-

INCREASED MACHINE TOOL PRODUCTIVITY RESULTING FROM

COALESCING PLATE FILTRATION

Increasing Productivity of Machine Tools

ABSTRACT This report provides results recorded from the application of a coalescing

plate separator to grinding and lathe coolant filtration. Use of the filter and nor- mal recommended practices in monitoring coolants significantly extended cool- ant life, increased the tool life of carbide inserts and grinding wheels an average of 25'10, and resulted in cleaner machines and coolant sumps. The use of de- ionized water is discussed. Both synthetic and water soluble coolants were tested with equally favorable results. The ability of this type filter to remove tramp oil and to maintain concentrations less than 0.2% is documented. The level of solid contaminants in grinding was reduced by 50% when compared to alternative filtration methods, and indications are that this measurement is the key to prolonged grinding wheel life.

TABLE OF KEY COMPARISONS TOOL LIFE - LATHE

Material Speed Feed Depth Insert Flank Wear Average Tool l ife Average Time InCreaSe

(mm) (minutes) Filtration Tool l i fe (Sfpm) (inlrev) (in) Comparison wlo CPS filtration With CPS in

(minutes)

1. AISI-1045 350 ,0128 ,100 K21 ,300 18.2 27.7 52% 2. AISI-1045 500 ,0128 ,060 K45 ,200 18.0 26.8 49% 3. AISI-1045 500 ,0092 ,060 K45 ,175 21.5 27.5 2a% 4. AISI-4340 350 ,0102 ,075 K21 ,300 16.0 20.5 28% 5. Class 40C.l. 400 ,0128 .lo0 K68 ,300 10.2 11.2 9.8% 6. Class 40 C.I. 400 ,0092 ,060 K68 ,250 12.7 18.5 45.6%

TOOL LIFE - GRINDER (Cubic inches Metal Removed Per Wheel Dressing) Material Conventional CPS improvement

Settling Tank Filtration

*CPS Filtration - Coalescing Plate Separator

Class 40 Cast Iron 20.76 24.07 15.9% AIS1 4150 Steel 10.97 51.74 371 .2%

(R-54-58)

COOLANT LIFE Withwt CPS Filtration With CPS Fillralion Improvement

Lathe. . . . . . . . . . . . . . . . . . . . 9 weeks (900 mach. hours) Grinding . . . . . . . . . . . . . . . . . lOdays(57 mach. hours) 47+ weeks(1200mach. hours) 2350%

52+ weeks(3400mach. hours) 577%

TRAMP OIL LEVELS OF COOLANT Without CPS Filtration With CPS Filtration Amount Removed Type Test

Production N.C. Lathe. . . . . . 4.6% during 9 week life 0.2% during 52 week life 95.6%

SUSPENDED SOLID MATTER PRESENT IN COOLANT (MilligramslLiter) Type Test Without CPS Filtration With CPS Filtration Reduction

Lab test - Lathe 254.8 187.3 26.5% Identical material - equal cutting time

(after filtration)

Identical material - equal cutting time

Production Grinder 54.5 21.5 60.6%

Lab test - Grinder 20.5 9.7 52.5%

EFFICIENCY OF FILTRATION Rotating Magnetic CPS Filtration

Drum Filter with Filtor Panmr

Removal of suspended solids mgi l 44.7% 69.7% 2

Introduction Many articles have been written in recent years about

the added manufacturing costs caused by a poor coolant control program: e ' Most articles conclude that coolant life can be prolonged if effective filtration is applied, and if levels of tramp oil from the machine's hydraulic and lubricating systems are reduced. The purpose of this technical report is to summarize results of using coal- escing plate separator filtration on machine tool appli- cations.

If tramp oil is to be removed by gravity from either water soluble or synthetic coolants, it must be allowed to rise to the coolant surface. The vertical velocity of oil droplets is a function of:

1. Density differential between oil and water - the

2. Size of the oil droplet - larger droplets rise faster

3. Temperature of the mixture - higher temperature

When Turbo/CPS plates are inserted in the rise path of oil droplets, fine oil droplets are coalesced (combined or joined) into sheets of oil on the bottom surfaces of the plates. The separation process is enhanced by the combination of droplets into a larger mass as the oil rises to the surface. The continually larger mass in- creases in velocity with distance from the tank floor.

Additional separation is gained by creating velocity changes in the laminar flow path that results in a higher incidence of droplet collision and coalescing into larger droplets. The patented TurbolCPS coalescing plates not only cause this velocity change to occur as coolant flows throughout the filter zone, but the 'A inch vertical separation of the plates minimizes the travel distance and time for oil to reach coalescing surfaces where formation of larger droplets occurs.

The same principle is applied to vertical plates, which are designed to remove solid materials. Laminar flow increases the settling rate of solid matter through the plate zone, and the plates provide barriers to suspended

greater the differential, the faster the oil rises.

(*Stoke's Law).

increases,vertical velocity.

solids. Since much of the solid matter present in ma- chining coolants has a natural affinity to fine oil droplets, successful removal of either oil or solid matter will assist the removal of the other contaminant.

In a typical application of coalescing plate filtration (reference Fig. l), contaminated coolant flows into a pre- liminary chamber where heavier solids settle out due to liquid vortex action. Coolant then passes over an inlet weir into the plate zone. Oil removed by the coalescing action rises to the surface and is removed by two oil skimmers. The oil removed is prevented from migrating to the outlet area by means of a dam. Clean coolant accumulates at the bottom of the filtration tank, flows under the oil dam, then upward over the outlet weir, and returns to the machine tool.

*Stoke's Law is used to compute the rise velocity of an oil droplet at 68°F:

9 V, = 1 8 ( i w - i o ) D2. where

V , = rising velocity of the oil droplet in

g = gravity constant (980 cm/sec2) p = viscosity of coolant solution in poises

cm/sec.

(about 0.02 - 0.05)

of water and oil s w and s o = densities(gm/cm3)or specific gravities

D = diameter of the oil droplet in cm.

With conversion factors included,

V, in inches/minute = ,001 286 (1- h) DE, where

in gm/cm3, and 10 = specific gravity of the oil or its density

D = micron diameter of the oil droplet

SEPARATED OIL OIL DAM

INFLUENT OUTLET 0IL.WATER - WEIR MIXTURE

CLEAN I, WATER

EFFLUENT

\ DRAIN

/7 DRAIN

INLET WEIR COALESCING PLATE ASSEMBLY

Figure 1 - Schematic Dlagram 01 TurbdFram Coalesclng Plate Separator

3

Application of Coalescing Plate Filtration to a Numerically Con trolled Lathe Objectives: To study effects of a coalescing plate sepa-

rator on a turning application. To observe physical characteristics of coolant over its useful life.

Test Description Location: Wiedemann Division of Warner & Swasey,

Machine: Warner & Swasey 1SC Model M-5009, Serial

Coolant: Master Chemical Trim-Sol - A water soluble

King of Prussia, Pa.

Number 2770349

oil coolant mixed at 50:l ratio.

The initial test of a Turbo/CPS coalescing plate separator was conducted at Wiedemann Division on a numerically controlled lathe. The designated machine used throughout the test was in operation an average of two shifts, performing work on a wide variety of materials, in typicai job shop quantity lot sizes. Most frequent materials machined during the eighteen months of testing included various grades of hot and cold drawn plain carbon steels, tool steels up to 5% chrome content, cast iron, AIS1 41 50, and small quan- tities of plastic and aluminum.

Coolant samples were drawn once a week during testing, with measurements taken on total suspended solids (milligrams per liter), particle size, distribution of the solids present, and tramp oil present (parts per mil- lion). All coolant analyses on this, and other projects described in this bulletin, were performed in accord- ance with APHA standard methods, 15th editionq0, and/ or ASTM standards.

Results From Normal Machine Operation The machine used for testing is typical of current

N.C. lathe design. Coolant used while cutting is passed through a chip conveyor that removes large swarf, to the coolant sump, located in the machine base. It is return- ed to the work piece area by a centrifugal pump, after passing through a fine mesh screen, which prevents large chips from damaging the pump.

Prior to the test, the machine's sump was thoroughly cleaned and all chips and residue removed. A fresh batch of Master Chemical's Trim Sol was added to the machine.

The coolant failed after running nine weeks, over 900 machine hours. During the test period, trump oil con- tamination averaged 4.6%, in spite of the cleaning prior to the start of the test. The life of the coolant was typical of what had been experienced prior to this study.

1st Test With Coalescing Plate Separator A TurbolCPS coalescing plate separator was in-

stalled as a bypass filtration device in the second phase of testing. In this case, coolant was removed from the sump and passed through the filter, then returned to the machine. Theoretical turnover of all coolant in the sump would occur every 64 minutes, however, a practical es- timate is that a complete filtration of the coolant occurs every two to three hours, because of restrictions in the machine sump affecting flow. Targeted concentration of

mixture used throughout the plant on machines using Trim Sol. In all testing, a refractometer reading of cool- ant concentration was taken weekly, and cooiant mix- ture was adjusted to maintain a 2% solution. In the final week of testing, a hydraulic leak increased the oil con- centration sharply, probably contributing to sudden failure of the coolant after eight weeks.

Comparison of data yielded the following results, with use of the coalescing plate separator:

1. Average tramp oil present decreased from 4.6%

2. Average weighted particle size decreased by

3. Total suspended solids decreased by 13.7% This statistic must be treated with care, because different materials machined will have a large impact on results. Subsequent tests on tool wear are more meaningful because identical materials were machined during testing and total time of machining was equalized. Refer- ence tests at Warner & Swasey R & D. and Le- high University).

-

-

coolant in this and the first test was a 50:l mixture, the -

to 0.4%.

21.4%

2nd Test with Coalescing Plate Separator Deionized water was used for the third phase of the

project, and the machine sump was again thoroughly cleaned prior to adding a new batch of coolant.

In studying ways to prolong coolant usage, Wiede- mann personnel realized increased life from the use of the de-ionized water. Water in the Philadelphia area is high in mineral content, and de-ionized water elimi- nates a constant mineral build up in the coolant, and helps in rejecting tramp

For the tests, pH and coolant concentration levels were maintained and fungus and bacteria counts were checked with dip sticks. Due to undetected hydraulic leaks which affected coolant life in the second test, an additional procedure was established. Hydraulic and gear case oil added to the machine was monitored, and the amount of tramp oil removed by the coalescing plate separator was measured. - Results: 2nd Test with Coalescing Separator Coolant Life

As of March 1, 1982 the coolant had not been changed since instailation - a period of one year. The only coolant added was to replace that lost to evapora- tion and through chip removal. Total machine time was over 3400 hours.

__

4

Tramp Oil In spite of close checks on the amount of oils added

to the 1-SC's hydraulic and gear system, the amount of tramp oil removed by the filter consistently exceeded the quantity added. Articles in the January and June 1981 issues of "Modern Machine Shop"' * suggest a possible cause. Over a 23 week period, the amount of gear and hydraulic oils plus coolant concentrate added equalled the amount of tramp oil removed by the filter's skimmer. Coolant concentrate could be seen in samples allowed to settle for a period of 24 hours. This separation of coolant concentrate and water occurred within three to four weeks after start up, and continued throughout the test. The level of tramp oil remaining after passing through the filter averaged 0.20% for the full year, and was nearly identical to the amount of tramp oil con- tained in samples drawn from the coolant nozzles at the spindle (0.21 %). This indicated that the by-pass system used was effective at removing tramp oil from the ma- chine, even though it did not filter all coolant prior to being routed to the workpiece.

Tool Life During tests using the coalescing separator, carbide

inserts were reported to last longer - an estimated 15 - 25%. When tools approached the end of their ex- pected life, castrophic failure of the tool because of face chipping was reduced. Based on these observations, a series of tests was conducted at Lehigh University, with the specific objective of measuring tool life when using the filter (see page 6 ).

The machine sump was examined after 4.5 months running with the filter, and was noticeably cleaner com- pared to the sump with only two months production with- out filtration. Because of improved cleanliness, bearing way life should improve, and the reduction in tramp oil should decrease the amount of misting or fumes gen- erated in cutting.8

The filter was cleaned three times during the one year period of this test. A rapid buildup of fungus us- ually indicated that the tank needed cleaning.

Increases in bacteria count were corrected by add- ing more coolant concentrate than normal. Average weighted particle size decreased 20%, compared to particle size without filtration, but conclusions must be tempered by the fact that the same amounts of the var- ious types of materials were not machined in the dif- ferent tests.

5

Effect of Using a Coalescing Plate Separator on Carbide Insert Tool Life Objective: TO determine differences in carbide cutter

life when coolant is processed through a coal- escing plate separator, compared with results when machine's original filtration equipment is used.

Test Description Location: Lehigh University - Department of Industrial

Engineering Manufacturing Process Laboratory Bethlehem. Pa.

Machine: LeBlond Engine Lathe - Serial Number 2NE676

Coolant: Castrol Superedge 7 - A water soluble oil coolant, mixed at 30:l ratio with deionized water.

The study was carried out in conjunction with a Mas- ter's thesis in the Industrial Engineering Depaflment.e

To eliminate as much variability in testing as possible, all materials used were ordered at the same time, from the same vendors. Kennametal carbide inserts were employed throughout testing, and for each type of material cut, the manufacturer's recommendations were followed.

Three materials were selected for study - AIS1 1045, AIS1 4340, and Class 40 cast iron. Heavy and medium cuts were run on an average of four bars of each type of material. Castrol Superedge 7, a water soluble oil coolant, was mixed at a 30:l ratio with d e ionized water, and concentrations, pH levels, bacteria and fungus counts were continuously monitored throughout the program.

The machine was thoroughly cleaned prior to the start of each experiment, and a fresh batch of coolant mixed prior to each control test. Comparative data plotted on graphs are based on 484 individual readings of flank wear at timed intervals in the life of the insert. Wear readings are concentrated in the flat-linear portion of the standard tool life curve, after tool break in, and prior to the sharp upward slope preceding failure. Full filtration of the coolant was achieved by passing all cutting fluids through the engine lathe's sump and, in the second phase of testing, through the coalescing plate separator prior to being discharged to machine sump.

Results AIS1 1045

After 30 minutes of machining at heavy cuts (depth = .loo"), tool wear was reduced 21%, as a result of using the CPS filter. At a lighter cutting depth of ,060 inches, wear was reduced 19% As shown on the graphs of curves (Fig.2,4),tool life measured at a con- stant flank wear (.300 mm for roughing and ,175 mm for a finishing cut) was increased 52% and 28% r e spectively.

Three different cutting conditions were tested on AIS1 1045 steel. In these tests, the larger the volume of the chip removed, the greater the improvement in tool life achieved by use of the CPS filter.

Fig.

TOOL WEAR (FLANK) VS. TIME

Material : 1045 Insert : KZ1 Depth : . l o 0 in. Feed : .0128 I n l r e v . Speed : 350 SFPM

0 5 i o 1.5 io 25 io Timehinutes)

TOOL WEAR (FLANK) VS. TIME

Material : 1045 Insert : K45 Depth : .060 in. Feed : .0128 in . I rev . Speed : 500 SFPM

Time (minutes)

TOOL WEAR (FLANK) VS. TIME

Material : 1045 Insert : K45 Depth : .060 in. Feed : .0092 i n . l r e v . SDeed : 500 SFPM

6 Time (minutes)

Cast Iron In examining the graphs, the "break-in" cuts in both

roughing and finishing operations on cast iron caused approximately the same tool wear when using either the CPS filter or conventional processing of coolant. However, after the break-in period, the curves show the same relationship as those for 1045 steel - except that tool life on cast iron was improved more on intermediate depth cuts than on heavy cuts. Tool life - measured at .300mm flank wear - improved by 10% on the rough- ing cu!, and 46% at cutting depths of ,060 inches.

AIS1 4340 This material was the first subjected to testing, and

several problems developed1 early in the test in instrv- mentation, tool holders, and variability between bars. One of the parameters placed on the experiment was that the same quantity of material be cut using the CPS filter as was cut without it, and that total time of cutting between the two control groups be as close as possible.

Data for strict comparison purposes was obtained on only two bars of 4340. An improvement of 28% in tool life at ,300 mm flank wear was recorded as resulting from use of the CPS filter on these bars (Fig. 7). The balance of the data was disregarded because of the problems cited above.

Nearly identical break-in periods of five minutes of cutting were required by all cutter inserts before dif- ferences in tool wear were indicated. Before the start of each 4340 test, the machine was cleaned and a new change of coolant added. It is entirely possible that the adverse effects of tramp oil and solid particulate matter in the coolant were not high enough initially to fully impact tool life on the first material tested. Although the experiment was not designed to run tools to failure, longer tool life was demonstrated with the use of the CPS than with conventional filtration. For example - three of nine inserts tested still were operating after 21 minutes of cutting using the CPS filter. Without the filter, ail but one insert had failed prior to 12 minutes.

General Obsetvations Cutting fluid concentration increased with time on

1045 and 4340 steels, but decreased in cutting cast iron. Cast iron particles generally have much higher sur- face area and are finer in size, thus tying up more oil globules in solution. Cast iron swarf discolored the cool- ant in both tests, but recovery to the natural coolant color was much more rapid when using the CPS. r e flecting removal of solid matter during the filtration p ro cess.

Individual data points of tool wear at a specific time tended to have less dispersion and hence tool wear can be expected to be more predictable. There was no sta- tistically significant difference in surface finish quality between the two control groups.

Analysis of coolant samples taken at regular intervals during testing resulted in an average 26% decrease in suspended solids, and 28% decrease in average weighted particle size when using the plate separator. Consumption of coolant concentrate declined by 45% for the same cutting time interval. 7

TOOL WEAR IFLANK) YS. TIME

Material : Cast Imn Dapth : ,100 in. F a d : .0121 inlrev

: 1OOSFpM : KS8

Fig. 5

TOOL WEAR IFLANK) VS. TIME

Material : Cart lion insert : K68 Depth : ,060 in. Feed : ,0092 in./rev Speed : UOO SFPM

Fig.

Fig.

6

TOOL WEAR IFLANK) VS. TIME

Material : U310

Depth : .075in. F e d : ,0102 in . I rev . So& : 350SFPM

7

Coalescing Plate Separator Filtration Applied to Grinding Objective: To study effects of a coalescing plate sepa-

Test Description Location: Grinding Machine Division

The Warner & Swasey Company Worcester, Mass.

Machine: W/S Model "Stepmaster ACC', O.D. Grinder (Serial #C29163)

Coolant: Buckeye Lubricants TAD-4500-NN - A synthetic coolant from the Amine complex chemi- cal family. Coolant concentrate in 50:l ratio.

rator in a grinding application.

Results of Testing Without Coalescing Plate Separator

Since this machine was used for machining a number of parts critical to the manufacture of precision grind- ing machines, it originally was equipped with a rotating magnetic drum type filter, for removal of ferrous par- ticles, and a fabric filter for removal of non-ferrous particles Coolant lasted a maximum of two weeks, and sometimes was changed in as little as six working days All coolant was routed through the filtration unit prior to being returned to the machine Samples of coolant were taken at the exit trough of the machine, leading to the filter (contaminated fluid), and at the coolant nozzle for the workpiece (clean fluid).

Test Procedure This test was similar to the first one, conducted at

the Wiedemann Division. A production machine being utilized an average of one shift was used for the study. Job shop quantities were typical runs, with the most common materials ground being various grades of cold and hot drawn steel, including 4150, some brass, cast iron, and nickel alloys, and a high chrome alloy steel.

Procedures established in previous tests were follow- ed. Coolant was monitored for pH levels, bacteria, fungus, and concentration levels. Whenever a fresh batch of coolant was added, the machine and all fil- tration tanks were cleaned of all swarf deposits. Cool- ant was recirculated in both tests when the machine was not in use Deionized water was not used in this test, because the water in Worcester, Mass. has signifi- cantly less mineral content than that in the Philadelphia area, where the first test was conducted.

The number of particles over 8 micron in size is not appreciably different leaving the filter compared to en- tering the filter. What filtration of the coolant does ac- complish, however, is a reduction in the total amount of solids of all sizes. If the efficiency of the filtration p ro cess is measured as:

1 -Total Suspended Solids at Filter Exit Total Suspended Solids at Filter Entrance

then the unit's efficiency during coolant life was 45%. Tramp oil averaged less than 0.005%, and was not considered a contributing factor in coolant failure. This machine was equipped with electric feed controls, so there was less possibility of tramp oil contamination.

Measured Results: Coolant Life - Ten working days - 57 machine hours. Average of Total Suspended Solids Leaving Machine - 98.4 milligramsllitel Average of Total Suspended Solids Leaving Filter - 54.5 milligrams/liter

Particle Size Distribution by Count (average for ten day test period):

Entering filter 93.28 5.53 1.03 0.13 0.03 - Leaving filter 91.41 7.25 1.11 0.18 0.05 -

Sample Location 0-<4P 4-<8P 8-<16P 16-<24P 24-<40P 740p

Test Results Using a TurbolCPS Coalescing Plate Separator Filter

Testing procedure was identical to that used for the magnetic drum filter. Throughout testing, coolant was kept as close to a 2% concentration as possible. Rela- tive acidity levels were monitored with a pH meter, and adjustments made as required.

Coolant Life Testing commenced in April 1981, and as of the date

this report was written, coolant was not changed in the machine - a period of eleven months. A total of 1200 machine hours were measured during the testing period (note that early in the test, operation of the machine was reduced to one shift).

The first filtration tank was physically cleaned approx- imately every three months of all swarf accumulated in the plates. After 25 weeks of testing, a new tank design, incorporating a swarf conveyor, was installed, which automatically removed solids filtered by the vertical plates. As was observed in the first test, tramp oil was practically non-existent. All coolant used by the machine was passed through the Coalescing Plate - Separator filtration tank.

Effectiveness of Solids Removal: Analysis of contaminated solid matter in coolant

samples taken prior to entering the filtration tank, and at the spindle of the machine (cleaned), showed the

-

~

8

following results over a 25 week period: Average of Total Suspended Solids Entering Filter:

Average of Total Suspended Solids Leaving Filter: 71 .I milligramdliter

21.5 milligrams/liter Contaminants left in the coolant after filtration d e

creased by 60%, as a result of using the Coalescing Plate Separator filter. Not only did the filter produce a cleaner coolant, but the overall level of solids exiting the machine also decreased by 28%, and it is assumed

Size of Particles in Microns: Sample Location 0-<4P 4-<8P

Entering filter 92.96 6.13 Leaving filter 93.34 5.79

that this reduction is attributable to a cleaner coolant entering the machine. The most important comparative measurement is the efficiency of filtration - 70% for coalescing plate filters versus 45% for a magnetic drum paper filter.

Particle size distribution by count was not significant- ly different than the former method of filtration, nor was it significantly different when measured at inlet and exit of the tank

- a-< IW 16-< 24p 24-< 40p >40p

0.81 0.09 0.01 -

0.75 0.1 1 - -

Particle Removal Over 8 Micron in Size Magnetic Coalescing Plate

Sample Location Drum Filter Separator Filter

Coolant after processing through filter 98.66 99.13 Coolant leaving machine 98.81 99 09

General Observations Throughout this test, and others conducted in this

report, machine operators and foremen were asked for observations and recommendations. These have been particularly valuable in establishing subsequent tests of a specific hypothesis, such as tool life.

Early in this test, the operator reported that he was obtaining a higher yield in number of pieces ground between dressings of the wheel. GMD personnel were asked to quantify this observation as well as possible, and they reported that, in their judgment, they could o b tain at least 25% more pieces ground without wheel dressing. They also indicated that this was dependent upon the type material ground. (Based on this observa-

tion, the wheel life test was conducted at Warner & Swasey's R & D facility - see pagelo). A Norton gen- eral purpose wheel of designation 32A70L5VBE - 30' diameter was used throughout testing, and was not changed. Prior to installation of the Coalescing Plate Separator filtration tank, coolant failure was usually pre- ceded by a gummy deposit build-up on critical parts of the grinding machine, followed by the coolant turning from clear to opaque. It also became viscous, with a tendency to stick to all surfaces. None of these char- acteristics were observed in the eleven months the coolant was in use with the Coalescing Plate Separtor. An improvement in the performance of the automatic wheel balancer also was noted.

9

Evaluation of the Coalescing Plate Separator Filter on Grinding Wheel Life

Objective: To evaluate the effect of using a coalescing plate filter on grinding wheel life, and to study other physical difference in the machining process as a result of using the filter.

Test Description Location: Warner & Swasey Research & Development

Equipment: Norton Surface Grinder Model N-246, Center, Solon, Ohio

Serial #240050. Wheels: Norton 32A46J8VBE - used for 304 stainless and AIS1 41 50 Norton 37C36KVK for Ciass 40 cast iron

Coolant: Anderson Oil Company Lusol96B, a synthetic cooiant mixed in ratios of 45:l with de-ionized water.

Test Procedure Three materials were selected for this study: 304

Stainless Steel, Class 40 Cast Iron, and AIS1 4150 steel hardened to Rc 54-58. Two hundred seventy hours of machining time were consumed under laboratory con- ditions. Parameters held constant throughout all testing were:

1. Downfeed of the grinding wheel. 2. Cross feed increments. 3. Table velocity. 4. Coolant flow rate. 5. Amount of material removed from each

specimen. Measurements were taken on grinding forces (hori-

zontal and vertical), wheel wear, volume of material re- moved, surface finish (horizontal and transverse) and coolant properties previously listed in prior tests.

The small surface grinder used for testing originally was equipped with a 30 gallon settling tank. To generate as much swarf as possible, it was decided to perform all testing at a depth of cut of ,001 inch downfeed for stainless steel and 4150, and ,0015 inch downfeed for cast iron, even though these are relatively heavy cuts - particularly on this small machine. Surface finish

ment as evidenced by the use of the heavy depth and medium grain wheel.

Stainless steel was the first material machined in

41 50. Originally, the determination that wheel dressing was required was based on an analysis of specific grinding energy, but the interrelationship proved erratic. However, in the final stages of grinding the first control batch of stainless with conventional filtration, a much better indicator of required wheel dressing was dis- covered. After this point, the determining factor for wheel dressing was a sudden deterioration in trans- verse surface finish (an increase of greater than 10 micreinches from an established pattern). No definitive comparisons are made of 304 stainless with respect to dressing time due to the procedural change, although it was the feeling of the research engineers that a definite improvement had occurred. Comparative statistics on cast iron and 4150 are presented below.

During the second phase of testing using the coal- escing plate separator, an equipment malfunction oc- curred that was not corrected until a series of finishing cuts had been completed. Repeating these cuts resulted in 16% more material (wheel consumption plus metal removal) entering the coolant system. This is most im- portant to keep in mind when analyzing results - be- cause the CPS filter showed improvement in spite of the handicap of additional contaminants discharged.

comparisons were not a prime objective of the experi- -

-

each control group, followed by cast iron and finally -

Conventional Coalescing Percent Filter Filter ImDrovement

1. Total Metal Removed per Wheel Dressing (in.3) a. 304 Stainless 21.96 Not Measured b. Class 40 Cast Iron 20.76 24.07 15.9 c. AIS1 41 50 Steel 10.97 51.74 371.2 (Rc 54-58)

*

‘Change in testing procedure made comparisons invaiid - see lex!, 2. Specific Grinding

Energy(in.-lb~.lin.~ x IOa) a. 304 Stainless 9.1 7 8.63 5.9 b. Class 40 Cast Iron 4.87 5.01 -2.87 c. AIS1 41 50 Steel (Rc 54-58) 7.84 7.34 6.4

3. Horizontal &Vertical Grinding Forces (Ibs.)

Horizontal Conventional WlCPS

Fllter a. 304 Stainless 13.73 13.53 b. Class 40 Cast Iron 11.16 10.88 c. AIS1 41 50 12.18 10.36 (Rc 54-58)

10

Vertical

Conventional WlCPS Filter

27.66 28.06 34.98 34.12 31.97 27.42

When composite force measurement comparisons are made:

Composite Force (ibs.) Conventional Coalescing Percent

Fiitrallon Filtration Change

304 Stainless 30.88 Class 40Cast Iron 36.72 AlSl 41 50 34.21

Force measurements and specific grinding energy are useful in describing the effect of better filtration on the machining process. Hardened AIS1 4150 gen- erates small hard swarf which will not embed in the aluminum oxide wheel and does not wear the wheel rapidly, but will dull it. Class 40 cast iron generates soft iron chips and graphite flakes which are easily em- bedded in the open silicon carbide grinding wheel and, while they do not wear it away, they plug the wheel, thus requiring more frequent dressing. The 304 stainless steel generates tough stringy swarf which does not embed in the aluminum oxide wheel. However, due to its toughness, it wears the wheel away much more rapidly than the other materials.

It must be amphasized that 304 stainless steel in both tests was being machined immediately after fresh cmlant was added to a clean machine. The build up of swarf in the coolant system, if allowed to recirculate over a long period of time, has an adverse effect on wheel life. It is believed that results of force and wheel dressing times for the stainless would have been a p preciably higher had it been tested as the third material in sequence, rather than the first.

4. Surlace Finlsh Surface finish comparisons were not a primary o b jective of the project, and wheels were selected for high metal removal rates. Differences between con- trol groups were too smaii to be statistically signifi-

31.15 + 0.9 35.81 - 2.5 29.31 - 14.3

cant, although the standard deviation of finished cuts was less when using the coalescing plate filter on four of six data groups. Additional testing in this area is needed.

Figure 8 is a graph plotting the level of contaminants suspended in coolant samples from the settling tank and the coalescing plate separator. These samples were drawn from the nozzle at the grinding wheel. The amount of solids passed by the coalescing plate separator is less than half the amount from the settling tank. It was significantly lower for every ma- terial tested. Average suspended solids for the settling tank. over the entire test were 20.51 milli- grams per liter versus 9.74 mg/ l when using the CP filter, a reduction of 52.5%. Particle size measured on a weighted basis by means of a Coulter counter averaged 10% less than con- ventional filtration. There was no statistical difference in particle size on a count basis, as 99% of the solids present were smaller than 8 micron in size, in both conventional and Coalescing plate filtration. This test reinforced a subjective opinion reached dur-

ing the tests at the Warner & Swasey Grinding Machine Division: that detrimental impact on grinding wheel life is more dependent on the ability of the filter to remove a high percentage of total suspended solids rather than particle size distribution.

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5. Filtration Elficlency

IO Y i IO 0

,Tlnr Hcxr,.,

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Fig. 8

References

(l) M. Albert, "Why Coolants Really Fail", Modern Ma- chine Shop, January, 1981, p. 1051 13.

(z) M. Albert, "New Thoughts on Coolant Control", Modern Machineshop, June, 1981, p. 102-1 12.

(3) John J. Obrzut. "Squeeze More From Cutting Fluids by Managing Them", 1981 International Conference on Trends in Convention and Non-Traditional Machin- ing ITT Research Institute.

(9 P.J.C. Gough, "Cutting Fluid Filtration For Machine Tools", Filtration and Separation, Nov./Dec. 1970, p. 708715.

(5) N. Williams, "Filtration of Coolants Pays Dividends", SME MR 7@254.

(@) "Evaluation of Methods of Extending the Life of Metal Cutting Lubricants", Production Engineering R e search Association of Great Britain, 1981. (Note: This is a PERA member report and inquiries should

be directed to Melton Mowbray, Leicestershire LE 13 OPE.)

(7) E. 0. Bennett, "The Effect of Water Hardness on the Deterioration of Cutting Fluid", SME MR 72-226. "Machine Design Considerations for Improving Metalworking Fluid Performance" SME MR 78252.

(3 K. C. Fu, "Effect of a Cutting Fluid Filter on Tool Wear and Surface Finish", M. S. Thesis, Lehigh Uni- versity, Bethlehem, Pa. 1982.

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(lo) "Standard Methods for the Examination of Water and Waste Water", 15th Edition, Copyright, 1981. Edited by the Joint Editorial Boards of American Public Health Association, American Water Works Associa- tion, and Water Pollution Control Federation. Printed at the officesof APHA, 1015 15th Street N.W., Wash- ington, D.C. 20005

Turbo Conveyors 11 11 Jenkins Rd., Gastonia, NC 28052

(704) 866--9123

Copyright 1982 by TurboConveyors

Form82TX-14 II 2/65

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