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Manuf. and Ind. Eng., 11(2), 2012, ISSN 1338-6549 © Faculty of Manuf. Tech. TUKE

Wear of Bronze Bearing Bushes After Finishing with Burnishing

Dimitar S. Georgiev, Tichomir G. Vasilev

Abstract The article published results of experimental studies of wear of bronze bearings bushes, after finishing with burnishing.

Research addresses two types of bronze alloys widely used in practice for making bronze bearings operate under boundary or mixed film friction.

Keywords: wear, bronze, bronze alloy, burnishing, surface plastic deformation, sleeve bearings;

1 Introduction Wear is divided into four general classes namely: adhe-

sive wear, surface fatigue of wear, abrasion and chemical wear [1, 2]. Usually wear is associated with loss of volume of material due to applied pressure and wear distance.

Wear influence mechanical properties of materials, micro-geometry of surface and geometry of contact. As an additional factor affecting on the wear may take the shaft absolute peripheral speed value.

Adhesion wear is associated with adhesive connection between friction surfaces. Physical and mechanical proper-ties of material have a general influence on the adhesion force value. The volume of wear material used next equ-ation [2].

(1) Were: Va – volume of wear material, m3; K – constant of wear , m3/MPa.m; N –bearing average pressure, MPa; H – hardness of softer material; V – shaft peripheral speed, m/s; t – bearing couple uptime, s;

Oil film protected layers low-lying on bearing surface, while upper layers experience recurrent waves of compres-sive and tension stress in the contact area. The periodic fatigue load contributes to surface fatigue wear. The expe- rimental number of cycles until fatigue wear of the bearing material is determined by equation [3]:

(2) Were exponent a depends on the type of lubrication and

mechanical properties of the rubbing bodies. In terms of the elastic contact he accepted value of 10 ÷ 15. pr – Pressure on real contact surface, Pa; σS – Yield stress of bearing material, Pa; k – Geometric contact configuration coefficient inclu-

ded roughness height of on the surface of solids (k = 0,18 ÷ 0,22);

µ - Coefficient of friction in the bearing pair; Burnishing process is finished processing holes by

surface plastic deformation. The main advantages of burni-

shing include: increasing hardness and strength of the deformation metal, lower roughness and high value of residual compressive stresses in the deformed layer [4].

The burnishing as a process that increases the hardness of the deformation surfaces would reduce the volume of ad- hesive material worn by eq.1.

Also if take into account the increase of yield stress (σS) by eq.2 - after burnishing, this would increase the number of cycles until contacting surface fatigue failure.

Main technological parameters of burnishing process are: interference of calibrating mandrel – absolute different-ce between mandrel and bush hole (i) and width of mandrels cylindrical part [4].

When amend burnishing technological parameters, reach the change of mechanical properties of deformed material, surface roughness and hardness and hence to a change in the degree of wear volume.

Purpose of this publication is to examine the impact of burnishing technological parameters on bearing material wear process.

2 Methods of experimental studies To amend burnishing technological parameters – inter-

ference and mandrel cylindrical part width are made three sets of mandrels with different widths respectively 0.76, 2, 5, 8 and 9.24 mm. The three sets are divided into three groups by nominal diameters 30, 35 and 50 mm.

Burnishing interference is controlled by the preparation sizes of samples, values are 0.18, 0.3, 0.6, 0.9 and 1.02 mm. These technological parameters value obtained on the basis of planned experiment in which a weight loss during opera-tion time is optimization parameters.

From equation (1) ignore hardness parameters, the effect of which will be examined later, can be derived the fol-lowing relationship for determining the coefficient of wear:

(3) Where: Vwear – Wear material volume, mm3; t – Processed time, s; V – Shaft peripheral speed, m/s; N – Average bearing pressure, MPa

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Recording of weight loss is done with an electronic scale accurate reporting of 0,01 g and a maximum weight of 200 g. The volume on the wear material is determined by difference in weight before and after wear process:

(4) Where: Gbefore – Weight of bush before wear process, mg; Garter – Weight of bush after wear process, mg; ρ – bronze density (~ 8.86 mg/mm3);

Assuming that is known the maximum export volume (Vmax), were rate (K) calculated by equation (3), shaft peri-pheral speed V and average bearing load N, can determinate the maximum operation time of bearing (tmax):

(5) The determination of maximum amount of wear depends

on nominal diameter of bearing pair, precision and absolute value of radial clearance.

Fig.1 shows a scheme used for studs of geometric de-pendence which connects parameters of bearing couple with the wear volume and depth of the worn material.

Fig. 1 Estimated scheme for determining

the maximum amount of export material depending on the wear depth

From the analysis of fig.1 is reached to the following relations:

(6)

(7)

(8)

(9)

Where: α – contact angle to bearing center, deg; Δh – wear depth, m; rл – bearing hole radius, m; Cr – radial bearing clearance, m; α’ – contact angle to shaft center , deg; rв – shaft radius, m;

For tolerances in the bearing bushes form can be used BDS 5634-79. Where hole diameter whit dimension 30÷50 mm for tolerance IT8, maximum form error is Δf =16μm. Were made three groups bushes: - from material CuZn5Sn5Pb5 whit nominal internal and

external diameter respectively 30 and 40 mm, nominal thickness 5mm;

- from same material whit nominal internal and external diameter respectively 35 and 55 mm, nominal thickness 10mm;

- from material CuSn12 whit nominal internal and external diameter respectively 50 and 60 mm, nominal thickness 5mm;

The prepared bushes were treatment with burnishing by technological parameters of the experimental plan.

The length on experimental bush is 15 mm. For expe-rimental setting is a realized scheme show on fig.2. The rotation shaft 1 mounted in the chuck of a universal milling 2 is positioned in bronze bush 3. Under bush is located a device 4 allows measuring the force.

Fig. 2 Photo of experimental set used for conducting

the wear process

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For bushings CuZn5Sn5Pb5 material with nominal hole 30 mm is not lubricated. Others bushes were lubricated with litium grease ”PRISTA LITHIUM 3”. Lubrication is evenly spread across on the bearing surface and the same for all tested samples .

Experimental results: Experimental results which will provide objective nature

of wear after burnishing are maximum operation time and wear rate.

The results are shown in fig.3 to fig.8.

Fig. 3 Wear rate Кwear, mm3/MPa.m calculated

by equation (3) after burnishing with different technological parameters for bronze bush CuZn5Sn5Pb5 nominal

diameter 30 mm without lubricating.

Fig. 4 Maximum operation time calculated by equation (5) after burnishing with different technological parameters for bronze bush CuZn5Sn5Pb5 nominal diameter 30 mm

without lubricating Maximum operation time is calculated for peripheral

shaft speed 1 m/s and average bearing load 1 MPa. The ma-ximum export volume is calculated for assembly H7/e8 and relevant nominal size.

The bearing length is accepted equal on internal diame-ter.

Fig. 5 Wear rate Кwear, mm3/MPa.m calculated by equation (3) after burnishing with different technological

parameters for bronze bush CuZn5Sn5Pb5 nominal diameter 35 mm with lubricating.

Fig. 6 Maximum operation time calculated by equation (5) after burnishing with different technological parameters for bronze bush CuZn5Sn5Pb5 nominal diameter 35 mm

with lubricating.

Fig. 7 Wear rate Кwear, mm3/MPa.m calculated

by equation (3) after burnishing with different technological parameters for bronze bush CuSn12 nominal diameter

50 mm with lubricating.

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Fig. 8 Maximum operation time calculated by equation (5) after burnishing with different technological parameters for bronze bush CuSn12 nominal diameter 50 mm with

lubricating.

Besides the influence of burnishing technological para-meters are examinants and bearing surface quality parame-ters. Of processed sleeves are measured absolute values of microhardness HV0.05 and Ra, μm roughness parameters.

Next two figures shows wear rate variation depending on the quality parameters of the bearing surface.

Fig. 9 Wear rate variation depending on bearing surface

roughness Ra, μm for different groups sample

Fig. 10 Wear rate variation depending on bearing surface

microhardness HV0.05 for different groups sample;

3 Analysis of results From the results of experimental studies performed up to

the following major conclusions: -incresing burnishing interference from 0,2 to 1,0 mm de-crease were rate of bearing surface under dry and lubricated friction in the range 25-75% for different widths on cylin-drical mandrels part – fig.3, 5, 7; -decrease widths on cylindrical mandrel part from 10 to 2 mm leads to a decrease on wear rate with 40-60%; -burnishing with interference 1 mm and widths on cylindri-cal mandrel part 2 mm leads decrease on were rate about 3-4 times for different materials and construction while maxi-mal exploitation time increase from 2 to 4 times. -for bearing bush made from material CuSn12 with nominal internal diameter 50 mm burnishing with interference 0,8 mm and width of mandrel 6 mm, wear rate accepts a mini-mal value and maximal exploitation time 4300 hours. -the greatest time of operation 8000 hours is achieved in bronze bushings CuZn5Sn5Pb5 material nominal diameter 35 mm treated with interference 1 mm and wide strip 2 mm – fig.6; -increase of roughness Ra, µm raises the wear rate, followed by decrease and increase again. The maximum value of the wear rate is at different values of roughness – fig.9; -influence of bearing surface hardness on the wear rate random character that conflict with the equation (1);

Conclusions From research it can be concluded that the burnishing

attached as a completed process for bearing bronze bushes increase the service life of dry and mix-film lubricated bearing.

Prof. Dimitar Svetlozarov Georgiev,

Tihomir Grishev Vasilev M.Sc., Technical University of Varna,

9010 Varna, Bulgaria,

E-mail: dsgeorg@abv.bg E-mail: t.vasilev@abv.bg

References

[1] ASM Handbook, Volume 18, Friction, Lubrication, and Wear Technology, ASM International, Metals Park, Ohio, 1992, p. 1878, ISBN 0-87170-380-7;

[2] Neale, M. J, Tribology Handbook, Second Edition, But-terworth Heinemann, 1996, ISBN 0 7506 11 98 7, p. 577.

[3] Крагельский И. В, М. Н. Добмчин, В. С. Комбалов, Основн расчетов на трение и износ. М., Машиностро-ение, 1977, 526 с.

[4] Проскуряков Ю. Г, Дорнование отверстий, Машгиз, 1961, 191 с.

[5] Бизяев, Г.Н, Повьiшение еффективности технологии изготовления тонкостенньiх колец подшипников на осно-ве совершенствования процесса свободного дорнования, Дисертация на соискание ученой степени кандидата тех-нических наук, Саратов, 2008;