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Teflon vs PEEK valve seats
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(Mechanical)
(OP)
19 Dec 18 16:24Hi guys,
I am purchasing some valves for a client using their datasheets.
1. The CL 150 valves specify RPTFE seats however the supplier is providing filled PTFE and High performance PTFE seats.
2. The CL 600 valves specify PEEK seats however the supplier is providing Teflon seats.
Are these acceptable alternatives? What properties should I compare to deem these materials as acceptable alternatives?
(Automotive)
19 Dec 18 17:01Teflon is the brand name for PTFE, so it looks like whatever your supplier you're using is only supplying one type of seat (PTFE) regardless of what is specified. RPTFE is just Reinforced PTFE - in order to determine what was specified vs. supplied you would have to consult the specs for the exact material specified to determine the filler material (probably glass) and what percent fill.
I know its not helpful but it is highly dependent on your application. I can say though that if an application calls for PEEK, PTFE will very likely not be an acceptable alternative. PTFE has excellent chemical resistance over a broad range of chemicals, but PEEK has far superior mechanical properties - especially so at high temperatures. I believe though PTFE being a fluoropolymer has slightly better chemical resistance than PEEK. "Better" is a relative term here though - you would have to again look at the material specs for each to determine if whatever chemical(s) in your working fluid is compatible with the material specified.
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Polytetrafluoroethylene or PTFE is the commonly used versatile, high-performance fluoropolymer made up of carbon and fluorine atoms.
Apart from being used in the kitchen, PTFE is used as a cost-effective solution for industries ranging from oil & gas, chemical processing, industrial to electrical/electronic and construction sector, etc. of the common applications of this polymer is non-stick coating in kitchen cookware (pans, baking trays etc.), hence, you can easily find this in your kitchen.
Properties
PTFE's melting point is around 327°C, and pure PTFE is almost totally chemically inert, highly insoluble in most solvents or chemicals, and thermally stable enough to be used between -200 degrees C and +260 degrees C without degrading.
Strengths
Highly flexible
Chemical resistant
Non-stick and electrically resistantThermal resistant
Modified PTFE
Characteristic
Lower deformation under load (cold flow reduced by a factor of three)Stronger and more versatile than regular PTFE
Denser polymer structure
Reduced permeation of chemicals and gases Down to half of the standard PTFE value
Smoother surfaces on machined parts
Higher transparency
Excellent weld ability
Properties
TFM, known as PTFE-TFM, is polytetrafluoroethylene with perfluoropropylvinylether as an additional modifier, giving a denser material which is stiffer, also creep resistant like PFA, and weldable.
Strengths
FDA certified
Better creep performance
Good electrical and mechanical properties
Lower permeability
Glass Fiber filled PTFE
Characteristic
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It improves cold flow resistance and wear resistance, widely used for piston ring., bearing, like gaskets etc.
Glass fiber is the most commonly used filler in PTFE as it offers much improved compression and wear properties
The material may also be inert gas sintered to further improve creep properties and reduce porosity and gas permeability but please be noted that would be a consequent loss of tensile properties.
Properties
Glass Filled PTFE is reinforced with glass fibers with the percentage varying between 5% and 40% depending on the needs of the application. As the filler percentage increases so does the properties the filler offers (increased compressive strength, lower deformation under load) but conversely the coefficient of friction properties of the material increases over that of virgin PTFE.
Strengths
Wear resistant
Improved hardness
Lower thermal expansion
Lower deformation under load
Non-conductive
Weaknesses
Higher coefficient of friction.
Abrasive filler unsuitable for some applications.
Resistance to gas permeation is reduced.
It will be damaged by hydrogen fluoride and strong alkalines.
Graphite Filled PTFE
Characteristic
Highly effective in sealing various types of chemicals. Graphite lowers the coefficient of friction and Graphite filled PTFE has excellent self-lubricating properties.
Properties
The percentages used vary between 5 and 15%. Graphite lowers the coefficient of friction and is, therefore, often added to other types of filled PTFE for improving this property. It improves the deformation under load, strength and, to a minor degree, the wear properties.
Strengths
Cold flow resistance
Low starting friction
Low coefficient of friction
Chemically resistant
Wear & Tear resistance
Excellent engine efficiency
Weaknesses
Not resistant to halogenides, elemental fluorine, CF3, molten alkali metal
Bronze filled PTFE
Characteristic
The addition of Bronze to PTFE gives better dimensional stability and lowers creep, cold flow and wear resistance. It increases hardness and compressive strength whilst also increasing thermal and electrical conductivity.
Properties
Reinforced with bronze powder with the percentage varying between 40% and 60%, resulting in a very hard wearing material.
Strengths
Extremely hard wearing material
Very heavy-high specific gravity
Electrically conductive
The best wear properties of any filled PTFE
Great deformation strengths
Good thermal conductivity
Weaknesses
Not suitable for electrical applications
Poor chemical resistance than other grades of PTFE
Carbon Fiber filled PTFE
Characteristic
It improves mechanical characteristics, such as wear resistance, load resistance characteristics and flexuaral strength. It is often the best choice in automotive applications such as shock absorbers and water pumps. It is an excellent material for use in piston rings, bearings and thrust washers.
Properties
Carbon Fiber lowers creep and increases flex and compressive modulus. It raises hardness properties and exhibits wear characteristics in water applications. A 15% fill is typically called out in certain AMS specifications (Aerospace Material Specifications), however customer specific fill percentages are available upon request.
Strengths
Improved Compression and Wear Resistance
Excellent Chemical Resistance
High Strength Properties
PEEK
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