No. 1, 1998 - Tribology in Industry

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If tlre value of function ytl$) rs close to -1, this would
mean that its membership is "beiter". In the range between
0 to I the membersliip function is linear. For any
type of sealing it is possible tc form a set of r membership
functions for n - operating conditions. Three functions
for compression seals are shown in Fig.3. Ihe number rr
for each one coulcl be different.
The mean value of membership function is
/1A
=
n
Iun{ri)
n
All membership functions are not of the same importance
for the decision rnaking. To quanri$'their irnportance
the weighting coefficients k; are introduced, Their value
could be ki < I or ki > 1. The mean value of membership
function will be detennined bv the eouation:
PA-
n
f-r
) K;'lt z lX;l
i-7
ti
\-r. / :
7''
The first step is tcl develop a procedure for calculating
the mean value of membership function ltA, ltB,ltc, ...,
for each type of sealing joint shorvn in Fig. 1 (t"ypesA, I),
C..).The sealing element with a greater value of membership
function will be rnore acceptable. The solutions
where even one fuzz,v function is equal to zero are not
acceptable.
Table L Sealing elernerts t+,ith ba.sic tibologic caractcrisrics
4. THE COMPUTATIONAL I'ROCEDURE
OF SEALING JOINT
The computaiioit is a procr:dlrre to establish the correlation
between dimensions, n)aterial. operating parameters
and operating conditions. Atler selection of the type
of seal, using the methocl dcscr:ibed in tire section 3, the
cornputation of seaiing joinis follows in such a rvay that
clirnensions, materials, friction klsses, wear, leakage.of
the fluid and heating are kept within the acceptable
values. The chosen characteristics of these paranteters
irre given in Tabie l.
The relationships are obtained mainly from the results of
experimental investigations brrt some could be calculated.
For example, the arial resistance in compression
seals (1)- Thble 1, could be either nieasured or calculated
if dimensiolis, pressure, material and roughness of surfacess
are known. The stress in seaiing p:rrts, fluid leakage,
and wear are in mutual correlation. In the case of spindle
packing, (2) and sealing rings (3), tlre relartions are based
r:n other theories lrecause the tribologic processes are
different. Axial sealing joints (4) are suitable for high slip
velocities and hirve lower contact pressure and resjstance.
Non-contact sealing joints (5) have the best caracteristics
for these conclitior.rs. The sealing principle there is
quite different. It is based on the increased hydraulic
resistance of fluid flon, throuljh tl.: clearance gaps in the
connection.
The selected trilrok-rgic variables in Table 1 show that
sealing connections belong to the tribologic systems.
The tribologic varilbles such as forces in the contacts,
stress, resistances. weAr, heating etc. clepencl on the cle-
lor.-
L\-
ta,E
lf ____
krn
Tibolog', itt itulrctrv, Volume 20, No. l, 1998.
29