Looking for a plastic/ceramic material USDA approved.

  • Thread starter Thread starter sgremore
  • Start date Start date
  • Tags Tags
    Material
Click For Summary

Discussion Overview

The discussion revolves around finding a plastic or ceramic material that is USDA approved, with specific properties suitable for use in a sealing application involving stainless steel components. The focus includes material performance under high temperatures, chemical resistance, and food-grade compliance.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant outlines the desired properties of the material, including a working temperature up to 500°F, low coefficient of friction, chemical resistance to caustic cleaners, and a coefficient of thermal expansion around 9.5 μin/in°F.
  • Another participant suggests using a Teflon tube for the air seal, questioning the pressure requirements and whether lubrication will be used, and mentions that 500°F is not excessively hot.
  • A ceramic sleeve made from Macor is proposed as a potential solution, although it is noted that its coefficient of thermal expansion is lower than the specified requirement.
  • One participant emphasizes the importance of thermal expansion for maintaining the air seal and proposes considering a bellows made from SS316 as an alternative.
  • A later reply indicates that the current material, Ultem, is failing due to chlorine concentration and mentions the high cost of Teflon as a concern.
  • Another suggestion includes a nickel-Teflon composite coating, though it is noted that this may not be cheaper than Teflon itself, and mentions other low friction composites that may not be suitable.

Areas of Agreement / Disagreement

Participants express various viewpoints on potential materials and approaches, with no consensus reached on a single solution. Multiple competing options are discussed, and the discussion remains unresolved regarding the best material choice.

Contextual Notes

Participants highlight limitations such as the need for food-grade materials and the specific chemical resistance required, which may affect the applicability of suggested solutions.

sgremore
Messages
2
Reaction score
0
I have been looking for hours tring to find a material with these properties.
Working Temperature up to 500° F
Low coefiecient of Friction
Chemical Resistance to Costic Cleaners (mainly chlorinated)
Coeffecient of Thermal Expansion around 9.5 μin/in°F
decent machine ability
made in 1/4" flat

The use:
it will bolted to a piece of stainless steel and act as a air seal while a moving piece of stainless is ran along the length of it. The force between the oposing conpents is not great just enough pressure to keep them touching.
 
Engineering news on Phys.org
So you want a sliding sleeve which can maintain a pressure seal (how much pressure?) Will there be any lubrication? 500 F = 260 C, so not very hot. You could probably use a teflon tube if the air seal will hold.

If you can use MoS2 (dry moly) as the lubricant you could use a ceramic sleeve. Macor is a machinable ceramic:
http://www.pgo-online.com/intl/kata...ceramic.html?gclid=CNfp4_72m7oCFasRMwodeG8Amw

There are many suppliers, and any experienced machinist can work with it - if they follow the directions! Requires sharp (new) carbide tooling, and obey the speed rules. Or you may be able to order the tube that you need. The coefficient of expansion is much lower than your specification.

Rather than look for something that meets all of your requirements, I would start with a vendor that has a good catalog of materials and sort down the list one property at a time, and see which is the most restrictive.

If you really want to maintain the air seal then the thermal expansion may be the critical issue. As an alternative why not use a bellows made from SS316?

http://www.flexicraft.com/Metal_Expansion_Joints/?gclid=CNqc5c_5m7oCFepFMgodezsAIA
 
Attached is the application, the friction or need of lubrication between the plastic/ceramic and the stainless is not nessecary also the movment is very slow maybe 6.0ft/min. We used Ultem and it is failing due to the chemical concentration of chlorine solution used to clean the machine. We thought about teflon but the cost is high. The length of this unit is 160' x 2 (both sides). Also the max temp is 360°F of this unit, and that is only at start up it drops down lower once all sections are running stable. The other big obsticle I am running into is that it needs to be Food Grade.
 
May be you could consider a nickel-Teflon composite coating, although probably it will not be cheaper than Teflon itself. There are also other low friction composites like the ceramic-teflon coatings used on frying pans but they are not so plastic. If you could use additional lubrication it would be easier for you to find an appropriate material.
 

Similar threads

Thermal insulating materials suitable for making piston and cylinder?
  • · Replies 6 ·
Replies
6
Views
2K