US 2138882 A
Description (OCR text may contain errors)
N. P. ROBIE Dec. 6, 1938.
ABRAS I VE Filed July 27, 1936 INVENTOR. NORMAN P RQBHE.
Patented Dec. 6, 1938 ABRASIVE Norman P. Robie, Niagara Falls, N. Y., assignor, by mesne assignments, to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Application July 27, 1936, Serial No. 92,939
This invention relates to abrasives and methods of making them. Its purpose is to yield superior abrasives having an improved degree of flexibility, strength, resilience and heat resistance in coated abrasives and improved strength and grinding texture in the case of numerous types of bonded abrasives.
There has recently come onto the market a new type of fabric produced from glass fibers which I have found to be very beneficial for incorporation in the manufacture of abrasives. In the broader sense I may utilize glass fibers in the form of woven fabric, felted pads, yarn or individual fibers, although as will be. brought out below certain types of abrasive are most advantageously prepared from the sheeted fibers in the form of either woven fabric or felt.
The glass fibers themselves are extremely small in diameter, ranging as low as .005 millimeter and hence are extremely flexible. Their tensile strength when considered individually is superior to that of steel wire per unit of cross sectional area. These individual fibers are commonly spun or twisted together to form a thread or yarn which possesses strength comparable with the best cellulosic textiles, but which in use is not damaged by temperatures which entirely kill the strength of cellulosic and other organic fibers. Hence the glass threads may be utilized in conjunction with adhesives or binders requiring temperatures at least as high as 500 F. to mature the binder, whereas the ordinary organic fibers are seriously injured by heating past 225 F.
I utilize these glass fabrics either as reinforcements by incorporating them within the abrasive mass or by applying them by means of suitable adhesives on the flat faces of grinding wheels and discs and also utilize them as a support for carrying the abrasive in the manner of sandpaper and other coated abrasives.
In such uses these glass fabrics possess many advantages over materials hitherto available. In comparison with metals for instance they possess a much lighter weight, the coemcient of expansion is readily adjustable by varying the composition of the glass so as to make it correspond with that of the abrasive mixture. Moreover, the glass does not smear or scratch in the manner of a metal reinforcement which comes into contact with the work being abraded, but rather imparts a certain degree of openness to the abrasive body which helps prevent burning of the work. The extreme flexibility of the material furthermore permits its incorporation as an intergranular reinforcing agent in grinding wheels.
Such reinforcements may be utilized with any of the customary low temperature abrasive binders such as resins, rubber, sodium silicate or the calcium aluminum silicate type covered by copending application Serial No. 89,845, filed July 9, 1936. In the latter two instances there is a considerable tendency for the binder to react chemically with the glass fibers, thus further increasing the adhesion thereto.
In the accompanying drawing:
Figure 1 represents diagrammatically a portion of a section through an abrasive article having abrasive grains adhesively held on one side only of a fibrous glass backing; and
Figure 2 represents diagrammatically a portion of a section through an abrasive article having abrasive grains on both sides of a backing or reinforcing fabric which is consequently embedded in the abrasive article.
In these figures, ill and 20 designate the fibrous glass fabric, H and 2| designate the adhesive substance, and I2 and 22 designate the abrasive grain.
Glass fabrics may also be incorporated to advantage in abrasive bodies which are cured at temperatures high enough to cause the glass to soften. In these cases however, the glass fuses to become a component part of the binding material and so loses some of its orginal characteristics. It nevertheless provides a continuous network of ceramic binder throughout the mass and in this way improves the strength of the wheel, although permitting grains whose useful life has been completed to break out of the wheel in the course of normal operation.
Having thus discussed the general purport of my invention I shall recite certain examples by way of illustration.
Example I In one method of applying my invention, I take woven glass cloth having twenty or more strands per inch and impregnate it with a resin mixture, as for example a mixture of 1 part of liquid phenolic resin of the grade marketed under the designation liquid Bakelite resin BR 1372 with 2 parts of powdered phenolic resin sold as Bakelite resin BR 2417. 'I'hisimpregnated cloth is then partially cured and cut into the desired shapes, such as disks. These disks are then placed centrally in a mold between level distributed layers of mixed resin binder and abrasive grain of the type customarily used for the production of resin bonded abrasive wheels. Additional layers of abrasive and additional glass fabric may be added if desired and when the mold has been filled to the desired depth, I press the entire mass and cure it in the normal way at temperatures approximating 350 F. Thin cutoff wheels may be fabricated in this way as well as wheels up to two inches or more thick.
Example II Woven or felted glass similarly impregnated and partially cured is pressed against the back of a resin bonded abrasive disk-and cured, thus providing a reinforcing backing for the disk.
Example 111 In the preparation of glass fabrics for use in an abrasive body of the ceramic type, as for instance silicate wheels or calcium aluminum silicate bonded wheels, I have found it desirable to impregnate the glass yarn with water before incorporating it. The glass as originally produced contains waxes or oils on the surface of the fibers to facilitate weaving them and this material tends to obstruct the impregnation with water. Hence it is desirable to leach out these interfering materials as a preliminary step. In utilization of the glass with binders of this sort the water filled yarn or cloth is placed in the wheel in a manner similar to that explained under Example I, additional abrasive mix added and the wheel pressed and cured in the ordinary way.
Example IV In certain instances I have secured my reinforcing action by incorporation of pieces of glass thread or yarn from to 2" long in the abrasive mix itself. I find that this is difilcult to do because of the tendency of the glass to ball up rather than to distribute properly. I have overcome this difliculty by applying to the glass fibers before incorporation in the abrasive mix a stiffening agent which is capable of reaction with or absorption by the binder to be used. For example, in the case of .mixes bonded with phenol formaldehyde resin. I impregnate the glass yarn with an aqueous solution of polyvinyl alcohol which I then allow to dry before cutting the strings into short lengths. Such strings can be readily mixed into the compound of abrasive and binder in mixers of the kneader type.
An alternative method of introducing small amounts of glass fibers into the mix is to first coat the glass with liquid resin and then add it to the mixture of powdered resin and abrasive grain. A certain proportion of material is taken into the mix in this way and any residue of uncombined glass fiber is then taken up by addition of further grain and dry powdered resin. Glass string in an' amount approximately 2% of the weight of the abrasive grain maybe incorporated in this way. Abrasives made by either alternative are pressed in the usual way and cured, for example by heating for 6 hours at F. and for 15 hours at 350 F.
It should be noted that glass fibers in bundles (i. e., in the form of string or yarn) may be utilized in this way although single glass fibers are not so satisfactory. The dimculty appears to be that the single fibers are pinched between abrasive grains and broken whereas there is sufilcient resilience in the bundled fibers to prevent damage from this cause.
Woven 'glass fabric is' particularly advantageous for the manufacture of coated abrasives for use under conditions where resistance to water is essential. In this way a non-shrinkable fibrous backing is available, so that the expensive pre- I shrinking operation can be dispensed with. Furthermore the adhesive which is used for coating the material can be subjected to a high degree of heat which not only increases its waterproof character, but decreases the length of time required for processing. This ability to withstand high temperatures also permits a wider choice of adhesives for coating abrasives of this sort than ispossibleinthe caseofcellulosicbackingssuch as paper or cloth which are damaged by high temperatures. Also acid catalysts to accelerate the cure of the resin may be used without injury to the backing. Hence it is within the scope of my invention to utilize woven or felted glass fabrics in the production of coated abrasives in general.
It is quite practical to use adhesives which require gigging temperatures above 225 F. and even above It is also possible to operate abrasives, particularly disks coated with such high temperature adhesives, at higher temperatures than is otherwise the case. This permits dry grinding instead of wet grinding in many operations with a consequent saving in both the equipment necessary and the accompfly nz mess.
In the fabrication of a characteristic coated abrasive I take a glass cloth consisting of from 16 to 40 glass threads per inch and size this cloth with a mixture of liquid and powdered phenolic resins. This sized product is then cured sufficiently to overcome any tendency to be tacky but not suiilciently to become brittle. It is then coated with a so-called making coat of a similar adhesive, after which abrasive grain is applied and the material again given a partial cure. Finally a sizing coat of similar adhesive material is applied on top of the abrasive grain and the complete coated fabric cured to the desired degree and thereafter flexed or otherwise processed as the operator may desire.
While I in general prefer to use woven glass fabric, it is also within the scope of my invention to use felted glass fibers impr sna ed with resin, rubber or other material to hold the fibers in the form of a strong sheet, and thereafter coat such sheet with abrasive.
A further advantage of belts and other coated abrasives-made on a fibrous glass backing is that the glass itself does not tend to imbibe water in service to the extent that cellulosic materials do and hence the backing does not tend to either tighten or loosen in the manner of cellulosic backings when subjected to water. For this reason I find it is at times advantageous to attach to ordinary coated abrasives, a backing composed of woven glass fabric to impart stiffness and strength.
Having thus described my invention and cited characteristic example by way of illustration, I desire protection thereon within the scope of the following claims:
1. In a coated abrasive, a backing comprising a woven glass fabric, a heat-hardened adhesive and a layer of abrasive grain attached to said backing by means of said adhesive.
2. A coated abrasive comprising a layer of abrasive grains attached to a fibrous glass backing by means of a phenolic resin binder.
3. A coated abrasive article comprising a layer of abrasive grain adhesively held to a flexible backing of fibrous glass.
4. As anovel article of manufacture, a heatresistant flexible abrasive article comprising. a backing composed of a woven glass fabric impregnated and coated with a rain adhesive heathardened at a temperature above 300 F. and carrying a layer of abrasive grain.
5. As a novel article of manufacture, an abrasive body compridng abrasive grains, a binder for the abrasive grains, and reinforcing means em? bedded in said abrasive body, said reinforcing means comprising fibrous glass fabric.
NOR-IAN P. ROBE. 1