Embed Size (px)
Citation preview
LOW TEMPERATURE SEALING CAPABILITY OF O-RINGS: THE RELATIONSHIP BETWEEN LABORATORY TESTS AND SERVICE PERFORMANCE
A technical paper presented by
James Walker & Co Ltd
Page 1 of 15 pages Low Temperature Sealing
LOW TEMPERATURE SEALING CAPABILITY OF O-RINGS: THE RELATIONSHIP BETWEEN LABORATORY TESTS AND SERVICE
PERFORMANCE
Abstract Many engineers or purchasing professionals have requirements for O-rings that operate at low temperatures. They rely on the information provided from technical data sheets, and in many cases will compare the minimum operating temperature claim from several seal suppliers before making their choice. The claims from different suppliers may be based on different test criteria which will vary in accuracy when it comes to predicting performance in the field. This paper is a critique of current practice regarding substantiating claims for minimum operating temperatures of O-rings.
It will study a range of laboratory tests, and look at the relationship between these values and actual sealing performance. The influence of polymer chemistry and compounding techniques will also be included. The intention of the paper is give some guidance to end-users regarding the reliable selection of products for critical applications where sealing performance at low temperatures is required.
There are numerous applications that require elastomer sealing components to operate at low temperatures. One example is sealing devices in well head and other drilling applications at high latitudes where the ambient temperature above and below ground is below 0°C for prolonged periods.
Fig. 1 Ram Powell Gas Platform Selection of a suitable elastomeric material for a given application has to be carried out in a systematic manner, as the other requirements for the particular duty must also be considered. Typically the selection process will follow the steps below.
• Chemical resistance• Mechanical property requirements• Operating temperature range• ‘Special’ features such as resistance to explosive decompression (ED).
The individuals involved in this process will in most cases rely on the low temperature (along with the other claims) made in the manufacturers literature. The means by which they were set, and possible limitations of the data are
Page 2 of 15 pages Low Temperature Sealing
generally not clear to the reader, who simply seeks a value with which to compare elastomers that meet the other performance criteria from various manufacturers. He or she will normally assume that the minimum operating temperature quoted represents the lowest temperature at which elastomer components will seal in all situations, unless caveats suggest otherwise.
Whilst applicable in other areas, the focus of this paper is on elastomers typically used in Oil and Gas applications, the most popular materials of which are HNBR (hydrogenated nitrile) and FKM (fluoroelastomer). A selection of low temperature claims for elastomers based on similar polymers designed for use at low temperatures from a number of manufacturers appears in Fig. 2. The reader will note that claims from the seal manufacturers are in some cases beyond that of the polymer manufacturers on which these materials will be based.
Page 3 of 15 pages Low Temperature Sealing
Manufacturer Polymer
Low temp claim, Deg C Test method
Nominal hardness
of compound
(Shore A/IRHD)
Polymer mfr A FKM / low temp, 64%F -31 TR10 70
Polymer mfr B FKM / low temp, 64%F -31 TR10 65
Polymer mfr C FKM / low temp, 64%F -30 TR10 70
Polymer mfr E
HNBR Low temp, some unsat., 17 to 20% ACN content -36 TR10 Not known HNBR Low temp, 'fully' sat, 17 to 20% ACN content -36 TR10 Not known
Polymer mfr F
HNBR Low temp, some unsat., 19.5 to 22.5% ACN Content -35 TR10 Not known HNBR Low temp, 'fully' sat., 19.5 to 22.5% ACN Content -35 TR10 Not known
Seal mfr A Low temp HNBR -40 Not specified 70 Low temp HNBR -40 Not specified 80 Low temp FKM -30 Not specified 75 Low temp FKM -37 Not specified 90
Seal mfr B Low temp HNBR -37 Not specified 90 Low temp HNBR -40 Not specified 80 Low temp HNBR -40 Not specified 70 Low temp HNBR -40 Not specified 80 Low temp HNBR -40 Not specified 70 Low temp HNBR -37 Not specified 90 Low temp FKM -40 Not specified 60 Low temp FKM -37 Not specified 75
Seal mfr C Low temp HNBR -40 ISO 812, Type B ASTM D2137, Method A 70
Low temp HNBR -40 Not brittle after 3 mins at -40C 60
Low temp FKM -40 Not specified 75 Low temp FKM -40 Not specified 75
Seal mfr D Low temp HNBR -40 Not brittle after 3 mins at -40C 70
Low temp HNBR -40 Not brittle after 3 mins at -40C
Low temp FKM -40 Not specified 75
Low temp FKM
-40 static -30
dynamic Not specified 85
Fig. 2: A comparison of low temperature claims made by polymer and seal manufacturers.
Page 4 of 15 pages Low Temperature Sealing
How do these low temperature claims relate to actual service performance?
O-RINGS: MECHANICS OF SEALING
Toroidal seals rely on an initial ‘squeeze’ which provides a sealing force between the contact faces. Pressure within the system further activates the seal, and increases the sealing force by that of the system pressure. The initial sealing force created by the squeeze on the seal, and maintained by the residual stress within it takes the overall sealing force above that of the system pressure. It is this balance of forces that forms the seal.
Fig 3, Balance of forces in an O-ring
Whilst the seal is energised by the system pressure, the residual stress within the elastomer is critical to maintain a sealing force above the pressure being contained. Excessive stress relaxation over time caused by physical and chemical changes to the seal material, will inevitably compromise its ability to function. At low temperatures, the residual sealing force can also reduce to a point where the system will fail.
FACTORS INFLUENCING LOW TEMPERATURE FLEXIBILITY OF ELASTOMERS
i) Molecular structure
In simple terms elastomers are based on rubber polymers made up of long chain molecules randomly arranged in coils which have been chemically cross-linked to form a three dimensional structure. Within their normal operating temperatures, the molecules will be free to rotate and the individual chain segments will remain flexible. As the temperature is decreased, the ability of the molecules to rotate is reduced as they move closer together. The glass transition temperature (or Tg) of an elastomer represents the temperature at which it ‘freezes’ though is not yet brittle. Chain mobility is restricted, and the elastomer starts to crystallise, becoming ‘leathery’ and unresponsive. The brittle point normally sits a few degrees below the Tg, though the distance between the Tg and brittle point can vary significantly between polymer types. The temperature at which the elastomer crystallises is predominantly influenced by its chemical structure. Introducing ‘irregular’ monomers reduces the tendency to crystallise, and as a consequence improves the flexibility of the polymer at low temperatures. The molecular structure of a rubber polymer has by far the greatest influence on the low temperature flexibility of the fully compounded elastomer, however other ingredients in the formulation can lower the Tg by a few degrees.
ii) Influence of compounding additives
With FKM, little can be done to change the Tg with regards to additives, though as with all elastomer types, lowering the hardness and/or the modulus can reduce the Tg typically by between 1 and 3°C. Perhaps the greates t
� O-Ring in housing
� Initial compression generates reactiveforces (sealing stress)
� System pressure increases forces andsealing stress within the seal.
Page 5 of 15 pages Low Temperature Sealing
compounding influence is the selective use of plasticisers in NBR’s (nitrile) and HNBR’s. The maximum gain in low temperature flexibility by the addition of for example DOS (dioctyl sebacate), will be in the region of 8°C below the capabilities of the unplasticised polymer. This must be tempered with a reduction in physical properties, and selective use of fillers can help the compounder achieve a more acceptable balance. A plasticizer loading of 10phr is a typical compromise.
It must be emphasised that if the elastomer is subjected to high temperatures, some of the plasticisers may be lost dependant on their volatility. Fig. 4 examines the comparative volatile loss of five plasticisers at 180°C (and 10phr loading); the maximum operating temperature suggested by at least one manufacturer, and then re-examines their low temperature properties in Fig. 5.
% Mass Loss of Plasticiser at 180C
0
20
40
60
80
100
120
0 19 24 28 45 56 72
Time, hours
Mas
s lo
ss, %
G30 PPA DOS TOT W95
Fig.4, Volatile loss at max operating temperature.
Page 6 of 15 pages Low Temperature Sealing
Changes in Gehman T70 Values After Ageing For 72 Hrs at 180C
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
G30 DOS PPA TOT W95
Plasticiser Type
T70
tem
pera
ture
, C
Before After
Fig 5, Low temperature properties before and after being subjected to a ‘maximum operating temperature’ of 180°C
It can be seen that any gain in the flexibility at low temperatures through the selective use of plasticisers in HNBR (or NBR), may be reduced or negated by the possibility of volatile loss at higher temperatures. If this level of thermal cycling is present in an application, the subsequent effects on low temperature flexibility will need to be considered.
iii) Influence of contact media
Whilst appropriate polymer selection should minimise absorption of contact media, small levels may find their way into the elastomers. These will act as a ‘molecular lubricant’ in a similar manner to a plasticizer. As a result, minor improvements to low temperature properties may be obtained. According to work by DuPont1, higher levels of swell show further improvements in low temperature sealing. Such effects could be due to a combination of increased lubricity and spacing within the polymer structure, and increases in seal cross section. It must be remembered however that swelling will reduce the mechanical properties of the seal, and could lead to problems with extrusion.
iv) The effects of system pressure
Elastomers are often considered to be incompressible. This is not strictly true, as the Poisson’s ratio of elastomers is slightly less than 0.5 (in the region of 0.46 to 0.49) so small levels of compression are possible. At pressures of 50 bar and above, the Tg of elastomers will shift due to this effect2,3,4 The mobility of the polymer chains will be more restricted as they are forced closer together, and as a ‘rule of thumb’ for every 50 bar pressure the Tg will move by 1°C. Inevitably this requires an elastomer with th e ability to remain flexible at temperatures lower than that of the application. Fig. 6 illustrates the low temperature flexibility requirement of an elastomer for an application at -40°C at increasing system pressures.
Page 7 of 15 pages Low Temperature Sealing
-47
-46
-45
-44
-43
-42
-41
-400 50 100 150 200 250 300 350
System pressure (bar)
Low
tem
p ca
pabi
lity
requ
irem
ent o
f sea
l for
app
licat
iona
t -40
C
Fig. 6, An illustration of increasing low temperature flexibility requirement at increasing system pressures due to Tg shift.
At the operating pressures typically seen for products such as O-rings in Oil and Gas applications, Tg shifts of several degrees can be encountered. In these instances the elastomers will need to be flexible at temperatures below that of the application at atmospheric pressure in order to allow for the Tg shift at the operating pressure.
To conclude, the low temperature performance can be influenced to a small degree by changes in hardness, modulus, contact media and in the case of NBR/HNBR by the selective use of plasticisers. If the elastomer is subjected to high temperatures before cooling, the effects of plasticizer loss will need to be considered. High system pressures will cause a Tg shift, and this must be allowed for when selecting a suitable elastomer grade for the application.
SOME COMMON LABORATORY TEST METHODS FOR MEASURING THE LOW TEMPERATURE PROPERTIES OF ELASTOMERS
i) Temperature Retraction ISO2921/ASTMD1329/BS ISO2921:2005
Essentially this stretches the sample by typically 50% and ‘freezes’ it in position using an alcohol bath cooled with solid carbon dioxide to -70°C (other temperatu res can be specified depending on the cooling media). The specimen is then allowed to retract freely while the temperature is raised at a uniform rate. Its ability to recover is measured as a temperature at a given %. The temperature to recover by 10% (TR10) is often used to establish the minimum operating temperature of an elastomer. Normally the % recovery is recorded every minute against temperature, and the results plotted on a graph. It is worth noting that the elastic modulus of an elastomer may influence the results independently of its low temperature properties.
ii) Gehman Torsional Modulus ISO1432/ASTM1053/BS903 A13
Small samples cut from sheet are placed in a carousel holder and immersed in an alcohol bath cooled as above. They are conditioned at the test temperature before being twisted using a calibrated wire, which after a simple calculation gives the torsional modulus. The temperature at which a torsional modulus of 70MPa (T70) is achieved has also been used to set a value for the minimum operating temperature of an elastomer. The absolute torsional modulus of a given material may to some extent influence the result. A minimum operating temperature can also be estimated by finding at which point a given ratio of torsional moduli between room temperature and a lower temperature is reached. This may in some circumstances be a more reliable option.
Page 8 of 15 pages Low Temperature Sealing
iii) Dynamic Mechanical Thermal Analysis (DMTA or DMA)
A small sample of elastomer is flexed and properties such as modulus and damping are measured over a range of temperatures at fixed frequencies. Elastic (E') and viscous (E'') moduli are recorded along with a ratio of these, Tanδ. From these data, an assessment of Tg and ‘Brittle Onset Temperature’ can be made.
iv) Differential Scanning Calorimetry (DSC)
DSC measures the heat flow associated with transitions in materials as a function of time and temperature. Basically DSC measures heat flow into or out of a sample as it is heated, cooled or held at a set temperature. This technique can provide a wide range of data including Tg.
v) Bend Brittle Test (E.g. DTD 458: 1948)
This somewhat crude test locates an elastomer sample between two jaws connected via a helical screw. After conditioning at the specified temperature in a cooled alcohol bath, the jaws are screwed together by a predetermined amount which subsequently flexes the sample which is then examined for splits or cracks. As can be seen, this is not a measure of elasticity and merely measures brittleness at a given temperature.
vi) Compression Stress Relaxometer BS ISO 3384:2005
Perhaps the most representative laboratory evaluation of potential sealing performance is the measurement of residual sealing force at a given temperature. This is possible via a Compression Stress Relaxometer. An elastomer button is compressed in a specially designed jig, and the residual sealing force in Newtons is measured by momentarily placing the jig in a CSR unit. The jigs complete with sample under a preset level of compression can be placed in an environmental chamber to condition the sample for specified periods of time at a given temperature. By this means, the residual sealing force at this temperature can be measured. It should be noted that BS ISO 3384 does not specify a procedure for testing at low temperatures stating ‘the methods [described] have been used for low temperature testing but their reliability under these conditions is not proven’.
MEASUREMENT OF ACTUAL SEALING PERFORMANCE OF O-RINGS AT LOW TEMPERATURES
The O-ring low temperature seal test as used by DuPont and quoted by some seal manufacturers was first reported in 19911. Values were for a 10% squeeze of a lubricated ‘214’ size O-ring under 200psi (13.6 bar) of nitrogen. The seal was energised and then the temperature was reduced slowly until leakage was measured. The value obtained was 13°C below the TR 10 temperature for Viton GLT. The 2003 report5 was under similar conditions but the squeeze was increased to 19%. Using this modified test the difference to TR10 was now 15°C. The 1991 evaluation proved that the increased squeeze would have this effect.
It is worth noting however, that this often quoted 15°C offset is actually the failure temperature and not a safe working temperature. This work was conducted on certain DuPont FKM polymers but, interestingly, this sealing at 10°C to 15°C below TR 10 is quoted for compounds using other, non-fluorocarbon polymers by some suppliers.
The claims of working 15°C below TR 10 are only theoretically applicable if the seal is of the same size, lubricated in the same way and pressurised with nitrogen at 200psi prior to reduction in temperature. In reality few seals would be pressurised before the temperature was reduced.
A report by Sandia Laboratories6 studied the failure temperatures of selected elastomer O-rings by pressurising after the seal had been conditioned at the test temperature. As would be expected, the failure temperatures were significantly higher.
Page 9 of 15 pages Low Temperature Sealing
ASSESSMENT OF LOW TEMPERATURE SEALING PERFORMANCE OF THREE ELASTOMERS BY JAMES WALKER
Following the excellent investigative work carried out by DuPont and the Sandia Laboratories, James Walker carried out a comparison of low temperature laboratory tests on three elastomer compounds. This was followed by an assessment of actual low temperature sealing performance when pressurised before a reduction in temperature (broadly as DuPont) and pressurised after the temperature reduction (broadly as the ‘Sandia Report’). The three compounds were:
• ‘HNBR LT’, A 90 nominal hardness HNBR with an ACN (acrylonitrile) content of 17 to 20% and a lowlevel of unsaturation.
• ‘FKM LT’, A 90 nominal hardness FKM tetrapolymer with a fluorine content of 64% for low temperatureapplications.
• ‘FKM ULT’, An 80 nominal hardness FKM of undisclosed polymer composition new to the market, withadded low temperature flexibility.
Whilst future evaluation will include two further sizes to study effects due to varying cross section, for expediency the test data below are based on one size of O-ring.
Fig. 7, Nominal dimensions of seals ( BS1806 size 316).
Seals moulded for this study utilised tooling that gave a measured compression of between 16.6 to 18.5%, giving a groove fill of between 82.9 and 86.1%. Dimensions were checked using an optical measuring device.
The test fixture was machined with three ports, each containing a single O-ring. The fixture was such that each port was independent of the other two. Each of the three ports housed a seal of the same nominal dimensions for each experimental run. Leakage was measured via sensitive flow meters, one connected to each port logged to an accuracy of 0.01ccm (cubic centimetres / minute). Temperature, pressure and leakage were recorded on to a PC. The test gas was nitrogen and the pressure (unless otherwise stated) was 100bar, the normal maximum recommended system pressure without back-up rings.
Page 10 of 15 pages Low Temperature Sealing
Fig. 8, Schematic of test fixture.
In order to allow the study of sealing properties at a range of temperatures, the fixture was housed in an environmental chamber. This unit is capable of maintaining temperatures between -75°C and +180°C to a n accuracy of ± 0.3°C. Cooling and heating rates and dwells are programmed via a PLC controller.
Fig. 9 Test Rig
Page 11 of 15 pages Low Temperature Sealing
The use of lubricants during the fitting of O-rings is well known, and for this exercise silicone grease was adopted as a surface coating. In an early experiment, seals moulded from a higher ACN content HNBR than that selected for this study were tested with and without a surface coating of grease. The difference in temperatures where leakage could be detected was considerable. Seals fitted ‘dry’ were less able to respond to changes in system pressure.
50-214 Size Port 1 Port 2 Port 3
No Grease -19.4°C -18.1°C -13.3°C Grease -31.8°C -35°C -33.1°C
Fig 10, System pressurised to 100bar, and temperature of test fixture reduced by approximately 1°C eve ry 3 minutes. Leakage recorded every 0.1°C.
As it is the sealability of the O-rings that is being measured rather than the grease, the lubricant was applied to the O-rings very sparingly. To confirm this each seal was weighed to 4 decimal places before and after grease application. It must be remembered that the Tg of ‘ordinary’ silicone greases is in the region of -56°C. To minimise any effects the grease may have on the results, a special low temperature grade (‘Molykote 33 Light’) with a Tg of -73°C was used for the study.
LEAK TESTING
Pressure Maintained During Cooling
This is the test method most likely to maintain sealability at low temperatures, as the seal is in an energised state during cooling. The seals were very lightly greased as described, and carefully fitted to the ports. The fixture was then cooled at approximately 0.3°C / minute with th e leakage logged at 0.1°C intervals. A leak rate g reater than 0.01ccm on one or more of the three seals was considered a failure. The minimum temperature at which all 3 seals simultaneously successfully held pressure was also recorded.
HNBR LT (316 Size) Temperature, °C Initial failure -54 (one seal leaked) Complete failure -57 (all 3 seals leaked) Min. sealing temp -53 (all 3 seals ok)
FKM LT (316 Size) Temperature, °C Initial failure -55 (one seal leaked) Complete failure -57 (all 3 seals leaked) Min sealing temp. -54 (all 3 seals ok)
FKM ULT (316 Size) Temperature, °C Initial failure -56 (one seal leaked) Complete failure -60 (all 3 seals leaked) Min sealing temp. -55 (all 3 seals ok)
Fig 11, Test results
Page 12 of 15 pages Low Temperature Sealing
Fig 12 Pressure Maintained During Cooling
-62
-60
-58
-56
-54
-52
-50
-48HNBR LT FKM LT FKM ULT
Elastomer Type
Tem
pera
ture
, C
Initial Failure
Complete failureMin sealing temp
Fig 12, Graphical summary: Leakage temperature range for all 3 seals in each material, and minimum temperature at which all 3 held pressure.
Pressure Applied After Cooling
With the seal in a ‘leathery’ state, the level of responsiveness will be far less. Using the same seals as the previous exercise, the fixture was cooled to the materials T70 or TR10 (whichever was lowest). The temperature was held at each set point for 60 minutes prior to pressurising to 100 bar. A failure was recorded if leakage on one or more of the seals greater than 0.01ccm was noticeable after 2 minutes. The temperature was dropped further at 1°C intervals until all 3 seals leaked. The rig was depressurised between readings.
HNBR LT (316 Size) Temperature, °C Initial failure -42 (one seal leaked)* Complete failure -46 (all 3 seals leaked) Min. sealing temp -41 (all 3 seals ok)
FKM LT (316 Size) Temperature, °C Initial failure -32 (one seal leaked)* Complete failure -40 (all 3 seals leaked) Min sealing temp. -31 (all 3 seals ok)
FKM ULT (316 Size) Temperature, °C Initial failure -42 (one seal leaked)* Complete failure -46 (all 3 seals leaked) Min sealing temp. -41 (all 3 seals ok)
* Initial failure recorded on port 3 in each case. At the time of writing this work is being repeated.
Fig 13, Test results
Page 13 of 15 pages Low Temperature Sealing
Fig 14 Pressure Applied After Cooling
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0HNBR LT FKM LT FKM ULT
Elastomer Type
Tem
pera
ture
, C
Initial Failure
Complete failureMin sealing temp
Fig 14, Graphical summary: Leakage temperature range between single seal failure, all 3 seals and temperature at which all 3 seals held pressure.
Taking the FKM ULT, a further test to establish the effects of pressure increase and reduction on sealability was carried out. The test fixture was cooled to the minimum sealing temperature (-41°C), and a reduced pr essure of 50 bar was applied. The O-rings continued to seal effectively at this temperature.
A further exercise studied the effect of increased pressure on low temperature sealing capability. At 175 bar the O-rings sealed effectively down to -45°C, giving an improvement of 5°C.
Taking the FKM LT, a further test to establish the effects of pressure increase and reduction on sealability was carried out. The test fixture was cooled to the minimum sealing temperature (-31°C), and a reduced pr essure of 50 bar was applied. The O-rings continued to seal effectively at this temperature.
A further exercise studied the effect of increased pressure on low temperature sealing capability. At 175 bar the O-rings sealed effectively down to -40°C, giving an improvement of 8°C.
At the time of writing this work was yet to be carried out on the HNBR LT.
Page 14 of 15 pages Low Temperature Sealing
LABORATORY ASSESSMENT OF LOW TEMPERATURE BEHAVIOUR AND COMPARISON WITH LEAK TEST RESULTS
The same 3 compounds were evaluated for low temperature performance using Gehman Torsional Modulus, Temperature Retraction and Dynamic Mechanical Analysis (DMA). These test methods and associated test procedures were described earlier. Fig. 15 summarises the results alongside the leak test data.
HNBR LT FKM LT FKM ULT Temperature Retraction, TR10
-36°C -31°C -40°C
Torsional Modulus, T70
-40°C -31°C -40°C
Tg (established by DMA*)
-31.7°C -18.8°C -27.3°C
Brittle Onset Temperature, (established by DMA*)
-45.8°C -36.0°C -45.6°C
Min. sealing temp (pressurised before temp. drop)
-53°C -54°C -55°C
Min sealing temp (pressurised to 50 bar at test temperature)
Data not yet available -31°C -41°C
Min sealing temp (pressurised to 100 bar at test temperature)
-41°C -31°C -41°C
Min sealing temp (pressurised to 175 bar at test temperature)
Data not yet available -40°C -45°C
*Carried out by RAPRA (Rubber and Plastics Research Association)Fig. 15, Laboratory Test Results With Summarised Leak Test Data
CONCLUSIONS
Temperature Retraction TR10 values are normally close to those of Gehman Torsional Modulus T70. In this particular data set, the Gehman T70 temperatures align well with the leakage temperatures obtained when the temperature was reduced without system pressure. This is more reflective of ‘real life’ applications. The Tg’s obtained by DMA had little relevance, however there may be a link between ‘Brittle Onset Temperature’ and the minimum temperature a static elastomer O-ring can be made to seal when pressurised after reaching its operating temperature.
Based on our findings to date there appears to be a temperature down to which static O-rings will seal at pressures of at least up to 175bar, which the writers refer to as ‘Full Sealability’ . These data suggest this to be represented by the temperature at which a Gehman value of T70, or a Temperature Retraction value of TR10 is achieved. If the tests suggest different temperatures, select the lower of the two.
Immediately below this, the elastomer becomes very ‘leathery’ and unresponsive. If the system is pressurised first, the O-rings will seal at much lower temperatures. This is however not so representative of the majority of applications. Different elastomers will have varying distances between the onset of increasing stiffness, and brittleness. DuPont suggested that static O-rings will seal at 15°C below the TR 10 value. Under certain conditions this could be the case, though Fig. 15 puts the differences between 15 to 23°C dependant up on material. The writers refer to this as the region of ‘Conditional Sealability’ , where factors such as level of squeeze, volume fill, lubrication and system pressure will have a profound influence on the effectiveness of a seal.
As the reader will note, the study has not at this stage studied the effects of stress relaxation or other ageing effects on low temperature performance.
Page 15 of 15 pages Low Temperature Sealing
FURTHER WORK
The testing will continue with two further seal cross sections, and the remaining HNBR LT tests. The effects of temperature cycling, stress-relaxation, increased groove fill and housing finish along with other materials will follow. Data from Compression Stress Relaxation (CSR) testing will also be compared to leak test results. This will attempt to find a link between residual sealing force and sealing performance. Work at higher operating pressures will be conducted to further investigate the effects of pressure on Tg shift.
ACKNOWLEDGEMENT
The authors gratefully acknowledge the help and assistance provided by Stephen Winterbottom in the preparation of this paper.
REFERENCES
1. Revolta, W., ‘Low temperature Sealing Capabilities of Fluoroelastomers’, ‘Rubber World’, Oct. 1991.2. K.D. Pae, C. L. Tang & E.S. Shin-American journal of applied physics vol 56 (1994)3. Wen Chou V Wang & Edward J Kramer-Journal of polymer science polymer physics edition vol 20 1371-
1384 (1982)4. G Gee-Polymers vol 7 (1966)5. Thomas, E., ‘New Fluoroelastomers Developments for Aerospace Sealing Applications’, DuPont Dow
Elastomers6. Bronowski, D. R., ‘Performance Testing of Elastomeric Seal Materials Under Low and High Temperature
Conditions’, Sandia National Laboratories, 2000
James Walker Asia PacificTel: +65 6777 9896Fax: +65 6777 6102Email: [email protected]
James Walker AustraliaTel: +61 (0)2 9721 9500Fax: +61 (0)2 9721 9580Email: [email protected]
James Walker Benelux(Belgium) Tel: +32 3 820 7900Fax: +32 3 828 5484Email: [email protected]
(Netherlands)Tel: +31 (0)186 633111Fax: +31 (0)186 633110Email: [email protected]
James Walker BrasilTel: +55 11 4392 7360Fax: +55 11 4392 5976Email: [email protected]
James Walker ChinaTel: +86 21 6876 9351Fax: +86 21 6876 9352Email: [email protected]
James Walker DeutschlandTel: +49 (0)40 386 0810Fax: +49 (0)40 389 3230Email: [email protected]
James Walker FranceTel: +33 (0)437 497 480Fax: +33 (0)437 497 483Email: [email protected]
James Walker IbericaTel: +34 94 447 0099Fax: +34 94 447 1077Email: [email protected]
James Walker Inmarco (India)Tel: +91 (0)22 4080 8080Fax: +91 (0)22 2859 6220Email: [email protected]
James Walker IrelandTel: +353 (0)21 432 3626Fax: +353 (0)21 432 3623Email: [email protected]
James Walker ItalianaTel: +39 02 257 8308Fax: +39 02 263 00487Email: [email protected]
James Walker Mfg (USA)Tel: +1 708 754 4020Fax: +1 708 754 4058Email: [email protected]
James Walker New ZealandTel: +64 (0)9 272 1599Fax: +64 (0)9 272 3061Email: [email protected]
James Walker NorgeTel: +47 22 706800Fax: +47 22 706801Email: [email protected]
James Walker Oil & Gas (USA)Tel: +1 281 875 0002Fax: +1 281 875 0188Email: [email protected]
James Walker South AfricaTel: +27 (0)31 304 0770Fax: +27 (0)31 304 0791Email: [email protected]
James Walker UKTel: +44 (0)1270 536000Fax: +44 (0)1270 536100Email: [email protected]
James Walker worldwide sales and customer support
BP/DML4380 1012/1mPIIL2360697
Registered Office: James Walker Sealing Products and Services Ltd, Lion House, Oriental Road, Woking, Surrey GU22 8AP, United Kingdom. Reg No. 00264191 England
© James Walker 2012
