Editor & Publisher of Metal Finishing News called me up and asked me whether I could write a chapter on Blast Cleaning for the 2nd Edition of the Book titled "Shot Peening - A Dynamic application and its Future". I could not resist the offer and agreed to his proposal. A complete chapter titled "Introduction to Blast Cleaning" is added to the 2nd edition which is likely to be published in November 2009. I am sure the readers will benefit from the same. Your comments and advice are also welcome.

For questions contact ananda@mfn.li

Trainer Column
by Ananda Talukdar, 
Official MFN Trainer
More Information at www.mfn.li/trainers