Dvidson hienergy-90

1. Z
I
v
LaeaSociety of
Manufacturing
Engineers
1990
C ALL RIGHTS RESERVED
M R90-369
High-energy Dry
Process Finishing
author
DAVID A. DAVIDSON
Vice President
PEGCO Process Laboratories, Incorporated
Bartlett, New Hampshire
abstract
This paper outlines and details several applications where the combination of high-
energy finishing equipment and dry process media technology has improved surface
finishes, reduced finishing costs dramatically, and ameliorated serious finishing effluent
disposal problems.
conference
International Manufacttiring
Technology Conference ‘90
September 6, 1990
Mass Finishing
Chicago, Illinois
index terms
Deburring
Superfinishing
Polishing
Society of Manufacturing Engineers l One SME Drive l P-0. BOX 930
Dearborn, Michigan 48121 l Phone (313) 271-1500

2. SME TECHNICAL PAPERS
This Technical Paper may not be reproduced in whole or in part in any
form inciuding machine-readable abstract, without permission from the
Society of Manufacturing Engineers. By publishing this paper, SME does
not provide an endorsement of products or services which may be discussed in
the paper’s contents.

3. MRW-389
Many manufacturers are now finding that very refined, reflective surface
finishes can tie generated with a minimum of direct labor by marrying dry pro-
cess mass finishing technology and high speed centrifugal barrel finishing
equipment. [The common industry accepted acronym is CBF].
CBF finishing equipment holds high promise in helping both manufacturers
of precision tolerance parts who require low RMS finishes as well as manufactur-
ers of consumer oriented items such as fashion, costume and precious jewelry.
A problem that many manufacturers seem to be facing is the serious shortage of
skilled and well motivated workers to operate important manual polishing
operations. in the past it was considered expensive and labor-intensive .to utilize
manual finishing or polishing operations. With the high-employment economy that
exists today, it is not just expensive, it is simply not feasible. it has ‘become
impossible to find people who are sufficiently motivated and qua?ity conscious to
staff these types of operations.
Additionally some recent studies have shown that those engaged in this
tyPe of work are at high risk for developing carpal tunnel or repetitive motion
syndrome, a potential workmen’s compensation morass that many companies are
understandably anxious to avoid. All of these considerations pose serious
production and quality control problems for even modestly sized manufacturers
who had been dependent on manual finishing processes to develop their final
finish. In recent years many small and larger companies have taken a serious
look at mass finishing equipment and methods to relieve them of this burden.
Some have tried to modify “wet” process finishing methods which utilize
-abrasive embedded media made from resin-bonded plastic materials or extruded
- and fired ceramic shapes. These materials have proved to be very useful in many
applications for smoothing and clearing parts of casting imperfections, and
removing surface blemishes from stampings or blankings. However, the dull matte
surface finish left by these types of abrasive media is too unattractive and
unappealing to render the product a consumer acceptable surface finish. To
remedy this some have utilized wet burnish operations which employ various
shapes of high-density metal (hardened steel or stainless steel) or non-abrasive
ceramic media to develop reflective surfaces. Often, however, these surfaces fall
short of the buff-equivalent surfaces needed. Further operations to improve
surface quality have been rendered more difficult because the very heavy den-
sity media involved has “peened” or work-hardened the surface of the garts.
Occasionally, there is some confusion surrounding the term “burnishing”,
as it appears to mean different things to different peoele. In wet process
finishing parlance “burnishing” is used to describe reflectivity generating
processes where results are obtained by utilizing the compressive weight of the
media to level the part surface and enhance reflectivity (or luster). As used in
the dry process finishing industry the word assumes a quite different character,
here it is used describe the pre-polish operations which prepare part surfaces
for the final finish or polish operation. ft should be also understood that “wet
burnish” and “dry process” methods achieve reflectivity in rather different ways.
The wet burnish method uses the weight of very heavy non-abrasive media to
flatten and level metal surfaces by compressing them. Dry process media utilizes
ultra-fine abrasive materials which level surfaces incrementally by means of
carefully controlled material removal.

4. iQ?90-389-2
Many firms have had considerable success in adopting alternative processes
with tumbling or vibratory finishing equipment and dry media. The dry media
involved may take a variety of different sizes, shapes and surface textures.
Unlike their plastic and ceramic wet process cousins, these media do not have
abrasive grains or particles embedded in them, but are coated with fine abrasive
materials. As a general rule they are of much lighter density than synthetic
media which led to generally longer cycle times than was the case with wet pro-
cess materials. Their major advantage however was their ability to produce
surface effects that were often close or equivalent to those obtained by. marual
buffing. A secondary consideration was that dry materials did not create the ef-
fluent waste disposal problem common to many wet finishing methods. With the
advent of high energy equipment many manufacturers can be offered the best
of both worlds. (Note: However there is a cost associated with utilizing high
energy equipment and the resulting shorter time cycles. See graphs in Figure
1.1 The very highly refined surfaces that dry process media and compound
combinations can develop can be achieved in relatively short cycle times thanks
to high pressures generated in CBF equipment.
Practical Considerations for Dry Finishing in High Energy CBF Equipment
Much work has been done in recent years on developing and improving dry
process media and compounds. These types of material have found a growing list
of applications in all of the major types of mass finishing equipment [including
conventional rotary barrels, bowl and tub vibrators, and high energy finishing
equipment such as centrifugal barrel (C8 F), centrifugal disc (CDM), and
spin/spindle or drag finishing equipment. Dry process material has proved to be
useful for producing both precision industrial finishes and very highly refined
reflective finishes for cosmetic or decorative applications such as jewelry. These
materials have become a key component in the surface preparation of precision
parts within the aerospace, medical, electronic, ball and roller bearing,
fineblanking, plating, electroplating and coating industries.
In comparing conventional and high energy processes some have made the
mistake of thinking of centrifugal barrel processes as simply accelerated barrel
finishing. The reasoning behind this assumption is flawed. Despite the obvious
parallels in the two processes, the forces at work in each are actually quite
different.
Barrel Finishing is a positive displacement method. Most of the work is
accomplished within a gravity induced slide zone developed by the rotational
motion of the barrel. In centrifugal barrel equipment the opposing rotational
forces induced by the counter-rotating barrels and turret can produce pressure
of media against parts that are many times the force of gravity. The most
significant recent event regarding CBF equipment is the development of new
generation dry finishing materials which can truly, when utilized properly, rival
hand-buffed finishes.
The media volume requirements of each type of machine differ greatly as
well, especially where dry media and compounds are concerned. Ideally barrel
equipment would be filled to 50% volume capacity in order to achieve the longest
possible slide zone and optimum efficiency. Dry media loading requirements of
C8F equipment can take advantage of the fact that slide zone requirements are
much more modest than the conventional barrel as most of the rubbing or

5. LMR~O-389-3
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6. ~HFSO-389-4
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7. HR90-389-5
wearing action of media against parts is caused by centrifugally induced
pressures. This is a distinct advantage for CBF equipment as fill levels of 90%
or more can be utilized to protect fragile or delicate parts. [Filling CBF barrel
compartments to only 50% of volume capacity with dry materials would in fact be
ill-advised. Fill levels must be higher than this to protect against part-on-part
impingement.
One advantage CSF equipment brings to the finishing engineer’s arsenal, is
the ability to use dry media for cutting, smoothing and polishing processes
within restrictive time cycle constraints. This has been particularly useful tc
those firms experiencing serious waste water disposal problems. To give an
example one manufacturer in the Northeastern United States was emoloying a 48
hour wet tumbling cycle to smooth their small stainless steel parts into the low
RMS numbers. This process employed a large number of conventional tumbling
barrels which created a waste stream of effluent in excess of 10,000 gallons oer
day. This entire system was replaced with two CBF machines (SEE Fig. 6) of
three cubic foot capacity each. A two step process involving dry granular media
was developed. Time cycles were reduced from 48 hours to 4 hours (two 2 hour
steps), effluent discharge was reduced to zero. The parts had greatly improved
reflectivity, and the average RMS finish on the parts was improved from the 10
RMS obtained with conventional tumbling equipment and materials to the 4-5 RMS
range.
Another application where dry process materia’ls have been found to be
useful is in easing precious metal salvage problems in the jewelry industry. Many
manufacturers of precious metal jewelry who utilize wet process media f’nd it
difficult to reclaim 100% of the precious metal fines. Dry deburring and polishing
media made from natural materials can ease this situation, as they are easily
burned and consumed in the refining process.
A follow on technology has developed for precision industrial parts as a
result of the research and development on processes to develop ultra-refined
surface finishes for the jewelry industry. Similar high energy processes have
utilized to develop highly refined finishes for critical components such as aircraft
engine turbine blades and the like. Considerable documentation is now available
to show just how refined these surfaces can be made. The graph and photomicro-
graphs in Fig. 3-4 show some interesting surface changes that have taken place.
On the blades tested, the initial Ra measurement was in the range of 75-90 Ra (Ra
= arithmetic mean of peaks from the mean line). After a multi-cycle processing
in a CBF machine (SEE. Fig. 5) this Ra has been reduced to the 5-9 Ra area.
Observation with an SEM (Scanning Electron Microscope) utilizing back-scatter
emission seem to indicate surface and sub-surface fractures have been removed.
As the photomicrographs in Fig. 3 and 4 indicate substantial changes in the
surface have taken place. Both the profilomter data and photomicrographs
indicate a negative skew to the polished blade (a surface that has more valleys
than oeaks) and that a plateauing of the part surface has occured. A typical
cast, ground or machined part has a positive skew (more peaks than valleys).
From a functional viewpoint the negative skew created on the CBF-polished blade
is very desirable from a fluid or aero-dynamic sense. Blades processed to
develop this type of surface will have significantly smoother, less turbulent flow
than that which is characteristic of positive-skew surfaced blades.

8. LWO-389-6
RRNK TfkYLOR HOBSON
Ferm Talysurf: Series
RANK TAYLOR HOBSO
Form TalysurF Series
EGCO-blade as received-O.D. PEGCO-blade polished-O.D. -
86/98 14:1s:02 27/86/98 14:30:39
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9. MR90-389-7

10. MR90-389-8
Wet Finishing Discharge Problems
One of the most pressing problems faced by those involved in surface
finishing is compliance with an increasingly stringent maze of regulations
designed to protect underground water resources from industrial contaminarts.
Enforcement of these regulations by both Federal and State agencies oiten border
on the draconian. Many types of mass finishing processes that utilize synthetic
(ie. ceramic and/or plastic) media generate an aqueous effluent which poses a
threat to underground water resources. Treatment of the effluent is difficult
and costly and often involves considerable managerial commitment to monitor
adequately. Alternative finishing strategies are available, but usually require
overcoming substantial corporate and technological inertia.
.
The question that comes to many minds is: Is it rea77y worth the effort?
Is the problem rea77y that bad, or has it been bbwn out of proportion?
What follows is a discussion of how serious the problem is. Despite the
appearance of an inexhaustible supply of potable water many are being compelled
to realize that water is indeed a finite resource.
The danger to water supplies is two-fold -- consumption and contamination.
Lets look at consumption first. In addition to the 87 gallons that all ‘225,000,OOO
of us use on average daily for our personal use, the amount of water utilized in
common industrial and agricultural applications is simply staggering, it numbs the
mind. For examp7e -- 60,000 gallons of water was utilized to make the 2000 or
so pounds of steel used to make your family car. Furthermore, when you take the
same car to the service station, bear in mind that each gallon of fuel you out ir7
the tank consumed four gallons of water in the refining process. Then start
multiplying that by the tens of millions of cars on American roads.
Agricultural uses of water is no less demanding. It has been estimated that
there are 200,000 large capacity wells draining water from the Ogallala aauifer
or underground reservoir. This aquifer is the nation’s largest, it runs under
six midwestern states and covers an area exceeding 60,000 square miles. Desoite
it’s size overpumping has depleted this reservoir to the point where water levels
have dropped over 15 feet in some places. Based on current consumption some
hydrological engineers feel that the aquifer may be pumped dry in forty years
or less, and may require one-thousand years to fully recover. Bear in mind, this
is the water supply for the some of the world’s most productive farmland.
Overpumping has also created a critical situation for some of the nation’s largest
metropolitan areas, especially those in the Southwest. Water tables in the Dallas-
Fort Worth, Texas area have been lowered by more than 390 feet in the past 25
years. Houston, Texas is actually sinking into the ground, and may sink fourteen
feet before the end of the century if future demand is met from ground water
sources. In an interview conducted by the U.S. News 8( World Report some time
ago, Senator Daniel Moynihan was quoted as saying “On the floor of the Senate,
I once said that y6u can live with out oil and you can even live with out love,
but you can not live without water . ..Run down the aquifers under the Southwest,
and in 50 years’ time, no Phoenix [Arizona]. Sorry, friend, the water is gone.
That’s a real - and irreversible - crisis.”
.
But consumption is only one side of the problem. The largest threat to
water supplies is contamination. Hydrologist’s have discovered in recent years
that the earth’s ability to filter and clean water as it percolates through the

11. MR90-389-9

12. MR90-389-10
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ground has been grossly overstated. It was thought that the earth ‘tself would
purify the chemicals as underground water trickled through various layers of the
earth. Within the last decade it has been ascertained that many hazardous ,
chemicals are not filtered out but percolate through to the aquifers, contaminat-
ing them for generations to come.
The Environmental Protection‘ Agency has estimated that in the United
states alone -- 1.5 trillion gallons of hazardous waste leaks into the underground
water system annually. When it is recalled that one gallon of hazardous wet waste
can contaminate 20 million gallons of underground water to unsafe levels, the cft-
used phrase “Water, water everywhere - but not a drop to drjnk” takes on a
whole new meaning.
This is not just an American problem. In viewing the situation from an
international perspective one commentator was moved to maintain that “wars in
the twenty-first century will not be fought over oil, they will be fought over
water.”
All of this discussion has fostered a perceptible change in public attitudes
toward environmental issues. So much so that one CEO of a large company
quoted in a recent Wall Street Journal article was moved to observe that t5e
public now perceives companies that damage the environment in about the same
light as people who make cash withdrawals from 7-11’s with a shotgun.
This should give those within the industry strong incentive to seriously
consider adopting metal finishing strategies that hold the formation of waste
effluent to a minimum. To this end several dry process media manufacturers are
committed to a research and development program to provide industry with the
widest possible variety of dry process deburring and surface finishing products.

13. MR90-389-ll
REFERENCES
Threats to the World’s Water, J.W. Maurits la Riviere, in Scientific American, Vol.
261, No. 3, September 1989, pp. 80-94
The Water Crisis - Are We Really Running Dry ?, AWAKE !, Nov. 22, 1986 Vol. 67,
No. 2, pp. 5-8
Save the Environment without Destroying Your Profits, --“Managers Journal” by
John Baden, Wall Street JournaJ, Aug. 21, 1989, Vol. CCXIV, No. 35, Page A8
Almost Buffed, PRODUCTS FINISHING, Davidson, D. A., reprint of December, 1986
issue
Current Applications for Hardwood Media in Dry Process Mass Finishino, SYE
TECHNICAL PAPER MR-85, Davidson, 0. A., Society of Manufacturing Engineers
(SME), Dearborn, MI., 1985
Developments in Drv Process Mass Finishing, SME TECHNICAL PAPER MR89-147,
DAVIDSON, D. A., Society of Manufacturing Engineers (SME), Dearborn, Ml., 1989
Refinino Plastic Surfaces bv Mass Finishinq Methods, PLASTICS ENGINEER ING,
Davidson, D. A., April, 1986, reprint.
Developments in Drv Process Pre-Plate Finishina, AESF TECHNICAL PAPER,
Davidson, 0. A., American Electroplaters and Surface Finishers Society I nc.,
-Orlando, FL. 1987