US2635399A

US2635399A - Method for grinding carbide tools

Info

Publication number: US2635399A
Application number: US221765A
Authority: US
Inventors: Jr William H West
Original assignee: Thompson Products Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1951-04-19
Filing date: 1951-04-19
Publication date: 1953-04-21
Anticipated expiration: 1970-04-21

Description

April 21, 1953 w. H. WEST, JR

METHOD FOR GRINDINGCARBIDE TOOLS Filed April 19, 1951 Patented Apr. 21, 1953 METHOD FOR GRINDING CARBIDE TGOLS William H. West, Jr., Madison, Ohio, assignor to Thompson Products, Inc., Cleveland, Ohio, a

corporation of Ohio Application Apr-i119, 1951, Serial No. 221,765

8 Claims.

The present invention relates to a method for the absorption of heat in an abrading operation in which a cutting tool is surfaced by means of abrading contact with an abrasive surface.

One of the most common high speed cutting tools in industrial use today consists of a steel shank which is suitably recessed in one end to receive a hard metal insert composed of mate rial such as metallic carbides known commercially as sintered carbides.

In shaping or dressing the carbide tool to a desired configuration, which usually involves bringing the carbide tipped tool into abrading contact with a moving abrasive surface, the removal of heat presents a critical problem. The amount of heat generated in this type of grinding operation is dependent upon the grinding pressure and the surface area being ground.

In such a grinding operation, it is imperative that the carbide tipped tool be kept at a temperature below that at which the temperature diiferential between the carbide tip and the steel body of the tool is large enough to crack the carbide tip from thermal stresses. The difference in coefiicients of thermal expansion for carbides and steel vary ouite significantly, as the coeflicients of thermal expansion for carbides range from about 2.8 l in./in./ F. to l.0 10 in./in. F., while the coefiicient for steel is about 8.2 10- in./in./ F.

In grinding such tools, the steel body often heats up to a temperature where it fuses into the grinding wheel. When this occurs, the wheel must be resurfaced to permit accurate grinding of subsequent cutting tools.

There are two methods now commonly employed for grinding carbide tipped tools. One of these is a dry grinding process in which the carbide tipped tool is pressed directly against the moving abrasive surface, with or without the introduction of compressed air during the grinding operation.

This process has the advantage that the'operator has good visual control over the operation. However, the dry grinding process suffers from the drawback that the grinding operation must be interrupted to permit the tool to cool to avoid cracking the carbide tip from thermal stresses. In some instances, the, tools are rotated during the grinding operation so that a portion of one tool is being ground while other tools in various stages of grinding are cooling, but this technique is rather costly in that itre quires excessive handling of the tool by the oporator and excessive inventory. Another disadvantage of the dry grindingprocess is the inherent danger of burning the operators hand by heat conducted by the tool being ground.

Another process for grinding carbide tipped tools consists in maintaining a continuous flow of liquid coolant over the carbide edge as the edge is being ground. This type of process has the advantage of being able to remove a greater amount of stock in one grind than is possible with dry grinding, as the liquid coolant is able to dissipate some of the heat liberated during grinding. The presence of the liquid also acts to remove dust formed. Consequently, the wheel life and grinding action are slightly better in this type of process than in dry grinding.

However, the wet grinding operation has the disadvantages resulting from the inability of the operator to see the surface being ground. Another of the disadvantages resides in splashing of the coolant against the operator and on the floor. Further, grinding wheels do not absorb the coolant uniformly, so that they are often rendered out of balance by unequal absorption of liquid coolant. Furthermore, tools which have been wet ground must be wiped perfectly dry after the grinding operation, or otherwise protected against rust.

The present invention is concerned with a method for grinding carbide tipped tools by directing a stream of liquefied gas into the area of contact between the carbide tool and the abrasive surface, so that the heat of the grinding operation is dissipated in volatilizing the liquefied gas to a vapor. The liquefied gas introduced into the area of abrading contact serves the function of a heat control medium through its volatilization.

The preferred coolant used in the process of this invention is carbon dioxide, but other normally gaseous materials such as liquid air might be employed. It is desirable, however, to use a gaseous material which is non-toxic unless special means can be provided to remove the volatilized gas during grinding.

An object of the present invention is to provide a method for cooling abrading operations.

Another object of the present, invention is to provide a method of grinding carbide tipped tools easily without danger of cracking the carbide tip due to excessive thermal stresses.

A still further object of the invention is to provide av method of grinding carbide tipped tools in which the grinding may be carried out in a rapid manner, and in which the abrasive surfaces employed in the grinding operation having a longer effective life than in any previously used grinding operation.

Other and further objects of the invention will be apparent to those skilled in the art from the following description of the annexed sheet of drawings which, by way of a preferred example only, illustrates one embodiment of the invention.

On the drawings:

Figure l is a plan View of a grinding assembly for surfacing a carbide-tipped tool; and

Figure 2 is a diagrammatic elevational view of the apparatus, illustrating the means by which the stream of coolant material is introduced into the abrading zone.

As shown on the drawings:

In Figures 1 and 2, reference numeral I D designates generally an abrasive wheel mounted for rotation about its central axis.

The grinding wheel I is shown in position to grind the surface of a cutting tool I! which is held in fixed position by means not shown against the abrasive periphery of the grinding wheel III. The cutting tool I I may consist of a generally rectangular shank I2 of steel or other material having a high resistance to tensile stress. An insert I3 composed of sintered metal carbides, such as Carboloy, is secured within a recess I4 of the shank I2 as by means of brazing, or the like. From Figure 2, it will be apparent that the forward edge of the insert I3 extends slightly beyond the forward edge of the shank I2.

A source of liquefied coolant gas, such as carbon dioxide, is introduced from a gas cylinder I5.

The liquefied carbon dioxide leaving the cylinder I5 passes through a valve I1 and through a conduit I8 which feeds a flexible tube I 9. A pressure gauge 20 is provided in the flexible line I9 to determine the existing carbon dioxide pressure in the line.

The fiexible tube I9 directs liquefied carbon dioxide into a housing 22 disposed near the periphery of the abrasive grinding wheel Ill. As shown in Figure 2, the housing 22 contains a restricted passageway 23 communicating with the line I9. The restricted passageway 23 discharges through a small orifice 24 in a manner such that a stream S of liquid carbon dioxide is directed in a direction tangential to the periphery of the grinding wheel I0 at the area of contact between the carbide insert I3 and the periphery of the grinding wheel I0.

In order to maintain the carbon dioxide in a liquid condition at least until it reaches the discharge orifice 24, the passageway 23 must be sufiiciently strong to hold a back pressure in the tube I9 sufliciently high to prevent gasification in the tube. Further, the orifice must be arranged so that it will not release the pressure inside of the outlet 24 and thereby permit cooling in the nozzle or in the tube with subsequent icing or development of frost in the tube.

Consequently, as shown in Figure 2, the liquid flows to an orifice '24 in a thin disk 23A, which is a part of the nozzle 23. Since carbon dioxide flashes from liquid at approximately 70 lbs. per square inch, the thin disk minimizes the distance in which the carbon dioxide pressure changes from approximately 960 lbs. per square inch to atmospheric pressure. Thereby, it permits optimum control of the critical flash point aiding in preventing expansion in the nozzle and formation of an ice block.

The shutoff valve I1 is utilized to control flow of liquid carbon dioxide from the cylinder I5 to 4 the orifice 24. With the cylinder at room temperature, the carbon dioxide pressure is approximately 960 lbs. per square inch. Refrigeration of the ylinder reduces the pressure and increases the heat absorption capacity of the carbon dioxide.

By directing the stream S at the area of contact between the carbide insert I3 and the periphery of the grinding wheel I6 in a direction tangential to the periphery of the grinding wheel I0, the stream S serves to blow away dust from the cutting tool I I or from the grinding wheel I0 during the abrading operation.

After impinging upon the abrading area A, the liquid in the stream S vaporizes and the latent heat of the vaporization of liquefied gas directly in the area of liberation of heat developed by the abrading operation provides an efiicient heat transfer to maintain the cutting point of the carbide insert I3 at any desired temperature. The vaporized or gasified liquid then moves away from the cutting tool II and the grinding wheel I0 so that a film of ice will not be built up to insulate the abrading area.

By maintaining the stream 5 in liquid form directly up to the abrading area A, the latent heat of vaporization, amounting to 247 B. t. u per lb. of carbon dioxide is available for heat absorption. Since the liquefied carbon dioxide boils at l09.6 F., an additional heat absorption of 32 B. t. u. per lb. is also available as the gasified material is warmed to room temperature. This smaller amount of heat absorption capacity is, however, not necessarily all retained in cooling the cutting tool and abrasive wheel, since it is preferable to direct the gas away from the area A to insure dust removal and eliminate icing.

The rate of feed of the carbon dioxide should be controlled by regulation of the size of the orifices 24 and pressure in the tube I9 to supply just enough cooling and lubricating effect to carry out the grinding operation. The diameters of the orifices are dependent on the type of tools being ground, the initial liquid carbon dioxide temperature, and the distance between the orifice and the edge being ground. The distance between the orifices and the area where the heat is generated is normally the place where the greatest amount of carbon dioxide contacts the area.

Experimental tests have shown that it is not necessary to have a constant flow of carbon dioxide striking the tool continuously during the grinding operation, and the operator may interrupt the flow of carbon dioxide intermittently, until the temperature rise indicates that more coolant should be fed to the abrading area.

From the foregoing description, it will be understood that the grinding and resurfacing of carbide tools by means of an abrasive surface is improved and expedited according to this invention by feeding liquid carbon dioxide or other liquefied gas directly to the area of contact between the tool and the abrasive surface to utilize the latent heat of vaporization of the liquefied gas for simultaneously cooling and lubricating the operation.

It will be understood that various modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. The method of grinding a carbide cutting tool which comprises contacting said cutting tool with an abrasive surface, relatively moving said tool and said surface to resurface said cutting tool, and directing a stream of a liquefied gas which is gaseous at room temperatures and atmospheric pressures at the area of contact between said tool and said surface.

2. The method of grinding a carbide cutting tool which comprises contacting said cutting tool with an abrasive surface, relatively moving said tool and said surface to resurface said cutting tool, and directing a stream of liquefied carbon dioxide at the area or" contact between said tool and said surface.

3. The method of grinding a carbide cutting tool which comprises contacting said cutting tool with the suriace of a rotating wheel having abrasive characteristics, and directing a stream of a liquefied gas which is gaseous at room temperatures and atmospheric pressures tangentially to the surface of the wheel at the area of contact between said tool and said wheel.

4, The method of grinding a carbide cutting tool which comprises contacting said cutting tool with the surface of a rotating wheel having abrasive characteristics, and directing a stream of liquefied carbon dioxide tangentially to the surface of the wheel at the area of contact between said tool and said wheel.

5. The method of grinding a carbide cutting tool which comprises contacting said cutting tool with the surface of a rotating wheel having abrasive characteristics, directing a stream of a liquefied gas which is gaseous at room temperatures and atmospheric pressures to the area of contact between said tool and the surface of said wheel, absorbing heat from the grinding operation through the latent heat of vaporization of the liquefied gas, and directing the gas away from the tool and the wheel.

6. The method of grinding a carbide cutting tool which comprises contacting said cutting tool with the surface of a rotating wheel having abrasive characteristics, directing a stream of liquid 6 carbon dioxide to the area of contact between said wheel and said tool, maintaining an atmosphere of carbon dioxide in a state of vaporization at said area, and directing the resulting gas away from said tool and said wheel.

'7. The method of grinding a tool which comprises contacting said tool with an abrasive surface, relatively moving said tool and said surface to re-surface said tool, releasing adjacent the area of contact of said tool and said surface a liquefied gas which is gaseous at room temperatures and atmospheric pressures, and directing the released gas in a stream to said area of contact between said tool and said surface.

8. The method of grinding a cutting tool which comprises contacting said cutting tool with the surface of a rotating wheel having abrasive characteristics, releasing liquefied carbon dioxide adjacent the area of contact between said tool and said wheel, and directing the released carbon dioxide in a stream tangentially to the surface of said wheel at said area of contact between said tool and said wheel.

WILLIAM H; WEST, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 375,821 Hyde et a1. Jan. 3, 1888 1,016,585 Solem Feb. 6, 1912 1,302,907 Gabus May 6, 1919 1,311,992 Perkins Aug. 5, 1919 1,862,135 Bucky June I, 1932 2,182,952 Todd et al Dec. 12, 1939 2,384,225 Wilson Sept. 4, 1945 OTHER REFERENCES Diamond Tools, by Paul Grodzinski, published by Anton Smit & Co. Inc., 333 W. 52nd St, New York 19, N. Y., 1944.