US3648349A - Method for treating a hot-rolled metal body and the like - Google Patents

Abstract

A hot-rolled metal body emerges from between the last two rolls of the rolling-mill train in a hot, solid, and relatively scalefree condition and passes immediately into a treatment chamber prior to any substantial formation of scales on the body. In this chamber a powder, consisting of a mixture of reducing agents and substances which fuse at the temperature of the body, are blown against it and melt. On cooling, this melt hardens to form a glassy, enamellike coating which breaks in the region of any surface flaws to indicate the presence of the latter and protects the body from further scaling as it further cools.

Description

United States Patent Schaumburg Mar. M, 1972 [54] METHOD FOR TREATING A HOT- 2,458,715 1/1949 Marencik et a1 .29/424 ROLLED METAL BODY AND THE LIKE 2,762,115 9/1956 Gates ..29/424 3,169,310 2 1965 G'b t l ..29 [72] Inventor: Georges Schaumburg, bis rue de Londres, 1 son 6 a /527 4 Momlgny'les'MetZ France Primary ExaminerJohn F. Campbell [22] Filed: June 23, 1969 Assistant Examiner-Victor A. Di Palma [21] PP 835,359 Attorney-Karl F. Ross [57] ABSTRACT 30 F A l' P rlt 1 reign pp cation no y Data A hotrolled metal body emerges from between the last two June 24, 1968 Germany ..P 17 71 666.4 rolls of the rolling-mill train in a hot, solid, and relatively scale-free condition and passes immediately into a treatment 2 /4 9 4 9. ,2 .-.9; chamber prior to any substantial formation of scales on the 7/23 body. In this chamber a powder, consisting of a mixture of [51] Int. Cl ..B23q 17/00 reducing agents and Substances which fuse at the tempetawre [58] held of Search 2 1 of the body, are blown against it and melt. On cooling, this I l3 117/2 8/23 melt hardens to form a glassy, enamellike coating which breaks in the region of any surface flaws to indicate the [56] References cued presence of the latter and protects the body from further scal- UNITED STATES PATENTS mg as It further @015- 2,442,485 6/1948 Cook ..117/50 2 (Ilaims, 7 Drawing Figures c mnmm com-inn PATENTEDMAR 14 I972 3, 648 34 9 sum 1 ur a INVENTOR. GEOB GES SC'HM/HBUEG ATTORNEY PATENTEDHAR 14 m2 SHEEY 2 0F 3 m tlllllrllbiL lxiifll r wuFumFoum mJmmXmJ E h w u INVI'JN'I'OR. GEORGES SCHA PATENTEDHAR 14 m2 3. 648 349 sum 3 or 4 INVLNTOR.

GEORGES SC'HAUMBUQG BY ss K rl Tn ATTORNEY METHOD FOR TREATING A HOT-ROLLED METAL BODY AND THE LIKE FIELD OF THE INVENTION The present invention relates to a method of and an apparatus for treating a hot-formed metal body and, more particularly, a hot-rolled metal body.

The invention also relates to a method of and an apparatus for hot-rolling of steel bodies and to a technique for detecting surface flaws or defects thereon.

BACKGROUND OF THE INVENTION In the rolling of a metal body, a heated ingot, billet, bloom or slab is passed between a plurality of pairs of rolls of successively narrowing spacing so that the slab or ingot is lengthened and narrowed. This operation is preferably carried out with the billet in a hot condition.

As the body leaves the last pair of rolls in the rolling train it is quite hot and relatively scale free, since the mechanical compression of the body effectively descales it. This condition does not last long since the body starts immediately to scale at high temperatures in the ambient oxidizing atmosphere. The scaling is detrimental in itself, in that it roughens the exterior of the workpiece, and has the further effect of so obscuring or hiding any surface flaws on the workpiece that they pass notice altogether, thereby giving rise to an imperfect finished product. Removal of these scales is often carried out by a time-consuming operation, such a pickling or sandblasting, so that production is also hindered by the need for these steps.

OBJECTS OF THE INVENTION It is, therefore, the general object of the present invention to provide an improved method of and an apparatus for treating a hot-formed metal body.

A more specific object is to provide such a method and apparatus which overcome the above-mentioned difficulties particular to hot-rolled metal bodies.

It is another object of this invention to provide an improved method of detecting surface flaws in hot-formed bodies and especially hot-rolled steel bodies.

Still another object of this invention is to provide a method for protecting hot-rolled steel bodies against scaling and also to improve markedly the quality of hot-rolled steel bodies obtainable from a rolling mill.

SUMMARY OF THE INVENTION The above objects are attained, in accordance with some features of the present invention, by a method of treating a metal body which emerges in a hot, solid, and relatively scalefree condition from a hot-forming stage, specifically in a rolling mill, and passes directly into a treatment chamber. A powder consisting of a mixture of reducing agents to remove any slight scales and glass-forming substances which fuse at the temperature of the body, is blown against the exterior of the body as it passes through this chamber. The powder fuses and, on cooling of the body, solidifies to form a glassy, enamellike coating which ruptures in the region of surface flaws on the body, thereby enabling their observation, while sealing the body off from the atmosphere to prevent any further scaling.

In accordance with another aspect of the invention, the method involves the steps of hot-forming a steel body and, prior to any substantial formation of scale thereon or after an initial treatment of the hot slightly scaled body with a reducing agent, forming a thin flowable liquid-glass or enamel coating on the body. Upon hardening of this coating, it not only seals the surface against chemical attack and scaling, but (of even greater importance from the point of view of this aspect of the invention) itself is indicative of the presence of surface flaws as noted below. These flaws, not readily visible otherwise, can then be eliminated by conventional techniques.

This treatment chamber, according to further specific features of the present invention, is fitted with at least one nozzle which is connected through at least one blower to a hopper containing the above-described powder. The nozzle is formed with a Venturi restriction and a small pipe opening longitudinally into the nozzle is connected to a source of gas under pressure to accelerate the powder and project it out of the nozzle against the body. An inert gas, a reducing gas, or simply air can be used as propellant.

The powder can be a mixture of oxides of silicon, magnesium, aluminum, and iron, along with metallic sodium, boron, or potassium, or a compound of these chemicals. Zinc borate, according to a further feature of the present invention, has proven useful in the enamel layer in that the final product is effectively zinc coated upon removal of the coating.

In accordance with yet a further feature of the invention, the coated and cooled body can be stripped of its temporary glassy coating, for instance in a straightening station, and subsequently recoated for greater permanence by spraying with paint, lacquer, a synthetic-resin protective coating, or the like. Such a method is particularly advantageous in that the glassy coating is quite easy to remove from the body, i.e., more easily removed than the customary scale, so that the body can be completely processed in one continuous operation.

Prior to the enamel coating, it is possible to subject the body to treatment with a reducing agent, such as hydrogen or methane, to remove any slight scale thereon. In this case, there is no need to admix reducing agents such as powdered reducing metals, with the powder.

In an alternative embodiment the body, which can be a continuous rod, wire, sheet or the like, is simply passed through a fluidized bed of the above-described metal and metal-oxide powders to coat it. In any case, the coating must be thin enough to rupture in the region of any flaws, or to allow the flaws to be seen through the coating, while being tough enough not to flake off immediately as the workpiece is transported.

Thus, a key feature of the present invention is the formation of a glasslike coating upon the surface of a hot-formed body while it is still in the heated condition and susceptible to sealing, of a relatively thin and brittle character upon cooling. This enamel layer, which may be composed of any conventional enameling composition, dispensed in the liquid or solid state and merely solidifiable on the body and/or fusible thereon utilizing the heat of the body, surprisingly is capable of providing a visible indication of surface flaws or defects in the body. While the mechanism of this system is not fully understood, it would appear that the enamel film ruptures, fractures or breaks in the presence of surface flaws, e.g., pits, striations, projections, contamination areas, cracking and similar defects, either as a consequence of thermal stress during cooling, or mechanical movement of various portions of the defect area, etc. or as a result of an inability to adhere effectively to these regions, thereby producing a fracture zone in the region of the defects. This marking or indication of the defects permits the defective material to be removed or otherwise monitored to ensure that the finished product will be free from the flaws. The enamel layer does not remain as tenaciously upon the body as would a slag layer or other scale-forming material, but rather can be broken away with ease as will be apparent hereinafter.

While reference has been made above to enamel and glasslike material as capable of fulfilling the requirements of the present invention, it may be noted that numerous enamel compositions which are capable of melting at a wide range of temperatures including the temperatures at which the metal (steel) body emerges from the hot-forming stage, are known and may be used in accordance with the present invention as long as the material is applied to the body with a viscosity sufficiently low to enable the liquid material to flow into a uniform thin film coating the body. This film, which may have a thickness of the order of microns, e.g., 5-10 microns, may either be applied in the form of a liquid coating or glass or may be applied in a powder stream, e.g., designed to fuse to flow along the surface at the temperature of the body, but in either case will be a glassy substance.

When powders are used, it is preferred to direct them against the body in high-velocity aerosol-type jets, the velocity being controlled by compressed air. At sufficiently high velocity, the powder effectively penetrates the surface skin of the metal, which can be assumed to be substantially free from scale, and is rapidly heated by its intimate contact with the metal to the melting point of the powder and thereabove, whereby the molten droplets coalesce to form a liquid glass film upon the surface of the metal. Preferably, this treatment is carried out in a tubular chamber enclosing the body and open at its ends-to permit the body to pass through the chamber. The latter is provided with a configuration geometrically similar to that of the body, i.e., a chamber of circular cross section when the body is a continuously cast rod of circular cross section.

As noted earlier, an important feature of this invention resides in the provision of reducing agents in the treatment process to eliminate any scale which may have been formed on the body prior to coating with the enamel layer. Thus, the body may be treated with a reducing gas or reducing agents, e.g., sodium, potassium and like reducing metals may be employed, the reduction products and the oxidized metal compounds resulting from the reducing reaction being incorporated in the subsequently formed enamel coating. In this respect, it may be noted that scale layers, when composed of the slag-formed present in metallurgical systems are of a glassy nature and are soluble in the glasslike enamel coating applied in accordance with the present invention.

In applying the powders, preferably in the form of a powder mixture of the character set forth above, it has been found to be advantageous to provide a tandem array of blowers, the first receiving a mixture of powders and air and constituting a loosening means whereby the powders are dispersed in the airstream to form a flowable mixture. In the second or downstream blower, the powder/air mixture is accelerated to a high velocity and propelled to a discharge nozzle trained upon the hot-metal surface. Between this nozzle and the second blower, there may be provided a venturi injector to which compressed air is fed to regulate the velocity of the powder/air mixture directed against the workpiece surface.

While the invention is effective with hot-formed metals of any type, it has been found that hot-rolled products deriving from a rolling mill in which hot ingots or blooms are rolled in a heated state, and continuous casting arrangements offer the best sources of the bodies which are treated in accordance with this invention. Of course, the steps enumerated above apply whether the bodies are rolled or continuously cast, and either type of body may be subjected to the subsequent treatment as indicated earlier to form a final and more or less permanent coating therein.

DESCRIPTION OF THE DRAWING The above and other objects, features, and advantages will become more apparent from the following description, reference being made to the accompanying drawing, in which:

FIG. I is a perspective view of a rolling mill embodying the principles of the present invention;

FIG. 2 is a vertical section through the rolling mill of FIG. 1;

FIG. 3 is a perspective view of a continuous casting installation embodying the principles of the present invention;

FIG. 4 is a vertical section through the installation of FIG. 3;

FIG. 5 is a vertical section through another apparatus embodying the present invention; and

FIGS. 6 and 7 are sections through a metal body at two separate stages in its treatment according to the present invention.

SPECIFIC DESCRIPTION As seen in FIGS. 1 and 2, a slab or sheet 3 is formed between two rolls 23 and 23' of a last rolling stage 1 of a rolling train. This slab 3 emerges from between these rolls 23 and 23' in a very hot, solid and relatively scale-free condition. It is transported by driven rollers 2 through a chamber 22 where it is subjected to the reduction effects of a reducing gas, e.g., hydrogen, carbon monoxide, methane or mixtures thereof, to remove any slight scale formations which might have come into being thereon.

The slab 3, still hot, then enters an inlet 4a of a treatment chamber 4. As it passes through this chamber 4 it is contacted on all its surfaces by a powder P which is a mixture of reducing-metal and metal oxide particles that fuse on the surface and form a very hard, inflexible enamellike glassy coating (see FIG. 6). In addition, other substances (e.g., zinc) needed for the later surface treatment of this body can be added to this powder in the form of the material itself or as another substance (e.g., zinc borate) which produces the desired coating or alloying substance in situ.

These powders are held in a hopper 11 which is closed by a vane 17 and connected through a conduit 12 to a funnel 26 feeding a first aerating blower 9 in turn connected to a second driving blower 10. A conduit 13 leading from this second blower 10 is formed with a Venturi restriction 15 just downstream from the end of a narrow pipe 14 into which compressed air is fed. Thence the aerosol particles P are expelled through a nozzle 8 onto the slab 3 all around the latter. Thus another nozzle 18 can be connected also to the blower 10 and the pipe 14 to cause the fine particles P to impinge against the underside of the slab 3 in a region 27 free of rollers 2.

After the treated slab 3 exits through an outlet opening 4b of the chamber 4 it passes along a region 5 where it cools and the coating becomes very hard. FIG. 6 shows the slab 3 with its hardened coatings C.

Further downstream the slab 3 passes through a straightening station 6 where three rollers 28a c bend the slab 3 sufficiently to break free the coating C. Due to the regularity of this coating, it is easily removed. This coating is, however, very tight on the metal body 3, since the surface of the body 3 reacts to some extent with the wetted powders P to form the coating C.

Finally a coating station 7 having a plurality of nozzles 7a sprays a more flexible protective coating M, e.g., paints, upon the surface of the cooled slab 3. This coating M is shown in FIG. 7.

Because of the thinness of the coating C, any flaws, as shown at F in FIG. 6, will not be covered; the coating C will break in the region of these flaws F. Thus, an observer in the region 5 can clearly see them and mark the slab 3 in this region so that it can be later discarded.

In this manner, the flaws are easily recognized and there is no need to do a major descaling of the sheet 3, since any slight scale is removed by the gas in the chamber 22 or the oxides sprayed against it in the chamber 4 and, for the rest of the cooling time, the sheet 3 is covered by a very tight, nearly continuous glassy coating. Removal of this coating C has been found to be very simple once the sheet 3 is fully cooled and further scaling is no longer a problem.

FIGS. 3 and 4 show an alternative embodiment of the present invention. Here, molten metal is poured from a ladle 16 into a funnel la on top of a mole 1' of a continuous casting installation. A metal body in the form of a thick wire 3' leaves the base of this mold l and is bent through by driven rollers 3 of hyperbolic profile and through a chamber 22' similar to the chamber 22 of FIGS. 1 and 2.

A boxlike chamber 4' is equipped with two nozzles 18 and 8' connected through a powder-aerating apparatus to a hopper 11' just as in FIGS. 1 and 2, common reference numerals referring to common structure. This wire 3 is here coated according to the method and principles set out in connection with FIGS. 1 and 2.

As the wire 3' leaves the box 4', it is gripped between rollers 5'. 1

In this embodiment, the enamel coating is not stripped off the wire 3', since it serves to protect the wire during shipping and handling, and relatively easily removed when desired. This coating also serves to accentuate and make more visible flaws in the surface of the wire 3', as described above for FIGS. l and 2.

FIG. 5 shows a further embodiment of the invention having in this case a treatment chamber 4". Here a fluidized bed is formed around a continuous workpiece 3" reiding on rollers 2". The workpiece 3" is very hot and relatively scale free. A blower 21 having an output connected through a conduit 20b to the bottom of the chamber 4" and an input conduit 20a connected to the top of this chamber 4" serves to fluidize minute metallic and metallic oxide particles P fed into the chamber through a conduit connected to a hopper 11" above the chamber 4". In this way the workpiece 3 is very efficiently covered by the powder, so that it can move at high speeds through the chamber 4" and still be adequately coated.

SPECIFIC EXAMPLE EXAMPLE A A steel body is hot-formed and enters the treatment chamber at a temperature somewhat below its melting point. It is sprayed with a mixture of powders such that substantially equal parts of SiO AI..O Fe o CaO, MgO, Na, K, and B mixed with and carried by air strike the surface of the body. This mixture reduces the slight scale on the surface and fuses to form a glassy enamellike coating over the entire exterior of the body, the fused mixture flowing to cover all of its surface to a thickness on the order of say 5 to microns. As the body cools, the enamel coating breaks in the region of any flaws on it.

EXAMPLE B A steel wire is formed by rolling and enters a treatment chamber as above. In this chamber it is: sprayed with a powder whose prime constituent is zinc borate. The hard, enamellilce coating is formed as above. Then the body is fed through a straightening apparatus which removes the coating and is found to be zinc coated in the sense that zinc is alloyed with surface zones of the metal body.

Iclaim:

l. A method of accenting and removing surface flaws in a hot metal body emerging in a substantially scale-free state from a forming stage, comprising the steps of:

a. applying a glassy coating of a thickness of about 5 to 10 microns to the surface of said body by continuously depositing on said surface of said body as it emerges from said forming stage a glass-forming substance fusable at the temperature of said body and prior to substantial scale formation thereon;

b. selectively cracking said coating in the region of surface flaws of said body by cooling said coating on said body; and

c. removing said flaws from said body at regions thereon visually accented by cracks in said coating.

2. The method defined in claim 1 wherein said forming stage is a rolling stage from which said body emerges continuously and said substance is a powder containing a reducing agent and applied to said body by blowing said powder thereagainst.

Claims (1)

1. 2. The method defined in claim 1 wherein said forming stage is a rolling stage from which said body emerges continuously and said substance is a powder containing a reducing agent and applied to said body by blowing said powder thereagainst.

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