US1989886A

US1989886A - Manufacture of safety razor blades

Info

Publication number: US1989886A
Application number: US666641A
Authority: US
Inventors: Roth Otto
Original assignee: Gillette Safety Razor Co
Current assignee: Gillette Co LLC
Priority date: 1932-05-13
Filing date: 1933-04-18
Publication date: 1935-02-05
Anticipated expiration: 1952-02-05

Description

Feb. 5, 1935. o. ROTH 1,989,886M

MANUFACTURE OF SAFETY RAZOR BLADES Filed April 18, 1933 a a J'Q M 4 m m m 'JA/VZ/VTOR @fra-%% Patented Feb. 5, 1935- UNITED STATES PATENT OFFICE MANUFACTURE OF SAFETY RAZOR BLADES Application April 18, 1933, Serial No. 666,641

A 7 Claims. The present invention relates to the manufacture of safety razor blades of the thin flexible type havingac'ontinuous slot of substantial length, e. g., extending substantially over the whole length ,5 of the cutting edge of the blade, and having end portions which are intended to be bent transversely and maintained in a position of curvature during use, and whose medial parts are substan' tially softer than the cutting edges.

With known methods of producing such blades it is difllcult to obtain the desirable degree of hardnessof the cutting edges, if the medial area is to be sufliciently soft to permit the blade to flex without risk of fracture. Moreover such prior methods are very liable to produce distortion of such blades so as to render it commercially impracticable to produce therefrom finished bladeswith an even cutting edge by grinding in the strip. a

The object of the presentinvention is to facilitate obtaining differential hardening, and to enable the manufacturer to obtain more easily such different conditions of edge and medial hardness as he may desire.

What are the optimum conditions is to some extent a matter of opinion. It has been found that a blade with an edge hardness of about 850 i on the Vickers hardness testing machine and a hardness of 650 or less near the medial projec- 30 tions gives good results in practice, but it should be observed that with these blades it a matter of great difllculty to obtain exact figur'es.

The new process is characterized by the employment of an electric current in connection with 35 a blade of such configuration and proportion that there is a substantial diiferenee between the density of the current flow in difierent portions of the blade, the greatest density of such flow being in the end portions where the metal should 40 be of ,the lowest degree of hardness, and least density at and near the cutting edge, the heating eil'ect at each point being proportional to PR, where I is the density-of the current flow at such point and R the resistance.

45 To obtain this differential density the current is applied to a hardened bladehaving a medial slot of substantial length, and end portions so shaped that the breadth of metal available for the passage of the current through such end portions is substantially less than that so available in the medial portion of the blade, whereby the density of the current flow in such end portions is increased beyond that near the cutting edges.

The length of the slot has an important effectinproducing thisresultashasalsoitstermi- Great Britain May 13, 1932 nal form. With a slot of substantially even breadth and the current entering and leaving at the ends of the blade the density of the current flow' near the medial line of the blade will also tend to be somewhat greater than at or near the cutting edge, since the path from electrode to electrode is less near such medial line.

I The process is applicable to blades of known shape, e. g., such as those shown in U. S. Letters Patent Nos. 1,869,327, 1,850,902 and 1,858,316 since the end portions of such blades possess the requisite qualities above described.

The method is applicable both to,cases where blades are hardened and/0r tempered in the strip, and where individual blades are hardened and/or tempered separately.

The present invention is particularly suited forv ered to leave substantially equal portions. thereof on adjacent blades.

, The process may be carried out by first subjecting the strip to any known hardening process and then subjecting it to the electrical treatment by which the blade is tempered so as to give the desired edge hardness and the less hardened end portions simultaneously.-

Owing to the fact that the end portions of the blade atwhich the current enters and leaves are of less cross sectional area than the main portion of the blade the current density will be substantially greater at the end areas than along the main portion of the blade, whereby such a differential tempering is obtained between the end areas and the main portion of the blade as will give the blade the characteristics hereinbefore referred to.

In order that the invention may be the more readily understood reference is hereinafter made. to the accompanying drawing, in which:-

Fig. 1 is adiagrammatic view of one form of apparatus for carrying out the present process, and

Fig. 2 shows part of a strip of blade blanks adapted to be treated by the process.

Referring to the drawing, the strip of blade blanks a after being hardened by passingthrough a hardening apparatus 1 is caused to bridge a gap in an electric circuit, so that with a blade having a longitudinal slot the current will divide into two parts between the successive necks.

- For this purpose the strip passes to the electrical treatment apparatus comprising spaced apartpairs of contact blocks 9, 9a and 10, 10a. The blocks are held to the strip by light spring pressure so that they form yielding clamp contacts. The blocks 10, 100. are water cooled, a. part of the water cooling system being indicated by 11. The water in the blocks 9, 9a is preferably insulated from the contacts.

The blocks 9, 9a and 10, 10a are units an open circuit 11a, having therein a variable re stanc'e 12, a single pole switch 13, an ammeter '14, and the secondary winding 15 of a transformer, the primary winding 16 being connected to the mains by a double pole switch 17. 18 is a volt: meterconnected across the circuit 11. The circuit 11 is closed by that part of the strip which for the time being bridges the gap between the contact blocks 9, 9a and 10, 10a.

A .working example of voltage and amperage for a strip in which the blades are proportioned as shown each blade being about 43 mm. long is 20 volts, 40 amps, with 40 blades between the contacts, the speed of strip going through being 200 blades a minute.

The strength of the current is so chosen with respect to the rate of feed of the strip, and the distance the contacts are spaced apart, that'in the time that the blade is subject to the heating effect of the current the necks c are softened the desired amount, while reducing the edge hardness I of the strip to that desired.

By the present invention the following factors,

rent near the ends compared to that of other portions of the blade, and by experiment or calculation these factors can be so varied as to obtain a great variety of differences of temper.

Further, where the current is applied to a strip containing a number of blades, the differentiation of current density may be increased by nicking or the like, so that the breadth of the parts by which the current enters or through which it flows is decreased. Nicks d at the necks between the blades are shown in Fig. 2.

Apart from the specific advantages above described the use of the electric current avoids many of the difliculties attached to other methods of tempering.

What I claim is:- 1. Process for the production of thin flexible razor blades with high edge hardness and relatively softer medial end areas, comprising applying an electric current to a hardened blade having a medial slot of substantial length, the cross sectional area of the end portions of such blade being substantially less than that of the intermediate portion so that the density of the current is substantially greater over the medial end portions than at or nearv the cutting edges.

2. Process for the production of thin flexible razor blades with high edge hardness and relatively softer medial end areas, which comprises applying an electric current to a hardened strip of blades whichare provided with a longitudinal slot of 'substantiallength, the portions of such stripbetween the slots being of substantially less cross sectional area than that of the remaining part of the strip so that the density of the current is substantially greater over the medial end portions of the blades than at or near the cutting,

edges.

3. Process for the production of thin flexible razor blades with a high edge hardness and relatively softer medial end areas, comprising applying an electric current to a plurality of hardened blades which are provided with a longitudinal slot of substantial length and are each connected longitudinally in strip form by necks of substantially less cross-sectional area than the main portion of the blade so that the density of the current will be substantially greater over'the medial end portions of the blades than at or near the cutting edges.

4. Process for the production of thin flexible razor blades with a high edge hardness and relatively softer medial end areas, which consists in hardening a plurality of blades which are each provided with a longitudinal slot of substantial length and are connected longitudinally in strip formby necks of substantially lesscross-sectional area than the main portion of the blade, and then applying an electric current to such strip so as simultaneously to temper the blades and to reduce to a greater extent the hardness of the necks by the differential current density set up along the strip.

5. Process for the production of thin flexible razor-blades with a high edge hardness and relatively softer medial end areas, comprising applying an electric current to a plurality of hardened blades which are each' provided with a longitudinal slot of substantial length and are connected longitudinally in strip form by necks of substantially less cross-sectional area than the main portion of the blade so that the density of the current will be substantially greater over the medial end portions of the blades than at or near the cutting edges, the said current entering and leaving through externally cooled electrodes.

6. Process for the production of thin flexible razor blades with high edge hardness and relatively softer medial end areas, comprising hardening a blade having a medial slot of substantial length and then applying an electric current to the blade so as simultaneously to temper the bladeat or near the cutting edges and reduce to a greater extent the hardness of the medial end areas of the blade, the cross-sectional areas of the end portions of'such'blade being substantially less than that of the cutting portion so that the density of the current is substantially greater over the medial end areas than at or near the cutting edges.

7. Process for the production of thin'flexible razor blades with high edge hardness and relatively softer medial end areas, comprising applying an electric current to a hardened blade having a medial slot of substantial length, thecrosssectional area of each end portion of such blade being substantially less than the combined crosssectional area of the cutting-edge-bearing portions'so that the density of the current is substantially greater over the medial end portions than at or nearthe cutting edges.

. OTTO ROTH.