CH716485A2 - Method and device for producing a coating on a surface. - Google Patents

Abstract

The invention relates to a method for producing a coating of a surface of at least one surface of a bulk material-like part or substrate. The coating is carried out with zinc, the surface to be coated being heat-treated together with the zinc at a temperature of preferably 300 ° C to 420 ° C. A technologically better and more cost-effective coating of the surface with zinc should be made possible. For this purpose, a reaction space is loaded together with the parts to be coated, zinc powder and preferably a filler and then subjected to static vibration or unbalance for mixing and dynamic vibration or unbalance for vibratory conveyance during a coating period.

Description

The invention relates to a method for producing a coating of a surface of at least one surface of a bulk material-like or piece goods-like part or substrate. The coating is carried out with zinc, the surface to be coated being heat-treated together with the zinc at a temperature of preferably 300 ° C to 420 ° C.

The invention also relates to a device for producing a coating on a surface.

To protect the surfaces of parts made of corrosion-prone materials, for example steel, it is known to apply a thin zinc layer on the surfaces concerned. This can be done, for example, by hot-dip galvanizing, electro-galvanizing or sherardizing.

A coating method based on sherardizing is disclosed, for example, in EP 2271784 B1. Here, the part to be galvanized is heat-treated with zinc powder mixed with an inert filler such as sand or ceramic at a temperature of approx. 350 ° C to 415 ° C in a heated, rotating drum. After filling, the drum is hermetically sealed and heated. The coating takes place as a diffusion coating process in which zinc diffuses from the gas phase into the surface layer of the part to be galvanized.

[0005] The disadvantage of sherardizing is a high consumption of zinc due to oxidation due to the atmospheric oxygen initially present in the drum. The part to be galvanized must also be fixed in the drum.

[0006] In EP 2271784 B1 it was therefore proposed to set the oxygen content in the drum to less than 5% by volume and to only supply gas with an oxygen content of at most 100 ppm during the heat treatment. A flux, for example aluminum or zinc chloride, should also be added to the treatment room before the heat treatment.

The parts to be galvanized can be attached to a rotatable frame outside the drum, which is then inserted into a reaction chamber of the drum. The frame used can rotate, tilt, swing, vibrate or oscillate in the reaction chamber during the heat treatment.

In another method for the heat treatment of components according to DE 102012015844 B4, components are inserted into a heating chamber in which a fluidized sand bed is located. The fluidization of the sand bed is switched off as soon as a component is inserted. The component is subjected to a heat treatment in a static sand bed, the sand bed being fluidized at least once briefly during the heat treatment and the component being moved in the process. The heat treatment is then continued in the static sand bed.

In a fluidized bed furnace according to DEOS 3700452, the underside of the working space is bounded by a porous plate. Gas flows through this porous plate, which is intended to whirl up aluminum oxide particles in the working space, so that a fluid is formed which, when heated, serves as a heat carrier. According to the teaching of DE 10349425 A1, a fluidized bed contains fine-grained fluidized material that is fluidized and heated with gas. Subsequently, parts to be cleaned with deposits are used. The deposits are gasified by oxidation with oxygen contained in the fluid gas and the parts are thus cleaned.

[0010] Fluidized beds can also be used to coat surfaces. For example, EP 2906354 B1 discloses a fluidized bed coating device for coating the surface of particles with a liquid. The liquid is introduced into a coating chamber with a spray nozzle, the spray nozzle having an ultrasonic driver. Using ultrasound, the liquid is atomized into a cloud of fine liquid particles in order to achieve good wetting and coating.

The invention is based on the object of developing a method for producing a coating of a surface, in particular a metallic surface, which is intended to enable a technologically better and more cost-effective coating of the surface with zinc, which in particular is more reproducible and homogeneous than with conventional methods , for example according to EP 2271784 B1.

[0012] The object is achieved with the features of claim 1.

According to the invention in particular a metallic surface of a part is coated with zinc in a closed reaction chamber, the surface to be coated being heat-treated together with the zinc at a temperature of preferably 300 ° C to 420 ° C in an atmosphere. The reaction space is loaded with the parts to be coated, zinc powder and a filler and then subjected to static vibration or unbalance for mixing and dynamic vibration or unbalance for vibratory conveyance during a coating period.

[0014] The parts are pourable or like bulk goods or piece goods.

In the context of the invention, bulk material means bulk material, such as, for example, granules or spherical parts and parts that can be handled like bulk material, for example screws or pins. Piece goods can include piece goods, such as, for example, housing-shaped parts.

[0016] The batch size located in each case in a trough-shaped torus or in a torus in the form of a ring or tire for heat treatment and coating is preferably approximately 1-50kg, larger batches being possible.

Preferred embodiments of the method according to the invention are disclosed in the dependent claims.

Static vibration or an imbalance and dynamic vibration or imbalance are carried out simultaneously, over a coating period of at least 10 minutes or even less.

The filler is advantageously a granulate, in particular sand, an aluminum or a ceramic granulate.

The thickness of the zinc layer to be achieved on the part surface is regulated by means of the heat treatment temperature and the heat treatment duration, and the atmosphere in the reaction chamber can be low in oxygen and, for example, have an oxygen content of max. 100 ppm during the heat treatment and coating process.

The coating is preferably carried out with zinc, the surface to be coated being heat-treated together with the zinc at a temperature of preferably 300 ° C to 420 ° C. The coating can take place in one or two layers, whereby the second layer can also contain materials other than zinc.

A continuous process is proposed which enables a technologically improved coating of the surfaces of bulk material-like parts by means of a simplified device and a simplified process sequence and thus lower unit costs compared to the prior art.

From vibratory grinding (barrel finishing), a generally discontinuous process, it is known to bring the parts to be ground and the grinding bodies together into a treatment room, for example a drum. The drum is inclined or arranged horizontally and rotates around its longitudinal axis. Instead of a rotating drum, a pot-shaped container and its contents can be made to vibrate by means of a vibrator, which should be particularly suitable for large and heavy parts. Continuous processes with screw-shaped containers are also possible. In all process variants of vibratory grinding, neither heating nor coating of the parts to be ground takes place.

A sub-object of the invention is to create a device for producing a coating of a surface, in particular a metallic surface.

The inventive device for producing a coating of a surface, in particular a metallic surface with zinc has a preferably closed reaction chamber in which the surface to be coated together with the zinc at a temperature of preferably 300 ° C to 420 ° C in a Atmosphere is heat treated. The reaction space can be acted upon by means of an unbalance drive during a coating period with a static vibration or unbalance for mixing and a dynamic vibration or unbalance for vibration conveyance.

The essence of the invention thus consists in replacing a rotating, cylindrical reaction chamber or reaction vessel with a static and vibrating reaction vessel, in particular a torus (tire) or a trough, with a heat treatment taking place in the reaction vessel in order to thermodiffusion of zinc particles in layers of parts close to the surface. The vibration contains the components - vibration for mixing parts, zinc particles and a granulate (filler) by means of a static unbalance, for example generated in the center of the torus, - vibration for moving or vibrating (tumbling) of parts, zinc particles and granulate along a central axis of the torus by means of a dynamic unbalance, for example below the torus ".

During the process there is a constant close contact of the granulate with the parts and the zinc powder.

The dynamic imbalance is the more important component, since it enables the conveying movement of parts, zinc particles and granules in addition to mixing. Drives are, for example, oscillating armatures or three-phase motors with unbalance weights. An advantage of the torus is that the parts to be coated perform several cycles and thus all parts are subject to the same temperature differences.

An essential advantage of the method according to the invention is that the parts to be coated are moved more intensively and there is more (active) contact with the zinc compared with the prior art.

In principle, the method can also be used for other heat treatment methods.

The invention is described in more detail below in exemplary embodiments with reference to a drawing. In the drawing, FIG. 1 shows a schematic representation of a static imbalance, FIG. 2: a schematic representation of a dynamic imbalance, FIG. 3: an oven according to the invention with a cylindrical or trough-shaped reaction chamber, FIG. 4: an oven according to the invention with a tire-shaped reaction chamber and FIG. 5: the furnace according to FIG. 4 in a second embodiment.

In a first embodiment, bulk-like parts made of steel, here screws, sand (filler) and zinc powder are introduced into a torus furnace 1 (FIGS. 4, 5) with a tire-shaped reaction space 9. The entry takes place from a supply chamber 10 via a feed lock 7 into the reaction space 9.

Would be possible, for. B. also an embodiment of the reaction chamber in the form of a pipe square, a trough (Fig. 3) o. A. The torus furnace 1 can be heated to a temperature of up to approx. 450 ° C. by means of a heating device (not shown). A conventional drive motor 11 for generating a static imbalance (vibration) is arranged in the central axis 2, in the example below the reaction chamber 9, see FIG. 1. The drive motor 11 also serves to generate a dynamic imbalance (FIG. 2). The drive motor (s) can, however, also be provided elsewhere.

In a first embodiment (FIG. 4) two dynamic unbalances 13 and one static unbalance 12 (provided in the area of the tire. In a second embodiment (FIG. 5) only one dynamic unbalance 13 is arranged.

After filling the toroidal furnace 1 with a batch of zinc powder, steel screws and sand, a known thermal diffusion process follows with simultaneous action of the static and dynamic imbalance and, after its completion, the emptying of the reaction chamber 9 via discharge lock 8 and a separation of the coated steel screws from the sand-zinc powder mixture, for example within the reaction chamber. Locks are advantageously required to keep the zinc dust in the reaction space.

The thermal diffusion process comprises, in a manner known per se, heating the toroidal furnace 1 and the materials of the batch to preferably 300 ° C. to 420 ° C. and maintaining the temperature for heat treatment and coating of the steel screws with zinc. Once the intended layer thickness has been reached, the parts are cooled down, with the granulate remaining in the warm cycle.

Sand can also allow additional abrasive cleaning of the steel screws during the thermal diffusion process.

During the entire thermal diffusion process, but at least in the phases of heating and heat treatment and coating, the unbalance drives for generating a static and dynamic unbalance (vibration) run along the central axis 2 of the toroidal furnace 1.

The size of a batch in the example is 1-50kg, of which, for example, about 50% is allotted to the steel screws and 50% to the sand-zinc powder mixture. In the example, a fill level of the toroidal furnace 1 of approx. 50% is to be achieved. The remaining volume contains normal ambient air or a protective gas, for example a nitrogen-air mixture.

With a torus diameter of 1m and a diameter of the “tire” of 20cm, a throughput of approx. 200kg / h is possible with a holding time for heat treatment and coating of 30min, and approx. 600kg / h with a holding time of 10min. Much larger torus and hoop diameters are possible. Shorter holding and coating times are also possible.

This first embodiment corresponds in its productivity to the previously known thermal diffusion process in a rotating cylindrical furnace, but the productivity and the quality of the coating are significantly higher.

In a second, more preferred embodiment, an oven in the form of a rotating cylindrical or trough-shaped oven 4 is used. This comprises a cylindrical reaction space 5, a supply chamber 6, a feed lock 7 and a discharge lock 8 (FIG. 3). In the reaction space 5, a roller, not shown, is advantageously arranged to support a conveying movement in the direction of the longitudinal axis of the furnace 4. In the example, two dynamic imbalances 13 are provided on the side of the furnace 4, as well as a static imbalance 12 each on the end faces of the furnace 4 in its longitudinal axis (FIG. 3).

The furnace 4 is operated in a continuous batch process and is constantly at operating temperature for heat treatment and coating, d. H. approx. 300 ° C to 420 ° C.

Batches consist of zinc powder, steel screws and sand, for example 1-50kg, of which about 50% are allotted to the steel screws and 50% to the sand-zinc powder mixture, with zinc powder and sand constantly remaining in the reaction chamber 5. The degree of filling is again estimated at about 50%, so that the remaining volume of the reaction chamber 5 of the furnace 4 contains predominantly protective gas. The steel screws are fed in via the supply chamber 6 and the reaction space 5 is loaded via the feed lock 7.

The thickness of the zinc layer produced is controlled by means of a temperature-time curve, the roller preferably rotating several times during this time, at a constant speed. After the coating has taken place, the coated steel screws are discharged through the discharge lock 8. The discharge lock 8 is provided with at least one sieve in order to separate parts of granulate and zinc powder. The granulate can thus be fed back into the furnace 4 without cooling and the hot parts can cool outside the furnace 4.

However, zinc powder, parts and filler can also be supplied individually or mixed in both versions. This also in order to influence the heating / cooling and / or the atmosphere in the furnace.

In the examples described, the weight of a bulk material-like part can be up to approx. 20kg.

In both embodiments, the unbalance drives are arranged in such a way that the vibrations are not entered into the frame assemblies and the floor. The frame and floor are isolated from the vibrations.

The locks 7, 8 have a tightness that keeps the zinc dust in the furnace 4. Alternatively, a corresponding negative pressure could also be provided in the furnace 4.

During the entire operating time of the furnace 4, but at least during the heat treatment and coating, the unbalance drives for generating a static and dynamic unbalance (vibration) run along the longitudinal axis of the furnace 4.

The furnace 4 is advantageously operated continuously in a continuous process, but can also, as described by way of example, be used for coating in batches. With a continuous batch process, the expenditure for thermal energy is up to four times lower than with a batch process in a rotating cylindrical furnace, especially if zinc powder and the granulate or filler remain in the furnace. In general, mixing and temperature constancy in the furnace 4 are better.

Instead of sand, aluminum granules can also be used as fillers. In principle, it would also be possible to dispense with a filler and let the zinc powder take over its tasks of keeping warmth and, if necessary, abrasive cleaning.

In the case of large torus (tire) or reaction chamber diameters, heaters can improve the homogeneity of the heating transversely to the conveying direction. If necessary, the energy consumption can be reduced by means of heat exchangers.

An externally heated, hot protective gas, for example nitrogen, can be fed in, preferably in a closed circuit and optionally in conjunction with a heat exchanger.

Since parts, filler and zinc powder are not only mixed transversely to the reaction axis, but rather the parts can "wander", there is greater uniformity in the temperature profile of the heat treatment on the parts and thus a more uniform layer formation.

The intensive movement of parts, filler and zinc powder can start the zinc thermal diffusion even at lower temperatures than in the rotating cylindrical furnace.

In both embodiments, temperature, gas, movement or degree of filling sensors can be arranged in the tire or reaction space.

The parts to be coated are fed in cleaned in the usual way. For cleaning, the filler could also be vibrated together with the parts, similar to vibratory grinding. Passivation (tempering) after the thermal diffusion could also take place in the furnace via a gaseous compound or a further layer can be introduced.

List of the reference symbols used

1 toroidal furnace 2 central axis 3 conveying movement / conveying direction 4 furnace 5 reaction chamber 6 supply chamber 7 feed lock 8 discharge lock 9 reaction chamber 10 supply chamber 11 drive motor 12 static imbalance 13 dynamic imbalance

Claims (13)

1. A method for producing a coating of a surface, in particular a metallic surface with zinc, in a closed reaction space, the surface to be coated being heat-treated together with the zinc at a temperature of preferably 300 ° C. to 420 ° C. in an atmosphere, thereby characterized in that the reaction chamber (5, 9) is loaded with parts to be coated, zinc powder and preferably a filler, and is then subjected to static vibration or unbalance for mixing and dynamic vibration or unbalance for vibratory conveyance during a coating period. 2. The method according to claim 1, characterized in that static vibration or imbalance and dynamic vibration or imbalance are carried out simultaneously. 3. The method according to claim 1 or 2, characterized in that static vibration / unbalance and dynamic vibration / unbalance over a coating period of at least 10 minutes. or less. 4. The method according to any one of claims 1 to 3, characterized in that the filler is a granulate, in particular sand, aluminum or ceramic granulate. 5. The method according to any one of claims 1 to 4, characterized in that the parts are pourable. 6. The method according to any one of claims 1 to 5, characterized in that the thickness of the zinc layer to be achieved on the part surface is regulated by means of the heat treatment temperature and heat treatment duration. 7. The method according to any one of claims 1 to 6, characterized in that the atmosphere in the reaction space (5, 9) is low in oxygen and / or has an oxygen content of at most 100 ppm. 8. Device for producing a coating of a surface, in particular a metallic surface with zinc, in a reaction chamber, the surface to be coated being heat-treated together with the zinc at a temperature of preferably 300 ° C to 420 ° C in an atmosphere, characterized in that that the reaction space (5, 9) can be acted upon during a coating period with a static vibration or unbalance (12) for mixing and a dynamic vibration or unbalance (13) for vibratory conveyance. 9. The device according to claim 8, characterized in that the reaction space (5, 9) is toroidal, cylindrical or trough-shaped or is designed in the form of a horizontal container, respectively. is formed as such a shaped shell. 10. Apparatus according to claim 8 or 9, characterized in that the reaction space (5, 9) is coupled to at least one drive motor (11) each for generating a static and a dynamic imbalance. 11. Device according to one of claims 8 to 10, characterized in that the reaction space (5, 9) is provided with a feed lock (7) and a discharge lock (8). 12. Device according to one of claims 8 to 11, characterized in that the discharge lock (8) is provided with at least one sieve. 13. Device according to one of claims 8 to 12, characterized in that the reaction space (5, 9) is closed or open.