C~neo~ov
VOL. 5. No. 11
CARBOLOY-A
1399
NEW TOOL MATERIAL
Tungsten carbide, an extremely hard but brittle material, has been combined with cobalt, a tough and strong metal, to produce the hardest cutting material yet developed in a research laboratory. One would not think of cutting a screw thread in a glass rod with the usual tool-steel cutter-but it can be done with the new material. The only way in which a hole could be actually bored through concrete has been with a diamond drill, although, of course, it has been possible to make a hole in rock with the noisy "star" hammer; but the new material has made it possible to drill through concrete without expensive diamond-tipped equipment. Glazed porcelain is another example of a material that cannot be handled with tool-steel cutters, but it succumbs to a tool made of tungsten carbide and cobalt. Strange as it may seem, there are materials soft enough to be whittled with a pocket knife, and yet so abrasive that tool-steel cutters are dulled quickly and rendered useless. Genelite, composed of copper, tin, and is such a substance, s T ~ ~ T 1 h . T c . CUTG L A * ~ WITH CARBDLOV and hard rubber, molded compounds such as Bakelite, and mica likewise spoil tool edges quickly. There are hard steels that cannot be handled with tool-steel cutters, some not being cut at all and others with difficulty, and here again the new cutter shows its superiority. And even though the tip of the new cutter should become heated to a bright red-a temperature that would be disastrous to its predecessors-it continues calmly with its work, for the material has no temper. The new material, named carboloy, was announced by Dr. S. I,. Hoyt of the Research Laboratory of the General Electric Company a t the annual convention of the American Society for Steel Treating held a t Philadelphia, October 11, 192S. Its Physical Properties That carboloy is a hard material is amply shown by window panes in the laboratory rooms, for deep scratches have been made in the glass with the material. And not only glass but natural sapphire, next below diamond in the scale of hardness, car1 he scratrhed with carholoy. If held against
the side of an emery grinding wheel, a carboloy cutter will wear a deep, narrow groove into the stone, whereas the usual tool materials would be worn away by such treatment. In the course of laboratory determinations of the properties of carboloy it was found that the usual method of using the Rockwell test for quantitatively obtaining the hardness of the material
Dr. S. L. Hoyt, Research Lal~oralory, General lilectric Company, holding in his left hand a piece o i Bakelite with metal inscrt and a piece of glazed porcelain, both of which were c u t with carboloy. On the table and in his right hand are representative carboloy tools.
could not be employed-the point of the diamond wore and crumbled in too short a time if the diamond penetrator was loaded with a weight. It was necessary to use the penetrator without a load. The test showed that common hardened tool steel has an average maximum hardness of 8.50 of the Brinnell scale, that the hardest steel may be taken as about 1000, and
VOL.5, No.
CARB~L~Y
11
1401
that the hardness of carboloy runs 2000 and above. Tungsten carbide without cobalt has a strength of less than 50,000 pounds per square inch. The addition of cobalt increases the strength of the material to more than half that of highspeed steel, carboloy having a strength of 275,000 pounds, and quenched and tempered highspeed steel 425,000 pounds. Toughness is an equally im- I portant property when considerine cuttine materials. The
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does not crumble even though Wmr%A N D I ~ E R P Gnoovn CUT IN CLASSW ~ the supporting block of copper Cnnm~ou shows marked indentations as a result of the blows from the peen. The ability of carboloy to make intermittent cuts on metals further attests its strength and toughness.
Since carboloy has no temper to be "drawn" by the heat generated during cutting operations and since i t is much harder than the materials
I
machined, even at elevated temperatures, it has a distinct advantage over steel tools, which are frequently softer than the machined materials and
which cannot be used at elevated temperature,. Cutting nickel steel t heat was effected when the point of the carboloy tool was at a h r i ~ h red
without the tool showing any ill effects. The tungsten carbide material does not pit or tarnish, and is dissolved in acids only with great difficulty. When cutting metals a t the speeds usually employed, the moderate temperatures have not been observed to be harmful. If the speed of operation
CnnnoLou C,INCRETE I~KILI,
Showing tip.
Showing core of concrete.
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