US1658248A - Finishing grinding stone - Google Patents

Description

Patented Feb. 7, 1928.

UNITED STATES ERNEST I. MARS, OF CHICAGO, ILLINOIS.

r'rnrsnrne GRINDING stronn. 7

No Drawing.

My invention relates to artificial stones for abrasive and polishing purposes. Viewed in its general objects, my invention aims to provide a composition stone for this purpose which can easily be manufactured with a highly uniform distribution of the abrasive ingredient, or of both abrasive and polishing ingredients; which will require no poisonous ingredients for its manufacture;

10 and in which the relative proportion and hardness of the abrasive and polishing ingradients can readily be varied according to the material on which the stone is to be used.

16 My invention also provides a composition 7 for this purpose in which the body material (namely the material that has the abrasive and polishing ingredients distributed through it) can be varied considerably in 20 its own hardness; and in which this body material will gradually wear away to form a suitable muck when the stone is used for Wet grinding, so that this muck can carry off the abraded particles of the material 2 which is being ground; and in which this body material is somewhat abrasive and is of such a nature that the detached particles of the object on'which the stone is used will not adhere to this'material.

In its immediate commercial aspects, my

invention is particularly suited for the manufacture of stones to be used in the last step of the grinding of the copper printing cylinders employed on multicolor printing presses,

such as the so called rotogravure presses. Hence I am describing my invention 'more particularly with the ingredients proportioned for that purpose, although I do not wish to be limited to these particular pro- 40 portions or to the abrasive and polishing ingredients hereafter specifically mentioned. Owing to the high cost of such a copper printing cylinder, it is customary to use the cylinder repeatedly for different imprintings by grinding off the raised printing surface and again etching anew surface on it. For this purpose, the raised portions are first ground off by comparatively rough abrasive means, after which the cylinder is subjected to a finish-grinding; To insure a uniform diameter and a freedom from scratches, it is important that the abrasive ingredients in the stone employed for this finish-grinding should bedistributed through the stone is with highdegree of uniformity, thatthe' body material be uniform in hardness Application filed March 18, 1927. Serial No. 176,581.

not to wear irregularly, that the stone be free from hard spots and unduly hard abrasive portio'nswhich would produce scratches,

and also that the detached particles of copper will not attach themselves to the stone. N 0 natural stone has yet been found to meet these severe requirements, and even the grinding stones imported for this purpose require a good deal of subsequent hand labor for removing scratches. natural abrasive stones do not attord a sufiicient polishing for the cylinders, so that considerable later hand labor is also neededto finish this polishing.

In experimenting with various possible body materials for carrying the needed abrasive and polishing materials, I havediscovered magnesia cements to be superior to all materials previously suggested for the same purpose, namely cements composed of magnesium carbonate or oxide, combined with magnesium chloride. I have also found that the impurities found in commercial magnesite (which contains approximately'70 percent of magnesium salts and approximately.

5 percent of water) will not interfere with the use of ordinarymag'nesite asthis body material, thereby considerably reducing the cost of the stone. Furthermore, I have found'that by employing a suitable proper-- tion of another salt of magnesium, namely magnesium sulphate (which is commercially available under the name of Epsom salts), I can retard the drying of the magnesia cement so as to increase the hardness of the resulting stone to such adegree that the detached particles of copper will not imbed themselves into it. p g V In manufacturing, a finish-grinding and polishing stone for use on copper printing plates, I have found the following proportions satisfactory: magnesite 40 ounces, crocus 48 ounces, jewelers rouge 8 ounces, Epsom salt 8 ounces, magnesium chloride 16'ounces, water 3 pints.

Moreover, the

The magnesite, crocus and rouge are first h sifted separately through screens (desirably 300 mesh) and then thoroughlymixed while dry, while the magnesium chloride and the Epsom salts are dissolved in the water to form a solution. The mixture of the sifted dry ingredients is then worked up with this solution to a mass of uniform consistency,

, which is forced through a screen (desirably of about;50 f mesh, for breaking lumps and subdividing the plastic evenly) hering to it.

into a bronze mold Y which has previously been waxed to prevent the mass from ad- Left exposed to the air at ordinary temperatures, this plastic mass hardens in from 24: to 30 hours to form the desired stone.

In the finished stone, the abrasive (crocus) and the polishing ingredient (rouge) form nearly one half of the entire weight, or about double the proportion of the active ingredients in artificial stones heretofor rov osed for the same ur 3056 so that P P l my'stone is unusually eiiicientin proportion to its weight and size. Moreover, the mag nesia cement when thus diluted by the abrasive ingredient is in itself an abrasive of a degree of hardness suitable for having a grinding action on copper, thereby increasing the effectiveness of my stone,

in using such a stone for wet grinding, I. have, found that the surface wears 'evenlen.

and that the water and the grinding pol.- tions of the body material form the so.- called muck in adesired consistency for carrying off the detached particles of copper. I have also found that any marks still, left in the copper (if any) are so fine as to require only a quite small amount of hand polishing to remove them. Moreaver, no poisonous materials are employed in the manufacture of my stone, so that I eliminate the danger heretofore encountered in making such stones with litharge as an ingrec'li'ent ofthe body material. 7

However, I do not wish to be limited to the above mentioned proportions of the various ingredients or to the above recited protedure in the manufacture of my stones, since changes might obviously be made without departing from the spirit of my invention and from the appended claims. Nor do I wish to be limited to the crocus as the abrasive or to rouge as the polishing ingredient when such an ingredient is also employed, or to the use, of the stones of my invention for grinding copper.

For example, the degree of fineness of the resaaas (such as Epsom salt) used with it, thereby correspondingly modifying the grinding action of this body material and also adapting this material to prevent the adhering of detached particles harder than the copper of the usual printing plates.

' I claim as my invention:

1. A stone for griding and polishing copper, comprising a hardened and abrasive cement softer than copper and uniformly impregnated with a finely powdered abrasive andv finely powdered rouge, the abrasive being harder than copper, the total weight of the, abrasive and rouge being more than forty per cent of the weight of the. stone.

2. A. grinding stone comprising the hard ened product of an intimate mixture of a magnesia salt or salts, a finely divided abra= sive and a finely divided polishing material, with an aqueous solution of magnesium chloride mixed with a relatively small proportion of magnesium sulphate.

A grindingstone comprising a magnesia cement hardened under the influence of a retarder and uniformly impregnated with a mixture of finely ground crocus and rouge, the proportion of the orocus to the rouge being about eight to one, and the total weight of the crocus and rouge being more than forty percent of the weight of the stone.

i. A grinding stonecomprising the product resulting from the hardening of the plastic mass produced by intern tingling the following ingredients in approximately the proportions recited, namely: 40 ounces magnesite, e8 ounces crocus, 8 ounces jewelers rouge, 8 ounces Epsom salts, 16 ounces magnesium chloride and 3 pints water.

Signed at Chicago, Illinois, March 16th.

ERNEST P. MARS.