Gaskets
Table 1 . List of all tests carried out
Dichtungstyp durchgeführte Versuche Prüfung
TF 3 mm Leckage 40 bar
Temperatur [° C ]
-150
TF 3 mm E-Modul -50 TF 3 mm E-Modul -100 TF 3 mm E-Modul -150
TF 3 mm PQR 30 MPa
TF 3 mm PQR 30 MPa
TF 3 mm PQR 30 MPa
-50
-100
-150
ePTFE 2 mm E-Modul -100 ePTFE 2 mm E-Modul -150
ePTFE 2 mm PQR 30 MPa
-150
NA 2 mm E-Modul -150
NA 2 mm PQR 30 MPa
NA 2 mm PQR 30 MPa
-100
-150
The gasket parameters Q smax and EG determined from these curves are tabulated . The compression test at -50 ° C shows a continuous increase in the elastic modulus . The TF gasket shows stronger deformations at the gasket stress levels above 60 MPa . At -100 ° C , a similar behavior only occurs in the last step above 80 MPa . The gasket shows no signs of damage . The modulus of elasticity increases steadily as a function of the gasket stress . In the compression curves at -150 ° C , no gasket damage can be identified up to a load of 100 MPa . The course of the modulus of elasticity at -150 ° C increases continuously with increasing gasket stress up to 100 MPa in all tests . The lower the temperature , the bigger the curve slope which shows a stiffer material with higher E-Modulus . The maximum tested gasket stress was set at 100 MPa at all temperatures . No damage to the test specimens was found in the tests carried out . Figure 3 shows the different compression curves for -50 , -100 and -150 ° C . The lower the temperature , the less the seal deforms as the load increases .
E-Modulus [ MPa ] E-Modulus [ MPa ]
Figure 4 . E-Modulus comparison of PTFE at 30 MPa and different temperatures .
Figure 5 . E-Modulus comparison of different materials at -150 ° C .
1
0,5
0
5000 4000 3000 2000 1000
0
0,68
4621
4621
strukt . PTFE ePTFE NA
Figure 6 . PQR comparison of TF at different temperature .
Figure 4 compares the EG values at 30 MPa and the different temperatures . As the temperature decreases , the modulus of elasticity increases at the same time . The modulus of elasticity at RT is 1063 MPa and at -150 ° C the modulus of elasticity is already 4621 MPa . Figure 5 compares the E-modulus of TF with ePTFE and NA . ePTFE is slightly higher than the TF , which is also caused by the thinner initial thickness of the ePTFE gasket . The fiber gasket , which is also 2 mm thick , has a significant higher E-Modulus .
Creep relaxation test Creep relaxation tests were carried out at different temperatures and with a stiffness of 500 kN / mm . The initial gasket stress was set at 30 MPa .
E-Modulus : -150 , -100 , -50 and 23 ° C
3173
2604
[ -150 ° C ] [ -100 ° C ] [ -50 ° C ] [ 23 ° C ]
E-Modulus of different gasket materials at -150 ° C
6614
Creep relaxation [ PQR ] between -150 and + 150 ° C
0,7
0,77
31606
[ -150 ° C ] [ -100 ° C ] [ -50 ° C ] [+ 23 ° C ] [+ 150 ° C ]
0,77
0,43
1063
The creep relaxation factor PQR for TF was tested in a range from 0.64 to 0.77 , for NA at 0.91 to 0.93 and for ePTFE at 0.89 . Figure 6 shows that cooling down from ambient to -150 ° C the PQR result decreases . Temperature expansion has a significant impact . Figure 7 illustrates the shrinkage of PTFE as it cools down to -150 ° C . Figure 8 compares the PQR of TF with ePTFE and NA . The different gasket thicknesses of TF , ePTFE and NA must be taken into account . The lower the PTFE gasket thickness , the higher the PQR value . ePTFE shows a higher PQR versus TF . The fiber gasket has the highest PQR value . The fiber gasket is so hard at -150 ° C that no further deformation of the gasket occurs . In terms of safety , elastomer
38 Valve World February 2024 www . valve-world . net