Frosty Posted May 13, 2016 Share Posted May 13, 2016 Welcome aboard Mike, glad to have you. If you'll put your general location in the header you might be surprised how many of the IFI gang live within visiting distance. Just telling us in one post isn't going to stick to our memories once we open another one. Most blades on blower impeller fans are straight or angled into the direction of rotation. They also fit the case much more closely even a snail like yours. The place to search for wicked cool home made blacksmithing equipment is the 3rd. world. I can't find the file or link but there was a series of pics of a vendor in Viet Nam, I believe, who sold hand crank blowers made from bicycles and tin cans. The shells were made from all kinds of . . .things. What RPM are you shooting for? I don't know if you're going to want to drive that directly off a motor, that's a BIG impeller fan and it looks very heavy. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Teachagmech Posted May 13, 2016 Share Posted May 13, 2016 well judging by the calculations earlier in this thread, somewhere in the neighborhood of 2000 rpm. if I can get away with lower, i'll reduce the speed by either a speed control or rigging a jack shaft and belt drive. Like I said, if nothing else, its a fun project to say I've built one. Also, the backward spiral on the vane design can increase the air velocity at the tip of the fan blades, thus increasing pressure. I may end up going for a 3rd revision on the fan blade assembly and making an even steeper backward pitch to lessen the volume of air, but increase the pressure at the outlet. I'm not a fluid engineer either, but this is what my research has lead me to believe. The rotating portion of the fan is only made of 3/16" plate and weighs only slightly more than a new grinder wheel. If I burn up the grinder motor, I'll know it was too heavy. if it works well enough but is too big, I can always build another smaller version. Like I said originally this was going to be a hand cranked blower so I was looking for larger diameter to get the critical blade speed with lower RPM. Now that I'm putting a motor on it, I can easily go smaller which would be less strain on the motor which will let it run closer to its no load speed of 3600rpm. Quote Link to comment Share on other sites More sharing options...
Frosty Posted May 13, 2016 Share Posted May 13, 2016 I'm not saying it's a bad design and I can't do the math, just because the diagrams you present are counter intuitive doesn't mean anything. LOTS of stuff is counter intuitive and I've been wrong so much in my life it doesn't bother me anymore so long as I don't endanger: (in order of importance) Other people, Myself, Other's property, My property, including tools. Finishing a project falls behind those requirements. It's been many years since I saw a flow diagrams for impeller blowers. IIRC the forward curving blades cause the flow to move faster than the impeller. I can't say about a backwards facing blade impeller, there wasn't a diagram let alone a flow chart for one in the blower book I was looking at. I was killing time at the heavy duty shop waiting for a quick fix on a piece of equipment. I'd read through operator, parts, repair, etc. manuals rather than slow jobs down helping. I didn't read any of it, I skimmed the: pictures diagrams, charts and headers. The blower manual caught my eye because I was wondering why the vanes in my Champion 400 were straight tube sections. All that said is just to admit my opinion is far from expert, it's "seesay" sort of like hearsay. The flow charts for the exhaust side of a turbo charger was really bewildering. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Teachagmech Posted May 13, 2016 Share Posted May 13, 2016 Bewildering is an understatement! I'm fascinated by them. Don't know how variations do what they do, but it's neat to see. Update: the poor little bench grinder is gonna burn up before the fire ever gets hot. I bent the vanes about 30 degrees further, rebalanced the rotor, and noticed a pretty substantial pressure increase. Not as much air, but is much more resistant to cavitation. I'm gonna make a Jr version. Closer to 7" I think. Quote Link to comment Share on other sites More sharing options...
Teachagmech Posted May 20, 2016 Share Posted May 20, 2016 alright, well I have success! my blower Jr has a 7.5" diameter wheel. its driven off of a broken bench grinder motor. the smaller fan size allows the grinder motor to come off the start cycle, run at almost full rpm, and doesn't show many signs of getting hot. I've fixed a shroud around the motor to direct the intake air over the outside case of the motor to help aid in cooling. its a bit noisy when running open with no restriction, but quickly quiets down when a load is placed on it. Now to build the forge! as you can see below, the grinder motor has seen better days. the guard broke off and took a chunk of the bearing support with it. that side is pretty useless, so I just cut the end of the shaft off. The intake shroud is 22ga galvanized sheet that I had lying around. I hemmed the edge and sent it through the roller to kinda match the radius of the snail. the tab tack welded to the end was just to add a little load to the fan to quiet it down. i also recut the cover plate to restrict the intake air to the motor side. I ended up cutting the other opening larger. still to do: replace the power cord build the forge make fire shape metal! Quote Link to comment Share on other sites More sharing options...
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