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  • Air Compressor Question

    Hello All,

    I just wanted to say first off, thank you for the valuable information that everyone posted on the other topic I recently brought up. I recently did some powder coating jobs for the first time and they worked out perfect! Thanks for all the guidance!

    This topic, however, is about basic specs on my brand new air compressor. I have a 1.5 hp 33 gal air compressor that is rated SCFM @ 40 psig = 6.3, and SCFM @ 90 psig = 4.9.

    Because I am trying to get a sandblasting cabinet, I want to know if this compressor will handle a 5-7 CFM sandblasting cabinet/job, but I was unsure if SCFM is the same as CFM or if they were possibly different.

    That's were you guys come in!

    Thanks for the help and look forward to all your contributions!

  • #2
    Re: Air Compressor Question

    John Henry;
    Pop over to the "Other Metal Finishing Questions" list and read the posts in the "Advice on a serious sandblaster" thread..
    Sandblasting, like electroplating, powdercoating, etc. "looks easy", but there is a lot of knowledge and "tricks of the trade" behind the scenes..
    I'll tell you right now, the "Siphon Feed" type blasting guns aren't worth blowing up.. they often require 90psi just to work.. You will burn up a 1.5HP/33CFM Compressor trying to blast with a siphon feed gun..
    Get a Pressure Pot blaster, about a 100lb capasity minimum, dial the compressor output air down to 60psi and input pressure to the pressure pot to 50psi and blast away! You'll save your equipment AND get the job done before you retire. ;-} (and get a "real" 5hp, twin cylinder, two stage, 60/80gal tank compressor),
    I use my Pressure Pot blaster in a dedicated "blasting room" as well as in my cheap, plastic, Chinese made blasting cabinet.. It does everything I need it to do.. (I restore cars!)
    Charles

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    • #3
      Re: Air Compressor Question

      If you plan to blast at no more than 40psi, then it may keep up for short bursts. I don't know what you would blast at 40psi except to clean soft metals. Stripping paint would be an arduous task except for maybe rattle-can lacquers. Your tip would probably be no larger than 3/32" so you'd be limited in the media you could use. At a usable blasting pressure of 80-90psi, you're going to be waiting for the compressor to fill the tank.

      Figure about 25-50% duty cycle--Blast 15 seconds, wait one minute. (If your rated cfm is close.) Check your pump output. A 33gal tank is about 4.4cf. Time how long it takes to fill an empty tank to 90psi. At a pump rating of 4.9, it should take less than a minute. Delivery FROM the tank will be at a much higher flow. Normal 1/4" fittings will flow about 20cfm at 90psi. With media, it's reduced to about 15-17cfm at the tip. At 15cfm, your tank will empty in about 15 seconds and will take about a minute to refill. If the blast cabinet is rated 7cfm (tip size dependant), then you can blast for about 37 seconds before stopping and waiting for the pump to catch up. With a small tip, blasting one square foot could take over 10 minutes of blasting time plus the wait time. If you can live with that, then it may work for you.

      Yes, CFM and SCFM refer to the same thing. BUT, manufactures don't test each machine. The rated SCFM is a design rating for the pump at a certain rpm. The output could be (and usually is) much lower due to the regulator, fittings and hoses. To media blast with any measurable progress and remain awake, you should look at a minimum of 15-17 SCFM @ 90psi compressors. More air (cfm) means faster work so the bigger the better.

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      • #4
        Re: Air Compressor Question

        oops, sorry if I posted in the wrong section, but thanks for the info. I guess I will just buy one of the pot blasters and wire into a cabinet to make it a little easier on the air compressor.

        Thanks again!
        Last edited by John_Henry; 05-12-2009, 08:58 AM. Reason: spelling

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        • #5
          Re: Air Compressor Question

          you can pretty easily build a a cabinet, It doesn't have to be fancy, just a box with a door, a window a sloped bottom and some holes for your gloves


          i didn't follow any plans and just slapped one together out of scrap plywood, nothing really to it






          and since you have a small air compressor, you can use an angle grinder with a wire wheel to do most of it, and just use the blaster for touch up

          Comment


          • #6
            Re: Air Compressor Question

            Originally posted by John_Henry View Post
            oops, sorry if I posted in the wrong section, but thanks for the info. I guess I will just buy one of the pot blasters and wire into a cabinet to make it a little easier on the air compressor.

            Thanks again!
            before buying a pot blaster you better check first for the cfm requirement needed to run it , i might be wrong but i don t think you will have much success with a pot blaster with the compressor you have
            http://www.peintureenpoudrepb.com
            http://www.polissagepb.com
            http://www.powdercoatpb.com
            baz

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            • #7
              Re: Air Compressor Question

              but a pot blaster should use less air then a siphon feed, right?

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              • #8
                Re: Air Compressor Question

                Originally posted by j4str View Post
                but a pot blaster should use less air then a siphon feed, right?
                Not really. They actually take more air. Some of the air moves through the pressure pot to force the media into the mixer stage. That portion of the air flow is reduced as it carries the media. They're just more efficient with the air they use and the media flow is adjustable.

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                • #9
                  Re: Air Compressor Question

                  so which then, would be more feasible recommendation for this size air compressor?

                  a pressure pot or a siphon fed sandblaster?

                  I think I have become a little more confused, because I thought I could get a pot blaster that could hold anywhere from 80-100 lbs that would be suitable for the specifications on the compressor.

                  thanks for the advice guys.

                  Comment


                  • #10
                    Re: Air Compressor Question

                    I was thinking that this air compressor would meet my needs for a pressure pot blaster.

                    Eastwood Co. - Eastwood 100lb Pressure Abrasive Blaster

                    its the eastwood 100lb pressure blaster that requires 6-25 cfm at 65-125 psi.
                    I am not trying to use the thing for a production line, but for occasional jobs that I get on the side to prep for powdercoating.

                    Let me know what y'all think

                    Comment


                    • #11
                      Re: Air Compressor Question

                      The size of the tip and media type will make the difference. With your compressor tank size, you won't get much blast time and you'll be waiting for the tank to refill. As I said, the pressure blasters are more "air efficient" as they will work better than a siphon feed blaster even with the same amount of air. To use them at their peek efficiency, they do require more air though. As air flow drops off, so does the media flow unless you keep adjusting it. (Read monotonous PITA)

                      The time-numbers I presented above are for emptying your tank. Obviously, when the pressure drops below ~50psi, you're going to loose substantial blasting power. That size compressor just wasn't designed for blasting but the air tank can supply short bursts of blasting power.

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                      • #12
                        Re: Air Compressor Question

                        I think I would look for a compressor, but HF has a 100 lb pot blaster cheaper you may want to look at. But a small compressor will work itself to death for sure.

                        - Harbor Freight Tools - Quality Tools at the Lowest Prices
                        Who says you can't teach an ole dog new tricks?

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                        • #13
                          Re: Air Compressor Question

                          well i bought the "plans" Not much of plans, more or less a couple of pictures of a setup he built, with a light description



                          I won't give out his deep dark secret details of the "plans" but the idea is to feed a siphon feed gun pressurized media instead of making it suck it up itself


                          build a tank, apply 5-10 psi and route your siphon feed hose to the bottom of the tank.

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                          • #14
                            Re: Air Compressor Question

                            Plans? What plans? There's no secret to the way a pressure feed tank works. The media feed/mixer portion is probably the only critical part. I made mine. I could have saved you the price of the plans. Cripes, maybe I should start selling real plans.

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                            • #15
                              Re: Air Compressor Question

                              Maybe this is a stupid question, but is it the size of the pressure blaster (lbs that it holds) that creates a problem for the cfm specs of the compressor, or just the fact that it requires 6-25 cfm? If this is the case, could I just lower the size of the pot blaster to maybe 50 lbs even though it would take a bit longer to reload?

                              I mean at 90 psi on my compressor I am pushing about 5 cfm ( just one under the requirement). I was thinking that due to the size of the tank (33 gallons) I would be able to use my air supply to give me good little bit of blasting, and then give the compressor a rest. Like I said, I am not trying to use it for a continuous use here, it's simply to do on the side jobs. I wouldn't be running the compressor for an hour straight or anything.
                              Last edited by John_Henry; 05-14-2009, 06:15 PM.

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