US 2073501 A
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March 9, 1937. A. R. STARGARDTER COLORING AND HARDENING STEEL Filed 0018, 1932 ZZZ? 7 7763 Patented Mar. 9, 1937 UNITED PATENT OFFICE COLORING AND HABDENING STEEL Application ()ctober 8,
This invention relates to the treatment of steel in producing hardened and tempered articles with blued or other colored surface finish. In one aspect it consists in a novel method characterized by the step of subjecting the heated steel to the oxidizing action of the products of combustion of an air gas mixture of controlled composition while the steel is heated to its critical point preparatory to the hardening step. In another 1 aspect it consists in novel apparatus herein shown as adapted for use in practicing such method. While my invention is of general application, it has a particular held of use in the treatment of strip steel, such, for example, as that employed in the manufacture of safety razor blades, and it is herein disclosed as it is carried out in that field.
It will be understood that when steel is heated to temperatures above its lower critical point in preparation for hardening and while in contact with the atmosphere or a medium having an oxidizing efiect equal to or greater than the atmosphere, the surface of the steel is oxidized far beyond the blue color, becoming gray and also it is inclined to scale.
I have discovered that by limiting and controlling the oxidizing efiect of the atmosphere or gas mixture surrounding the steel while the latter is heated above its critical point, preparatory to hardening, a blued finish may be imparted to the steel independently of its hardness or temper. By varying the oxidizing effect of the gas mixture in contact with the steel, the color of its finish may be varied as desired and blue or other colors secured. It is thus possible to produce steel articles of any desired degree of hardness having a surface finish of any color desired and bearing no predetermined relation to the hardness of the steel. For example: I may impart a clued finish to glass-hard steel, or to steel of a hardness corresponding, in the ordinary drawing process, to straw color. In other words, by my invention I am enabled to produce a colored steel of any desired degree of hardness having any desired surface color merely by modifying the conditions under which the usual step of heating the steel preparatory to hardening is carried out.
In my prior Patent No. 1,948,192 granted February 20, 1934, I have disclosed and claimed a method of treating steel of this general character and adapted particularly to be carried out in connection with a gas-fired furnace. The method of the present invention is adapted to be carried 55 out in connection with such furnaces or with 1932, Serial No. $36,823
furnaces heated by any other method and any form of heat in-put. it is also adapted to the successful treatment of certain grades of steel which have not heretofore been treated with entire success by the method of my earlier patent, since by means of the present invention a closer and more discerning control is attainable.
One gas mixture suitable for carrying out the method of the present invention is the product of the combustion of air and illuminating gas, mixed in proper proportion and burned out of contact with steel to be treated. Such products of combustion have an oxidizing efiect upon the steel which is less than that of atmospheric oxygen so that when the steel is heated to or above its critical point in the presence of this gas, a limited surface oxidation takes place and this may be restricted to that corresponding to a blue or other color. In carrying out the method of my invention, the products of combustion thus prepared are caused to flow along the strip steel while the latter is being fed through a zone in which it is heated to a temperature above its lower critical point. The strip is accordingly colored by oxidation at the same time and in the same heat by which it is prepared for hardemng.
While the method of my invention is not limited to any specific apparatus, I have herein shown one example of a construction which possesses certain advantages when employed in carrying out the method. This apparatus consists in a fitting providing a chamber in which the strip to be treated and the gas mixture are first brought into contact with each other and from which they are simultaneously advanced to the mufiie or other member defining the heated zone.
The nature of my invention will be best understood and appreciated from the following description of one manner in which it may be carried out in connection with the novel apparatus shown in the accompanying drawing, in which:
Fig. 1 is a. plan view of the apparatus, certain portions thereof being broken away to expose the path of the steel strip;
Fig. 2 is a corresponding view in front elevation;
Fig. 3 is a view in longitudinal section on an enlarged scale of the mixing chamber and burner; and
Fig. 4 is a view in cross-section on the lines 4-4 of Fig. 3.
As shown in the drawing, the apparatus is supported at convenient height upon a bench or 2 frame ln which is provided at one end with a bracket l2 for the supply reel 14 from which the strip steel is drawn and at the other end with a bracket I6 for the receiving reel l8 upon which the treated strip -steel is rewound. The steel strip is advanced through the apparatus under tension by a pair of feed rolls 20 which are arranged to be driven at appropriate speed by means not herein shown. In passing from the supply reel I 4 to the receiving reel l8, the steel strip is guided in a straight line path successively through a gas chamber 22, a heater 32, chilling plates 62 and a drawing heater 64. These are mounted in a straight line upon the surface of the bench or frame l0 and adjacent to each other, so that the strip may pass without interruption directly from one to the next in the series.
The gas chamber 22 comprises a T-shaped fitting having an inclined interior partition or'wall 24 located midway between its ends and provided with a slit which constitutes an inlet port for the passage of the steel strip I5. The side inlet of the fitting is directed rearwardly and interiorly threaded for connection with the combustion chamber 38. The inner end of the T fitting is exteriorly threaded to receive the coupling 28 which serves as the connecting medium between the gas chamber and an elongated muflle 38 of the heater 32. The muiile 38 of the heater 32 is maintained by any suitable medium, such as gas or electricity, at a temperature above the lower critical point of the steel being treated, for example above 1400 F. and the strip steel is heated to that temperature in its passage through the mufile.
The inlet 26 of the gas chamber or receiver is connected through a union 34 and nipple 36 with the lower end of the combustion chamber 38. This chamber 38 has a square bottom 40, into which the nipple 36 is threaded, and a square top 42 perforated to receive a burner 50 which will be presently described. The side walls of the combustion chamber are rectangular and it has an interior flue which is formed by a pair of elongated porcelain shells or sleeves 46 rectangular in cross-section as shown in Fig. 4 and arranged end to end between the ends 42 and 40 of the combustion chamber. The space between the outer side walls of the combustion chamber and the shells 46 is filled with refractory heat-insulating material such as asbestos in which may be embedded spacing members 45. The shells 46 are exteriorly threaded and wound in the threads thereof is resistance wire 48 by which the combustion chamber may be maintained at a temperature above the ignition point of the gas mixture to be burned.
The burner or mixing nozzle 50 is provided with a reduced outlet which extends through the inlet end 42 of the combustion chamber. The outer end of the mixing nozzle is closed by a perforated plug 52 into which is threaded the end of a gas pipe 54. The periphery of the burner is perforated by air inlet ports 55 and provided with a circumferential channel for a perforated ring 56, by turning which the eifective area of the air inlet ports may be adjusted. The contacting ends of the shells 46 are notched to form an opening midway of the inside of the mixing chamber and with this communicates a laterally-extending sleeve 58 forming an outlet passage. The outer end of the sleeve 58 is closed, or partially closed, by a slidable damper 60 and in this manner the amount of burning gas escaping from the mixing chamber may be regulated independently of the combustible mixture delivered to the flue by the burner 58. The combustible mixture supplied by the burner is ignited and burns with a flame extending inwardly into the mixing chamber. The products of this combustion are further heated in the chamber which is maintained at an elevated temperature by the resistance wires 48 and then the hot products of combustion are discharged through the nipple 36 and proceed into the mufile 30 via the receiver 22.
In carrying out the method of my invention with the apparatus herein illustrated, illuminating gas is supplied to the burner 50 and delivered to the outer end of the combustion chamber 38, inspirating with it a regulated'amount of air through the ports 55. The interior of the combustion chamber is maintained at a temperature above the ignition point of the gas so that the latter is immediately ignited upon leaving the burner and burned with a flame which may completely fill the chamber and pass into the nipple 36. The products of combustion pass out of the outer end of the combustion chamber through the union 34 and enter the intermediate or gas chamber 22. The pressure of the gas thus delivered and its composition are controlled to some extent by opening or closing the ports 55 and also the damper 60 in the upper side of the combustion chamber. The gaseous products of combustion are delivered directly upon the steel strip l5 which is led into the muille 30 through a narrow slit in the partition 24. The current of the hot products of combustion is defiected by this partition towards the furnace 32 and fiows with the strip l5 through a slit or orifice in the end of the muiile 30, enveloping the strip in its passage through the heated muflie, where the steel strip is maintained at a temperature above its lower critical point, as, for example 1400 F.
It will be noted that the strip and the gaseous products of combustion are first brought together in the gas chamber 22 and then simultaneously advanced or delivered from this to the receiving end of the mufile 30. In its passage through the muflie, the steel strip I5 is oxidized by the hot products of combustion in the manner above explained. The strip thus colored passes directly from the furnace 32 to chilling plates 62, preferably water-cooled and effective to harden the strip continuously as it is moved between them. The hardened and blued strip next passes to the drawing furnace 64 which is heated to a temperature appropriate to draw the temper of the steel strip from the very hard condition in which it leaves the chilling plates 62 to the temper best suited for the purposes for which the strip steel is intended.
It will be observed that the feeding rolls 20 maintain the strip I 5 under tension in passing from the supply reel l4, retaining it in a smooth fiat condition during the steps of heating and oxidizing in the furnace 32. Treatment of the steel in this condition contributes to the formation of a smooth, continuous and homogeneous surface finish.
Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:--
1. The method of hardening and coloring steel, which consists in heating the steel to a temperature above its lower critical point, burning an air-gas mixture out of contact with the steel and controlling the resulting products of combustion so that they have a predetermined oxidizing effect which is less than atmospheric, leading said products of combustion in a current contacting the heated steel, and then chilling the steel and thereby producing a hardened and colored product.
2. The method of hardening and coloring steel, which consists in burning an air-gas mixture in a closed chamber out of contact with the steel and controlling the resulting products so that they have a predetermined oxidizing effect which is less than atmospheric, leading said products of combustion to the steel and flowing them in a current along the surface of the steel while the latter is heated above its critical point, thereby oxidizing the same to a limited degree, and then chilling the steel to produce in one operation a hardened and colored product.
3. The method of hardening and coloring strip steel, which consists in advancing the strip through a heated muflle, burning an air-gas mixture outside the muiiie and controlling the resulting products of combustion so that they have a predetermined oxidizing efiect which is less than atmospheric, leading the products of combustion to the steel in a path disposed at an angle to the direction of movement of the strip in the muflie, causing said products of combustion to envelop said strip while the latter is heated above its critical point and to oxidize the surface thereof,
to a temperature above the critical point of the steel, flowing into contact with the strip in the heated zone the products of combustion of an air-gas mixture of controlled composition having a predetermined oxidizing effect less than atmospheric, the major portion whereof being burned out of contact with the strip, and then chilling the strip to produce at a single operation a hardened and blued steel strip.
5. The method of continuously hardening and blueing strip steel, which consists in drawing the strip through an elongated muiile heated to a temperature above the critical point of the steel, burning outside the muffle an air-gas mixture of controlled composition to produce products of combustion of a predetermined oxidizing eflect which is less than atmospheric, conducting said products of combustion into contact with the surface of the strip while the latter is maintained by the muflle at a temperature above the critical point of its steel, and then progressively chilling the strip immediately upon leaving the mume to produce a hardened and blued product.
6. The method of continuously hardening and blueing strip steel, which consists in feeding the strip through a zone heated to a temperature above the critical point of the steel, and as the strip enters said zone, admitting thereto, through a restricted orifice and at relatively high velocity, gaseous products of combustion having an oxidizing effect less than that of atmospheric oxygen, and subsequently chilling the strip and thereby producing a hardened and blued strip.
ALBERT R. STARGARDTER.