US3144361A

US3144361A - Pretreating iron or steel

Info

Publication number: US3144361A
Application number: US841408A
Authority: US
Inventors: Klinghoffer Stefan
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-11-10
Filing date: 1959-09-21
Publication date: 1964-08-11
Anticipated expiration: 1981-08-11

Description

Aug. 11, 1964 s. KLINGHOFFER PRETREATING IRON OR STEEL 2 Sheets-Sheet 1 Filed Sept. 21, 1959 Aug. 11, 1964 Filed Sept. 21, 1959 s. KLINGHOFFER 3,144,361

PRETREATING IRON 0R STEEL 2 Sheets-Shem 2 WATER '27 -25 "60 6.] 5mm r 023 n BATH FILTER. nn-ER REGENERATING CONCENTRATE DESCALING a.

PHOSPHATING RON mm BATH PHOSPHATE PHOSPHATE oxlolzmc PRECIPITATION 64 v WATER. AGENTS TANK 05E F ZQQ LOHASP E- El I I" 10 ,-PATENT f FURNACE I LEAD i: BATH 24 y*'wA'rER.

5 I 29 23 I BATH FILTER. FlLTER. REGENERATING CONCENTRATE i'r' l r-DESCALING a E PHOSPHATINO mun IRON BATH PHOSPHATE PHOSPHATE OXIDIZING PRECIPITATION AGENTS (D TANK .34 v ;6/ o? 64 V wA'rER-' STE/#4 R INVENTOR -I; D YING ;:l TUNNEL WATER ,I;; 64/E DRIVEN HASP ATTOR N EYS United States Patent 3,144,361 PRETREATING IRON 0R STEEL Stefan Klinghofier, Postfach 39, Linz (Danube), Austria Filed Sept. 21, 1959, Ser. No. 841,468 Claims priority, application Germany Nov. 10, 1955 13 Claims. (Cl. 1486.16)

The present invention relates to a method of preparing iron and steel workpieces such as wires, strips, bands, plates, sheets, pipes and the like for coldworking. The invention more particularly relates to a method of preparing iron and steel workpieces such as wires, strips, bands, plates, sheets, pipes and the like for coldworking by application of a phosphate coating thereto, in connection with which the workpieces are descaled and phosphatized in one operation. The invention is a continuation-in-part of application Serial No. 620,032, now abandoned.

Scaled wires, strips, bands, sheets, plates, pipes and the like, can, as is known, not be directly cold-drawn. It is known that such articles can first of all be freed of their layer of scale by treatment of the articles in a sulfuric acid or hydrochloric acid bath. They are then washed with running water and finally dipped into milk of lime in order to roughen the smooth surface obtained by the pickling with acid sufiiciently for the entrainment thereof by the drawing means.

It is furthermore known to dip into a phosphating bath, workpieces which have been descaled with an acid pickling agent and thereafter neutralized. The crystalline phosphate film layer formed on the wires should effect the desired roughening of the surface with the formation of a suitable absorptive lubricant support.

Up to the present time, the phosphate coatings employed for the coldworking were made exclusively by employing the phosphating baths which were customarily used for the production of rustpreventative coatings.

Such baths, due to the fact that the acid concentration thereof is very low, require, however, a complete prior elimination of the layers of scale by a preliminary pickling process effected with hydrochloric or sulfuric acid. The practice heretofore customary as pretreatment coldworking consists therefore of the following steps:

(1) Pickling the scaled wires, etc. in a hydrochloric or sulfuric acid bath: Duration to 30 minutes;

(2) Rinsing with cold water: Duration 2 to 4 minutes;

(3) Rinsing with hot water: Duration about 2 minutes;

(4) Phosphating: Duration 1 to 5 minutes;

(5) Rinsing with water: Duration 2 to 4 minutes;

(6) Drying;

(7) Oiling, greasing or soaping.

The use of phosphate coatings has not been widespread since phosphatizing of the pickled workpieces normally results in higher expenses, than, for instance, in the case of wires, liming, which in itself is cheap, so that phosphatizing was avoided as uneconomical. The phosphate coating produced could also not be deposited with the required degree of fineness, so that as a result of too thick a phosphate coating being deposited the dreaded screeching in the drawing-die and baking of the dies ensued. This led, not only to a considerable wearing out of the drawing tools and thus to a higher expense for the replacement thereof, but also more frequent interruptions in operation which, in its turn, gave rise to an increase in operating expenses due to a decrease in production.

R 3,144,361 Patented Aug. 11, 1964 The object of this invention is to provide a preliminary treatment for metal surfaces whereby scale is rapidly and cheaply removed.

A further object of the invention is to provide a preliminary treatment for metal surfaces to produce protective phosphate coatings in a rapid and economical manner.

Another object of the invention is to provide a preliminary treatment for metal surfaces whereby scale is rapidly and cheaply removed and the metal surfaces have rapidly and cheaply imparted thereto a protective phosphate coating, the same being accomplished employing only one bath.

Other objects and characteristic features of the invention will become apparent as the description proceeds.

The method in accordance with the invention consists essentially in that only one bath is used for the descaling and phosphating. The bath is characterized in that it contains more free phosphoric acid than bound phosphoric acid. The articles are dried immediately after being withdrawn from the bath at elevated temperature without rinsing, whereupon they may be treated with lubicants such as oils, greases, soaps or the like.

The bath is characterized in not only that it is more acidic than the common phosphating baths, but that it is not as acidic as the conventional pickling baths consisting of phosphoric acid. In these phosphoric acid pickling baths the equilibrium for the formation of a phosphate coating is shifted so far from the point at which secondary and tertiary zinc phosphate and manganese or iron phosphate can be formed that only a very thin phosphate layer can be formed. These known baths act only as pickling agents but not for the production of phosphate coatings. The extent of the thickness of any film obtained i.e., of iron phosphate is of the magnitude 0.1-0.5 micron only. This result is due not only to the much higher concentration of phosphoric acid but also to the fact that after pickling the metal is always rinsed or washed with water so that after leaving the pickling bath no further reaction between the acid and iron surface is possible. A phosphate coating of a thickness of only 0.1-0.5 micron is neither suitable for drawing nor as supporting film for a lubricant in the drawing operation. For these reasons, it is impossible to prepare a scaled surface for drawing using the known pickling process with phosphoric acid.

In the process according to the present invention the composition of the bath is chosen in such a manner that the concentration of the phosphoric is just high enough to carry out the descaling operation. Since the concentration of the bath in phosphoric acid is lower than in the common phosphoric pickling baths a phosphate coating improved to a degree is already formed in the bath. But the main film formation process starts after the wire has left the descaling and phosphating bath. The iron surface takes with it a certain quantity of the bath liquid which forms a liquid film on the metal surface. Contrastively to all the known pickling and phosphating operations, this film of liquid is not rinsed or washed off. During the passage of the wet wire through the drying pipe very rapid chemical reactions between the acid and the iron start. As a result of these reactions so much of the phosphoric acid is consumed that the pH-value of the bath is shifted to a higher value, and that range of pH is reached in which a thicker phosphate coating can be formed. Since only a very small volume of liquid is taken from the surface of wire the phosphate coating is formed very quickly. This is abetted in that the temperature for drying is rather high and some water is evaporated by the currents of warm air. The bath of the invention makes it possible to descale and phosphate in using only the single bath and then that both operations occur practically simultaneously. The thickness of the obtained phosphate coating is much bigger than 1 micron and is usually of the order of about 5 microns. These coatings are eminently suitable for the drawing process.

The known phosphating baths have a pH Value of more than 2.0 since the equilibrium for forming phosphate coatings lies in the range of about pH=3.0-3.5. The conventional phosphate baths are therefore not sufficiently acidic that they can remove scale or rust, which must therefore just be removed either chemically by pickling or mechanically, e.g., by sand blasting prior to forming phosphate coatings. This separate step for descaling involves, as noted above, separate baths for the pickling acid, water rinse, phosphate coating bath, water rinse, i.e., four baths in separate tanks. Therefore not only much more equipment and room but also more time is needed in order to obtain a descaled and phosphate coated surface suitable for a drawing operation. According to the invention only one bath is preferably used and the treatment time accordingly reduced from at least 20 minutes up to about 1-3 minutes only. The economic and technical advantages of such a process are self evident.

The invention can not be compared to the conventional pickling or conventional phosphating since the acid contained in the descaling and phosphating bath is much lower than in the known pickling baths and on the other hand is higher than in the conventional phosphating baths so that a descaled and phosphate coated surface can be obtained in reasonable short time. In order to assist the weaker pickling action of the weaker acidic descaling bath according to the invention, a mechanical descaling process is simultaneously used so that the pickling action of the used bath has not to carry out the whole descaling business.

The descaling and phosphatizing bath used in this connection can have a temperature of 20 to 99 C. The lower the bath temperature, the longer the time of immersion must be. In order to take the operating conditions into consideration, the phosphating bath is preferably maintained at a temperature of 70 to 99 C. The drying of the treated workpieces is effected at temperatures below 200 C.

The method in accordance with the invention can be carried out both intermittently and continuously by dipping or spraying.

In the former case, the workpieces, such as wires and the like, are suspended in the form of coils, rolls or bundles, preferably in loosened condition on a suitable device, for instance a horizontal rod, into the phosphatizing bath whereupon they are drawn out of said bath after about 60 to 120 seconds and dried either in air or in a drying oven. They are then immediately ready for drawing and can either be subjected immediately to cold working or else stored previously for some time.

In the continuous method, the wires, bands, strips, sheets, plates and the like are, for instance, drawn in loosened form through the bath, the rate of passage is such that the required time of immersion is assured. In this connection, the units are connected with each other, before entrance into the bath, preferably by welding the ends together. Frequently, however, due to lack of space, it is not possible to use elongated baths. In such case, an apparatus is used which will be described below.

In accordance with one embodiment of the invention, there can be used for the descaling of the wires, strips, bands or the like, a combined chemical-mechanical method.

To be sure, it has recently frequently been proposed to descale scaled wires mechanically, i.e., by bending.

The changes in the physical properties of the material which are caused thereby, however, had an unfavorable effect in the drawing process and have prevented the smooth wire surfaces from carrying along with them the customary lubricant. Furthermore, in this way complete descaling is not obtained and small uncontrollable particles of scale which lead to an increased wear of the drawing dies always remain on the metal surface.

In accordance with the invention, the scaled wires, strips, bands and the like are descaled in the phosphatizing bath itself by a system of rolls, this system bending the wires, for instance, in three directions and with the cooperation of the hydrogen developed between the scales upon dipping into the acid bath liquid, the scale is caused to peel off. The scale which has peeled off deposits on the bottom of the container where it can be removed from the bath by means of a known conveying device. In this way, the bath is prevented from becoming weakened by the dissolving of the scale and from rapidly becoming enriched in iron.

The descaling phosphatizing bath, for carrying out of the invention, contains, in aqueous solution, phosphoric acid, a phosphate such as zinc or manganese phosphate and a known accelerating agent such as zinc nitrate, chromic acid or sodium nitrite. The bath preferably consists of 2 to 7% up to 10% by weight total phosphoric acid, 0.2 to 2% by weight phosphates and 0.1 to 1.0% by weight of the accelerating agent. The time of treatment of scaled articles in such a bath is from 1 to 3 minutes.

In this method, after the descaling and derusting of the wires and without rinsing prior to the drying, there is produced on the wires a coating of phosphate which has a thickness of a few microns and is well-suited as carrier layer for the lubricant during the drawing process.

As can be noted from the pertinent specialized literature, on facilitating coldworking by the application of phosphate coatings, different heavy-metal phosphate coatings behave differently with respect to the coefficient of friction and thus the force expended during the drawing, in connection with the different grades of iron and steel varies. Zinc and manganese phosphate coatings behave more favorably than iron phosphate coatings.

It is therefore advantageous to increase the proportion of zinc or manganese phosphate in the phosphate coating and reduce the proportion of iron phosphate, or to be able to adjust the ratio of zinc or manganese phosphate to iron phosphate in the coating in the manner which is most favorable for the given grade of iron or steel.

It has now been found in accordance with the invention that it is possible to influence the zinc or manganese phosphate content of the phosphate coatings produced by changing the composition of the pickling and phosphating bath solution. If, for instance, the content of free phosphoric acid in proportion to bound phosphoric acid in the treatment solution is reduced, the content of iron phosphate in the phosphate layer drops with a simultaneous increase in the content of zinc or manganese phosphate. In this connection, the ratio of free to bound phosphoric acid can be varied within rather wide limits, for instance, from 10:1 down to about 2.5 :1 without the pickling and phosphating action of the bath being thereby substantially changed. If such a change in the ratio of free to bound phosphoric acid is effected, the proportion of iron phosphate in the coatings can be changed between and 60 mol percent Without changing the other operating conditions, the lower content of iron phosphate corresponding to a lower ratio of free to bound phosphoric acid. The balance, namely 5 to 40 mol percent of the coating consists of Zinc or manganese phosphate. With the composition of the pickling and phosphating bath maintained within the above ranges, there are therefore always obtained phosphate coatings in which the proportion of iron phosphate in the coating always predominates.

The bath for the pickling and phosphating in accordance with the present invention can be prepared by disconcentrate can be used both for the initial preparation of the bath and for supplementing the spent bath. Such a concentrate contains to 85% total phosphoric acid, 2 to 22% phosphates, and 1 to accelerating agent.

It has now furthermore been found that it is possible to bring the content of zinc or manganese phosphate above the content of iron phosphate in the coating if the phosphate coatings obtained are subjected to an aftertreatment in a second phosphating bath. The phosphate coatings which are preferably already richer in zinc and manganese and have been prepared by the method outlined above are introduced, after leaving the pickling and phosphating bath, without rinsing or drying, into a second phosphating bath, which contains approximately equal amounts of free and bound phosphoric acid or less free phosphoric acid than bound phosphoric acid. This bath is able extensively to dissolve the iron phosphate of the phosphate coating already present and to replace it by Zinc or manganese phosphate. The phosphate coating then contains less than about 10 mol percent iron phosphate and therefore consists practically solely of zinc or manganese phosphate. After leaving the second phosphating bath, drying is effected without rinsing, namely at a temperature below 200 C.

The articles being worked can also in this two-bath process be treated batchwise, for instance, in the form of wire coils, or continuously in a continuous-passage process i.e., the pull through method previously described.

The second phosphating bath preferably has the following composition: 0.4 to 3% free phosphoric acid, 0.5 to 4% zinc or manganese phosphate and 1.0 to 2% accelerator. As accelerating agent, there can be used the sub stances already indicated above. The treatment in the second phosphating bath is effected at a temperature of about 60 to 100 C., and preferably 90 to 98 C. for a period of to 60 seconds.

For the preparation of the second phosphating bath, the respective substances can be dissolved individually in the corresponding quantity of water; however, it is more advisable to use a concentrate which can serve both for the initial preparation of the phosphating bath and for replenishing the spent bath. The preparation of the bath ready for use is effected, for instance, by diluting a solution which contains 4 to 60% free phosphoric acid, 5 to 80% zinc or manganese phosphate and 1 to 20% accelerating agent, such as nitric acid, zinc nitrate, sodium nitrite, chromate or the like.

It has also been found advantageous to use, in order to increase the effectiveness of the baths in accordance with the present invention, longitudinal waves selected from the spectrum of infrasonic, audible and ultrasonic vibrations by incorporating corresponding apparatus of known construction. For instance, sonic apparatus, such as manufactured by the Rhewum Rheinische Werkzeugund Metallwarenfabrik, can be used for this purpose.

Furthermore, it has been found that the phosphate layers which have been produced by the method described above are suitable not only for the preparation of wires for cold shaping, but also of other workpieces of iron and steel and iron alloys, such as bars, sections, pipes, strips, bands, sheets, plates and the like. Thee articles may also be subjected in scale-covered and rusted condition to the single bath or 2-bath pickling and phosphating process and thus be prepared for the cold working.

One form of apparatus which can be used for the continuous carrying out of the pretreatment method of the invention consists of an elongated heatable container for the bath liquid through which one or more wires, strips, bands, plates, sheets or the like are pulled at a speed corresponding to the length of the container and required time of immersion. If the immersion time should be, for instance, 90 seconds and if the container has, for instance,

a length of 12 m., then the required speed is 8 in. per min;

Since evaporation results in losses in water at the operating temperature, the container is preferably provided with a cover in order to avoid any extensive evaporation. However, provision must be made that even in the case of slight water losses, fresh, preferably distilled water or Water of condensation is added, either automatically or by hand.

In order to avoid that the wires, strips, bands, plates, etc. which leave the bath remain too long in the steam produced at the bath temperature which steam has an unfavorable influence on the phosphatizing and would cause a Wmte color of the phosphate coating, the articles are caused to pass through a, preferably heated, pipe provided with a vent pipe or through a preferably heated tunnel equipped with a vent pipe.

The pipes or tunnels are mounted on the side of the container for the bath liquid, and as a matter of fact below the level of the liquid, and are charged with hot air in counter-current, which air then escapes through the vent pipe entraining steam therewith.

The wires, strips, bands, plates, sheets, etc. which leave the bath in dry state through the heated pipe or the tunnel can either be wound into a coil or rolls or be conducted in an elongated state, directly to the cold drawing machine.

Another apparatus suitable for the continuous carrying out of the pretreatment method of the invention, comprises a container for the bath liquid which is preferably provided with a cover and in which there are arranged one or more hasps or reels located one behind the other, on which, for instance, a wire which unwinds from a loose hasp is wound upon a reel.

The rolls or reels are preferably so arranged that they can be removed from the bath liquid in order to introduce a new wire.

In order to permit the Wetting of the Wire with the bath liquid to be as complete as possible, the cylindrical or conical hasps or reels are provided on their periphery with preferably outwardly tapered, longitudinal grooves or with bars of varyipg cross-section spaced apart equidistantly from each other in the longitudinal direction.

The apparatus for the chemical-mechanical descaling of the wires, strips, bands, and the like, consists therein that in the above-described tank or bath device there is furthermore arranged a system of rollers for bending wire strips, bands and the like, so that the scale, which is loosened by the formation of hydrogen drops off more readily. The mechanical descaling is effected in this connection by rollers or cylinders arranged in the stripping bath itself, the axes of which are either parallel or at an angle to each other. For the descaling of wires, they are arranged at an angle, preferably right angles to each other, the wire being so conducted over the rollers in such a manner that the direction of bend changes at each roller or cylinder. In the case of bands, strips, sheets, plates and the like, parallel arrangement of the rollers or cylinders is sufiicient.

Preferably, there is arranged in the container for the carrying out of this method an oblique, i.e., slanting partition wall terminating below or above the liquid level and provided with a hole or slot for the passage therethrough of the wire or strip, band, sheet, plate or the like, which wall, together with a conically developed part of the bath container, serves to collect the scale which has cracked or split off.

The wall terminating above the liquid level has the advantage that the scale particles, possibly suspended in the liquid do not pass into the other portion of the bath and so dilute the phosphating bath.

The scale collected in the conically developed part of the bath container is removed from the bath by means of a known conveyor device.

After operating for some time with this method, the iron becomes more and more concentrated in the phosphoric acid pickling and phosphating bath. This iron comes both from the dissolving of the scale and from the phosphating reaction itself. When the iron content has exceeded a certain limit, the bath no longer gives dependable phosphate coatings suitable for cold working. The upper limit of the iron content is about g. per liter. If this limit is exceeded, the bath is no longer suitable for the desired purpose. In order not to have to throw it away and replace it by freshly prepared bath, the bath is regenerated in accordance with the invention.

Aside from the fact that the old phosphating bath still contains free phosphoric acid, as well as heavy metal phosphates which would be lost if the bath were thrown away, it is also generally not permitted by local police ordinances and regulations to discharge into sewers or rivers solutions containing free acid and heavy metal salts, including iron salts. The free acid not only causes damage to the sewer pipes, building foundations, etc., but also very strongly damages the biological life in the rivers. A very strong mortality of the fish in the waters concerned is the result. Iron salts are also very injurious to the biological life of the river and further give rise to the formation of large quantities of iron mud. It is therefore necessary to neutralize the acid waste water of the pickling and phosphating solutions before discharging them into the sewers or rivers and to eliminate the heavy metal salts by precipitation with milk of lime, for which not only are chemicals required but also large installations which take up a large amount of space and result in high expenses. The eliminating of the acid Waste baths is therefore not only very undesirable but also costly.

The present invention provides a method, the purpose of which is to make the pickling and phosphating baths of the invention continuously suitable for use and whereby they can be continuously regenerated so that it is no longer necessary to replace the pickling and phosphating bath from time to time by a fresh bath and discharge the old solution, i.e., to neutralize it, etc. This method consists, in accordance with the invention, in that the dissolved iron compounds when they have reached a given iron concentration in the bath as a result of its continuous operation, are converted, by the addition of known oxidation agents, from divalent form into trivalent form. Since primary ferric phosphate in contradistinction to primary ferrous phosphate is only difficultly soluble in acid phosphating and pickling baths, it precipitates out and can be removed as bath mud or sludge.

This precipitation by an addition of oxidizing agents can be effected either intermittently or continuously but the addition of the oxidizing agents should be effected in such a manner that the iron is precipitated entirely or only down to a desired final concentration. The oxidizing agent should, however, never be present in the bath in excess with respect to the dissolved divalent iron.

The addition of the oxidizing agent can be effected also in a continuous circulation system in which a part of the liquid bath solution is continuously withdrawn, the concentrated iron is precipitated by the addition of oxidizing agent, the bath mud is eliminated and the regenerated solution, after being possibly freshened to the desired bath concentration, is returned again to the pickling and phosphating containers.

The mud produced from the iron compounds, which mud consists to the greater part of ferric phosphates, can be eliminated either by allowing it to settle out before a longer period of operation, for instance overnight, or by filtration. After possibly washing with water, it can either be thrown on the dump heap or be used to produce phosphate-containing fertilizers or else be worked up to phosphoric acid.

As oxidizing agent for separating the difiicultly soluble iron phosphates, the following enter into consideration, hydrogen peroxide, chlorates, nitrites, nitrates, nitric acid, the introduction of ozone-containing air, or ozone-containing oxygen, potassium permanganate, organic and inorganic percompounds and the like. Mixtures of two or more oxidizing agents may also be used. The addition of oxidizing agents is effected advisedly with the same in aqueous solution. It can be effected batchwise, continuously or in a circulatory process. The amount of oxidation agent added is so adapted to the existing iron content that bath analysis shows that an excess of the oxidizing agent has been avoided.

The method in accordance with the invention affords the advantage that the pickling and phosphating baths can be used in continuous operation for a practically unlimited period of time without costly renewals of the bath or the necessity of rendering the same suitable for disposal.

It is already known to eliminate from phosphating baths the enriched iron salts by the addition of oxidizing agents such as hydrogen peroxide, chlorate, nitrite and the like and oxidation of the bivalent iron ions to trivalent iron ions and the thereby possible precipitation as difiicultly soluble ferric phosphate.

In such a method, a small excess of hydrogen peroxide is continuously maintained in the phosphating bath. In another known phosphating process, there is added in a circulatory process only sufiicient nitrite to keep the iron content at a value of less than 1 g. per liter and at the same time keep the pH of the bath constant. In accordance with another known phosphating process, the quantity of hydrogen peroxide added is A to /8 of the zinc content, the bath temperature is preferably 25 to 50 C. and the pH of the bath is slightly above the pH of the phosphating equilibrium.

In the present process, not only is a slight excess of the oxidizing agent or agents always avoided, but the pH of the bath, which after all is to act both as pickling bath and as phosphating bath, is considerably less than in the customary phosphating baths, namely less than 1.5. Furthermore, in the strongly acid pickling and phosphating solutions in accordance with the present invention, the maintenance of a constant pH is not of essential importance since the content of phosphoric acid can vary within large limits. As a result of this situation, the present method is also considerably simpler to carry out in operation than the regeneration processes in connection with the customary pure phosphating baths.

The invention can be better understood in connection with the accompanying drawings which illustrate several forms of apparatus which may be used in carrying out the invention, and in which:

FIG. 1 shows diagrammatically a longitudinal section through an apparatus in accordance with the invention;

FIG. 2 shows, also diagrammatically, a longitudinal section through another apparatus in accordance with the invention;

FIG. 3 shows diagrammatically the sketch and flow scheme for the process for descaling and phosphating, together with the regeneration of the bath for batchwise operation;

FIG. 4 shows diagrammatically the outline and the flow scheme for the continuous descaling and phosphating of wire together with the regeneration of the bath liquid.

FIG. 5 shows diagrammatically a longitudinal section of the combined process for the descaling and production of a zinc phosphate coating in continuous operation, together with the regeneration of the bath liquids.

In a container 1 which is filled with a bath liquid up to the level 2, there are arranged two rollers, 3, 3', on which the wire rod 5 unwinding from the idle reel 4 is rolled up in series. The container 1 is provided on the side with a pipe 7 through which the wire rod 5 passes after leaving the bath. The pipe 7 carries a vent pipe 6 and is fed with hot air through the opening 8. In this connection, the steam present in the pipe 7 is discharged throughthe vent pipes 6. The spaced bars of the rollers are shown at 21.

In FIG. 2 a system of rollers 13, and 13', is arranged in a container for the bath liquid. in addition to the reel-s 15 and 15'. The container 9 is filled up to the level 11 with a bath liquid such as described above. A wire rod 12 which unwinds from the idle reel 4 is bent in three directions in the system of rollers 13, and 13', and freed of scale. The scale 14 which has come off collects on the bottom of the container 9 in the space which is formed by a partition wall 10 provided with a hole 16 for the passage of the wire 12 and through the conical portion of the container 9. The scale 14 can be removed from the bath by a continuous or non-continuous conveying device, by the arrangement of the crock shown at 18, the hoisting device shown at 17, the means for discharging the scale as shown at 20. The wire is wound onto the two reels 15, 15 after it has left the system of rollers, 13, and 13', and leaves the bath through the pipe 7.

In FIG. 3 the system of descaling and phosphating is shown for batchwise operation including the regeneration of the bath liquid. The bath is in the container 60, provided with an inlet for heating steam and outlet for condensed water. From time to time or continuously a part of the bath liquid is taken from the container 60 at 61 and led through a pipe with shutter 62 to a precipitating tank 22. To that tank are added the oxidizing agents needed for the precipitation of the iron-III-phosphate such as hydrogen peroxide, or sodium nitrite, the same being supplied from the container 32. The liquid containing the precipitate is passed through one of the two

filters

23 and 23 respectively, where the iron phosphate is removed from the liquid. Water and concentrate are added to the clean bath, in accordance with the analysis, at 24 and 25, respectively. The concentrate is contained in the container 26. The clean and regenerated bath liquid is then returned to the descaling and phosphating bath at 27 and thence to the tank 60.

Referring to FIG. 4, the scaled wire 28 is unrolled from the loose hasp 29. The wire passes then a patenting furnace 30 and a bath 31 consisting of molten lead and enters afterwards the descaling and phosphating bath, contained in the tank 33. The bath liquid is heated by steam coils, preferably of lead, whereby the steam enters at 63 and condensed water is removed at 64. 34 is an opening for the removal of air. The process for the removal of iron phosphate from the bath and for the regeneration of the bath liquid is exactly the same as described for FIG. 3. The descaled, phosphated and dried wire is then rolled up in the driven hasp 35. Afterwards it is drawn.

In FIG. is shown diagrammatically the combined process for the production of a mainly zinc phosphate containing phosphate layer, together with the regeneration of the two bath liquids. The bath I, which is stronger in acid and descaling properties but which produces a mainly iron phosphate containing phosphate layer, is contained in tank 38, while the bath II, which has only weak descaling power but which can produce a thicker zinc phosphate coating is contained in the tank 39. The wire 40 is unrolled from hasp 41 and passed through bath I in container 38 and then immediately through bath II in container 39. After leaving the bath 39, the wire passes through the pipe 42 wherein it is dried by a countercurrent of warm air. Overflowing bath liquid I is collected in the two containers 43 and 44 and pumped by pump 45 to the system of precipitating of iron phos phate and its filtration, replenishing of water and concentrated bath solution, which system is schematically shown at 46. This system 46 corresponds completely to that One shown in FIGS. 3 and 4.

The overflowing bath liquid II is collected in the containers 47 and 48 and pumped by means of the pump 49 to the regeneration unit 50, where the iron phosphate is precipitated, filtered and the bath liquid II is regenerated by addition of water and concentrate of bath II. This system 50 is also the same as already described in FIGS. 3 and 4. The phosphate coated and dried wire is rolled up in the hasp 51.

10 The mechanical descaling equipment which is shown in FIG. 2 may also be used in bath I and is not specifically shown in the FIGS. 3-5.

The following examples illustrate the invention.

Example 1 In a tank provided with coil heating, there is prepared a bath which contains, in aqueous solution, 6% total phosphoric acid, 0.8% zinc phosphate and, as accelerating agent, 0.2% sodium nitrite. The bath is maintained at 96 C. and loose coils of basic Bessemer wire suspended on a horizontal bar are immersed for 2 /2 minutes into the bath and then rapidly pulled out of it and dried in the air or in a drying oven at 115 C. The phosphate coating produced in this manner has a thickness of about 3 microns and contains about 5 mol percent zinc and 95 mol percent iron phosphate.

Example 2 The bath contains 5% total phosphoric acid, 0.5% thereof in the form of manganese phosphate and 4.5% as free phosphoric acid, as well as 0.1% chromic acid as accelerating agent. The bath liquid is charged to a container such as shown in FIG. 1. The container is provided with two cylindrical reels having a diameter of cm. each and a circumference of 2.83 m. At the temperature of the bath of 98 C., the speed of passage of the inter-annealed (patented) steel wire (2.5 mm. C-content 0.2%) treated in the bath is 2.5 m. per second. The immersed wire has a length of 225 m. and is wound 40 times around each reel. The time of immersion of the wire in the bath is 90 seconds. The thickness of the phosphate coating produced is 3 to 4 microns. It contains 4 mol percent manganese phosphate and 96 mol percent iron phosphate. The phosphated steel wire is drawn in the customary manner.

Example 3 Section irons are immersed for 4 min. at C. in a scale-covered condition in a bath which contains 5.57% total phosphoric acid, 0.83% thereof bound to zinc and 4.74% thereof as free phosphoric acid, as well as 0.1% sodium nitrite as accelerator, and are dried, without washing, at C. The phosphate coating obtained in this manner contains about 30 mol percent zinc phosphate, in addition to about 70 mol percent iron phosphate. The section irons are then soaped and cold-drawn.

Example 4 Scale-covered pipes are immersed for 3 minutes at 98 C. in a bath which contains 4.1% free phosphoric acid, 0.8% zinc monophosphate and 0.25% nitric acid as accelerator. Thereupon they are pulled out of the bath and immediately dipped into another bath (time of immersion 30 seconds) which contains 0.6% free phosphoric acid, 1.4% zinc monophosphate and 1.2% Zinc nitrate as accelerator and has a temperature of 98 C. After removal from the bath, the pipes are dried, without washing, at C. The phosphate layer formed in this manner contains about 88 to 90 mol percent zinc phosphate and 10 to 12 mol percent iron phosphate. After soaping, the pipes are drawn.

Example 5 A 2,000 liter bath for pickling and phosphating contains 15 g. per liter of iron, the concentration of which is to be reduced to 3 g. per liter. Hydrogen peroxide is used as oxidizing agent. Since 12 g. per liter and therefore a total of 24 g. of iron are to be precipitated, 36 kg. of 20% hydrogen peroxide solution are added. The precipitate formed is filtered off and discarded. The bath which has been purified in this manner, can be used again, after it has been brought up to strength by adding the spent amount of acid and cations so that it again has the desired bath concentration, for the pickling and phosphating.

1 1 Example 6 A scale-covered hot-rolled sheet is treated by a spray process effected at 95 C. for 2 minutes in a tunnel with a solution which contains 4.7% free phosphoric acid and 0.8% phosphoric acid bound to zinc as well as 0.25% nitric acid as accelerator, and then dried in a further part of the tunnel at 130 C. The sheet which has been descaled and phosphated in this manner is cut into blanks and deep-drawn in the customary manner. The solution employed is regenerated in the manner indicated in Example 5, in a continuous fashion, by the addition of about 1.5 kg. of hydrogen peroxide solution per kg. of iron to be precipitated, followed by filtration of the precipitated ferric phosphate, freshened with a concentrate containing 47% free phosphoric acid and 8% phosphoric acid bound to zinc as well as 2.5% nitric acid, heated to 95 C. and again sprayed in the tunnel.

The method of the present invention differs fundamentally from the known manner of facilitating non-cutting, cold-working by means of phosphate layers in that in the known methods, descaling is first of all effected in a separate operation by pickling with sulfuric acid or hydrochloric acid, followed by washing and then by phosphating in the customary anti-rust phosphating solutions, and then again rinsing. This method of operation thus requires several different baths and several containers for each solution, and a time of about 20 to minutes. This manner of operation in separate steps is necessary for the reason that the ordinary rust-preventative phosphating baths contain too little free acid and therefore cannot dissolve thicker rust or scale layers. If an attempt were made to effect descaling and phosphating simultaneously with the customary rust-preventative phosphating baths, there would be obtained either no phosphate coating at all on the scale-coated workpieces or else the layer formed would have such insufficient strength of adherence that it would be forced away from the iron surface for instance upon the drawing of for example, the coated wire in the drawing dies. It was therefore necessary, prior to effecting the phosphating in the customary rust-preventative phosphating baths, to effect descaling with sulfuric acid or hydrochloric acid and to thoroughly clean the workpieces following their removal from the pickle bath so as to remove any solution adhering to them after the descaling.

If the method of the present invention is compared with this known manner of procedure, the following essential advantages can be noted. In the method of the invention, descaling and phosphating is effected simultaneously since the bath contains more free phosphoric acid than bound phosphoric acid and its pH is below 1.5. It is therefore also able to dissolve layers of scale. The present method thus consists solely of the following steps:

(1) Pickling and phosphating the scale-covered Wires, bands, strips, plates, sheets, pipes and the like in a single bath and at the same time, preferably in the pull-through process: Time, 13 min.

(2) Drying, immediately thereafter, without rinsing: Time, less than 1 min.

(3) Oiling, greasing or soaping.

The present method therefore differs very radically from the ordinary phosphating methods. Since the bath, in accordance with the invention exercises substantially simultaneously a descaling and phosphating action and since the rinsings are also eliminated, only a single container is required. The total time of treatment, including drying is only 1-3 min.

The stronger phosphoric acid could possibly impair the formation of a phosphate layer of more than one micron such as is necessary for the cold working, since it brings the phosphating solution out of the so-called hydrolysis equilibrium, i.e., the formation of secondary and tertiary metal phosphates is made difficult. The main coating formation however proceeds in the case of the present invention predominantly upon the drying at elevated temperature. The descaled article carries solution along with it upon moving out of the phosphating bath, which solution then leads in a short time to the formation of a thicker layer of phosphate on the surface-of the metal articles at the increased temperature. In contradistinction to rust-preventive phosphating, rinsing is futhermore not effected in the present process, since the adhering phosphating solution is required for the formation of the layer. The phosphate layer produced, of an approximate thickness of a few microns, is already sufficiently thick to serve as a lubricant support, but on the other hand, not thick enough to cause increased wear of the drawing dies.

To be sure, cleaning methods for rusted iron objects are already known in which baths having a higher content of free phosphoric acid are used. In them, however, the phosphoric acid is intended to exert predominantly merely a descaling action and no layers or only very thin layers are formed, these layers, however, not being sufficient for cold-working.

Another advantage of the invention, resides in the possibility of controlling the zinc or manganese content of the phosphate layers by modifying the composition of the pickling and phosphating solution.

Another advantage of the invention resides in the greater healthfulness of the operating conditions, since instead of the hydrochloric acid and sulfuric acid baths there are used phosphate baths which can be regenerated in accordance with the invention whereby their life is practically unlimited. The discharging of the hydrochloric or sulfuric acid as pickling baths and of the customary phosphating baths into rivers makes the rivers unsuitable for human bathing and kills the fish. Their discharge into sewers extensively damages the lining of the sewers. Since the life of the bath in accordance with the invention is practically unlimited, the discharging thereof into rivers and sewers scarcely enters into question.

Another advantage of the present invention consists in the shortness of the time of immersion, which reduces the bath volume to a minimum and results in a considerable saving in space.

The word simultaneous or simultaneously as used in the specification and claims is not to be strictly construed. The terms are used to indicate not only one bath is used and that with just one operation, there can be achieved both descaling and phosphating. Obviously the two results are not simultaneously achieved, but the phosphating follows immediately the descaling, although some coating starts to occur in the bath.

I claim:

1. In the method of pretreating iron and steel scaled workpieces to be cold-drawn, wherein the workpieces are descaled and coated with a crystalline phosphate, the improvement of descaling and ortho-phosphate-coating the said scaled work-pieces by a single treatment bath by the steps of (a) contacting the workpiece with a single liquid treatment bath having a temperature of between 20 and 99 C. consisting of an aqueous solution containing more free phosphoric acid than bound phosphoric acid, there being present in said solution from 2 to 7% by weight of total phosphoric acid and 0.2 to 2% by weight of phosphates, and maintaining it in said bath until the workpiece has been descalcd to the bare metal base, and (b) thereafter removing the workpiece from the bath and directly drying the adhering liquid on the base metal after said contacting thereby to provide a phosphate coating on the descaled workpiece.

2. Process according to claim 1, which comprises increasing the proportion of phosphates other than iron phosphate and decreasing the proportion of iron phosphate in the coating produced by maintaining the ratio of free to bound phosphoric acid in the treatment bath within the limits of 10:1 and 2.5: 1.

3. Process according to claim 1, which comprises preparing said single treatment bath from an aqueous concentrate containing in solution 10 to total phosphoric 13 acid, 2 to 22% phosphates and 1 to 20% of an accelerating agent selected from the group consisting of zinc nitrate, chromic acid, nitric acid, sodium nitrate, and mixtures thereof.

4. Process according to claim 1, which comprises adding to said treatment bath an oxidizing agent selected from the group consisting of hydrogen peroxide, chlorates, nitrites, nitrates, nitric acid, air, ozone-containing oxygen, potassium permanganate, and sodium permanganate, whereby at least a predetermined proportion of bivalent iron salts present in said treatment bath are converted into diflicultly soluble alkaline ferric phosphates, separating out said phosphates, said oxidizing agent being added in an amount not exceeding the amount necessary to oxidize said bivalent iron salts present in said treatment bath.

5. Process according to claim 1 wherein said bound phosphoric acid is a metal phosphate selected from the group consisting of iron phosphate, zinc phosphate, manganese phosphate and mixtures thereof. 7

6. In the method of pretreating iron and steel scaled workpieces to be cold-drawn, wherein the workpieces are descaled and coated with a crystalline phosphate, the improvement of descaling and ortho-phosphate-coating the said scaled workpieces by a single treatment bath by the steps of (a) contacting until said workpieces are descaled the workpiece with a single liquid treatment bath having a temperature of between 20 and 99 C. consisting of an aqueous solution containing more free phosphoric acid than bound phosphoric acid, there being present in said solution from 2 to 10% by weight of total phosphoric acid and 0.2 to 2% by weight of phosphates, (b) removing the workpiece from the bath and immediately thereafter contacting the workpiece with a second liquid treatment bath in which the free phosphoric acid is less than the bound phosphoric acid consisting of an aqueous solution containing from 0.4 to 3% by weight free phosphoric acid and 0.5 to 4% by weight of bound phosphoric acid, and (c) thereafter removing the workpiece from the second bath and directly drying the adhering liquid on said workpiece after said contacting to provide a descaled and phosphate-coated workpiece.

7. Process according to claim 6, which comprises preparing said single treatment bath from an aqueous concentrate containing in solution 10 to 85% total phosphoric acid, 2 to 22% phosphates and 1 to 20% of an accelerating agent selected from the group consisting of zinc nitrate, chromic acid, nitric acid, sodium nitrate, and mixtures thereof, and preparing said second treatment bath from an aqueous concentrate containing in solution 4 to 60% free phosphoric acid, 5 to 80% bound phosphates and 1 to 20% of an accelerating agent selected from the group consisting of zinc nitrate, chromic acid, nitric acid, sodium nitrate, and mixtures thereof.

8. In the process for treating scaled iron and steel work pieces for improving their quality to be cold-drawn in which the work pieces are descaled and coated with crystalline phosphate, the improvement which comprises contacting the scaled work pieces with an excess of a solution consisting essentially of water containing in solution 27% by weight of total phosphoric acid, the amount of free phosphoric acid exceeding the amount of bound phosphoric acid, 05-2 by weight of a metal phosphate selected from the group consisting of zinc phosphate, manganese phosphate and mixtures thereof, and 0.22% of an accelerating agent selected from the group consisting of zinc nitrate, chromic acid, nitric acid, sodium nitrate, and mixtures thereof and ethyl ester of chloroacetic acid, said solution having a temperature of from about 20 C. to 99 C. and maintaining it in the bath until the work piece has been descaled to the bare metal base, and thereafter removing the work piece from the bath and directly drying the adhering liquid on the base metal so treated at a temperature below 200 C.

9. In a method of treating a scaled elongated iron or steel work piece, such as wire, wherein the work piece is descaled and coated with a crystalline phosphate, the improvement of descaling and ortho-phosphate-coating the said work piece by a single treatment bath by the steps of continuously drawing the work piece through a single liquid treatment bath having a temperature of between 20 and 99 C. consisting of an aqueous solution containing more free phosphoric acid than bound phosphoric acid, there being present in said solution from 2 to 7% by weight of total phosphoric acid and 0.2 to 2% by weight of phosphates, and maintaining it in said bath until the work piece has been descaled to the bare metal base, and directly drying the adhering liquid on the base metal of the work piece after passage through and removal from said bath thereby to provide a phosphate coating on the descaled work piece.

10. In a method of treating a scaled iron or steel work piece wherein the work piece is descaled and coated with a crystalline phosphate, the improvement of descaling and ortho-phosphate-coating the said scaled Work piece by a single treatment bath by the steps of: first, putting the work piece in contact with a single liquid treatment bath having a temperature of between 20 and 99 C. consisting of an aqueous solution containing more free phosphoric acid than bound phosphoric acid, there being present in said solution from 2 to 7% by weight of total phosphoric acid and 0.2 to 2% by weight of phosphates, and maintaining it in said bath until the work piece has been descaled to the bare metal base, and thereafter removing the work piece from the bath and directly drying the adhering liquid on the base metal to thereby provide a phosphate coating on the descaled work piece.

11. In a method as claimed in claim 10, wherein said bound phosphoric acid is a metal phosphate selected from the group consisting of iron phosphate, zinc phosphate, and manganese phosphate.

12. In a method for treating a scaled iron or steel Work piece, wherein the work piece is descaled and coated with a crystalline phosphate, the improvement of descaling and ortho-phosphate-coating the said scaled work piece by putting the work piece in contact with an excess of a solution consisting essentially of water containing in solution of from 2 to 7% by weight of total phosphoric acid, the amount of free phosphoric acid exceeding the amount of bound phosphoric acid, of from 0.5 to 2% by weight of a metal phosphate selected from the group consisting of zinc and manganese phosphates, and of from 0.2 to 2% of an accelerating agent selected from the group consisting of zinc nitrate, chromic acid, nitric acid, sodium nitrate and mixtures thereof, said solution having a temperature of from 20 C. to 99 C., and maintaining it in said bath until the work piece has been descaled to the bare metal base, and thereafter removing the work piece from the bath and directly drying the adhering liquid on the base metal so treated.

13. In a method of pre-treating a scaled iron or steel work piece, wherein the work piece is descaled and coated with a crystalline phosphate, the improvement of descaling and ortho-phosphate-coating the said scaled work piece by the steps of: putting said Work piece, until it has been descaled, in contact with a first liquid treatment bath having a temperature of between 20 and 99 C. consisting of an aqueous solution containing more free phosphoric acid than bound phosphoric acid, there being present in said solution from 2 to 10% by weight of total phosphoric acid and 0.2 to 2% by weight of phosphates; removing the work piece from the bath and immediately thereafter putting the work piece in contact with a second liquid treatment bath in which the free phosphoric acid is less than the bound phosphoric acid consisting of an aqueous solution containing from 0.4 to 3% by weight free phosphoric acid and 0.5 to 4% by weight of bound phosphoric acid; and subsequently removing the Work piece from the second bath and di- References Cited in the file of this patent UNITED STATES PATENTS 5 Allen Nov. 19, 1929 Bigeon July 20, 1937 Locleesen Mar. 4, 1941 Caugherty Dec. 21, 1943 Jernstedt Feb. 29, 1944 16 Tanner Dec. 25, Thompson et a1. Apr. 8, Lum July 18, Holden et a1. Sept. 12, Bourgeaux Nov. 4, Andressen et a1. Jan. 13, Larsen et al Mar. 17, Kane Aug. 25,

FOREIGN PATENTS Austria July 10,

Claims

1. IN THE METHOD OF PRETREATING IRON AND STEEL SCALED WORKPIECES TO BE COLD-DRAWN, WHEREIN THE WORKPIECES ARE DESCALED AND COATED WITH A CRYSTALLINE PHOSPHATE, THE IMPROVEMENT OF DESCALING AND ORTHO-PHOSPHATE-COATING THE SAID SCALED WORK-PIECE BY A SINGLE TREATMENT BATH BY THE STEPS OF (A) CONTACTIN G THE OWRKPIECE WITH A SINGLE LIQUID TREATMENT BATH HAVING A TEMPERATURE OF BETWEEN 20 AND 99*C. CONSISTING OF AN AQUEOUS SOLUTION CONTAINING MORE FREE PHOSPHORIC ACID THAN BOUND PHOSPHORIC ACID, THERE BEING PRESENT IN SAID SOLUTION FROM 2 TO 7% BY WEIGHT OF TOTAL PHOSPHORIC ACID AND 0.2 TO 2% BY