Metal surface refinement using dense alumina-based media

A process for the refinement of metal surfaces of objects, in which a mass of elements, including a quantity of objects having relatively rough metal surfaces, and a solution capable of converting said surfaces to a softer form, are introduced into the container of a mass finishing unit and are rapidly agitated therein for a period of time to Produce relative movement among said elements and to maintain said surfaces in a wetted condition with said solution, for conversion of any metal exposed thereon, on a continuous basis, so as to thereby effect a significant reduction in roughness by chemical and mechanical action;

• wherein the improvement comprises the inclusion in said mass of elements of a quantity of relatively heavy and nonabrasive solid media elements, the amount and size of which are selected to promote relative sliding movement thereamong and with respect to said objects, under the conditions of agitation, said media elements being composed of a mixture of oxide grains having diameters of about 1 to 25 microns, fused to a coherent mass and having a density of at least about 2.75 grams per cubic centimeter and a diamond pyramid hardness value of about 845 to 1,200, as determined by ASTM method E-384 using a 1,OOO gram load, and being substantially free of discrete abrasive particles, the composition of said media elements being such that the average weight reduction thereof is less than about 0.1 percent per hour, as determined in a vibratory bowl having a capacity of about 280 liters, substantially filled with said media elements and operated at about 1,300 revolutions per minute and an amplitude of 4 millimeters, with a soap solution flowing through the bowl at the rate of about 11 liters per hour, and also being such that said media elements will remain substantially free of sharp edges during said period of time, said quantity of media elements having a bulk density of about 1.70 to 2.5 grams per cubic centimeter, said improvement also including a step, effected prior to said period of time, of conditioning said media elements for a period of at least one hour, and in the absence of said objects, so as to round-off sharp edges thereof.

A process for the refinement, to a burnished condition, of metal surfaces of objects, in which a mass of elements, including a quantity of objects having relatively rough metal surfaces, and a solution capable of converting said surfaces to a softer form, are introduced into the container of a mass finishing unit and are rapidly agitated therein for a period of time to produce relative movement among said elements and to maintain said surfaces in a wetted condition with said solution, for conversion of any metal exposed thereon, on a continuous basis, so as to thereby effect a significant reduction in roughness by chemical and mechanical action, and in which said mass of elements is thereafter so agitated in said container with a liquid that is inert to said metal, substituted therein for said solution;

• wherein the improvement comprises the inclusion in said mass of elements of a quantity of relatively heavy and nonabrasive solid media elements, the amount and size of which are selected to promote relative sliding movement thereamong and with respect to said objects, under the conditions of agitation, said media elements being composed of a mixture of oxide grains fused to a coherent mass having a density of at least 2.75 grams per cubic centimeter, and being substantially free of discrete abrasive particles, the composition of said media elements being such that the average weight reduction thereof is less than about 0.1 percent per hour, as determined in a vibratory bowl having a capacity of about 280 liters, substantially filled with said media elements and operated at about 1,300 revolutions per minute and an amplitude of 4 millimeters, with a soap solution flowing through the bowl at the rate of about 11 liters per hour, said quantity of media elements having a bulk density of at least about 1.70 grams per cubic centimeter, said liquid being substituted for said solution without removal of said mass of elements from said container.