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tently higher than at 9%.
Repeated tests were carried out but is was found that the scatter of results is con-
siderable and therefore it is rather difficult to suggest any governing law. This is
believed to be linked to the lack of dimensional accuracy of the O-rings tested.
Analysis of experimental error is given in a later section.
3.2. EFFECT OF O-RING MATERIAL
The performance of a PTFE-encapsulated O-ring was compared to that of an Fig. 6. Friction force against gauge pressure for teflon-encapsulated seal at 9% and 16% squeeze.
ordinary rubber O-ring as shown in fig. 7. It can be seen that the PTFE-encapsu-
lated O-ring shows significantly lower friction than the conventional single-mate-
rial O-ring type seal. The seals of ordinary design could only be tested over a limited
pressure range. The force required to overcome the friction exceeded the limits of
the test rig. However, it can be seen from fig. 7 that the rubber-only O-ring seals per-
form differently from the teflon-encapsulated O-ring seal. The gradient of the
curves representing frictional performance of the rubber se~tls is greater than that
of the PTFE-encapsulated seal with the force increasing far more quickly with
increasing pressure. This could well reflect the difference in hardness of materials tested. The PTFE-encapsulated silicone O-ring had a hardness of 90 as measured
on Shore A scale, while the hardness of the natural rubber O-ring was 60.
This friction behaviour can be explained in the following way. The exclusively
rubber seals are all much more compliant than the teflon-encapsulated seals. This
means that, when pressurised, the exclusively rubber seals have more tendency to
be deformed and extruded between the shaft and the seal gland. As a result of such
extrusion there is a greatly increased resistance to motion and hence frictional
force.
As mentioned previously, a shaft with its surface ground to 0.2 #m was used
throughout the studies and, therefore, the results presented are pertinent to this spe-
cific roughness. However, the effect of roughness on the performance of O-ring
type seal considered in this paper could be significant.
3.3. EFFECT OF LUBRICATION
A series of tests were carried out on teflon-encapsulated O-rings by adding differ-
ent lubricating fluids to the shaft/seal interface. The results of these tests are shown
in fig. 8. The friction forces measured under lubrication conditions were, as antici-
pated, significantly less than those recorded under dry conditions. The differences
in the magnitude of frictional force between oil and grease used are not very signifi-
cant. The high-melting-point grease gave the lowest values. The results demon-
strate that if any lubricant was to enter the shaft/seal interface the frictional force
would vary greatly and in an unpredictable manner. If consistent values are to be
found it is clearly important to ensure that lubricating liquids cannot enter the
shaft/seal interface during operation.
Since all the friction measurements were carried out at the commencement of对O型环式密封件的摩擦和直线运动开始时轴的表压之间关系调查结果进行提出和讨论。多个不同的O形圈的材料进行了研究，与最低的摩擦在干燥条件下被发现是由聚四氟乙烯包覆硅胶密封条生产。大量的润滑流体摩擦密封进行了研究与效果结果包括。