US3428443A - Barrel finishing media - Google Patents

Description

Feb. 18, 1969,

H. F- DAVIS, JR

BARREL FINISHING MEDIA Sheet g H6. 2 52 Z 0 soml-OC OZOO" PE [UJ 0:0:

.IOO a 4 0 IO 20 3O 4O 5O 6O /FUSED ALUMINA POWDER IN BAUXITE BODIES METAL REMOVED (%,CUMULATIVE) s is lb TIME (HOURS) INVENTOR. HOWARD F. DAVISJR ATTORNEY --MED|A LOSS (PERCENT PER HOUR) -RATE OF cur (PERCENT METAL REMOVED PER HOUR m '6 HOURS) Feb. 18, 1969 IS, JR 3,428,443

BARREL FINISHING MEDIA Filed July 26, 1965 Sheet 2 of 2 I I I 0 IO 20 3O 4O 5O 6O 70 FUSED-ALUMINA POWER INVENTOR.

HOWARD F. DAVIS,J

ATTORNEY United States Patent 3,428,443 BARREL FINISHING MEDIA Howard F. Davis, In, Grand Island, N.Y., assignor to The Carborundum Company, Niagara Falls, N.Y., a corporation of Delaware Filed July 26, 1965, Ser. No. 474,820 US. Cl. 51-309 Int. Cl. C04b 31/16, 31/18, 31/02 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to novel barrel finishing media and to a method of making the same. It further relates to barrel finishing operations in which this novel finishing media is used to remove surface irregularities and to finish or improve the surface of articles.

Barrel finishing is a surface conditioning operation in which a mixture of metallic or non-metallic parts, abrading media, and various compounds is placed in a container and the container is then rotated or vibrated for the purpose of improving the surface condition of the parts such as by rounding corners, deburring, descaling burnishing and the like. Barrel finishing operations are generally preferred over manual grinding operations in the fabrication of metal parts, for barrel finishing is more economical. Furthermore, barrel finishing reduces the time for accomplishing the desired processing result and provides a more uniform product treatment than is obtained by manual grinding or other abrading operations. For the purpose of the present invention the term barrel finishing includes finishing by a tumbling operation as well as by a vibrating operation.

The abrading media used in such barrel finishing operations is commonly referred to as barrel finishing media or tumbling media, both terms being considered as synonymous for the purposes of this invention. Barrel finishing media comprises bodies of various kinds and shapes which are suitable for the intended purpose. If it is intended that the barrel finishing media be used for removing metal from metal articles, the rate of metal removal from the article, i.e. the rate of cut, should be high and the rate of media loss must not be too great, or the finishing cost is excessive. On the other hand, if the rate of metal removal is too low the barrel finishing operation also becomes commercially unfeasible.

Heretofore preformed media used in barrel finishing operations generally has been mainly of the porcelain or fused adbrasive-vitrified bond types. The porcelain type media has the property of exceptionally long life in both rotary and vibratory machines (that is, the rate of media loss is low), but the rate of cut (i.e. stock removal from the workpiece) is extremely low. The fused abrasivevitrified bond media also lacks the desired combined prop erties of long media life and high rate of stock removal. Recently, an improved tumbling media has been developed in which the media is formed from finely divided bauxite which has been extruded to form shapes and then sintered. While the wear-resistant properties and life of such sintered bauxite media are superior to the previously used products, the rate of cut of media of this type has been unsatisfactory for some surfacing operations. Thereice fore, there is a present need in the industry for a barrel finishing media which provides a high rate of stock removal and which also has long life.

It is, therefore, an object of the present invention to provide barrel finishing media which is superior in use to barrel finishing media available heretofore.

A further object of this invention is to provide barrel finishing media which provides a high rate of stock removal when used in barrel finishing operations.

A further object of this invention is to provide barrel finishing media having an improved cutting rate and wear-resistant properties over barrel finishing media available heretofore.

Another object of the present invention is to provide preformed bodies for use as media in barrel finishing operations, the media being highly efiicient in use.

A further object is to provide a method of forming a barrel finishing media that has a high rate of cut as well as good media life in use.

A still further object of the present invention is to provide an improved barrel finishing operation which comprises the use of media having a high rate of stock re moval and a low rate of media loss.

Various other objects and advantages will appear from the following description of the invention.

In the drawings, FIGURES 1, 2 and 3 are graphs illustrating the results of comparative tests of barrel finishing media.

As mentioned above, barrel finishing media formed from bauxite which has been comminuted, formed to shape, and sintered has wear-resistant properties which are superior to other available types of tumbling media, but such sintered bauxite media has been found deficient in its rate of cut in some applications. It has how been discovered that sintered bauxite media can be greatly improved by mixing finely divided fused alumina With the bauxite prior to forming the media to shape. Thus, it has been found unexpectedly that sintered media formed from a mixture of microcrystalline bauxite and powdered fused alumina has a rate of cut when used in barrel finishing operations which is much greater than that of sintered media formed from bauxite alone. Furthermore, the rate of cut of the sintered bauxite-fused alumina media of this invention is significantly superior to other known types of barrel finishing media, including fused alumina-vitrified bond type media. It has also been discovered that the rate of cut of the media of this invention increases rapidly with increasing additions of the powdered fused alumina to the bauxite.

In general, the novel barrel finishing media of the present invention can be formed by a process which includes the steps: comminuting bauxite into microcrystalline particles; forming .a mixture of the comminuted bauxite and finely divided fused alumina; forming the mixture into shapes or bodies; and firing the bodies to sinter them. Media formed in this manner, when used in a barrel finishing operation, has a rate of cut which increases with increasing powdered fused alumina content and is in all cases greater than that of sintered bauxite media containing no fused alumina. Also, the media life of media according to this invention may be increased by increasing the temperature at which the media is fired.

More specifically, the novel barrel finishing media of the present invention may be formed in the following manner:

Bauxite, in its natural state, contains hydrated alumina, and minor amounts of silica, titania, iron oxide, and other impurities. For the purposes of the present invention it is preferred to use bauxite which has been calcined, although uncalcined bauxite may also be used. During calcination most of the water is removed from the bauxite.

For example, a typical analysis of a calcined Surinam bauxite is:

Percent A1 85 .67 sio 3.44 Fe O 5.85 TiO 3.73 CaO Trace MgO 0. 10 Ignition loss 1.21

While Surinam bauxite is preferred, natural bauxites from other sources as well as synthetic bauxites may, of course, be used in carrying out the invention.

The calcined bauxite is comminuted to an average particle size of not more than about 5 microns. Preferably, a major proportion of the microcrystalline particles of comminuted bauxite is less than microns is size, with not more than 5 percent larger than microns and with the average particle size being between about 2.5 microns and 5 microns. The bauxite may be reduced to such fine particle size in a number of ways. One way is to crush the bauxite to 40 mesh in a roll crusher and then wet grind it in a ball mill, utilizing steel, flint, or alumina grinding bodies until the desired particle size is obtained. Alternatively, the bauxite may be comminuted in a jet mill using air or steam. If the bauxite is comminuted by a wet grinding operation, the resulting microcrystalline particles of bauxite may be dried in any convenient manner, such as in an oven.

A mixture is then formed comprising the microcrystalline comminuted bauxite and finely divided fused alumina. The amount of fused alumina in the mixture may vary from about 10 percent to about 80 percent of the mixture, with the preferred amount of the alumina additive being within the range of from about 20 percent to about 60 percent. Increasing the amount of the fused alumina fines in the mixture, as noted above, causes an increase in the rate of cut of sintered media formed from the mixture. However, the rate of media loss is increased somewhat by the addition of increasing amounts of the fused alumina. Therefore both of these factors must be considered in producing barrel finishing media according to the present invention. Thus, when stock removal is of prime importance and media life is a secondary consideration, the mixture may comprise amounts up to 80 percent of the fused alumina fines to provide media having an extremely high rate of cut. In operations where media life is the chief concern but a good rate of cut is is still desired it is preferably to include lesser amounts of the fused alumina powder in the mix. Thus, using the same sintering conditions, media containing 10 percent of powdered fused alumina with 90 percent bauxite powder will have a lower media loss and a lower rate of out than media containing larger amounts of the fused alumina fines. In any event, however, sintered bauxite media containing fused alumina as an additive will have a higher rate of cut than bauxite media containing no fused alumina.

In accordance with the present invention, the powdered fused alumina should have a particle size of about 100 mesh and finer (US. Standard Sieve Series), with the preferred particle size being 240 mesh and finer. A small amount of a suitable organic temporary binder, such, for example, as starch, cellulose derivatives, waxes, and the like or an inorganic temporary binder such as bentonite may be added to the mix. Such temporary binders are well known and other suitable ones may be used. In general the amount of temporary binder used is of the order of 2 percent8 percent, the amount varying with the nature of the mix and the binder.

Water is then added to the dry mixture to provide a plastic or workable mass having a consistency suitable for the media forming step. While the amount of water to be added will vary, depending on the type of forming operation used, type of bauxite, humidity, etc. generally the amount will be between about 22 to 50 liters per kg. of the dry mixture.

After the dry ingredients and the water have been thoroughly mixed, the plastic mass is formed into shapes or bodies which are to constitute the barrel finishing media. Although other methods of shaping the mass into geometrically shaped media may be employed, such as, for example, pressing, molding, slip casting and the like, it is preferred to extrude a mass of proper consistency through a die to form a rod or column of the desired cross sectional shape and then cut the extruded rod or column into bodies of the desired length by suitable means such as moving wires or blades. If extrusion is used it is preferred to add to the dry ingredients, before mixing with water, a small amount of a conventional extrusion plasticizer such as Tennessee ball clay. This may be used in amounts within the range from about 1 percent to 5 percent.

The plastic mass can be extruded in a rod or column having any desired cross sectional shape including round and polygonal, e.g triangular or square. For most purposes media with triangular cross sections are preferable, such shapes usually showing higher rates of out.

Barrel finishing media of the present invention may be of various sizes. The cross sectional dimensions as well as the length may be varied as desired. If triangular shaped bodies are formed, the lengths of the sides of the triangle preferably are from about 0.3 cm. up to about 6.0 cm. and the thickness or length of the bodies preferably is between about 0.3 cm. and about 6.0 cm. Obviously, for some uses even larger or smaller bodies may be required.

If an organic temporary binder is used in forming the media bodies, the shaped bodies are preferably first heated in an oxidizing atmosphere at a temperature sufficient to burn out the temporary binder. This temperature should not exceed about 1100 C. and is preferably between about 750 and 1000 C. The time required to burn out the temporary binder will depend upon the particular binder used, the specific temperature within the range stated above that is used, and the method of kiln loading employed for this purpose, If only an inorganic binder such as bentonite has been used, the oxidizing step is eliminated.

The shaped bodies are then heated to a higher temperature in order to sinter them. Although a neutral or reducing atmosphere may be used, an oxidizing atmosphere is preferred since this will prevent or minimize reduction of the oxide impurities in the bauxite with consequent production of glass that may weaken the bond between particles or cause bloating. Excellent results have been obtained by heating the shaped bodies in saggers in a gas fired kiln but other known apparatus and equipment may be employed. In a gas fired kiln suitable oxidizing atmospheres may be produced by supplying to the kiln up to about 20 percent of air in excess of the amount necessary for complete combustion of the gas.

The time and temperature employed in the sintering step should be carefully controlled. If the sintering temperature is not sufficiently high or the time of sintering is not sufiiciently long, the resulting product will not have sufiicient strength. On the other hand, if the temperature is too high, sintering together of the individual bodies occurs, making it necessary to break them apart. Suitable sintering temperatures are in the range between about 1400 C. and 1750 C. While sintering time may vary according to the particular temperature and atmosphere employed and with the particle size and composition of the mix used, it should be between A hour and 6 hours at maximum temperature and is preferably between about /2 and 2 hours at 1500.

After sintering, the media bodies are allowed to cool at any rate consistent with high temperature kiln practices. The media may then, if desired, be subjected to a conditioning cycle to remove minor edge faults and residue left on the surface of the media by the cutting process. One method by which this conditioning may be accomplished is by tumbling the media with water for about to 30 minutes in a rotating barrel.

While the bulk density of the media decreases with auger-type ex-truder from which the material was extruded through a die having a triangular opening. The extruded rod was cut to the desired length by a wire cutter.

The shaped bodies were loaded into shallow saggers, placed in a kiln fired with natural gas, and sintered at a increasing amounts of the powdered fused alumina, it is 5 temperature of about 1490 C. for about three hours with generally within the range from about 1600 kg./cu. meter a slight excess of air. The resulting fired bodies were trito about 2080 kg./ cu. meter for triangularly shaped media angular plates approximately 2.2 cm. on each triangular approximately 2.2 cm. on each triangular side and approxside and 1.25 cm. thick. The specific gravity of sintered imately 1.25 cm. thick. Also, the bulk density of the 10 bodles was about 3.62.

media increases somewhat with increasing sintering tem- Example II g a Thedspeclfic ghravflty of s-lntered bodleg W1-11 A series of mixes was prepared in order to demonstrate g t a z fig f gg g i g g 13 53 32:3 3; 1 (1) the improved results obtained by using barrel fimshlng Barrel finishing media produced according to the 1f media according to the present invention as compared to method described above is a dense product However 0 sintered bauxite tumbling media Prepared by the Same rocess but co mm s of 1s 0..

the amount of fused alumma present and the smtermg alumina in the media In 0rd b f temperature employeid it is i describe cryst'ifl comparison a standard rocedlir e wa s tz llofveil f i inali structure of the media of this lnventlon except 1n gener1c g barrel finishing medi: from each of flhe mixes Specified terms Generally w the medla 1s fired at low Smtenng below Thus in each case media was formed accordin to temperatures, that 1s temperatures of from about 1400 C. th 6 ed r d S ribed EX 1 I g to about 1500 0, even for several hours, the sintered GP G u e e c m amp 6 media comprises microcrystalline bauxite having finely Parts divided fused alumina particles uniformly dispersed Mix No Fused therein. In other words, when such low sintering tempera- Bauxite Alumina tures are used, the fused alumina fines can at least partially Powder be distinguished under a microscope from the microcrys- 100 0 talline bauxite in the fired bodies. However, when the g8 g8 bodies are sintered at higher temperatures, that is, tem- 70 30 peratures of from about 1550 C. to about 1750 C., even, g8 $8 in some instances, for only about an hour, microscopic 30 70 exafniItatiml of the bodies reveals a tendenpy for recrys' The other mix components ie bentonite ball clay and tallization and/or crystal growth of the mlcrocrystalline water were used in percenta'e's of 3 2 a bauxite to produce a substantially granoblastic crystalline 35 fively with respect to the abrgasive i onent structure, i.e. having a texture in which the crystals are nentsin an of the mixes p p irregular and angular and resemble a mosaic. The extent ch 1111): was formed into bodles and fired accordm of such crystail grPWth or recrystanlzatpn ls dependent to the procedure of Example I to provide triangular plate? not only on sintering temperature and time but also on a roximatel 2 cm on each tria 1 d 125 the amount of fused alumina fines in the media as well pp y ngu at 81 e an cm. thick. The resulting media 1n each case was evaluated The Y speclfic examp lnusirate more deaf-1y to determine stock removal characteristics In the unithe manner m Whlch the P i mientlon can be can-led form test procedure followed for all the media tested althfiugh a prisent g Is not to be construed barrel finishing operations were conducted with the ap as eing imite to t e speci c proportions and/or condi- 4 tions Set forthin the eXamPles- 33315 and materlals and under the conditions speclfied Example I Machine: Pangborn-Carborundum Vibrator (CVA-3), Previously calcined Surinam bauxite having approXihagmg g gffif i f afpmxlmately (L085 meter mately the composition described hereinbefore was milled 5O g i b for a suificient length of time to produce a microcrystal- .R m non'a raslve pOhh1I.1g ald line powder having an average particle size of about 2.5 compnsmg a mlxmre 180p Top anol. and a noli'lomc surmicrons. A mixture having the following composition was 2 53: 2; g lz i gg i g i g 1 22 2 2 2: dlssolved m then re ared. I

p p Parts W Water: 1.9 hters at beginning of test and 0.47 liter after two hour rinse. Sunnam bauxite (average 2.5 m1c1'ons) 90 every Fused alumina powder (240 mesh and finer) 10 Metal specimen. S.A.E. No. 1020 cold rolled steel Bentonite (200 mesh and finer) 3 g. g' 'a 2 Tennessee ban clay (325 mesh and finer) u 2 ime. ixteen ours tota. edra rinsed every two hours Water 35 and compound and water added.

In conductlng the tests the vibrating machine was filled The dry mater als were charged to a mlxer and blended with media to approximately 95 percent of capacity and for about five minutes. The water was then slowly added the compound, water, and specimens were added. Metal to the dry m xture to provide an extrudable mass. The loss of the specimens was determined every two hours by total lTllXlIlg time was about 3 0 m1nutes The material was F drying and weighing them. The results of the test are then discharged from the mixer and introduced into an shown in Table I.

TABLE 1 Mix Ahllligeda DBusllg Metal Removed by Media (percent, cumulative) Rate in en 1 y, No. Powder, kg.lcu. 2hrs. hrs. 6l1rs. 8hrs. 10 hrs. 12 hrs. 14 hrs. 16 hrs 03 t (percent) meter 0 2, 307 0. s4 1. 05 1. 1s 1. 32 1. 46 1. 51 1. 10 2, 034 0. 85 1.13 1. 45 1. 71 1. 95 2. 1s 2. 22 20 1, 986 0.82 1.13 1. 42 1. 70 1. 97 2. 1s 2. 41 2. 53 .154 30 1, 905 1. 05 1. 2. 0s 2. 56 3.01 3. as 3.82 4. 19 260 40 1, 905 1. 23 1. 94 2.60 3. 24 3.83 4. 41 4. 9s 5. 51 340 50 1,890 1. 12 1.85 2. 75 3. 42 4. 17 4. s0 5. 52 s. 15 .385 ,s10 1. 25 2.10 2. 94 3. 74 4. 54 5. 20 5. 93 6. 67 .416

Average percent metal removed per hour in 16 hour period.

These test results are further illustrated in FIGURES 1 and 2. FIGURE 1 is a graph showing the increase in metal removal with increasing fused alumina content of the media, the curves being numbered from 1 to 7 inclusive, and depicting, respectively, the cumulative percent metal removed by media formed from the correspondingly numbered mixes of Example II. Table I and FIGURE 1 clearly show that all of the media containing the fused alumina fines were superior in metal removal to bauxite media, prepared and tested under the same conditions, which contained no fused alumina fines. FIGURE 2 is a graph, based on the test results of Example II, which shows how the rate of cut of sintered bauxite barrel finishing media containing finely divided fused alumina increases with increasing amounts of the fused alumina powder.

From the results of these tests, as shown in Table I and illustrated in FIGURES 1 and 2, it is evident that sintered barrel finishing media according to the present invention is greatly superior in stock removal and rate of cut to sintered bauxite media without fused alumina fines.

As indicated above, while the rate of cut of the sintered bauxite-fused alumina media of this invention increases rapidly with increasing amounts of fused alumina fines therein, the media loss in barrel finishing operations also increases, other conditions being the same, with an increase in powdered fused alumina in the media. By controlling the amount of fused alumina fines and the sintering it is possible to provide media having a desired balance between high rate of cut and high media loss. This has not been possible with media available heretofore such, for example, as the fused alumina-vitrified bond media. In such vitrified media, the rate of cut of the media is a function of abrasive content, and media life is dependent on the strength of the abrasive-bond composition. Lowering the abrasive content in such media has the effect of increasing media life but at the same time decreasing cutting rate.

In order to compare the rate of cut and media loss of media according to the present invention with media of the fused alumina-vitrified bond type the following test was made.

Example III Barrel finishing operations as described above in Example II were carried out with batches of the seven sintered bauxite media resulting from the sintering of bodies formed from the mixes set forth in said example. A commercially available media containing 30 percent fused alumina grain and 70 percent vitrified ceramic bond, which is presently accepted in the industry as the best media available for application in vibratory machines, was also tested using the same procedure. As illustrated in FIG- URE 3, the results of the comparative tests showed:

The rate of cut (Curve A) of the fused alumina-vitrified bond media was approximately the same as the rate of cut represented on Curve B as that of media according to the present invention containing 20 percent finely divided fused alumina. 0n the other hand the media loss of the fused alumina-vitrified bond media (Curve C) was approximately the same as that of media according to the present invention containing 50 percent finely divided fused alumina as shown on Curve D. Thus through the range of compositions which include from about 20 percent to about 50 percent fused alumina fines in a sintered bauxite media, media according to the present invention has a higher rate of cut and a lower media loss than the conventional fused alumina-vitrified bonded media.

In the tests described above the media loss was determined by weighing the media as charged into the vibratory finishing machine and weighing again, after drying, upon completion of the tests, the difference in weight representing media loss.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses or adaptations of the invention following the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth or as fall within the scope of the appended claims.

Percentages, parts and proportions as set forth herein are by weight unless it is otherwise specified.

I claim:

1. A barrel finishing media which consists of preformed and sintered bodies consisting essentially of bauxite and fused alumina particles dispersed substantially uniformly therethrough, said fused alumina comprising from about 10 percent to about 80 percent.

2. A barrel finishing media as defined in claim 1 in which the fused alumina comprises from about 20 percent to about 60 percent of said bodies.

3. A barrel finishing media as defined in claim 1 in which said bodies have a substantially granoblastic crystalline structure.

4. A barrel finishing media as defined in claim 2 in which said bodies have a substantially granoblastic crystalline structure.

5. A barrel finishing media as defined in claim 1 having a specific gravity in the range from about 3.0 to about 3.7.

References Cited UNITED STATES PATENTS DONALD I ARNOLD, Primary Examiner.

US. Cl. X.R.

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