EP0987350B1 - Process and apparatus for applying a phosphate coating on workpieces - Google Patents

Description

The invention relates to a method for applying a phosphate coating with controlled layer thickness as an aid in a non-cutting cold forming of low-alloy or non-alloyed steels in the form of wires or rods with the use of electric current.

Furthermore, the invention comprises a device for applying a phosphate coating with controlled layer thickness as an aid for a non-cutting cold forming of low-alloyed or unalloyed wires or rods made of steel, consisting of at least the components: electrolytically operable phosphating unit, drying device, supply, supply and Discharge devices for the wire or rod.

For a chemical surface treatment of workpieces, in particular of iron-based alloys, as a temporary corrosion protection and sliding aid in a chipless shaping or the like cold forming or as a preparation and part of a surface refinement, an application of phosphate coatings has long been proven and is state of the art. A phosphating of the workpieces is carried out in a treatment bath containing as main components phosphates, usually alkali or zinc phosphate and reaction accelerating oxidizing agent in aqueous solution.

Optimum film formation conditions can be achieved by precise tuning of the phosphate concentration, the type and amount of the accelerating agents added, and the temperature and pH in the bath.

The phosphate layers formed mostly consist of two layers, the former firmly adhering to the workpiece and the upper layer part has low adhesion. In a practical application of the phosphating therefore process conditions are to be selected, in which the loosely lying layer part is formed as small as possible. Furthermore, the process conditions determine the structure of the phosphate coating, which structure is to a great extent the Adhesion of a lubricant on the surface affected.

For buffing, drawing and the like of steel bars, wire and solid profile, sufficient adhesion of the phosphating and its full durability over several successive processing or forming operations is of crucial importance, with a fine crystalline phosphate layer providing a good anchoring opportunity for the lubricant a tearing off of the lubricating film is prevented.

In order to achieve a non-cutting deformation, for example, pulling steel wires with high degrees of deformation and low wear of the tools, for example, the dies in savings of Zwischenglühbehandlungen, it is important that the surface of the workpiece both over its circumference and over its longitudinal extent has a high adhesive strength, a uniformly formed, required thickness and a finely crystalline surface structure of the phosphate layer. The correct phosphate layer thickness is of particular importance because excessive layers, if necessary, significantly increase the friction, in particular during the first method step or during the first pull. On the other hand, phosphations which are too thin or uneven over the circumference of the workpiece tend to rupture the layer in the course of drawing, which can lead to inferior surface qualities of the product and lower durability of the drawing dies of the last draws.

For a treatment of steel wire, dipping processes and continuous processes are known in which mainly chlorate or nitrate / nitride-accelerated zinc phosphate treatment baths are used. In a dipping treatment, wire coils are introduced into a treatment bath for a certain period of time, and it may be advantageous if the phosphating treatment bath is positioned in the process of the dressing together with other treatment tanks and integrated in a room or in a street. If, in doing so, the wire bundles are suspended from a conveyor with automatic program control during the individual treatment steps, essentially the same layer weights can be achieved while the bath composition remains the same. at however, uneven and / or incorrect coating thicknesses may be formed in the event of disruptions in the sequence program.

It is also known, in order to meet the requirements with regard to a circumferentially same layer thickness, to perform a phosphating in a continuous process. In this case, however, it is necessary to use large treatment bath lengths and / or low and, in particular, constant flow rates and / or high treatment bath temperatures with mostly high concentrations of accelerating oxidants, which may be less economical and / or involve major process problems. Furthermore, coarse, in particular coarsely crystalline, layers are often formed in the highly accelerated phosphatizations, which may be disadvantageous for subsequent drying and soap soaking, and in particular for drawing the steel or wire.

To facilitate the cold forming of stainless, alloyed steels, DE 25 05 836 A1 discloses that the surfaces are treated cathodically in an acidic phosphating solution containing a chelate compound. In this case, zinc is first deposited by the electric current onto the surface of the stainless steel, and then a lubricating film is formed in a phosphating step.

US-2,812,296 discloses a method for treating the surface of steel sheet to increase corrosion resistance and improve the adhesion of a lacquer layer to make this sheet usable as a substitute for tinplate in the manufacture of cans for packaging purposes. In this case, cathodically applied to the sheet in the passage through an acidic solution containing phosphate ions and ions of a chromium salt in which the chromium presents hexavalent, which is a very advantageous basis for a coating.

Furthermore, from EP 288 853 a method for the preparation of workpieces titanium or titanium alloys, in which the workpieces are immersed in an aqueous, acidic zinc phosphate-containing phosphating solution and a zinc phosphate coating is produced on the surface by cathodic electrolysis. Titanium and titanium alloys are more chemically resistant than steel, so that it is difficult to apply suitable lubricant carrier layers.

The invention has for its object to overcome the shortcomings of the previously known phosphatizing treatments and to provide an economical method with which a firmly adhering, fine crystalline phosphate coating with a constant in cross-section and selectable thickness and with the same over the length basis weight on workpieces of iron-based alloys, especially on low-alloy steel wires, can be applied. In this case, a consistency of the coating should be achievable even with different treatment times and different ion concentrations in the treatment bath.

Furthermore, it is an object of the invention to provide a device with which the above phosphate coatings can be created.

The object is achieved in a generic method in that the wire or rod moves in the longitudinal direction relative to the device and thereby successively brought at least its near-surface region to an elevated temperature between 45 ° C and 120 ° C, passed through at least one treatment bath and during the passage through a phosphating unit with a lead time between 1.5 and 19 seconds, the surface is cathodically phosphated under the influence of electrical current such that when phosphating perpendicular to the longitudinal extent of the wire circumferentially a same potential course in the treatment bath by a substantially tubular order the wire arranged anode takes place and the electrical parameters are adjusted so that the current density on the wire of 0.5 to 20 A / dm ² reaches and the thereby applied layer dried after the removal of the wire from the bath or allowed to dry.

The advantages provided by the invention are to be seen essentially in that at short treatment times, so with high efficiency, a fine crystalline, well-adhering phosphate coating, which is variable in its layer thickness by the electrical values in the cathodic electrolysis, is applied with high quality. This makes it possible to form desired phosphate layer thicknesses on the workpiece surface by adjusting the cathode current density largely independent of fluctuations in the phosphate concentration in the proportion of the lower-dose accelerating oxidizing agent, the temperature and the pH of the bath. If, for example, instead of favorable residual phosphate layers of 0.5 to 1 g / m ² on the finished drawn steel wire material, a relatively strong phosphate coating of 5 to 15 g / m ² for further processing, for example for cold upset wires, are desired, it can be done in a simple manner These can be achieved by increasing the electric cathode current. However, it is important that at least the near-surface region is brought to elevated temperature before introducing the workpiece or the wire into the phosphating bath in order to form a fine-crystalline layer structure immediately after introduction.

The advantageous phosphate layer formation on the workpiece can be assisted, if this is brought to a temperature between 45 ° C and 120 ° C and the treatment bath is maintained at one between 45 ° C and the boiling point thereof, preferably with the proviso that the bath temperature is equal to or lower than the workpiece surface temperature is set.

Both for the adjustment of the electrical values for the cathodic electrolysis and for the formation of a circumferentially constant layer thickness on the workpiece, it has proven to be particularly favorable if during phosphating the workpiece, electrically connected as a cathode, perpendicular to its longitudinal extent circumferentially the same Potential course is created in the treatment bath, wherein a passage through an essentially tubular arranged around the workpiece anode and the electrical parameters are adjusted such that a current density at the workpiece of 0.5 to 20 A / dm ² , preferably from 5 to 10 A. / dm ^{2 is} reached.

If the anode is further advantageously formed in the phosphating bath in such a way that its current density is kept at a value of 0.1 to 0.6, in particular about 0.3 times the current density at the workpiece surface, electrolysis parameters which are easily controllable can be achieved particularly effectively become.

In order to form an advantageously firmly adhering, finely crystalline layer, it is favorable if the workpiece is moved through the treatment bath at a speed of 5 to 500 m / min, preferably of 30 to 100 m / min, and on the surface of which a phosphate coating of 1 to 50 g / m ² , preferably from 5 to 15 g / m ^{2 is} applied. Although higher deposition rates could bring further economic process advantages, but cause a coarse structure of the phosphate coating, which thereby can cause a deleterious effect on the soaping and especially at the first draft of the cold deformation of the wire.

Both the quality and the uniformity of the phosphating can be increased if the electrical values in the cathodic electrolysis are controlled as a function of the cation concentration in and of the respective throughput time of the workpiece by the phosphating with the proviso that the coating thickness over the workpiece length in the is kept substantially constant and that at an interruption of the continuous movement, the workpiece dug out of the treatment bath or the bath level is lowered below the workpiece level. This also makes it possible to largely eliminate a negative effect of the same on the product quality in the event of plant malfunctions.

A particular advantage with regard to a continuous, highly economical phosphating can be achieved if the workpiece is pickled in its direction of passage before a supported by the action of electric current, in particular a cathodic phosphating. It has proved to be useful when anodic pickling in the run with a current density on the workpiece between 20 and 100 A / dm ² , preferably between 40 and 80 A / dm ² carried out and the pickling bath at a temperature between 45 ° C. and 95 ° C is maintained.

The electrical power supply of the device can be simplified and their controllability can be effectively obtained if the electrolytic pickling and the like phosphating be electrically connected in series and supplied with regulated DC voltage.

The material flow can be improved and the quality assurance of the coating can be increased if the workpiece with a cross-sectional area of 0.003 to 700 mm ² descaled immediately after removal from the supply and / or linearly.

The further object of the invention is achieved in a device of the type mentioned above in that the individual components of the device each have such an embodiment and arrangement that the wire or rod in the longitudinal direction through this durchbewegbar and is machinable therein and that the phosphating unit at least one heating device for a moving wire or rod is arranged upstream, wherein the electroluminescent electrolysis unit for phosphating comprises at least one tubular electrode surrounding the wire and has a supply and on - and outlet side an overflow device for the phosphating.

The advantages that are achieved by this embodiment of the device according to the invention result essentially from the fact that in an economically operable continuous system by means of an upstream heating device for the wire or rod best conditions for a fine crystalline phosphating with control of the phosphate layer thickness are created. It is also important that the electrolysis unit has a substantially concentric surrounding the workpiece electrode so that circumferentially the same potential variation or a same cathode case of the voltage is reached to the workpiece surface and favorable conditions for phosphating with constant layer thickness are given. In this context, a movement in the phosphating or a supply of unused Reactant on the workpiece surface important, which according to the invention by overflow devices, which prevent shyness and erosion, can be achieved.

In order not to cause excessive coating thicknesses despite a disruption of the workpiece pass through the phosphating bath, it is favorable if the phosphating unit, which can be supplied with electric current, in the phosphating bath area and / or in its supply or discharge area has a device for rapidly lowering the bath level below the level of the workpiece.

Further, if the electrolytically operable phosphating unit at least one, preferably substantially identically constructed pickling unit, preferably immediately upstream, a particularly economical and safe phosphating with high product quality can be achieved.

The course of the coating can be promoted in terms of design and formation of the phosphate coating on the workpiece when the phosphating unit and the pickling unit and / or the supply means for the liquid phosphating and pickling media have controllable heating means for these.

With regard to the electrical power line and contact training can be provided in a favorable manner that the tube electrode of the pickling unit and the tube electrode of the phosphating unit with the negative and positive pole of a controllable DC voltage source can be connected and that the workpiece can be formed without connection in each case as the anode and cathode ,

Both for easy insertion of the workpiece as well as for improved service conditions can be provided that the substantially concentrically arranged around the wire tubular electrode of the phosphating and / or the pickling unit, seen in the axial direction formed by at least two shell segments and at least a portion of Shell segments can be raised or swung out.

It has proved to be particularly effective with regard to avoiding short circuits in the electrolytic bath when at least the underside of the tubular electrode or a shell segment arranged in this way is provided with bores or is embodied in lattice form.

If, furthermore, the heating device is designed as an induction or conductively acting system and at least after the heating device, preferably before and / or after the pickling unit of the phosphating unit and optionally the drying device, a temperature measuring device for detecting and / or regulating the workpiece temperature is arranged, and when all measuring devices of the device are connected to a central measuring and / or regulating and / or documentation unit, a fully automatic operation of the device for applying a phosphate coating and highest quality of the coating can be achieved.

Fig.1

Eine Durchlauf-Phosphatier-Einrichtung

Fig.2

Eine kontinuierliche Beiz- und Phosphatier-Einrichtung in Tandemanordnung

In the following the invention will be explained in more detail with reference to drawings showing only one embodiment. It shows:

Fig.1

A continuous phosphating device

Fig.2

A continuous pickling and phosphating in tandem arrangement

1

Werkstückvorrat

11

Werkstück

2

Richtanlage

3

Erwärmungseinrichtung

4

Beizeinheit

40

Beiz-Medium bzw. Flüssigkeit

41

Rohrelektrode

42

Zuführung

43

Überlaufeinrichtung

44

Überlaufeinrichtung

45

Vorrichtung zur Absenkung des Badniveaus

46

Beizbadspiegel

5

Phosphatiereinheit

50

Phosphatiermedium

51

Rohrelektrode

51'

Kontaktrolle

52

Zuführung

53

Überfaufeinrichtung

54

Überlaufeinrichtung

55

Vorrichtung zur Absenkung des Badniveaus

56

Phosphatierbadspiegel

6

Trocknungseinrichtung

7

Verformungseinrichtung

8

Gleichspannungsquelle

T₁

T₂

T₃

Temperatureinrichtungen

T₄

T₅

Z

Bewegungseinrichtung des Werkstückes

Below, the reference numerals, which are valid for Fig.1 and Fig.2, listed.

1

Workpiece stock

11

workpiece

2

straightening plant

3

heater

4

Staining

40

Pickling medium or liquid

41

tubular electrode

42

feed

43

Overflow device

44

Overflow device

45

Device for lowering the bath level

46

Beizbadspiegel

5

Phosphatiereinheit

50

Phosphatiermedium

51

tubular electrode

51 '

Contact role

52

feed

53

Überfaufeinrichtung

54

Overflow device

55

Device for lowering the bath level

56

Phosphatierbadspiegel

6

drying device

7

deforming means

8th

DC voltage source

T ₁

T ₂

T ₃

temperature facilities

T ₄

T ₅

Z

Movement device of the workpiece

1 shows a device according to the invention for applying a phosphate coating to wire, which is subsequently deformed in a drawing device. The individual components of the device are created and arranged for a passage of the wire. From a drum or a collar 1, a pickled wire rod 11, axially directed by a for example Biegerichtanlage, and introduced into a controllable heating device 3. A regulation of the particular inductively or conductively acting on the wire heat plant can be done by a downstream temperature measuring T ₁ .

A downstream in the passage direction Z of the wire 11 phosphating unit 5 has a container for a phosphating medium 50 and has at least one feed 52 for this. Inlet and outlet sides, the container in each case has an overflow device 53,54, through which the wire 11 can be spent largely frictionless through the phosphating. For faults or for an insertion of the wire 11, the phosphatizing bath level can be lowered by means of a device 55. A tubular electrode 51 in the container, which may be made in segmental form, is substantially concentrically positionable about the wire 11 and has a connection to the PLUS pole of a controllable DC source 8 with its MINUS pole connected to a contact roller 51 '. A heater (not shown) for the phosphating medium 50 may be disposed in the container or in a supply vessel. By means of temperature detection means T ₃ T ₄ T ₅ , the measured values are preferably supplied to control device, the surface temperatures of the wire and those of the bath are detectable.

The phosphating unit 5 is arranged downstream of the washing means 11, not shown in FIG. 1, for the wire 11, which wire subsequently passes through a drying device 6 and optionally a soaping device and is deformed in a drawing bench 7.

2, a device 5 for applying a phosphate coating with an upstream pickling unit 4 is shown schematically in FIG. In FIG. 2, the pickling unit 4 has basically the same structure as the phosphating unit 5, but may have a different structure. It is important that, because a pickling in the same line as applying a Phosphatierüberzuges, the pickling parameters are tuned with concentration of pickling liquid, temperature of the pickling medium and the wire, electrolysis conditions and pickling time and the like on the wire speed. Particularly advantageous is a current flow through the tube electrode 51 in the phosphating medium 50 via the wire 11 and via the tube electrode 41 in the pickling liquid 40 at a connection of the electrodes to a controllable Gieichsiromquelle. 8

Claims (20)

1. Method for applying a phosphate coating with controlled film thickness as an aid in the non-cutting cold forming of low-alloy or unalloyed steels in the form of wires or rods using electrical current, wherein the wire or rod is moved in the longitudinal direction relative to the apparatus and in succession at least the area thereof close to the surface is brought to an increased temperature of between 45°C and 120°C, passed through at least one treatment bath and, during transit through a phosphating unit with a transit time of between 1.5 and 19 seconds, the surface thereof is cathodically phosphated on exposure to electrical current in such a way that, during phosphating, an extensively uniform potential profile is obtained in the treatment bath perpendicularly to the longitudinal extent of the wire by a substantially tubular anode arranged around the wire and the electrical parameters are adjusted in such a way that the current density at the wire reaches from 0.5 to 20 A/dm² and the film so applied is dried or left to dry after removal of the wire from the bath.
2. Method according to claim 1, wherein the wire is brought to a temperature of between 45°C and 120°C and the treatment bath is held at such a temperature between 45°C and the boiling point thereof, preferably with the proviso that the bath temperature is set to be equal to or lower than the wire surface temperature.
3. Method according to claim 1 or claim 2, wherein the wire or rod is phosphated during transit through a phosphating unit with a transit time of between 4 and 9 seconds and a current density of 5 to 10 A/dm².
4. Method according to any one of claims 1 to 3, wherein the anode in the phosphating bath is so configured that its current density is kept at a value of 0.1 to 0.6, in particular at approximately 0.3 times the current density at the wire surface.
5. Method according to any one of claims 1 to 4, wherein the wire is moved at a speed of 5 to 500 m/min, preferably 30 to 100 m/min, through the treatment bath and a phosphate coating of 1 to 50 g /m², preferably 5 to 15 g/m², is applied to the surface thereof.
6. Method according to any one of claims 1 to 5, wherein the electrical values during cathodic electrolysis are controlled as a function of the cation concentration in the phosphating bath and of the respective transit time of the wire through said phosphating bath, with the proviso that the coating thickness is kept substantially constant over the wire length and that, on interruption of transit, the wire is lifted out of the treatment bath or the bath level thereof is lowered to below the wire level.
7. Method according to any one of claims 1 to 6, wherein the wire is pickled upstream of cathodic phosphating in the transit direction thereof.
8. Method according to any one of claims 1 to 7, wherein the wire with a cross-sectional area of 0.03 to 700 mm² is descaled and/or linearly straightened directly after being taken from the supply.
9. Method according to any one of claims 1 to 8, wherein pickling is assisted by the action of electrical current, in particular anodic pickling is performed in transit with a current density at the workpiece of between 20 and 100 A/dm², preferably between 40 and 80 A/dm² and the pickling bath is kept at a temperature of between 45°C and 95°C.
10. Method according to any one of claims 1 to 9, wherein the electrolytic pickling bath and the similar phosphating bath are connected electrically in series and supplied with controlled direct voltage.
11. Apparatus for applying a phosphate coating with controlled film thickness as an aid in the non-cutting cold forming of low-alloy or unalloyed steel wires or rods, consisting of at least the following components: electrolytically operatable phosphating unit, drying means, supply, feed and discharge apparatus for the wire or rod, characterised in that the individual components of the apparatus in each case exhibit such an embodiment and arrangement that the wire or rod (11) may be moved in the longitudinal direction (Z) therethrough and processed therein and that at least one heating means (3) for a wire or rod (11) in transit is arranged upstream of the phosphating unit (5), wherein the electrolysis unit (5) for phosphating suppliable with electrical current comprises at least one tubular electrode (51) surrounding the wire (11) and has a feed (52) and overflow means (53, 54) for the phosphating bath (50) on both the inlet and the outlet side.
12. Apparatus according to claim 11, characterised in that the phosphating unit (5) suppliable with electrical current comprises, in the phosphating bath area (50) and/or in the feed or discharge area thereof, an apparatus (55) for rapid lowering of the bath level (56) to below the height of the wire (11).
13. Apparatus according to either one of claim 11 or claim 12, characterised in that a preferably mechanical descaling installation and/or a straightening installation (2) for the wire (11) is arranged upstream of the heating means (3).
14. Apparatus according to any one of claims 11 to 13, characterised in that there is arranged upstream of the electrically operatable phosphating unit (5) at least one pickling unit (4) of preferably substantially identical construction.
15. Apparatus according to any one of claims 11 to 14, characterised in that the phosphating unit (5) and the pickling unit (4) and/or the supply means for the liquid phosphating and pickling media comprise controllable heating means for the latter.
16. Apparatus according to any one of claims 11 to 15, characterised in that the tubular electrode (41) of the pickling unit (4) and the tubular electrode (51) of the phosphating unit (5) are connectable with the negative and positive poles of a controllable direct voltage source (8) and in that the wire may be configured in terminal-free manner in each case as anode and cathode.
17. Apparatus according to any one of claims 11 to 16, characterised in that the tubular electrode of the phosphating (5) and/or pickling (4) unit arranged substantially concentrically around the wire takes the form in each case of at least two shell segments, when viewed in the axial direction, at least one part of the shell segments being of removable or swing-out construction.
18. Apparatus according to any one of claims 11 to 17, characterised in that at least the underside of the tubular electrode or a shell segment arranged in such a way is provided with holes or is of lattice-type construction.
19. Apparatus according to any one of claims 11 to 18, characterised in that the heating means (3) takes the form of an induction or conductively acting installation.
20. Apparatus according to any one of claims 11 to 19, characterised in that a temperature measuring means (T₁) (T₂ T₃ T₅ T₀) is arranged to determine and/or control wire temperature at least downstream of the heating means (3), preferably in each case upstream and/or downstream of the pickling unit (4), of the phosphating unit (5) and of the drying means (6), and in that all the measuring means of the apparatus are connected with a central measuring and/or control and/or record-keeping unit.

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