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Making a Blast Room Productive

August 8, 2013

markblastprep

Linked In Discussion with Claude                     

Claude:  We’re a powder coater company subcontracting surface treatment on metal parts. We want to improve our sandblasting process.

We have a 20′ X 30′ room with two operators (two 100 PSI hoses). We use aluminium oxyde and process HRS, aluminium and stainless steel. Specs are SSPC-SP6 to SSPC-SP10. We’re in operation up to 100 hours/week. I need to find a more productive and ergonomic approach. We want to build a new room and I’d like to find the most productive way to process this operation. Automatic system could be an option. We are a custom coater so we process a lot of different parts (more than 20 different models/day).

Mark Hanna

Mark Hanna

Hi Claude,

Let’s look at your situation.
First, why two operators? Labor is your biggest cost. Unless there is a lot of detailed work, I’d rather put that compressed air energy into one nozzle, appropriately sized for the job. (You would need a fairly strong blast man, of course, to handle it.)  Also, there are safety considerations having two guys shooting grit in a 20 x 30 room. To give you an idea (keeping other factors consistent), two guys running #4 nozzles might produce 300+ sq ft / hour and use about 200 CFM. One man using a #6 nozzle and about the same CFM could match or exceed that performance. Those rates depend upon a lot of factors of course, so this example is just for comparison. If your guy can handle it, consider a compressor upgrade first, and then size up the nozzle so that you can get the work done in 40 hours. That second worker could become a setup guy to speed things up, and the two could change positions during the day.

Nozzles could make a difference, too.  Some nozzle designs are up to 40% more productive than popular older nozzles. You might want to put a quick-change coupling on the end of the blast hose and change out nozzles to suit the immediate job at hand. (Ex: long venturi, fan, 45-degree, and banana nozzles). Replace nozzles when worn. Use high quality nozzles with long life liners.

What kind of media recovery system do you have? Two things to consider:  First, sweeping grit takes a lot of time and effort away from producing parts, so look into full recovery floors in your new setup.  Second, your recovery system should be fine tuned so that it is extracting dust from reused grit:  Blasting with dusty media is counterproductive.

Operator training is also important.  Operators should know different techniques. They should also have the equipment tuned properly. The grit valve should be set so that you are entering a minimum of abrasive into the blast hose because it is velocity that gets the work done fast, and too much grit slows the air stream. Buy a nozzle pressure tester because actual blasting pressure can be quite different than that at the air compressor, and it’s an inexpensive way to reveal an easy-to-remedy problem. Speaking of operators, do yours have appropriate respirators with heater / air conditioner?  Making the environment better can help boost operator productivity.

I see that you are using aluminum oxide, which is a great choice.  It works fast, is reusable many times over, isn’t dusty, and can leave a nice finish. What grit size is it? You’ll need to get the profile that’s indicated on the spec. But if you can move to a finer grit range you might get more work done, because you’ll have more particle hits per second. Again, this is job dependent, and some work requires a coarser grit to knock off heavy rust, etc. In my opinion, virgin alox holds up better and cuts faster.

How is the visibility?  You’ll want very good lighting and a dust collector that pulls at least 50 feet per minute cross draft: more is generally better. If you don’t have good visibility you’re likely doing a lot of rework.

Material handling: Consider how crane slots, turntables, dollies, rotisseries, racks (etc.) would help speed the operation and make it safer.  Of course, material handling that is best for you depends upon your variety of workpieces.

Automation may work, but it sounds like the variety of your parts would preclude a single type of machine. A robotic blaster could be the exception – I sold one for mold cavity cleaning and the productivity is phenomenal.

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