FR2782327A1 - Method for preventing the adherence of scale to a stainless steel heating surface - Google Patents

Abstract

A method for preventing the adherence of scale on a stainless steel heating surface (5) to come into contact with hot water in the vessel (1) of a boiler, a coffee machine or an electric teapot. The stainless steel heating surface is subjected to electrolytic polishing. An Independent claim is also included for the heating plate of an electric boiler made up of a stainless steel dish (4) treated by this method.

Description

Method for preventing scale adhesion on a heating surface by

  The present invention relates to a method for preventing the adhesion of scale on a stainless steel heating surface intended to be in contact with the water to be heated in the container of a

  kettle, coffee maker or electric teapot.

  The advantage of making such heating surfaces in stainless steel lies in the fact that this steel is resistant to hot water and that it is of high quality.

  food unlike other metals.

  However, the mineral elements contained in hot water eventually deposit on the stainless steel surface, forming a layer of tartar which is difficult to clean because it strongly adheres to the surface and decreases the thermal efficiency of heating when

  the surface carries an electrical heating resistance.

  In addition, the tartar layer in the presence of the chlorine contained in the water promotes oxidation by pitting of the stainless steel, pitting which by their presence generates an even stronger adhesion of the limestone and

  shorten the life of the heating element.

  The object of the present invention is to remedy

to the above drawback.

  According to the invention, the method is characterized in that said stainless steel heating surface

  is subjected to electrolytic polishing.

  Electropolishing of metal parts is well known to those skilled in the art. This process involves immersing the stainless steel surface to be treated in an electrolytic bath and applying a voltage between an electrode and the stainless steel surface. The electric current created between the two electrodes achieves on the steel surface

  stainless polishing both uniform and fine.

  It has surprisingly been found that the electrolytic polishing thus produced makes the heating surface of stainless steel, much less adherent with regard to tartar than an untreated surface or having undergone a simple mechanical polishing and protects

also oxidation stainless steel.

  According to a preferred version of the invention, said heating surface is a stainless steel cup fixed to the bottom of an electric kettle, the face opposite to that intended to be in contact

  with water carries an electric heating resistance.

  In the case in particular of electric kettles, the stainless steel heating cup bears on its face opposite to that intended to be in contact with water, either an armored resistance fixed by brazing, or a resistive layer applied by screen printing. The firing of the screen-printed layer at a temperature of the order of 9000C has the effect of strongly oxidizing the face of the cup intended to be in

contact with water.

  The electrolytic polishing carried out according to the invention has the effect of eliminating the oxide layer

  above and make the surface non-sticky to

live tartar.

  According to a preferred version of the method according to the invention, the surface having undergone electrolytic polishing is covered on its face intended to

  be in contact with water, through a layer of gold.

  It has been found not only that this layer of gold adheres strongly to the surface of stainless steel having undergone electrolytic polishing, without it being necessary to apply to the surface an undercoat, for example, of silver, but that layer of gold

  further reinforced non-adherence to it.

  of scale, and protection against corrosion.

  The invention also relates to a heating base in particular of an electric kettle constituted by a

  stainless steel dish treated according to the process below

  above. Other features and advantages of

  the invention will also appear in the description below

  after. In the accompanying drawings given by way of nonlimiting examples: - Figure 1 is a partial longitudinal sectional view of an electric kettle comprising a heating base treated according to the process according to the invention; - Figure 2 is a diagram illustrating the

  electrolytic polishing process.

  The electric kettle shown on the

  Figure 1 comprises a container 1 of plastic.

  Near the bottom 2 of the container, the side wall 3 of the container 1 supports the peripheral edge of a cup

heater 4 in stainless steel.

  According to the invention, the method for preventing the adhesion of scale on the face 5 of the cup 4 exposed to the water to be heated in the container 1, consists in subjecting the cup 4 in steel

  stainless to electrolytic polishing.

  As shown in FIG. 2, this electrolytic polishing consists in immersing the stainless steel cup 4 in an electrolytic bath 6, in connecting this cup 4 and an electrode 7 also immersed in the

  electrolytic bath 6 to a current source 8.

  In the example shown in FIG. 1, the face 9 of the cup 4 opposite to the face 5 intended to be in contact with the water to be heated carries a resistive layer deposited by screen printing. The ends of the resistive circuit are connected to an external source of

current through conductors 10.

  The screen-printed resistive layer undergoes baking at a temperature of the order of 900 ° C.

  effect of strongly oxidizing the face 5 of the cup 4.

  The electrolytic polishing of the cup 5 not only has the effect of eliminating the above oxide layer, but also of making the electrolytically polished face 5 practically non-adherent with respect to the scale formed during the successive heating of 'water

until boiling.

  In the case where the face 9 of the cup 4 carries an armored electrical resistance fixed by brazing, the electrolytic polishing of the cup 4 can be carried out before fixing by brazing of the armored resistance. According to a preferred version of the invention, the face 5 of the cup 4 electropolished is covered with a layer of gold. This layer of gold can

  have a thickness between 0.1 and 1 μm.

  It was found that the gold layer adhered perfectly to the electropolished surface and that it was not necessary to apply to the face 5

  polishes an undercoat such as silver or the like.

  It was found that this layer of gold resisted the thermal, mechanical and chemical stresses undergone by the cup 4 during the successive heating and cooling cycles. And in addition, this layer of gold can further reduce

  the adhesion of tartar to the dish.

  Of course, the invention is not limited to the example which has just been described and many modifications can be made to it without departing from the

part of the invention.

  Thus, the method according to: the invention can be applied to any piece of stainless steel intended to come into contact with the boiling water of a kettle,

  a coffee or electric teapot.

Claims (6)

  1. Method for preventing the adhesion of scale on a stainless steel heating surface (5) intended to be in contact with the water to be heated in the container (1) of a kettle, a coffee maker or a electric teapot, characterized in that said stainless steel heating surface (5) is subjected to a electrolytic polishing.   2. Method according to claim 1, characterized in that said heating surface (5) is a cup (4) made of stainless steel fixed to the bottom of an electric kettle, the face (9) opposite to that intended to be in contact with water wears a electric heating resistance.   3. Method according to claim 2, characterized in that said heating resistance is applied by screen printing on said face (9), the electrolytic polishing being carried out after this application by screen printing to remove the oxide layer resulting from the cooking of the screen printed layer.   4. Method according to one of claims 1   to 3, characterized in that the surface (5) having undergone electrolytic polishing is covered on its face intended to be in contact with water by a layer Golden.   5. Method according to claim 4, characterized in that the thickness of the gold layer is between 0.1 and 5 pm.   6. Electric kettle heating base consisting of a stainless steel cup (4) treated according to the process in accordance with one of the claims 1 to 5.