Pressure-Bottles.com | Elastomer Availibility
HydroTrole Limited - Serving the offshore oil and gas exploration and production industries since 1963.
Common Elastomer Availability from MEMBRANO_FLEX Ltd. Div of LDI Ltd
for you to choose from:-
Information Source - edited from "KEVIN-TECH" aka Kevin Bebb's
Technical Notes - LDI Ltd. in-house proprietary , since 1963.
The compound ingredient percentages are chosen by LDI Ltd. to cause
similar physical properties, and from advice by the Rubber &
Plastics Research Association (aka RAPRA.) and others. :-
In the uncured / un-polymerized state,: (more information at the bottom of this page)*
To be easily transfer-injectable over distances greater than 3x the
item diameter, without the use of long oil alkids etc. for
plasticization.
In the cross linked / polimerized state, to have :-
1. Elongation at break in excess of 600%,
2. UTS greater than 2000 psi (140 bar)
3. IRH Shore "A" scale hardness 55-60,
4. Good compression set resistance for seal-points.
5. The use of "non-leaching" plasticizer
IE that crosslinks within the cured material.
6. No Sulfur.
MATERIAL TO CHOOSE FROM.
Note - "LDI" are not compatibility engineers .
Be sure to check your selection against the "O" rings Seal, gasket,
valve diaphragm, pump packings that have proved satisfactory for
your system.
Errors and Omissions Excepted. "E&OE"
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ASTM ELASTOMER DESIGNATIONS WITHIN LDI Ltd (MembranoFlex)
AVAILABILITY :-
"FFKM", "PIB" , "EP" "EPDM" "EPR" , "ECO", "FKM", "CSPE", "NR",
"CR", "NBR", "MQ, VMQ, PVMQ, FVMQ," "T Also ST". Etcetera
Butyl Rubber
Poly-Iso-Butylene
aka "PIB" , newer Halobutyl
Not easily "bondable".
Temperatures
tear resistance fail
Typical Uses Automobile inner tubes
Other Oxygen permeation resistance
More Detail
http://en.wikipedia.org/wiki/Butyl_rubber
Nordel TM EPCAR TM , VISTALON TM
Generic - EPT Ethylene Propylene Terpolymer Peroxide Cured
aka EP,"EPDM" (D M Diamine-Monomer not understood - it is no longer
a monomer when polimerized),
aka also "EPR".
Temperatures 300 F
tear resistance good
Typical Uses water based, wide applications (not OILS, Hydrocarbons)
Other Good abrasion resistance, low cost
More Detail
http://www3.interscience.wiley.com/journal/104021283/abstract?CRETRY =1&SRETRY=0
Fluoro Elastomers
aka "FKM"
Trade names Fluorel TM, Viton TM
Common variants "A", "B", "B50","E60C", "GS"
Temperatures HIGH
tear resistance BAD
Typical Uses, result of much hype, Viton TM Thought to be a panacia.
Other Expensive, elongation / elasticity very poor, & NOT for low
temperature use at all.
More Detail
http://www.knovel.com/web/portal/browse/display?_EXT_
KNOVEL_DISPLAY_ bookid=1323
Hypalon TM (Per Dupont is Obselecent)
Chloro-Sulfonated PolyEthylene
aka "CSPE" & synthetic rubber (CSM)
Temperatures :- extremes
tear resistance
Typical Uses Chemical Resistance
Other
More Detail
http://en.wikipedia.org/wiki/HypalonNatural Rubber "Indico"
aka "NR"
Temperatures moderate
tear resistance good , ebrasion resistance good
Typical Uses ambient temperature hose
Other Highly elastic - diametric opposite to fluoro-elastomers.
More Detail
http://www.rubber-stichting.info/
Nitrile rubbers,
Butadiene-Acrylonitrile,
aka "NBR" (in a low grade aka "Buna N")
Common Variants :
a. Low temp Nitrile - to negative 70 50 F? C?
b. High Temp Nitrile -
c. Hydrogenated ("HNBR") Increase properties , and some CO2
permiation resistance
d. FDA ingredient versions, White,
Temperatures according to variant
tear resistance, Fair, abrasion resistance good
Typical Uses Hydrocarbon liquids, fluid power hydraulics
Other Reasonable price
More Detail
http://www.ashtabularubber.com/nitrile-page.html
Silicone Rubber - wide varieties
aka MQ, VMQ, PVMQ
Fluoro-silicone
aka FVMQ
Temperatures up to 500 F
hot tear resistance BAD
Typical Uses external environments UV resistance, and medical
Other difficult to inflate without tearing for tool release
More Detail
http://www.dowcorning.com/content/rubber/silicone-
rubber.aspx
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GENERAL COMPARISONS
http://www.ashtabularubber.com/elastomerselection-page.htmlGENERAL NOTE - CAVEAT A typical elastomer compound may have at
least :-
The named Elastomer, an activator, an accelerator, the curing -
cross linking agent ,
a plasticizer (PREFERABLY cross-linking) anti ozonant, fillers
typically chimney /
furnace black, etc . Up to a dozen constituents.
The performance of any one of the above available synthetic
"rubbers" depends on
the experience of the compound formulator and a full disclosure by
the end user of
all the details of the actual application.
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NON ELASTOMERS - IE "PLASTOMERS".
"Flexflon" TM
aka LDI "DW series"
PTFE that has been raised to 730 F gell temperature
converting all PTFE sintered prcipitate particles
into one homogeneous plastic.
Imparts some resilience and enable flexibility when
combined with concentric wave shaped corrugations.
Servicability as PTFE
Availability membranes up to 305mm diameter, 320 in3
5.25 Liter .
Virgin PTFE,
aka LDI "DF series"
has bonded high temp EPT backing to provide some resilience -
to impede the "cold flow" of PTFE. and slow the rate of
permeation experienced with virgin PTFE (aka "Teflon" TM) because
of its sintered particulate nature.
Availability Membranes up to 454mm diameter, 1000 in3
16.4 liter .
Trade names / trade marks, noted here in "TM" are the property of
their respective technology owners. Predominantly "Dupont Dow Elastomers"
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Elastomer Specification for superior quality membranes used as separators between liquids and a gas within hydropneumatic devices such as pulsation dampers and water hammer preventors , and accumulators offered by Pulseguard and associates.
In the uncured / un-polymerized state,:
A synthetic rubber product is made by heating the raw material. In other words rubbers are "THERMOSETS" they set up because of heat. So before heat is applied they are just a mushy dough . They have not set.
(This is the opposite of "plastics" meaning thremoplastics - they become plastic - they flow because heat melts them, and when you cool them they set or become a solid)
The process of setting for rubbers (becoming a solid object) is called "curing".
Curing for a rubber is actually polymerizing - the process of going from a monomer to a polymer - going from very short chain molecule to a long chain molecule by cross linking* of the molecular parts.The process causes the elastic strength.
so the simplest way to say it is In the uncured / un-polymerized state,:
In this dough mushy state To be easily transfer-injectable - means to be easily caused to flow by processes called rubber transfer and rubber injection
(we use a combination of the two processes - so it is called "trans-injection")
The point about trans-injection is quality, is that the mold tool is closed - no part of the actual space (called the cavity) that defines the dimensions of the membrane being moulded is moving during the injection process - therefore the dimensions are maintained more exactly - than other products where one part of the tool moves toward the other - generally called "compression moulding"
over distances greater than 3x the item diameter,
means what it says - but the point is that each elastomer formulation (while having other VITAL requirements of strength and elasticity and chemical compatibility) must also be able to be squirted in its final place.
This is a great challenge.
without the use of long oil alkids etc. for plasticization.
anyone can easily make an elastomer formulation easily squirtable / more plasticized for use over a long distance - simply by mixing oil with the formulation - but then that oil will come out of the rubber over time, and the moulded membrane will become porous . The normal oil used by the "cheaters" is called a "long oil alkid"
IN THIS NEXT SECTION WE ARE DEFINING THE CHARACTERISTICS
OF THE MEMBRANE WHEN IT HAS BEEN MOULDED - HAS CURED BY HEATING
In the cross linked *see above / polimerized state, to have :-
In the cured state - after the heating (usually between 20 minutes and [24 hours for viton] ) - when it has become an elastic moulding
1. Elongation at break in excess of 600%,
how elastic is it - you can stretch it to 6 times longer than in relaxed state, before it brakes - AKA "E@B"
2. UTS greater than 2000 psi (140 bar)
Ultimate Tensile Strength
3. IRH Shore "A" scale hardness 55-60,
International Rubber Hardness on scale called "Shore A" reading between 55 and 60 on that scale. (this is a relatively soft figure, "O" rings are for example usually about 70, some rubber gaskets are as high as 90 - 100 is like ebonite.
4. Good compression set resistance for seal-points.
Compression Set is failure to recover with elastic force, this is usually demonstrated by folding a membrane tightly, and then watching it recover from the creasing fold line. The challenge is to keep the very long E@B figure (which cheating can be dun by a "state of undercure" whilst also having good resilience - so that seals at the perimeter do maintain forceful contact with the seal groove.
Achievable by heating the perimeter of the mould tool more than the membrane area in the center !!
5. The use of "non-leaching" plasticizer - IE that crosslinks within the cured material.
The plasticity is achieved by the combination of the characteristics of several of the 20 or so constituents of the formulation - the main one being the "plasticizer" - the object here is to use a plasticizer that becomes part of the curing reaction and finnish up be being a part of the very long chain polymer - the longer the chain the generally more elastic the final product - this statement number 5 prohibits the use of oil as a plasticizer.
6. No Sulfur.
Sulfur is a cheap and common "curing agent" was always use in natural rubber AKA
"Indico" and "Gum stock" (as it came out of the cuts in the bark of the rubber trees).
The problen with the use of sulfur is that it comes out of the final moluded product over time.
You may remeber the rubber handle bar hand grips on old bicycles - when they got old, the surface became naty and sticky in summer - that was becauuse they used sulfur in the formulation.