Blast Cleaning Operations Analysis

 

BLAST CLEANING OPERATIONS ANALYSIS
Objectives of the Operations Analysis:

  1. To determine whether the abrasive work-mix is in proper balance for effective cleaning.
  2. To determine whether contaminants are being removed from the work-mix.
  3. To determine whether usable abrasive is being wasted because of improper separation.

The High Cost of Improper Operation:

  1. Use of a work-mix that is too coarse can increase cleaning cycle time by 30%, or more.
  2. Use of a work-mix that is too fine can increase cleaning cycle time by 30%, or more.
  3. As little as 2% sand contaminant in work-mix can increase equipment parts wear by 50%.
  4. Inadvertently increasing the size of the separator take-out material by just one shot/grit size (about .005") can increase abrasive consumption by as much as 25%.

ABRASIVE WORK-MIX

An efficient abrasive work-mix contains well-balanced distribution of large, medium, and small pellets. The large pellets, with maximum impact value, perform the major task of loosening thick, tightly adhering contaminants; the smaller particles, containing the largest number of pellets per pound, provide the coverage necessary for fast removal of the lighter contaminants.

The size distribution of the work-mix is constantly undergoing change because of abrasive deterioration, caused by normal fracture-failure and flaking-failure.

Separating practice is a major factor in maintaining a stabilized and balanced work-mix, but the manner in which new abrasive is added can be even more important. Ideally, small and frequent additions should be made (preferably during each operating shift), at a rate which will compensate for abrasive consumption.

CAUSES OF INEFFICIENT, HIGH-COST BLAST CLEANING OPERATIONS
Work-Mix

  1. Work-Mix too coarse. Can be caused by:
    a) Large and infrequent additions of new abrasive. (Be sure sample was not taken immediately after an addition.)
    b) Excessive air passing through the separator, pulling out medium and fine-size abrasive.
    c) Excessive carry-out with the work.
  2. Excessive fines in the work-mix. Can be caused by:
    a) Insufficient air through the separator.
    b) Excessive time lapse between additions.
    c) Large, sporadic additions of recycled abrasive from floor spillage or system leakage.

Discard

  1. Usable abrasive lost via separator discard. Can be caused by:
    a) Excessive air passing through the separator.
    b) Improper distribution over separator shed plates.
    c) Holes in separator shed plates.
  2. Usable abrasive lost into dust collector. Can be caused by:
    a) Excessive air through the system.
    b) Plugged expansion trap, or worn baffle.
    c) Dust build-up in dust collector pipes.
  3. Usable abrasive lost through scalping system and coarse refuse discharge. Can be caused by blocked or plugged scalping screens.

9 Out of 10

9 out of 10 blast cleaning operations are wasting, on the average, from 15% to 25% of usable abrasive because of improper separator and operation.

9 out of 10 blast cleaning operations experience, rather frequently, either poor cleaning or slow cleaning (longer than necessary cycle time) because of out-of-balance work-mixes.

9 out of 10 blast cleaning operations do not maintain current and accurate data on abrasive consumption (expressed as pounds used per wheel-hour, or pounds used per unit of work cleaned).

"I never gave them hell. I just tell the
truth and they think it's hell."
H. Truman

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