US2027065A - Method and apparatus for heat treating high speed steel - Google Patents

Description

Jan. 7, 1936. c. B. SADTLER- 2,027,065

METHOD AND APPARATUS FOR HEAT TREATING HIGH SPEED STEEL Filed Oct. 15, 1930 ATTORNEY-5 Patented Jan. 7, 1936 PATENT OFFICE r METHOD AND APPARATUS FOR HEAT TREATING HIGH SPEED STEEL Chester B. Sadtler, Rockford, 111., assignor to Barher-Colman Company, Rockford, 111., a corporation of Illinois Application October 15, 1930, Serial No. 488,77 3

9 Claims.

The invention relates generally to the heat treating of steel and more particularly to a method and apparatus for heat treating high speed tool steel.

The general object of the invention is to provide a new and improved method and apparatus for heat treating steel which will function at high temperatures without causing scaling or other deterioration of the surface of the steel.

Another object is to provide a novel apparatus together with an improved method whereby tools already formed and sharpened may be heated relatively slowly and uniformly to high temperatures without losing their form or cutting edge and so that any distortion or enlargement is uniform in character and readily compensated for.

Another object is to provide a new and improved apparatus for heating a treating bath uniformly and to the desired high temperature without undue deterioration of the container for the bath or the article being treated.

Further objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawing, in which:

Figure 1 is a central vertical section through a preferred form of the apparatus.

Fig. 2 is a plan view thereof with certain portions broken away.

Fig. 3 is a fragmentary section along the line 3-3 of Fig. 1.

While the invention is susceptible of embodiment in many diflerent forms, I have shown in the drawing and shall herein described in detail one such embodiment with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be pointed out in the appended claims.

As illustrated in the drawing the preferred form of the invention comprises a furnace having a base portion 5., an annular side wall 6 positioned'on and extending upwardly from said base portion and surrounding a recess 1 in the base portion, and a cover 8 positioned on the wall and substantially closing the upper end thereof. These parts of the furnace define a central furnace chamber 9 the floor of which is formed by a refractory bed Ill positioned in the recess 1.

A crucible or container H is positioned on the floor of the chamber 9 and contains a bath l2 in which the articles to be treated are immersed during the treating process. This container is pref erably made of pure nickel. It is herein shown surrounded by an annular wall or muflle I3, of a material having a high thermal conductivity such as bonded silicon carbide or carborundum, which is spaced uniformly from the container wall and 5 extends above the top thereof and is arranged to transmit heat to the container and heat the container and bath uniformly as hereinafter more fully described. The bath in the preferred form of the invention is substantially pure fused boric 10 oxide, the container ll being open at its upper end so that an article such as a cutter l4, may be inserted by means of a suspending rod I5.

The floor It as indicated herein comprises a layer of crushed fused alumina which is placed 15 upon a layer of brick IS. The crushed fused alumina may be placed in the bottom of the furnace and rammed to as compact a mass as is possible. A bed comprising approximately fifty percent crushed fused alumina of one-half to one and one-half inch size and fifty percent of four to sixteen mesh has been used with success. In this way an eifective support is provided so that when the carborundum mullle and nickel container are placed on top of this alumina bed and the furnace is brought up to temperature, there is no appreciable settling of either the muflle or nickel container. The alumina is unaffected either chemically or mechanically, by the carborundum or nickel and is substantially non-sintering. If, during operation of the apparatus boric oxide should drip onto the furnace floor, the crushed fused alumina is preferably agitated or worked at intervals of approximately a month so as to prevent the alumina from sintering.

The cover 8 of the. furnace comprises side tiles I1, baflle bricks l8 at the ends and a pair of laterally movable doors l9 and 20. As indicated most clearly in Fig. 3 the bricks 3 project over the combustion chamber and form baflles' which force the furnace gases to pass over the upper edge of the carborundum mufile and thence outward under the sliding doors. I'he doors are herein disclosed as having bricks 2| protecting their lower sides and are mounted by means of ball bearings 22 on rectilinear ways 23 so as to permit them to be separated and enable an operator to insert and withdraw materials into and from the bath. The doors are preferably covered by sheet nickel pans 24 which cover the entire doors and serve to collect any boric oxide which may drip from the cutters as they are removed from the bath and also drippings when the container is bailed out. This effectively prevents rapid deterioration of the brick work which might otherwise become somewhat impregnated by the boric oxide.

The nickel container holding the bath of fused boric oxide is heated uniformly by the muffle l3 which surrounds and is uniformly spaced from the Wall of the container. The cylindrical wall 6 of the furnace is provided with openings 25 for tuyeres for the admission of combustion gases. These openings are preferably positioned so that the gases will be admitted in lines tangent to the cylindrical muflle I3. This produces a rotary movement of the gases around the muffle and help to maintain a more uniform temperature in the furnace. Since the muffle extends above the top of the container, cold spots above the bath are avoided. The temperature of the bath may be determined by a suitable thermo-electric pyrometer 26, a second pyrometer 21 being preferably provided to indicate the temperature surrounding the container.

By using pure nickel for the container for the boric oxide bath there is no constituent present which will oxidize under the conditions of ordinary gas fired furnaces. The combustion gases admitted to the furnace produce a flame which has a slightly reducing effect with respect to the nickel so that there is no oxidation at the temperatures maintained. The high melting point of nickel provides ample margin in high speed steel treating wherein the temperature rarely exceeds 2400 F. and therefore the container does not contaminate the bath with metallic oxides. Furthermore there is no rapid deterioration of the container.

The process consists in immersing one or more tool blanks, such as the formed cutter I4, suspended on a nickel rod, into the bath of fused boric oxide in the container. The cutters may be either preheated or may be immersed cold. If they are cold the initial heating is at a relatively slow and uniform rate since a film of boric oxide immediately congeals around each cutter and acts as an insulating material and prevents direct contact of the cutter with the hot liquid bath, thus enabling the temperature of the cutter to be raised at a practically uniform rate throughout its mass. As the melting point of the boric oxide is reached around 900 to 1000 F. this film disappears and the heating proceeds more rapidly due to the direct liquid contact with the cutter. Because of the surrounding muffle, transmission of heat to the container is substantially uniform and uniform heating of the bath is obtained.

The pyrometer 25 provides a check on the temperature and hence on the heating and as the temperature approaches the desired point, the cutter may be inspected to see if it is finished. When the treatment is finished, as determined preferably by color and light test, it is removed from the boric oxide bath and quickly subjected to the next operation which is generally a cooling medium. When cutters are withdrawn from the container the viscosity of the molten boric oxide is such that it forms a film on the cutters and seals the surface of the cutters against the oxygen of the air. Although this film of boric oxide hardens quickly on cooling, it is readily soluble in an alkaline solution such as sodium carbonate and is useful in protecting cutters and preventing oxidation while they are being transported from the treating bath to the cooling medium. The transposition of the cutters from one bath to the other is effected very quickly while oxidation. the bath attack the container appreciably, it has the film of boric oxide is effective to prevent exposure of the cutters to the air.

After the cutters have been removed from the fused boric oxide bath they may be given such cooling, drawing and other treatments as may be desired.

The apparatus as disclosed herein is particularly adapted for successful and efficient use of the method. The provision of a cylindrical mufiie surrounding and extending above the bath container provides for uniform heating of the container and bath, and the bed formed of nonsintering refractory inaterial provides an effective support for muflle and container. The use of a boric oxide bath in a. nickel container prevents the formation of metallic oxides and by transferring the heated articles quickly from the furnace to the cooling means, the film of boric oxide remaining on the articles is effective to prevent Since neither the heating gases nor a long life. Furthermore due to the slow and uniform heating obtained by utilizing the method herein disclosed, any distortion or enlargement of the cutters is uniform in character and may be readily compensated for in the preceding forming and sharpening operations.

I claim as my invention:

1. An apparatus of the character described comprising, in combination, a furnace having a furnace chamber into which the heating medium is admitted around the sides, a refractory bed on the floor of said chamber, a container of pure nickel positioned in the chamber, and a. muffle surrounding and extending above said container and spaced uniformly therefrom for heating said container uniformly.

2. A method for heat treating high speed steel which comprises immersing a steel article into a bath of fused boric oxide, heating said bath to the desired temperature in a container of pure nickel so as to prevent the formation of metallic oxides in the bath, and transferring the heated article quickly to a quenching medium while the article is protected from contact with air.

3. A method for heat treating high speed steel which comprises immersing a steel article into a bath of fused boric oxide, heating said bath to the desired temperature in a container capable of withstanding said temperature without causing the formation of metallic oxides in the bath and then quenching the article.

4. A method for heat treating high speed steel which includes immersing a steel article into a bath of fused boric oxide and heating said bath to the desired temperature in a container adapted to prevent the formation of metallic oxides in the bath.

5. A method for heat treating high speed steel which comprises heating the steel article to the desired temperature in a bath of fused boric oxide contained in a crucible of pure nickel and then quenching the heated article in an oil bath before any oxidation occurs in air.

6. A method for heat treating high speed steel which comprises heating the steel article to the desired temperature in a bath composed substantially entirely of fused boric oxide and then quenching the heated article before it becomes oxidized in air.

7. A method for heat treating high speed steel which comprises immersing a steel article into a bath of fused boric oxide preventing the formation of metallic oxides in the bath by holding the bath in a container of pure nickel, and maintain- 75 ing uniformity in the heating ofthe bath by a mufile uniformly surrounding and extending above the container.

8. An apparatus of the character described comprising, in combination, a furnace having a furnace chamber into which the heating medium is admitted around the sides, a refractory bed on the floor of said chamber, a container of pure nickel positioned in the chamber, a muifle sur- 10 rounding and extending above said container and spaced uniformly therefrom for heating said container uniformly, and a bath of fused boric oxide in said container.

9. A method for heat treating high speed steel which includes immersing a steel article into a bath of fused boric oxide and heating said bath to the desired temperature in a nickel container adapted to prevent the formation of metallic oxides in the bath.

CHESTER. B. SADTLER.

Images