Accelerated Method for Determining Wear Caused by Abrasion FOSTER DEE SNELL AND KURT W. HAESELER, Foster D. Snell, Inc., 305 Washington St,, Brooklyn, N. Y.
the apparatus is a horizontal blade ETERMINATIOS of the Equipment was designed to measure the mounted on a verticalshaft so that effect of wear on a given the blade revolves just above the comparative rate of wear of travertine and surface over a period of time is sample, pushing six steel cubes an artificial travertine flooring. A silicon around and around over its sura, problem s i m i l a r in m a n y face. At the same time silica carbide block fastened to a reciprocating ways to estimating the effect of stucco sand is fed onto the surarm was loaded to a weight of 3000 grams aging or of w e a t h e r i n g on a face of the sample. The abrasive product. Choice must be made and operated at 30 cycles per minute. Obis changed three times during the wearing operation, which is ordibetween observing the material servation shows that after the surface skin narily for 6000 revolutions of the actually in use over an extended is removed from the stone a steady rate of blade. The results are expressed period of time or of devising a in terms of the depth of wear wear is obtained with the particles of fine method whereby the action can obtained as measured by a midust from the stone as the actual wearing crometer mounted in a movable be accelerated so as to obtain block on a bridge. substantially the same effect in a agent. The silicon carbide block does not Other a p p a r a t u s has more shorter period of time. An accontact the stone. By replacement of the general application but is based on celerateld method is preferable the same principle of exert in g block with a blackboard eraser liberally abrasion by revolving the abradand in many cases e s s e n t i a l . supplied with chalk the equipment was ing element against the sample. The u s u a l u n c e r t a i n t y then One design (3) consists of an upused for measurement of the rate of wear of arises as to how well the artificial right leather wheel which rolls conditions imposed correspond a glass blackboard. A miniature machine with constant slippage on a path of test samples mounted on a to the actual conditions of use. operating on the same principle was dehorizontal revolving disk. SandI n starting accelerated wearsigned and used for comparison af efficiency is fed as the abrasive. Another ing tests on flooring materials (9) measures wear of l e a t h e r , of tooth pastes in removal of mucin several years ago, the apparatires, etc., against arotatingabrading member in terms of loss of maplaques. The equipment appears to be of tus that had already been proterial per unit of abrading powder. posed f o r such a purpose rather general applicability. Another (a),which has been made seemed to have a number of the subject of a patent, rotates disadvantages. I n an effort to blocks of the materials to be compared under predeterminedpressure around a raceway constructed make thte ditermination correspond more closely to conditions of the desired abrading agent. of normal use, a different type of apparatus was set up and the problem approached from a different viewpoint. The There seemed to be two disadvantages common to all apparatus so developed was found later to apply to the study these methods. With respect to flooring particularly, obof abrasion on other types of surfaces also. With simple servation shows that the wear that occurs very seldom results modifications it is believed applicable to shoe leather, the from rotary motion of an abrading surface. The tread of enamel fof compacts, linoleum finishes, and other articles feet on a floor or stairway in general produces reciprocating receiving frictional wear. The illustrations given are of three motion. With respect to any surface, the abrasive action typical applications. Similar equipment is known to be in occurring naturally will only in rare cases be as harsh as that. use in industry but no details of design have been published imposed in these accelerated tests. There may be other so far LLS the authors know. It is therefore given as a fundamental differences between the abrasives as well. Unmethod .which may be found applicable to diverse problems doubtedly the wear on flooring varies as to the nature of and whiieh is believed to have advantages over the methods the materials causing it. I n the extreme case it is partially already in print. due to sharp particles. I n the normal case examination shows that it is caused by particles of the material itself or of Of the various methods for determining hardness, only a few very fine dirt, which, in most cases, are neither sharp nor measure the type of abrasive action occurring on floors. The hard. In setting up a different type of abrasive measurement Dorry apparatus (6) for testing road materials measures the hardness of a cylindrical sample by abrading it against a steel apparatus, therefore, two specifications were established : disk with crushed quartz under a weight of 1250 grams. The (1) that the motion of the abrading element should be in a duration of the test is for 1000 revolutions of the disk and the straight line rather than circular; and (2) that the abrasive results are expressed in terms of hardness where hardness equals action used should correspond as closely as possible to that 20 minus one-third the loss in weight of the sample in grams. This apparatus has been modified (7) for application with speciwhich would cause the normal wear when the material being mens cut from flooring. studied was in use and therefore consist of only fine, relatively Another apparatus, rather similar in principle, but designed nonabrasive particles such as those derived from the material particularly for application to flooring, was developed by Kessler under test. For general applicability it must be possible to (6).,In this method, three specimens of the material are abraded against a disk which revolves at 45 r. p. m. A wei ht of 2000 vary the abrasive used. grams is applied on each specimen and No. 60 artitcia1 alumiThe use of fine particles of the material under test as the num oxide is fed constantly onto the disk as the abrasive. The abrasive, in place of other miscellaneous dirt, is believed to disk is rotated for 5 minutes and the specimens are weighed in introduce no serious variable so long as the material under terms of hardness where hardness equals the reciprocal of the loss in volume times a factor. Correlation with service measurements test is of a fine-grained structure. It does not seem to be an was only fair, but is believed adequate to permit prediction of unreasonable extension of Kessler’s work (,5) to assume that, service wear. if the use of coarse abrasive correlates with service results, Still another method designed especially to test flooring is the correlation with service will be as good or better when fine that used by the Dow Chemical Company (1) on magnesia ceabrasive is used. Further there is nothing inherent in the ment composition flooring. In this case the essential feature of
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than high pressure as well as towards mild rather than harsh abrasive for the study of normal wear. The specimen to be tested was marked off into 5-cm. (2-inch) sections along the 45-cm. (18-inch) strip. The depth of wear after given periods of operation of the abrading arm was measured in each section of the worn strip by a stud m i c r o m e t e r s u i t a b l y mounted in a frame constructed for the purpose. The micrometer was sufficiently delicate so that measurements were reproducible to 0.0025 cm. (0.001 inch). Any FIGURE 1. APPARATUSUSEDON FLOORING material, such as flooring, on which measurements of abrasive resistance are to be made, generally has different characequipment which prevents the use of sharp particles such as teristics a t the surface than in the body of the stone. Usually silica sand if extreme conditions are to be measured. The the surface is harder, and there are aIso minor surface irreguequipment is, however, primarily for measurement of normal larities. The same would be the case with nearly any flat rather than for abnormal wear. Naturally, when the second specification is adopted, the solid. Therefore, a firmly bonded silicon carbide block was used as the abrading element. This caused the initial cut in duration of the test period must be considerably greater than Kessler’s 5-minute period, in order to obtain an apthe surface to be obtained quickly, as desired. The space between the abrasive crystals in the block soon become filled with preciable effect. However, the action is still an accelerated powder derived from the specimen and thereafter the abraone, since the motion can be made continuous as contrasted with actual use, where the impact of an abrading element, sive action is similar to that obtained in actual wear. Exsuch as a footstep on flooring, occurs only intermittently and amination shows that the abrading member is not in contact a t irregular intervals. with the flooring after this initial period, but is riding on a layer of dust particles derived from the flooring which are in turn the actual abrading agent, just as in stepping on the Tests on Flooring floor the abrading agent is the fine dirt, not the shoe. The rate of wear a t the very beginning of the test is not The apparatus as originally set up for tests on flooring and representative and would not be, even if the abrading element shown in Figure 1was as follows: were already filled with debris from the specimen. The rate A 0.75-horsepower motor operating through a speed reducer of wear in the remainder of the test is substantially constant was set up t o produce reciprocating motion of an arm, operating and the abrasive action then occurring may be reasonably at 30 cycles per minute. The arm carried the abrading element assumed to have a constant ratio to the rate of natural wear. with an additional weight imposed so that the total weight of the After some time the silicon carbide block becomes impeded abrading element was 3000 gram3. The abrading element itself consisted of a block of appropriate material, the surface of which by excessive accumulated particles on the surface of the measured 15 em. (6 inches) long and 2.5 cm. (1 inch) wide. This specimen, so that it is desirable to brush off this accumulation moved lengthwise over the face of the specimen being tested. a t regular intervals depending on the nature of the surface. The machine gave a stroke of 30 cm. (12 inches), so that abrasion The block itself should not be brushed and thus actual abraoccurred over a strip about 45 cm. (18 inches) long with the center of this strip receiving the greatest amount of wear. If sion by the block is avoided. To accelerate the test further desired this strip might be composed of two materials of not and thus measure drastic wearing conditions, the normal vastly dissimilar hardness in order to compare their rate of wear detritus from the floor could be replaced by a layer of abrasive at the same time, such as of black and of white marble to be laid in such as emery, replaced a t suitable intervals as in the Dow alternating blocks. apparatus (1). The apparatus may be operated for as long a period as The selection of the weight is a compromise. The weight seems desirable for the particular material under study. to be used must not be so great as to cause active contact of The study for which the machine was originally designed the abrading element with the flooring. Rather it should be was a comparison between the wearing qualities of travertine cushioned by the fine dust resulting from the wear, or by abramarble and an artificial travertine made of a magnesium oxysive supplied. Observation shows that the movement of a chloride cement composition. For this purpose the maxishoe over the flooring, which is believed to be the time of mum period of operation was a total of 60 hours and the greatest wear, is before the major portion of the weight is minimum 18 hours, depending on how quickly an appreciable applied and as the foot is being lifted. For those reasons a wearing effect was obtained. In all cases the machine was weight slightly over 1 pound per square inch was used instead stopped and the surface brushed off a t 6-hour intervals, measof the estimated 10 pounds per square inch present when the urements of the depth of wear being made a t those times. weight is all on one foot. Katurally, many variables, such Results were expressed in terms of depth of wear per as rubber and leather heels, women’s small heels, etc., must be hour as calculated from the micrometer measurements a t 6blended into the composite. Except in the case of actual hour intervals. If preferable, of course, the loss in weight slippage, the foot does not move after the full weight is apor in volume in a given period could be determined instead. plied and the heel touches the floor. Using the micrometer readings on the center sections of the It should also be noted that the abrading member passes specimen where the wear was deepest, and eliminating the over the floor being tested a t the rate of 60 times per minute, first readings obtained before the rate of wear became conso that even with the lesser weight the rate of wear would be stant, representative values for the two types of flooring mateexpected to be considerable. I n view of these considerarial were as follows: tions conservatism dictates a tendency towards low rather
ANALYTICAL EDITION
MAY 15, 1936 Travertlne Artificial travertine compared
0.1067 mm. (0 0042 inch) wear per hour 0 0254 mm. (0 0010 inch) wear per hour
Accumulation of extensive data showing the rate of wear a t various points on the stone was found unnecessary after adequate data for interpretation had been assembled. Correlation between different determinations was very satisfactory, considering the type of determination. The results quoted have, of course, no general applicability but refer only to relative values on the types of material compared. Thei,e results, obtained several years ago, have been confirmed qualitatively by observations on floors in use. No method of exact measure of rate of wear has been applicable t o floors under our observation. Kessler (6) points out the variable effect of humidity on the abrasive action in his apparatus and specifies that comparative tests should be run a t the same relative humidity. No attempt was made to control the humidity in this study, and minor irregularities in the results may have been due to this cause. Since the authors’ machine was operated for a period of 18 to 60 hours in comparison with Kessler’s test period of 5 minutes, variation in humidity was not as important and the average rate of wear over the entire test period was consistent. As another comparison this equipment performed 30,000 to 100,000 complete cycles as compared with 225 to 6000 for the other types of equipment referred to. The effect in wet wear would be expected to be less than when dry, because the water film would interfere with the contact between the finely divided particles and the stone. This was substantiated. For determinations of wet wear a separatory funnel was arranged to drip water continuously on the surface of the specimen, so that it was kept wet throughout the test period. The results under these conditions slhowed that after the rate of wear became constant it amounted to less than 0.00254 mm. (0.0001 inch) per hour for both travertine and the artificial travertine.
Glass Blackboard Tests While this apparatus was originally developed for use on flooring materials, it was found to have more general applicability. As an example, the apparatus has been used to study the behavior on wearing of a composition glass blackboard. I n that case, it was possible to exert abrasive action corresponding very closely to that occurring in use. I n place of the silicon carbide block, an ordinary 6.25 X 15 em. (2.5 X 6 inch) blackboard eraser was mounted a t the end of the arm. The eraser was filled with chalk beforehand and chalk powder was spread on the surface of the piece of blackboard being tested. The eraser was loaded with a weight of 2 kg. and a pad of cloth placed under the sample
FIGURE2. MINIATURE APPARATUS
193
to take up any irregularities in pressure. The excess chalk on the surface of the sample was removed and a fresh supply added every 6 hours throughout the test. No quantitative measurement of the results was made in these tests, as the primary interest was in the appearance and writing surface of the boards after an extended period of use. Instead, the macroscopic and microscopic appearance of the blackboard surface, with and without chalk, were recorded photographically as previously published (8). Micrometer measurements might be made in the same way as on the flooring if desired. On the basis of an estimate of the average amount of erasing a blackboard receives in schoolroom use, it was calculated that an hour’s operation of the machine corresponded to approximately 2 years of actual service.
Abrasive Efficiency of Tooth Pastes Still another application of the apparatus, and one certainly far removed from tests on flooring, was its use to compare the relative abrasive efficiency of tooth pastes. In this instance, the interest was in comparison of different abrasives against a standard surface, rather than comparison of the resistance of different surfaces to a standard abrasive. A much smaller machine was built for this purpose, following the same principles as those already described for the larger machine. The miniature apparatus is illustrated in Figure 2. A 0.25-horsepower motor, a, is attached t o the gear-reducing unit, b. Through the eccentric, c, and connecting rod, d, the abrading element is given a reciprocating motion of about 100 strokes per minute. The steel plunger, d’, fits snugly into the metal shoe, e, the bottom of which is surfaced with a plate glass. The plunger is guided by a brass tube, f. A glass plate, g, carrying the surface t o be abraded, h, is held in place by two iron clamps. The combined weight of the plunger and metal shoe gives a load of 160 grams.
Abrasives are present in tooth pastes in order to remove the film of mucin which builds up on the teeth. They must be sufficiently abrasive to be effective but not so drastic as to injure the teeth. The standard surface against which the tooth pastes were compared consisted of a mucin plaque prepared as follows. A suitable quantity of mixed human saliva was collected and centrifuged to throw down the mucin (4). This mucin was then spread upon a thoroughly clean flat glass plate as evenly as possible. When nearly dry, it was subjected to the vapors of formaldehyde for several hours in order to form a hard, tough film, corresponding closely to the mucin films formed on the teeth. The plaques so produced were about 10 em. (4 inches) square, and each was marked into four equal sections. In order to simulate conditions of use exactly, the abrading element would have to be a brush, corresponding to a toothbrush. However, use of a brush would introduce the complication of having varying amounts of the different tooth pastes run up into the bristles and out of contact with the mucin plaque. A glass surface was therefore used as one offering no variables. In carrying out the tests, definite quantities of tooth paste were intimately mixed with fresh human saliva and the mixture was deposited on one section of the mucin plaque. Similar mixtures of other tooth pastes to be compared were deposited on the other sections of the plaque. The plaque was then set in place in the machine and abrasion applied to the extent of 100 strokes of the arm on each of the four sections. At the end of the operation the plaque was removed, rinsed gently, and the four sections compared as to relative degree of removal of the film and presence or absence of striations. The results obtained showed definite and reproducible differences between the tooth pastes compared.
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I n terms of any one accepted as standard, greater or lesser abrasion can be obtained and recorded photographically.
Summary The apparatus described presents a method of relative comparicjon of wear on materials. It is known to be in use in industry but not previously described and has the following advantages : Kormally a mild rate of wear is obtained, but this can be varied if desired. No special equipment is required for preparation of the specimen. Adjacent blocks to be laid alternately in the same floor can be compared. The equipment is easily assembled in any laboratory. The large number of cycles tends to eliminate accidental variations. With suitable modification it is applicable to many types of materials.
VOL. 8, NO. 3
It has the following disadvantages: The large number of cycles requires a substantial time for the operation. A large specimen is required for the full-size machine, Literature Cited Dow Chemical Co., "Plastic Magnesia, Cements," Magnesium Chloride Service Bull. 9, Midland, Mich., 1927. Fahrenwald, F. A., U. S. Patent 1,678, 110 (July24, 1928). Geister, C. H., J.A m . Ceram. SOC.,9, 121-5 (1926). Haeseler, K. W., and Fain, J. M., Dental Cosmos (September, 1935). Kessler, D. W., PTOC.Am. SOC.Testing Materials, 28, 11, 855 (1928) ; Bur. Standards J.Research, 11,635-48 (1933). Page, L. W., Proc. Am. SOC.Testing Materials, 13, 983 (1913); Goldbeck, A. T., and Jackson, F. H., Jr., U.S.Dept. Agr. Bull. 4 4 , 7 (1912). Shank, J. H., A m . SOC.Testing Materials, preprint (1935). Snell, F. D., and Fox, B. S., J . Chem. Education, 8, 320-7 (1931). Williams, Ira, U.S. Patent 1, 711,866 (May 7, 1929).
RECEIVED March 12, 1935.
An Inorganic Liquid Mixture for Temperature Baths in the Range 100' to 250' C. BERT E. CHRISTENSEN AND ANNE E. KING Oregon State College, Corvallis, Ore.
I
T IS common laboratory practice to employ for temperature baths in the range 100" to 300" C. sulfuric acid, paraffin
or fusible alloys (3, 6, 7, 9), all of which oils, bath waxes (6,8), are subject to rather serious limitations. In regard to other materials (1, 8, 4) which can be used, the literature is indeed meager. In connection with some work on organic oxidations it was necessary to employ a bath having the following specifications: (1) temperature range 125" to 250" C., (2) relatively high heat capacity, (3) no fuming a t the temperature of operation, (4)transparent after long usage, (5) material easy to remove from glassware, and (6) offering no fire hazard. The organic substances which are usually employed in the work do not meet the five latter requirements. Of the inorganic materials, only the fusible alloys and sulfuric acid can be used in this range. Metal baths are objectionable on two counts: their relatively low heat capacities and high specific gravities, Sulfuric acid is rather satisfactory except that, on account of fuming, its use is limited to the hood, and some danger is entailed in handling it while hot. Since the usual fusible salts cannot be employed in this range, other inorganic substances were investigated. Of these, ortho- and metaphosphoric acids appeared to have many desirable properties. Metaphosphoric acid forms a clear liquid above 150" C. which solidifies on cooling. A series of experiments was conducted using 85 per cent orthophosphoric acid as a diluent.
Experimental Mixtures containing various amounts of 85 per cent orthophosphoric acid to a given weight of metaphosphoric acid were prepared. Before being employed in the bath, each was given an initial heat treatment, which consisted of raising the temperature slowly to 260" C. and holding until rapid evolution of steam had ceased. After this treatment, the solutions appeared to possess constant thermal properties.
Test runs were made on various mixtures which had received this treatment, to determine which were most suitable for use over the given temperature range. The results are tabulated in Table I. TABLEI. TESTRuxs Composition by Weight KO. 86% HaPo' HPOs
Maximum Temperature Before H10 evolved on Before seoond heating fuming
c.
1
2
3 4 .5
1 2 3 4 6
1 1
1 1
1
Above 250 Above 250 Above 250 Above 250 Above 250
c.
340 340 340 340 340
State a t Room Temperature Solid Visoous Less viacoue
Mobile Mobile
For most purposes KO.4 seemed highly satisfactory, in that it is liquid a t room temperature. No. 2 can be used more satisfactorily in the higher temperature ranges up to 340" C. but is solid at 20" C. A bath such as S o . 3 has been used for over a month in this laboratory with no apparent change in properties. These liquids, in addition to satisfying all the aforementioned requirements, possess a very small temperature gradient, as rising temperature causes expansion which results in the circulation of the liquid.
Literature Cited (1) (2) (3) (4) (5)
(6) (7) (8) (9)
Boynton, W. H., Chem. TradeJ., 69, 30 (1921). Clark, E. P., J . Assoc. Oficial A g r . Chem., 16, 418-20 (1933). Grellert, M., Apparatebau, 42, 229-30 (1931). Hutter, Chem. Fabrik, 1931, 498. Levine, Harry, and Lanari, Raymond, IKD. E m . CHEM.,26, 696 (1934). Murman, Ernest, Chem.-Ztg., 27, 129 (1924). Pauling, F. H., German Patent 571,361 (February 21, 1931). Robertson, G. R., IND.EXQ.CHEM.,15, 701 (1923). Staudt, Erich, Chem.-Zfg., 54, 9 (1930).
RECEIVED March 4, 1936.
