J. Pošta, R. Zewdie

Czech University of Agriculture, Faculty of Engineering, Prague, Czech Republic

The development of biodegradable hydraulic liquids is supported by several realities, Those are an effort to decrease the significant area contamination of live environment by the leakage of hydraulic liquids during the breakdowns and accidents of machines with hydraulic mechanisms, an effort discover an alternative for oil products and for non food use of agricultural soil, etc. (Zewdie, 1997).

The majority of research and developmental works concerning these problems leads to the area of effects and behaviors of these liquids in nature and to the area of their initial properties. Less attention is directed toward other problems, e.g. to the changes of the properties of these liquids during their exploitation and their influence on mechanisms which were proposed for the work with the liquids of oil origin.

The authors worked on the methodics of the judgment of the overall effectiveness of the use of biodegradable hydraulic liquids, on the methodics of their tests and the selection of suitable diagnostic signals. The goal of the work presented in this contribution was to verify the suitability the proposed diagnostic signals and to find out their dependency on the time of operation. The verification was carried out on biodegradable hydraulic liquid of Czech provenance PRIMOL EKO 36H.

The choice of diagnostic signals

The methods of the analysis of hydraulic liquids could be possible to divide from the point of their objectives in two main groups (Pošta, 1995):

a) methods to determine the technical condition of the exploited oil,

b) methods to determine the technical condition of the hydraulic aggregate as a whole and its elements.

According to the main objective obtainable and appreciable diagnostic signals are selected. Amongst the most frequent diagnostic signals, generally used for the evaluation of the condition of an oil, are usually included (Havlíèek et all., 1989; Pošta, 1995; Zewdie, 1997):

• overall content of impurities,
• viscosity,
• point of inflammation,
• content of water,
• alkalinity (reserve of alkalinity),
• acidity,
• point of solidity, etc.

As another important indicator for the complex judgment of the technical condition of the whole hydraulic system, and especially hydraulic liquid, it is usually considered the quantity of the soft impurities (Pošta, 1997).

These impurities arise with the presence of water and oxygen as the result of the chemical oxidation (getting older). The process is accelerated by the catalytic effect of metals, especially in the form of the rubbed particles with large surface, by the performance of temperatures and the electrostatic field. Oxidized products polymerize, create strong glued layers which intercept hard impurities and assist in the advancement of wear in parts of the mechanisms. The air in the liquid in addition to improves the conditions for the rise of cavitation which increases noise, lessens or reduces efficiency, increases the heat strain of the liquid.

Some authors (Grunda et al, 1990; Chrást, 1996) emphasize the deterioration of the properties of biodegradable oils as a result of the increase in acidity and show the aggressivity of the liquid to some types of India-rubber.

The methods of tests

The following diagnostic signals were examined:

• overall content of impurities; values (% of the overall content of impurities) were determined by an instrument TCM-H which works on the principle of measurement of transmission of light by a sample of the tested oil, adapted by the described method,
• kinematics viscosity; it was measured by an instrument UBBELOHDE using temperatures 40 ^oC, 55 ^oC, 65 ^oC 80 ^oC,
• number of acidity; it was discovered by titration a solution of potassium hydroxide, the values are in mg KOH/g,
• regime of wear out; it was determined by the values measured by attaining direct reading with a magnetic analyzer PMA. The wear out regime of this machine is shown by the relative presence of large rubbed particles (over 15 m m) in overall impurities. When the amount of large particles exceeds limitations, leads to the wreckage regime.

The course of examinations

The experiment were carried out in a laboratory. The test appliance was made up from two basic blocs which create high pressure hydraulic aggregate and the test appliance.

High pressure hydraulic aggregate of the type HAE-70 32 12 is the product of TECHNOMETRA Praha. It contains three piston radial hydraulic pump at used appliance driven by a three phased asynchronized electric motor.

The test appliance was made up from serially produced elements which create three functional parts:

• primary hydraulic circle attached to a high pressure aggregate,
• secondary hydraulic circle mechanically united with the primary circle created regulatable pressure with an autonomic hydraulic circle,
• electrical circle which enables automatic operation and registration of the number of working cycles.

After the preparation of the appliance the test of operation took place for 22 hours (7411 cycles). Before the start of the experimental operation the high pressure aggregate was filled with hydraulic liquid PRIMOL EKO 36H. After the end of the experimental operation the liquid was renewed with the same specification sort. The experiment continued for 400 hours (118 242 cycles). Samples of the liquid were taken every 50 hours during the operation. Physic-chemical analysis of the samples were performed in the laboratories of The Department of the Quality and Reliability of Machines of The Faculty of Engineering and The Department of Chemistry of The Faculty of Agronomy of The Czech University of Agriculture in Prague.

During the examination the temperature of the liquid in primary circle was kept at 54± 3 ^oC. The pressure was kept at @ 14 MPa.

The results of the selected analysis are in the table 1 and in the folloving graphs. Each analysis was performed repeatedly, presenting its average values.

From the recorded courses of the values of every signal, it is clear that all signals react at the increased time of operation. The indicators "content of impurities" and "change of acidity" vary with the time of operation almost linearly which make them preferable as diagnostic signals. For the indicator "viscosity", it is possible to assume progressive growth. This assumption seems to be accepted by the results of the experiment however with regards to the extent of the experiment and the number of samples tested it is not so far possible this indication consider unambiguously certain. The unassumable anomalies are demonstrated by the signal “regime of wear out". The explanation of these anomalies cannot be given since the three work hypotheses, their verification have not been completed.

With regard to obtained results, taking into account to their reproducibility by the single varieties of analyses and to the demand factor of analysis, it is possible to state that as suitable diagnostic signals for the basic judgment of the changes in the properties of biodegradable liquids in operation there were confirmed signals "content of impurities", "viscosity" and "number of acidity". These signals are also sufficiently sensitive so consequently they can be utilized to predict the condition of the liquid.

With regard to the gained results and taking into account to their conditions of the examination it is possible also to state that biodegradable hydraulic oil PRIMOL EKO 36H is, from technical point of view, very well utilizable in hydraulic aggregates under mild operational conditions in which the temperature of oil does not exceed by the manufacturers suggested level of 60 ^oC.

GRUNDA, B. - SKOUPÝ, A. - PØIBYL, F.: Minerální a rostlinné oleje v lesnické praxi. (Mineral and plant oils in forest practice.) Lesnická práce, 69, 1990 (8), p. 359-361

HAVLÍÈEK, J. - LEGÁT, V.- POŠTA, J.: Metodika diagnostiky hydraulických soustav s AHSP. (The metodics of the diagnostics of the hydraulic systems with AHSP.) /Výzkumná zpráva/. Praha, MF VŠZ, 1989, 44 p.

CHRÁST, V.: Hodnocení úèinnosti organických odmašovacích pøípravkù. (The evaluation of the effectiveness of organic degreasing agents.) In: Sborník vìdeckého semináøe "Ekologické aspekty výroby a zabezpeèování provozu techniky", Praha 1996, p. 59-61, ISBN 80-213-0285-2

POŠTA, J.: Technologie údržby a oprav strojù. (The technology of the maintenance and repairs of machines.) ÈZU, Praha, 1995, 196 p.

POŠTA, J.: Vznik a pùsobení oxidaèních produktù v hydraulickém oleji. (The rise and functioning of the oxidizing products in the hydraulic oil.) In: Sborník pøíspìvkù, 2. mezinárodní symposium “Quality and Reliability of Machines”, SPU Nitra, 1997, p. 108 - 112, ISBN 80-7137-375-3

ZEWDIE, R.: Vliv biologicky odbouratelných kapalin na životnost prvkù hydraulických soustav a celková efektivnost jejich užití. (The inpact of biodegradable liquids on the life of the elements of hydraulic systems and overall effectiveness of their use.) /Disertaèní práce/, TF ÈZU, Praha, 1997, 131 p.

The address of authors:

Doc. ing. Josef Pošta, CSc.

Dr. ing. Retta Zewdie

Faculty of Engineering

Czech University of Agriculture

Kamýcká 129

165 21 Praha 6 - Suchdol

Phone: 02/24383266

E-mail: POSTA@TF.CZU.CZ

The extended summary

The development of biodegradable hydraulic liquids is supported by several facts. One of them is the effort for the decrease of significant surface contamination of environmental life by leakage of hydraulic liquids during breakdowns and accidents with machines with hydraulic mechanisms, another effort for the discovery of the alternatives to oil products, an effort for the non foods use in agricultural field, etc.

The majority of the research and developmental works about this problem leads to the area of effects and behavior of these liquids in a natural environment and in an area of their initial properties. Less attention is directed to other problems, e.g. in the changes of the properties of these liquids during their exploitation period and their influence on the mechanisms which were proposed to the work with liquids of the oil origin.

The goal of the work presented in this contribution was to verify the acceptability of the proposed diagnostic signals and to find out their dependence on the time of the operation. The verification was accomplished with biodegradable hydraulic liquid of Czech provenance PRIMOL EKO 36H.

The following diagnostic signals were verified:

• overall content of impurities,
• kinematics viscosity,
• number of acidity.

The examinations were conducted in a laboratory for a duration of 400 hours. The control samples of the liquid were taken every 50 hours during the operation. During the test temperatures in the primary circle on 54 ± 3 ^oC were kept. The pressure was set at @ 14 MPa. The physical-chemical tests of samples were carried out in the laboratories of The Department of the Quality and Dependability of Machines of The Faculty of Engineering and The Department of Chemistry of The Faculty of Agronomy of The Czech University of Agriculture in Prague.

The results prove that as suitable diagnostic signals for the basic judgment of changes in properties of biodegradable liquids in the operation are positive signals "content of impurities", "viscosity" and "number of acidity". These signals are also sufficiently sensitive so it would be possible to use them for the prediction of the state of the liquid.

The results also confirm that biodegradable hydraulic oil PRIMOL EKO 36H is, from technical point of view, very well adaptable in hydraulic aggregates with mild operational conditions in which the temperature of oil does not exceed by the manufacturer specifications of 60 ^oC.

biodegradable hydraulic liquid; viscosity; content of impurities; regime of wear out; diagnostic signal

Zkoušky byly provedeny jako laboratorní, po dobu 400 hodin. Kontrolní vzorky kapaliny byly odebírány každých 50 hodin provozu. Během zkoušky byla udržována teplota kapaliny v primárním okruhu na 54 ± 3 oC. Zatěžovací tlak byl udržován na @ 14 MPa. Fyzikálně - chemické zkoušky vzorků byly prováděny v laboratořích katedry jakosti a spolehlivosti strojů technické fakulty a katedry chemie agronomické fakulty ČZU v Praze.

Výsledky rovněž dokládají, že biodegradovatelný hydraulický olej PRIMOL EKO 36H je z technického hlediska velmi dobře použitelný v hydraulických agregátech s mírnými provozními podmínkami, ve kterých teplota oleje nepřekračuje výrobcem uváděnou hranici 60 ^oC.