Unique Problem With Air Tool...

[Joe AutoDrill]

I'm copying both the metalworking and woodworking groups. I hope this doesn't piss anyone off too badly. I believe the answers and knowledge that may get passed around is mutually beneficial. Thus the breach in newsgroup etiquette.

Anyhow... I've got a unique problem.

I sell a product that acts basically like an air cylinder. It has a tube (hard chrome plated inside for you metal guys) with a quill (hard chrome plated also) and some rubber seals inside.

One of my customers is a medical giant. They can't have ANY type of lubricant in the cylinder as they run the drill or the FDA comes in and gives them hell.

So... They basically super-dry their air with a desiccant and dryers so that it is down to 0.01% humidity or less and use absolutely no oil whatsoever inside the unit.

After 2-3 years of running like this, the unit doesn't stroke so well. The seals are dried out and the cylinder, although still sealed properly, needs up to 80 PSI air to stroke at all. Normally, they stroke at 15 PSI or so...

Anyone know of a lubricant that could be used that would not cause medical (food grade or better maybe?) issues?

Can't use oil, grease, dry powder stuff, etc. Can't even use water...

I was thinking something like medical grade alcohol or acetone that disappears all by itself if it gets to the atmosphere... But I bet there is a better option.

Thoughts?

As a side note, the tube and quill will stroke millions of times with no lube without wearing out. We've done long-term tests... The tolerances between quill and tube are around 0.001" and the quill diameter is around 3" if it matters.

Having just read a bunch of posts about air tools and proper lube made me think that there might be an expert in here with some ideas...

Regards, Joe Agro, Jr. [phone]

01.908.542.0244 Automatic / Pneumatic Drills: Spindle Drills: Tapping: Site:

[Ignoramus32217]

I see this as a win-win situation, an opportunity to sell them a new cylinder every couple of years, and charge them $100 per hour installing said cylinders.

i

[Pete C.]

I suspect you need to simply change the seal material. Possibly something like a teflon seal would do the job, not require lubricant or dry out.

[Proctologically Violated©®]

Hear ye, hear ye, Merka at its finest!

But, donchaknow, who ultimately winds up footing the bill, and where does sed bill get shoved?

Inyway, maybe a seal that itself wears/self-lubricates nicely, like mebbe teflon, delrin, nylon, some composite?

Chemically speaking, anything with a lubricating viscosity is not likely to evaporate quickly, and vice versa, and then you'd proly need fairly copious amounts of it, as in a bath of sorts.

But, if contamination/biocompatibility is the Fed's real issue, mebbe a joint-type synovial fluid would be acceptable? But the R&D, approval, alladat would no doubt be prohibitive for you, unless the company is really gung ho and will foot the bill.

My understanding is that AstroGlide and the new KY jellies are perty bio-compatible, and if they work on the cylinder, mebbe you could skim some off the top, and give the ole marriage a li'l boost, eh? Speaking of cylinders'n'shit....

But sheeit, iffin they charge any more for this g-d astroglide/KY jelly shit, I may just have to resort to foreplay..... goodgawd.....

[Joe AutoDrill]

I can't "stretch" the teflon seal over my quill to get it to the seal groove... I might be able tu cut it, but then they might complain about air leakage.

[Joe AutoDrill]

Yep. And they've got a bunch of 'em... But I feel guilty workign that way if a simple answer might exist.

I told the guy (joking around) to use "slippery air" like Argon or Nitrogen and he thought I was serious. I felt bad about that too. :)

[Leon Fisk]

Have you looked into what kind of seals they use in the oiless air compressors? I understood that it was some sort of teflon seal. Maybe you could duplicate whatever they are doing...

[Tom Watson]

Is the MTBF on this unit significantly less than other elements of the system that have a similar, or greater replacement cost?

Regards,

Tom Watson

[Leo Lichtman]

Some random thoughts: Since you can't stretch the seal to get it into the groove, how about unscrewing the end of the piston to expose the groove?

I once toured a tea-bag factory, and they were using a special non-toxic lubricant on the staple wire (holding the string to the bag.)

How about using a teflon liner in the cylinder?

How about making the piston out of teflon or nylon?

[Joe AutoDrill]

Unknown.

Regards, Joe Agro, Jr. [phone]

01.908.542.0244 Automatic / Pneumatic Drills: Spindle Drills: Tapping: Site:

[nhurst]

I just replaced the piston and sleeve on my oiless air compressor last week. The seal is clamped between the head of the cylinder and held in place by a screw. The teflon is just a ring that seals against the sleeve and slides back and forth.

I was under the impression that teflon is carcinogenic if ingested, which is why you should toss pots and pans with flaking teflon on them.

-Nathan

[Joe AutoDrill]

The quill is a solid piece of steel machined to spec. Nothing to disassemble.

Wonder if it was tea flavored?

Tolerances are too close. Liner would have to be 0.0005" or less or the quill would have to be resized and re-chrome plated, then reground... Redesigning the machine is not an option. It would be like saying to change the engine on a car to solve a fuel problem.

Not nearly durable enough. Plus, it goes back to the redesigning the machine thing.

If I can't find something to simply inject into the system that fixes the problem, they will have to run dry.

Regards, Joe Agro, Jr. [phone]

01.908.542.0244 Automatic / Pneumatic Drills: Spindle Drills: Tapping: Site:

[Tom Watson]

It would be interesting to know this.

"Failure" could be an applied metric that references PSI needed to cycle, or a specific cycling rate. At a certain point either of these could become critical to the proper functioning of the system.

If your unit has a MTBF that is in line with other elements of the system, it would be reasonable to conclude that there is a MTBF for the system as a whole and that the replacement of your unit would be covered under general maintenance, making your product immune from being singled out as the primary cause of system failure.

Regards,

Tom Watson

[RicodJour]

You are breach-free in this instance. Cross-posting is preferable when the topic pertains to two groups as it will eliminate most duplication of answers.

As others have said, Teflon comes to mind first. Perhaps you can warm the Teflon to a more plastic state and slip it into place?

Wiki had this to say about PTFE: "Due to its low friction, it is used for applications where sliding action of parts is needed: bearings, bushings, gears, slide plates, etc. In these applications it performs significantly better than nylon and acetal; it is comparable to ultra high-molecular weight polyethylene (UHMWPE), although UHMWPE is more resistant to wear than Teflon. For these applications, versions of teflon with mineral oil or molybdenum disulfide embedded as additional lubricants in its matrix are being manufactured."

and this: "Other polymers with similar composition are also known by the Teflon name: * PFA (perfluoroalkoxy polymer resin) * FEP (fluorinated ethylene-propylene) They retain the useful properties of PTFE of low friction and non- reactivity, but are more easily formable. FEP is softer than PTFE and melts at 260 =B0C; it is highly transparent and resistant to sunlight."

Your answer will probably be in there somewhere.

R

[Joe AutoDrill]

Not a concern. They are happy with the unit and are even happy sending it back to us for rebuilds regularly... But I always look for a bettr answer for my customers. No need to shaft them if there is a simple answer out there someplace. I sell enough untis that rebuilds don't make a difference between cold cereal and steak for dinner.

[Doug Miller]

In article , "Joe AutoDrill" wrote: [...]

Surely the FDA has a list somewhere of approved lubricants?

[Pete C.]

"Coiled" teflon backup washers are pretty standard items in pneumatic and hydraulic components and they can be coiled into a groove. The air pressure should push the coil together enough to minimize leakage.

Also take a look at the V-ring seals on McMaster.com, they look like you could cut them and have minimal leakage as long as you stack them with the cuts located opposite each other as you stack them.

Another possibility on McMaster.com is the "Spring loaded PTFE shaft seals" which may have enough play to let you fit them.

[Tom Watson]

KY?

Regards,

Tom Watson

[dpb]

Joe AutoDrill wrote: ...

...

...

Not on a direct solution, no...

Curiosity--is this in an actual medical device or used in the manufacture of a device? Might have bearing on how to approach, I don't know.

Only suggestions I would have would be (a) have you tried working w/ the FDA "advice/guidance for approval" side instead of enforcement? Same overall organization but different hats. Not my baliwick but coworker did some consulting work in medical device area and actually did get some useful feedback that way, and (b) any chance you could find somebody in local/state university w/ the med school/med-engineering school in the field that might talk to you?

--

[Chris Friesen]

Don't think so, they use it for surgical purposes. I believe the problem with flaking teflon on pots is that it exposes you to bare aluminum underneath which has been associated (though not definitively) with Alzheimer's. That said, plenty of restaurants cook on bare aluminum.

Chris