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O形密封件摩擦性能英文文献和翻译(4)

时间:2017-01-02 15:04来源:毕业论文
All O-ring seals tested had the same dimensions, i.e. inside diameter 24.77 mm (to be used with 25 mm shaft diameter) and cross section diameter 5.33 mm. However, a number of other seal designs have a


All O-ring seals tested had the same dimensions,  i.e. inside diameter 24.77 mm (to
be used with 25 mm shaft diameter) and cross section  diameter 5.33 mm. However,
a  number of other  seal designs have also been tested for comparison of perfor-
mance. A special design  of  seal  is a PTFE-encapsulated O-ring. The central core  is a
solid O-ring moulded  in silicone  rubber. This  is surrounded  by a tube of  PTFE. The
seal design  aims  to combine  the sealing  performance  of  an elastomer  with  the chem-
ical resistance and low friction of PTFE. The core provides  the sealing action and
the elasticity  required for continuous  reset of  the seal after compression, although
not quite as much as a  standard elastomer O-ring. Over long periods of time the
PTFE tube protects  the  seal  from  hardening  and  thus  the  elasticity  is maintained.
Despite the apparent simplicity of  the seal, a number of precautions have to be
taken  to ensure correct operation of  the O-ring  seal. The dimensions  of  the seal and
its housing are critical. Poor surface finish of the mating element  can also lead to
excessive  wear of  the seal. In general,  it  is  important  that  the seal  comes  into contact
with  no sharp machined  edges.
The O-ring materials  tested are given  in  table 1.
2.4. INSTRUMENTATION
The studies required accurate measurement of axial displacement of the shaft
(not greater  than a fraction of a millimetre)  as the rubber materials used had a ten-
dency  to creep  before  large movement  of  the shaft occurred. The axial displacement
of  the shaft was measured using two inductive  transducers; one was active and the
other  one passive.  The  transducers were able  to  detect any  change  in  distance
between the  transducer and a  ferromagnetic material through a variation in the
inductance  in the coils within  the probe. The output from the two probes was sent 3. Discussion  of results
3.1. PTFE-ENCAPSULATED  SEAL
The results of  testing are shown  in fig. 5 and refer to the seal  tested over  the entire
10 MPa operating pressure range at 9% squeeze. As expected, increasing the pres-
sure differential across  the seal increased the friction force considerably. Indeed,
the frictional force at 10 MPa was over  five  times  that at atmospheric  pressure. This
increase  in  friction  force  is  undoubtedly  related  to  the  increase  in contact  area
between the seal and the shaft,  resulting from inevitable seal extrusion due to the
pressure differential.
The curve representing  the relationship between friction and pressure is not lin-
ear.  It  shows an  initial period of increase in friction followed by a  second period
where  the gradient is less and finally a third period where there is again a rapid rise
in friction. A possible reason for this behaviour could be asigned  to the fact that the
seal  is made of  two materials with  entirely  different mechanical  properties.
A  series of measurements were  taken  for  the PTFE-encapsulated O-ring  at  a
value  of 16% squeeze. They  are  shown in fig.  6  together with  those found at  9%
squeeze. The graph shows  that at 16% squeeze  the frictional force values are consis- O形密封件摩擦性能英文文献和翻译(4):http://www.youerw.com/fanyi/lunwen_1699.html
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