International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 2 – Jul 2014
Effect of Surface Grinding Process Parameters on Surface
Quality of Natural Rubber (NR) Liner’s of pipe line
Rajni Kinalkar1
1
2
Prof. M. S. Harne2
M.E. Scholar, Mechanical Department, Government College of Engineering Aurangabad,
Aurangabad, Maharashtra
Assistant Professor, Mechanical Department, Government College of Engineering Aurangabad,
Aurangabad, Maharashtra
Abstract--- Corrosion is one the severe problem in pipe system
used in industry. To protect pipes from erosion various liners
are used according to their application. Rubber lining is a
rubber sheet or membrane used for protection from corrosion
in aggressive chemical environments. There are several rubber
lining applications some of which include resistance to acid,
chemicals and alkalis, abrasion resistance, infect protection. It
is important to protect pipe from erosion simultaneously it is
important to provide tight leak proof pipe joints. To acquired
leak proof joints the flange face should be of required surface
finish, flat surface and also parallelism. Present work is related
to surface grinding of natural rubber liner of pipe. To get the
desired surface finish the process parameters are studied and
the optimum working conditions are achieved by using the
Response Surface Method. RSM is used for planning and
conducting the experiments.
Keywords: Surface Grinding, Elastomer, Design of
experiment, OVAT, RSM, Optimization.
I. INTRODUCTION
Corrosion of piping has been a substantial problem for
many years. In order to overcome the problem of corrosion
a wide variety of corrosion resistant alloys have been
employed as well as lining of pipes such as steel pipe with
rubber, plastics & the like plastics that is synthetic resinous
or synthetic elastomeric material such as rubber have found
wide applications in area when corrosion resistance is
required. [1]
Rubber lining is a rubber sheet or membranes used for
protection from corrosion in aggressive chemical
environments. There are several rubber applications some of
which include resistance to acidic and alkaline chemical
corrosion, abrasion resistance, infect protection. This type
of rubber liners are used in Chemical, mining, fertilizer,
electrochemical, steel, transportation and environment
sector etc. one of the advantage is linings can be produced
in different thicknesses to use in a variety of industrial
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situations. Along with above advantages it also posses
excellent to superior physical properties maximum tensile
strength, elongation, abrasion & tear resistance, excellent
noise and vibration attenuation property, unaffected by
mechanical stresses or rapid temperature changes and not
that much expensive. [2]
Oftentimes under service condition such lined pipe may
be subject to temperature cyling wherein temperature
approaches the softening temperature of lining & what was
originally installed as tight leak proof joint becomes leaky
due to slow deformation of the liner material in the flange
region. It would be advantageous if there were available
improved lined pipe joint. It would also desirable if such as
improved lined pipe joint showed substantial increased in
service life. [1, 2]
Flange liner to provide a flat face with optimum surface
finish is very desirable. If the flanging operation does not
provide a flat face, exposed elastomeric face may be
machined flat by milling, turning or grinding depending on
rubber liner composition’s properties. [3]
Elastomers have the unique material properties of very low
elastic modulus and high percentage of elongation before
fracture. These properties make the effective material
removal and precision machining of elastomers a technical
challenge. The early research in elastomer machining was
conducted by Jin and Murakawa [4].
Jie Luo observed and experimentally proved that
Elastomers have very low thermal conductivity. Under
cyclic loading, elastomers exhibit significant hysteresis,
which contributes to their energy absorption capability.
Elastomers also have a very low elastic modulus and high
percentage of elongation before fracture, which makes the
machining of elastomers a challenge.Cutting speed was
demonstrated to be critical. At high cutting speed, smoke
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International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 2 – Jul 2014
was generated and became environmentally hazardous. At
low cutting speed, the surface roughness was high and
material removal was not effective. [5]
In the present scenario company have special purpose
designed Hard rubber flange face machine system which is
used for making flange surface of Hard Rubber liner to
provide desired surface finish, flatness and pallarelism. For
Hard Rubber Milling process used, if we continued using
the milling cutter for machining of Natural Rubber then
there will be ploughing which results in the very poor
machined surface. Natural Rubber is very soft as compare to
Hard Rubber.
we have constraint that we have to use same machining
system for machining of natural rubber. Also for The rubber
lined pipe joint the average roughness (Ra) should be in the
range of 3.2 to 6.5 µm [3] considering all limitation and
advantages it is preferable to use grinding for natural
rubber.
The response variable is an unknown function of the
process variables, which are known as design factors. In the
present study, the design factors selected are: machining
speed and feed, while other parameters have been assumed
to be constant. The required surface finish of natural rubber
liner at the flange face is 3.2 µm. The parameters that were
observed to be significant after pre-experimentation are
considered for further study. OVAT (One Variable At time)
is used to determine interaction between the factor rather
than individual effect of each factor on the output
performance characteristics (response) .In this work OVAT
also used to select the range for the optimization which is
also called as pre-experimentation [8].
RSM (Response Surface Method) procedure was carried
out as follows:
a) 13 numbers of experiments were performed for adequate
and reliable measurement of the response of interest.
b) A mathematical model of the first-order response surface
with best fit was developed.
c) The direct and interaction effects of the process
parameters were represented through direct effects plots and
two-dimensional contour plots.
Grinding process is widely used machining process in
industry for surface smoothing and finishing. Grinding
process involves a material removal by the contact between
grinding wheels with a randomly structured topography
In order to define the experimental region considered,
with the workpiece. The quality of a machined surface is
preliminary experiments were carried out to determine
becoming more and more important in order to satisfy the
narrower, more effective ranges of process parameters
increasing
demands
of
sophisticated
component
before designing the experimental runs.
performance, longevity, and reliability so that they can
achieve their functions according to geometric, dimensional
B. Response Variable Selected
and surface considerations. An understanding of surface
Ra is used to describe the roughness of machined
finish provides much advantage in avoiding failures;
surfaces. it is useful for detecting general variations in
enhance component integrity and costs saving. Surface
overall profile height characteristics and for monitoring an
roughness is generally regarded as an important factor in
established manufacturing process. hence, in present study
terms of fatigue life performance. Grinding is most
the roughness parameters ra have been selected as the
commonly used as a finishing process to achieve material
response variable.
removal and desired surface finish with acceptable surface
integrity, dimensional tolerance and form tolerance [6]
C. Equipment and Tools Used
Experiments were carried out on special purpose design
Surface grinding can be defined as the machining of
Flange face machine, using a grinding wheel. Grinding
surface of the work piece while it is rotating with a grinder
wheel is diamond flaring cup grinding wheel. This type of
and the grinding feed is given parallel to the axis of the
shape particularly used for surface grinding.
work piece and at a distance that will remove the surface of
the work.
II.
MATERIALS AND METHODS
A. Design of Experiment
The design of experiments technique is a very
powerful tool, which permits us to carry out the modelling
and analysis of the effect of process variables on the
response variables [7]. The response variable is an unknown
function of the process variables, which are known as
design factors.
Photograph 1: Grinding wheel
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International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 2 – Jul 2014
D. Workpiece Material
E. Roughness Measurement
Roughness measurements were done using a Portable
The present study was carried out on stainless steel pipe on
Surface
Roughness Tester TR200. Roughness was
which soft natural rubber liner is present. In present case the
measured
on the rubber liner at flange face at different
natural rubber act as liner as well as gasket of pipe.For
positions.
Its
operating range is Ra= 0.01 – 40 µm.
achievement of leak proof clamping the liner surface should
be parallel to the flange face therefore any projections that
are objectionable to soundness of lining shall be removed F. Experimental Conditions
The experiment is conducted to study effect of process
by grinding after vulcanization. Also there is needed to get
parameter
i.e. Machining Speed and Feed on the surface
the surface finish and dimension of the liner as per
quality
of
flange face lined with natural rubber. The
requirement.
Response surface method (Face centered Central Composite
Design) was applied for conducting the experiments. One
Physical Properties of Natural Rubber liner:
variable at time (OVAT) was used to select the range of
input parameters. During OVAT the speed varied
Excellent
Good Fair Poor
independently from 16 to 32 rpm and the feed was varied
Abrasion Resistance 
independently from 1 to 5 mm. By analyzing the results of
OVAT the range selected for the experimentation are 24 to
Compression set

26 rpm for Machining Speed and 2.5 to 3.5 mm for Feed.
Elongation

Flame resistance
Gas permeability


Low temperature
flexibility
Tear resistance


Tensile strength
III. RESULTS AND DISCUSSION
The response parameter in this experiment is surface
roughness (Ra), the targeted value for it is 3.2 µm. Minitab
14 was used for planning the design of experiment. Further
its results are analyzed in the same software. The model is
generated by regression analysis and the results are
validated using the graphical tool method.
As per the experimental design, 13 trials were carried out
and its results are shown below in Table 1.

Chemical Properties of Natural Rubber Liner
Excellent
Good
Air
Alcohols


Dilute acids and
bases
Gasoline

Fair
Hydrocarbon
solvents
Oil
Run
Order
1
Speed
Feed
Ra
24
3
3.208
2
26
3.5
3.401
3
24
3
3.208
4
24
3
3.208

5
24
2.5
3.364

6
26
3
3.721
7
22
2.5
3.208
8
24
3
3.208
9
24
3.5
2.858
10
22
3.5
2.641
Poor

Oxidation

Ozone

Radiation

11
24
3
3.208
Steam

12
26
2.5
3.848
13
22
3
3.021
Sunlight
Water


Table 1. Face Centered Central Composite Design
Mathematical models for process parameter machining
speed and feed were obtained from regression analysis
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International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 2 – Jul 2014
using MINITAB 14 statistical software to predict the
surface roughness. The obtained regression equation is:
Ra= 0.558 + 0.175 Speed - 0.507 Feed
B. Effect Of Process Parameters On Surface Roughness
Main Effects Plot (data means) for Ra_1
Speed
3.7
Feed
3.6
3.5
Mean of Ra_1
A. Validation Of Model: Graphical Tools
It is usually necessary to check the fitted model to ensure
it provides an adequate approximation to the real system.
Unless, the model shows an adequate fit, proceeding with
investigation and optimization of the fitted response is
likely to give poor and misleading results. Graphical tools
can be used for validation of the models. The graphical
method characterizes the nature of residuals of the models.
A residual is defined as the difference between an observed
value and its fitted value. The figure 1 below shows the
residual plots Ra
3.4
3.3
3.2
3.1
3.0
2.9
22
24
26
2.5
3.0
3.5
Figure 2: Main Effect Plot for Ra
The effect of process Machining speed and Feed on
Surface roughness is shown in main effect plot (Figure 2).
In this figure it can be observe that Ra value of surface is
increases as the machining speed increases from 22to 24
rpm. However from speed of 24 rpm the Ra value sharply
increases. It is because of the natural rubber is softer
elastomer and its behavior under machining is quite
different than the other materials.
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The figure 3 below shows the 2-D contour plots for the
Ra value against speed and feed. The contour plots are the
graphical representation of the regression equation used to
visualize the relationship between the response and
experimental levels of each factor.
Contour Plot of Ra_1 vs Speed, Feed
26
Ra_1
< 2.8
- 3.0
- 3.2
- 3.4
- 3.6
- 3.8
> 3.8
2.8
3.0
3.2
3.4
3.6
25
Speed
In the normal probability plot of the residuals shown in
figure1, the data was plotted against a theoretical normal
distribution in such a way that the points should form an
approximate straight line, and a departure from this straight
line would indicate a departure from a normal distribution,
which was used to check the normality distribution of the
residuals.
It is reasonable that the assumptions of normality were
satisfied for the data. The plots of residuals in the normal
probability plot of the residuals shown in figure1, the data
was plotted against a theoretical normal distribution in such
a way that the points should form an approximate straight
line, and a departure from this straight line would indicate a
departure from a normal distribution, which was used to
check the normality distribution of the residuals.
It is reasonable that the assumptions of normality were
satisfied for the data. The plots of residuals versus the fitted
values and residuals versus the order of the data indicated
no obvious pattern, implying that residuals of the models
were randomly distributed. As well, the histogram of
residuals has shown the normal distribution for Ra and it is
little bit negatively skewed.
Also as the feed of the machining increase the surface
becomes more and smoother within the selected region, it is
reflected in gradual decrement of Ra value and the plot
obtain from the Ra. From this we can conclude that the
surface quality of flange enhances as the machining speed
decreases and feed increases. There is smoother change in
the Ra value as the feed increases but incase of the
machining speed, the Ra value is smoothly increases up to
24 rpm then further it sharply increases. This indicates that
the Machining speed is more influencing factor than the
feed.
24
23
22
2.50
2.75
3.00
Feed
3.25
3.50
Figure3. Contour plot for Ra verses Speed, Feed
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International Journal of Engineering Trends and Technology (IJETT) – Volume 13 Number 2 – Jul 2014
C. Response Surface Optimization:
The objective of the experiment is to obtain surface
finish of value Ra=3.2 µm with speed and feed at optimum
level. By applying the Response Surface Method in the
above experiment the model has generated which is check
for adequacy by analysis of variance and validated using
graphical tools. The result is tabulated in the table 2.
Response
Ra
3.2
Optimum Condition
Speed
Feed
24
3.0
1
Trials
[1]
[2]
[3]
[4]
[5]
D. Confirmation Test:
In Order to test the predicted result, confirmation
experiment has been conducted by running another four
trials at the optimal settings of the process parameters
determined from the analysis. It was found that variance in
recorded value is not significant.
Observation
REFERENCES
[6]
[7]
[8]
[9]
Walter H. West, Lined Conduit, United states Patent, 3,650,550,
Mar 21, 1972
Philip A. Schweitzer, P.E, Miscellaneous lined piping system,
Corrosion-Resistant Piping Systems, page no. 191-200
E. Marston (BPE), F. Zezula, Piping Joints Handbook, Document
No. D/UTG/054/00,
Jin, M., and Murakawa, M., 1998, High-Speed Milling of Rubber
(1st Report) -Fundamental Experiments and Considerations for
Improvement of Work Accuracy, Journal of the Japan Society for
Precision Engineering, Vol. 64, No. 6, pp. 897-901.
Jie Luo, Machining of Elastomers, dissertation submitted in partial
fulfillment of the requirements for the degree of Doctor of
Philosophy (Mechanical Engineering) in The University of
Michigan 2005
Z.W. Zhong, V.C. Venkatesh, Recent Developments in Grinding of
Advanced Materials, International Journal of Advanced
Manufacturing and Technology, 41(2009) 468-480.
E. Marston (BPE0), Piping Joints Handbook, Document No.
D/UTG/054/00, May 2000
Douglas C. Montgomery, Design and Analysis of Experiments, 5th
Edition, John Wiley and Sons, Inc.‖
Jiju Antony, Design of Experiments for Engineers and Scientists,
Elseveir Science & Technology Books, October2003.
Average
Ra
1
2
3
4
3.21
3.35
3.18
3.29
IV.
CONCLUSIONS
3.25
Response surface methodology (RSM) is applied
to optimize the process parameters for machining of flange
face lined with natural rubber by galvanized surface grinder
tool. The optimum conditions are achieved to get the
required surface finish. The conclusion drawn from this
experiment is:
1.
2.
3.
The natural rubber being soft elastomer , it behaves
differently from the other materials during the
machining.
The surface finish gets better at low speed and high
feed. The observed optimum condition to achieve the
required surface finish for the Speed and feed is 24 rpm
and 3.0 mm
The result of present investigation is valid within
specified range of process parameters
Also the prediction made by Regression Analysis is in good
agreement with Confirmation results.
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