• Determination of activation energy π www . valve-world . net Valve World August 2023
An earlier investigation by this team concluded that elastomer life prediction using tensile property ageing could be unreliable , so this new study was carried by a working group ( James Walker , Kastas , Dupont , PPE and Cetim ) on the effects of thermo-oxidative ageing on compression stress relaxation ( CSR ) and compression set ( CS ), which was suggested to be able to give more accurate life prediction data .
Experiments
The group carried out a series of accelerated ageing tests on a specific rubber material in their laboratories . The material , which was selected and supplied by PPE , was a fluoro elastomer
Sealing
Arrhenius seal life prediction project :
To investigate the life prediction and the impact of ageing on elastomer seals , the Elastomeric & Polymeric Seals Division of the European Seal
Association ( ESA ) initiated a new study in 2019 .
results and analysis
( FKM ) with a hardness equal to 75 Shore A . Two types of samples were manufactured : ISO 815-1 Type B buttons ( 6,3 ± 0,3 mm thick and 13,0 ± 0,5 mm diameter ], and two sizes of O-ring to ISO 3601-1 ( SC-214 and SC-329 ).
Ageing conditions To apply accelerated ageing on the samples , three temperatures were selected ( 100 , 150 and 200 ° C ) for CS and the maximum temperature was limited to 180 ° C for the CSR jig . The six durations of the ageing phase were fixed to 24 , 72 , 168 , 336 , 672 and 1008 hours ( 42 days ). The ageing was carried out in an oven equipped with thermocouples connected to continuous recorders .
step |
step |
step |
( i ) |
( ii ) |
( iii ) |
By Benoît Omnès , Senior Expert in Sealing Technologies , Cetim
( a )
( b )
Figure 1 . ( a ) Test fixture with button to apply the compression set and ( b ) main dimension to evaluate the value of CS ( before ( i ), during ( ii ), and after ( iii ) compression ).
H 0
H 2
H 1
Force sensor
O-ring sample
O-ring secondary
About the author Benoît holds a PhD in Engineering Science , specialising in Material Mechanics . He has been a Senior Expert in Sealing Technologies at Cetim ’ s Fluid & Sealing Technology department since 2007 . Benoît ’ s primary focus is on the modelling , FEA simulation , and experimental characterisation of elastomeric seals in static sealing systems . Additionally , since 2017 , he has been responsible for coordinating R & D projects within the lab and partnerships .
Figure 2 . Sealing force relaxation apparatus ( CSR jig ) for O-ring SC-329 .
• Average
• Standard deviation
( 1 )
CS values or CSR
• Power law model *
• Exponential model **
• P-T-t model *
* For CS and ** For CS and CSR Figure 3 . steps of treatment to study the evolution of compression set and compression stress relaxation
( 2 ) Modeling
( 3 )
Arrhenius approach
• end of life criterion
• Ln ( t ) vs 1 / T
• Determination of activation energy π www . valve-world . net Valve World August 2023
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