The Ervin POSTER: Trouble-Shooting the Blastcleaning Process

VOLUME NO. VIII: ISSUE No. 5 JULY 1988
THE ERVIN POSTER: TROUBLE-SHOOTING THE BLASTCLEANING PROCESS
CHALLENGE NO. 1: AIM – KEEPING YOUR AIM ON TARGET

For sure – nothing good can or will happen in blastcleaning if the abrasive blast­-stream isn't properly aimed and the kept on target! The target, of course, is the work­piece being processed – not the blast equipment wear-parts (they get more than enough abuse by abrasive rebound – the last thing they need is to be hit by direct impact of the abrasive stream).

Of the three critical variables described and explained in Ervin's Trouble-Shooting Poster – (1) aim of the abrasive blast-stream; (2) proper work mix size-distribution; and (3) throwing full abrasive capacity of the blast wheel – the "aim" variable has to be the No. 1 challenge. It's as simple as this: If the abrasive (right or wrong size mix – full or partial load) doesn't hit the work-piece, nothing good can or will happen. In fact, disaster is the only thing that happens.

AIM — If you are duck hunting and miss the ducks, don't blame the shot. Blame the aim!

AIM — Likewise, if you are blast cleaning, blast peening, or blast etching, and are not achieving the required finish results, (and, to add insult to injury, you find the equipment wear and tear totally out of hand), don't blame the shot (or grit). Blame the aim!

AIM — The No. 1 challenge in blast cleaning.

DON'T TAKE THE BLAST STREAM AIM FOR GRANTED

Among the findings of a recently completed two-year survey of more than 100 major blastcleaning operations conducted by Ervin Industries' Blastcleaning Task Force was this:

Aim in blastcleaning was being taken for granted. Aim was seldom given any thought.

When Ervin's Task Force asked: "When did you last run a check on your shot-blast pattern?” all too many didn't understand the question, never having done it. Too many said they felt it was unnecessary because the blast-wheel clock-dial setting was where it had always been.

In tumble-blast equipment, where the work-pieces are contained in a so­-called barrel, operators tended to assume there was no way the blast-stream could miss the work – "Isn't it like shooting fish in a barrel?". Most operators with monorail equipment, spinner-hangers, or swing-tables, seemed to believe their blastcleaning was like "shooting at a sitting duck" because the blast-wheel is in a fixed position with the work-pieces being moved into the path of the blast-stream. Yet, in all too many instances, Ervin's Task Force found blast-wheel aim to be off target to the point where a significant portion of the blast-stream was striking against equipment wear parts instead of the work. As little as a 10% shift in blast pattern aim can reduce cleaning efficiency by as much as 25% – plus producing an unacceptable quality of finish.

WHEN AIM IS OFF-TARGET, TROUBLES COMPOUND

  1. Obviously when the blast-stream misses areas of the work-piece, incomplete contaminant removal will result.
  2. Excessive parts wear will occur in those areas where the equipment receives direct impact of the abrasive blast-stream.
  3. Along with this excessive and extraordinary wear on replacement parts will come increased blast machine down-time — productivity will suffer.
  4. Because the equipment wear parts are so much harder than the work being cleaned, abrasive consumption will increase sharply whenever the blast-stream impacts directly on those hard wear parts.
  5. Invariably, when it is discovered that contaminant removal is incomplete and spotty, operators resort to increasing exposure time to the blast­-stream. Ervin's Task Force found many instances where blast cycle-time had been increased by 50% or more. This is when the troubles and problems really compound. Bad as it is when misdirected aim causes the problems listed above in (2), (3) and (4), now that these factors are multiplied by the 50% or more increase in blast-cycle time, a bad situation has been compounded into disaster.
    (Despite the increase in blast-cycle time, world-class finish is still not assured because misdirection of the blast-stream hasn't been corrected – those same areas of the work-piece are still not receiving direct impact. Rebound impact is the only way those areas will be hit – rebound off the equipment wear parts. A difference in finish quality will continue to exist between work-piece areas that receive direct impact and those areas that receive only random rebound hits.)
  6. Obviously, when blast cycle-time is increased, fewer units of work are processed per shift – i.e., productivity is slashed; unit costs of blastcleaning skyrocket; shipments to customers are delayed. This is the road to disaster.

YOU CANNOT TAKE BLAST STREAM AIR FOR GRANTED, BECAUSE YOU CAN TAKE FOR GRANTED — THE INEVITABILITY OF WEAR — WEAR OF BLAST WHEEL COMPONENTS.

Reasonable, and amazingly good, wear tolerance has been built into the blast wheel componentry. But, when wear goes beyond that built-in tolerance, the components can no longer perform properly. The blast pattern will shift – the abrasive blast-stream aim will go astray. Then will come those troubles and problems that are described in Ervin's Blastcleaning Trouble Shooting POSTER.

Ervin's POSTER goes beyond the recitation of the problems that can happen when the three critical variables slip out of control. The POSTER includes guidelines for controlling those variables – guidelines to help get your operation back on track. Quoted below is the POSTER Guideline section dealing with attaining the proper blast pattern aim:

  1. Check location of blast-pattern "hot spot" regularly. (Test-blast a metal target plate placed at normal work height for 20-30 seconds. Hot-spot should be approximately 8" in advance of wheel center-line.)
  2. Inspect, daily, degree of wear of wheel components:
    • Impeller: change when leading edges exceed ⅛” wear.
    • Control cage: change when beveled edge exceeds ¼” wear.
    • Vanes/Blades: change when grooving is ½ thickness of blade.
    Excess wear of wheel components distorts blast-pattern and causes "hot-spot" to shift. (10% shift can cause 25% loss of cleaning efficiency.
  3. Do not permit sand or excess fines in the work mix. (2% sand content can double wear rate on wheel components.)
  4. Establish records of parts replacement vs. wheel hours operated, so preventive maintenance can be utilized.

The guideline steps are simple and basic – common sense and, when implemented, that "aim" variable can be kept under control! Once you understand and appreciate the disaster scenario that can come with a mis-fired blast pattern, you will recognize that the time and effort involved in following through on the above four guideline steps represents very little time and effort for tremendous benefit. You will understand you simply cannot afford not to implement those guideline steps.

If you need help to get started on the POSTER Guideline steps, Ervin stands ready to help in any way we can. Call on your Ervin sales representative - he'll see that you get the assistance you need. Ervin's Technical Bulletin, Volume VII, Issue 1, dated February, 1987, deals with Guideline Steps 1 and 2 above. Ervin's "Blast­cleaning Operation Analysis Cards" are available to guide you on Step 3. And Ervin will make available “Abrasive Addition" cards that provide for collecting the data mentioned in Step 4. We hope our listing the troubles – all six of them – that come when the aim is off target got your attention to the point where you will be inspired to request copies of the items referred to above.

THE POSTER

You are urged to post Ervin's Blastcleaning Trouble-Shooting POSTER at each of your blastcleaning machines. We would like the POSTER to serve as a daily reminder of the problems that can happen when the operation gets out of control.

And, hopefully, realizing how serious and how disastrous the troubles can be if the operation is allowed to get out of control, you will accept the Guidelines for controlling the three basic variables as challenges you can and will meet.

There is no better place to start than to go after Challenge No. 1 – AIM – the subject of this issue of Ervin's Technical Bulletin.

Download the Technical Bulletin here.

or Call Ervin Today at 1-800-748-0055

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