2. Granite & Marble Polishing with Diamond Tools
Abstract • Floor polishers, radial arm polishers, slab polishers, tile and line
polishers can all benefit from the use of a diamond tool based
It has long been the practice of those polishing granite and
polishing strategy.
marble surfaces to use the conventional abrasive mediums of
silicon carbide, aluminum oxide and magnesite. These materials • Tooling changeovers and associated downtime and labor cost
are relatively bulky and generate a considerable amount of envi- can be dramatically reduced when switching to diamond tools.
ronmentally undesirable residue when mixed with the stone sludge.
• Environmental issues associated with the tooling are greatly
They wear quickly and are the source of machine downtime and
reduced and or eliminated.
considerable labor attention for the required frequent tooling
changes. When viewed from a Total Cost perspective, diamond tools repre-
sent real value for the stone polishing industry.
Recent developments in the application of diamond
superabrasives have shown superior results to the previous meth- Discussion
ods. Diamond tooling is volumetrically far more efficient than
Abrasive Technology, Inc. is a major manufacturer of superabra-
conventional polishing media, resulting in less downtime and
sive tools for a wide range of industries. In its quest to meet
labor for tooling changes. Further, the tool residue from the
customers’ needs, it has undertaken a major product develop-
polishing process is quite small and the associated compounds do
ment program focused upon the polishing of stone using spe-
not contribute significantly to environmental problems.
cially designed diamond tools. This development was brought
This paper discusses the use of diamond superabrasives about in an effort to increase the stone finishers’ productivity by
and the unique operating parameters required in order to success- reducing the downtime and labor costs associated with frequent
fully polish granite and marble with this very efficient new technol- tooling changeovers. Further, this work was aimed at reducing
ogy. Directions for optimization of the operating parameters are the environmental problems associated with the large volume
also provided to assist the practitioner in the fine tuning of his and types of compounds currently being generated as polishing
process. residue.
Conclusions GE Superabrasives is one of the largest superabrasives manufac-
• Recent developments in diamond tool technology have dramati- turers in the world. They have made considerable efforts to
cally changed the range of applications that can benefit from further the science of superabrasive applications. A large num-
diamond polishing tools. ber of testing and development programs have been aimed at
improving the manufacturing processes for stone products.
• Outstanding finishes can be produced in less time than has been
previously possible using conventional abrasives. A joint development program between Abrasive Technology
• Both marble and granites, from a medium hard Charcoal Black and GE Superabrasives was born out of these two firms’ mutual
to a difficult Mahogany, respond favorably to the use of diamond interests in furthering the stone polishing industry’s technology
tools. and productivity.
• Concrete aggregates have also responded well to diamond tool The approach taken was to obtain a special polishing machine
polishing. that could mimic the operating range of a large variety of
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2
3. polishing machine types. No one machine adequately covered Finally, the range of traverse speeds varies widely over the many
the broad range of conditions being used in the field across the types of equipment and applications. Figure 4 shows that the
various manufacturing processes and machines. Further, be- GP72M machine is capable of producing all but the highest
cause of the engineering nature of the project, a precise set of traverse speeds, as equipped.
controls would be needed. After reviewing a number of “name”
machine builders’ equipment and discussions with some recent POLISHING MACHINES - TRAVERSE SPEED RANGES
purchasers and users, a modified Park Industries, Inc. Model
GP72M slab polisher was chosen as the test machine capable of GP72M
mimicking a wide variety of machines and polishing conditions.
MACHINE TYPES
Slab/Tile Line
The light loads of floor polishers and radial arm polishers (50- Floor
150 lb.) represented the low end of the load spectrum. The
heavier loads of the slab and line polishers (200-500 lb.) charac- Radial Arm
terized the high end of the range. The range of loads possible 0 10 20 30
TRAVERSE SPEED (fpm)
40 50 60
with various field equipment and the broad span of the GP72M
are shown in Figure 1. Figure 4
POLISHING MACHINES - LOAD RANGES The Park GP72M was specially built, installed and calibrated
over a three month period in late 1991. Calibration was given
GP72M
special attention to insure that the settings would be accurately
described in any published materials and so that the results
MACHINE TYPE
Slab/Tile Line
could be replicated to the maximum extent possible in the field.
Floor
Applied loads were verified over the operating range using an
Radial Arm
NIST traceable digital electronic scale as the master. The load
0 50 100 150 200 250 300 350 400 450 500
cells built into the GP72M were received calibrated by the
LOAD (pounds) manufacturer. However, we wanted to verify the accuracy and
Figure 1 repeatability over the operating range as installed. We used
linear regression statistics to evaluate the results. A detailed
A broad range of spindle speeds (175-700 RPM) and associated
explanation of this type of analysis can be found in books such
surface speeds (780-3030 SFPM) were also needed to cover the
as “Evaluating The Measurement Process” by Donald J. Wheeler
range of machine capabilities existing in the field today. The
and Richard W. Lyday, SPC Press, Knoxville, Tennessee.
typical field ranges for RPM are shown in Figure 2. We chose the
extended range of spindle speeds on the GP72M because of our A similar approach was taken in the analysis of spindle RPM over
special test plans. the motor’s operating range and under various loads. A trace-
POLISHING MACHINES - SPINDLE SPEEDS
able reference contact tachometer was used as the master.
Linear regression analysis was also conducted.
GP72M
Traverse speed accuracy and repeatability under a full range of
loads and RPMs were also verified by the same techniques. A
MACHINE TYPE
Slab/Tile Line
traceable reference stopwatch was used and “gates” were marked
Floor
out on a slab using a steel rule. The machine was started and the
Radial Arm
gate crossings were used to start and stop the watch. Since the
0 200 400 600 800 1000 1200 1400 1600
distance between gates was known as well as the time taken to
SPINDLE SPEED (rpm) traverse the distance, the average velocity could be calculated.
Figure 2 We made no attempt to work with instantaneous velocities. A
range of traverse speeds at various loads and spindle speeds
Water delivery had to cover, in a controlled way, a range from
were measured and analyzed using the same linear regression
slightly damp to flooded (0.5-10.0 GPM). This is usually a fairly
approach. The engineers at Park really had fun with the “crazy”
loosely controlled variable in most production applications.
group from ATI and GE Superabrasives. With their help, the
The broad ranges represented in the field are shown in Figure 3.
machine was successfully calibrated to our satisfaction and was
POLISHING MACHINES - WATER FLOW RATES
made ready to ship.
The GE Superabrasives Applications Development Center in
GP72M
Worthington, Ohio was chosen as the site for conducting the test
program. This modern facility houses many state-of-the-art
MACHINE TYPES
Slab/Tile Line
machines used to evaluate a broad range of diamond application
Floor
technologies.
Radial Arm
A test plan was developed using statistically based Designed
0 1 2 3 4 5
WATER FLOW RATES (gpm)
6 7 8 9 10
Experiments. Variables evaluated included abrasive types, bond
systems and associated characteristics, operating parameters
Figure 3 and stone types. The output characteristics were stone reflec-
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3
4. tance, depth of color, overall appearance, and tool wear. Tests number of passes required, were varied over a considerable
were conducted almost continuously over a 24 month period. range during the test program. The table values produced signifi-
The tooling formulations were developed in response to the cantly better results than any others tested. We recognize that
output characteristics initially measured. Progressive improve- field conditions are often less than optimal. Also, production
ment was incorporated into each succeeding level of tool design equipment often lacks the adjustment and control features
and testing. The various stones’ finish sensitivities to both small necessary to obtain the table values exactly. However, three
and large changes in the operating parameters were also quan- things can be stated definitely. First, deviation from the table
tified. values detracted from the optimum finish and productivity
numbers we achieved during testing on the specific piece of
In order to minimize test time and facilitate rapid decision
White Cherokee marble we used. Second, no one is using THE
making, we decided to use a 9 inch diameter head. Typical
exact piece of White Cherokee marble we used. Consequently,
production systems use up to an 18 inch head. We focused upon
some changes in operating parameters may be useful. However,
surface feet per minute (SFPM) values rather than RPM in order
the table values represent a well tested and proven set of
to have a valid and scalable test plan. Also, we chose a Munich
parameters for a starting point when polishing marbles in this
resin based shoe shape. This is very much like a scaled-down
range. Third, care must be taken when changing parameters. We
version of the Frankfurt shoe that is typical through out much of
found interactions between parameters that significantly af-
the industry. Our head was equipped with 4 shoe holders at 90
fected finish. An interaction between load and water flow rate,
degree intervals. Water was delivered through the center of the
for example, would mean that at light loads, water flow should be
spindle. A rubber doughnut separated the shoe holder plate
low for optimum finish, but that at heavier loads, water flow
from the spindle and provided some compliance for the head.
should be high to maximize reflectance, a reversal or interaction
We used a rough concrete block to open the tools before polish- effect. This is shown in Figures 5 & 6. Figure 5 shows the
ing. We had to abandon this method in short order when the interaction in a two-dimension view. The actual relationship
block became well polished and quite uniform. This represents between water flow and load for one set of tools is shown three
only one aggregate composition and a rigorous test was not dimensionally in Figure 6.
conducted. However, we were pleasantly surprised with the
results. It does appear to be a promising application. The POLISHING INTERACTION OF
OPERATING PARAMETERS EXAMPLE
similarity of this material to Terrazzo would suggest that similar 72
results might be possible for Terrazzo. We finally resorted to 70 WATER LOW
using a sandstone block to open the tools. This worked well 68
REFLECTANCE
66
through the rest of the test program.
64
WATER HIGH
The recommendations that follow are based upon this testing 62
program and only apply to the tools specially developed in this 60
program. Other tools, formulated differently, if used with these 58
LOAD LOW LOAD HIGH
operating parameters, would probably not produce the same
Figure 5
high quality finish and productivity achieved with the OPTI-
MIZED SYSTEM presented here. The presence of interactions at various grit levels and over
several stone types is quite real and presents a special problem
Marble polishing for the production stone finisher. The only reliable way to deal
Table 1 shows the working parameters that produced the best with this reality is to conduct full factorial style tests. For
results when polishing White Cherokee marble. example, in Figure 7 we have a test that would be one of the best
ways to evaluate two levels of load and two levels of water flow
Optimized Operating Parameters for White Cherokee Marble so that any possible interaction effects are taken into account.
with Tech Shine™ Pads & Diaglo M™
30 metal TWO WAY INTERACTION
STONE POLISHING EXAMPLE
(if req.'d) 50 120 220 400 800* Buff
Head Perimeter 850
Surface Speed (sfpm)
73
Total Load Across 60 100 130
4 Munich Pads (lb) 71
REFLECTANCE
Water Flow Rate (gpm) 1 0.5 69
Traverse Speed (fpm) 67
5
3
65 2.6
Pass Overlap: 1/2 head 2.2
63 1.8
Number of Passes 2 70 1.4
WATER
FLOW
72
74
76
1 (GPM)
78
80
*This grit may not be necessary when buffing with DiaGlo M™ LOAD (LBS)
Table 1 Figure 6
Each of the variables, surface speed (SFPM), load (LB.), water While the exact values (low and high) may not be known, the
flow rate (GPM), traverse speed (FPM), pass overlap and the levels should at least be repeatable. By evaluating all four
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4
5. combinations, the practitioner can determine the combination Granite polishing
of these two parameters that represents the most effective set of
Table 2 shows the working parameters that produced the best
operating conditions. Simply selecting the combination that
results when polishing Charcoal Black and Mahogany granites.
produces the best results is quick and easy. A statistically
22 DESIGN As in the marble testing, each of the variables (surface speed
(SFPM), load (LB.), water flow rate (GPM), traverse speed (FPM),
LOAD
pass overlap and the number of passes required were varied
LOW HIGH over a considerable range during the test program. The table
WATER LOW values produced significantly better results than any others
FLOW
HIGH
tested. Similarly, field conditions will vary the results and affect
which parameter levels work best. The table values represent a
well tested and proven set of parameters for a starting point
Figure 7
when polishing granites over this range. Also as in the marble
trained engineer can provide additional insights into the mean- testing, we found that care must be taken when changing param-
ing of the results. Issues related to statistical significance and eters. There are interactions between parameters that signifi-
relative importance of each of the variables can be helpful when cantly affect finish (ref. Figures 5 & 6). In granite, as in the marble
conducting additional trails. However, it has often been true that work, the only reliable way to deal with this reality is to conduct
the “best” set of conditions, based upon statistical analysis is full factorial style tests (ref. Figure 7).
also the “best” of the four combinations tested. A more rigorous
approach would also include replication (repeats) of each of the Optimized Operating Parameters for Charcoal Black & Mahogany Granites
with Tech Shine™ Pads & Diaglo X™
four cells. Finally, the four combinations need to be run in
30 metal
random order to minimize the risk of making an incorrect (if req.'d) 50 220 600 800 1800 3500* Buff
decision due to other factors changing during the test runs. This Head Perimeter 1410
is a very light overview of the statistical engineering consider- Surface Speed (sfpm)
ations. We went well beyond just testing for the “best” single run. Total Load Across
4 Munich Pads (lb)
350 300 100
If you are interested in employing such methodologies but are Water Flow Rate (gpm) 0.5
somewhat unfamiliar with the details, you may want to also avail Traverse Speed (fpm) 5 5 6 7
yourself of someone with Statistical Engineering expertise. This Pass Overlap: 1/2 head
simplified outline is presented to provide the most help to the Number of Passes 4
broadest audience in the belief that small test plans and incre- *This grit may not be necessary when buffing with DiaGlo X™
mental improvement can provide real productivity gains to
many operations. Table 2
The reflectance values obtained during our testing are shown in The reflectance values obtained during our testing are shown in
Figure 8. These values have been further validated through “in Figure 9. These values have also been further validated through
the field” production testing. field testing. The last column of Figure 9 (Amb. Temp.) is not an
actual work step but rather, just permitting the block to cool
Field trials have also shown that 3000 - 5000 sq.ft. can be
down (from over 200+F.) to ambient temperature. The reflec-
produced from a complete set of pads before the end of life over
tance often improves by 10 - 15 reflectance points.
a range of marble types.
This product family has run in production at between 200 and CHARCOAL BLACK & MAHOGANY GRANITE
with TECH SHINE™ PADS & DIAGLO X™ COMPOUND
300 sq.ft. per hour per grit size. We estimate around $0.30 per
sq.ft. in tooling costs for the complete job. Every job will be 90
different and stone properties, equipment characteristics and 80
operator skill make these values good for rough estimating but 70
60
should not be construed as exact. Your own experience over
REFLECTANCE
50
several jobs will be your best indicator of your true tooling costs.
40
WHITE CHEROKEE MARBLE
30
TECH SHINE™ PADS & DIAGLO M™ COMPOUND
20
100
10
90
0
80
30m 50 220 600 800 1800 Buff Amb.Temp.
70 GRIT SIZE
REFLECTANCE
60
50 Figure 9
40
30
Field trials in production have also shown that 2,000 - 3,500 sq.ft.
20
10
can be produced from a complete set of pads before the end of
0
30m 50 120 220 400 800 Buff
life over a range of granite types.
GRIT SIZE
Figure 8
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5
6. This product family has run in production at between 100 and This nomograph is designed for the Tech-Shine™ Munich style
150 sq.ft. per hour per grit size. We estimate around $0.70 per pads. Their contact area, binder formulation and abrasive prop-
sq.ft. in tooling costs for the complete job. These values should erties are all built into this nomograph. For these tools, the
be good for rough estimating but should not be construed as optimum contact pressure for most pads was found to be around
exact. Your own experience over several jobs will be your best 9.5 psi (reference the center line and also Tables 1 & 2.) Your
indicator of true tooling costs for your operation. available head load could be different from the one at which we
tested. In order to set up your equipment at the optimum contact
Field operating considerations pressure, you would use the Figure 10 nomograph if you want to
We have found that THE two most significant variables for use the Tech-Shine™ Munich style shoes. For example, if you
controlling polishing results are the contact pressure on the placed a scale under your machine’s head and found that it
stone and the tool rotational velocity. Of course, the proper produced a 200 pound load on the stone when installed on the
values will be different for different tools from different sources. machine, you would do the following. First, draw a straight line
Also, we know that stone varies widely. However, for a given through the 200 pound mark on the right vertical line and also
stone, the two key variables that the producer can control are through the 9.5 psi mark on the center vertical line of Figure 10.
the load on the stone and its resultant contact pressure and the Continue the line until it contacts the left vertical line. Read off
surface feet per minute being produced by the motor RPM and the left vertical line the number of pads you should be using.
the diameter at which the tools are operating. Water flow is also Using this example, the proper number of pads would be 8. At
important. This is somewhat less critical than the above men- your 200 pound head load on the stone, you will achieve the
tioned variables. Also, we have observed that 5-7 gallons per optimum contact pressure for the Tech-Shine™ Munich pads
minute appears to be a very wet surface (flooded). Conversely, when you have 8 pads on the head. If your load is so small or large
for these stone types and with the Tech-Shine™ tools running at that constructing the proper line results in a value that is beyond
the above specified parameters, a water flow rate of 0.5 gallons the range of 3 to 9 pads, you can call Abrasive Technology’s
per minute produces a semi dry looking trail behind the polish- Customer Support or take steps to bring your machine’s head
ing head. Some operators have used a bucket and stop watch to load into a more typical range. If your head load results in a “# of
check their water flow rates and this should be relatively easy to pads” recommendation which is halfway between two values,
do. Also, we have observed a number of polishing machines that we suggest that you start with the smaller number of pads and
have been retrofitted with various water flow regulating valves thereby increase your contact pressure above the optimum.
to permit repeatable and accurate water flow control. This is assuming that you cannot easily obtain the weight that
would produce the optimum contact pressure. If for example,
In order to assist the polishing technician in the set up of the
your machine’s head load on the stone was 90 pounds, a straight
equipment, we have developed special charts that can help
line through 90 pounds and the 9.5 psi mark would project onto
guide machine setup for the key variables of contact pressure
the “# of pads” at around halfway between 3 and 4 pads. Since 3.5
and surface speed. The charts are called nomographs. These
pads is not practical, you should consider if you could increase
allow the operator to get a proper setup without using a calcula-
your head’s weight on the stone. Using the nomograph, and
tor and without having to deal with complex equations. Figure
connecting a line between 4 pads and through the optimum 9.5
10, for example has three vertical lines labeled “# of Pads”,
psi, the optimum load would be around 100 pounds. If you could
“Contact Pressure”, and “Head Load”.
increase your machine’s head weight by 10 pounds (going from
ATI TECH-SHINE™ PADS 90 to 100) you would be operating at the optimum contact
MUNICH STYLE
CONTACT PRESSURE NOMOGRAPH pressure of 9.5 psi with four Tech-Shine™ Munich pads. How-
500
ever, adjusting the head load may not be possible. In such cases,
we suggest that you start with the nearest whole number of pads
400
that is the lessor of the two. This will increase your contact
70 300 pressure. If this results in unfavorable wear, you may want to try
60
50 operating with one additional pad to get longer life.
40
RECOMMENDED
FOR MOST PADS 30 200 Since the Frankfurt style Tech-Shine™ pads are different in
3 20 construction, they need their own nomograph. If you are using
these pads, you should determine the optimum number of pads
4 using Figure 11. The correct value is obtained in the same
5
• 10
100
90 “straight line” manner as was previously explained for the Munich
6
5 80 style pads. All the same considerations apply just as they did
4 70
7
3
with the Munich style nomograph. However, because of the
60
8 differences in pad construction, the scales are different from
9 2 50
those for the Munich shoes. The optimum contact pressure for
1
Tech-Shine™ Frankfurt style pads is 9.5 psi, just as it is for the
CONTACT
Munich style Tech-Shine™ shoes.
# OF PADS HEAD LOAD
PRESSURE ON STONE
(PSI) (LBS)
Figure 10
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6
7. ATI TECH-SHINE™ PADS For those using satellite or planetary heads, you need to achieve
FRANKFURT STYLE
CONTACT PRESSURE NOMOGRAPH the optimum surface speed indicated on the nomograph (1400
500
sfpm for granite and 850 sfpm for marble). You will need to
calculate your surface speed by the maximum OD method for
400
each rotational center and then add or subtract the one from the
50
300 other, depending upon the directions of rotation of each axle.
40 The equation to be used if your parameters are beyond the
30
200 nomograph’s is as follows:
RECOMMENDED 20
FOR MOST PADS
Rotational Speed (sfpm) = 3.14*Diameter(in)*RPM/12.
3
• 10
If you are unsure, call the Abrasive Technology Customer Sup-
100
5 90 port Line for assistance.
4 4 80
3 70
5 60
Field results
2
6 50 When diamond tool polishing systems started out in 1987, they
1 were only used for edge polishing. Now all radial arm polishers
# OF PADS CONTACT
PRESSURE
HEAD LOAD
ON STONE
can take advantage of the settings proven in the work done as a
(PSI) (LBS)
part of the development program reported in this paper. Line
Figure 11 polishers are also now beginning to convert along a similar path.
Finally, the polishing technician needs to achieve optimum In the case of floor restoration and off-hand polishing of both
surface speed values for best performance. The nomograph of marble and granite, a number of contractors have reported
Figure 12 will assist in the determination of RPM and Head significant performance improvements with the use of diamonds.
Diameter to achieve the optimum rotational surface speed. You Reductions in process time of over 50% have resulted in signifi-
will notice that there are two optimum surface speed dots. The cant profitability increases.
upper one is for granites and the lower one is for marbles. The superior abrasive characteristics of diamond results in a
Otherwise the nomograph operates in the same straight line significant increase in life. At least as important is the conform-
simple manner. Usually, the RPM is fixed and not adjustable by able nature of diamond tooling relative to the rigid nature on
the technician. Consequently, the head diameter is the only way conventional silicon carbide tooling. It is a well-known fact that
that the technician has to regulate the resultant surface speed. the random deep scratches often produced by silicon-carbide
To simplify things, we only used the maximum diameter at which tooling result in much rework and therefore, lost profits. We are
polishing elements come into contact with the stone. We made aware of contractors reporting 30 - 50% rework time with conven-
no attempt to locate the center of the pads or another feature. All tional abrasives and virtually zero rework with diamond tooling.
of our work used the OD for estimating the surface speed. Since
the nomograph is built around the OD values, you should also The inventory space and handling costs associated with conven-
use OD measurements. Fortunately, this is an easy dimension to tional abrasives are 50 sets of bricks to 1 set of diamond tooling
obtain. for comparable grits. The ratio falls to 20:1 on grits of 800 or finer;
ATI TECH-SHINE™ PADS but there is still a huge difference. Diamond tooling represents
PERIMETER SURFACE SPEED
NOMOGRAPH a savings in inventory and handling costs.
800
700
Summary
Both marbles and granites can be polished to world class levels
600
with maximum productivity using the Tech-Glo™ diamond tool
500
system. All types of stone work from initial high volume produc-
tion to restoration can benefit greatly from the use of such an
optimized system.
400
RECOMMENDED 2000
FOR GRANITE Special thanks
18
1500
17
16 • 300
Several individuals at GE Superabrasives and Abrasive Technol-
15 ogy contributed greatly to this work. Without their ideas and
14 1000
900 efforts, this paper would not have been possible. My apprecia-
13
12
• 800
700
tion goes out to them. Thanks team!
11 600
200
10 500
9 400
RECOMMENDED
8 FOR MARBLE 150
300
HEAD DIAMETER ROTATIONAL RPM
(INCHES) SPEED
(SFPM)
Figure 12
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7
