US2414474A - Resilient abrasive disk - Google Patents

Description

Jan. 21, 1947. c. c. MARCH 2,414,474

RESILINT ABRAs IVE DISK Filed June 3,. 1944 inverti/La7? Patenteddam 2l, 1)9-47 UNITED,- STATE nEslLmN'r Anneslvn Disk l Cecil C. March, St'. Paul, Minn., assignor to Minnesota Mining & Manufacturing Company, St. Paul, Minn., a corporation of Delaware Application June 3,1944, sensi No. 538,577

solenne. (ci. sis-195) This invention relates to 'improvements 'in abrasive devices',- and especially to improvements in abrasive-coated disks for detachable and renewable application 'to the grinding heads of rotary grinding machines. Grinding-heads of this type are disclosed, for example, in the R. P. Carlton Patent No. 1,686,898 of October 9, 1928.

Coated abrasive products which, although useful also in various other forms. are of particular utility in the form of abrasive disks, have heretofore commonly been made with a composite backing` comprising a layer of cloth bonded toa comparatively stid but resilient sheet material such as vulcanized fibre (i. e.` so-called ilsh fibre), with abrasive `grains bonded to the exposed cloth surface. While animal glue has been used bothv as the combining adhesive for laminating the clothto the sh fibre, forimpregmating the cloth layer and also as the abrasive 2 c also be strong and relatively stili and at the same time suitably flexible, in order to transmit the rotary motion off the grinding machine from the vcentral portion of the disk tothe peripheral porportion ofthe disk against the workpiece so as to obtain effectivecuttingactlon of the abrasive grains on the workpiece. By the use of a hard and firm combining bond for laminating thev 1 cloth and stiff sheet of vulcanized bre or theA like (in the combination where my cloth layer has a presize or lmpregnatlng treatment with an elastic or yieldable material such as a. vinyl surface of the 'cloth (furtherremoved from the fish bre) prior tothe application of the making coat.

I have discovered that both of such structures, i. e. where -glue irnpregnates the cloth and where phenol' aldehyde resin impre'gnates the cloth -1ayer,provide disadvantages and drawbacks in different from that -used to treatandimpregnate.

the cloth (especially from thel grit-coated side thereof).

. An 4abrasive-grain shows'v'maximum cutting eillciency when it is securely anchored in a hard and-rm bond so that it cannot be displaced Ato "a 'less' eifective position by pressure against the workpiecewhich `it, vis desired to abrade. It is thereforeadvantage'ous to use a hard and rm abrasive bond where an efficient cutting actionV isdesi'red` (as distinguished from' a mere polish-` actionl.-v The compositebacking member of an abrasive-coated disk. to be satisfactory, must butyral resin) I have found that I can improve the force whichcan be exerted upon the workpiece during the cutting or grinding operation without very appreciably affecting the ability of my disk to withstand rotatlcn'in use. My hard, firm combining bond. as used in my structure,

has the eect of adding 'to the strength and stiff A ness of the ilsh' bre Without greatly cutting down the ability of the disk to withstand flexing. The known hard rigid and rm resin bonding agents have, however, an unfortunate tendency towards brlttleness. Flat abrasive disks heretofore made with such resins, asthe abrasive bond and impregnant for the cloth, are diiilcult to attach successfully to the grinding head of the rotary grinding machine, since even the slight depression or bending of the centralA portion of the disc bythe retaining clamping bolt of the grinding head (such as illustrated in the previously mentioned Carlton patent) when thesame is tightened in place is ordinarily suilcient to cause radial cracking, which accelerates subsequent failure of the disc. Even where mechanical means are available to avoid this diculty,

l`a further problem is encountered; in use, the

when using these hard and brittle resin mate-v rials, the substitution of various flexibleybonding agents has heretofore been suggested for the abrasive bond'or binder coat. Where these flex- .ible materials are used as abrasive bonding agents, however, relatively inefficient abrading the abrasive grains to be displaced into less effective cutting positions.

In one previously suggested method for the production of a disk structure, a resilient thermoplastic bonding material is applied as the combining agent between asheet material, such as fish nbre or a iiber-reinforcedvresinous sheet, and

- rigidly held together to an to shear or rupture the fibers. Qn the other hand. brittle fibrous materials, which when flexed or y a layer of cloth; acoating of a thermosetting resin is then applied as an abrasive bond to the uncoated cloth surface (thus also impregnating the cloth), followed Vby an application of abrasive grains, and by heat curing of the thermosetting resin to the hard rigid stage.l

During application, and to a' further extent durj ing the preliminary stagesof heat curing; .the

thermosetting resin thoroughly impregnates the cloth'from the grit-coatedvsurface thereof; and, after curing is complete,'this furnishes a hard rigid support for the abrasive grains, but it definitely limits the utility of the abrasive disk structure as a whole, as I have now discovered.

Among other things, with this construction, the

cracked are very low or entirely lacking in tensile strength, may be high in compression resistance. The separate constituents of the novel composite backing of this invention are therefore (based e uponv this explanation) seen to be so located as to utilize their most valuable qualities or char-v` acteristics, respectively. Since this is so, the thickness of the flexible' resilient layer in par- V ticular may, if desired,` be considerably reduced from previously accepted requirements.

example of an abrasive disk with an em-1 brittledcloth layer is shown by N. E. Oglesby Patent No. 2,333,035, granted October 26, 1943. As previously stated, however, my objective is almost they direct opposite; that' is, I desire a disk where the layer of the backing which is adjacent to the y makingl coat is tough, resilient and capable of withstanding bending'. distortion and repeated flexing during use, without breaking up.`

bonding qualities between the sh fibre and the cloth have, in general, been deficient, and other y deciencies have also been encountered, including inability of the disk satisfactorily to withstand repeated flexing.

I have found that much improved flexibility of an abrasive-coated disk may be secured, while still providing a strong andeflicientlyilrm and sufiiciently sti and hard backing member, byr

of the vsheeted a properly positioning arelatively minor amountof flexible resilient material within my disk structure.

In my novel type of disk, Ipreferably bond a layer of cloth to a sheet of fish fibre by meansof a4 heat-convertible synthetic resin, e'. g. a thin layer of a phenol aldehyde resin, which is then cured to form a firm bond. I then coat and impregnate thev exposed side of the cloth with an elastic, yieldable synthetic resin which may be comprised of polyvinyl butyral resin for example,

in an amount suillcient to prevent any substan tial penetration of thesubsequently applied. ing coat into the cloth. I next apply an abrfalslv bonding or making coat of heat-convertible thetic resin, and a layer of abrasive grains;

the Atreated cloth surface. Following 'this a and sandsizing coats are suitably cured.' The presence of the relatively thin cross-section of elastic, yieldable synthetic resin, in the cross-section of the composite backing most subject to bending and to tensile stress.- affords this new abrasive device special advantages in utility, performance characteristics and durability.

A possible explanation of the unexpected eectiveness of this limited amount of flexible material in flexibilizing the composite product and in preventing cracking and breakup of the product e during application and use may be 'as follows:

' sandsize coating is usually applied. The makingvv e 67o '.finthiscombined abrasive disk structure To quickly illustrate and explain my invention, e f

reference is made tothe accompanying drawin in which: e

Figure 1 is a representation (exaggerated as to size) of a vertical cross-section of a portion ofade according to the a sheet abrasive articlem present invention;

Figure 2 is a perspective view of'a disk fo brasive material shown in Figure 1`; and

, Figure 3 is a plan-'view of the sheeted abrasive article of Figure 1, with layers successively broken f away to showl the construction... e Vi ',.Brieily, a layergor thickness kof cloth l2 is bonded by a'combining adhesive AIl lto a sheet of tough, comparatively stiifand hard yet moderately flexible and resilient.backing-material Il,`

-to form acomposite backing. The exposed surface of cloth-is treated (impregnated or presized) l with a! flexible resilient film-forming material dj'successively with a binder coat I4,` one e dre-'layers of 'abrasive particles i5 and lastly a andsize coat I8.. Preferred specific elements trated -,by the legends on the drawing,

`'a'.'mmpzei' vu1canizea aber or asn Aaber of ten m lbs. per ream (480 sheets 9" x 11'f), which-is a material well-known in the art-(forexampleysee' the Carlton Patent No. 1,686,898) is coated on one side with 13.6 lbs. per ream of ka 95% solution of a heat-hardenableV phenolic lresin as a combining adhesive, and then combined with a cloth drills, having a threadcount of 72 x 48 and a thickness of .017 inch,originally weighing one pound per 2.75 Vyards 27.5 inches in width, which has been kier boiled for removal of sizing, and which therefore weighs about 16 lbs. per ream.

The'. concentrated, viscous resin solution slightlypenetrates and impregnates the surface of the or abrasive-coated side of the backing is placed e under tension. Fibrous materials are best able to resist bending and tension when the stresses v applied are equalized over the individual bers; they'are least able to resist such forces when cloth. but in the main, leaves the cloth unimpregnated. After heating the laminated structure to remove the solvent and to set up or parc tially cure the combining adhesive, so that thev two laminations will not be pulled apart during subsequent operations, the `exposed cloth side of :the combination backing is impregnated and presized with 12.75 lbs. per ream of a 24% solution of a thermoplastic flexible resilient, elastic nlm- 75. forming material' containing polyvinyl butyral extent which will tend `v rmed i Illie impregnated surface of the cloth is then y are illuse i1 (0.010 inch) thickness and 'weighing approximately 25 polyvinyl butyrai ("vinynte resin as a maior ingredient. and the solvent. is removed by evaporation. An abrasive bond,

which may be a solution ot a he'at-hardenable j phenolic resin, is next applied to the exposed sur-V face of the impregnated cloth, followed by a layer of abrasive grains and (after intermediate removal of solvent-and partial heat curing of the abrasive bond) by a nal sandsize coating oi a rasive grains may be used. (The proportion o1 sandsize adhesive to making adhesive varies considerably with the size of the abrasive grains.)

A strong, tough, eillcient grinding or abrading device is thus obtained which can be fashioned into disks for detachable and renewable application to the rotary grindingheadsoi disk sanding machines, and which when in use will permit ,the application of relatively high pressures of the disk against the workpiece, while eiiectively resisting breakup or disintegration of. the disk and while still maintaining elcient abrading qualities. y

The presize solution called for by the present example is prepared by mixing the following ingredients in a churn until a homogeneous solu-v tion is obtained: l

` 1 Parts byweight XYSG" produced and sold by Carbide and Carbon Chem. Corp., New York) v 15 Coumarone-indene resin (Cumar CX grade produced and sold by the Barrett Division of Allied Chemica1l and Dye Corporation,

New York) 15 Tricresyl phosphate 10.5 2-ethoxy ethanol 80 Hydrocarbon solvent (a high solvency type containing aromatic fractions) 50 vulcanized fiber, or other suitable or equivalentstiff but resilient sheet material, may be used in various thicknesses, for example from 5 mils (0.005") to 30 mils (0.0307) depending on the grit size of the abrasive grains, the pressure to be applied bythe disk against the workpiece, the

character of the workpiece, the weight and type of combining bond, and on other considerations.

Various suitable heat-setting resinous'abrasive bonds and methods for their preparation and use have been known, as for example shown in the copending application of Byron J. Oakes, Serial No. 293,192, Patent No. 2,357,350. Illhe use of such resins as combining adhesives, abrasive bonds, and/or as sandsize coatings is contemplated herein. Such resins may be carrled to a desired viscosity and stage of reaction by preliminary heating, and may then be diluted and their viscosity reduced with solvents such as 2-ethoxy ethanol prior to application. Subsequent heating of the coated webremoves the solvent and further 'rms up the resin to the required degree. The resins used as combining adhesive, abrasive .binder (i. e. making coat), and sandsize coating may if desired be of the same composition. However, it is usually preferred to use resins which have been more completely reacted, or which are capable of reacting more rapidly at a given temperature, for the abrasive' bond, and more particularly for the sandsize, than for the previously applied combining adhesive, in order to obtain sumcient curing of the later coats without overcuring of vthe earlier coats. The final curing of the resinous bonds may be accomplished in succe'ssive stages wherein the temperature is gradually. increased. t

The amountv of heat-'reacting resin to be employed as the combining coat depends, at ieast in part. on the thickness and stiffness of the vulcanized fiber or other sheet material, andl on the weight (or thickness)I of the cloth. Where a thin, relatively ilexible sheet material is employed, a heavy resin coat may be used to impart additional stiffness and strength to the combina-` tion backing. However, the amount and iiuidity of the resin must' not.be sc great as to allow it to penetrate or impregnate the entire thickness of the cloth portion of the backing. Inv

general, it is found desirable to allow the combining adhesive to penetrate the cloth toa depth oi' about 10% of its thickness.

The amount of ilexible resilient presize ma-l terial used to impregnato the remaining thick-l ness ofthe cloth portion of the combination backing may also vary within quite wide limits. For example, when using the vulcanized ber and cloth specied in Example 1, advantageous results havebeen obtained with 'as low 'as 6.8 and as high as 28,3 lbs. per ream of the presize solution therein disclosed. These amounts approximate 10 and 50% respectively of the hard resinous combining .bond of -the example, when calculated on the solids basis. The lower weights of presize impart less ilexibility, and furthermore have in some cases resulted in decreased adhesion of -the abrasive bond to the surface of the backing, possibly due to blistering caused by thel presence of air entrapped in' the voids in the surface resulting from incomplete impregnation by the presize material. On the A other hand, the higher weights of presize may impart undesirably high iiexibility, and may also permit loss of abrasive, when the disk is in use, by lowering the strength of bond between abrasive bonding material and backing. In this case, the cloth is possibly so well lled :by the presize thatl the abrasive bond material cannot obtain mechanical anchorageby penetration :into

the body'of the cloth, or perhaps the increased thickness of the flexible resilient layer permits excessive deformation 4and resulting breakage For the polyvinyl butyral base presize solutio speciedin Example 1 there is substituted` an equivalent amount of the yfollowing formula:

Polyvinyl butyral as in Example 1- 2 137 Liquid resinous plasticizer (hydrogenated methyl abietate; Hercolyn,. produced and sold by Hercules Powder Co., is such a resin) y50 Carbon black... 0.5 2-ethoxy ethanol 1:85 75 Xylol Parts by weightv l' l tantos` The 'phenol-formaldehyde heat-setting resiny may be of the same type as used for 4the combining .adhesive and/or the abrasive bond. .During the subsequent heating of the abrasive sheet, this,v resin also sets up or cures to amore advanced o "In this example,l aliquid reslnous plasticizer takes'the place oi both the liquid plasticizer and the coumarone-indene resin used in Example 1,

and similarly advantageous properties are ob-v tainedin the iinished abrasive sheet'material.

In some instances. and particularly where heavy grit sizes require the use of highly viscous abrasive bonding material, it has been found desirable to apply a preliminarypresizecoat of a more dilute solution of the same or a similar abrasivebonding material, Thusin Example 1,

a second presize consisting of 12.75 lbs. per ream of a solution of heat-hardenable phenolic resin of the same composition as the abrasive bond but containing only 65% solids is applied after the application and drying of the original 'thermo- .plastic flexible resilient nlm-forming presize.

This second presize, by virtue of .itsimproved fluidity, penetrates the voids of the treated cloth and thereby securesbetter adhesion to the cloth than would the.heavier,.less fluid abrasive bond r ify applied directly. The presize is dried, and partially .cured by heating if desired, before the f `abrasivek bond isapplied to the backing,

Example '3V maleate, in a-water dispersion'and in the presenceioigaSuitablercatalyst according to methods 4well-know"`in'the 9 .1't.f:to produce a dispersion of yinap CODO ugh-,1i lexibleresilient, film-,forming This dispersion'may be applied to the backing c i'=Examplea. l in-place oi the presize ere;described, and the abrasive sheet material-completed as before, -t'o produce an improved type of abrasive disk having `useiful properties.

f A Example 4 A. ,pmsucized br nexibmzea heat-setting Aphenolic resin may in-'some cases be substituted for ,the vflexible presizeof Example 1, where somewhat less exibility is suilicient. The following' forinulahasv been foundto'sive' good results:v

Parts bylweight PhenolLIormaldehyde heat-settingresinrlgf12.5 Diethyleneglycol maleate 42.5 2-'ethoxy ethanolg.; '1.5

stage, but the'presence of the diethylene lglycol maleate renders the final product suillciently'ilexible and resilient so that the abrasive sheet shows desirable improvement over the conventional type which contains no ilexibilizing agent.

While the phenol-formaldehyde resin itself is here heatsetting, the final composite plasticized resin product isless rigid than would be the heatset resin alone. and for the` purposes of this invention-is therefore equivalent to a thermoplastic resin. *Y

Various other materials may also be used inl some cases, either` alone or in combination, as the iiexible presize layer I 3. Polymerized racrylates and'methacrylates, and inter-polymers of acrylatesand methacrylates with othernienibers-r of the same class or with otherv polymerizable materials such as alkyl fumarates or. maleates, for example inter-polymerized methyl ethyl acry- 5 late-amyl fumarate may be used, application beging from'solution in volatile organic solvent or from aqueous dispersion; suitabletackifying or otherwise modifying resins and the like may be added where necessary. Plasticized` glutinous malo terials, such as animal glue plasticized with form anilide, mylbe employed; where such compositions are subject to the eects of moisture, or high temperature with high humidity, they may be tanned or rendered waterproof and heatresistant by the action of aldehydesl or other tanning agents. Drying oils or drying oil varnishes are also suitable for use as the flexible 4presize layer; thus a linseed oil varnish containing either the usual varnish resins, or preferably containing a rosin adduct formedby heating together one part of maleic anhydride with three parts offrosin, and containing also suilicient metallic driers to provide rapid and thorough drying of the varnish to a firm non-tacky but resilient illm, may be g5 used. Likewise alkyd resins, such -as'may be formedby condensation of polybasic acids with glycerol or glycol, may be used, as may also cer--v tain cellulose derivatives suitably plasticized and compounded, as with tacklfying resins. Rubber,

reclaimed vulcanized rubber, and synthetic rubber such-as polymerized chloroprene, polymerized butadiene-styrene, polymerized butadiene-acrylonitrile, and the like, may also be suitably compounded andused for the saturation of the outer portions of the cloth layer to provide flexibility and resiliency of the composite structure. In general, any flexible, elastic, tough, yieldable, resillent, coherent material may be used which `has the'followin'g properties: f

40- 1. It must not. attack the cellulosic'bers of the cloth layer I2 so as to impair the /strength thereof.

2. It must be able tov withstand `the temperatures encountered during heat curing' of the abrasive bond and-during the use of the abrasive disk, without becoming brittle and also without unduly softening.

3. It must have suillcient ilexibility and bel suiliciently'yielding t0 Permit equalization of stresses encountered vin the outer portion of the l. cloth layer.

4. It must present a r abrasive bond coat will eiectivelyadhere.

5. VIts solution or 'dispersion in a volatile liquid vehicle must lbe capable of penetrating and impregnating the exposed and untreated portion of thecloth layer I2.

.The 'improved abrasive-coated sheet of this invention thus consists,I as will have become apparent from considerationof the speciilcation, of a strong hard ilrm compression-resistant back layer, a strong hard firm abrasive layer, and an interposed flexible elastic .yieldable resilient layer so situated that it" provides 'maximum flexibility to the composite structure while still avoiding anyunwanted softness.' Thehardilrm and strong back layer is well-bondedv and full-y bodied, and is capable of transmitting aconsiderable amount of force from the central portion to the peripheral or abrading portion of a disk cut from the material without vbuckling-orv delaminating. The hard firm abrasive .layer is well-bonded Vand strong so that Athe abrasive grains accomplish a `maximum cutting action.

1s 'rae semble-resilient `layer; of the sheet. due

surface to which the 9 largely to its location in the composite structure as well as to its composition, provides desirable exibility and freedom from breakup and disintegration, without limiting the cutting or abrading eiciency of the abrasive sheet or disk.

AI claim:

1. A exible abrasive disk of the coated abrasive type comprising a layer of vulcanized ber, a hard iirm thermoset phenol-aldehyde resin combining bond, alayer of cloth bonded to said vulcanized fiber by said combining bond and having the bers adjacent said vulcanized liber firmly incorporated within said combining bond, a layer of flexible resilient impregnant comprising polyvinyl butyral within the remaining portion and at the outer surface of said cloth. a hard rm strong thermoset phenol-aldehyde resin abrasive bond adherently bonded to said outer surface of said impregnated cloth, and a vlayer of abrasive grains bonded by the said abrasive bond.

2. A iiexible abrasive disk of the coated abrasive type comprising a layer of vulcanized ber of about `10 mil thickness and Weighing about 25 lbs. per ream; a layer of cloth drills weighing about 16 lbs. per ream; a coating of thermoset hard and rm phenolic resin combining adhesive forming a firm, strong bond between said ber and said cloth, andfurther form ing a hard rm strong iilling and unifying agent for not more than about 10% of the total thickness of said cloth; a layer of thermoplastic iiexible and resilient cloth sizing material comprising polyvinyl butyral synthetic resin, forming an adherent, yieldable lling agent for that portion of said cloth layer furthest removed from the vulcanized ber layer, said layer of cloth sizing material weighing approximately 3 lbs. per ream; and a further layer of thermoset hard rm and strong phenolic resin containing interspersed partly exposed abrasive grains. said layer being adherently bonded to said iilled cloth layer.

3. A iiexible abrasive disk of the coated abrasive type comprising a layer of vulcanized fiber, a hard iirm thermoset synthetic resin. com-` bining bond, a layer of cloth bonded to said vulcanized ber by said combining bond and having the bers adjacent said vulcanized ,fiber rmly incorporated within said combining bond. a layer of flexibile resilient impregnant comprising a thermoplastic synthetic resin having approximately the yieldability' and elasticity of polyvinyl butyral resin within the remaining portion and at the outer surface of said cloth, a hard firm strong thermoset synthetic resin abrasive bond adherently bonded to said outer surface of said impregnated cloth. and a layer of abrasive grains bonded by the said abrasive bond.

4. A flexible abrasive disk as deiined in claim l 3, further characterized in that, in lieu of said CECIL C. MARCH.

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