US2898254A

US2898254A - Method of inducing permanent set in razor blade strip

Info

Publication number: US2898254A
Application number: US431285A
Authority: US
Inventors: Forsberg Frank
Original assignee: Gillette Co LLC
Current assignee: Gillette Co LLC
Priority date: 1954-05-20
Filing date: 1954-05-20
Publication date: 1959-08-04
Anticipated expiration: 1976-08-04

Description

States Patent METHQD 0F ENDUCING PERMANENT SET IN RAZUR BLADE STRIP No Drawing. Application May 20,1954 Serial No. 431,285

8 Claims. (Cl. 148-2'1.5)

This invention relates to hardened steel razor blades in coiled strip form and pertains more specifically to such razor blades having high hardness and being capable of being bent on a relatively small radius without danger of breaking.

It has previously been proposed to provide so-called reel-type razors in which a razor blade in continuous strip form is fed from a supply coil through a holder to a take-up reel, the portion of the blade in the holder being the only operative portion of the blade at any given time. Advancing a fresh portion of the blade from the supply coil into the holder provides a fresh cutting edge without the necessity for changing individual blades. One of the problems involved in the manufacture of such a razor has been to provide a strip razor blade having sufficient hardness so that it will provide a keen cutting edge and maintain that edge for a sufliciently long period of time. Blades having the desired degree of hardness are quite brittle, as is well known, and can safely be bent only slightly without danger of breaking, so that it has been necessary either to provide a supply coil and take-up reel so large in diameter that the Ice Patented Aug. 4, 1959 razors, the coiled blade strip, which may be as much as 50 inches or more in length, is ordinarily maintained in tightly coiled configuration on a radius as small as 50 to 70 times its thickness for a period of many months before use; and it has been found that even though the coiled blade may be intact when it leaves the factory, it

v is subject to breakage during the storage period. The

razor has been bulky and unwieldy to handle or else to Another object is to provide a hardened steel razor blade strip capable of being coiled ona relatively small radius and of being maintained in such coiled configuration for an extended period of time without breakage.

Still another object is to provide a simple and inexpensive method of making a hardened steel razor blade strip capable of being bent on a relatively small radius without danger of breaking.

Other and further objects will be apparent from the description which follows.

It has been found that optimum sharpness and edgeretaining properties in steel razor blades are obtained when the blade has a Vickers hardness number (2 kg. load) from 785 to 850, preferably from 810 to 840. This hardness is customarily obtained by heating a' steel containing at least 0.50% carbon above the critical point, then quenching in water or on water-cooled plates. The steels usually employed have a. carbon content from 0.50% to 1.3%, preferably from 1.0% to 1.3%. However, obtaining this degree of hardness by conventional methods necessarily involves embrittlement of the blades, and the blade ordinarily cannot be bent on a radius much less than 100 times the thickness of the blade and main tained in this condition for any extended period of time without danger of breaking. In the case of reel type thickness of the blade strip is not critical, although most satisfactory results have been obtained with blade strips from 0.002 to 0.004 inch thick. The thinner the blade, of course, the longer the blade strip may be for a coil of given outside dimensions.

In accordance with the present invention, the razor bladestrip may be hardened and sharpened in the usual manner, then is coiled upon itself on a radius sufficiently large so that breakage does not occur during the few hours ordinarily required to complete the processing. While in this coiled configuration, the blade is heated at an elevated temperature which is ordinarily no greater than 350 F. for a peroid of time sufiicient to set the blade permanently in a coiled configuration and is then allowed to cool in air to room temperature before there has been any substantial reduction in hardness of the blade.

If desired, of course, the blade strip may be sharpened after it has been permanently set in coiled form, although in practice it has been found to be more convenient to sharpen the blade prior to the setting operation of the present invention. Any of the other conventional steps in blade manufacture such as etching, lacquering, etc. may likewise be carried out in any desired order either before or after the heat-setting operation.

The exact temperature which may be employed for the heat-setting operation will depend at least in part upon the composition of the steel. In the case of ordinary medium or high carbon steels containing from 0.50% to 1.3% carbon and not over 0.50% chromium, the temperature of the setting operation should not exceed 350 F. in order to avoid decrease in hardness. Usually the temperature is from 250-340 F., although a temperature from 280-330 F. is preferred. In the case of corrosion-resistant steels containing relatively large amounts of chromium, from about 4% to about 15% by weight, the maximum temperature which may safely be employed without reduction in hardness is somewhat less.

The time'for the setting operation also varies widely. Near the upper limit of the temperature range, only very short times, of the order of 1 to'2 minutes or less, may be employed without decreasing the hardness of the blade strip. At lower temperatures, the heating may be continued for a period of from several minutes tomany hours without sacrifice of hardness.

When the method of the present invention is applied -to blades having a very high hardness, of the order of of the blade strip may be initially, it is desirable to ad- 7 just the temperature and time of the treatment so that the finished blade has a Vickers hardness number (2 kg. load) of at least 7 85, preferably from 810 to 840.

The heating means employed is not critical. The blade strip may simply be heated in a'hot-air oven .or it may be immersedin hot.oil, molten salt, or any other suitable heatingmeansmay be employed. 7

When the heating has been continued for a suflicient period of time to give the desired set to the blade strip, the blade is allowed to cool in air at ordinary room temperature, following which it is found that the blade not only retains permanently a coiled configuration, but is capable of being bent about a relatively small radius and maintained in that bent condition for extended periods of time without breakage. The rate of cooling is not critical, and there is no necessity for quenching or accelerated cooling.

If desired, the operation may be repeated, coiling th blade about a smaller radius for the second operation than for the first.

It has also been found that the blade may advantageously be baked, before coiling, under the same conditions of temperature and time as outlined above and that this baking step makes it possible to coil the blade on a smaller radius for the heat-setting operation. For example, in the case of a steel blade strip having a thickness of 0.003 inch and a Vickers hardness number of 785-850, the strip cannot ordinarily be coiled on a radius much less than 0.25 inch without danger of breaking within a few hours. However, when the blade has been baked in air at 300 F. for 15 minutes, it may, after cooling, be coiled on a radius of 0.175 inch without risk of breakage for several hours, a period of time sufficient to enable the coiled strip to be heated as described above in order to set the strip in permanently coiled configuration. In either event, whether the strip is baked before coiling or not, the finished strip, after the heat-setting operation, may safely be maintained coiled on the same radius as employed during the setting operation for an indefinitely long period of time without risk of breakage.

It is believed that the hardening step as conventionally carried out leads to the presence of occluded hydrogen in the steel and that the baking step removes this hydrogen, thus restoring the inherent toughness of the steel, since the same results can be obtained by immersing the hardened strip in boiling water for about six minutes, or merely by letting the hardened strip stand at room temperature for one to two months. However, I do not wish to be bound to this theory.

Although, as indicated above, a conventional hardened blade strip cannot safely be coiled on a radius much less than about 100 times the thickness of the strip and maintained in that coiled configuration for an extended period of time without danger of breaking, it has been found that the strip, after hardening and sharpening by conventional methods, may be coiled on a radius about 85 times its thickness and maintained in that configuration for 21' period of several hours, which is sufiicient time under normal commercial operating conditions to carry out the heat-setting operation of the present invention. If desired, as pointed out above, the blade strip may be baked before coiling, in which case the strip may be coiled on a radius about 60 times its thickness and maintained safely in that configuration for a period of several hours to permit the heat-setting operation to be carried out. In either event, following the heat-setting operation to set the blade strip permanently in coiled form, the blade strip, upon release from confinement, will expand somewhat but will maintain a permanently coiled configuration, the inner radius of the coil being from about 200-500 times the thickness of the strip, and an outer radius from about 300 to about 700 times the thickness of the strip. Once the strip has been permanently set in such a coiled configuration, it is capable of being coiled or wound on a still smaller radius, of the order of 50-60 times its thickness and maintained in that configuration under confinement for an indefinite period of time without danger of breakage. Furthermore, the blade strip so treated may be bent quite sharply in feeding it to and from operative position in the razor without risk of fracturing it, provided that the bend is in the same sense as the permanent set of the strip. It should be noted that in the case of blade strips which have only a single sharpened edge, any burrs which are left on the unsharpened edge by the slitting operation during the fabrication of the strip are preferably disposed at the inner face of the strip as ultimately coiled.

The following specific examples are intended as an illustration of myinvention, but not as a limitation upon the scope thereof:

Example 1 A steel strip about 50 inches long, 0.1875 inch wide and 0.003 inch thick was slit from a ribbon of steel having a carbon content of 1.1% to 1.3%. The strip was hardened by heating above the critical temperature, then quenching on water-cooled plates to produce a strip having a Vickers hardness number of about 820. One edge was sharpened on a conventional machine sharpener to a razor edge.

The sharpened and hardened razor blade strip thus produced was wound upon a mandrel having a radius of 0.25 inch (0.5 inch diameter) to produce a coil having an outer radius of about 0.375 inch, being held in this configuration by a suitable ring clamp. The strip in coiled form was heated in a hot-air oven at 320 F. for 12 minutes, then allowed to cool in air to room temperature. Upon release from confinement, the coiled strip expanded to a coil having an inner radius of 1.63 inches and an outer radius of 2.13 inches.

The strip was then rewound upon a second mandrel having a radius of 0.175 inch and confined without a ring clamp having an inner radius of 0.313 inch. The strip, while maintained in this coiled configuration, was again heated in air for 12 minutes at 320 F. and allowed to cool in air to room temperature. Upon release from confinement, the strip expanded to a coil having an inner radius of 1.13 inches and an outer radius of 1.63 inches. This strip could readily be coiled on a radius equal to that on which it was wound during the second heat-setting operation and could be maintained in that coiled configuration for an indefinite period of time without breakage of the strip. Furthermore, the strip could be flexed even more sharply in the same sense as the curvature of the coil without breakage. The Vickers hardness number of the finished strip was not measurably different from that of the strip before the heat-setting operations.

The untreated strip razor blade, after hardening and sharpening, usually broke within a few days if maintained in a coil having an inner radius of 0.25 inch.

Example 2 A sharpened razor blade strip was prepared as described in Example 1, the Vickers hardness number of the strip being about 840. The strip was then baked for 15 minutes in a hot-air oven at 300 F. and allowed to cool in air to room temperature, after which it was wound upon an arbor having a radius of 0.175 inch, the completed coil being held within a ring clamp having an inner radius of 0.313 inch. While maintained in this coiled configuration, the strip was heated for 15 minutes in a hot-air oven at 300 F., then allowed to cool in air to room temperature. When released from confinement, the strip assumed a coil configuration having an inner radius of approximately 1.13 inches and an outer radius of approximately 1.63 inches. The Vickers hardness number of the finished strip was approximately 830.

The finished strip could be readily maintained in coiled configuration, the inner radius of the coil being 0.175 inch and the outer radius being 0.313 inch, for an indefinite period of time without breakage.

Example 3 A number of sharpened steel razor blade strips about 50 inches in length and having a Vickers hardness number of 785 were prepared as described in Example 1. The strips were coiled upon an arbor having a radius of 0.25 inch and confined in coiled configuration by a ring Heating, minutes: Free outer radius, inches In each case the Vickers hardness number of the finished strip was not measurably less than the initial hardness.

It was found that all of these strips could safely be coiled to an inner radius of 0.175 inch and an outer radius of 0.313 inch and maintained in that coiled configuration indefinitely without danger of breakage.

Although, as indicated by the preceding specific examples, the time and temperature of heating may vary considerably, it has been found, as indicated above, that ordinary hardened steel containing 0.5% to 1.3% carbon cannot be heated for much over 1 to 2 minutes at 350 F. without appreciable loss of hardness. On the other hand, the same steel strip may be heated for about 1 /2 to 2 hours at 300 F. without appreciable reduction in hardness, and at 250 F. the heating may be continued for many hours Without loss of hardness. At lower temperatures, of course, a longer time is required to obtain any given degree of permanent set, as shown in Example 3 above.

A single heat-setting operation as described above may sufiice to produce the desired permanent set in the razor blade strip, or, if desired, a plurality of such heatsetting operations may be carried out, the razor blade strip in each successive operation being coiled On a smaller radius in order to achieve an ultimate radius smaller than can be obtained in a single heat-setting step.

Although I have herein described specific embodiments of my invention, I do not intend to limit myself solely thereto, but to include all the obvious variations and modifications within the spirit and scope of the appended claims.

I claim:

1. The method of making a hardened steel strip razor blade capable of being coiled upon a small radius and maintained in coiled form for an extended period of time without breakage which comprises providing a hardened steel razor blade strip having a Vickers hardness (2 kg. load) from 785 to 850 and a thickness from 0.002 to 0.004 inch, coiling said strip upon itself on a radius sufliciently large so that breaking of the strip is avoided, heating said coiled strip at an elevated temperature up to 350 F. to set the strip permanently in a coiled configuration, the maximum temperature and time of said heat ing being controlled to prevent substantial'reduction of the hardness of the strip.

2. The method of making a hardened steel strip razor blade capable of being coiled upon a small radius and maintained in coiled form for an extended period of time without breakage which comprises providing a hardened steel razor blade strip having a Vickers hardness (2 kg. load (from 785 to 850 and a thickness from 0.002 to 0.004 inch, coiling said strip upon itself on a radius sufiiciently large so that breaking of the strip is avoided and larger than the radius on which the strip is ultimately coiled, heating said coiled strip at an elevated temperature up to 350 F. to set the strip permanently in a coiled configuration, the maximum temperature and time of said heating being controlled to prevent substantial reduction in hardness, and subsequently coiling said strip upon a second radius smaller than the first said radius.

3. The method of making a hardened steel strip razor blade capable of being coiled upon a small radius and maintained in coiled form for an extended period of time without breakage which comprises providing a hardened steel sharpened razor blade strip having a Vickers hard- .ness (2 kg. load) from 785 to 850 and a thickness from 0.002 to 0.004 inch, coiling said strip upon itself on a radius sufficiently large so that breaking of the strip is avoided and larger than the radius on which the strip is ultimately coiled, heating said coiled strip at an elevated temperature from 250 to 340 F. to set the strip permanently in a coiled configuration, discontinuing the heating before substantial reduction in hardness occurs, subsequently coiling said strip upon a second radius smaller than the first, again heating the coiled strip at an elevated temperature from 250 to 340 F. to set the strip ermanently in a coiled configuration smaller than the P first said configuration, and discontinuing the heating before substantial reduction in hardness occurs.

4-. The method of making a hardened steel strip razor blade capable of being coiled upon a small radius and maintained in coiled form for an extended period of time without breakage which comprises providing a hardened steel sharpened razor blade strip having a Vickers hardness (2 kg. load) from 785 to 850 and a thickness from 0.002 to 0.004 inch, heating said strip at an elevated temperature from 280 to 330 F. to toughen said strip without substantially reducing its hardness, coiling said toughened strip upon itself on the desired small radius, heating said coiled strip'at an elevated temperature from 280 to 330 F. to set the strip permanently in coiled configuration, and cooling said strip before substantial reduction in hardness occurs.

5. The method of making a hardened steel strip razor blade in coil form which comprises providing a hardened steel sharpened razor blade strip having a Vickers hardness (2 kg. load) from 785 to 850 and a thickness from 0.002 to 0.004 inch, coiling said strip upon itself on a radius sufficiently large so that breaking of the strip is avoided, and heating said coiled strip at a temperature from 250-340 F. to set the strip permanently in a coiled configuration without substantially reducing its hardness.

6. The method of making a hardened steel strip razor blade in coil form which comprises providing a hardened steel sharpened razor blade strip having a Vickers hardness (2 kg. load) from 785 to 850 and a thickness from 0.002 to 0.004 inch, coiling said strip upon itself on a radius at least about times as great as the gauge of the strip, and heating said coiled strip at a temperature from 300340 F. to set the strip permanently in a coiled configuration without substantially reducing its hardness.

7. The method of making a hardened steel strip razor blade in coil form which comprises. providing a hardened and sharpened ferritic steel razor blade strip containing at least 0.50% carbon having a Vickers hardness (2 kg. load) from 785 to 850 and a thickness from 0,002 to 0.004 inch, coiling the strip on a radius sufiiciently large so that breaking of the strip is avoided, and heating said coiled strip at a temperature from 280-330 F. to set the strip permanently in a coiled configuration without substantially reducing its hardness.

8. The method of making a steel strip razor blade containing at least 0.50% carbon and having a Vickers hardness number (2 kg. load) of 810 to 840 and a thickness from 0.002 to 0.004 inch, said blade being capable of being maintained coiled upon itself on a radius approximately 50 times as great as the thickness of the blade for an extended period of time without breakage, which method comprises providing a sharpened razor blade strip having a hardness from Vickers number 810 to 850 and a thickness from 0.002 to 0.004 inch, coiling said strip upon itself on a radius sufficiently large,

at least about 85 times its thickness, so that breaking 7 of the strip is avoided, and heating the strip at a temperature from 280-330 F. to set the strip permanently in coiled configuration Without reducing its hardness below Vickers number 810, the inner radius of the finished coiled strip when free from restraint being from 200 to 500 times the thickness of the strip and the outer free radius thereof being from 300 to 700 times the thickness of the strip.

116,266 Cary June 27, 1871 8 Lovell Apr. 7, 1885 Roth Jan. 28, 1930 Steinmetz et a1 Sept. 8, 1936 Lee et a1 Sept. 28, 1937 Mailman Nov. 11, 1941 Camras July 12, 1949 Meletti Apr. 10, 1951 Stewart Jan. 19, 1954 Gent ;;1 Apr. 5, 1955 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,898,254 August 4, 1959 Frank Forsberg It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 55, for "850360" read 850 -86O column 4,- line 28, for "Without" read Within Signed and sealed this 5th day of January 1960,

(SEAL) Attest:

KARL'H"AXLI1\E ROBERT c. WATSON Commissioner of Patents Attesting Officer

Claims

1. THE METHOD OF MAKING A HARDENED STEEL STRIP RAZOR BLADE CAPABLE OF BEING COILED UPON A SMALL RADIUS AND MAINTAINED IN COILED FORM FOR AN EXTENDED PERIOD OF TIME WITHOUT BREAKAGE WHICH COMPRISES PROVIDING A HARDENED STEEL RAZOR BLADE STRIP HAVING A VICKERS HARDNESS (2 KG. LOAD) FROM 785 TO 850 AND A THICKNESS FROM 0.002 TO 0.004 INCH, COILING SAID STRIP UPON ITSELF ON A RADIUS SUFFICIENTLY LARGE SO THAT BREAKING OF THE STRIP IS AVOIDED, HEATING SAID COILED STRIP AT AN ELEVATED TEMPERATURE UP TO 350*F. TO SET THE STRIP PERMANENTLY IN A COILED CONFIGURATION THE MAXIMUM TEMPERATURE AND TIME OF SAID HEATING BEING CONTROLLED TO PREVENT SUBSTANTIAL REDUCTION OF THE HARDNESS OF THE STRIP.