INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Gas impermeable plastics suitable for ultrasonic welding

Gas impermeable plastics suitable for ultrasonic welding

(OP)
I am looking for suggestions of a plastic I can use as a gas impermeable package. The key is that this plastic needs to have a low permeablility, good strength, and also be suitable for ultrasonic welding. Any help or advice would be greatly appreciated

RE: Gas impermeable plastics suitable for ultrasonic welding

Mylar might work. Note that permeability is as much a function of how the product is produced and its form as it is about the base polymer.

Butyl rubber is not a plastic, but has very low gas permeability.

Matweb.com has gas permeability coefficients listed for a variety of polymers, typically films. Some films are less permeable to polar molecules, and vice versa, and thus you may find that a multi-layer composition would work best, depending on the mix of gases you are trying to seal.

RE: Gas impermeable plastics suitable for ultrasonic welding

(OP)
Thank you. I will be sealing pressurized nitrogen in a molded plastic package. Would Mylar be conducive with ultrasonic welding?

RE: Gas impermeable plastics suitable for ultrasonic welding

(OP)
Is it possible to mold mylar? My understanding was that it is used primarily in films. I would need a robust plastic that would be acting as a housing for other parts.

RE: Gas impermeable plastics suitable for ultrasonic welding

No polymers are "impermeable". The question is how much permeability can you tolerate. Mylar is a brand name for DuPont Polyester films. The films are usually highly oriented so heating them to the melt point will usually result in tearing or very weak seams

RE: Gas impermeable plastics suitable for ultrasonic welding

And, how much pressure are you going to seal, and whether the rest of your system is up to the task of sealing in pressurized nitrogen?

We once had an interesting discussion, during a design review, about whether we needed a bladder, a pressure relief valve, or some such, to handle the pressure changes from temperature in the pressurized dry nitrogen we were putting into a test instrument. When the system was actually built, the first time we purged the system, it was so leaky that the pressure drop to ambient in about 30 seconds.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers

Of course I can. I can do anything. I can do absolutely anything. I'm an expert!

RE: Gas impermeable plastics suitable for ultrasonic welding

(OP)
The pressure of the sealed nitrogen will be 22 psi at room temp and the max operating temp of the part will be 150C. We are essentially attempting to change from using a metal can and epoxy too acheive a hermetic seal, to using a ultrasonically welded plastic container. That being said, the application is in automotive so the permeability of the pastic will need to be low enough so the nitrogen will not leak for the life of the part.

RE: Gas impermeable plastics suitable for ultrasonic welding

Nylons ultrasonically weld pretty well and are compatible with automotive environment. There are about a million grades, fillers, additives, etc. Permeation is a function of permeability, area, thickness & time. You need to specify how much permeation you can stand. How long is the life of the part? How much of the nitrogen can leak out?

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Gas impermeable plastics suitable for ultrasonic welding

Note that adding a high aspect ratio grade of a platy filler can help your barrier properties. Look for a the highest aspect ratio mica you can find. Mica filled polymer grades are commercially available.

Chris DeArmitt PhD
President - Phantom Plastics LLC

Consulting, ideas and training on plastic materials
www.phantomplastics.com

RE: Gas impermeable plastics suitable for ultrasonic welding

A 150C polymer pressure vessel?! Very unlikely.

RE: Gas impermeable plastics suitable for ultrasonic welding

"Would Mylar be conducive with ultrasonic welding? "

I think you can ultrasonically weld the films and have them hold up okay, but as CP said, I think these are multi-layered films where an inner bondable layer for welding is included in the construction. The films are produced with the idea that impermeable bags be made from them, for e.g. food products and/or medical products where oxygen spoilage or contamination with water vapor are issues.

"Is it possible to mold mylar?"

Getting low permeability from a molded part is more of a crapshoot, for reasons the real experts above have noted. It is possible to add metallization, and other barrier coatings, which can affect permeability.

"the permeability of the pastic will need to be low enough so the nitrogen will not leak for the life of the part. "

That is a non starter, in my opinion, but you don't state what the "life of the part is" - I'm assuming something more than 1 year. It might be possible with a fairly heavy metallized polymer, multi-layer construction. That said, I'm not certain that even the metal can with epoxy seal would hold up for multiple years - has that ever been tested? I.e. if this is an arm-wave goal and not a hard spec., and the real requirement is that the unit simply function well over the years, then maybe.

What is the real reason for the nitrogen blanket - is it to prevent moisture intrusion? Oxygen intrusion? There are absorbers or "getters" for these contaminants, which if included inside the capsule could help.

RE: Gas impermeable plastics suitable for ultrasonic welding

(OP)
Thank you all for the help. We would like the shelf life of the part to be around 10 to 15 years, however we have yet to define an exceptable amount of nitrogen leak in our spec. The nitrogen within the part is primarily used as a dielectric and arc extinguisher. The main spec involved with the nitrogen is that the voltage must be able to be ramped to 12kV without arcing across the contacts. If this spec is not met, it is assumed the nitrogen level within the part is too low. That being said, the execptable amount of nitrogen leak would still always have to pass this 12kV test.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close