Fluoroelastomer Rubber Technical Information
| Table of Contents |
|---|
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Sealing Force and Temperature Resistance Range of Fluoroelastomer Sheet |
|
New Fluoroelastomer Products with Improved Chemical Resistance |
Introduction to Fluoroelastomers Used as Gasket Seals
Fluorocarbon elastomers are specialty polymers that possess excellent resistance to elevated temperatures and aggressive chemical media. The products described in this paper are based on Viton polymer produced by DuPont Performance Elastomers and Fluorel polymer produced by Dyneon 3M Company. Each manufacturer has a full range of elastomer types to choose from and offers excellent technical assistance when needed. Both suppliers strive to continuously improve the polymers currently being marketed and also to develop new polymers to withstand the ever changing chemical environment. Mosites Rubber Company has purchased material from each source for over 30 years and we have witnessed the evolution of this type elastomer from a few grades to three distinct families with over 50 polymer grades. An explanation of the differences in the product lines is shown below.
The Fluorocarbon elastomers consist of three basic polymer families. The first is a copolymer of vinylidene fluoride and hexafluoropropylene, commonly referred to as Type A. This family has a fluorine content of approximately 66%. The second family is a terpolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene, with a fluorine content of approximately 68% and is referred to as Type B polymer. The third type is the tetrapolymer family or Type GF, consisting of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene and a proprietary cure site monomer that allows the material to be vulcanized with peroxides. This family has a fluorine content of approximately 70%. Fluorine content is an important consideration in choosing a material to use as a gasket seal, because the higher percentage fluorine polymers have greater resistance to swell and degradation from most fluid exposures. Methyl alcohol (methanol) can be used to illustrate this effect.
| Polymer Type | Percentage Fluorine | Volume Swell in Methanol |
|---|---|---|
| A Type | 65% to 66% | 90% (168 hrs @ 73°F) |
| B Type | 67% to 68% | 40% (168 hrs @ 73°F) |
| GF Type | 69% to 70% | 5% (168 hrs @ 73°F) |
The type of curative or vulcanization agent used will also influence the physical properties and eventual life expectancy of the fluorocarbon seal in service. Here again, three basic chemical families are used to effect vulcanization of the polymers; the diamines (one type imparts a characteristic cinnamon odor); the bisphenol or contained curative system; and peroxides. When the elastomer was first introduced, the only system available was the diamine curatives. The compression set properties were not very good on these materials, typically from 30 to 50%. The bisphenol cure system was marketed to overcome this deficiency and resulted in very low compression set values (less than 20%), making the elastomer attractive for critical o-rings and other high temperature seal applications. Peroxide cures became possible with the introduction of the GF family of polymers, and together they provide the highest chemical resistance properties available.
The curative chosen must work in combination with an appropriate metallic oxide or “acid acceptor” in order for vulcanization to proceed. The metallic oxide reacts with and neutralizes any acidic byproducts generated during the vulcanization process. The most commonly used metallic oxides are magnesium oxide, calcium oxide, zinc oxide, calcium hydroxide and lead oxide. If the rubber gasket is required to seal against aggressive acids such as nitric, acetic, hydrofluoric or hydrochloric acid, the lead oxide acid acceptor is preferred, due to the fact that it forms an insoluble salt after vulcanization is complete. This salt will not further absorb acid or moisture and thus contribute to degradation of the seal. Most fluoroelastomer compounds will resist chemical attack by sulfuric acid, even without special compounding, and are commonly used to seal against this corrosive chemical.
By discussing with our customers, exactly what service conditions the fluorocarbon seal will need to resist, we can recommend the best available polymer formulation. Mosites Rubber Company stocks a full range of sheet materials, in various thicknesses and widths. We will also work with our customers to develop custom formulations if necessary.
Mosites Rubber Company Fluorocarbon Seal Compounds
The physical properties shown below were obtained on molded 0.080" thick ASTM samples. They are typical of the various compounds but they should not be used to set Quality Control Specification minimum requirements.
| Compound | Description |
|---|---|
| #1035 | 80 Durometer, Acid Resistant, Viton B |
| #1047 | 75 Durometer, Non Specification Fluoroelastomer |
| #1055 | 70 Durometer, Non-Black, Non Specification Fluoroelastomer |
| #1097 | 70 Durometer, Commercial Grade, Viton A |
| #10116 | 75 Durometer, Low Compression Set, Viton E-60-C |
| #10125 | 60 Durometer, Acid Resistant, Viton B |
| #10131 | 70 Durometer, Non Black, FDA Approved, Viton A |
| #10138 | 75 Durometer, Specification Grade, Viton A |
| #10149 | 55 Durometer, Non Specification Grade, Viton A |
| #10212 | 70 Durometer, Peroxide Cured, Viton GF |
| #10213 | 75 Durometer, Acid Resistant, Viton B Extrusion |
| #10228 | 75 Durometer, Specification Grade Fluoroelastomer |
| #10281 | 45 Durometer, Non Specification, Fluoroelastomer |
| #10317 | 60 Durometer, Non Specification, Viton A |
| #10320 | 75 Durometer, No Post Cure, Viton GF |
| Compound | Mosites #1035 |
|---|---|
| Description | 80 Durometer, Acid Resistant, Viton B |
| Hardness (Shore A) | 82 |
| Tensile Strength (psi) | 1907 |
| Elongation at Break (%) | 277% |
| Modulus at 100% Elongation (psi) | 683 |
| Tear Strength – Die C Tear (ppi) | 144 |
| Specific Gravity | 1.88 |
| % Compression Set (22 hours at 350° F) | 30% |
| Compound | Mosites #1047 |
|---|---|
| Description | 75 Durometer, Non Specification Fluoroelastomer |
| Hardness (Shore A) | 75 |
| Tensile Strength (psi) | 1000 |
| Elongation at Break (%) | 200% |
| Modulus at 100% Elongation (psi) | 650 |
| Tear Strength – Die C Tear (ppi) | 100 |
| Specific Gravity | 1.89 |
| % Compression Set (22 hours at 350° F) | 36% |
| Compound | Mosites #1055 |
|---|---|
| Description | 70 Durometer, Brown, Non Specification Fluoroelastomer |
| Hardness (Shore A) | 72 |
| Tensile Strength (psi) | 835 |
| Elongation at Break (%) | 232% |
| Modulus at 100% Elongation (psi) | 633 |
| Tear Strength – Die C Tear (ppi) | 133 |
| Specific Gravity | 1.99 |
| % Compression Set (22 hours at 350° F) | 44% |
| Compound | Mosites #1097 |
|---|---|
| Description | 70 Durometer, Commercial Grade, Viton A |
| Hardness (Shore A) | 70 |
| Tensile Strength (psi) | 1000 |
| Elongation at Break (%) | 175% |
| Modulus at 100% Elongation (psi) | 600 |
| Tear Strength – Die C Tear (ppi) | 125 |
| Specific Gravity | 1.97 |
| % Compression Set (22 hours at 350° F) | 36% |
| Compound | Mosites #10116 |
|---|---|
| Description | 75 Durometer, Low Compression Set, Viton E-60-C |
| Hardness (Shore A) | 75 |
| Tensile Strength (psi) | 1700 |
| Elongation at Break (%) | 180% |
| Modulus at 100% Elongation (psi) | 1000 |
| Tear Strength – Die C Tear (ppi) | 185 |
| Specific Gravity | 1.85 |
| % Compression Set (22 hours at 350° F) | 7% |
| Compound | Mosites #10125 |
|---|---|
| Description | 60 Durometer, Acid Resistant, Viton B |
| Hardness (Shore A) | 62 |
| Tensile Strength (psi) | 2207 |
| Elongation at Break (%) | 523% |
| Modulus at 100% Elongation (psi) | 242 |
| Tear Strength – Die C Tear (ppi) | 118 |
| Specific Gravity | 1.90 |
| % Compression Set (22 hours at 350° F) | 33% |
| Compound | Mosites #10131 |
|---|---|
| Description | 70 Durometer, Non Black, FDA Approved, Viton A |
| Hardness (Shore A) | 74 |
| Tensile Strength (psi) | 1552 |
| Elongation at Break (%) | 181% |
| Modulus at 100% Elongation (psi) | 773 |
| Tear Strength – Die C Tear (ppi) | 131 |
| Specific Gravity | 2.15 |
| % Compression Set (22 hours at 350° F) | 14% |
| Compound | Mosites #10138 |
|---|---|
| Description | 75 Durometer, Viton A, Mil R-25897-E, Type II, Class I |
| Hardness (Shore A) | 75 |
| Tensile Strength (psi) | 1560 |
| Elongation at Break (%) | 235% |
| Modulus at 100% Elongation (psi) | 682 |
| Tear Strength – Die C Tear (ppi) | 131 |
| Specific Gravity | 1.88 |
| % Compression Set (22 hours at 350° F) | 16% |
| Compound | Mosites #10149 |
|---|---|
| Description | 55 Durometer, Non Specification, Viton A |
| Hardness (Shore A) | 55 |
| Tensile Strength (psi) | 1000 |
| Elongation at Break (%) | 530% |
| Modulus at 100% Elongation (psi) | 175 |
| Tear Strength – Die C Tear (ppi) | 85 |
| Specific Gravity | 1.68 |
| % Compression Set (22 hours at 350° F) | 37% |
| Compound | Mosites #10213 |
|---|---|
| Description | 75 Durometer, Acid Resistant, Viton B Extrusion |
| Hardness (Shore A) | 75 |
| Tensile Strength (psi) | 2000 |
| Elongation at Break (%) | 295% |
| Modulus at 100% Elongation (psi) | 800 |
| Tear Strength – Die C Tear (ppi) | 136 |
| Specific Gravity | 1.90 |
| % Compression Set (22 hours at 350° F) | 60% |
| Compound | Mosites #10228 |
|---|---|
| Description | 75 Duro Fluoroelastomer, Mil-R-83248C, Type II, Class I |
| Hardness (Shore A) | 75 |
| Tensile Strength (psi) | 1790 |
| Elongation at Break (%) | 175% |
| Modulus at 100% Elongation (psi) | 1050 |
| Tear Strength – Die C Tear (ppi) | 120 |
| Specific Gravity | 1.84 |
| % Compression Set (22 hours at 350° F) | 10% |
| Compound | Mosites #10320 |
|---|---|
| Description | 75 Durometer, No Post Cure, Viton GF |
| Hardness (Shore A) | 76 |
| Tensile Strength (psi) | 2684 |
| Elongation at Break (%) | 268% |
| Modulus at 100% Elongation (psi) | 741 |
| Tear Strength – Die C Tear (ppi) | 130 |
| Specific Gravity | 1.81 |
| % Compression Set (22 hours at 350° F) | 5% |
Mosites #1028 Closed Cell Viton Sponge Sheeting
Mosites Rubber Company offers a soft, closed cell, Viton Sponge product in molded sheet sizes up to 30" by 56" and in thicknesses of 1/8", 1/4", 3/8", and 1/2". The material has the same excellent chemical resistance as standard dense Fluoroelastomer sheet, with the advantage of providing low closing pressure, leak proof seals. The service temperature range is from -40° F to +400° F, but resistance to compression set is poor at high temperature. The molding process results in an integral single sheet of microcellular foam with a thin, slightly denser “skin” on each surface. This skin makes the sheet stronger and more resistant to tearing than it would be if it were cut or sliced from a thicker sheet of product. The drawback in this manufacturing process is that control of overall thickness is more difficult and the thickness tolerances accepted by our Quality Control Department are more generous, typically +0.050"/-0.033".
The material has been tested by NASA at their White Sands Test Facility for flammability, and for VOC out gassing. These tests are critical for satellite and spacecraft applications and Mosites #1028 Viton Sponge has been certified for use on the Shuttle and the Space Station. The product is compatible with Liquid Oxygen (LOX) and is an excellent thermal insulation material.
| Physical Properties of Mosites #1028 Viton Sponge | ||||
|---|---|---|---|---|
| Sheet Thickness | 1/8" | 1/4" | 3/8" | 1/2" |
| Density (lbs per cubic foot) | 19 | 17 | 15 | 10 |
| 25% Compression Deflection (psi) Original Heat Aged 7 Days at 400°F |
6.5 9.0 |
5.5 7.5 |
4.0 6.0 |
3.5 5.0 |
| % Compression Set (22 hours at 75°F) | 27% | 13% | 14% | 17% |
| Low Temperature Brittleness (°F) | -10° | -10° | -10° | -10° |
| Hardness (Shore 00) Typical* | 48 | 45 | 44 | 40 |
| Thickness Tolerance (Production Sheets) | +0.050 -0.030 |
+0.060 -0.060 |
+0.080 -0.080 |
+0.125 -0.125 |
* Not to be used for setting Quality Control Requirements.
General Chemical Resistance of Fluorocarbon Elastomers
Fluorocarbon elastomers, in general, are resistant to automotive oils and fuels, aircraft jet fuels and lubricants, chlorinated solvents, aromatic solvents, water and salt solutions, aqueous acids and some hydraulic fluids. They are attacked to varying degrees by strong caustics; polar solvents such as acetone and MEK; ammonia; hydrogen sulfide; high ph amine corrosion inhibitors and red fuming nitric acid. As previously discussed, some properties such as acid resistance can be enhanced by the choice of polymer type and compounding ingredients. We have run comparative tests on several of our sheet gasket compounds in various fluid media and those properties are shown on the following pages.
Some applications require that the fluoroelastomer not only resist the swelling effect of the fluid medium, but it must not contaminate it due to the extraction of various chemicals from the polymer seal. One such application is deionized water used in nuclear powered, electric utility facilities. The compounding ingredients used in manufacturing fluoroelastomer sheeting or other types of rubber sheeting, can contain impurities that could leach into the fluid stream. The elastomers themselves, although generally of a high molecular weight and very stable in nature, can lose ions or salt compounds upon extended fluid immersion. Usually this loss is measured in parts per million (ppm) and is insignificant in overall seal integrity. In order to address this industry with an appropriate seal, Mosites Rubber Company has tested several of our sheet materials for leachable chloride. The extraction was performed with deionized water for 24 hours at reflux (212° F); followed by 16 hours at room temperature (75° F). Chloride analysis was by ion chromatography. The results are listed below.
| Compound | Leachable Chloride | |
|---|---|---|
| Mosites #10125 | 0.5 x 10-6 Micrograms / gram | |
| Mosites #10138 | 0.9 x 10-6 Micrograms / gram | |
| Mosites #10228 | 0.9 x 10-6 Micrograms / gram | |
Fluoroelastomer compounds also withstand the cumulative effects of radiation exposure. The mode of failure is embrittlement due to hardness increase as exposure time increases. They will typically remain usable until exposure to 1 x 108 rads of Gamma radiation.
Sealing Force and Temperature Resistance Range
of Fluoroelastomer Sheet
Aside from chemical resistance, the other advantage of Fluoroelastomer products is the excellent resistance to high temperatures. Customers often ask, “what is the service life of this seal?” This is a difficult question to answer and depends on a number of factors, such as the type of fluid or chemical it is sealing against; the temperature of the service environment; whether the seal is static or under dynamic flex conditions; the sealing pressures involved; and most importantly- the attention and care given during the installation and flange tightening procedure. The rubber seal can be mechanically damaged or torn by improper bolt torque technique.
The degree of compression necessary to achieve a leak free seal is dependent on the internal pressure and temperature of the fluid stream; the parallelism of the flange surfaces; the design of the seal area ( machined groove, perimeter backing ring; or smooth flange); and the composition of the flange and piping (metal or resin/fiberglass). For most seal applications, a maximum deflection in the gasket thickness of 25% is recommended. We have tested several of our sheet compounds for compressive strength at various percentage deflections and they are shown below.
| Compression Deflection Table | |||||
|---|---|---|---|---|---|
| % Compression Deflection Compressive Strength (psi) |
5% | 10% | 15% | 20% | 25% |
| Mosites #1035 | 29 | 89 | 152 | 220 | 304 |
| Mosites #1055 | 29 | 90 | 159 | 236 | 337 |
| Mosites #1097 | 20 | 76 | 139 | 207 | 292 |
| Mosites #10116 | 57 | 127 | 200 | 288 | 395 |
| Mosites #10125 | 37 | 83 | 137 | 197 | 269 |
| Mosites #10138 | 69 | 156 | 239 | 333 | 446 |
| Mosites #10149 | 16 | 61 | 113 | 170 | 239 |
| Mosites #10212 | 48 | 99 | 153 | 211 | 280 |
| Mosites #10228 | 32 | 101 | 176 | 265 | 373 |
Life Expectancy
According to published life expectancy data, when subjected to continuous elevated temperature aging, a typical high quality Fluoroelastomer compound can maintain 50% of its original tensile strength for the following times.
| Life Expectancy | |
|---|---|
| 350°F | 200,000 hours |
| 400°F | 30,000 hours |
| 450°F | 4,000 hours |
| 500°F | 600 hours |
| 550°F | 100 hours |
| 600°F | 30 hours |
Low Temperature Resistance
Fluoroelastomers normally have low temperature brittle points of approximately -40° F, depending on thickness of the sample. A 1/32" thick sample will have better flex properties than a 1/8" thick sample of the same material. Even though a sample has a brittle point of -40° F, it may lose the ability to stretch and recover at a much higher temperature (up to 0° F). Temperature Retraction tests (TR-10%) are usually performed on seal materials used for low temperature environments. Special Fluorocarbon polymers are available that provide flexibility down to -60° F and TR-10% values down to -25° F. Mosites #10282 compound contains this special polymer base and will meet the requirements of Mil-R-83485, Type II. A physical property data sheet on this product is shown below.
| Compound | Mosites #10282 |
|---|---|
| Hardness (Shore A) | 73 |
| Tensile Strength (psi) | 3150 |
| Elongation at Break (%) | 160% |
| Modulus at 100% Elongation (psi) | 1875 |
| Tear Strength (ppi) | 114 |
| % Compression Set (22 Hours at 350° F) | 4% |
| 10% Temperature Retraction (° F) | -30° F |
| Specific Gravity | 1.84 |
Storage and Handling of Fluoroelastomer Products
Fluoroelastomer sheeting is expensive and should be stored in a clean, dry area where it can be protected from punctures or damage by sharp objects, until it is used. The material is extremely inert to damage by weathering or ozone and our company policy has been to give a shelf life for cured sheeting of 5 years from the date of manufacturing. This is an arbitrary number, assigned by our Quality Control Department, with the knowledge that the material will be usable for much longer periods of time. The material can be retested and recertified, if concern over the use of out of date inventory becomes an issue with our customers.
As a general rule, Fluoroelastomer sheet contains no hazardous ingredients and in its vulcanized sheet form poses no handling problems. If subsequent grinding operations are performed on the sheet material, it is imperative that no tobacco products be allowed in the area. The polymer can liberate hydrofluoric acid upon combustion and it is possible that the powdery residue from grinding could contaminate cigarette or pipe tobacco. For more detailed safety information, consult the standard Material Safety Data Sheets (MSDS), which are available upon request for each product.
New Fluoroelastomer Products with Improved Chemical Resistance
The chemical industry has been faced with the need for improvement in the production of basic commodities, such as gasoline, while at the same time being increasingly impacted by local and Federal environmental regulations. Leakage or spills due to gasket failure, involve expensive cleanup and time consuming paperwork. The development of new polymer bases has allowed rubber sheeting manufacturers to offer improved gasketing materials to the chemical industry, but cost is still a determining factor governing usage. For several years, Kalrez – a DuPont Dow elastomer, has been generally considered the most chemically resistant elastomer available. Cost was extremely high, and due to process difficulties, it was marketed only in finished goods form (molded O-rings or seals). Recently, polymers approaching Kalrez in resistance have been introduced and some of these Fluoroelastomers are described below.
1. Mosites #2924 – BRE (Base Resistant Elastomer)
2. Mosites #2902 – a polymer based on Aflas TFE/P (TetraFluoroEthylene / Propylene)
3. Mosites #10322 – Viton ETP (Extreme Viton)
4. Mosites #10327 – High Fluorine Content (73% Fluorine) Fluoroelastomer
5. Mosites #10328 – Perfluoroelastomer (3M / Dyneon equivalent to Kalrez)
6. Mosites #10314 – Viton GF compound as a control
Original Physical Properties
| Compound # | #2924 | #2902 | #10322 | #10327 | #10328 | #10314 |
|---|---|---|---|---|---|---|
| Hardness (Shore A) | 71 | 74 | 76 | 82 | 73 | 75 |
| Tensile Strength (psi) | 2130 | 2789 | 1760 | 2971 | 2150 | 2760 |
| Elongation at Break (%) | 366% | 243% | 284% | 364% | 128% | 276% |
| Modulus at 100% Elongation (psi) | 467 | 881 | 774 | 635 | 1650 | 576 |
| Modulus at 300% Elongation (psi) | 1872 | – | – | 2107 | – | – |
| Tear Strength (ppi) | 121 | 117 | 124 | 207 | 126 | 142 |
| Specific Gravity | 1.68 | 1.58 | 1.82 | 1.94 | 2.02 | 1.81 |
| % Compression Set (22 hours at 350°F) | 52% | 15% | 61% | 12% | 53% | 9% |
| Approximate Base Cost/pound | $20/lb | $21/lb | $200/lb | $25/lb | $2500/lb | $20/lb |
An immersion study was performed on these polymer choices in fluid compositions that involve a broad range of chemical resistance characteristics. Both high and low ph fluids were evaluated; as were aromatic and oxygenated solvents. Due to polymer cost, the perfluoroelastomer was not tested. Published data shows the fluid media chosen to have little or no effect on this polymer.
Acid Resistance – 72 Hours at 158° F in 37% Hydrochloric Acid
| Compound # | #2924 | #2902 | #10322 | #10327 | #10328 | #10314 |
|---|---|---|---|---|---|---|
| Hardness (Shore A) | -6 pts | 0 pts | 0 pts | -3 pts | – | 0 pts |
| Tensile Strength (psi) | -22% | -5% | -24% | -7% | – | +5% |
| Elongation at Break (%) | -5% | -3% | -0% | +2% | – | -2% |
| Modulus at 100% Elongation (psi) | +11% | +16% | -40% | +3% | – | +7% |
| Modulus at 300% Elongation (psi) | +2% | – | – | -9% | – | – |
| Tear Strength (ppi) | -15% | -12% | -18% | +1% | – | -7% |
| % Volume Swell | +15% | +3% | +3% | +0% | +2% | +4% |
Base Resistance – 72 Hours at 250° F in 50% Sodium Hydroxide
| Compound # | #2924 | #2902 | #10322 | #10327 | #10328 | #10314 |
|---|---|---|---|---|---|---|
| Hardness (Shore A) | 0 pts | 0 pts | +1 pts | -3 pts | – | -1 pts |
| Tensile Strength (psi) | -30% | +12% | -7% | -13% | – | +0% |
| Elongation at Break (%) | -13% | -8% | -12% | -6% | – | -4% |
| Modulus at 100% Elongation (psi) | +9% | +3% | -13% | -1% | – | +5% |
| Modulus at 300% Elongation (psi) | +2% | – | – | +2% | – | – |
| Tear Strength (ppi) | -10% | -8% | -11% | +7% | – | -4% |
| % Volume Swell | +1% | +1% | +1% | -5% | +1% | +1% |
Aromatic Solvent Resistance – 72 Hours at 75° F in Toluene
| Compound # | #2924 | #2902 | #10322 | #10327 | #10328 | #10314 |
|---|---|---|---|---|---|---|
| Hardness (Shore A) | -24 pts | -19 pts | 0 pts | -1 pts | – | 0 pts |
| Tensile Strength (psi) | -71% | -61% | -23% | -6% | – | -14% |
| Elongation at Break (%) | -39% | -54% | -12% | +3% | – | -10% |
| Modulus at 100% Elongation (psi) | -41% | -1% | -26% | +2% | – | -6% |
| Modulus at 300% Elongation (psi) | – | – | – | -10% | – | – |
| Tear Strength (ppi) | -57% | -67% | +2% | -4% | – | -0% |
| % Volume Swell | +35% | +51% | +7% | +0% | +2% | +1% |
Oxygenated Solvent Resistance – 72 Hours at 75° F in Methyl Ethyl Ketone
| Compound # | #2924 | #2902 | #10322 | #10327 | #10328 | #10314 |
|---|---|---|---|---|---|---|
| Hardness (Shore A) | -42 pts | -19 pts | -7 pts | -23 pts | – | -22 pts |
| Tensile Strength (psi) | * | -79% | -25% | -59% | – | -87% |
| Elongation at Break (%) | * | -66% | -16% | -46% | – | -81% |
| Modulus at 100% Elongation (psi) | * | – | -30% | -55% | – | – |
| Modulus at 300% Elongation (psi) | * | – | – | – | – | – |
| Tear Strength (ppi) | * | -76% | -21% | -53% | – | -68% |
| % Volume Swell | +267% | +73% | +19% | +37% | +9% | +186% |
| *Sample was too swollen and distorted to test. | ||||||
The above tests show the importance of matching a seal material to the fluid environment it will see upon installation. Information about service conditions and temperatures must be considered before a compound can be recommended.
Mosites #10320 FKM Pressure Distribution Pad
Introduction
The manufacture of composite aerospace articles quite often involves the co-vulcanization of flat or contoured panels with various shapes of strengtheners (J-stringers; I-Beam stiffeners; C-channels; etc). In order to assure proper consolidation of the composite pre-preg at these bond joints and to prevent movement of the reinforcing members during autoclave cycles, rubber cauls are employed. These rubber cauls are shaped to the configuration of the tool cavity and are intended to be reusable. A high temperature resistant elastomer that has good dimensional stability upon extended cure cycling is necessary.
Some aircraft manufacturers use castable RTV silicone for these rubber parts; others specify a non silicone containing elastomer for the application (butyl; chlorobutyl; etc). The above mentioned elastomers have advantages and disadvantages, but the need remains for a more durable elastomer product.
Mosites Rubber Company has developed a fluorocarbon elastomer that appears ideally suited for this application. It exhibits low shrinkage upon vulcanization; withstands extended head age cycling with minimal further shrinkage and can be co-cured with epoxy prepreg reinforcement if a more rigid, less flexible rubber part is desired. Because it is a fluorocarbon polymer, exposure to temperatures up to 450°F will have no adverse effect on the cured rubber part.
The material is supplied in uncured or “B” stage calendered sheet form, 1/16 inch thick x 54 inches wide. Other thicknesses widths may be available as special order request.
Physical properties shown below were obtained on 0.080 inch thick ASTM samples. They are typical of Mosites #10320 but should not be used to set Quality Control Specification minimum values.
| Mosites #10320- Original Properties | |
|---|---|
| Hardness (Shore A) | 78 |
| Tensile Strength (psi) | 2980 |
| Elongation at Break (%) | 158 |
| Tear Strength- Die C (ppi) | 143 |
| Shrinkage Length Width |
3.4% 3.2% |
Procedure for Curing Mosites #10320
The procedures outlined below are general recommendations for film bagging and autoclave curing of a typical pressure intensifier lay-up.
A. Preparation of Mold or Tool Surface
1. Lay-up tooling or molds are usually aluminum. They should be cleaned with solvent to remove oil or residue from previous cures. (Acetone; MEK; etc.)
2. The tooling should be coated with suitable release agent. Teflon Aerosol Spray available from several manufacturers imparts good release characteristics. (Freekote; Cadco #1000; etc.) Allow any residual solvents in the release coating to air dry.
B. Fabrication of The Mosites #10320 Intensifier
1. Rolls of the uncured fluorocarbon should be removed from refrigerated storage and allowed to warm to room temperature.
2. Cut the uncured sheet, using a pattern, to give a minimum of scrap. If multiple plies are necessary to achieve the desired thickness, the surface of the uncured sheet can be wiped with MEK or acetone to increase tack. This also allows seams or joints to be more readily adhered and positioned.
3. If prepreg reinforcement is desired, layers of carbon/epoxy or fiberglass/epoxy can be positioned during the lay-up procedure.
4. Since the product is compatible with epoxy resins, any surface that could possibly contact the resin system during a cure cycle must be protected with release film. (TFE or FEP). Several manufacturers supply release film that has been treated on one side for adhesion to rubber. This material bonds quite readily to Mosites #10320 with no further preparation.
5. Film bag the lay-up in standard fashion suing appropriate breather system and apply vacuum. The lay-up can be held under vacuum overnight to aid in compaction and forming if desired or it can be placed immediately into the autoclave for vulcanization.
C. Vulcanization of the Lay-Up
1. Cure the tool assembly for 1 hour at 350°F and at least 60 psi autoclave pressure. Thick sections may require longer vulcanization times. The schedule shown below should be followed.
- Autoclave- Cure Mosites #10320 for 1 hour at 350°F for the first 1/8 inch of thickness. Cure an additional 5 minutes at 350°F for each extra 1/8 inch of thickness.
- Oven- Cure the lay-up by ramping the oven temperature from 175 F to 350 F in increments of 25 F. Allow 1 hour at each temperature step. After completion of the cure time, allow the part to cool to room temperature before removal from the tool. Post cure as above, if necessary.
2. When the cure time has elapsed, allow the tooling to cool before removing the rubber part. It is now ready for use.
Bonding Instructions
Some applications for Mosites #10320 may require that the material be bonded to an aluminum surface. This can be done quite easily during the vulcanization process using the following recommendations.
1. Clean the aluminum surface to be bonded to remove any machine oil or dirt that could interfere with the bond.
2. Abrade the surface of the aluminum by sand blasting or hand sanding with sand paper or emery cloth.
3. Rinse this abraded surface to remove any loose particles left from the sanding process.
4. Prime the abraded, aluminum surface with 3M Dynamar FC-5150 Metal Bonding Agent. Allow the primed surface to dry for at least 30 minutes before proceeding with the cure cycle.
5. Place the uncured sheet of Mosites #10320 over the primed surface. Cover with a reusable vacuum blanket or film bag to apply adequate pressure and air removal. Autoclave cure as per recommended curing instructions.
Storage Requirements for Mosites #10320
Mosites #10320 is supplied in uncured or “B” stage calendered roll form. For best results the material should be used within 6 months of receipt of shipment. It should be stored under refrigerated conditions, below 40°F. Material should be tagged in order to use older material before it becomes outdated.
