METHOD FOR PRODUCING A ZINC COATING OPTIMIZED FOR COEFFICIENT OF FRICTION ON A STEEL COMPONENT

Abstract

A method for producing a zinc coating optimized for coefficient of friction on a steel component. In order to provide such a method resulting in a coating having good corrosion protection properties, good adhesion and a stable, constantly low coefficient of friction, including in the case of repeated use of the steel component, in particular multiple draft, wherein the method can be carried out both easily and cost-effectively, a zinc coating is first applied to the surface of the steel component by a galvanic deposition process and subsequently a heat treatment is carried out at a temperature of below 420° C. for the specific forming of intermetallic zinc-iron phases in the galvanically deposited zinc layer in order to optimize the coefficient of friction of the steel component.

Claims

1. A method for producing a friction-optimized zinc coating on a steel component, having the steps of: applying a zinc layer to the surface of the steel component by a galvanic deposition process and subsequently carrying out a heat treatment at a temperature of below 420° C. for the specific forming of intermetallic zinc-iron phases in the galvanically deposited zinc layer in order to optimize the friction value.

2. The method for producing a friction-optimized zinc coating on a steel component according to claim 1, wherein the application of a zinc layer and all subsequent method steps for producing the zinc-coated steel component are carried out at temperatures of below 420° C.

3. The method for producing a friction-optimized zinc coating on a steel component according to claim 1, wherein the holding time of the heat treatment is between 20 minutes and 10 hours, or between 20 minutes and 6 hours, or between 30 minutes and 4 hours.

4. The method for producing a friction-optimized zinc coating on a steel component according to claim 1, wherein the heat treatment is carried out at a temperature between 250° C. and 310° C., whereby a ζ-phase of the iron-zinc is formed.

5. The method for producing a friction-optimized zinc coating on a steel component according to claim 1, wherein the heat treatment is carried out at a temperature of between 340° C. and 360° C., whereby a δ-phase of the iron-zinc is formed.

6. The method for producing a friction-optimized zinc coating on a steel component according to claim 1, wherein the surface of the steel component is pickled and/or pre-galvanized before the zinc layer is applied.

7. The method for producing a friction-optimized zinc coating on a steel component according to claim 1, wherein, before the zinc layer is applied and/or after pickling and/or after pre-galvanizing, a further heat treatment is carried out against possible hydrogen embrittlement, which is carried out at temperatures of between 200° C. and 250° C.

8. The method for producing a friction-optimized zinc coating on a steel component according to claim 1, wherein, after the zinc layer has been applied, the zinc surface is passivated by means of an organoceramic coating.

9. The method for producing a friction-optimized zinc coating on a steel component according to claim 1, wherein the heat treatment for forming the zinc-iron phases takes place with the use of a temperature-resistant passivation layer following the passivation.

10. The method for producing a friction-optimized zinc coating on a steel component according to claim 1, wherein the zinc layer is applied to the surface of the steel component in the galvanic deposition process by an alkaline zinc electrolyte containing nitrogen-containing polymers.

Description

[0036] Several embodiments of the invention are subsequently described in more detail with reference to a drawing. The FIGURE shows:

[0037] FIG. 1 a schematic flow diagram of a method for producing a zinc coating with an optimized zinc coating on a steel component.

[0038] In a first embodiment of the method for producing a friction-optimized zinc coating on a steel component, a pure zinc coating is first applied to the surface of a steel screw for an electrical terminal block by means of a galvanic deposition process. A cyanide-free alkaline zinc electrolyte in aqueous solution is used, wherein the solution preferably also contains nitrogen-containing polymers. The use of this alkaline zinc electrolyte results in the nitrogen-containing polymers being at least partially incorporated in the zinc coating, as a result of which the steel screw has significantly more stable friction values.

[0039] Immediately after the coating, a heat treatment is carried out, for which the zinc-coated steel screw is heated to 300° C. for 30 minutes in a furnace in order to form and stabilize a ζ-zinc-iron phase between the surface pure zinc and the steel surface of the coated steel screw. This optimized layer structure is characterized in this case by the stabilization of the ζ-phase in the transition area from the zinc layer to the base material. The course of the friction value is characterized by an almost constant friction value over ten tightening cycles, and the scatter of the coefficients of friction could also be significantly reduced as a result.

[0040] Alternatively, the duration of the heat treatment can be between 20 minutes and 4 hours. In any case, only one temperature cycle is carried out with a single heating, holding at 300° C. and cooling. Such a heat treatment to form an intermetallic zinc-iron phase can be carried out, for example, in a continuous furnace, wherein the steel screws are heated up to 300° C. at a heating rate of about 10 K/min and held at this temperature for 30 min. This is followed by cooling in still air, in particular at a cooling rate of about 5 K/s.

[0041] In addition, however, heat treatment exclusively at a lower temperature and for a longer period is possible. For this purpose, for example, the steel screws are heated up to 250° C. in a chamber furnace at a heating rate of about 10 K/min to form an intermetallic zinc-iron phase and held at this temperature for about 6 hours up to 10 hours or longer. This is followed by cooling in still air, in particular at a cooling rate of about 5 K/s.

[0042] Particularly preferably, the heat treatment at 300 C is not followed by complete cooling, but the steel components are then kept at a temperature of 250° C. for a longer period, in particular 6 hours, as shown in FIG. 1. This achieves a more uniform result over all the steel components and a more undisturbed, uniform layer structure of each steel component.

[0043] In another embodiment, the electroplating of a steel component of an electrical contact element is carried out using a cyanide-free, alkaline zinc electrolyte. Passivation is carried out immediately thereafter, wherein organoceramic layers formed predominantly from chromium and/or zinc oxides are applied to the galvanized surface of the steel component.

[0044] Subsequently, as the last production step of the steel component, a heat treatment of the zinc-coated and passivated component is carried out in a furnace at a temperature of 300° C. for a period of 30 minutes.

[0045] Another embodiment proceeds from a component identically coated with zinc, wherein heat treatment takes place in two steps. First, the component is heated to 350° C. and held there for 30 minutes. Subsequently, the component is cooled to 300° C. and held there for a further hour.

[0046] After complete cooling, passivation is carried out, which can be done by means of a non-heat-resistant passivating agent.