FR2828213A1 - ANTI-CORROSION TREATMENT PROCESS - Google Patents

Abstract

Process for the anti-corrosion treatment of at least one sensitive zone (5) of a first part (P) made of steel (1a, 1b) in dynamic contact with a zone of a second part also made of steel (1a), characterized in that the sensitive zone (S) of the first part is cleaned beforehand, an electric arc is created between two metal wires (F1, F2) to produce a liquid metal whose electrochemical potential is higher than that of steels of said first and second parts, and said liquid metal is sprayed onto said first part area so as to produce an anodic coating (M) for the cathodic protection of the second part.

Description

<Desc / Clms Page number 1>

 The present invention relates to an anti-corrosion treatment method and to the use of this method for protecting a sensitive area of a suspension device for motor vehicles.

 In general, when two steel parts are in permanent or intermittent dynamic contact, their respective connection zone is the seat of abrasion phenomena mainly linked to mutual friction. When these parts have a surface coating (organic paint or metallic deposit), the latter is quickly damaged and exposure to climatic variations and in particular to bad weather initiates corrosion and accelerates its effects such as the appearance of rust.

 To combat these phenomena, one solution consists in interposing between these parts a metallic material (zinc, aluminum, etc.) capable of playing the role of a consumable anode with respect to the steels constituting said parts. This mode of protection requires the establishment of electrical continuity between the steel to be protected and the consumable material as well as the presence of an electrolyte. Electrical continuity appears as soon as the steel and the consumable material previously coated, are exposed and come into direct contact following the abrasion of the parts. At the same time, a conductive medium consisting of debris and foreign bodies originating from projection phenomena forms, in the presence of moisture, the electrolyte necessary for the operation of the electrochemical cell.

 The material placed at the anode is generally used in the form of a metal insert fixed to the sensitive area of one of the parts by gluing, riveting, crimping, etc.

 However, given the importance of the forces exerted by the parts towards each other, in particular in a suspension strut, it turns out that this fixing is not sufficiently reliable.

 As a result, the expected battery effect does not occur effectively and that the cathodic protection of the parts is not satisfactorily ensured.

 The present invention aims to solve these technical problems.

 This object is achieved, according to the invention, by means of a method of treating at least one sensitive zone of a system consisting of a

<Desc / Clms Page number 2>

 first part and a second part made of steels which are intended to be in dynamic contact, characterized in that the prior cleaning of the sensitive area is carried out, an electric arc is created between two metal wires to produce a liquid metal whose electrochemical potential is greater than that of the respective steels of said first and second parts, and said liquid metal is projected onto said zone so as to produce an anodic coating for cathodic protection of the steel (1 a, 1 b) on said zone.

 According to an advantageous characteristic, said anodic coating has a roughness (Ra) greater than 25 m.

 According to a specific mode of implementation, said sensitive zone is located on the first part and a layer of phosphating and a layer of paint are applied to the second part at least in the part in contact with the sensitive zone of the first part.

 Preferably, said layer of paint is applied by cataphoresis.

 According to an advantageous characteristic, said liquid metal is projected by means of a flow of compressed air.

 According to another characteristic, the two metal wires consist of the same metal or of two different metals chosen from zinc, aluminum or one of their alloys.

 Preferably, the preliminary cleaning of the sensitive area is carried out by sandblasting.

 According to an implementation variant, a layer of paint is then applied to said anodic coating.

 According to another variant, a layer of phosphating and a layer of paint are applied to the second part at least in the zone in contact with the first part.

 According to another characteristic, the liquid metal is projected onto the sensitive area before any phosphating, painting, galvanizing and assembly of the parts.

 Another object of the invention is a use of the process defined above to protect from corrosion at least one sensitive zone of a lower and / or upper cup and / or the end turn of a spring respectively forming the first and second pieces of steel in contact in a vehicle suspension device.

<Desc / Clms Page number 3>

 The protective coating is obtained according to the invention by electrothermal spraying using a torch supplied with compressed air or a neutral gas.

 The protection of the steel parts is ensured, firstly, mechanically by the surface finishing layer then, secondly, after abrasion of this layer, by the electrochemical attack of the anodic metallic coating, underlying in contact with the stripped steel of the part placed in the cathode position.

 The protective metallic coating is applied in liquid form and has, after cooling, a high adhesion to steel, which gives it a reinforced hold on the part.

 In addition, this coating has a very pronounced roughness favorable to the positioning and wedging of the parts in contact. Thus, the intense friction generated between the spring and the cup in a MacPherson type suspension device is likely to update the rough protective coating by jointly reducing the path of the spring and by preventing the rotation of the terminal turn, which improves the efficiency and reliability of these suspension devices.

 The invention will be better understood on reading the description which follows with reference to the accompanying drawings, in which: - Figure 1 shows a schematic view of an embodiment of the method of the invention; - Figures 2A and 2B show schematic sectional views of parts treated with a first variant of the method of the invention respectively before and after abrasion of the surface finishing layers.

 - Figures 3A and 3B show sectional views of parts treated by a second variant of the method of the invention, respectively before and after abrasion of the surface finishing layers.

 FIG. 1 represents an embodiment of the method of the invention applied to the anti-corrosion treatment of a piece P of steel, materialized here by a flat wall.

 The part has a sensitive zone S intended to come into dynamic contact with another steel part, not shown. The

<Desc / Clms Page number 4>

 zone S must therefore be treated to protect the subsequent assembly of the two parts from corrosion.

 To this end, the zone S is previously cleaned or pickled, and is then placed opposite a torch T intended for the electrothermal projection of a protective metallic coating. The surface of the area is optionally sanded to improve the adhesion of the protective coating.

 The zone S is delimited so as to encompass the surface intended for the contact of the part P with another part.

 The torch T comprises a housing B in which are fixed two metal wires Fi, F2, brought to an electrical potential and forming electrodes. The wires Fi, F2 are moved longitudinally in sheaths Gi, G2 and their respective ends protrude outside the housing B at the center of a deflector D.

 The two sheaths G1, G2 are maintained in a precise spatial orientation with respect to each other by means of an adjustable spacer E. The optimum inclination a between the wires F1, F2 is between 25 and 35.

 According to the invention, an electric arc is created between the ends of the metal wires Fi, F2 to bring their temperature to values between 4000 C and 5000 C. The metals constituting each of the wires are in the molten state during the entire projection phase.

 In the space inside the housing B, between the sheaths G1, G2 and the spacer E, a flow of compressed air A or neutral gas is injected producing a flow of gas entraining the droplets of liquid metal to speeds between 100 and 200 m / s. This flow is intended to project the liquid metal at high temperature against the surface of the area S to be treated.

 As the filler metal M accumulates on the zone S, the wires F1, F2 are consumed and it is necessary to advance them inside the sheaths at predetermined speeds.

 The composition of the filler metal is determined according to the formula of the steel constituting the part P and that of the other part intended to come into contact with it.

 The filler metal which forms the protective coating results from the mixture in the liquid state of the metals of the wires F1, F2.

<Desc / Clms Page number 5>

 The two wires can be made with the same metal or with two different metals.

 These metals are chosen from zinc, aluminum or an alloy of the latter.

 The choice of the relative sections and of the advance speeds of the two wires also makes it possible to adjust the proportions of the different metallic elements in the projected mixture and therefore in the anodic coating M.

 When the coating thickness M reaches the desired value, the metal spraying is stopped and the part P is sent to a welding station, and / or a galvanizing station, and / or a surface treatment workshop by phosphating and paint where the coated part receives a mechanical protective coating before the part P is assembled with another part. The coating M has a roughness whose value (Ra) is greater than 25 m, which prevents any untimely subsequent movement of the part P relative to the other parts in contact.

 Figures 2A and 2B show partial sectional views of a vehicle suspension device. This device comprises in particular a lower cup C of steel on which the end turn of a spring R of hardened steel comes into bearing contact. The cup C is itself assembled, for example by welding, to a shock absorber tube (not shown) to form a strut.

 FIG. 2A represents the turn of the spring R and the lower cup C treated by the method of the invention in the initial state. The coil consists of a section of hardened steel 1a and a layer of phosphating and paint 2a.

 The cup C has a thickness of steel 1b, an anodic protective coating M and a layer of phosphating and paint or galvanization 2b.

 The spring R like the cups and more particularly the lower cup C are, in service, the seat of abrasion phenomena linked to the respective contacts and friction of the spring on the cups.

The coatings of these parts, whether organic or metallic, are fairly quickly damaged and climatic variations initiate

<Desc / Clms Page number 6>

 corrosion phenomena leading in particular to the appearance of red rust.

 After wear of part of layer 2a of the spring and layer 2b of the cup, as shown in FIG. 2B, the steel 1a of the coil is in direct contact with the anodic coating M.

 The coating M being metallic and therefore a good electrical conductor, it is thus established, by contact, a continuous electrical connection with the steel 1a.

 Furthermore, an electrochemical medium is formed in situ in the presence of moisture, debris and / or foreign bodies, favored by the aging and degradation of layers 2a and 2b. The contact zone between the spring R and the coating M of the cup C then becomes the site of a phenomenon of galvanic coupling.

 The electrochemical potential of the coating M being lower than that of the steel 1a, it is the metal of the coating which is attacked in priority.

This selective attack thus preserves the steel 1a from corrosion, the steel 1b being protected by covering.

 Another variant of the process of the invention consists in applying the protective anodic coating to the terminal coil (s) of the spring.

 The implementation of the thermal spraying of the coating is carried out after a shot peening operation of the spring making it possible to benefit from the good state of cleanliness and reactivity of the surface condition of the spring.

 Once shot blasted, the spring is placed on a carousel-shaped presentation machine comprising a sandblasting station and an electric arc projection station. The sandblasting operation can be omitted if the surface condition induced by shot blasting is sufficient to impart a sufficient level of adhesion of the deposit on the spring.

 For aesthetic reasons, the protective anode coating must be deposited only on the terminal coil and not on the intermediate coils. To do this, a mask is placed between the terminal turn to be treated and the remaining part of the spring. The springs are oriented on the presentation machine and the jet of molten metal is directed on the side of the terminal turn by means of a robotic arm.

<Desc / Clms Page number 7>

 The mask is made of a material resistant both to the temperature of the molten metal and to the shock of the projection of the metal jet and can integrate an internal cooling circuit.

 The electric arc projection precedes the surface finishing operation which must implement a range of multimaterial phosphating compatible with the presence of zinc or aluminum on the spring. The spring can be coated by cataphoresis or by dusting.

 Figures 3A and 3B show partial sectional views of a vehicle suspension device. This device comprises in particular a lower cup C of steel on which the end turn of a spring R of hardened steel comes into bearing contact. The cup C is itself assembled, for example by welding, to a shock absorber tube (not shown) to form a strut.

 FIG. 3A represents the lower cup C and the turn of the spring R treated by the method of the invention in the initial state. The cup C is made of a thickness of steel for stamping 1b and a layer of phosphating and painting or galvanizing 2b.

 The coil of spring R has a steel section 1a, an anodic protective coating M and a layer of phosphating and paint 2a.

 The spring R like the cups and more particularly the lower cup C are, in service, the seat of abrasion phenomena linked to the contacts and to the respective friction of the spring on the cups.

The coatings of these parts, whether organic or metallic, are fairly quickly damaged and climatic variations initiate corrosion phenomena leading in particular to the appearance of red rust.

 After wear of part of the layer 2a of the spring and of the layer 2b of the cup, as shown in FIG. 3B, the steel 1b of the cup is in direct contact with the anode coating M of the spring.

 The coating M being metallic, it is established by contact an electrical continuity between the steel 1b and the anodic coating M.

 In the presence of a conductive poultice formed in the presence of moisture and composed of debris and foreign bodies, the area

<Desc / Clms Page number 8>

 of contact between the cup C and the metal layer M deposited on the spring R is the site of a phenomenon of galvanic coupling.

 The electrochemical potential of the coating M being lower than that of the steel 1 b, it is the metal of the coating M which is attacked in priority. This selective attack preserves the steel 1b from corrosion, the steel 1a being protected by covering.

 A last variant of the process finally consists in depositing a protective anodic coating on each of the parts to be protected, the galvanic coupling only being established when the wear of one of the metallic coatings is complete.

Claims (10)

1. Method for anti-corrosion treatment of at least one sensitive zone (S) of a system consisting of a first part (P) and a second part (R) made of steels (1a, 1b) which are intended to be in contact, characterized in that the sensitive zone (S) is cleaned beforehand, an electric arc is created between two metal wires (F1, F2) to produce a liquid metal whose electrochemical potential is greater than that respective steels of said first and second parts, and said liquid metal is projected onto said zone (S) so as to produce an anodic coating (M) for the cathodic protection of the steel (1 a, 1 b) on said zone.  2. Method according to claim 1, characterized in that said anodic coating has a roughness (Ra) greater than 25 m.  3. Method according to claim 1 or 2, characterized in that said sensitive zone is on the first part (P) and a layer of phosphating and a layer of paint (2a) are applied to the second part at least in the part in contact with the sensitive area of the first part (P).  4. Method according to one of the preceding claims, characterized in that said layer of paint (2a, 2b) is applied by cataphoresis.  5. Method according to one of the preceding claims, characterized in that said liquid metal is projected by means of a flow of compressed air (A).  6. Method according to one of the preceding claims, characterized in that the two metal wires (F1, F2) consist of the same metal or of two different metals chosen from zinc, aluminum or one of their alloys.  7. Method according to one of the preceding claims, characterized in that the prior cleaning of the sensitive area (S) is carried out by sandblasting.  8. Method according to one of the preceding claims, characterized in that a phosphating layer and a layer of paint (2b) are applied to said anode coating (M). <Desc / Clms Page number 10>  9. Method according to one of the preceding claims, characterized in that the liquid metal is projected onto the sensitive zone (S) before any paint phosphating operation, galvanization and assembly of the parts (P, R).  10. Use of the method according to one of the preceding claims to protect from corrosion at least one sensitive area of a lower cup (C) and / or upper and / or the end turn of a spring (R) forming respectively the first and second pieces of steel in dynamic contact in a vehicle suspension device.