GB2103251A

GB2103251A - Apparatus for cooling moving solid bodies

Info

Publication number: GB2103251A
Application number: GB08221373A
Authority: GB
Inventors: Carl Kramer; Gunther Woelk
Original assignee: WOELK GUENTHER
Current assignee: WOELK GUENTHER
Priority date: 1981-07-24
Filing date: 1982-07-23
Publication date: 1983-02-16
Also published as: IT8267939A0; CH648865A5; IT1155572B; GB2103251B; DE3129254C1

Abstract

The invention provides an apparatus for cooling the moving surface of a solid body, for example semifinished metal products or the surface of rollers or a roller stand. In the apparatus a free stream (3) of a gas/liquid mixture is directed onto the surface (5) of the solid body by a nozzle (1) which is in an inclined position to the surface (5). <IMAGE>

Description

SPECIFICATION Apparatus for cooling moving solid bodies This invention relates to an apparatus for cooling the surfaces of solid bodies.

High cooling rates are often required for the refining of semifinished metal products, in particular sheets and plates. Thus, for exampie, for the age-hardening of high-strength light metal sheets and plates, cooling rates of much higher than 1000 per second have to be attained. The achievement of such high cooling rates necessitates very high heat transition coefficients, i.e. coefficients in the range of a few 1,000 W (m2 KO).

Thus, in cooling apparatus of this type, blowing with a stream of cold gas, for example air at ambient temperature, is usually insufficient and instead a cooling liquid, for example water, has to be used. The cooling liquid is sprayed onto the surface of the solid body to be cooled, for example by spray nozzles.

A disadvantage of such apparatus is that the start of cooling cannot be exactly delimited, so that in the case of sensitive products an inadmissible pre-cooling results at a lower cooling rate, because the cooling point cannot be precisely defined.

Thus, an object of the present invention is to provide an apparatus for cooling the surface of a solid body of the type specified, in which the above-mentioned disadvantage does not occur.

In particular, a cooling apparatus is to be proposed which ensures the precisely defined, virtually "abrupt" start of the cooling effect, at a high cooling rate.

According to the invention there is provided an apparatus for cooling the moving surface of a solid body, comprising a slit nozzle which is positioned at an incline to the surface and directs a stream of a gas/liquid mixture onto the surface, and a concavely curved Coanda guide surface which is provided on the side of the stream remote from the surface of the solid body.

Preferably, the slit nozzle is positioned at an angle of from 300 to 600 to the surface.

The advantages which are achieved by the present invention are based in particular on the fact that a gas/liquid mixture impinges on the surface to be cooled as a sharply delimited flat stream at a certain angle of incline, for example from a slit nozzle. Thus, the complete liquid flow is guided in the advance direction of the solid body to be cooled under the effect of the gas flow and, upon the impact of the liquid component of the stream, liquid does not flow away from the impact line against the advance direction. This means that the above-mentioned pre-cooling, which happens when the liquid is able to flow away in an uncontrolled manner on both sides of the impact iine, cannot occur.

In order to achieve an intensive contact between the liquid and the surface to be cooled, the slit nozzle must not be inclined too much towards the normal to the surface, so that an adequate impetus flow component still remains perpendicularly to the surface of the material.

When an impetus flow component of this type is present, a free stream is always divided, for equilibrium reasons, into a greater part which flows in the direction of the incline, and into a substantially smaller part which flows against the incline. The away-flow against the incline is substantially reduced by the combination of gas flow and liquid flow, because the gas flow exerts a type of "drag effect" on the liquid flow. This drag effect may be varied by the selection of a suitable ratio of gas rate to liquid rate in the free stream, depending on requirements. Moreover, by selecting a substantially faster rate for the gas flow compared to the liquid flow, an increased convention of the liquid over the surface of the material to be cooled may be achieved. This results in short residence times of the cooling agent and in only slight cooling agent evaporation.This is essential, in particular when using relatively expensive, deionised water as the cooling liquid, since in this manner, the consumption of cooling water may be maintained at a low level. Moreover, the rapid gas flow promotes the removal of liquid vapour which forms on the hot surface of the material to be cooled and which, in the case of a layer of vapour forming between the liquid and the surface of the material, leads to a substantial reduction in the cooling effect.

In order to prevent the above-mentioned smali part of the cooling liquid from flowing away against the incline of the slit nozzle and from thereby resulting in an indefinite impact line and thus cooling line, a curved guide surface is positioned on the side of the free stream of the gas/liquid mixture remote from the surface to be cooled, which surface uses the Coanda effect and guides the gas flow on a tangential or approximately tangential path to a precisely defined region of the surface to be cooled. After impacting the surface, the drops of liquid are guided virtually exclusively in the direction of flow over the surface of the material to be cooled, being substantially guided by the slightly deflected gas flow.This means that virtually no cooling liquid flows against the incline of the slit nozzle, so that the cooling effect starts in a precisely defined, virtually abrupt manner along a precisely defined line.

In this case, it is also essential for an awayflow impetus, for example towards the edges of the surface of the material, to be imparted to the liquid by the rapid gas flow. This facilitates the drying of the material surface which is subsequently required.

Moreover, a definite position of the cooling line with respect to the orientation of the material surface to be cooled and the direction of movement thereof may also be produced by the cooling effect which is delimited in a precisely linear manner. As a result of this, the bulging and warping effect which almost always occurs during the coventional quenching operation of thin metal strips and sheets may be avoided or reduced. This bulging and warping is attributed to the fact that, because a precisely delimited cooling line is not present, different areas of the strips and sheets are cooled to a different extent and thus they each have a different cooling contraction, these differences being determined by chance.

Due to an incline of the start of the cooling line with respect to the direction of movement of the material to be cooled, for example in the case of strip installations the forwards direction of the strip, a defined cooling contraction of the strip may be achieved.

An embodiment of the present invention will now be described in more detail in the following, by example only, and with reference to the accompanying drawings, wherein: Fig. 1 is a perspective view of one embodiment of a cooling apparatus according to the present invention; Fig. 2 is a cross section through the cooling apparatus of Fig. 1; Fig. 3 is a top view on a cooling apparatus having an arrow-shaped slit nozzle; and Fig. 4 is a curve showing the temperature along a solid body cooled in the apparatus of Fig.

3.

The apparatus which is illustrated in Figures 1 and 2 for cooling the top, flat surface of a solid body, for example a metal strip or sheet which is moved in the direction of arrow 12, has an outer pipe 9 for the supply of a gas flow. An inner pipe 10 for the supply of a liquid flow is positioned in the centre of the outer pipe 9. The inner pipe 10 has holes 11, through which the liquid issues in the direction of a slit nozzle provided on the outer pipe 9, and mixes with the stream of gas coming from the pipe 9.

A guide grid 2 is installed in the in-flow region of the slit nozzle 1, the division of the grid corresponding to the division of the holes 11, so that one liquid stream passes in each case through one guide grid channel, without being disturbed by other constructional elements.

A slit tube 13, made for example of plastics, is positioned inside the pipe 10 for the supply of the cooling liquid. By turning the pipe 10 in the direction of arrow 14 around the inner, slit tube 13, different holes in the pipe 10 may be brought into the working position. Consequently, it is easily possible to vary the quantity of liquid delivered by changing the hole size in the pipe 10 for the supply of the liquid.

The gas flow supplied by the pipe 9 and the liquid flow issuing from the holes 11 of the pipe 10 mix and flow together through the channels of the guide grid 2 to the outlet opening of the slit nozzle 1 which they leave as a free gas/liquid stream 3. A curved guide surface 6 is positioned on the side of the free stream 3 which is remote from the surface of the solid body 5 to be cooled, one end of this surface 6 being attached to the slit nozzle 1, first of all bending towards the stream 3 and then moving away again from the centre line of the stream 3.

The slit nozzle 1 is positioned at an angle of about 450 to the flat surface of the solid body 5 or to the perpendicular to the surface.

In the embodiment according to Figures 1 and 2, the slit nozzle 1 is positioned above the surface, so that the guide surface 6 is also positioned above the free stream 3 and first of all extends downwards in the direction of the free stream 3 and then changes to a direction which generally extends tangentially to the surface.

If the slit nozzle is positioned below the surface to be cooled, which is also easily possible, the arrangement simply has to be reversed accordingly.

Due to the Coanda effect, the gas flows along the guide surface, i.e. it travels in the direction indicated by the arrows in Figure 2, so that it does not impinge on the surface to be cooled at the angle of incline of the slit nozzle 1, but runs generally tangentially to the surface. During this procedure, the individual droplets of liquid are entrained by this tangential gas flow so that virtually all the liquid continues moving in the flow direction. Thus a precisely defined, sharp, linear delimitation 4 is produced for the start of cooling.

In this case, it is essential that according to the illustration in Fig. 2, the cooling effect only starts on the right-hand side of the line 4, i.e. the part of the surface which is on the left-hand side of the line 4 is virtually uncooled and is thus not subjected to the above-mentioned, disadvantageous uncontrolled pre-cooling.

A gap is formed between the top covering of the slit nozzle 1 and the guide surface 6 (see Fig.

2), through which gap secondary air may be drawn in by suction by the free stream 3, as is indicated in Fig. 1 by reference numeral 8 and by the relevant arrows.

Fig. 3 illustrates one design of this cooling apparatus which may be used when the warps and bulges of the material to be cooled, which often occur during rapid cooling, are to be avoided or at least reduced. For this purpose, the slit nozzle 1 in a top view is in the shape of an arrow which points in the direction of movement 12 of the material 5. Consequently, the delimitation lines 4 of the cooling region are also in the shape of an arrow pointing in the direction of movement.

Of course, a different shape, for example an opposite arrow-shaped or a curved adjustment of the cooling delimitation 4 may also be produced by a corresponding design of the slit nozzle 1.

In Fig. 4 below the material surface illustrated in top view in Fig. 3, a temperature curve is plotted schematically along the line 1 5 parallel to the direction of movement of the material 5.

Since, as mentioned, a notable pre-cooling does not occur, the temperature only changes suddenly when the delimitation line 4 passes through the material to be cooled 5.

Claims

1. An apparatus for cooling the moving surface of a solid body, comprising a slit nozzle which is positioned at an incline to the surface and directs a stream of a gas/liquid mixture onto the surface, and a concavely curved Coanda guide surface which is provided on the side of the stream remote from the surface of the solid body.

2. An apparatus according to claim 1, wherein the slit nozzle is positioned at an angle of from 30 to 600 to the surface.

3. An apparatus according to claim 1 or 2, wherein the Coanda guide surface is attached to the slit nozzle.

4. An apparatus according to claim 3, wherein a gap for the passage of a secondary gas flow induced by the stream is formed between a lip of the nozzle of the slit nozzle and the Coanda guide surface.

5. An apparatus according to any of claims 1 to 4, wherein the slit nozzle is arrow-shaped.

6. An apparatus according to claim 5, wherein the slit nozzle converges in an arrow shape in the direction of movement of the surface.

7. An apparatus for cooling the moving surface of a solid body substantially as herein described with reference to Figs. 1 and 2 or Fig. 3.