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.

1. 9
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

2. 10
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

3. 11
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.

4. 12
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
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