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Measuring the coefficient of friction in the bearings in the adopted four-member mechanism for unsteady motion.

Abstract: The bearing shell on which the measurements were performed have three different diameters. The material of the bearings is polytherafluorethylen (PTFE) and polyamide 6.6 with addition of molibdenite (Mo[S.sub.2]). The mechanism is analyzed for two different angle velocities of the operating part. Forces in the mechanism were determined using the computer. These forces were derived without taking in account the variable load on the bearings, and the results were presented graphically.

Key words: bearings, sliding bearings, lubrication of the bearings, the coefficient of friction

1. INTRODUCTION

If designed and lubricated correctly, the plain (Sliding) bearings can carry heavy loads at a high rotational speed. These bearings are light in weight, have small radial dimensions and do not require special equipment for manufacture.

Plain beatings offer the advantage of noiseless operation and a high damping ability under cyclic and impact loads.

The reducing friction in bearings is often important for efficiency, to reduce wear and to facilitate extended use at high speeds and to avoid overheating and premature failure of the bearing. Essentially, a bearing can reduce friction by virtue of its shape, by its material, or by introducing and containing a fluid between surfaces or by separating the surfaces with an electromagnetic field.

2. MEASUREMENT METHODS AND MATERIALS FOR BEARINGS

We used these materials for our experiments:

Poly (difluoromethylene), which is produced under various names (U.S. teflon; Japan-polyflon, etc.), belongs to thermoplastics most resistant to high and low temperature (190[degrees]-260[degrees]C)(83--535 K).

These materials manufactured in the form of plates, profiles, tubes and more recently in the form of foil.

Polyamide 6.6 with the addition of molybdenum disulphide (Mo[S.sub.2]) is also known by various names (U.S. plaskon, Zytel, Germany-ultramid, durethan;

England-maarnyl, etc.), and is one of the thermoplastic poly condensate (Pllana, 1984).

In our experiments, we performed measurements of the impact force moments of friction, coefficients of friction and angle of friction in the bearings, for this purpose a specially constructed mechanism which is shown in Fig. 1.

[FIGURE 1 OMITTED]

3. PLACENTA SLIDING BEARINGS

The influence of the forces on the bearings investigated by changing the placenta of sliding bearings in the working link mechanism.

These placentas were done in three dimensions inside diameter, and to 60 mm, 70 and 80 mm. The fig. 2 shows the two test sample.

[FIGURE 2 OMITTED]

4. THE CALCULATION OF THE FRICTION COEFFICIENT

Based on the diagrams for all combinations of loads, of speed of the samples of sliding beatings and of change of the angle oscillating link mechanism, and by using the calibrated chart, and the above mathematical procedure, were constructed tables of calculated moments of friction.

From these results the appropriate coefficient of friction for the defined characteristic points of the oscillatory link mechanism has been calculated radial forces of different weights:

5. RESULTS

For each radial force were obtained curves for the case with lubrication (LIS grease and without lubrication), Fig. 3 and 4.

a) the case when the experiments were carried out without lubrication

b) the case when the experiments were performed with lubrication (grease LIS).

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

6. CONCLUSION

On the basis of experimental tests in the adopted four-member mechanism of the device for testing the placenta sliding beatings, this can be concluded:

1) In most experiments it has been confirmed that the friction coefficient in the sliding bearings decreases by increasing the radial forces in the placenta of the sliding bearings.

2) In terms of lubrication, the coefficient of friction is reduced by approximately half the value without lubrication.

3) Considering the low values of the coefficient friction for both materials, there is the possibility of replacing the expensive Teflon with polyamide 6.6 with the addition of molybdenum disulphide (MoS2).

4) With the measurements it is proved that by increasing the dimensions of sliding beatings it comes to the decreasing of the friction coefficient, and thus also to the decreasing of the moment of friction.

7. REFERENCES

Butenschon, Hans-Jurgen. (1976). The hydrodynamic cylindrical bearings of finite width under transient load, Karlsruhe, Techn. Univ., Diss., 1976

Decker, H. K. (1980). Machine Design (translation into Croatian), Zagreb, 1980

Hinzen, H. (2001). Machine Design 2, Oldenburg Verlag Munchen Wien, 2001

Lang, Otto R. Steinhilper, Waldemar. (1978). Bearing analysis and design of bearings with constant and time-varying load, Springer, Berlin, 1978

Pllana, G. 0984). Study of the dimensions of bearing on the dynamic properties of manipulators, Master Thesis, Faclty of Mechnical Engineering and Naval Architecture, Zagreb, 1984

Rieg, F.; Kaczmarek, M.(Hrsg.) (2006). Handbook of Machine Design, Cads Hanser Verlag Munchen Wien, 2006.

Szeri, Andras Z. (1998). Fluid film lubrication, Cambridge Univ. Pr. Cambridge, 1998
Tab. 1. Coefficient sliding friction and the amount of
consumption in dry friction

Materials The Fraying
 coefficient ([micro]m/Km)
 of friction

POLIAMID 0,32 to 0,35 0,7
6.6 + MoS2
TEFLON (PTFE) 0,22 21

Tab. 2. Some mechanical features of these materials (* Values
in parentheses for polyamide refer to dry material, * Values
outside brackets refer to polyamide 4 months after the
normalization of the air at 20[degrees]C and 65% relative humidity
(the manufacturer)

 Materials

 TEF POLIAM
Mechanical Properties by LO ID
 N 6.6+
 (PT MoS2
 FE)

DIN 53 455 Yield on N/[mm.sup.2] 15 (80) 50
53 371 the train

DIN 53 452 Yield N/[mm.sup.2] 19 (94) 27
 bending

DIN 53 371 modulus N/[mm.sup.2] 400 (3200)
 1500

DIN 53 455 Elongation
53 371 at break % 400 (130) 250

 Volume kg/[m.sup.3] 220 1150
 weight 0

Tab. 3. Calculated friction coefficients

 G (N) [F.sub.R] (N)

1 20 189.3
2 40 378.4
3 60 567.6
4 80 756.6
5 90 851.4
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Author:Pllana, Gani; Maliqi, Rashit; Azemi, Fatmir
Publication:Annals of DAAAM & Proceedings
Article Type:Report
Geographic Code:1USA
Date:Jan 1, 2011
Words:968
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