US2001911A - Abrasive articles - Google Patents

Description

c. E. wooDDELl. Er AL May 21, 1935..

ARAsIvE ARTICLES 2 Sheets-Sheet; l

Filed April 21, 1952 INVENTORS GHARL E. woonDnLL. CHARL s. NELSON BY RoY UNC-oud ATTORNEY May 2l, 1935 c. E. wooDDELL ET AL -2,001,911`

ABRASIVE ARTICLES Filed April 21, '1952 2 sheets-sheet 2 lNvENToRs CHARLES E. WOODDELL CHARLES s. NLLsoN -By ROY |.\NGQ\.N

' ATTORNEY Patented May 2l, 1935 UNITED STATES- rATsN'T ori-ics ABRASIVE ARTICLES vania Application April 21, 1932, semi Np. escasez- 411 claims.

This invention relates to the manufacture of abrasive articles and has for its object the provision of new and improved abrasive articles and methods of making the same.

5 There are two general types of abrading processes; one employing a rigidly bonded article, such as any of the well-known forms of abrasive wheel, and the other employing an abrasivearticle that is flexible, such as sheets, belts or disks lo made of abrasive-coated paper or cloth and composite articles such as set-up wheels. This invention is concerned with the production of improved abrasive articles suitable for carrying out processes ofthe latter type.

The abrading action of the well-known flexible abrasive articles made of abrasive-coated paper or cloth differs from that of the relatively inflexible abrasive wheels, in that the flexible artciles tend to follow and can be used to closely follow the contour of the work operated upon, whereas the relatively inflexible abrasive wheels tend to change the contour of the work and thus, in many cases, are unsuited for the finishing of irregularly shaped surfaces.

One form of flexible abrasive article heretofore known has been made by coating a sheet of such material as paper or cloth with adhesive material and then depositing onthe adhesive a layer of abrasive granules. Attempts to make these abra- :m sive articles with more than a single layer of abrasive grains have not been successful because of several reasons. One reason for the failure is the loss of flexibility with added layers of abrasive grain and -another reason is the impractivcability of the process of making multi-layer articles by alternately coating with adhesive and then with abrasive granules. A third and important objection to the heretofore known multilil layer abrasive articles has been the decrease in 40v the openness or porosity of the abrasive coating as succeeding layers were added.

Ou'r improved product comprises a somewhat flexible backing material to carry' the assembly as a Whole and numerous small portions of bonded abrasive material carried by the backingmaterial and united thereto by means of a layer of a flex-- ible and resilient intermediate material, the bonded material being sufciently discontinuous to permit flexing of the article as a whole. Such a discontinuous facing may be defined as a fissural facing. 'I'he abrasive body in one form of such a structure consists of a plurality of abrasive blocks mounted on a flexible and yieldable backing and separated from each other on the sides by narrow fissures.A

In order that suitable dressing action may be secured to permit the Vabrasive to work continuously rather than filling and ceasing to cut properly, it is desirable that the abrasive be somewhat friable. rThis is a common characteristic of abrasive mixes which are well-known inthe art, however, and the method of producing such mixes is not a part of this invention. Specific examples'which will further aid in understanding this type of structure and its method of production are given below.

By practicing our invention We are enabled to make the abrasive coating of any desired thickess without losing the flexibility and yieldability or resilience so greatly needed in abrasive articles of this general type; and, moreover, our invention enables use not onlyv to secure the desired openness or porosity, but also to incorporate any abrasive characteristic or characteristics that are dsired. Our invention permits of this great latitude because it does not depend upon the alternate application of adhesiveand abrasive grains in the production of a thick coating of abrasive material. We provide yieldability by introducing a layer of yieldable material between the abrasive and the backing. This yieldable intermediate layer serves to join theI abrasive to the backing and may be made of such material or of such thickness that any desired degree of yieldability may be obtained.

Flexibility in articles made in accordance with our invention depends not only on the nature of the backing and adhesive, but also upon the fact that the abrasive facing is made of a number of small, separate sections of regular or irregular shape, instead of being continuous as in the ar- ,ticles known heretofore. This discontinuous or fissural facing of abrasive material' can be secured by various methods', such as providing a continuous facing and then fracturing the facing into small, separate areas, or attaching separately fashioned pieces of the desired area and shape in any desired pattern. In this latter method the bonding material used in forming the granular material into the desired shapes can be of any type, such as glue, shellac, synthetic resin, alkaline silicates or vitrified bonds, such as clays, glasses and so forth. Y

Sincethe yieldability of abrasive articles-made in accordance with our invention is not entirely dependent upon the characteristics of the backing material, we can utilize many different kinds of material for the backings. Among the `materials that are useful as backingis are paper, cloth of various kinds (including wire cloth), nbre.

thin sheet metal, wood and, in those articles that need not be iiexible, thick sheet metal or other forms of metal.

Our invention may be illustrated by the attached drawings, in which:

Figure 1 shows a top View of a section of an abrasive article embodying one modication of our invention;

Figure 2 shows a cross-sectional view through the line II-II of Figure l;

Figure 3 .shows a top view of a section of an abrasive article embodying another modification of our invention; l

Figure 4 shows a cross-sectional view through the line IV-IV of Figure 3;

Figures 5 and 6 show the faces of abrasive disks embodying modifications of our invention;

Figure 7 shows an end view of a wheel embodying one modication of our invention;

Figure 7A- shows in fragmentary section a modication of the wheel shown in Figure 7;

Figure 8 is a perspective view, partly broken away, of a polishing wheel with a wood center or drum;

Figure 9 is a fragmentary cross-sectional View taken parallel to the axis of rotation of one modification of the type of wheel shown in Figure 8;

Figure 10 is a similar cross-sectional View of another modification of the type of Wheel shown in Figure 8;

Figure 11 is a similar view of still another modication of the type shown in Figure 8.

In carrying out our invention as illustrated in Figures 1 and 2, we prepare the backing material l, which may be of paper, cloth or other suitable material, with a priming coat of adhesive (not shown in the drawings). This adhesive material may be a mixture of rubber and sulphur in suit? able proportions, which mixture is dispersed in benzol or other suitable material (for examplea dispersion of the yieldable material hereinafter exempliiied), or it may be a colloidal dispersion of an isomer of rubber of a lesser degree of unsaturation than rubber. rial is known to the trade as Vulcalock cement and is particularly serviceable where the backing material is metal. In applying any of these cementitious materials to metal backings it is desirable to remove al1 oils, greases, scale and other foreign material before applying the adhesive. Organic backing materials, such as paper vor cloth, require that the-adhesive be free from residual acids and other deleterious substances ior the best results.

When the' volatile portion of the priming coat of adhesive has been removed, a layer 2 of yieldable material is applied. One such yieldable material is soft rubber which we apply in the form, for example, of an unvulcanized sheet. The thickness of the sheet, as well as the composition, depends upon the degree oi' yieldability required. Sponge rubber provides a greater degree or yieldability than a similar composition without pores. One suitable substance for use as the yieldable material may be prepared by compounding:

the resin sold under the trade name Age-Rite" One form of this latter mate- The yieldable material 2, such as the sheeiI rubber mentioned above, is then coated with ladhesive, such as rubber and sulphur in benzol or Vulca10ck. After the benzol has been removed, the abrasive coating 3 is applied and the assembled article is cured or vulcanized.

In the modification shown in Figures 1 and 2, the abrasive facing is applied in strip or sheet form. For purposes of illustration, this strip or sheet of abrasive material may be described as a mixture of abrasive. grains and rubber bonding material, although as noted above, other kinds of bond can be employed, since yieldability is provided for by the intermediate layer of soft rubber, so that it is not necessary for the bond to be of yieldable character.

One form of abrasive facing comprises a milled sheet composed of Parts by weight Smoked sheet rubber 8 Sulfur 4 Mineral rubber 2 Abrasive grain 86 The mineral rubber referred to i's an asphaltic substance well-known in the rubber industry as a softener, and is sold under various trade names such as MRX Softener. The abrasive grain may be silicon carbide, fused alumina, etc., and is of the size best tted for the particular purpose for which the abrasive article is to be used. The llers are first thoroughly milled into the sheet rubber and the milled sheet is then cut to the desired size and shape.

As an example of other abrasive compositions suitable for our purpose, we cite the following mix: 1

100 parts (by weight) of abrasive grain 10 parts (by weight) of powdered phenolic condensation resin, such as Redmanol -41/2 parts (by weight) of flint The grain is rst moistened with a mixture of 40% cresol and 60% furfural, after which the Vother materials are mixed in. The mix is pressed into abrasive pieces of the desired form in steel molds, which, after being removed therefrom, are cured at 350 F. for 12 hours.

A typical ceramic abrasive mix for our purpose comprises 80% abrasive grain and 20% of a mixture of 40 parts slip clay, 50 parts bond clay (kaolin) 5 parts feldspar and 5 parts flint. vThe mixture of these materials is molded and vitried in the manner well-known in the 'art of abrasive manufacture. Y

The abrasive strips or pieces made from mixes as illustrated above are applied to the layer of yieldable material as described, and the assembly (comprising backing material rubber and bonded abrasive) is then subjected to heat and pressure to vulcanize the intermediate layer of rubber and the abrasive bond, if rubber has been used as the bond. This 'vulcanization may be carried out, for example, at 150 C. while theiarticle is under a suitable restraining pressure to prevent deformation or excessive porosity. Those skilled in the art will appreciate that various temperatures and pressures may be required and can be used depending upon lthe composition and nature of the iinished product desired.

Flexibility in the article made according to the fore or after the vulcanization treatment. The

Aabonen continuity of the abrasive facing can be interrupted at intervals by cutting it with a'sharp blade before the vulcanization step or with a thin abrasive wheel after vulcanization. Flexibility also can be secured after vulcanization by a process known 'as flexing. In flexing the article, theabrasive coating is broken at intervals without impairment of its adhesion to the intermediate layer; for instance, by drawing the article around bled in the same manner as described above,

and then, instead of applying the abrasive and its binder in sheet form, the separate pieces, such as 5 in Figure 4 of bonded abrasive, are positioned onthe intermediate yieldable material. The vulcanization is then carried out in the same manner as described above.

In Figures 3 and 4 the abrasive pieces 5 are shown as strips of trapezoidal cross-section extending across the entire width of the backing. It will beobvious to those skilled in the art that other shapes can be used and that a great number of patterns or configurations c an be produced by combining pieces of different sizes and shapes.

Figures 5 and 6 illustrate the adaptation of our invention to abrasive discs. In Figure 5 the abrasive segments 6 are illustrated as being greater i'n length than in width. Figure 6 shows the abrasive pieces in the form of buttons 'I which may be made of vitried ceramic abrasive or other suitable material. These abrasive disks can be made in the manner described above -or they can be made by using a mold toform all of the separate pieces 6 or 'l at one time. By this latter method a moldhaving tlie desired number of suitably shaped and arranged cavities is provided to receive the abrasive mix. We have found it desirable to have the corners and edges of the abrasive pieces illustrated in Figures 5 and 6 rounded where they come in contact with work, in order to avoid scratching.

'I'he cavities of the mold are filled with the desired abrasive mix, pressure is applied through a movable plunger and the plunger is removed from the mold. The intermediate yieldable material is then laid in the m'old with an adhesive rubbercoated surface in' contact with the exposedends of the abrasive pieces. The opposite, side of the sheet of yieldable material is then coated with adhesive rubber and, after the solvent has been removed, is covered with the backing material. Pressure and heat are then applied to vulcanize the intermediate rubber as well as the rubber of the abrasive bond.

Figures 7, 7A, 8, 9, l0 and l1 illustrate an application for which'we have found'our invention to be particularly welll-adapted; -namely, to the manufacture of ayieldable polishing wheel to,be used in place of the conventional set-up wheel, in which case the backing material comprises a cylinder or drum. t

The set-up wheel is one of the oldest forms of abrasive wheel and is used at the present time in practically as original form, even the ,manufacture of abrasive wheels has advanced to a point where they are regarded not as crude implements for removing excess material but as instruments for precision operations. because it possesses properties not found in the so-called bonded abrasive articlesand because it possesses features that make it more economical to use under some conditions than the more highly developed bonded abrasive articles. It is used, to the exclusion of all other types of bonded abrasive articles, in certain operations requiring the removal of the scratches produced by rough grinding or even finish grinding with the new common bonded abrasive articles, or, in other words, in the polishing industry. As-heretofore known, it has comprised a center of wood, laminated cloth or compressed felt with abrasive grains attached to the periphery by means of glue or other similar.

' adhesive.

The yieldability of the set-up wheel as it is first made is very limited in amount because the glue and abrasive coating o n` the wood, cloth or felt center are not in themselves very yieldable. This fact has led the user of set-up wheels `to produce yieldabiiity in the abrasive facing by the practice of pounding it with a blunt instrument to fracture the glue and cause the coating to become what is known as flexed. The glue coating, when broken into minute fragments, does not adhere tenaciously to the center material and soon permits the abrasive particles to become Vseparated from the center material when the wheel is placed in op- Itisstlllused eration. The yieldability attainable is so limited glue-bonded abrasive in that itdoes not extend i through to the body of the backing but'only to the soft rubber tie bond.v See, for example, the f ractures in' Fig. 2 through abrasive parts 3 extending only to the surface of the yieldable layer 2. Thus, We retain a. very strong'adhesion ofthe abrasive to the backing while increasing the yieldability and cutting action of the peripheral abrasive face. We have found that a wide rangeof yieldability is obtainable without sacrificing the highly desirable long life of the`less `yieldable wheel.

vIn the modification shown in Figure 7A, an abrasive strip 3' is molded with teeth 5' which are originally united at the base. This abrasive strip is'formed in a manner similar to that employed in making the original strip indicated in its later fractured form in Figures 1 and 2. The abrasive strip may be molded and cured as a flat strip or as on the rubber strip 2 by means of cement as hereinbefore described.

As an alternative method for use in making the type of wheel shown in Figure 7A, the strip 3',

Y either cured or uncured, is cemented 'in its unfractured form on the resilient strip 2 while the' latter is in an uncuredcondition. The cementv and rubber are then cured-in place on the superatedat temperatures of approximately 210 F.'

porting body, suitable pressure being 'applied to assure intimate contact of the component parts.

Fracturing of the unbroken portion of the abrasive between the teeth is brought about by the application of external force, for example, by means of a series of blows with a rounded instrument. The segments may also be separated by applying the wheel to an external obiect (such as a rotating cylinder) by suitably varying the pressure and tangential forces. Even without special fracturing operations, segmental fracture will occur through the abrasive at the points of least resistance if the abrasive article be applied to the work without previous fracture. This may re'-l quire several minutes of abrading action before thefracturing is complete.

Anotherv outstanding difference between the wheels manufactured by our process and those made of glue by the previously known methods is that wheels made according to our invention will withstand higher operating temperatures than are permissible with glue bonded wheels. Glue deteriorates greatly if it is subjected to a temperay ture materially above 150 F. and thus wheels containing a glue bond require extremely careful control of the grinding operation to insure the maintenance of low temperatures. Wheels made by our process, on the other hand, may be op- Without deleterious eects upon the binder. As a result of this, faster grinding and consequently greater production per manhour or machine hour may be obtained with wheels made by our process.

Wheels made according to our invention have a further advantage in connection with the heat generated during grinding in that a cooling medium; e. g., water, may be applied during the grinding operation. This is a decidedly new feature in set-up wheels and is of great advantage because it permits a faster rate of grinding with consequent greater production per man hour or machine hour. It is of considerable advantage also because certain classes of work are ruined if the temperature produced during grinding exceeds a certain value. By conducting the grinding operation in the presence of water the temperature is kept down and the work is better iinished in less time.

In making our improved polishing wheel we may use a center H of wood as illustrated in Figures 8, 9 and 10 or of a fabric (see Figures 7, '7Al and 11) of any degree of compactness according to the requirement of the operation for which it is made'.

Our wheel may be fabricated by attaching to the periphery of the center by means of an adhesive a yieldablematerial 2, as described in the making of disks or belts, and cementing to the yieldable material pieces of bonded abrasive E (Figure 7) or a layer of bonded abrasive 3 (Figures 8, 9, 10y and 11) A typical example' of a mix suitable for forming the bonded abrasive portion may be prepared by compounding Parts by v weight Smoked sheet rubber 8.0 Sulphur A 1.6 Calcined magnesia 0.8

` Abrasive grains 89.6

on a rubber mili and then calendering the mixture to the desired thickness. A strip of the acogen above mixture, cut to the desired width for attaching to the center, is coated on one side with the adhesive and applied to the yieldable material with the adhesive side of the abrasive strip in contact with the yieldable material. The ends of the abrasive strip are cut to provide a smooth joint.

After the abrasivestrip has been applied to the wheel it is subjected to pressure while the rubber is being cured. One way of securing this pressure is to apply a metal band that has been dusted 87 parts (by weight) of abrasive grain '8 parts (by Weight) of rubber in dispersed form 4 parts (by weight) of sulphur 1 part (by weight) of calcined magnesia.

The dispersed rubber being in'liquid form, perlmits the various materials to be mixed in a stirring or kneading machine instead of on the usual rolls used in rubber compounding.

The mixture thus made is then dried to a point where it becomes easily separated into `small particles of grain and bond by passing it through a screen. The moisture content at this stage is usually between and 10%. The screened mix yis then further dried to a moisture content of approximately 0.3% or less and is then disintegrated to providea mix in which the particles are discrete. This method of preparing the mix is fully disclosed and claimed in United States Patent No. 1,976,798.

The center is prepared in the manner described hereinabove with a coat of cement and a layer of the bond. 'I'he prepared center is then centrally located within a circular band of the desired diameter. The space between the center and the band is then filled with the abrasive and dispersed rubber mix described above. In iilling this space, the rubber is preferably introducedv at a temperature of approximately 180 F. to 200 F., when it will ow readily in a manner similar to dry, granular mixtures. The desired quantity of abrasive-dispersed rubber mix is forced into the space by any suitable means, as by tamping or pressing. Vulcanization of the rubber is accomplished in the manner described in the previous example.

This latter process is adaptable to mixes containing a resinous binder and abrasive grains. A

typical example of such a mixture is as follows:

1000 parts (by weight) of abrasive grains;

100 parts (by weight) of potentially reactivel phenolic condensation resin;

20 parts (by weight) of granular yieldable material, such as cork, wood flour or leather dust;

35 parts (by weight) of solvent or plasticizer, such as furfural, cresol or mixtures thereof.

The abrasive grains, bond and resilient particles may be mixed before the liquid is added, but we prefer to meisten the abrasive grains with the solvent or plastiche: mst and uien mix' in the bond and resilient material. The plasticizecly asmuch s' the curing of phenolic condensationv resins to produce the insoluble, infusible stage is a time-temperature function, the curing may be carried on Aat a temperature consistent with the "absence of deteriorating effects upon the wood, felt or canvas center. Articles of greatly diierent resiliencies may be produced by this method by altering the proportions of grain, bond and.

resilient granules. It is possible, at least for some purposes, to produce articles by this method` `that are sufficiently resilient without having been lfractured by blows from a blunt instrument.

Added resiliency may be produced, however, by

'striking theperiphery a number of blows with a blunt instrument without producing the destructive eifects resulting from such practice when glue is used as-the adhesive,

, Another type of mixture that is adaptable to this method of manufacture is one containing a thermo-plastic binder, such as glycerol-phthalic anhydride reaction product. Such a mixture may be made up and attached to the center inthe same manner as described above for the phenolic condensation resin mixture.

A modification that is particularly vadaptable to a wheel made on a wooden center, although it is useful also in those with felt or canvas cenl -ters, includes the use of a layer I3 of felt, canvas,

yrubber or other yieldable and resilient material between the center I l and the abrasive body 3 (Figure 10) In making wheels according to this modification the center is covered with the resilientl material to the desired thickness and the abrasive layer is formed according to one of the methods disclosed above.

As an alternative method of making our improved set-up wheel, a belt may be prepared as illustratedin the examples and used as the abrasive coating for a drum by merely forcing it over the drum, the step of cementing it thereto being omitted. Slipping of the belt on the drum may be prevented by expanding the drum by mechanically attaching the two or by other means. In some cases it is desirable to cement the fabric belt to a thin sheet metal belt, such as .005 to .010 inch steel, .in order to reduce the tendency of the fabric to expand when subjected to centrifugal forces.

While we have given specific details concerning vthe materials used, the steps and sequence of steps in carrying outour invention, and several modifications of our invention for illustrative purposes, we do not wish to be limited by these details but rather to define our invention by the appended claims.

. We claim: v

l. An abrasive article comprising a backing, a sheet of soft sponge rubber adherently cemented to said backing, and a` plurality of blocks of bonded abrasive adherently attached to the sheet of soft rubber.

2. An abrasivevwheel comprising a supporting drum, a metal band mounted o n the periphery of said drum, a sheet oi yieldable material having a fabric backing, said fabric being cemented to said metal band, and a series-of separate but closely spaced abrasive blocks cemented to said yieldable material, whereby the abrasive blocks are resiliently supported on' the drum and adapted to individually yield under the pressure of grinding. s w t 3. A ilexible -abrasive device comprising aflexible metal band, a layer of soit rubber cemented to the band, and bonded abrasive material cemented, yto the layer of soft rubber, .the abrasive material being divided into blocks and the layer of rubber being of suilicient thickness to permit the device to yield locally.

4. A iiexible abrasive device comprising a continuous flexible band, a layer of yieldable material cemented to the band, and bonded abrasive material cemented to the layer of yieldable material, the abrasive material being divided into blocks to form a iissural facing and the layer of yieldable material being of sufficient thickness to permit the abrasive material to yield locally.

. 5. An abrasive article comprising a supporting I drum and a flexible and yieldable abrasive device mounted on the periphery of drum, said device comprising Ya flexible metal band and a plurality `of blocks of bonded abrasive material attached to said band by a layer of resilientrubber of sufficient thickness to permit material movement of -said blocks under the pressures applied in grinding.` Y

6. An abrasive wheel comprising a supporting drum, a metal band mounted on the periphery of said drum, a sheet of yieldable material cemented to said metal band, and a series of separate but closely spaced abrasive blocks cemented,

to said yieldable material whereby the abrasive blocks are resiliently supported on the drum and are adapted to yield individually under the pressure of grinding.

'7. An abrasive article comprising a ilexible metal disk and a plurality oi blocks of bonded abrasive material attached to said disk by a layer ofv resilient rubber of suiiicient thickness to permit material movement of said blocks with respect to said disk.

8. An abrasive article comprising a flexible backing and a plurality of blocks of bonded abrasive material attached to said backingby a layer of resilient material of suiiicient thickness to permit substantial yielding of said blocks under the pressures applied in grinding.

9. An abrasive wheel comprising a supporting drum provided with a peripheral layer of yieldable material, a flexible endless band mounted on the layer of yieldable material, and a discontinuous multilayered coating of bonded abrasive material attached to the outer surface of said band by a layer of cement, said abrasive coating being sufficiently discontinuous and said cement being of a character to permit ilexure of the device under the pressures applied in grinding, whereby the abrading surface is resilientl" supported on the drum and is adapted to yield locally under the pressure of grinding. 1

10. An abrasive article comprising a flexible backing and an abrasive facing therefor consisting of closely spaced but separate relatively endless band and an abrasive facing therefor consisting of closely spaced but separate -relatively thick rigid blocks of bonded abrasive material individually attached' to a surface of said endless band by a layer of cement, said blocks being small enough and said cementbeing of such a character and thickness as to permit local exure of the article under the lpressures applied in grinding whereby the abrading surface is adapted to yield locally without disrupting the cement to an extent sucient to cause the abrasive blocks to become detached.

CHARLES E. WOODDELL.

CHARLES S. NELSON.

ROY LINCOLN.

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