OK, I have a lifting problem at work and need to support approx 200Kg in a very controlled manner. Likely solutions include some sort of airbag inflated to take the weight and pressure adjusted to raise or lower the item.
Anyone know of suppliers of the lifting bags used instead of jacks for cars...I would prefer one working off compressed air rather than plugging into the exhaust gas of the car.
Alternatively, are inner tubes still available? If so what sort of weight might they support (lying flat on the ground with a circular weight supported on the doughnut of the inner tube) without a constraining wheel/tyre.
(The item is a very fragile spherical mirror 1.5m in diameter)
Thanks
StarGazer
Mods, hope this is motoring related enough! If not please move to the IHAQ thread.
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A very interesting question!
While an inflatable device will be able to provide vertical lift, it may not offer any rotational stiffness. If the mirror tilts, the air may simply displace, allowing the mirror to continue to tilt. This may, or may not be a problem in your intended application. If this is an issue, then it may be necessary to use a number of inflatable devices, indepentently inflated, placed under different areas of the mirror to provide tilt stiffness.
If you wedge an air bag under a car, tilt stiffness is not a problem, the other three wheels of the car provide that!
Is this the first time the mirror is being integrated into the intstrument. If not, how was the mirror initially integrated? If it is the first time, can the transportation fixture be used to enable the mirror to be lifted without applying any local stresses to the brittle mirror material. Have the manufacturers of the mirror issued handling and/or integration instructions?
A point which I suspect you are well aware of is that the slightest surface defect, if subject to tensile stress, can cause a crack that can propagate to fail in a brittle material with low fracture toughness. This I suspect is one of the factors which is making an inflatable lifting solution attractive, a) minimising the chance of introducing a surface defect, and b) distributing the applied force over as large an area as possible.
I hope that helps, please let us know if it goes successfully!
number_cruncher
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There are inflatable offroading equipment designed to lift 4WD, you may want to find one them.
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>>Mods, hope this is motoring related enough! If not please move to the IHAQ thread.
I'm fascinated. If you tell me what you're up to then I'll let it stay here, at least until you have an answer.
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OK, will try and post some pictures later today.
Basically I have a mirror 1.5m in diameter and 150mm thick which is concave and silvered on the upper concave surface. It is sitting in a box and I can lift it using slingsbelow and a lifting frame above. No problems with this.
To integrate it into an instrument it has to be fitted to a support frame which will then hold the mirror vertical. Once vertcal all the weight is taken by a band around the edge.
My problem is in supporting the weight while it is being attached to the support frame and band while horizontal. (the slings and lifting frame have to be removed by this point).
We had always intended some sort of airbag, my thoughts we going towards a car inner tube as it will spread the weight, have no hard points and is toroidal in shape so the convex rear surface of the mirror will sit very stably in the inner tube. Also once the support frame has been moved to the vertical and the weight taken by the band the inner tube can be deflated and removed.
I have no problems with the mirror handling....this is a small one for me! but I havent seen a car inner tube since I was a kid using it to shoot the rapids at Symonds Yat. Looking on the web I find many trade suppliers prepared to offer bulk discounts but I only want one! I havent tried calling KwikFit yet but I may have to resort to them.Probably looking for 600mm outside diameter.
Alternatives might be the inflatable jacks used by fire engines, 4*4s etc but as number cruncher mentions I would require at least 3 to make the support stable to sideways movement. Also the ones I have found this morning on the web are rather large. I am looking for a small 30cm diameter pad if I have to use three individual supports.
So I am really looking for inner tube shops where I can buy just one! Or any other bright ideas?
cheers
StarGazer
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Lots of commercial vehicles still use inner tubes, including tractors and diggers. Your mistake might be that you are looking for a car supplier.
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Thanks Mark, now looking promising, the idea of a car inner tube was one of those late night 'bright ideas' but I havent seen one for ages. A truck or digger sized one looks to be ideal and my engineer says the loading should be ok. Now phoning around trying to locate a supplier.
cheers
StarGazer
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Hi Stargazer,
snip -------8<------------
We had always intended some sort of airbag, my thoughts we going towards a car inner tube as it will spread the weight, have no hard points and is toroidal in shape so the convex rear surface of the mirror will sit very stably in the inner tube.
snip -------8<------------
Although I haven't tried it, I'm not at all sure a car inner tube would provide the stability you describe.
If, say, you don't have the centre of mass of the mirror directly above the centre (of vertical support) of the inner tube, then one part of the mirror will tend to compress the inner tube more. Air will simply leave this part of the circumference of the inner tube, and squish round to a relatively unloaded part - the inner tube will not develop any proportional, stiffness type, force to resist the motion. Your mirror would continue in its motion unless you also restrain it by other means.
I think that the use of a number of independent inflatable devices, possibly inner tubes, is necessary to avoid this problem.
number_cruncher
p.s., at a guess, do you work at ROE?
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If, say, you don't have the centre of mass of the mirror directly above the centre (of vertical support) of the inner tube, then one part of the mirror will tend to compress the inner tube more. Air will simply leave this part of the circumference of the inner tube, and squish round to a relatively unloaded part - the inner tube will not develop any proportional, stiffness type, force to resist the motion. Your mirror would continue in its motion unless you also restrain it by other means. I think that the use of a number of independent inflatable devices, possibly inner tubes, is necessary to avoid this problem.
Placing the centre of mass of the mirror in the centre of the inner tube is not a real problem, the support frame will give some stiffness but cant take the weight in the orientation.
Problem with several independent airbags is thet to raise or lower I would need to adjust 3 supports (or connect all 3 together).
number_cruncher p.s., at a guess, do you work at ROE?
No, see my profile, should be able to work it out
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The offset centre of mass was just one possible disturbance that the inner tube alone would not be able to resist.
If you have other means of providing restraint for uncontrolled motion in place throughout the operation, then my comments about stability are not applicable.
Connecting the air supply to all three inner tubes together would give you the same near zero roll/pitch/tilt stiffness problem I was talking about.
number_cruncher
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I think the fire brigade type airbags would be a mistake as they would tend to be unstable. with no weight on them they attempt to become a sphere. A suitable diameter lorry tyre sounds ideal with the one provisio - they can deflate in milliseconds if punctured.
Martin
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If sudden deflation of the solitary lorry inner tube would be a likely problem then how about a small car tube inside the lorry one as a back up in case of catastrophic failure?
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How about a tractor inner tube with a lorry one inside it? Would have thought if you put a fairly high pressure inside it then you probably won't have too much problem with it tilting. Think to the inflatable rings you get at the beach and they can be pretty solid if sufficient pressure is used.
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