US1526894A - Method of heat-treating cutting tools - Google Patents

Description

A. E. BELLIS METHOD OF HEAT TREATING CUTTING TOOLS Filed Sept. 8, 1923 INVENTOR JZrZZzuLEZ BYC ATTOQN Y'- Patented Feb. 17, 1925.

V UNITED STATES A 1,526,894 PATENT OFFICE.

ARTHUR E. BELLIS, OF' NEW HAVEN, CONNECTICUT, ASSIGNOR T BELLIS HEAT TREATING COMPANY, OF BRANFO-RD, NECTICUT.

CONNECTICUT, A CORPORATION OF CON- METHOD OF HEAT-TREATING CUTTING- TOOLS.

Application filed September 8, 1923. Serial No. 661,558.

To all whom it may concern.-

Be it known that I, ARTHUR E. BELLIS, a citizen of the United States, and a resident of New Haven, county of New Haven,

and State of Connecticut, have invented cer-- tain new and useful Improvements in Methods of Heat-Treating Cutting Tools, of

which the following is a specification.

This invention relates to an improved methodpf heat treating cutting tools and in its broader aspect, contemplates the heat treatment of the tool in such manner that maximum hardness of all parts of the cutting point or points of the tool is secured,

while other portions of the tool possess a high degree of toughness and resistance to tensile strains.

In the heat treatment of cutting tools and particularly, high speed tools such as rock drills, it has heretofore been the general practice to subject the tool to immersion in a lead bath or to treatment in a muffle furnace. In the lead bath treatment, owing to the relatively high viscosity of the lead,

there is an unequal distributiomof heat and different parts of the tool which it is desired to subject to the same heat treatment, are heated to relatively different temperatures. Likewise, in the use of a muffle furnace, it

has been found exceedingly diflicult, if not impossible, to secure a uniform heating of the different parts of the tool.

By means of my improved method, to be hereinafter described in detail, "I am en- 85 abled to subject different portions of the tool element to heat treatment for relatively different periods of time and secure an absolutely uniform temperature of all parts of the different sections or portions of the 4.0 tool, so that a desired degree of hardness may be obtained in different portions of the tool, as for instance, the cutting point or points, while the remaining portions of the tool may be treated so as to secure maximum toughness or tensile strength thereof-z To this end, in carrying out my improved method, I employ a bath, consisting of chemical salts capable of being heated to a relatively high degree without volatilization. In a bath of this character, the cutting oints of the tool are first immersed and t e remaining portion of the tool is then slowly immersed in the bath so that such portion of the tool is subjected to the heat period of time, will be of less hardness, but

very tough and capable of resisting high tensile strains.

I have found the improved method particularly advantageous in the heat treatment of rock drills for the purpose ofsex curing maximum hardness and resistance to frictional wear of the bit points of thedrill while the pilot end of the drill which is mounted in the rotary cutting head will be of great tensile strength. It has been found that drills thus treated require resharpening only at relatively infrequent intervals, the cutting edges of the bit points retaining their sharpness for a relatively long period of time. While I have referred to' the invention as especially adapted for the heat treatment of rock' drills, it will wise be advantageously employed in the heat treatment of cutting tools employed for various other purposes where maximum hardness of the cutting point with a high degree of tensile strength in the other parts of the tool is required.

In the accompanying drawing I have illustrated a conventlonal type of rock-drill, the illustrated example showing the drill body 5 provided with a bit having four diametrically extending cutting points 6 at one of its ends. The body 5 at its opposite end is formed with the threaded pllot shank 7 whereby the drill is connected to the rotary cutting head in the usual manner. The specific tool which I have selected for purposes of illustration constitutes no essential part of the present invention, and it will, therefore, be understood that my improved method of heat treatment may be applied in connection with tools of various sizes and shapes provided with a greater or. less various other salts.

number of the cutting points and used for a variety of different purposes.

In one practical embodiment of my invention I provide a salt bath, such for instance as that disclosed in my Patent, No. 1,491,510, issued April 22, 1924, the said bath preferably consisting of an eutectic mixture of a plurality of salt components.

One characteristic bath may consist of sodium chloride (NaCl) and sodium carbonate (Na GO in such relative proportions that the mixture has a melting point less than that of the individual salt components and a volatilization tem erature of approximately 1600 F. The me ting point temperature and the volatilization temperature will of course, vary in accordance with relative proportions of the salt components. I have also found it advantageous in many cases to use chromium salts in place of the chloride and it will, therefore, be understood that the above reference to a particular salt bat-h composition implies no limitations as the bath might be prepared from It is, however, an essential characteristic of the bath that it has very low viscosity and, therefore, rapid heat conductivity so that all parts of the bath solution are uniformly heated to the same temperature.

In the heat treatment of rock-drills such as that illustrated in the drawing, for a drill having a carbon oontentl of .40 of 1% or greater, the bath is heated to a temperature of approximately 1520 F. and maintained at such temperature during the entire heat treatment period. The cutting points of the drill bit are then immediate- 1y immersed in the bath solution from the cutting edges thereof to a point substantially-that indicated by the line B in the drawing. The immersion of the bit is then slowly continued so that approximately 110 seconds is consumed in the immersion of the bit to the point indicated by the line C, it being noted that this portion of the immersion movement includes the main body part of the bit. The remainder of the bit, consisting of the pilot shank 7, is then immediately immersed and allowed to remain in the bath for a. period of ten seconds. It will thus be apparent that the whole period of heat treatment extends through approximately two minutes after which the tool is immediately withdrawn and quenched in Water. After quenching of the tool, the pilot end 7 thereof is immersed in a bath similar to that above referred to having a temperature of 700 F. for a period of two minutes to draw the temper of the metal.

After the tool has been treated in the manner above described, it will be found by test that the bit pgoints 6 of the tool be-' tween lines A and have a hardness of 90 schleroscope While the body portion of aeaaeee the-tool between the lines B and C has a hardness varying from 90 to 55 schleroscope While the remaining pilot end portion of the tool between the lines C and D has a hardness of 55 schleroscope. It will of course be apparent that these stated degrees of hardness are only approximate and that it is not to be expected in the operation of the improved method, that variations thereof will not occur. Indeed, in some cases it might be found desirable to increase or decrease the hardness of the different portions of the tool by subjecting the same to the heat treatment temperature in the bath solution for greater or less periods of time than those stated.

However, in general practice it has been found that substantially the stated degrees of hardness of the different parts of the tool give the best results particularly in the operation of rock-drills, which, as is well known, are frequently subjected to very severe usage. By reason of the fact that the heat treatment of the different parts of the tool occurs in a bath of, low viscosity, all parts of the bit points Will be heated to precisely the same temperature and will, therefore, possess exactly the same degree of hardness throughout their structure. The same is-also true of the intermediate body section of the tool and of the pilot end portion. It is also a characteristic feature of the bath that when the tool is withdrawn therefrom all of the surfaces are covered with a film of the bath material which affords a complete protection against oxidization from the atmosphere. As this bath solution does not possess the tenacity of a lead bath, it will not adhere to the metal surface at spaced points and thus subject certain portions of .the tool to prolonged heating. 7

Accordingly, it will be seen that by means of my improved method the necessity of regrinding or sharpening the bit points at more or less frequent intervals is, to a certain extent, obviated and the drill may be continuously used for a relatively long period of time without requiring re-sharpening. Also, by the uniform heat treatment of the pilot end of'the drill for a shorter period of time, a uniformly tough homogeneous structure thereof is obtained which will offer maximum resistance to tension or torsional strains.- Accordingly it will be appreciated that by heat treating the drills in accordance with my present invention,

the maintenance and operating cost of rock U remaining portions of the tool in thebath for varying periods of time so that when the tool is withdrawn from the bath and quenched, the cutting part thereof will possess a higher degree of hardness than the remaining portions of the tool.

2. In the art of heat treating cutting tools, that step which consists in quickly ii'nmersing the entire cutting part of the tool in a fused salt bath and then slowly continuing the immersion ,of an intermediate portion of the tool during a definite period of time and finally quickly immersing all of the remaining portion of the tool where by when the tool'is withdrawn from the bath and quenched, the cutting part thereof will possess the greatest degree of hardness, while the other portions of the tool .will

successively decrease in hardness.

3. In the art of heat treating cutting tools, that step which consists in quickly immersing the entire cutting part of the tool in a fused salt bath maintained at a constant temperature, and then slowly con-' tinuing the immersion of an intermediate portion of the tool during a definite period of time and finally, quickly immersing all of the remaining portion of the tool whereby when the toolis withdrawn from the bath and quenched, the cutting part thereof will possess the greatest degree of hardness, while the other portions of the tool will suecessively decrease in hardness.

4. In the art of heat treating cutting tools, that step which consists in quickly immersing the entire cutting part of the tool in a fused salt bath having a temperature of approximately 1520 F., and then slowly continuing the immersion of an intermediate portionof the tool during a definite period of time and finally, quickly immersing all of the remaining portion of the tool whereby when the tool is withdrawn from the bath and quenched, the cutting part thereof will possess the greatest degree of hardness, while the other portions of the tool will successively decrease in hardness.

5. The method of heat treating rock drills having a cutting bit at one end and a pilot at the other end whichconsists in quickly immersing the cutting parts of the bit in a fused salt bath maintained at a constant temperature and then slowly continuing the immersion of the intermediate body section of the tool through a definite period of time and then finally, quickly immersing the pilot end of the tool and subjecting the same to the'temperature of the bath solution for a relatively short period of time, whereby, when the tool is withdrawnfromthe bath and quenched, the cutting parts thereof will possess the greatest degree of hardness while the intermediate and pilot end portions of and then finally, quickly immersing the pilot end of the tool and subjecting the same to the temperature of the bath solution for a relatively short period of time, whereby when the tool is withdrawn from the bath and quenched, the cutting parts thereof will possess the greatest degree of hardness while the intermediate and pilot end portions of the tool will gradually decrease in hardness, and thereafter drawing the temper of the pilot end of the tool by immersing the same in a salt bath ofrelatively low temperature fora period of two minutes.

7. The method f heat treating rock drills having a cutting bitat one end and a pilot atthe other end which consists in quickly immersing the cutting parts of the bit in a fused salt bath having a temperature of approximately 1520 F. and then slowly continuing the immersion of the intermediate body section of the tool through a definite period of time and then, finally quickly immersing the pilot end of the tool and subjecting the same to the temperature of the bath solution for a relatively short period I same in a salt bath having a temperature of approximately 700 F. for aperiod of two minutes. i I

In testimony that I claimthe foregoing as my invention, I have signed my name hereunder.

ARTHUR E. BELLIS.

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