Ñåêöèÿ 3/Îòðàñëåâîå ìàøèíîñòðîåíèå
Zhetesova
G.S., Zharkevich O.M., Buzauova T.M., Pleshakova E.A.
Evaluation of the wear cuffs in friction units of hydraulic jacks
Karaganda State Technical University, Kazakhstan
Great influence
on the wear sleeves in mobile tribounit "piston-seal" of hydraulic
jacks of mechanical supports has condition of contact surfaces lip seal and
piston, and also presence of a "the third body": the lubricant is in
the form of film frictional transfer [1]. When working tribounit is experienced
higher wear rate due to changes in the structure and properties of the surface
layers of wetted parts and lubricant.
The process of
tribounit "piston - seal" wear dramatically is enhanced with:
- increase in the relative sliding velocity;
- beats and irregular geometry of the contacting surfaces;
- operation at
the "start" and "stop";
- presence of
abrasive in the friction zone;
- changing temperature and humidity of the environment
[2].
As a
result there is variety of defects: traces of abrasive wear, breach of surfaces
of parts geometry, volume restriction or swelling of the polymer seals etc.
Wear
rate is determined by formula:
, (1)
where 
– specific wear, adopted
at 100 0C and relative sliding velocity of 1 m/s; 
– critical temperature
of destruction of cuff material; 
– coefficient
determining influence of temperature; 
, 
– coefficients
determining effect of relative sliding velocity.
Wear rate for the
whole period of operation can be written formula:
, (2)
where 
– thickness of the layer
worn on the friction way 
.
1 - metal part; 2 - polymer
part; 3 - film of friction transfer
Figure 1 -
Scheme of metal-polymer system
If we consider
that tribounit "piston-seal" is a metal-tribosystem (Figure 1)
consisting from the metal part 1 and part 2 of the polymer, which are in
contact with the polymer film of friction transfer 3, wear rate is determined
by wear
of the polymeric material (sealing)
, the value of which can be calculated by the formula [3]:
,
(3)
where 
– mass of the wear of the material in contact
element for seal; 
– density of the polymer seal material; 
– surface area of friction.
Two materials for packing seals of hydraulic jacks for mechanical supports were
considered in our case: rubber K20 and polyurethane LUR-PT. Characteristics of cuff materials are presented
in Table 1.
Table 1- Characteristics of cuff materials
|
Characteristic |
Value of the characteristic |
|
|
Rubber K20 |
Polyurethane LUR-PT |
|
|
Tensile
strength, MPa |
12,7 |
35 |
|
Elongation at break (at least),% |
300 |
500-600 |
|
Hardness
units. Sor |
40 - 50 |
55 - 97 |
|
Demolition, m3 / t. Dzh |
45 - 80 |
11,25 - 26,6 |
|
Density, kg/m3 |
1,37 |
1,259 |
Using formula (2)
we obtained following values of wear-out rate of
hydraulic jacks seals (Table 2).
Table 1- Values of wear-out rate of hydraulic jacks seals
|
Friction unit |
Wearing part; material |
Conditions of wear |
Wear-out rate Ih |
|
|
Counterbody |
Loading parameters; environment |
|||
|
piston-seal |
cuff; rubber K20 |
cylinder 40H |
υsl = 0,1 ì/c; Ð = 40 ÌPà lubricant: water-oil emulsion VNIINP-117 |
1,5·10-8 |
|
cuff; polyurethane LUR-PT |
5·10-8 |
|||
Wear rate of
polyurethane is 3 times lower than wear rate of rubber K20. It can be concluded
about the resource of the cuffs. When using rubber K20 resource of cuff is 3
months, but polyurethane LUR-ST resource is approximately 1 ÷ 1,2 year.
References:
1.
Garkun D.N. Triboengineering. -
Mashinostroenie, 2000. - 424 p.
2.
Kondakov L.A. Seals and
sealing technology. - Mashinostroenie, 1994. - 448.
3. Mashkov JK Composite materials based on
polytetrafluoroethylene. Structural modification. - Mashinostroenie, 2005. –
240 p.