Abstract:
A soleplate for a clothes pressing iron, composed of: a metal sheet having a lower surface that will be directed toward fabrics to be ironed, a lower surface layer that extends form the lower surface and an interior region that is separated from the lower surface by the lower surface layer, the lower surface layer being mechanically hammer-hardened, or work hardened, to have a hardness greater than the hardness of the sheet prior to being mechanically hardened; and a coating that is hard and resistant to scratching covering the lower surface.

Description:
BACKGROUND OF THE INVENTION 
   The present invention concerns soleplates for clothes pressing irons. 
   It is known that the soleplates of pressing irons should have a pressing surface that slides easily on fabrics, but should also resist stresses, attacks provoked by an overly vigorous cleaning or rubbing of the soleplate on hard components of clothing, such as zippers, hooks, or buttons. 
   In order to resist these stresses, which are capable of creating scratches that will reduce the sliding performance of the soleplate, efforts have been made to harden the ironing surface of the soleplate. 
   French patent FR 2581402 thus describes an enameled aluminum soleplate, which has the drawback that application of the enamel requires production means that are substantial and costly. 
   It is also known to harden surfaces by mechanical treatment, for example by impacting such surfaces with shot or microbeads as described in the patent FR 2803310, but this treatment can be insufficient to enable the treated surface to withstand the strongest attacks. 
   Another hardening procedure consists in depositing on the surface to be treated a hard coating by a sol-gel process, as described in the patent EP 0640714. Such a coating is thin, highly resistant in and of itself to attack, and economical to produce. However, the metal support of the coating being ductile, the coating can be dented and can deteriorate. 
   The patent WO 9813544 describes an iron having an aluminum soleplate plate that includes an anti-friction coating containing an inorganic polymer. The anti-friction coating is deposited on an intermediate hard coating that is harder than aluminum. However, the provision of this intermediate coating adds significantly to the cost of manufacturing the soleplate. 
   BRIEF DESCRIPTION OF THE INVENTION 
   The present invention provides a pressing iron soleplate that is improved by the deposition of a hard scratch resistant coating on the ironing surface, but does not have the disadvantages discussed above. 
   For this purpose, the invention provides a pressing iron metal soleplate which is treated at the surface that will be in contact with fabrics by a mechanical hammer-hardening, or work hardening treatment, a treatment that is noteworthy in that the ironing surface is, in addition, covered by a coating that is hard and resistant to scratching. 
   The metal constituting the soleplate, generally an aluminum alloy or stainless steel, is normally relatively soft. A hard, thin coating placed in this support does not resist shocks. The coating can be pressed into the metal and deforms to retain a residual impression of the impact. The present invention provides a significant improvement in this regard in that the preliminary mechanical hammer-hardening treatment causes the soleplate to resist denting of the surface by shocks or impacts experienced by the iron on hard, projecting bodies, which permits the coating deposited on the surface to resist deformation without flaking or chipping away. 
   Preferably the mechanical hammer-hardening treatment is a treatment with microbeads or shot. 
   The treatment is carried out not to effect only a simple cleaning of the surface, but to modify the surface to a certain depth without any notable abrasive effect. 
   Multiple shocks produced by impacting beads of shot on the metal surface results in a hammer-hardening that increases the hardness of the metal surface. The impacts, being multiple and close to one another, do not adversely affect the evenness of the surface, which assumes a matte appearance. 
   The coating deposited on the surface can be an electrolytic coating such as a hard chrome plating, or a metal coating formed by chemical deposition, or plasma deposition, or vapor deposition under a vacuum, or any other deposition producing a coating that improves the ironing surface. 
   According to one possibility, the hard coating resistant to scratching is a chemically deposited nickel coating. 
   Advantageously, the soleplate coated with nickel is heated to a temperature of the order of 230° C. for several hours. 
   This thermal treatment at a temperature lower than the annealing temperature of the soleplate produces a hardening of the coating. 
   In another version, the hard scratch-resistant coating is a ceramic layer obtained by a physical vapor deposition (PVD) process. 
   A PVD process permits a large variety of deposits to be produced. In addition to a simple metallization, for example with nickel or chromium, the most well known deposits appropriate for ironing soleplates are nitride or carbonitride of titanium, aluminum-titanium nitride, chromium nitride, or zirconium nitride. 
   Preferably, the ceramic deposit is a layer of chromium nitride. 
   This deposit is easily sufficiently hard for use on an ironing surface, has a very good resistance to chemical agents and abrasion, a lower degree of roughness than titanium nitride, and a good coefficient of sliding friction. 
   Preferably, the hard scratch-resistant coating is a coating comprising an inorganic chemical structure deposited by any suitable, known sol-gel process. 
   Numerous known processes, for example, from the patents owned by companies such as Datec, or INM or Protavic, permit a scratch resistant coating to be obtained on a metal part by a sol-gel process. These economical processes permit the production of hard coatings that are highly adherent and whose structure is based on a network having inorganic mineral bonds. Coatings that are resistant to scratching and that present a smooth surface permit easy sliding on fabrics. These processes generally include a phase of placing an organo-metallic precursor into solution, a hydrolysis phase, and, after spreading on the surface to the covered, a baking phase that can be at relatively low temperature. 
   Preferably a sol-gel process is selected to obtain a hard scratch-resistant coating on the sole plate with process temperatures that are below the annealing temperature of the underlying metal and that preserve the hardness of the hardened surface. 
   An excessively high temperature, close to or greater than the annealing temperature, would relax the internal strains of the hardened metal and could lead to deformation of the soleplate. In addition, an excessively high temperature would lead to an enlarging of the metal grains and would reduce the hardness by counteracting the hardening treatment. 
   For aluminum soleplates, depending on the alloy selected, the annealing temperature would be in the range of 325° C. to more than 400° C. To obtain a suitable coating, one would choose a process that does not require very high baking temperatures, for example that described in U.S. Pat. No. 5,644,014. Soleplates of stainless are annealed at higher temperatures, which increases the possibilities for the choices of processes and the coatings that can be obtained. Preferably, the constituent metal of the soleplate is stainless steel or an aluminum alloy. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a side elevational view, partially in cross section, of a clothes pressing iron equipped with a soleplate according to the present invention. 
       FIG. 2  is a reproduction of a microphotograph of the soleplate of  FIG. 1  in the vicinity of its ironing surface. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , according to one preferred embodiment of the invention, which is illustrated, the soleplate  1  of a pressing iron  2  is essentially composed of a stainless steel sheet  11  whose thickness can be between 0.4 and 1.5 mm. Soleplate  1  is heated by a heating block  3 , which may be made of aluminum, and into which is overmolded a conventional heating element  4 . An iron according to the invention can be a steam iron or a dry iron. 
   Stainless steel sheet  11  is covered on it ironing surface  13  with a hard scratch-resistant coating  14 . 
   Coating  14  adheres securely to surface  13  of sheet  11 . In accordance with a further feature of the present invention, surface  13  is preliminarily subjected to a mechanical treatment, similar that described in French patent 2803310, involving impacting essentially nonabrasive particles onto the surface. 
   The crystalline structure of sheet  11  is modified at surface  13  by the mechanical treatment, essentially to a depth P that is preferably between 25 and 35 microns from the ironing surface. This modification substantially increases the strength and hardness of sheet  11  at surface  13 . 
   Preferably, the surface of sheet  11  that is covered by coating  14  has grains that have been deformed by compression in a direction perpendicular to the surface, the number of metal dislocations per unit of volume being 40% greater than that in the metal within sheet  11  at locations that have not been affected by the hardening treatment. 
   Preferably, the Vickers hardness of surface  13  of sheet  11  is at least 25% greater than that measured within sheet  11  at locations remote from the surface. 
   According to a first embodiment, coating  14  has a structure with an inorganic base comprising chemical chain bonds, which metals such as silicon, zirconium, titanium, and aluminum for example can produce essentially with oxygen. 
   Fabrication of the coating is preferably in accordance with the description in U.S. Pat. No. 5,644,014. In effect, the coatings that can be produced with these means have desirable qualities for an ironing soleplate. In particular they are mechanically more resistant to scratching than the metals that they cover. Being anti-adhesive, they facilitate sliding of the iron on the fabrics. 
   In addition, the baking, or curing, temperatures are relatively low, preferably of the order of 90° C. to 350° C., and more preferably around 180° C., which avoids heating sheet  11  to a temperature that could relax the internal strains in the metal that result from the hardening treatment. In particular, a temperature is selected that would preserve the size of the deformed metal grains and the hardening, as well as the basic shape of the part. 
   As a result, coating  14  can be very thin, for example with a thickness less than 10 microns. A shock applied to this coating is transmitted to the hardened metal, which can safely resist shocks of substantial magnitude. The coating will then not be deformed or break. 
   In addition, the resulting coating is essentially transparent, which preserves the metallic appearance presented by a stainless steel sheet. 
   According to another embodiment of the invention, which is quite satisfactory in combination with the exterior hammer hardening of sheet  11 , coating  14  can be composed of chromium nitride deposited by a PVD process. Chromium nitride has a hardness of the order of three times that of stainless steel. After mechanical hardening, the iron soleplate is placed in an enclosure at low pressure. Ions produced by electron bombardment of one or several targets of conductive material, preferably of chrome, are transported in the form of a ionized gas onto the surface of the soleplate and condense thereon. Over their travel path, the ions can react with low pressure gas in the enclosure, preferably nitrogen, and can be combined therewith, to produce, preferably, a very hard layer of chromium nitride on the soleplate. This process does not produce any heating, and thus does not destroy the hardening the soleplate. 
   The hammer-hardened soleplate can also be clad by PVD deposition of pure metals or alloys. However, it is preferable to select the coating from among ceramic compounds such as nitrides of chromium, titanium, zirconium, or zirconium and aluminum, and titanium carbonitride, whose hardnesses are approximately the same as or greater than that of chromium nitride. 
   A very hard nitride layer, the thickness of which is of the order of 1 to 5 microns, is sufficient to give the soleplate an excellent resistance to scratching. The layer, supported by a hardened metal, will not break when exposed to localized stresses such as those produced by an impact of the iron on a zipper or a button of a garment. 
   By these means, there is obtained a pressing iron soleplate that slides easily during ironing and is insensitive to scratching. 
   The embodiment of  FIG. 1  can also be constructed with sheet  11  made of aluminum, which is hammer-hardened, and a coating  13  that can be applied at process temperatures that will not relax the hardened structure of the aluminum. In addition, suitable coating, or cladding, processes other than the sol-gel process may be employed. 
   This application relates to subject matter disclosed in French Application Number FR 0203124, filed on Mar. 13, 2002, the disclosure of which is incorporated herein by reference. 
   The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without undue experimentation and without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. The means, materials, and steps for carrying out various disclosed functions may take a variety of alternative forms without departing from the invention. 
   Thus the expressions “means to . . . ” and “means for . . . ”, or any method step language, as may be found in the specification above and/or in the claims below, followed by a functional statement, are intended to define and cover whatever structural, physical, chemical or electrical element or structure, or whatever method step, which may now or in the future exist which carries out the recited function, whether or not precisely equivalent to the embodiment or embodiments disclosed in the specification above, i.e., other means or steps for carrying out the same functions can be used; and it is intended that such expressions be given their broadest interpretation.