Problems of Selection of Lubricants for Ethylene High-Pressure Compressors. 4. Investigation of Antifriction Properties of Naphtene and Polyglycol Oils during High Loading of Solid Lubricant Pair

The antifriction properties of naphtene and polyglycol oils during little loading with lubrication of pair bronze-tungsten-carbide-alloy WK-6 (WK-ll) and graphelon-20-WK-6 (WK-11) and high loading with lubrication of pair ball-bearing-high-chromium steel ШХ -15 - steel ШХ -15 are investigated. New correlations of viscous-and-thermal and antifriction properties of different polyglycol oils permit to creating effective composition on its base. The dependence of seizure loading during testing on FBFM on the molecular mass of different polyglycols, wear spot on the axial loading and boundary loading on concentration of additives in naphtene and mineral oils are found. The mean-square relative deviation of diameter of spot of wear from the spot by Hertz give generalization assessment of antiwear properties of lubrication oils. four-ball friction machine, properties, bronze, graphelon-20 , mineral, naphtene, polyglycol and polybutene oils.

For large technological lines was required equipment, which guarantee high coefficient of using working times.One of the essential factors directed to this was using synthetic lubricants with high antiwear and antiseizure properties.
Use of naphtene and polybutene oils for lubrication of friction pair of the ethylene high-pressure compressors substantially decreases using coefficient of compressors equipment, but use of polyglycol oils decreases properties of polyethylene -dielectrical and sanitarianhygienical indexes and resistance to atmospheric and electromagnetic influences.
Alloying of compressors lubricants with viscous, antiseizure or others additives substantially decreases temperature of flashing and decreases dielectrical properties of polyethylene.
The ways of finding effective compressors oils are alloying of oils with high-temperature or viscous additives, which are similar to accordingly naphtene and polyglycol oils and also synthesis of new polyglycols.
antiwear properties which are brought in let use them for assessments of others lubrication materials.
In general: wearing of specimens from bronze during lubrication with polyglycol oils 1.31-5.86time in friction on BK-11 and 1.11-4.84time in friction on BK-6 bigger than with naphtene oil.
It is necessary to give an estimation of the antiwearing and antiscratching properties on the results of tests on a four-ball friction machine.The specific loads of 1850-7500 MPa can be achieved in contact of working bodies of a four-ball friction machine.

Four-ball friction machine
Comparable characteristic of loading capacity and antiwear properties of lubricants on four-ball friction machine in high-load contact conditions lets choose the most effective one.
Tests were carried out on four-ball friction machine [15][16][17][18], Machine parameters and wear indexes were found: 1) relative sliding velocity = =0.576 where N -axial loading on three balls; 3) friction coefficient: where F fr -friction force; l -distance from the rotation axis to the contact point of lever with tensiometer (l = 83 mm); f fr -force, that bends tensilebeam: 4) static initial specific loading P N , which stands lubrication layer at the end of friction: where d H -diameter of elastic deformation area by Hertz, which is calculated by Hertz's formula: where E -modulus of ball's elasticity (for steel ШХ-15 Е = 2.1•10 5 N/mm 2 ); N -normal loading on 3 balls [N]; 5) specific loading, which is at the end of friction: where d w -wear spot diameter; 6) overfall of specific loading, which stands lubrication layer at the beginning of sliding:

8) hydrodynamic effects, which characterize conditions of boundary friction were calculated by formulas:
• at the beginning of testing • at the end of testing where d Wi , d Hi were chosen from N = 200 N to N ≈ N cr .
(seizure) by 100 N + d w at N cr (seizure).

10) during analysis of antiwear properties of oils conditional antiwear index was used [3]:
= (20)  For each series average diameter of wear spot, dispersions, mean-square deviations, coefficients of variation and Cochran's criterion were calculated.For three series coefficient of variation varied from 2.58 to 12.46.Table values of Cohran's and Student's criterions were taken by [23].
Proxy interval for average value: For the third series: G calc = 0.2356, which is less than from the table G T {N = 9; n = 5; α = 0.01} = 0.3934 and G T {N = 9; n = 5; α = 0.05} = 0.3344.This confirms homogeneity of dispersions row (9).Error of experiment for the third series: Proxy interval for average value: Joining up of first and third series of tests has lead to such statistic assessments: G calc = 0.2173, which is less than from the table G T {N = 14; n = 5; α = 0.01} = 0.29624 and G T {N = 14; n = 5; α = 0.05}= 0.25114.This confirms homogeneity of dispersions row (14).Error of experiment: Proxy interval for average value:

Antifriction properties
Loading capacity and antiwear properties were tested on four-ball friction machine (FBFM) [15; 16; 17; 18; 19]: balls from the steel IIIX-15(HRC 52-54) with diameter 12.7 mm, loading time l min., rotation number of upper ball 1140 rot./min.(during testings of polyethyleneglycols rotation number of upper ball 1470 per minute) and 4 hours and rotation number 1470 per minute during tests on loading capacity and antiwear properties accordingly (in last test axial loading N=200 N; N i =82 N).
Results of tests on FBFM on loading capacity (seizure loading on one ball N i ) and antiwear properties (average diameter of wear spot d i ) are adduced in Tabl.3-5 and shown in Fig. 1.In this case we have a row by antiwear properties: polyglycols > polybutene compositions > naphtene.It is known, that increasing of moisture in polyglycol oils decreases antiwear properties of oils and quality indexes of polyethylene.
Information of testing of relations of wear spot (d) with the axial loading (N), loading on ane ball in the teoretical point of contact (N i ) and average initial preassure in the contact point (P c ) for fluids is demonstrated on fig.4-11.
Testing of mixtures of polyglycol oil and glycerin shows, that antiwear properties of such mixtures substantially become worse when content of glycerin is more than 3% in polyglycol oil (tabl.7).Input of viscous polybutene additives to naphtene oils up to 5% decreases wear of steel, and input of more than 5% -not substantially influences on wear.From, the synthetic oils Orites 210 DS has the highest antiwear properties (Fig. 6).
As it seen from the fig.9, ramified polypropyleneglycols on the base of glycerin give substantial increasing of loading capacity, when molecular mass of oligomer increases.
) where d b -ball's diameter (d b = 12.7 mm); ω -angular rotation velocity of upper ball; α -angle in the base of pyramid from the balls (between tetrahedron height and edge -rib of tetrahedron), which (when diameter of balls d b = l2.7 mm) equals 35°20'; where ρ -density of oil [kg/m 3 ]; η -dynamic viscosity of oil [N•s/m 2 ]; ν -kinematic viscosity of oil [m 2 /s]; υ -sliding velocity [m/c]; d H , d w -diameter by Hertz and diameter of wear spot; N i -normal loading on one ball Ha [N]; 9) generalized wear index (by testing results on seizure loading or long-duration wearing:

Fig. 2 .
Fig.2.Dependence of mean diameter of wear spot of steel balls (steel ШX-15) during tests on FBFM on concentration (c v ) of mineral oil in PVBE: 1 -Risella-33; 2 -industrial 45 oils; 3 -vaseline medical.Testing conditions: n=1470 rot./min., N=200 N (N і =82 N), f=24.5 s -1 , τ=4hours., d e =12,7 mmThat is, more «soft» conditions of boundary friction leas to smaller values of wear, when loading conditions of tests are relatively small.That is why index d w , when N i →min in 4 hours is not enough informative relatively with assessment of antiwear properties of oils.

Fig. 3 .
Fig. 3. Dependence of boundary loading on one ball from steel ШX-15 during tests on FBFM on concentration of PVBE in naphtene oil Risella-33 (number of upper ball rotations: 1-835; 2-1470).Testing conditions: τ=l min., d e =12.7 mm More information give results, when Ni→min in 30 hours of tests (Fig. 1), or realization of long-duration tests (4 hours) in boundary of loadings from N i =80 N to N i =362 N (Tabl.6).In this case we have a row by antiwear properties: polyglycols > polybutene compositions > naphtene.

Fig. 5 .
Fig. 5. Relation of wear spot (d) with the axial loading (N), loading on one ball in the theoretical point of contact (N i ) and average initial pressure in the contact point (P c ) for fluids: 1 -vaseline oil (medical); 2 -industrial oil-20; 3 -compressor house oil -12 M; 4 -aviation oil MC-20.Testing of wear from loading during long-duration tests (Tabl.6), which determine temporary resistance of lubricant to thermomechanical influences shows the advantages of Risella-33 over naphtene oil NKM-40 and advantages of polyglycol oil Laprol over Orites.Input of viscous additives into naphtene oil also decreases wear during long-duration testing, but critical loadings do not change much (Tabl.6i 7).From, the synthetic oils Orites 210 DS has the highest antiwear properties (Fig.6).As it seen from the fig.9, ramified polypropyleneglycols on the base of glycerin give substantial increasing of loading capacity, when molecular mass of oligomer increases.In Fig.12dependence of seizure loading on one ball on molecular mass of polyglycols is represented:• linear polypropyleneglycols (1);• ramified polypropyleneglycols on the base of glycerin (2);• statistics copolymers of propylene and ethylene oxides (70%) Laprol (3);

Table 2
Statistic findings of wear tests on FBFM

Table 5
Antifriction and viscous-and-thermal properties of polyglycol oils

Table 8
Criterions of assessment of oils antiwear properties

Table 9
Comparable characteristic of antiwear properties of oils based on the criterions d w , J 1 -J 4