View Full Version : Plastic lube? PVC Delryn. and milling tips?

04-20-2010, 03:35 PM
Hi I'm curious about a PVC valve in my hot tub. I had to replace the old one it was 12 years old chalky and galled. I have looked on the web for some kind of lube. All I can find as a reference is Stearic Acid as a mold release. Stearic Acid is a modified animal fat. I wracked my brain to remember what I had around the house that might have Stearic Acid and I thought NeoSporin might, I dunno, but that is what I used.;) It seems to work fine for now, but with time and heat I dunno.

Does anyone have a better Idea? I think the greasy stuff in the Neosporin might dry up and cake after some time.

Also I plan to machine some Delryn and when finished it will need some kind of lube too but it wont come in contact with human touch.

Oh and when milling Delryn can you please offer some advice for a first timer such as spindle RPM cutting lube requirements, clearances for brass slider operating under 150-180 degrees Fahrenheit. I want to make a solinoid driven diverting valve body for solar heated water. Oh yes, and do O ring seals hold up as a seal for a plunger in Delryn? Should I be using Delryn or something else like 6061 aluminum?

Thanks for your help and advice, from rainy California


Liger Zero
04-20-2010, 03:44 PM
Acetal resins are sensitive to acid (http://en.wikipedia.org/wiki/Acid) hydrolysis (http://en.wikipedia.org/wiki/Hydrolysis) and oxidation (http://en.wikipedia.org/wiki/Oxidation) by such agents as chlorine (http://en.wikipedia.org/wiki/Chlorine), for example. Thus low levels of chlorine in potable water supplies (1-3 ppm) can be sufficient enough to cause stress corrosion cracking (http://en.wikipedia.org/wiki/Stress_corrosion_cracking) to develop, a problem which has been experienced in both the USA and Europe in domestic and commercial water supply systems. Defective mouldings are most sensitive to cracking, but normal mouldings will succumb if the water is hot.

Widespread failure of acetal mouldings in potable and hot water supplies resulted in one of the largest class actions (http://en.wikipedia.org/wiki/Class_action) in the USA when acetal plumbing (http://en.wikipedia.org/wiki/Plumbing) fittings cracked and caused flooding of homes, a problem exacerbated by similar problems with polybutylene (http://en.wikipedia.org/wiki/Polybutylene) pipework. The acetal fittings tended to fail first, followed by the pipework.

I am working on a molding job and can't be distracted from the press for very long, but I will look into the issue a bit for you. I'm thinking based on the application a change of material may be warranted. This came from Wiki, BTW.

04-20-2010, 03:45 PM
Soapy water is usally one of the first I hear in refrence to plastic lubes.. I never liked the idea of water on my machines, So I just use generic rapidtap, works well, other then its a little dark and needs to be all wiped off afterwards. Doesnt seem to attack the plastic any... also a lot of work I just do dry, UHMW doesnt mind dry, Acrylic... Kinda likes lube but if you get feeds/speeds right, lube isent really needed.

If your looking for a lube for your old valve, go to home hardware and find some pottable water safe grease. Im pertty sure its plastic safe and its basicly designed for potable (drinkable) water valves and such.

04-20-2010, 05:07 PM
Thanks for the feed back.

I dont like the idea of water on my new HF 3 in 1 mill either. I'm pretty new at machining and materials. I'm retired from the computer industry, servers and Video Conferencing installations etc.

I learned something. When looking on the Internet for project info. I should check wikipedia first for interactions.

I guess in the machining world the knowlege one must have is akin to a Dr. One must know about chemical and mixed Material interactions plus the material's physics. It all makes sense. Other wise I would end up trying and erroring.

Thank goodness there are good folks like you around who are willing to share your experience and keep me out of the weeds.

Liger Zero
04-20-2010, 05:42 PM
No problem! It's good to have folks like you around as well, plenty of computer questions pop up on here.

04-20-2010, 05:57 PM
Nylon and Delrin (trade names) wear well together and often need no lubricant. I don't know if this helps you or not with your configuration.

Nylon does swell with moisture so that's something to consider. Some grades more than others.

Liger Zero
04-20-2010, 06:04 PM
There are charts on supplier websites that can help. Also the suppliers themselves will answer direct questions.

Delrin is NOT recommended for hot chlorinated water applications at all. Bears repeating.

I am "off duty" at the moment but possibly UHMWHDPE might be an option, depending on the grade you select and the ultimate temp of your application maybe even a PVC material.

04-20-2010, 07:28 PM
Here is a handy materials compatibility chart.Select your material and then the chemical you want to check and click submit.


04-20-2010, 08:50 PM
I have a small CNC trainer that uses plastic nuts for the leadscrews (the thing is rugged as heck!!!! Do not let that fool you, it is called an EXPERT MILL by Intelitek- Love their machines!). They use TRIGEL lubricant for this. Expensive as heck, but it works quite well, for I have had the machines since 2004 and there have been no bind ups. Put some on a plastic RV valve for a water diverter, little dab will do you, has worked well since then and freed it right up.

04-21-2010, 03:57 AM
According to the MSDS Trigel 300S is a 8.5% PTFE grease.
I love MSDS documents, they always show what's in the proprietary products :D