THE INFLUENCE OF LIMITING STATES ON TRIBOLOGICAL PROPERTIES OF ECOLOGICAL LUBRICANTS Текст научной статьи по специальности «Электротехника, электронная техника, информационные технологии»

ENGINEERING SCIENCES

THE INFLUENCE OF LIMITING STATES ON TRIBOLOGICAL PROPERTIES OF ECOLOGICAL

LUBRICANTS

1Toth Frantisek 2Tokoly Pavol 3Nogli Dusan

13 Faculty of Engineering, Slovak University of Agriculture in Nitra 2 Faculty of Special Technology ,The Alexander Dubcek University of Trencin

Abstract. The article describes the usage of ecological oil as an amid-substance in the friction seating of hydraulic and transmission systems of equipments working in the agricultural area. Tested friction seating was composed of pair sleeve - shaft, while sleeve was made from B 60 material and shaft was made from steel 16MnCr5. The experimental tests were carried out on the equipment Tribotestor M'06, where lubricating material (medium) was the ecological oil Fuchs PLANTOHYD 46 S (permitted temperature range: -30 °C to 90 °C). The measurement test itself was carried out in two temperature ranges, in ambient temperature (without heating) and with oil heating to 70 °C. The overall experiment duration was set to 70 min. At the beginning of the test it run-up was set to 10 min. where load force was in range 500 - 3000 N (every 120 s. load was increased by 500 N step). The results of the experiments were processed using statistical methods and on the basis of them the relation offriction coefficient and temperature between the time of test duration were established. The information about mass loss and change of roughness of both tribological elements were also statistically processed.

Keywords: ecological oil PLANTOHYD 46 S, sliding bearing, tribological properties

INTRODUCTION. Progressive change in attitude towards the surrounding environment is reflected in all social life areas, increased usage of ecological processes and resources is supported by legislation changes on the national, but mainly on the international level. As far as agriculture is concerned it is also included with the areas of agricultural primary production incorporated.

The market with ecological lubricants is spreading significantly and one of the products offered are ecological oils usable in hydraulic and transmission systems. The experimental test was aimed exactly at this group of products where the ecological oil PLANTOHYD 46 S (FUCHS Lubricants (UK) Plc) was chosen for the assessment of tribological properties. The tested product is an universal oil usable in all hydraulic and circulating systems, where the usage of oil class ISO VG 46 is required. It is used for mobile and static hydraulic systems, i.e. mainly in equipments, which operates in environments with near danger of leakage of hydraulic fluid with direct threat (contamination) of soil, underground or surface water. After leakage it flows on water and it may be easily removed, it is not penetrating into underground water, but it keeps itself mainly on upper (surface) layers of soil, where it is fast biologically decomposable. Base fluid (and also used additives) is toxically harmless, it does not contain heavy metals and chlorine compounds, it is biologically decomposable to more than 96 % according to the CEC-L-33-A-93. The scope of product usage is within the range -30 °C to 90 °C, with temperature peaks around 95 °C the usage of lubricant is allowable with respect to its boundary viscosity. The lubricant oil benefits are the following [13]:

- made of sustainable raw materials,

- good corrosion protection,

- rapidly biodegradable (OECD 301 B),

- multi-range character (streamlining number of types),

- excellent lubricating properties,

- low evaporation losses,

- very good viscosity-temperature characteristics,

- good low temperature performance,

- excellent shear stability,

- natural cleaning capacity,

- high aging resistance,

- very good wear protection.

Characteristic properties of tested lubricant are listed in table 1.

Table 1. Properties of PLANTOHYD 46 S [14, 15]

Properties Units Value Test method

ISO VG - 46 DIN 51519

Kinematic viscosity: mm2/s DIN EN ISO 3104

at - 20 °C 1500

at 0 °C 330

at 40 °C 48

at 100 °C 9.4

Viscosity index - 184 DIN ISO 2909

Density at 15 °C kg/m3 920 DIN 51757

Colour ASTM 1.0 DIN ISO 2049

Flash point in open °C 300 DIN ISO 2592

cup acc. to Cleveland

Pourpoint °C -45 DIN ISO 3016

Neutralisation number mgKOH/g 1.1 DIN 51558-1

Scuffing and scoring failure load 12 DIN ISO 14635-1

test, FZG A/8.3/90 stage

Air release at 50 °C Min 5 DIN ISO 9120

Vickers pump test, type V105C - weight loss vane - weight loss ring mg mg pass < 30 < 120 DIN 51389

Effect on sealing 80 °C ISO 6072

materials:

HNBR, 1008 h: Shore - 3.3

- change of Shore A hardness % + 5.8

- relative change of volume Shore % + 1.0 + 0.5 ISO 6072

FKM, 1008 h:

- change of Shore A hardness

- relative change of volume

The assessed lubricant is compatible with materials usually used in hydraulic systems, particularly e.g. in the area of construction, water treatment, agriculture and forestry. Another testing possibility of ecological oils is its use in hydraulic systems in laboratory or in real conditions [4, 5, 6]. The aim of the article is to assess tribological properties by experimental tests carried in boundary oil temperature state.

MATERIALS AND METHODS. For experimental tribological tests of the ecological oil Plantohyd 46 S was used the universal measuring device Tribotestor M'06 (fig. 1), where the following can be experimentally performed:

a) boundary loading test (seizure test),

b) boundary speed test (speed seizure test),

c) load rating test for P-V diagram determination,

d) operating life test (durability).

Fig. 1 Measuring device Tribotestor M'06

The experimental device is composed of three main parts:

- testing part: power unit with rotational motion of samples, vertical load force and measuring head,

- pneumatic circle and electronic devices,

- controller unit: desktop PC allows starts, operating, management, data collecting and test evaluation.

The experiment was conducted through the use of seizure test, while before the beginning of the experiment the so-called heating device serving as heater was installed in the friction part on the Tribotestor M'06. This heater heated test head to the desired temperature of 70 °C. The heating device was composed of three parts:

- simple PID regulator,

- temperature sensor J (Fe-CuNi) with range - 40°C to + 500°C,

- electronic relay in heavy duty case (SSR RS 230 V 10 A DC IP).

a) b)

Fig. 2. Measuring head a) measuring head detail, b) test sample detail b) [8].

In the figure 2a is measuring head and test sample detail is in figure 2b. Friction node is composed of a pair of solids creating surface contact and by rotating testing solid (shaft) against friction bearing. Friction bearing itself (KaJo Metal, B 60) is pressed onto measuring head, all bronze - centrifugally casted with dimensions $ 30r7 x $ 25 F7 x 20 mm [10]. Testing shaft sleeve (14 220) was pressed onto cylindrical portion of supporting shaft dimensioned $24,960 mm (outer diameter) and 25 mm in length.

The supporting shaft was attached to power unit with the shrinking cone connection using tightening force through an internal wheel in the cone. Lubrication of friction elements by the tested ecological oil was done by gravitational dropping through the measuring head upper part.

Both friction elements were weighted before and after the experiment on the precise weights Voyager Pro VP 613CN and roughness was measured with the portable surface roughness tester

Mitutoyo SJ-201 (tested parameter: Ra - arithmetical deviation value of absolute profile deviations in n points of profile on base length).

During the experimental test shaft rotation equals 180 rev./min (clockwise). The test time was set to 70 min. with the 10 min. run-up phase. The loading force in the run-up was set to range 500 to 3000 N, where the load was increased by 500 N step every 120 s [7]. In the second series of the experimental tests measuring head heating was set to 70°C before the beginning of the test, all other parameters remain the same with first round of experimental tests.

RESULTS AND DISCUSSION. The recorded results of experimental measuring of the ecological oil Plantohyd 46 S on the experimental device Tribotestor M' 06 were statistically processed and assessed. Their results were the charts of friction coefficient (Fig. 3) and temperature (Fig. 4) depending on the test duration (valid for both temperature sets of measurements). The course of the curves showing separate waveforms were generated by the method of least squares.

In Fig. 3 it is possible to see the course of friction coefficient value of the PLANTOHYD 46 S during both temperature modes, where right after launching the test the friction coefficient value was increasing up to the time of 700 s. and after the test time passing slowly it decreased and then stabilized on the final value. During the test with ambient temperature (without heating) was the course of friction coefficient value more equal (flat course), the absolute value was stabilized approximately on number 0,01. The friction coefficient value during heating decreased more exponentially and the final value was stabilized on number 0,04. From listed above is clear, that with the influence of increasing temperature the friction coefficient increases, what can occur e.g. during increased operational loading of equipment.

„ „„

Friction coefficient (with heating)

■ Friction coefficient (without heating)

0,05

0,Q4 0,03

0,02 ^■fflSinini .'L^r^___,, , ,

o,oi

■ ol S M 5 S « r*i rvi n* r>i N f*> ro m i*> v Time, s

Fig. 3 Course offriction coefficient value of ecological oil Plantohyd 46 S with heating

and without heating

The course of temperature depending on the test duration is shown in figure 4, where these values serve as an example of heat conducting by using the ecological oil PLANTOHYD 46 S from the friction node area.

Fig. 4 Temperature course of the ecological oil Plantohyd 46 S with heating

and without heating

Precise weights Voyager pro VP 613CN offered information about mass loss of both friction elements (table 2). Assumption was confirmed, i.e. sleeve as a softer material reached higher mass loss in relation to both temperature modes. The value of average mass loss of sleeve without heating reached 0,024 g and the average value of mass loss during mode with heating was 0,014 g. The average values of mass losses of shafts were in both cases lower than sleeves following the value of 0,006 g in no heating mode and the value of 0,005 g in heating mode.

Roughness of the sleeve and shaft was determined by the portable surface roughness tester Mitutoyo SJ-201. The value of roughness Ra average change defines the change of friction element roughness during the experimental test duration (table 3). In this indicator the ecological oil reached during the experimental test without heating the lowering of sleeve surface roughness Ra in the point of contact value 0,626 ^m and in relation to the heating mode was the surface roughness Ra change on value -0,603 ^m. The value of surface roughness Ra average change of tested shaft during the mode with heating was higher than the surface roughness Ra change of tested shaft during the experimental test without heating.

Table 2. Values of average mass losses

Weight loss (g)

Fiichs Plantohyd 46 S without heating

Bearing shell Shaft

Material pair Number of experiment al test Before experiment After experiment Difference Before experiment After experiment Difference

o iN 1 37.607 37.585 0.022 400.762 400.751 0.011

T 2 37.496 37.475 0.021 398.259 398.253 0.006

I -) j 37.394 37.372 0.022 400.419 400.414 0.005

iN 4 37.430 37.403 0.027 400.738 400.736 0.002

<= m 5 37.352 37.336 0.016 410.221 410.215 0.006

O 6 37.453 37.432 0.021 404.767 404.770 -0.003

o 7 37.681 37.646 0.035 408.143 408.140 0.003

CQ S 37.390 37.360 0.030 394.432 394.416 0.016

Average 0.024 0.006

Fuclis Plantohyd 46 S with heating

Bearing shell Shaft

Material pair Number of experiment al test Before experiment .After experiment Difference Before experiment After experiment Difference

o iN 1 37.701 37.687 0.014 407.589 407.585 0.004

o) 2 37.253 37.241 0.012 402.153 402.147 0.006

1 ^ j 36.915 36.903 0.012 405.506 405.503 0.003

iN 4 37.052 37.033 0.019 398.054 398.05 0.004

<= m 5 37.658 37.644 0.014 404.359 404.353 0.006

O 6 37.581 37.565 0.016 403.458 403.454 0.004

o <o 7 37.351 37.339 0.012 406.246 406.242 0.004

CQ § 37.199 37.184 0.015 401.385 401.379 0.006

Average 0.014 0.005

Roughness of the sleeve and shaft was determined by the portable surface roughness tester Mitutoyo SJ-201. The value of roughness Ra average change defines the change of friction element roughness during the experimental test duration (table 3). In this indicator the ecological oil reached

during the experimental test without heating the lowering of sleeve surface roughness Ra in the point of contact value 0,626 ^m and in relation to the heating mode was the surface roughness Ra change on value -0,603 ^m. The value of surface roughness Ra average change of tested shaft during the mode with heating was higher than the surface roughness Ra change of tested shaft during the experimental test without heating.

Table 3. Values of roughness Ra average change

'Ra' change ([.tin)

Fuehs Pbntohyd 46 S without heating

Bearing shell Shaft

Material pair Number of experiment al test Before experiment After experiment Cliange Before experiment After experiment Cliange

o <N 1 1.195 0.770 -0.425 0.370 0.370 0.000

<N ÑT 2 1.205 0.585 -0.620 0.445 0.365 -0.080

i -> J 1.315 0.285 -1.030 0.335 0.340 0.005

<N 4 1.305 0.820 -0.485 0.410 0.405 -0.005

tí GQ 5 1.270 0.580 -0.690 0.350 0.355 0.005

O 6 1.280 0.885 -0.395 0.455 0.420 -0.035

o ■o 7 1.110 0.665 -0.445 0.410 0.405 -0.005

m 8 1.240 0.310 -0.930 0.415 0.395 -0.020

Average -0.628 -0.017

Fue lis Pkntohyd 46 S with heating

Bearing shell Shaft

Material pair Number of experiment al test Before experiment After experiment Cliange Before experiment After experiment Cliange

o <N 1 1.255 0.795 -0.460 1.105 1.23 0.125

<N ÑT 2 1.220 0.575 -0.645 1.06 0.94 -0.12

-> J 1.325 0.550 -0.775 0.885 0.745 -0.14

(N 4 1.365 0.920 -0.445 1.105 0.715 -0.39

tí GQ 5 1.290 0.598 -0.692 1.1 0.855 -0.245

O 6 1.314 0.756 -0.558 0.906 0.756 -0.15

o ■o 7 1.285 0.611 -0.674 1.09 0.959 -0.131

m 8 1.305 0.727 -0.578 1.12 0.939 -0.181

Average -0.603 -0.154

CONCLUSION. The main focus of the article was on the definition of usage possibilities of the ecological oil PLANTOHYD 46 S in designated tribological friction system, during reaching boundary state and that particular temperature of the contact point of two friction elements. The course of friction coefficient during the experimental test had a descending character in relation to both temperature modes. At the end of the experiment was reached lower value in no heating temperature mode, which was stabilized on the friction coefficient value 0,01. However, the ecological oil with heating of the contact point before the test had significantly higher level of the friction coefficient value descending during the experiment, which started stabilizing slowly on value 0,04 before the end

of the experiment. Lower mass losses were during mode with heating and that with sleeve and shaft also. The surface roughness Ra change was approximately the same during both temperature modes, but higher surface roughness Ra change occurred during the heating mode with shaft. On the basis of listed values above we can discuss about possible usage of the ecological oil PLANTOHYD 46 S in friction systems, in complete temperature range stated by the producer.

ACKNOWLEDGEMENT. This paper is prepared within the project VEGA 1/0227/15 Study of tribological characteristics of the new high hard coatings on materials suitable for gearings.

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