US3592618A - Abrasive article having a metal filler and an active filler - Google Patents

Abstract

THE INVENTION COVERS AN ABRASIVE ARTICLE WHICH IS CONSTRUCTED WITH TWO OR MORE FILLED CONSTITUENTS THAT CO-REACT TO FORM A GRINDING AID. GENERALLY, THE FILLERS COMPRISE A METAL AND A METL SALT WHICH UPON THE APLLICATION OF HEAT REACT TO IMPROVE THE GRINDING EFFICIECY WHEN COMPARED WITH ABRASIVE ARTICLES CONTAINING EITHER OF THE TWO CONSITUTENTS THAT MAKE UP THE NOVEL FILLER COMBINATION. ONE OF THE PREFERRED FILLER CONSTITUENTS IS A REINFORCING SUBSTANCE; THE OTHER IS AN ACTIVE GRINDING AID.

Description

United States Patent 3,592,618 ABRASIVE ARTICLE HAVING A METAL FILLER AND AN ACTIVE FILLER Gardner E. Alden, Fayville, Mass, assignor to Avco Corporation, Cincinnati, Ohio No. Drawing. Continuation-impart of abandoned application Ser. No. 523,523, Jan. 28, 1966. This application Mar. 10, 1969, Ser. No. 805,799

Int. Cl. C08g 51/12; 324d 3/02 US. Cl. 51-298 7 Claims ABSTRACT OF THE DISCLOSURE This invention, which is a continuation-in-part of application S.N. 523,523 rfiled Jan. 28, 1966, now abandoned relates to abrasive articles, such as grinding wheels, and more particularly to grinding wheels containing an improved filler combination.

It is an object of this invention to provide grinding wheels with improved strength characteristics which may be operated at greater speeds than normal and at heavier grinding pressures,

It is another object of this invention to provide wheels with a high safety factor in operation.

It is another object of this invention to provide grinding wheels which give added value to the consumer in terms of overall grinding cost.

A further object of the invention is to provide a grinding wheel having a combination of exceptional strength and good grinding efficiency.

It is still another object of the invention to provide an improved filler composition for an abrasive article comprising at least two materials that react synergistically during a grinding procedure to provide an active grinding aid. One of the materials imports added strength to the abrasive article.

These and other objects will become obvious fro-m the following description.

In recent years the steel and iron working industries have been striving for increased production at reduced cost. in response to their demands the grinding machine manufacturers are working to develop machines which will operate at greater speeds and at greater pressures. The grinding wheel manufacturers, in turn, are being called upon to provide wheels which are stronger and safer to operate at these high speeds and pressures, and still maintain an attractive cost picture for the ultimate consumer.

One method commonly used to alter the characteristics of a grinding wheel is by the addition of fillers to the bond of the wheel. Fillers are added for many reasons. There are inert fillers which reinforce the wheel but do not contribute to the grinding performance. There are so-called active fillers which break down during the grinding process and enhance cutting action. Fillers are sometimes added to act as lubricants. Low-cost fillers may be added to decrease the cost of the wheel when premium-priced ingredients are present. It is often difiicult to select a filler or combination of fillers which will contribute beneficially to more than one property of a grinding wheel. For example, addition of one filler may contribute high centrifugal and impact strength to a grinding wheel, but the metal removal rate drops drastically. Conversely, a certain filler may produce a fast, cool cutting wheel, but a wheel that is inadequate in strength. Various high-priced fillers may produce effective wheels, but are economically out of reach of the consumer. The novel combination of fillers according to this invention provides organic bonded grinding wheels that have good grinding characteristics, extremely high tensile and impact strength, and are economical to use.

In accordance with the invention in an abrasive article having abrasive grains held together by a bond, a filler for the bond has at least two ingredients which upon the application of heat co-react to produce a grinding aid.

The novel features that are considered characteristic of the invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment.

It has long been known that chemical compounds which contain sulphur or halogens such as chlorine and fluorine, among others, are advantageous as fillers in grinding wheels. Many of these compounds break down during grinding with the evolution of volatile grinding aids at the point of grinding contact. These fillers are known as active fillers or grinding aids. It has also been known that such decomposing fillers tend to weaken the bond of the grinding wheel. This is not an entirely detrimental effect because the bond must break down to release the dulled and worn abrasive particles. However, the optimum amount of decomposing filler must be carefully calculated to provide a bond which will break down fast enough to expose fresh abrasive particles when needed, and yet not so fast that it will release the abrasive grits prematurely.

Another problem to be faced in the formulation of grinding wheels is the provision of a Wheel with adequate strength against centrifugal force and impact. Various types of strengthening elements such as glass, asbestos and mineral fibers are often used. Such strengthening mediums are compatible with organic bonding materials, but are completely inert and often impede grinding action.

Where metal particles have been used in quantities sufiicient to strengthen grinding wheels it has been found that the cutting action of the wheels is greatly impaired. It appears that these particles prevent the bond from being broken down to release dulled and worn abrasive particles. It is for this reason that metal particles do not find general use as reinforcing mediums for grinding wheels.

Where, however, an active filler and a strengthening metal medium are judicially selected to cO-react as taught herein, the metal particle is reacted at the precise moment when its holding strength quality is no longer desired.

At the same time, as taught herein, the metal reacts with the active filler to release considerably more grinding aids in the form of decomposition products of the active filler. The overall effect is an extremely strong grinding wheel with improved grinding performance due to increased amounts of grinding aids for a given quantity of is finely powdered aluminum and finely ground iron pyrites.

The chemical reaction which takes place during the grinding process is as follows:

It is theorized that under the heat of grinding, the aluminum powder and the iron sulfide react at the interface of the work causing the above continuous reaction. The aluminum, which is a reducing agent, reduces the iron sulfide with the formation of aluminum oxide and the evolution of sulfur dioxide. The sulfur dioxide evolved acts as a grinding aid, as is well known. As the reaction continuously proceeds to completion with the formation of the stable, inert ingredients of iron and aluminum oxide, fresh, unreacted aluminum particles and iron sulfide are constantly exposed at the grinding face to continue the reaction process.

The reaction described above is exothermic. The heat given off contributes to more efficient decomposition of the active filler, and at the same time provides controlled thermal breakdown of the bond.

It is not intended to limit this invention to the use of aluminum and iron sulfide; other metallic powders, such as zinc, magnesium, cadmium, or copper may be used, as well as other salts; for example, lead, tin, or cadmium, halides, and sulphide.

A stoichiometric quantity of iron sulfide may be used for the theoretical conversion of all the aluminum powder to aluminum oxide, although varying amounts may, and have been used effectively, including an excess of each ingredient. Formulations containing an excess of aluminum powder seem to be preferred.

For test purposes, hot pressed snagging wheels were made with the new filler combination. In the example below, there is a description of the manufacture of a x 2 /2 x 8-inch snagging wheel in accordance with the present invention. It is to be understood that the manufacturing procedure set forth is purely by way of example and that any other manufacturing process may be used.

Furfural, as required as a wetting agent and plasticizer.

The abrasive may be any desired heavy duty snagging abrasive, either fused or sintered, or any abrasive combination suitable for the type and size wheel being made.

Other resins may be used than the example given; for example, Bakelite BRP 5417, or a modified resin such as Monsanto 795, or a combination of two or more resins.

The aluminum powder used was purchased from Bel mont Smelting and Refining Works, and is size designated 100-325 Aluminum Powder. The particle size range is as follows:

Percent 100 +200 mesh 200 +325 mesh 20 -325 mesh 50 The iron pyrites was obtained from Frank Samuel Co. This material is purchased in two sizes 80 mesh, and the second 325 mesh.

It has been found that it is often desirable to use a 50/50 blend of particle sizes of the ground pyrites. 1 prefer to use as fine a particle size as possible, but it was discovered that if the entire amount used is of the fine grind 325 mesh), the filler reaction may proceed too rapidly during the grinding process and result in excessive wear. However, the blend of the two particle sizes may be varied as desired, depending upon the type and size of the wheels being made.

The manufacturing procedure for the wheel above may be outlined as follows:

The abrasive was weighed and furfural added in a calculated amount. Mixing was done until the abrasive was uniformly wetted. The resin was weighed separately and blended with the fillers until a uniform, homogeneous blend was produced. The blended bond was then added to the wetted abrasive, and the ingredients carefully mixed until uniform. The wheel mix was then placed in a mold and hot pressed in the mold at a temperature of approximately 320 F. for about an hour. The wheel was then removed from the mold and cured in an oven at a temperature of approximately 350 F. for approximately 12 hours. The wheel was finished by standard methods.

As mentioned above, other methods may be used to manufacture wheels using this unique combination of fillers. Wheels may be made by cold press techniques, or other hot pressing methods may be used. Other resins may be desirable: for example, aniline formaldehyde, urea formaldehyde, butyral modified phenol formaldehyde resins, to mention a few.

The filler materials are, in relation to the bond matrix materials, such as resin, metal, vitreous material, etc., inert. In practice abrasive articles use a variety of bonding matrices according to application. The most widely used types are resin, metal, vitreous, rubber and shellac.

In the resin category the phenolics, epoxides, amides, are used by industry in commercial and industrial products.

A point to note is that no reaction takes place between the bond matrix material and the bond filler composition. Therefore any and all of the bond matrix materials specified or any other non-reactive system will function satisfactorily.

The wheel manufactured above was run in a two-part grinding test. The first portion of the test was run at high speed (15,500 s.f.p.m.) but at normal grinding pressure of approximately 600 pounds head pressure, grinding AISI Type 410 stainless steel billets. After the first timed grinding period, grinding was stopped and the amount of metal removed and amount of wheel wear were measured. Then, grinding was resumed with the grinding speed continued at 15,500 s.f.p.m. but with the head pressure increased to approximately 850 pounds. After the completion of a second timed grinding interval, grinding was stopped and measurements were again taken of the amount of metal removed and the amount of wheel wear. Grinding efiiiciency results were then calculated.

There are various methods of determining the efiiciency of a grinding wheel in terms of productive work as opposed to actual dollars spent. For some types of wheels a simple calculation of the number of cuts made during the useful life of the wheel is sufficient or the number of hours life per wheel. However, in heavy duty snagging wheels such as those tested above, an empirical factor is widely used throughout the industry. This figure has been derived as being the most representative of true grinding efiiciency in the terms of productive work accomplished, as measured by dollers spent by the consumer. This includes the factors of wheel cost, labor and overhead, metal removed, and wheel life. This empirical factor is designated as the Q factor and is calculated by the formula Q M W, where M represents the pounds of metal removed and W is the volume of wheel loss per hour of grinding. The ratio M/ W is sometimes used as an indication of cutting efficiency of a snagging wheel, but is not considered to be as true a representation in terms of ultimate value to the customer.

TABLE 1.GRINDING EFFICIENCY AT DIFFERENT GRINDING PRESSURES Head Wheel speed, pressure, Q s.f.p.m. lbs. M/W (M /W) The outstanding increase in the Q factor at the increased pressure shows the ability of these wheels to perform under extreme heavy duty conditions, with only a small decrease in cutting efliciency as calculated by M/ W. The wheel cut smoothly in both portions of the test.

Further series of wheels were made up in order to evaluate different proportions of aluminum and ion pyrites in the bond. Test results for these wheels are shown in Table 2 below. For comparison a control wheel was also run. The control wheel was made by a formulation designed for heavy duty operations and contained the previously best known filler combination for a high strength, heavy duty wheel. The control wheel contained an inert nonmetallic filler plus an active metal salt. All of the wheels used in the test were made in the same specification, with identical manufacturing methods. The only difference in the formulations was that wheels 1, 2 and 3 were made with varying proportions of the invention combination of fillers in the bond. In all cases the total amount of fillers composed approximately 36% by volume of the bond.

TABLE II.Q VALUE FOR WHEELS WITH VARYING PROPORTIONS OF FILLERS It can be seen from this table that the wheels made with the formulation according to this invention in each case outperformed the control wheel made with the previous best heavy duty filler combination. The operators comments were that the invention wheels ground freely, the wheel face appeared open after grinding and free from cracks. There was no heat welding of particles.

In order to evaluate the wheels for strength, wheels for speed test were selected from lots 2, '3, and control of those wheels run in the grinding tests described in Table II.

According to the Safety Code of the American Standards Association, snagging wheels of this type in a high strength bond are marked with a standard maximum operating speed of 9,500 s.f.p.m. However, over the past few years some wheels have been approved for operation at special speeds providing the wheel manufacturer and the grinding machine manufacturer take certain precautions. These special speeds may be up to 16,000 s.f.p.m., with 12,500 s.f.p.m. being the most often employed. It is required that each wheel be speed tested without damage at 1.5 times the maximum operating speed, or 14,250 s.f.p.m. for operation at 9,500 s.f.pm., and 18,750 and 24,000 s.f.p.m., respectively, for the higher speeds.

The wheels were first tested at 24,000 s.f.p.m., as required for wheels designed to operate up to 16,000 s.f.p.m. All wheels withstood this test speed and were carefully examined for incipient cracks. None were found. Then, one wheel was selected from each lot for speed test to destruction. These results are tabulated. in Table III.

TABLE III Lot number Breaking speed, s.f.p.m. 2 32,000 3 31,000 Control 27,000

Other wheels have been speed tested without breakage at speeds in excess of 33,000 s.f.p.m., the maximum capability of the test equipment.

This new combination of fillers need not be limited to snagging wheels. In order to test its effectiveness in another type of wheels, some 16-inch cut-off wheels were made. These were made by conventional manufacturing procedures of reinforced, hot pressed, cutting-off wheels. The formulation contained aluminum powder and iron pyrites in the bond in a l/ 1 volume ratio, with the total filler amount to about 35 volume percent of the bond.

In evaluating cutting-off wheels for strength, three separate tests are used. These are centrifugal, fiexural or push-out, and fatigue. All three tests are used because, in addition to the stresses imposed by rotation of the wheels, a cutting-off wheel may become lodged or jammed in the cut and be subjected to sidewise bending or flexing stresses. Therefore, the resistance of a cuttingoff wheel to excess side pressure or impact is equal to or more important than its centrifugal strength.

In the flexural or push-out test, the wheels are placed over a steel ring, and two steel flanges are bolted one on either side of the wheel, through the center hole. For a 16-inch diameter cut-off wheel 14 /z-inch ring is used and 8-inch diameter flanges. The wheel assembly is then mounted on a sensing element in a testing machine and pressure is applied at the center of the wheel with the load being applied at the rate of /2-inch per minute. The pressure in pounds is measured until the wheel is deflected to the point of failure.

For the fatigue test, the wheel is mounted on an arbor in a horizontal plane and rotated at 3800 r.p.m. (the maximum operating speed). At the same time, a 10-pound weight is applied to the periphery of the wheel and rotation continued for 3 minutes. At the end of the first 3 minute period five pounds are added, and the test is continued in this manner with 5 pounds load being added every 3 minutes until wheel failure. These results are expressed in the following manner: x where x=minutes of test to failure, and y =total pounds applied.

The results of these three tests are shown in Table IV comparing the invention wheels with two types of standard reinforced cutting-off wheels.

It will be seen from this table that wheels made with the formulation according to the invention are exceptionally strong in all three tests. The maximum recommended operating speed for this size wheel is 16,000 s.f.p.m. and these wheels were speed tested at 2% times this speed before failure. They are almost twice as strong in the flexural test as the strongest standard wheel and the fatigue tests surpass both other wheels by a considerable margin.

During the test program, wheels were made with this filler combination in varying percentages in the bond. Each combination showed strength advantages over wheels made with previously known and used fillers or filler combinations, and each ground satisfactorily. One of the preferred combinations I have found is a bond formulation composed of 60% by volume phenolic resin, 18% by volume each of iron pyrites and aluminum powder, and 4% lime. The lime is conventionally used to absorb the water which is formed during the cure of the resin, and to prevent swelling or bloating of the wheel.

The various features and advantages of the invention are thought to be clear from the foregoing description. Various other features and advantages not specifically enumerated will undoubtedly occur to those versed in the art, as likewise will many variations and modifications of the preferred embodiment illustrated, all of which may be achieved without departing from the spirit and scope of the invention as defined by the following claims.

I claim:

1. An abrasive article having a synthetic resin bonded abrasive grains, a filler for said bond consisting essentially of a metal selected from the group consisting of aluminum, zinc, magnesium, cadmium and copper; and a salt selected from the group consisting of halides or sulphides of iron, lead, tin and cadmium.

2. An abrasive article as described in claim 1 wherein the filler combination comprises the metal powder in the amount of 535% by volume of the bond and the metallic salt containing the halogen or sulphur in the amount of 530% by volume of the bond.

3. An abrasive article as described in claim 2 wherein the metallic powder is aluminum and said metallic salt is iron pyrites.

4. An abrasive article having synthetic resin bonded abrasive grains, a filler combination for said bond comprising at least a reinforcing material and an active filler which upon the application of heat co-react exothermically to produce a grinding aid composition, the reinforcing material consists essentially of a metal selected from the group consisting of aluminum, zinc, magnesium, cadmium and copper and said active filler is selected from the of the bond.

7. An abrasive article as described in claim 6 wherein the active filler is a blend of coarse and fine grit.

References Cited UNITED STATES PATENTS 524,085 8/1894 Buecher 51307 2,243,105 5/1941 Kuzmick 51-298 2,308,981 1/1943 Kistler 51307 2,729,553 1/1956 Price 5l298 3,113,006 12/1963 Kibbey 51298 3,246,970 4/1966 Zimmerman 5l298 3,385,684 5/1968 Voter 51298 DONALD J. ARNOLD, Primary Examiner U.S. Cl. X.R. 5l305, 307

27 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 592, 618 Dated July 13, 1971 Inventor(s) Gardner l n It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 34, for "epoxides" read--epoxies--; Column 5, line 14, for "ion" read --iron--; line 55, for "at special speeds" providing" read-- at "special speeds" providing--; Column 6, line 8, for "of" read--for--; line 11 for "amount" read--amounting--; line 24, for "Wheel 14-1/2" read--wheel a 14-1 /2-- Signed and sealed this 5th day of September 1972.

(SEAL) At te s t:

EDWARD M .FLETCHER JR ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents