EP1281786A1 - Anti-corrosion treatment - Google Patents

Abstract

A method for the anti-corrosion treatment of a surface (S), of a first component (P) of a system made up of this first piece and a second steel component which are destined to be in contact in a zone formed by at least a part of the surface of the first component and a part of the surface of the second component, consists of: (a) firstly cleaning the surface on the first component; (b) creating an electric arc between two metal wires (F1, F2) to produce a liquid metal; (c) projecting this liquid metal onto the surface of the first component to produce an anodic coating (M) for the cathodic protection of the steel of the second component. An Independent claim is also included for the utilization of this method for the anti-corrosion protection of at least a part of the surface of a lower and/or upper surface of a dish and/or one or more turns at the end of a spring forming the first and second steel components in dynamic contact in a vehicle suspension device.

Description

The present invention relates to an anti-corrosion treatment method as well as a use of this process to protect an area sensitive of a suspension device for motor vehicles.

Generally, when two pieces of steel are in permanent or intermittent dynamic contact, their respective area of bond is the seat of abrasion phenomena mainly linked to mutual friction. When these parts have a coating of surface (organic paint or galvanizing layer), the latter is rapidly damaged and exposure to climatic variations and particular to bad weather initiates corrosion and accelerates its effects as the appearance of rust.

One solution to combat these phenomena is to interpose between these parts a metallic material (zinc, aluminum ...) able to play the role of a consumable anode with respect to the constituent steel of one of the two parts in contact or simultaneously with respect to the two steels constituting said two parts. This protection mode requires establishing electrical continuity between the steel to be protected and the consumable material as well as the presence of an electrolyte. The electrical continuity appears when steel and material consumable previously coated, are exposed and come into contact direct following the destruction of the finish coatings, in particular by mutual abrasion of parts in dynamic contact. Together, a conductive medium, consisting of debris and foreign bodies 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 ...

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

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

The object of the present invention is to solve these problems techniques.

This object is achieved, according to the invention, by means of a method of treatment of at least a surface portion of a first part of a system consisting of a first part and a second steel part which are intended to be in dynamic contact in a contact zone dynamics formed by at least said surface portion of the first part and a surface portion of the second part, by the fact that performs the prior cleaning of at least said portion of the surface of said first part, an electric arc is created between two metallic wires to produce a liquid metal, said liquid metal is projected at least on said surface portion of said first part so as to produce a anodic coating for cathodic protection of the steel of which said second part, said anodic coating having a potential electrochemical weaker than that of the constituent steel of said second room.

Advantageously, the anodic coating has a lower electrochemical potential than that of the constituent steel of said second part regardless of the electrolyte present in the area of contact.

Thus, whatever the electrolyte considered, that is to say, which whatever debris and foreign objects are projected onto the system, electrochemical potential of the anodic coating of the first part is smaller than that of the steel making up the second part. In consequence, electrical continuity, forming the protection of the system, appears in the presence of moisture as soon as direct contact between the two parts of the system takes place.

According to an advantageous characteristic, said coating anodic has a lower electrochemical potential than the most small electrochemical potential of the two constituent steels of said first and second parts in dynamic contact.

According to another variant, a layer of phosphating and painting at least on said anodic coating of said second piece.

In fact, any other surface treatment aimed at protecting and covering the anodic coating of said second part can be envisaged, such as for example galvanizing.

Preferably, said layer of paint is applied by cataphoresis.

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

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

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

Preferably, the prior cleaning of said portion of surface of said first part is made by sandblasting.

Consequently, said first part has at least on the portion of surface intended to be treated by projection of a metal liquid, a surface condition suitable for good attachment of the deposit metallic. In particular, the surface is cleaned of all impurities and its surface condition presents an uneven relief conducive to the creation of connections between the deposited metallic coating and the steel of the first room.

According to another variant, a layer of phosphating and painting on the first piece at least on the portion of surface which forms with the surface portion of the second part the dynamic contact area.

According to another characteristic, the liquid metal is projected onto the first part before any phosphating, painting, galvanizing and / or assembling the two parts of the system.

Another subject of the invention is a use of the defined method above to protect from corrosion at least the end turn of a spring each forming with a lower cup and / or upper one first and second pieces of steel in dynamic contact in a suspension device for vehicle.

Preferably and for convenience of making different treatments on each of the two parts, the cup forms the first part of the system which is coated with metal spray, while the spring forms the second part presenting the protection cathodic induced by said anodic coating.

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

The protection of the second part is ensured, in a first time, mechanically by the surface finishing layers (in particular, the phosphate and paint layer), then in a second time, after destruction of these layers following mutual abrasion of two parts in contact, by cathodic protection resulting from coupling galvanic which is established between the second exposed part and the deposit metal of the first part placed in cathode position.

In fact, as soon as the steel constituting the second part appears in the contact area between the two rooms, following the attack by finishing layers, this steel comes into contact with the metallic deposit of the first room; it follows the birth of an electrical continuity between the two pieces which protects the second piece.

The protective metallic coating has a very roughness pronounced favorable to wedging and non-sliding of the parts in contact, despite the intense friction generated between the two parts. In particular, in the case of a MacPherson type suspension device, the two parts remain in contact well wedged, despite the high friction existing between the spring and the cup. Furthermore, the high roughness of the metallic coating caused by the type of deposit chosen (deposit under projection of liquid metal), ensures, when said coating is initially covered with a layer of phosphating and paint, a exposure of the first piece prior to that of the second piece coated with a layer of phosphating and paint only.

In addition, this protective metallic coating applied under liquid form has, after cooling, a high adhesion to steel, which gives it a stronger hold on the part.

• la figure 1 représente une vue schématique d'un mode de mise en oeuvre du procédé de l'invention ;
• les figures 2A et 2B représentent des vues schématiques en coupe de pièces traitées par une première variante du procédé de l'invention respectivement avant et après abrasion des couches superficielles de finition.
• les figures 3A et 3B représentent des vues en coupe de pièces traitées par une seconde variante du procédé de l'invention, respectivement avant et après abrasion des couches superficielles de finition.

The invention will be better understood on reading the description which will follow with reference to the appended drawings, in which:

• FIG. 1 represents a schematic view of an embodiment of the method of the invention;
• Figures 2A and 2B show schematic sectional views of parts treated by 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 surface portion S intended to come in dynamic contact with another steel part not shown in a contact area. The surface portion S must therefore be treated to protect the subsequent assembly of the two parts from corrosion.

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

The surface portion 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 F ₁ , F ₂ , brought to an electrical potential and forming electrodes. The wires F ₁ , F ₂ are displaced longitudinally in sheaths G ₁ , G ₂ and their respective ends protrude outside the housing B at the center of a deflector D.

The two sheaths G ₁ , G ₂ are maintained in a precise spatial orientation with respect to each other by means of an adjustable spacer E. The optimal inclination α between the wires F ₁ , F ₂ is between 25 ° and 35 °.

According to the invention, an electric arc is created between the ends of the metal wires F ₁ , F ₂ 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 included inside the housing B, between the sheaths G ₁ , G ₂ and the spacer E, a flow of compressed air A or neutral gas is injected producing a flow of gas entraining the metal droplets liquid at speeds between 100 and 200 m / s. This flow is intended to project the liquid metal at high temperature against the surface portion S to be treated.

As the filler metal M accumulates on the zone S, the wires F ₁ , F ₂ are consumed and it is necessary to advance them inside the sheaths at predetermined speeds.

The composition of the filler metal is chosen according to the formula of the steel making up part P and that of the other part intended to come into contact with him.

The filler metal which forms the protective coating itself results from the mixture in the liquid state of the metals of the wires F ₁ , F ₂ .

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

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

The choice of relative sections and feed rates of two wires also allows you to adjust the proportions of the different elements metallic in the sprayed mixture and therefore in the anodic coating Mr.

When the thickness of the coating M reaches the value metal projection is stopped and part P is routed to a welding station, and / or a galvanizing station, and / or a surface treatment workshop by phosphating and painting before being brought into contact against another part by assembly. M coating has a roughness with a value (Ra) greater than 25 µm, which limits any subsequent untimely movement of the part P relative to the other parts in contact.

The steel part P on which the anodic coating has been deposited, can further be processed using a range of "multimaterial" phosphating capable of reacting effectively with steel constituting part P, zinc and aluminum from the deposit. This range of phosphating contains, for example to increase its effectiveness, SiF6 fluorides capable of complexing with aluminum, which, when in solution, is poisonous for the phosphating bath.

Figures 2A and 2B show partial sectional views a suspension device for a vehicle. This device includes in particular a lower cup C in steel on which the turn end of a hardened steel spring R comes into bearing contact in a contact zone Z. The cup C is itself assembled, by 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 cup lower C treated by the method of the invention in the initial state. The whorl of the spring R consists of a section of hardened steel 1a and a layer of phosphating and paint 2a which initially covers preferably all the steel 1a, in any case at least the portion of Sa surface which corresponds to the surface in contact with the cup lower C.

The cup C has a thickness of steel 1b, a coating anodic protector M and a layer of phosphating and paint or of galvanization 2b at least on a portion of surface Sb which corresponds to the surface in contact with the spring R.

The spring R like the lower and upper 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 R on the cups in a dynamic contact zone Z. 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 rust red.

Consequently, in this embodiment, after wear part of layer 2a of spring R and layer 2b of spring cup C, as shown in FIG. 2B, the steel 1a of the coil is found in direct contact with the anode coating M in the area of dynamic contact Z formed by the contact, between the cup C and the spring R, of the two portions of surfaces Sa and Sb.

The contact zone Z evolves during the wear of the different coatings of parts R and C, for each of the parts, it is better to do these, and in particular, metallic deposition, on a respective surface larger than that defining the contact initial (before wear) between the two parts R and C. To ensure that the contact area is well coated, the coatings, especially the finishing coatings are carried out on the entire part to be treated.

The coating M being metallic and therefore a good conductor electric, it is thus established, by contact between the spring R and the cup C, a continuous electrical connection with the steel 1a of the spring R.

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

The electrochemical potential of the coating M of the cup C being lower than that of steel 1a of spring R, it is the metal of coating M of the cup C which is attacked as a priority. This attack selective thus preserves the steel 1a of the spring R from corrosion, the steel 1b remaining protected by sufficient covering of the coating M which is partially consumable.

Another variant of the process of the invention consists in apply the protective anodic coating on the coil (s) spring terminals.

The implementation of the thermal spraying of the coating is performed after a shot peening operation allowing benefit from the good state of cleanliness and responsiveness of the surface finish of the spring.

Once shot blasted, the spring is placed on a presentation in the form of a carousel comprising a sandblasting station and a electric arc projection station. The sandblasting operation can be suppressed if the surface finish induced by shot blasting is sufficient to give a sufficient level of adhesion of the deposit on the spring.

For aesthetic reasons, the anodic coating protector must be placed only on the terminal coil and not on the intermediate turns. To do this, a mask is placed between the coil terminal 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.

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

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

Figures 3A and 3B show partial sectional views a suspension device for a vehicle. This device includes in particular a lower cup C in steel on which the turn end of a hardened steel spring R comes into bearing contact in a contact zone Z formed by the portions of facing surfaces, Sa and Sb respectively, of the spring R and of the cup C. The cup C is itself assembled, for example by welding, to a tube shock absorber (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 consists of a thickness of steel for stamping 1b and a at least 2b phosphating and painting or galvanizing layer on the surface portion Sb.

The coil of the spring R has a section of steel 1a, a anodic protective coating M and a layer of phosphating and paint 2a, at least on the surface portion Sa.

In this other embodiment, after wear of part of layer 2a of spring R and layer 2b of cup C, as shown in Figure 3B, the steel 1b of the cup C is in contact direct with the anode coating M of the spring R in the area of contact Z.

As in the aforementioned embodiment, the coating M being metallic, it establishes by contact an electrical continuity between the steel 1b of the cup C and the anodic coating M of the spring R.

In the presence of a conductive poultice forming in presence of moisture and composed of debris and foreign bodies, the area contact Z between the cup C and the metal layer M deposited on the spring R is the seat of a phenomenon of galvanic coupling.

The electrochemical potential of the coating M of the spring R being lower than that of the steel 1b of the cup C, it is the metal of coating M of the spring R which is attacked as a priority. This attack selective protects steel 1b from cup C from corrosion, steel 1a from spring R being protected by a sufficient covering of coating M.

A final variant of the process finally consists in depositing a protective anodic coating on each of the parts to be protected, the galvanic coupling only established when the wear of one of the metal coatings will be complete. Each of these coatings anodic can also be covered with a topcoat type phosphating and painting or galvanizing.

Claims (13)

Method for anti-corrosion treatment of at least a surface portion (S; Sa; Sb) of a first part (P; R; C) of a system consisting of a first part (P; R; C) and a second piece (P; C; R) of steels (1a, 1b) which are intended to be in contact in a contact zone (Z) formed by at least said surface portion (S; Sa; Sb) of the first part (P; R; C) and a surface portion (Sb; Sa) of said second part (P; C; R),
characterized in that the prior cleaning of at least said surface portion (S; Sa; Sb) which is on the first part (P; R; C) is carried out, an electric arc is created between two metal wires ( F ₁ , F ₂ ) to produce a liquid metal, said liquid metal is projected at least on said surface portion (S; Sa; Sb) of the first part (P; R; C) so as to produce an anodic coating ( M) for cathodic protection of the steel (1a; 1b) constituting the second part (P; C; R), said anodic coating having a lower electrochemical potential than that of the steel (1b; 1a) constituting said second part (P; C; R). Method according to the preceding claim, characterized in that said anodic coating has a lower electrochemical potential than that of the steel (16; 1a) constituting said second part (P; C; R) whatever the electrolyte present in the contact area (Z). Method according to any one of the preceding claims, characterized in that said anode coating has a lower electrochemical potential than the smallest electrochemical potential of the two steels (1a; 1b) constituting said first and second parts (P; R; C) in touch. Method according to any one of the preceding claims, characterized in that a layer of phosphating and paint (2a; 2b) is applied at least to said anodic coating (M) of said second part (P; C; R). Method according to the preceding claim, characterized in that said phosphating layer is obtained by a range of "multimaterial" phosphating compatible with the metal of said anode coating (M) deposited on said first part (P; R; C). Method according to the preceding claim, characterized in that the said range of "multimaterial" phosphates comprises fluorides. Method according to any one of the preceding claims, characterized in that the said anodic coating (M) has a roughness (Ra) greater than 25 µm. Method according to any one of the preceding claims, characterized in that the said layer of paint (2a, 2b) is applied by cataphoresis. Method according to any one of the preceding claims, characterized in that the said liquid metal is projected by means of a flow of compressed air (A). Method according to any one of the preceding claims, characterized in that the two metal wires (F ₁ , F ₂ ) consist of the same metal or of two different metals chosen from zinc, aluminum or one of their alloys . Method according to any one of the preceding claims, characterized in that said preliminary cleaning of said surface portion (S) of said first part (P; R; C) is carried out by sandblasting. Method according to any one of the preceding claims, characterized in that the liquid metal is projected onto the said surface portion (S; Sa; Sb) before any paint phosphating, and / or galvanizing and / or d '' assembly of parts (P; R; C). Use of the method according to any one of previous claims to protect against corrosion at least one surface portion (Sb) of a lower and / or upper cup (C), and / or the end turn (s) of a spring (R) respectively forming the first and second pieces of steel in dynamic contact in a vehicle suspension device.

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