Experimental aspects regarding pressure determination to the narrow sliding radial bearing (L/d < 0,6) working under hard shocks.

Alexandrescu, Ioan Marius ; Cotetiu, Radu ; Cotetiu, Adriana 等

1. INTRODUCTION

The assessment was made on the experimental stand of the Tribology and Manufactural Engines Lab from the North University of Baia Mare, making use of the modern technology concerning the results'processing and acquisition.

The research was made using a HD radial bearing with L/D=0,5 and the spindle's diameter [d.sub.e] = 59,86 mm, and the bushing diameter [D.sub.e] = 59,93 mm, spindle's asperity 58-62 HRC, made of 18MoCr10, bronze bushing made of 88%Sn, 8%Sb, 4%Cu. The dynamic loading of the bearing is made through the lancing of a weight which hits the bearing at different heights. They were made assessments for heights between 5 and 40 cm, using a weight with m=5 kg, so as for H=5 cm we have [F.sub.1] = 1665 N, for H=20 cm we have [F.sub.2] = 2356 N, and for H=40 cm we have F3=3332 N. The static working conditions is presented for the following value H=0 cm. All the tests were made at a 40[degrees]C of the lubrifiant, being constant, available supply pressure pin having the following values, from 0,5 bar to 10 bar. Using a lubrifiant oil for bearings of LA 32 STR 5152-89 type, with the viscosity of 31,3 cSt at 40[degrees]C, it was focussed on the determination pressure distribution from the film to be lubricated in diferent places of the bearing s body (P1 - P5), with the help of pressure measuring dose with tensometric translators.

Figure 1 presents the bushing diagram in experimental assessments having L/D=0,5 (Alexandrescu, 2005).

[FIGURE 1 OMITTED]

2. EXPERIMENTAL DEVICES AND ACQUISITION CHAINS

In dynamic charging conditions, the pressure distribution was determined in the lubricated film in those 5 points on the bearing's body with the help of pressure measuring with tensometric translators. (Pay & Alexandrescu, 2004)

The translator is a manometer capsule at which the sensible element to pressure is an enclosed tube at one end whose inner part is connected to the oil whose pressure is measured. The tube is made of steel with elastic properties on which there are 4 tensometric stamps, each of them having the electric resistivity of 129 [OMEGA], two of them in axial direction, and two in perpendicular direction. The tensometric translators are used in large scale due the simpleness and the extended domain for application from 7 to 700 bar (Alexandrescu et al., 2005).

Those 4 tensometric stamps are connected in a tensometric bridge diagram, being related by an amplifier at the acquisition plate ADuC 812. Under the pressure variation influence, the thin wall of the dose is changing its shape; the stamps are changing its resistance.

Figure 2 presents the pressure measuring dose with tensometric translators made of steel 18 MC10 (Pay & Alexandrescu, 2004).

Figure 3 presents the pressure measuring chain in the lubricant film. The exhibition of the pressure measuring dose was made in the case of dynamic charging, on the manometer's exhibition stand, using the above chain, focusing on the variation exit sign and registering amplifier and the acquisition plate ADuC 812.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The pressure increase was made bar by bar, the dose distortion being linear with the pressure. It was established the dependency relation between the pressure and the tension in the exit point in mV (2,3 mV = 1bar [DELTA]p) (Alexandrescu et al., 2007).

ADuC 812 produce by Analog Device has an 8051-compatible microcontroller core supported by 8Kb Flash/EE program memory, 640 bytes Flash/EE data memory and 256 bytes data SRAM on-chip. The digital data can be sent to a PC via a standard UART Serial Port.

3. EXPERIMENTAL RESULTS

The pressure distribution in places P1-P5 of the bearing s body, depending on the static G and dynamic F charging conditions are presented in figure 4 for spindle's rotations n=370 rot/min, and available supply pressure [p.sub.in] = 0,5 bar.

[FIGURE 4 OMITTED]

4. CONCLUSIONS

The following conclusions may be taken into consideration:

* in all these situations the following fact is to bare in mind: the short time for pressure variation in dynamic charging (under 0,5 ms);

* the dynamic pressure from the moment of shock is increased when increasing the dynamic charging conditions; this increasing process refers to the all active zone, the dynamic pressure rise at the same time with the rise of dynamic charging, depending on the studied position of the periphery zone of the bushing the pressure leap being between 5,95 and 7,45 multiplied with static pressure;

* the static charging conditions of the bearing does not have an important influence regarding the changing in the pressure's values, as the static charging conditions gets bigger, so as the dynamic pressure is bigger; the existence of an optimum point from the viewpoint of carriage: any change in the functional parameters of the bearing leads to straying from the optimum value from the viewpoint of carriage; at the same time with the rise of static charging, the static pressure decrease; the ratio of film thickness sensitively influences carriage;

* research under factory, operational conditions, conducting operational test in labs, checking the already accepted technological solutions; conducting studies about the obtained products' long term testing and compared operational safety; conducting laboratory tests underoverloaded, strained conditions for items including high performance materials; giving the research tests' results to the interested economic units, editing and spreading those results;

* during the last few years and for the future period in Romania there is a prognosis which shows an accelerated industrial development and the industry is increasing demands for up-to-date materials. As part of this process, the North University of Baia Mare gave currency to a technical developing program on the basis of the results of the researches in using and replacing with friendly environmental materials.

5. REFERENCES

Alexandrescu, I. M. (2005). Behaviour study of radial bearings with hydrodynamic lubrification under conditions of shock and vibration running. PhD thesis, Technical University of Cluj-Napoca, 2005, Supervisor: PhD Eugen PAY Dr. H.C.

Alexandrescu, I. M.,; Pay, E., & Buchman, A. (2005). Experimental results regarding hard shocks behavior to the radial hydrodynamic working bearings. microCAD International Scientific Conference. Machine and Construction Design, University of Miskolc, 2005, pp. 1-12, ISBN 963-661-646-9.

Alexandrescu, I. M.; Cotetiu, R. & Ungureanu, N. (2007). Theoretical correlations regarding the instantaneous carrying force in the case of the narrow sliding radial HD working bearing under hard shocks. Automation in Production Planning and Manufacturing. 8th International Scientific Conference, 02--04 May 2007, Zilina--Valca, Slovak Republic, ISBN 978-80-89276-03-5, pag. 9-13.

Pay, E. & Alexandrescu, I. M. (2004). The HD lubrication limits of radial bearings. The 8-th International Conference on Tribology. Veszprem, 2004, pp. 247-252.

Pay, E. & Alexandrescu, I. M. (2004). Searches Regarding Radial Journal Bearings with HD Lubrication. Romanian Journal of Technical Sciences Applied Mechanics. Tome 49, International Conference on Manufacturing Systems ICMaS 2004. Bucuresti, Romanian Academy Publishing House ISSN 0035-4074, ISBN 973-27- 1102-7.