I have a Compressor which delivers air to a Resevoir Tank (about 2 diameter by about 4 foot long)- in between them is a Delair System to "dry" the air.

This air then goes to my machine to support the X, Z slides and the spindle.

My problem is that since it's freezing outside, the air seems to be chilling the spindle and slides giving non- repeatable results as the spindle warms and cools along with the slideways.

What do you reckon to sticking some sort of heating around the Air Resevoir Tank? Or is there a risk it would cause something to go bang?

The whole system is operating around 120 PSI

Many thanks in advance.

Is the machine driven by air?!

Thanks for replying :)

Yes, it's an air bearing spindle, the axes are "raised" by air and are moved by precision leadscrews with optical encoders to get the position feedback.

Additionaly, it's parked exactly by the back door where I go for my ciggy break... I really don't want bolts, nuts and bits of pipe whirring by my ear at 120 PSI if it does go pop! :)

Heating it up would be ok as long as the tank is not completely sealed during the temperature rise and you don't go crazy with the temp. Just like when you first fire up a hot water heater - you have to leave a hot water spigot cracked slightly to bleed pressure increase - you might want to allow for a small air leak during the tank heat up process to eliminate the temperature induced pressure build in a sealed vessel.

What is the CFM of the operated devices on the machine? Is it the main volume consumer from the compressor? My thought would be to warm the air for the machine only and leave the rest of the supply alone, but I don't know your set-up. If your compressor mainly serves the machine alone, then what you are talking about makes sense, I suppose. I think you might have a better chance by heating the supply line or building a heating section in the supply line. Without getting rediculous with cost, I am not sure how you could get enough heat in the air in the tank - seems like it might be easier to heat a few lengths of copper pipe (depending on volume) with self-regulating heat tape - or something like that.

This is an interesting dilemna....

Scott

Surplus Center has a few reasonably prices pressure relief valves;

http://www.surpluscenter.com/item.asp?UID=2005113008435010&item=4-1370&catname=

http://www.surpluscenter.com/item.asp?UID=2005113008435010&item=4-1536&catname=

Thannks Mx. I opened the compressor up and had a look for the CFM rating but couldn't find it. It's got to be reasonably high though:the actual pump itself stands about 2 1/2 feet tall and is around 3/4 foot diameter. It has an 8 litre capacity.

I'm thinking though that if I heat the pipes themselves when they come back into the building I will have the opposite problem- ie air too hot: the spindle does have liquid cooling but it's boke, so I might fix that and try your suggestion.

Thanks Beaker, my releif valve at the moment looks a bit grubby and rusty... I think that could do with replacing anyway :)

I have to assume that the air supply is rigid pipe, most likely steel pipe...if this is so then pick-up a few of those pipe warmer strips that you wrap around water-pipe and plug into an AC source to keep outside water pipes from freezing.

If the pipe if flexible...as in rubber / neoprene house then you could coil up some and immerse it into a container filled with water, the container and water being warmed by something like a hot-plate.

The tape you are talking about - self regulating heat tape - I just don't think it has enough arse to make much of a difference in such a dynamic application - it's made to overcome environmental changes, not processing changes.....hence the reason for the questions concerning volume.

Good suggestion with the hot plate, Viper. That's a very good idea - a coil of copper tubing submersed in warm water in a bucket - easy to regulate and control, easy to build, safe.....good idea!

Scott

Be sure to keep your tank drained! The water could freeze and that could/will cause the tank to blow.

Wouldn't the air expansion [cooling effect] at the spindle pretty much negate the effect of heating the source? I would think you would have to heat the source pretty significantly to make any difference at the spindle.

Quite a few good ideas there, many thanks! The pipes are 1.5" dia plastic and go stright from the compressor up to the ceiling level. They then enter the building and go across the roof to my lab.

I'm gonna see if the boss will fork out for a new air "dryer" with temperature control :) although I can hear the answer already hehe

Air bearings/spindles, slides in total will use a fair amount of air. Using that much air will cause the cooling effect that you have described. Due to the amount of air that you are using, heating the tank or lines will have little effect. You could even heat the tank with a torch and have only a marginal increase in temp. From your description it sounds like the compressor is outside and so is it's intake, sucking up all that cold air. The compressed/heated air is being fed into a cold tank and pipe.

If you can move the compressor inside or at least run a hose from the intake to the inside where the air is warmer or bring the high pressure line inside right after it exits the tank, don't let it run up the wall outside.

Last resort, get the liquid cooling working again and run warm water thru it but that would only take care of the spindle and not the slides.

heh! like the Signature :)

Good idea on the taking air from inside the lab and sticking it into the intake of the compressor.

Cold outside air will contain less moisture per volume then warm inside air at the same
relative humidity. When it is warmed up the relative humidity goes down, ie.
drier air.
What I think you need if the tank is outside or colder than the usage point, is
to heat the tank to about 40F, this will allow the tank to act as a air drier and
allow you to drain the tank. The air drier should be after the tank for the final
moisture removal. During warmer weather it will operate the same way but the air drier will, do most of the final moisture removal.
A air drier should be after the storage tank in all cases, otherwise it uses most of its energy cooling the hot air and not generating a dew point condition, use the tank or storage for the initial cooling, then the drier for the moisture removal.

I have one question. Is the plastic pipe rated for compressed gases? Isn't there some OSHA rules for temperature and pressure? Cold temperature would make the pipe more brittle.

*edited* To slow my,idea was already given hehe *edited*

Quite a few good ideas there, many thanks! The pipes are 1.5" dia plastic and go stright from the compressor up to the ceiling level. They then enter the building and go across the roof to my lab.

I'm gonna see if the boss will fork out for a new air "dryer" with temperature control :) although I can hear the answer already hehe

I am amazed that you have got away with plastic pipe for compressed air especially knowing how picky the safety laws are in the UK. You literally have a 1.5" diameter bomb running across the building.

This is something that should be corrected if you want to remove the possibility of having chunks of plastic shrapnel whistling past your ears at around the speed of sound.

But to get to your main query; what I get out of reading it is that your problems arise from varying air temperatures not cold air per se. When your machine is not operating the air in the pipe inside the building equilibrates to room temperature but when the machine is running the air does not spend enough time in the pipe to come up to room temperature. You start the machine and initially it is running on room temperature air but then after a short while it gets hit with cold air. The temperature transition is probably abrupt so the machine is differentially cooled which can be expected to cause all manner of problems in maintaining precision.

My suggestions is to fix two problems with one solution. The plastic pipe must be replaced; your personal safety requires that even if it was not illegal, which I am sure it is. Replace the plastic with something like 1.5" schedule 20 galvanized pipe and replace the straight pipe run with a labyrinth long enough to be confident the air spends enough time in the pipe inside the building to equilibrate to the building temperature when the machine is operating. You may have to find someone to do a calculation for heat flow across the pipe wall to get an estimate of the wall area needed and may find it is more efficient to run four 0.75" schedule 5 in parallel between two manifolds. This gives you the same interior cross section for the compressed air flow but twice the wall area of thinner material so the heat flow is better.

Jesus! you got me scared now so I went and checked the Air Pipes! they are NOT plastic as I first thought *phew*- they are like blue plastic coated Aluminium (Aluminum for my friends in the States :) - it says the following on them: "Transair Tube Aluminium 37 X 40 calibre. PMax 37 Bar. SI 118738/003" Whatever on earth that means hehe *checks Bar to PSi*- 37 Bar= 537 PSI which is cool 'cos I'm only at 120 PSI. But, at least it's not plastic :) I got 6 pipes going overhead to supply my main machine and a second machine and air hoses and was scared sh*tless then!

I think I may propose the idea to my boss that I only work in the summer so that the air intake is warm enough... what do you reckon the odds are on the idea being accepted? lol

When your machine is not operating the air in the pipe inside the building equilibrates to room temperature but when the machine is running the air does not spend enough time in the pipe to come up to room temperature. You start the machine and initially it is running on room temperature air but then after a short while it gets hit with cold air. The temperature transition is probably abrupt so the machine is differentially cooled which can be expected to cause all manner of problems in maintaining precision.

Totally correct :) I try and minimise the effect by programming the machine to do a Warm- Up Cycle an hour before I come in in the morning and programme it to do an idle cycle between one copmponent and the next so it's never allowed to cool down... 'tis a stressful job :) but that's why I get paid hehe

In fact! I may propose that my boss moves me and the machine to the Bahamas lol... we can all wish hehe!

Jesus! you got me scared now so I went and checked the Air Pipes! they are NOT plastic as I first thought *phew*-

Scared is good! Scared probably lives longer than not scared.

Bahamas idea probably no good; simply invert problem. Move machine and operator to join compressor outside then all experience same temperature.

eeek! noooo! Manchester in winter is blinking freezing lol.

Problem has been almost solved- the machine that I check what I'm making on (called a Form Talysurf) was playing up- got the company that makes it to send in an engineer to service it- he says the optics were dirty which was dropping the laser intensity and that there's no way I would get good measurements at 16 degrees celcius, which is what my lab was at last week.

Got some more heaters and got lab almost up to 20 degrees- not quite the Bahamas but getting comfortable- not that I'm bothered by the cold (I'm Scottish), but the machines abviously feel the cold, poor things! *buys a fleecy jacket for the machine* hehe

Presumably if the Talysurf doesn't operate correctly at 16 degrees celcius, then my diamond turning lathe wouldn't either :( I was fighting against too many variables and didn't really have a chance!