Abstract:
A razor head includes a housing and at least one integrally formed rigid razor blade. The housing has a top face defining a shaving window and an opposed stopping face. The razor blades are freely mounted in the housing and have a cutting edge portion and a guided portion. A bent portion is intermediate the cutting edge portion and the guided portion. A cantilever dimension, measured as the distance between the cutting edge and a guided portion axis, is between 1.1 millimeters and 1.8 millimeters. The guided portion cooperates with a guide so that each blade is independently translatable with respect to the housing along a sliding direction parallel to the guided portion axis under the effect of shaving forces applied to the blade during shaving.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. application Ser. No. 14/348,839, filed Mar. 31, 2014, which is a national stage application of International Application No. PCT/EP2012/069883, filed on Oct. 8, 2012, which claims the benefit of International Application No. PCT/EP2011/067451 filed on Oct. 6, 2011, the entire contents are hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The embodiments of the present invention relate to integrally formed rigid razor blades, razor heads having such blades, and their methods of manufacture. 
       BACKGROUND OF THE PREFERRED FIRST INVENTION 
       [0003]    In particular, the embodiments of the present invention are related to integrally formed rigid razor cutting members. 
         [0004]    In the field of mechanical wet shavers, it has long been provided with a shaver which has a head receiving one or more cutting members. 
         [0005]    Recently, the trend has been to provide cutting members which have a preferably L-shaped cross-section, with a cutting edge portion and a base portion which is angled with respect thereto in cross-section transverse to the length direction of the cutting members. 
         [0006]    An example of a commercially successful such product can be found in WO 2007/147,420. Such cutting members are so-called ‘supported blades’, in that the so-called ‘cutting part’, which has the cutting edge, is assembled to a planar portion of a different part, called ‘support part’ which preferably has the L-shaped cross-section. 
         [0007]    WO 2011/008851 also describes such a supported blade. 
         [0008]    Yet, the assembly of these two parts raises the following problems: It is logistically difficult to handle these two different parts; it is difficult to technically handle these very tiny parts in a manufacturing apparatus operating at speeds suitable to reach the demand; it is difficult to guarantee precision of this assembly at these operating speeds, and these assemblies may corrode at the location of the attachment, thereby reducing life expectancy of the overall product. 
         [0009]    Therefore, efforts have been made to replace these so-called ‘supported blades’ by integral bent blades. An example of such efforts can be found for example in US 2007/234,577. However, development of such an integral bent blade is very difficult. Indeed, in supported blades, it is possible to tailor the support part to its specific function, i.e. accurately providing the L-shape, and to separately tailor the cutting part to its specific function, i.e. optimized shaving performance. However, for integral bent blades, there is a need to provide a product with both excellent formability and cutting performance, while still considering the manufacturing process and cost issues. 
         [0010]    US 2007/234,577 proposed to use a material having a composition comprised of 0.35 to about 0.43 percent carbon, about 0.90 to about 1.35 percent molybdenum, about 0.40 to about 0.90 percent manganese, about 13 to about 14 percent chromium, no more than about 0.030 percent phosphorus, about 0.20 to about 0.55 percent silicon, and no more than 0.025 percent sulfur. However, this only defines at most 18% of the material composition. According to an example, US 2007/234,577 recommends the use of a stainless steel having a carbon content of about 0.4 percent by weight, and other constituents. However, US 2007/234,577 needs to apply a local heat treatment to increase the ductility of the portion of the blade to be bent. However, this additional step is complex to implement on an industrial scale. 
         [0011]    Another example of such efforts can be found in US 2007/124,939. However, this document defines a very general class of steels for their razor blades, namely with a very broad range of carbon content, between 0.50%-1.25%. The properties of these materials will extend in a very broad range. 
         [0012]    The embodiments of the present invention have objectives to mitigate the drawbacks described above. 
       SUMMARY OF THE PREFERRED FIRST INVENTION 
       [0013]    To this aim, it was surprisingly discovered that a razor blade of martensitic stainless steel with a higher carbon content would provide an optimal response to the competing requirements of formability of the bent portion and strength of the blade edge, while still being manufacturable with all the other listed requirements. 
         [0014]    In particular, an integrally formed rigid razor blade having a body with: 
         [0015]    a cutting edge portion extending about a cutting edge portion plane, and having a cutting edge at one end, 
         [0016]    a base portion extending along a base portion plane, 
         [0017]    a bent portion intermediate the cutting edge portion and the base portion, 
         [0018]    and whereift the body is made of martensitic stainless steel comprising mainly iron and between 0.62% and 0.75% of carbon in weight. 
         [0019]    In some embodiments, one might also use one or more of the features defined in the dependent claims. 
       BACKGROUND OF THE PREFERRED—SECOND INVENTION 
       [0020]    Other embodiments of the present invention are related to razor heads with movable, integrally formed rigid razor blades. 
         [0021]    In the field of mechanical wet shavers, it has long been provided with a shaver which has a head receiving one or more cutting members. The cutting members are mounted to move (mainly translate) inside the head when shaving. 
         [0022]    Recently, the trend has been to provide cutting members which have a preferably L-shaped cross-section, with a cutting edge portion and a base portion which is angled with respect thereto in cross-section transverse to the length direction of the cutting members. 
         [0023]    An example of a commercially successful such product can be found in WO 2007/147,420. Such blades are so-called ‘supported blades’, in that the so-called ‘cutting part’, which preferably has the cutting edge, is assembled to a planar portion of a different part, called ‘support part’ which has the L-shaped cross-section. 
         [0024]    In particular, the base portion is oriented along a base portion axis which defines the direction of movement of the cutting members in the head. 
         [0025]    Yet, the assembly of these two parts raises the following problems: It is logistically difficult to handle these two different parts; it is difficult to technically handle these very tiny parts in a manufacturing apparatus operating at speeds suitable to reach the demand; it is difficult to guarantee precision of this assembly at these operating speeds, and these assemblies may corrode at the location of the attachment, thereby reducing life expectancy of the overall product. 
         [0026]    Therefore, efforts have been made to replace these so-called ‘supported blades’ by integral bent blades. Although some patent documents show some drawings of razor heads with integral movable bent blades, it is believed that no commercial product is yet available with such features. It is believed to be due to the difficulty of designing such a product. Indeed, such drawings can for example be found in U.S. Pat. No. 4,621,424, filed as early as 1984. 
         [0027]    An issue with a product which would be designed according to the above drawing is that, during shaving, the blade might not remain sufficiently straight, and would be submitted to bending, thus deteriorating shaving performance, and/or would witness the apparition of micro-cracks, thus favoring corrosion. In 1990, US 5,010,646 proposed to solve these problems by providing corrugations on the blade. However, this product was probably difficult to manufacture, and the effect on shaving performance appears doubtful, so that further research on such products have then be abandoned. 
         [0028]    The embodiments of the present invention are to provide a head with integral bent blades. 
       SUMMARY OF THE PREFERRED SECOND INVENTION 
       [0029]    To this aim, a razor head is provided comprising: 
         [0030]    a housing having a top face defining a shaving window, and an opposed stopping face, the housing further comprising at least one guide, 
         [0031]    at least one integrally formed rigid razor blade, each freely mounted in the housing, and having: 
         [0032]    a cutting edge portion extending along a cutting edge portion axis, and having a cutting edge accessible through the shaving window, 
         [0033]    a guided portion extending along a guided portion axis, and 
         [0034]    a bent portion intermediate the cutting edge portion and the guided portion, 
         [0035]    wherein the cantilever dimension, measured as the distance between the cutting edge and the guided portion axis, is between 1.1 millimeter and 1.8 millimeter, 
         [0036]    wherein the guided portion cooperates with the guide so that each blade is independently translatable with respect to the housing along a sliding direction parallel to the guided portion axis, under the effect of shaving forces applied to the blade during shaving. 
         [0037]    It was discovered that the above-defined parameter was a key factor for the shaving performance of such a razor head. Keeping this parameter in the defined limits enables to optimize shaving performance. Indeed, for razor heads with razor blades having this dimension greater than 1.8, there is a risk to have a bigger head in order to have sufficient rinsability. 
         [0038]    Further, blade deflection would be difficult to control. 
         [0039]    For blades having this dimension lower than 1.1, handling and assembling becomes strenuous. Further, the probability of damaging the blade cutting edge during manufacturing increased dramatically. Also, controlling the spring force applied by lateral spring arms in heads with movable blades proved more difficult. 
         [0040]    In some embodiments, one might also use one or more of the features defined in the dependent claims. 
       BACKGROUND OF THE PREFERRED THIRD INVENTION 
       [0041]    Other embodiments of the present invention are related to integrally formed rigid razor blades. 
         [0042]    In the field of mechanical wet shavers, it has long been provided with a shaver which has a head receiving one or more cutting members. 
         [0043]    Recently, the trend has been to provide cutting members which have a preferably L-shaped cross-section, with a cutting edge portion and a base portion which is angled with respect thereto in cross-section transverse to the length direction of the cutting member. 
         [0044]    An example of a commercially successful such product can be found in WO 2007/147,420. Such cutting members are so-called ‘supported blades’, in that the so-called ‘cutting part’, which has the cutting edge, is assembled to a planar portion of a different part, called ‘support part’ which preferably has the L-shaped cross-section. 
         [0045]    Yet, the assembly of these two parts raises the following problems: It is logistically difficult to handle these two different parts; it is difficult to technically handle these very tiny parts in a manufacturing apparatus operating at speeds suitable to reach the demand; it is difficult to guarantee precision of this assembly at these operating speeds, and these assemblies may corrode at the location of the attachment, thereby reducing life expectancy of the overall product. 
         [0046]    Therefore, efforts have been made to replace these so-called ‘supported blades’ by integral bent blades. An example of such efforts can be found for example in US 2007/234,577. However, development of such an integral bent blade is very difficult. Indeed, in supported blades, it is possible to tailor the support part to its specific function, i.e. accurately providing the L-shape, and to separately tailor the cutting part to its specific function, i.e. cutting hair. However, for integral bent blades, there is a need to provide a product both with excellent formability and cutting performance, while still considering the manufacturing process and cost issues. 
         [0047]    US 2007/234,577 proposed a very short bent portion. In particular, the radius of curvature R of the inner face of the bent portion is to be set to 0.45 millimeter or lower. 
         [0048]    As recognized later in WO 2011/06760 by the same applicant, the stringent material requirements for the blade edges limit the amount blades can be bent consistently and accurately. WO 2011/06760 teaches to reduce the bending angle with, as visible on the drawings, a radius of curvature close to 0. 
         [0049]    However, it is rather believed that reducing the radius of curvature would favor unwanted apparition of cracks during manufacture. These cracks ought to be avoided, because they may cause permanent deformation to occur when shaving, thereby reducing shaving performance, or corrosion to start. 
         [0050]    The embodiments of the present invention are to mitigate the drawbacks described above. 
       SUMMARY OF THE PREFERRED THIRD INVENTION 
       [0051]    To this aim, it is provided an integrally formed rigid razor blade made of martensitic stainless steel and having in cross-section: 
         [0052]    a cutting edge portion extending along a cutting edge portion axis, and having a cutting edge at one end, 
         [0053]    a base portion extending along a base portion axis, 
         [0054]    a bent portion intermediate the cutting edge portion and the base portion, the blade having a concave face and an opposed convex face, 
         [0055]    and wherein the average radius of curvature of the bent portion at its concave face is between 0.5 and 1 millimeter. 
         [0056]    By increasing the radius of curvature of the inner face of the bent portion, the product can be manufactured by a rather mild manufacturing process, which would respect the constitutive material, and occurrence of cracks during this manufacture would be reduced. In some embodiments, one might also use one or more of the features defined in the dependent claims. 
       BACKGROUND OF THE PREFERRED FOURTH INVENTION 
       [0057]    In particular, other embodiments of the present invention are related to methods of manufacture of integrally formed rigid razor blades. 
         [0058]    In the field of mechanical wet shavers, it has long been provided with a shaver which has a head receiving one or more cutting members. 
         [0059]    Recently, the trend has been to provide cutting members which have a preferably L-shaped cross-section, with a cutting edge portion and a base portion which is angled with respect thereto in cross-section transverse to the length direction of the blade. 
         [0060]    An example of a commercially successful such product can be found in WO 2007/147,420. Such cutting members are so-called ‘supported blades’, in that the so-called ‘cutting part’, which preferably has the cutting edge, is assembled to a planar portion of a different part, called ‘support part’ which preferably has the L-shaped cross-section. 
         [0061]    Yet, the assembly of these two parts raises the following problems: It is logistically difficult to handle these two different parts; it is difficult to technically handle these very tiny parts in a manufacturing apparatus operating at speeds suitable to reach the demand; it is difficult to guarantee precision of this assembly at these operating speeds, and these assemblies may corrode at the location of the attachment, thereby reducing life expectancy of the overall product. 
         [0062]    Therefore, efforts have been made to replace these so-called ‘supported blades’ by integral bent blades. An example of such efforts can be found for example in US 2007/234,577. However, development of such an integral bent blade is very difficult. Indeed, in supported blades, it is possible to tailor the support part to its specific function, i.e. accurately providing the L-shape, and to separately tailor the cutting part to its specific function, i.e. optimized shaving performance. However, for integral bent blades, there is a need to provide a product both with excellent formability and cutting performance, while still considering the manufacturing process and cost issues. 
         [0063]    In particular, it is necessary to limit as much as possible the degree of deformations applied to the blades during their manufacture, so as to not introduce permanent deformations which would affect shaving performance. 
         [0064]    US 2007/234,577 proposed slots between to-be adjacent cutting members. However, it is still difficult to handle such tiny strips, or parts separated therefrom, at high speed. 
         [0065]    The embodiments of the present invention has an objective to improve the efficiency of the manufacturing process, while not adversely affecting the characteristics of the final product. 
       SUMMARY OF THE PREFERRED FOURTH INVENTION 
       [0066]    To this aim, a method of manufacturing an integrally formed razor blade is provided comprising: 
         [0067]    providing a strip having, in cross-section transverse to a long axis, a blade portion and a removable portion, wherein weakening holes are provided along the long axis between the blade portion and the removable portion, 
         [0068]    separating the blade portion from the removable portion by breaking the strip at the weakening holes, 
         [0069]    providing the razor blade with a profile having: 
         [0070]    a cutting edge portion extending along a cutting edge portion axis, and having a cutting edge at one end, 
         [0071]    a base portion extending along a base portion axis, and having an abutment edge at one end, 
         [0072]    a bent portion intermediate the cutting edge portion and the guided portion, wherein the abutment edge is corrugated along the long axis, with corrugations with a height of at most 0.3 millimeters. 
         [0073]    Thereby, the handled strip can be made longer, and easier to handle. Further, by using a pre-perforated strip, separation of the blade from the strip is performed by imparting minimal deformation to the strip, thereby improving the overall consistency of the manufactured product. 
       BACKGROUND OF THE PREFERRED FIFTH INVENTION 
       [0074]    In particular, a fifth invention is related to methods of manufacturing integrally formed rigid razor blades. 
         [0075]    In the field of mechanical wet shavers, it has long been provided with a shaver which has a head receiving one or more cutting members. 
         [0076]    Recently, the trend has been to provide cutting members which have a preferably L-shaped cross-section, with a cutting edge portion and a base portion which is angled with respect thereto in cross-section transverse to the length direction of the cutting members. 
         [0077]    An example of a commercially successful such product can be found in WO 2007/147,420. Such cutting members are so-called ‘supported blades’, in that the so-called ‘cutting part’, which preferably has the cutting edge, is assembled to a planar portion of a different part, called ‘support part’ which preferably has the L-shaped cross-section. 
         [0078]    Yet, the assembly of these two parts raises the following problems: It is logistically difficult to handle these two different parts; it is difficult to technically handle these very tiny parts in a manufacturing apparatus operating at speeds suitable to reach the demand; it is difficult to guarantee precision of this assembly at these operating speeds, and these assemblies may corrode at the location of the attachment, thereby reducing life expectancy of the overall product. 
         [0079]    Therefore, efforts have been made to replace these so-called ‘supported blades’ by integral bent blades. An example of such efforts can be found for example in US 2007/234,577. However, development of such an integral bent blade is very difficult. Indeed, in supported blades, it is possible to tailor the support part to its specific function, i.e. accurately providing the L-shape, and to separately tailor the cutting part to its specific function, i.e. cutting hair. However, for integral bent blades, there is a need to provide a product both with excellent formability and cutting performance, while still considering the manufacturing process and cost issues. 
         [0080]    One attempt at manufacturing bent blades can be found in US 2007/234,577. In this document, the blades are shaped by coining. However, it is believed that this process still provides a wide dispersion of resulting geometries. 
         [0081]    The embodiments of the invention has an objective to improve the consistency of the products existing from manufacturing process, i.e. to reduce the dispersion in geometry of the manufactured products. 
       SUMMARY OF THE PREFERRED FIFTH INVENTION 
       [0082]    A method of manufacture of an integral bent blade for a mechanical shaver, comprises: 
         [0083]    providing a flat strip of metal extending from a first edge to an opposite edge, 
         [0084]    bending the flat strip along a bending axis parallel to the first edge to result in an integrally bent product having opposed inner and outer faces, and comprising: 
         [0085]    a cutting edge portion extending along a cutting edge portion axis, and having the first edge at one end, 
         [0086]    a base portion extending along a base portion axis, and having the opposite edge at one end, 
         [0087]    a bent portion intermediate the cutting edge portion and the base portion, and 
         [0088]    after bending, applying a mechanical stress on the inner face of the bent portion. 
         [0089]    It has been discovered that application of this mechanical stress after bending straightens the bent blade, and thus reduces the amount of products which did not meet the requested geometrical specifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0090]    Other characteristics and advantages of the embodiments of the present invention will readily appear from the following description of some of its embodiments, provided as a non-limitative examples, and of the accompanying drawings. 
           [0091]    On the drawings: 
           [0092]      FIG. 1  is an exploded perspective view of a razor head according to an embodiment, 
           [0093]      FIGS. 2 a  and 2 b    are two opposed perspective views of an embodiment of an integral bent blade, 
           [0094]      FIG. 3 a    is a rear view of the blade of  FIGS. 2 a    and  2   b,    
           [0095]      FIG. 3 b    is a lateral view of the blade of  FIG. 3   a,    
           [0096]      FIGS. 4 a  and 4 b    are views corresponding respectively to  FIGS. 3 a  and 3 b    for a second embodiment of a bent blade, 
           [0097]      FIG. 5  is a view corresponding to  FIG. 3 a    for a third embodiment of a bent blade, 
           [0098]      FIGS. 6 a  and 6 b    are views corresponding respectively to  FIGS. 3 a  and 3 b    for a fourth embodiment of a bent blade, 
           [0099]      FIG. 7  is a schematic sectional view along line VII-VII on  FIG. 1 , 
           [0100]      FIGS. 8 a  and 8 b    are schematic views of intermediate products of the manufacture of a razor blade, 
           [0101]      FIG. 9  is a lateral view of an embodiment of a forming tool used for the manufacture of a bent blade, 
           [0102]      FIG. 10  is a chart of a manufacturing process for a bent blade, 
           [0103]      FIG. 11  is a perspective schematic view of a holding tool for a bent blade. 
       
    
    
       [0104]    On the different Figures, the same reference signs designate like or similar elements. 
       DETAILED DESCRIPTION 
       [0105]      FIG. 1  shows a head  5  of a safety razor (also called wet shaver), the blades of which are not driven by a motor relative to the blade unit. 
         [0106]    The shaving head  5  is to be borne by a handle extending in a longitudinal direction between a proximal portion and a distal portion bearing the blade unit  5  or shaving head. The longitudinal direction may be curved or include one or several straight portions. 
         [0107]    The blade unit  5  includes an upper face  6  defining a shaving window, and equipped with one or several cutting members and a lower face  7  which is to be connected to the distal portion of the handle by a connection mechanism. The connection mechanism may for instance enable the blade unit  5  to pivot relative to a pivot axis X which is preferably substantially perpendicular to the longitudinal direction. The connection mechanism may further enable selectively releasing the blade unit for the purpose of exchanging blade units. One particular example of a connection mechanism usable in the present invention is described in document WO-A-2006/027018, which is hereby incorporated by reference in its entirety for all purposes. 
         [0108]    The blade unit  5  includes a frame  10  which is made solely of synthetic materials, i.e. thermoplastic materials (polystyrene or ABS, for example) and elastomeric materials. 
         [0109]    More precisely, the frame  10  includes a plastic platform member  11  connected to the handle by the connection mechanism and having: 
         [0110]    a guard bar  12  extending parallel to the pivot axis X, 
         [0111]    a blade receiving section  13  situated rearward of the guard  12  in the direction of shaving, 
         [0112]    a rear portion  14  extending parallel to the pivot axis X and situated rearward of the blade receiving section  13  in the direction of shaving, 
         [0113]    and two side portions  15  joining the longitudinal ends of the guard bar  12  and of the rear portion  14  together. 
         [0114]    In the example shown in the figures, the guard bar  12  is covered by an elastomeric layer  16  forming a plurality of fins  17  extending parallel to the pivot axis X. 
         [0115]    Further, in this particular example, the underside of the platform member  11  includes two shell bearings  18  which belong to the connection mechanism  8  and which may be for example as described in the above-mentioned document WO-A-2006/027018. 
         [0116]    The frame  10  further includes a plastic cover  19  having a top face and an opposite bottom face, which faces the top face of the components of the platform  11 . The cover  19  exhibits a general U shape, with a cap portion  20  partially covering the rear portion  14  of the platform and two side members  21  covering the two side members  15  of the platform. In this embodiment, the cover  19  does not cover the guard bar  12  of the platform. 
         [0117]    The cap portion  20  of the cover  19  may include a lubricating strip  23  which is oriented upward and comes into contact with the skin of the user during shaving. This lubricating strip may be formed for instance by co-injection with the rest of the cover. The cover  19  is assembled to the platform  11  by any suitable means, such as, for example, by ultra-sonic welding, as explained in WO 2010/06,654, hereby incorporated here in its entirety for all purposes. 
         [0118]    The present description of a housing is exemplary only. 
         [0119]    At least one cutting member  24  is movably mounted in the blade receiving section  13  of the platform. The blade receiving section  13  may include several cutting members  24 , for instance four cutting members as in the example shown in the drawings. 
         [0120]    Each cutting member  24  is made of a blade which is integrally formed from a flat steel strip. 
         [0121]    In particular, one may use a martensitic stainless steel with the following composition (in weight):
       Carbon: between 0.62% and 0.75%,   Chromium: between 12.7% and 13.7%,   Manganese: between 0.45% and 0.75%,   Silicon: between 0.20% and 0.50%,   Iron: Balance       
 
         [0127]    Such an alloy has no more than traces of other components, and notably no more than traces of Molybdenum. 
         [0128]    The razor blade has a cutting edge  26  oriented forward in the direction of shaving and an opposed rear edge  54 . The cutting edge  26  is accessible through the shaving window of the blade-receiving section  13 , to cut hair. Each blade  25  preferably has an outer face  27  oriented towards the skin to be shaved and an opposed inner face  28 . The outer and inner faces  27 ,  28  of the blade include respectively two parallel main surfaces  29 ,  30  and two tapered facets  31 ,  32  which taper towards the cutting edge  26 . 
         [0129]    Each blade  25  extends longitudinally, parallel to the pivot axis X, between two lateral sides  33 ,  33 ′. For example, the lateral sides are straight. 
         [0130]    Each blade  25  preferably has a bent profile including: 
         [0131]    a substantially flat base portion  35  (for example substantially perpendicular to the shaving plane) having a periodically serrated edge  54 , 
         [0132]    a substantially flat cutting edge portion  39  comprising the cutting edge  26 , 
         [0133]    a bent portion  53  extending between the base portion and the cutting edge portion. The bent portion preferably has a concave face  28  and an opposed convex face  27 . The face of the blade having the concave face is called inner face, and the other one the outer face. 
         [0134]    When the blade is mounted to slide in the head, the base portion is also sometimes called “guided portion”. 
         [0135]    As shown in  FIG. 1 , each cutting member  24  is borne by two elastic fingers  44  which are molded as a single piece with the platform  11  and which extend towards each other and upwardly from both side members  15  of the platform. For example, all the fingers  44  extending from a given side member are identical. 
         [0136]    Besides, as shown in  FIG. 2 , the base portions  35  of the blades are slidingly guided in slots  45  provided in the inner face of each side member  15  of the platform. The slots are, for example, substantially perpendicular to the shaving plane. 
         [0137]    The blades  24  are elastically biased by the elastic arms  44  toward a nominal position. In this nominal position, the outer faces  27  of the blades, at each lateral end of the blades, bear against corresponding upper stop portions  52  which are provided on the bottom stopping face of each side member  21  of the cover, the side member  21  covering the slots  45 . 
         [0138]    Therefore, the nominal position of the blades  24  is well defined, therefore enabling a high shaving precision. 
         [0139]    In this nominal position, the inner faces  28  of the blades, at each lateral end of the blades, are borne by corresponding top portions  55  of the elastic arms. The distance between the two top portions is for example of 22 to 30 mm, preferably between 25 and 27 mm. 
         [0140]    The guiding slots  45  define a direction Y for the razor head. The direction Z is the normal to the X-Y plane. The base portion  35  extends in a base portion plane. The base portion axis is the main axis of the base portion other than its profile axis, i.e. other than the X axis. In the present embodiment, it is the Y axis. In other words, the main axis along which the base portion extends is the same as the axis defined by the slots  45  in the razor head. 
         [0141]    The cutting edge portion  39  extends in a cutting edge portion plane. The cutting edge portion axis is the main axis of the cutting edge portion other than its profile axis, i.e. other than the X axis. In the present embodiment, it is a U axis. In other words, the cutting edge portion axis extends in an X-U plane. A V axis is defined normal to the X-U plane. 
         [0142]    A first embodiment of a bent blade is shown on  FIGS. 3 a    and  3   b.  Below, some geometrical characteristics of the blade are given. The geometrical characteristics of the blade are here nominal characteristics, which do not take into account the actual geometry of the blade due to the manufacturing process or dispersion. In particular, due to the manufacturing process, thickness variations and/or bow, sweep, camber of some blade portions are possible, and are even intrinsic to the product. 
         [0143]    Following parameters are defined:
       t: thickness of the blade;   L: length of the blade from one lateral side  33  to another  33 ′;   H: height of the blade, measured along direction Y, from the rear edge  54  to the cutting edge  26 ;   D: cantilever dimension, measured along direction Z, from the cutting edge  26  to the plane of the base portion (X-Y);   a: included angle, measured between the base portion plane and the cutting edge portion plane;   Hb: height of the blade base portion, measured along direction Y, from the rear edge  54  to the bent portion  53 ;   R: radius of curvature of the inner face of the bent portion;   Hc: Extent of the cutting edge portion, measured along direction U, from the cutting edge  26  to the bent portion  53 ;   T: period of the serrated edge;   Ti: extent of the protrusion of the serration;   h: height of the serrated end.       
 
         [0155]    According to the first embodiment, a suitable razor blade shows the following geometric properties: 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Nominal 
                   
                   
                 Nominal 
                   
               
               
                 Parameter 
                 value 
                 Dispersion 
                 Parameter 
                 value 
                 Dispersion 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 T 
                 0.1 
                 mm 
                   
                 Hb 
                 1.43 
                 mm 
                   
               
               
                 L 
                 37.1 
                 mm 
                   
                 R 
                 0.6 
                 mm 
                   
               
               
                 H 
                 2.33  
                 mm 
                   
                 Hc 
                 0.28-1.14 
                 mm 
                   
               
               
                 D 
                 1.35 
                 mm 
                 +/−0.05 mm 
                 T 
                 5.3  
                 mm 
                 ±0.003 mm 
               
             
          
           
               
                 A 
                 108° 
                 +/−2° 
                 h 
                 0.13-0.32  
                 mm 
                   
               
               
                   
                   
                   
                 Ti 
                 2 
                 mm 
                   
               
               
                   
               
             
          
         
       
     
         [0156]    This value indicated for Hc is in fact an average between the value measured for Hc on both lateral sides of the blade. Due to the deformation of the blade, these two values were different, amounting in average to 0.81 mm and 0.85 mm, respectively. Hc might extend between 0.28 and 1.14 mm, preferably between 0.4 and 1 mm. 
         [0157]    Other embodiments were successfully manufactured, which showed satisfactory. According to a second embodiment, shown on  FIGS. 4 a    and  4   b,  the other parameters are alike, apart from a=112°, H=2.4 mm, Hc=0.96 mm. 
         [0158]    Yet another embodiment is shown on  FIG. 5 . This embodiment differs from the second embodiment mainly by different values for T and Ti. 
         [0159]    According to yet another embodiment, as shown on  FIGS. 6 a    and  6   b,  the rear edge is not serrated. The geometric datas for this embodiment are: 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Nominal 
                   
                 Nominal 
               
               
                   
                 Parameter 
                 value 
                 Parameter 
                 value 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 t 
                 0.1 
                 mm 
                 Hb 
                 1.57 mm 
               
               
                   
                 L 
                 37.1 
                 mm 
                 R 
                 0.6  
               
               
                   
                 H 
                 2.58 
                 mm 
                 Hc 
                 1.07 
               
               
                   
                 D 
                 1.45 
                 mm 
                 a 
                 112° 
               
               
                   
                   
               
             
          
         
       
     
         [0160]    As shown on  FIG. 7  below, a cutting plane (P) is defined for the head from the tangents to guard bar before the window receiving the blades and the cap behind it. Hence, upon shaving, a force will be applied to the blade by the user, along a direction F which is preferably normal to the plane (P). The blades  24  are oriented in the head  5  such that the cutting edge portion forms an angle with the cutting plane (P). In other words, the force F is applied preferably in the Y direction at approximately ±5°. 
         [0161]    According to the first embodiment of the present invention, tests have shown that, surprisingly, the above material provided a bent blade providing the best compromise between formability and cutting edge performance. In particular, the above material can be formed as a successful cutting edge of a razor blade, provided with current cutting edge processing including grinding, coating with a strengthening material and coating with a telomere layer. In addition, the above material can be formed as a successful bent region with enhanced consistency, high reproducibility, and without producing too much corrosion prone macro-cracks during manufacturing. 
         [0162]    These tests were performed both for a head with a blade according to the first embodiment above, and for another blade with an angle a of 112°. It is expected that this material would provide improved behavior even when modifying other parameters of the blade. In particular, it is believed to be verified for a taken between 95° and 140°; preferably between 108° and 112°, R over 0.4 mm, preferably between 0.5 mm and 1 mm, t between 0.07 mm and 0.12 mm, preferably between 0.095 mm and 0.105 mm, He between 0.28 mm and 1.14 mm, preferably between 0.4 mm and 1.0 mm. The thus obtained blade may also be used fixed in a razor head, if necessary. 
         [0163]    According to the second invention, with the blade edge portion  39  being supported only by the two springs  44 , the shaving force being applied along direction F therebetween, and the base portion constrained to move parallel to the X-Y plane, the dimension D has proven to be a critical dimension of the blade. 
         [0164]    Tests have shown that an optimum can be reached when the D dimension is selected between 1.1 mm and 1.8 mm. If D exceeded 1.8 mm, the blade would be submitted to large deflection during shaving, thereby reducing shaving performance. Head rinsability would also be reduced. Further, there would be a risk of appearance of macro-cracks in the blade, notably in the inner face of the bent region, and/or permanent deformation of the blade. Macro-cracks ought to be avoided, because they are a preferred site for the corrosion of the blade. Permanent deformation ought to be avoided, because it would negatively affect shaving performance. When D becomes lower than 1.1 mm handling and manufacturability are dramatically impaired. There is a risk of damaging the cutting edge during handling and head manufacture. Further, applying a suitable spring force on the blade becomes difficult. 
         [0165]    These tests were performed for a head with a blade according to the first embodiment above, but it is expected that heads provided with movable blades guided along their base portion axis, and with the selected D dimension would provide improved performance, even when modifying other parameters of the blade, such as its material, or other geometrical parameters. In particular, it is believed to be verified when the distance between the two contact points of the blade to the springs is between 22 and 30 mm, preferably between 25 and 27 mm, when a is taken between 95° and 140°, preferably between 108° and 112°, R over 0.4 mm, preferably between 0.5 mm and 1 mm, t between 0.07 mm and 0.12 mm, preferably between 0.095 and 0.105 mm, He between 0.4 mm and 1.0 mm, preferably between 0.81 mm and 0.85 mm. Such a preferential behaviour is also expected to be met for bent blades with lower carbon range, for example from 0.5% carbon in weight. 
         [0166]    According to the third invention, tests have shown that an optimum can be reached when the R dimension is selected over 0.5 mm, preferably over 0.55 mm. The R dimension is preferably lower than 1 mm. In other words, the radius of curvature of the outer face at the bent portion is at least 0.57 mm. The median radius of curvature at the bent portion is at least 0.535 mm. Indeed, when the radius of curvature is lower than that, it is difficult to manufacture the blade without generating high stresses which would cause the appearance of macro-cracks in the bent region. 
         [0167]    These tests were performed for a blade according to the first embodiment above, but it is expected that the above would remain true even when modifying other parameters of the blade. In particular, it is believed to be verified for a taken between 95° and 140°, preferably between 108° and 112°, t between 0.07 mm and 0.12 mm, preferably between 0.095 and 0.105 mm. The thus obtained blade may also be used fixed in a razor head, if necessary. 
         [0168]      FIG. 10  now schematically shows an example of a process for the manufacture of the above bent blades. 
         [0169]    At step  101 , one provides a strip of suitable material. The material is for example stainless steel in terrific form with secondary carbides, and having the above composition. A strip is any kind of product suitable to be manufactured into a bent blade as above. For example, the strip  56  is shown on  FIG. 8   a.  It is substantially straight. It has the thickness of the future razor blade. It has the length L of the future razor blade. Along the transverse height direction, it comprises, from top to bottom on  FIG. 8   a,  a cutting edge portion  57 , a to-be-bent portion  58 , a base portion  59 , and a removable portion  60 . The cutting edge portion  57 , the to-be-bent portion  58  and base portion  59  together define a blade portion of the strip. Notches  61  are provided, which extend oblongly along the long direction, between the base portion  59  and the removable portion  60 . 
         [0170]    In particular, the notches  61  are shaped to receive transport fingers of the manufacture apparatus, in order to transport the strip from one station to another, along the manufacturing line, and to hold the strip in respective stations, as will be explained below in relation to  FIG. 11 . 
         [0171]    At step  102 , a metallurgical hardening process  102  is performed on the strip. This process initiates martensitic transformation of the steel. 
         [0172]    At step  103 , the top edge of the strip, which is to become the cutting edge, i.e. the edge of the strip which belongs to the cutting edge portion  57 , is shaped as the cutting edge of a razor blade. This shaping is a sharpening process performed by grinding the edge to the acute required geometry. The cutting edge is defined by convergent faces which taper toward a tip having an angle of about 10°-30°. 
         [0173]    At step  104 , a strengthening coating is applied on the ground cutting edge. For example, the ground blades are stacked in a stack, with their cutting edges all oriented in the same direction, and a strengthening coating is applied thereto. The strengthening coating will comprise one or more layers with different characteristics. The layers may comprise one or more of metal(s) (notably chromium or platinum) and carbon (possibly in DLC form). This coating is for example deposited by sputtering. Sputtering may also be used to precisely shape the geometry of the cutting edge before or after coating. The global geometry of the cutting edge is maintained at this step. 
         [0174]    At step  105 , a telomere coating is applied on the blade edge. A suitable telomere is for example a PTFE. A suitable deposition method is spraying. 
         [0175]    What is referred to as being the blade body is the part of the blade which is made of steel, exclusive the coatings. 
         [0176]    At step  106 , a bending step is applied on the up-to-now straight strip. At the bending step  106 , one part of the strip is held, and a force is applied on the other part, so as to provide the strip with a bent portion  63 , as shown on  FIG. 8   b.  After this step, the cutting edge portion  57  is angled with respect to the base portion by preferably the above angle a. Permanent deformation is imparted on the bent portion. Bending could for example be performed by stamping. Alternately, bending could be done by a number of other suitable methods. A method which reduces the generation of macro-cracks in the strip, notably to its bent portion, is preferred. 
         [0177]    Due to the natural characteristics of the material, the bent strip exiting from this step will not have the nominal geometry described above. In particular, it will exhibit some degree of camber, bow or sweep. Further, due to the material&#39;s mechanical properties, the dispersion of the geometry of the products can be large. This is particularly the case when the process used for applying the bending is only mildly severe to the strip (in order to avoid appearance of cracks). In such case, the amount of spring-back of the material after deformation is high and hardly predictable. 
         [0178]    According to the fifth invention, at step  107 , a straightening step is performed. At this step, a forming process is used in order to reduce the dispersion in the geometry of products. In particular, permanent deformation is applied on the inner face of the bent portion of the strip. This permanent deformation straightens the overall blade, and reduces the dispersion in blade geometry among the products. 
         [0179]    As an example, as shown on  FIG. 9 , a straightening station  70  comprises a support  71  to receive the bent strip  72 . For example, the support  71  preferably has a V-shaped groove  73  having an included angle corresponding to the nominal angle for the bent blade. The bent strip is placed in the groove  73  with its outer surface resting on the arms of the V-shaped groove. It may be maintained there by any suitable means, such as by vacuum suction or the like. A deformation tool  74  is placed above the groove  73 . The deformation tool  74  preferably has a base  75  receiving a carriage  76  movably mounted with respect to the base  75  along the length direction of the strip (transverse to the plane of  FIG. 9 ). The carriage  76  bears a pressure-application tip  77 . The position of the pressure-application tip  77  with respect to the carriage  76  is settable, so as to bring the pressure-application tip at controlled distance to the base  71 . The distance between the edge of the tip  77  and the groove  73  will determine the level of pressure applied by the tip to the strip. 
         [0180]    The pressure-application tip may comprise a support  78  receiving a spring-loaded ball  79  at its edge. The ball has dimensions of the order of the bent portion of the strip. The support  78  allows rotation of the ball  79  therein. 
         [0181]    Upon use, the tip  77  is held in an upper position until a strip is placed in the groove  73 . The tip  77  is moved down until the ball  79  contacts the bent portion of the strip with suitable pressure. The ball  79  does not contact the straight portions of the strip. The contact is made at one lateral side of the strip. Then, the carriage  76  is moved with respect to the base  75  along the length of the strip until the other lateral side, to form the bent portion of the strip. The ball rolls during this movement. Possibly, this movement is performed back-and-forth. The tip  77  is then moved again to its up position, to remove the straightened strip from the straightening station  70 . [00132] The formed strip is controlled. For example, its geometry is measured with a suitable measurement apparatus. These measurements enable to set the level of pressure applied by the tip for straightening steps on future products. 
         [0182]    Back to  FIG. 10 , a cutting step  108  is performed. At this step, the removable portion  60  is removed, to result in the final bent blade. According to a fourth invention, it is made use of the notches  61  which are provided between the base portion and the removable portion of the blade, to remove the removable portion. It enables to remove the removable portion by imparting minimal stress on the bent blade, thus minimizing the level of permanent deformation applied to the bent blade, and potentially affecting its geometry. Further, as the cut part surface is minimized, initiation of corrosion is also reduced to the small cut area. 
         [0183]    Cutting can be performed in a cutting station  80  partially shown on  FIG. 11 . The station  80  preferably has a base  81  from which two lateral pins  82  extend. The pins  82  are shaped to enter in corresponding notches  61  of the strip, and together precisely locate the strip in the station. Vacuum may additionally be used to retain the strip in the station by suction. The strip, at various stages of its manufacture, can be held in manufacturing stations, and/or moved from one station to the next, using similar principles. 
         [0184]    In various embodiments, the order in which some of the above steps are implemented may be changed.