DE1276975B - Method for applying a metallic coating to a metallic, wire-shaped or strip-shaped material by immersion in a molten metal bath and device for carrying out the method - Google Patents

Description

Method for applying a metallic coating to a metallic, Wire or band-shaped material by immersion in a molten metal bath and device for carrying out the method The invention relates to a method for application a metallic coating on a metallic, wire-shaped or band-shaped item by immersion in a molten metal bath, preferably to apply an aluminum coating on a steel wire, the cleaned and metallic goods during movement caused by the weld pool to vibrate with a frequency that changes over time will.

The invention also relates to a device for performing the aforementioned procedure.

It is a method of applying a metallic coating a metallic good is known, in which the cleaned base metal is first carried out a flux and then passed through a molten bath with the coating metal will. In a similar process, the purified base metal is subjected to a reducing Atmosphere heated and then under the protective gas in the molten metal of the coating metal introduced. In both cases, pure metal surfaces should be in contact with one another so as to ensure complete wetting of the base metal with the molten To achieve coating metal and avoid the creation of uncovered areas. The use of liquid or gaseous flux is also known to be beneficial Disadvantages with itself. In addition, the goal pursued is only a very small one Speed of the material through the weld pool. Especially with The use of aluminum as a coating metal is uncovered areas of the base metal cannot be completely avoided even at unusually low throughput speeds. At low throughput speeds, the base metal is heated so much that that gas outbreaks occur from the base metal, which the coating in the area of the outlet break out of the bath and lead to uncovered areas.

Further, when using aluminum as the coating metal the molten bath must be maintained at a temperature of about 600 to 7 00 ° C according to the purity of the aluminum. As a result of the necessary low throughput speed, however, a steel wire, for example, is annealed and the high strength that may have been achieved by previous cold working is lost again, so that a coated steel wire with high strength cannot be produced. Similar difficulties, albeit to a lesser extent, arise with hot-dip galvanizing and hot-dip tinning in a continuous process.

Resulting in the production of coatings from aluminum on steel wires there are also difficulties in controlling the movement during movement the intermediate alloy layer resulting from the weld pool. In itself is the formation of an intermediate alloy layer between the base metal and the Coating metal advantageous because it improves the adhesiveness and solderability and the like can be improved. However, an excessively strong alloy interlayer is harmful. Because the working speed in the known hot-dip process is determined by other conditions, one has hitherto the formation of an alloy intermediate layer tried to suppress by additives to the coating metal. Indeed can on in this way the alloy interlayer can be affected. For example, can in the case of an aluminum bath, the formation of an intermediate alloy layer through addition can be reduced by a few percent silicon, but are reduced by the addition of silicon the corrosion resistance and the ductility of the coating are disadvantageous affects

There are methods for coating metal bodies with a metallic one Coating known in which ultrasonic vibrations are used. Be there Vibrations of a certain frequency, e.g. B. in the range of 20 to 50 kHz is used. It is also known to cause sound vibrations to apply for this purpose, but essentially vibrations with a certain frequency. But it has demonstrated that this process does not always produce a flawless coating with no uncovered Places results.

According to another known method for the production of coatings, Paints, etc., it is known to differentiate the body to be coated and the coating To expose vibrations with phase shift, so as to the surface of the to be coated To bring the body and the coating mass into opposing movements, so that these work into one another. Structure-borne noise should have the lowest frequency up to ultrasound, e.g. B. 800 kHz or more, can be used, for example is generated by alternating magnetic fields.

These known methods are essentially sinusoidal Forces used to generate the vibrations. But it has been shown that such Vibrations do not ensure a perfect metallic coating of a base metal can.

The invention is based on the object of a method of the above to create mentioned type, with which a wire or band-shaped metallic Can be provided with a metallic coating well at high speed, without resulting in uncovered areas. According to the invention, this is achieved by that on the wire or band-shaped material when entering the weld pool for production short-term random oscillations at least 40 impact pulses per second are applied with total acceleration values of at least 20 g, then the Good for avoiding standing waves in the weld pool while observing an immersion time is held for 0.5 to 8 seconds without tension, if possible, and finally the Vibrations of the material are dampened upwards before exiting the weld pool.

The impact impulses cause extremely diverse movements in the property caused which vibrations with essentially all lying in the audible range Cause frequencies with approximately the same acceleration values. During 40 to 60 strokes Per second the lower limit is likely to be, about 1000 strokes per second Second. Intermediate values between 100 and 1000 pulses per second meet practically all possible conditions. The cheapest value depends from the mass of the goods and from some dimensions of the impulses Device as well as the limitation of the movement of the goods in the direction of the impact pulses. The lowest frequency generated in the good should be of the order of 80 Hz. However, it can also be around 400 Hz without any disadvantages. The lack of frequencies below about 300 Hz requires higher overall accelerations, although not harmful but require unnecessary impact force. The highest frequency generated in the property can be more than 16,000 Hz, albeit the absence of frequencies above 3000 Hz is not a disadvantage.

Of particular importance are the acceleration values given to the goods, which are expressed as a multiple of the acceleration due to gravity g. The determining factor is the acceleration value that is caused by all oscillation frequencies (total acceleration). The movement evoked must be momentary and arbitrary. The result of it the resulting acceleration can be considerable from time to time in individual components fluctuate while the overall acceleration remains relatively constant. These Total acceleration must be kept at least at the value 20 g so that at Sufficient results can be achieved in the production of the coating. Total acceleration values of 5000 g have shown good results. But it will be the lowest acceleration values preferred because the vibration generator will wear out when the vibration force is effective is the least. The best acceleration value is also from the Depending on the type of material and the hardness, shape and dimensions of the Good thing, the construction of the vibrator and the associated movement of the goods in the direction of impact limiting device dependent and must for each device can be determined experimentally. The appearance of single peaks in the frequency acceleration curve is not harmful, although extremely high peaks in the lower frequency range under certain conditions for the formation of standing waves in the one from the weld pool outgoing end of the good can contribute. Such standing waves must be avoided when smooth transitions without defects are to be created. To have to So the vibrations at the end of the material emerging from the weld pool are so strong be attenuated as much as possible. It is also important to keep the goods as free as possible moving through the bathroom.

It is also important to keep the impact pulses very close to the entry point of the to to apply coating material in the molten bath, what with the invention Procedure is possible in a simple manner.

When using the method according to the invention, the wire remains or strip-shaped material only so briefly in the weld pool that the material is not significant is heated and so the physical properties are essentially unchanged stay. It is thus possible with the method according to the invention to also use steel wires and tapes to be provided with an aluminum coating with a tensile strength of more than 140 kg / mm2.

In the method according to the invention, the movement is preferably of the dxaht- or band-shaped material limited in the direction of lay. This allows the frequency range and the acceleration can be changed, namely increased a stronger limitation of the movement of the good that per impact pulse on the good applied energy. It also becomes the arbitrariness of the movement achieved enlarged.

On the other hand, a control of the applied energy is also through The number of impulses applied per unit of time can be changed. Is z. B. increases the limitation of the movement of the goods, the number of impact pulses must per unit of time to achieve the same results. Preferably however, the limitation is set permanently and the number of impact pulses is varied.

As a result of the great increase in wettability through the introduction of the vibrational movements described increases the size of the to the Coating bath heat transferred to the property. The heat transferred is so great that the immersion time in the bath must be limited to 8 seconds if the advantages of the invention are to be obtained. The immersion time is a function of the immersion length and the transport speed of the wire or band-shaped material through the bath. A minimum immersion time of approximately 0.5 seconds must be allowed for a to effect a sufficient coating. When as little change as possible is physical Properties of the base metal is required, the immersion time should be as short as possible, preferably no longer than 3 seconds. The maximum in this regard depends to some extent on the mass of the wire and the bath temperature away.

The invention is illustrated below with reference to the drawing using an exemplary embodiment explained in more detail. In the drawing, FIG. 1 schematically shows a side view, partly in section, a stretch for applying a coating covering the basics of the invention, FIG. 2 shows an enlarged longitudinal section of the coating vessel the F i g. 1, Fig. 3 a plan view of the device generating the vibrations, F i g. 4 shows a section along the line IV-IV of FIG. 3 and F i g. 5 is a side view the wire depressing device.

2 with a spool with a wire S on a supply reel 4 is designated, which is mechanically driven and with known controls, not shown is equipped for an independent adjustment of the speed. From the supply reel can the wire S through the cleaning tank 6, preferably a tank with a melted Etching agent, and then passed through a water rinse 8. Then can the wire can be passed through a tank 10 containing sulfuric acid diluted with water or contains hydrochloric acid and is followed by a water rinse 12. The one shown Cleaning device is essentially intended to lubricate and usually to remove compositions used in cold drawing of wire. The melted one Etchant falls the lubricant used in drawing in an easily removable one Form out, and complete neutralization and purification is achieved by the acid bath causes. Of course, more suitable methods can also be used for other materials be applied. Preferably the wire is then passed through a hot water cleaning tank 14 to further clean the wire and absorb as much gas as possible drive out and cause drying. The drying is essentially completed by a hot air dryer 16 or the like.

Subsequently, the wire is brought into contact with a rotatable impact generating installation V, by means of which the necessary oscillating movement is generated in the wire. An adjustable, resiliently mounted hold-down disk 18, which is arranged above the device V, holds the wire in the necessary contact with the device so as to limit the movement of the wire in the direction of the blows applied. The size of the limitation can be varied by adjusting the spring force on the disk 18. From the vibrator V the wire runs through a tube 22, one end of which is immersed in the bath 20 of the molten coating metal. A gas inlet port 24 is located near the lower end of the tube through which a non-oxidizing or reducing gas is continuously introduced which maintains a non-oxidizing atmosphere at the point where the wire enters the bath. If the gas is flammable, it can be ignited at the top of the pipe.

The movement acting on the wire S quickly removes anything absorbed gas or a film of water from the wire and breaks any oxide film, which is located on the bath surface, except when it becomes heavy slag generated. As a result, the steps for drying the wire and maintaining it are an oxide-free bath surface required for the present process for the manufacture of a quality aluminum coating are not essential for economic reasons intended. The flow of gas through tube 22 removes the vibration applied Gases and water vapor generated by the wire and holds the surface of the plating metal completely free of oxides at the point of entry of the wire, the desired Success is achieved without generating any harmful by-products. When coating with zinc or tin, drying of the wire is necessary Security measure.

The wire is fed into the molten metal with the aid of a pulley 26 submerged, from which it comes into contact with an adjustable, fixed rod 28 comes and then leaves the bath through a gas containing tube 30 and is deflected by a deflection pulley 24. The fixed rod 28 in connection with the pulley 26 serves to dampen the vibratory movement in the out of the bath emerging wire end and thus prevents the development of standing waves in the wire. A smooth movement of the wire, free from impact effects, is at the exit of the wire from the bath essential if a smooth and uncovered Make free coating is to be generated.

The tube 30 containing gas is intended to lighten the coating by removing the Bath surface kept free of oxides and slag at the exit point of the wire will. One end of the tube 30 is immersed in the bath surface. The pipe 30 is through inlet 32 non-oxidizing or reducing gas is supplied.

Cooling devices 35, which direct a stream of cold air or atomized water against the wire so as to inhibit the formation of an intermediate alloy layer, may be attached below the disc 34 at the exit of the wire from the bath. The devices 35 should be adjustable so that they can be set to any point between the bath surface and the disk 34 can. The disk 34 is attached at a sufficient distance above the bath to enable the wire to cool itself down to the solidification point of the coating metal. After the coating has solidified, the wire can be passed through a corresponding arrangement of disks through known devices 36 and 38 for further cooling, treatment or lubrication. The wire then arrives at a take-up reel 40 which is equipped with known drive means and control means (not shown) in order to enable the wire to be moved through the entire installation at a predetermined, constant speed. The control of the take-up reel 40 interacts electrically in a known manner with that of the supply reel 4, so that a uniform wire movement is achieved without substantial tension on the wire.

For the elimination of standing waves it is essential that the wire is not tightened during its passage through the plant. It must therefore When designing the system, care should be taken to ensure that the friction is so small is as possible and the number of pulleys or pulleys as small as possible is held. Therefore, if possible, continuous tanks should be used.

A preferred embodiment of the vibration generator V is shown in F i g. 3 and 4 shown. It essentially consists of a variable speed Motor 50 connected to a pair of opposed disks 52. A plurality of bolts or rods 54 are equidistantly spaced between these disks arranged so that the edge of the disc, as in FIG. 4 shown, something protrudes. the Arrangement is arranged on a plate 56 of the front wall of the immersion vessel 20 so that the edges of the disks 52 are slightly above the normal line of travel of the wire stand over. As a result, the wire rests loosely between the two disks 52, and, depending on the rotation of the disk, each bolt 54 hits it exercised.

The hold-down roller 18 is at a small distance above the Disk 52 is placed and rolls on the surface of the wire. She is on one Support arm 58 attached, which can be moved freely on a pair of support columns 60. A spring 62 is arranged between the support arm 58 and a fastening rod 64, which is adjustable on the support columns 60. As a result, the disc 18 urges the Wire resiliently against the rods 54 and resiliently limits the movement of the wire in the direction of the blows applied by the bars. The spring tension is limited the extent of the limitation and is by adjusting the location of the mounting rod 64 adjustable. A lateral displacement of the wire by the blows is through the protruding edges of the discs 52 prevented. They are known, not shown Means are provided to the speed of the motor 50 and thus the number of strokes to adjust. The direction of rotation of the motor 50 is selected so that the disks 52 be driven in the direction of wire movement through the plating bath, so that To largely prevent the occurrence of wire tension.

The following example serves to better explain the application and the results of the invention.

Example Cold-drawn, high-carbon steel wire, diameter 2.6 mm, grade SAE c-1085, with a tensile stress of more than 140 kg / mm2, was coated with an aluminum containing 3% silicon by hot dipping, the throughput speed being about 40 m / min fraud. In order to achieve a flawless coating without impairing the elongation properties of the steel, the following treatment sequence was used: The wire was fed without interruption from a supply reel 4 and successively through molten sodium hydroxide, which was in the tank 6 at a temperature between about 430 and 500 ° C was held, a water rinse 8, a cold bath of dilute hydrochloric acid 10 and a cold water rinse 12 to remove the drawing lubricant and other foreign matter from the surface of the wire. The cleaned wire was passed through the hot water tank 14 and the hot air dryer 16 for drying. The hold-down roller 18 was set so that a medium elastic jamming was achieved, and the vibrator V, which consisted of ten equally spaced bolts 54 of 8.4 mm diameter arranged on a circular line of about 130 mm in diameter, was driven so that 360 beats per second were applied to the wire. These individual configurations produced frequencies in the wire that were evenly distributed over the frequency range from 80 to 10,000 Hz, with a total acceleration of 1200 g. The wire was introduced into the coating vessel through tube 22 which was supplied with a small stream of natural gas through inlet 24, which gas burned off at the top of the tube. The bath was held at approximately 650 ° C. The immersion length of the wire in the molten bath was approximately 1.2 m, which means that the transport speed of approximately 40 m / minute resulted in an immersion time of 1.85 seconds. After the wire had passed the pulley 26, it left the bath contacting the fixed rod 18 through the gas-containing tube 30 in which a small flow of natural gas was maintained through the inlet 32 which burned off at the top of the tube. During its upward movement towards disk 34, the wire was allowed to naturally cool to the solidification temperature of the coating. The wire temperature was further reduced by passage through the hot water tank 36. An oil felt was then applied in the tank 38, and finally the coated wire was wound up by the take-up spool 40. A pure, shiny aluminum coating of approximately 0.011 g / cm 2 wire surface area was obtained. The coating was completely free of uncovered areas and could be deformed in the usual "wire knot test" without tearing or peeling. The intermediate alloy layer was uniform and somewhat smaller than normal. Tensile tests showed essentially no change in the physical properties of the base metal.

In general, wires from 1 to 6 mm have been coated successfully, all of the advantages of the present process have been achieved. Aluminum coatings on the order of 0.015 g / cm2 has been achieved for 2 mm wire in one Speed of about 61 m / minute. Likewise with 3.8 mm wire and one speed from 45 to 67 m / minute. It has proven to be advantageous for wires with a large diameter Proven to use a pulley and get the wire out of the bath instead of perpendicular inclined to let out. This reduces dragging on the pulley and avoids detrimental standing waves in the part of the bath emerging from Wire. Speeds of up to 88 m / minute (about six times the maximum speed possible for this) have been used. Working with high speed allow the immersion time to be reduced to less than 1 second. The short immersion time together with the fact that vibrations the type described greatly increase the heat transfer, ensure a Control of the formation of an intermediate alloy layer to the extent that it used to be was not attainable. This can be explained by the fact that the overdone Wire according to the example essentially free of an intermediate alloy layer can be made when the coated wire is released from the gas containing tube is cooled as it passes through the cooling device 35, using steam, sprayed water or simply a stream of cold air is illuminated. This result will be obtained even with a bath of essentially pure Aluminum achieved. By adjusting the position of the cooler 35 as a function of the wire speed can determine the optimal amount of alloy interlayer with good adhesion and gloss of the coating and other desired at the same time Properties can be achieved.

Instead of the wire used in the description above, a metal strip can also be provided. The wire can also be made up of a plurality consist of individual wires that are twisted together or in some other way are summarized.

While by the example the application of the invention to the manufacture of aluminum clad steel wire is the invention not limited to this. Rather, it can also be used advantageously for continuous Hot dip galvanizing or hot tinning of steel or other base metals used will.

Claims (4)

Claims: 1. Method for applying a metallic coating on a metallic, wire or band-shaped material by immersion in a molten metal bath, preferably for applying an aluminum coating to a steel wire, wherein the cleaned metallic material vibrates while moving through the weld pool is offset with a frequency that changes over time, characterized in that on the wire or ribbon-shaped material when entering the weld pool for production short-term random oscillations at least 40 impact pulses per second are applied with total acceleration values of at least 20 g, then the Good for avoiding standing waves in the weld pool while observing an immersion time is held for 0.5 to 8 seconds without tension, if possible, and finally the Vibrations of the material are dampened upwards before exiting the weld pool. 2. The method according to claim 1, characterized in that the movements of the wire or tape-shaped goods are limited in the direction of impact. 3. Device for carrying out the method according to claim 1 or 2, characterized in that in the vicinity of the point of immersion of the wire or band-shaped material (S) in the molten metal bath (20) a vibration generator (V) applying the impact pulses to the material consists from a pair of opposing disks (52) connected to one another at the edge with several bolts (54) , as well as an adjustable, resiliently mounted hold-down roller (18) to limit the vibratory movements of the material in the direction of impact, furthermore a die within the melt pool (20) Vibration of the goods (S) damping deflection roller (26) and a fixed rod (28) are provided and above the melt pool (20) known stripping, cooling and conveying devices (30, 32, 34, 35) are arranged. 4. Device according to claim 3, characterized in that the vibration generator (V) is designed to be controllable in its speed. Considered publications: German Patent Specifications Nos. 725 720, 925 389, 934393.