GB2165784A - Nozzle header for producing a flat laminar flow - Google Patents

Abstract

A nozzle header for producing a flat laminar flow includes a water tank 21, a flat water channel 23 provided adjacent one of the sides 22 of the water tank and a water supply pipe 24 with outlets 25 arranged inside the water tank. The nozzle header additionally includes a baffle plate 31 vertically arranged in front of the flat water channel to determine a position at which the laminar water wall is impinged on a high-temperature steel product to be cooled. <IMAGE>

Description

SPECIFICATION Nozzle header for producing a flat laminar flow The present invention relates to the cooling of steel products from high temperatures with cooling water and more particularly to a nozzle header for producing a flat laminar flow (laminar water wall) which is effective in uniformly and efficiently cooling such high-temperature steel products.

Generally, a flat laminar flow having a large cooling capacity and providing uniform cooling in the width direction of flat steel products is suited for the forced cooling or heattreament of on-line high-temperature flat steel products on a hot rolling line or reheated high-temperature flat steel products and the cooling of steel products with the flat laminarflow is used widely in steel mills and the like.

Devices heretofore known for producing a flat laminar flow include two types of nozzle headers, i.e., the open and closed types. The open-type nozzle header is so designed that a flat laminar flow is produced by causing the cooling water supplied through the plurality of outlets formed on the lower side of a water pipe to flow out from a slit nozzle and this laminarflow is impinged on a high-temperature flat-rolled steel product thereby cooling the steel product. On the other hand, the closed-type nozzle header is designed so that the cooling water supplied from a water pipe is contained in a tank and then flowed out through a slit thereby obtaining a flat laminarflow.

The slit nozzles of these constructions have disadvantages which will be enumerated below.

(a) Since there is the minimum flow rate required for maintaining a laminarflow in dependence on the size of the nozzle gap, if the flow rate is decreased beyond the minimum flow rate, air is entrained from the outlet of the slit nozzle so that the water stream discharged and falling from the slit nozzle results in a flow of water of discontinuous droppings having nonuniform particle sizes and thus it is impossible to maintain the desired laminar flow condition. If the flow rate is increased continuously, the flow velocity of the water from the nozzle is increased and the water flow discharged and falling from the slit nozzle takes the form of a turbulent flow thus failing to obtain the desired flat laminar flow.As a result, the range of flow rates that can be controlled by the single conventional slit nozzle is at the most about 5 times in terms of a maximum/ minimum flow rate ratio.

Since the conventional flat laminar flow nozzle headers have relatively small ranges of controllable flow rates as mentioned above, there are instances where they are inadequate for cooling high-temperature flat-rolled steel products of different thicknesses to the desired temperatures or they are impossible to make the required adjustments of the cooling rate. Thus, in an attempt to overcome these deficiencies, there has been proposed a slit nozzle of a variable gap type in which water flow forcing means is provided at the nozzle forward end to adjust the slit-like opening and this method has the disadvantage of requiring a complicate construction and increasing the equipment cost.

It is to be noted that here the term laminarflow is not the one which is specified by the definition of the ideal laminar flow, e.g., the Reynolds number Re ~ 2,000 but it is specified as a flow whose lower limit is the minimum flow velocity at which water fills the slit nozzle and continuously flows in the form of a flat flow and whose upper limit is a higher flow velocity at which upon impinging on a product to be cooled almost all the water wall discharged from the nozzle is scattered and it does not flow as a parallel flow over the surface of the product.

(b) Next, in the cooling of a high-temperature steel product with a flat laminarflow, to ensure a uniform flow distribution in the product width direction, that is, to make uniform the gap of the slit nozzle along the whole extent in the product width direction is essential for the uniform cooling of the product in its width direction.

If the width of a high-temperature steel product to be cooled increases so that the long side of a slit nozzle is increased, from the standpoint of processing accuracy it is difficult to manufacture the slit nozzle in a way that its gap is made uniform along the whole extent of the nozzle width. As a result, the gap of the slit nozzle becomes nonuniform in the lengthwise direction so that the flow distribution in the width direction of the product becomes nonuniform and the variation amounts to 15% thus making it difficult to uniformly cool the high-temperature steel product in its width direction.

(c) With the closed-type nozzle header constructure, if air enters into the header from the outside, the air bubbles are entrained on the water wall so that not only the water wall is disturbed deteriorating the cooling capacity but also the maintenance of a stable laminar flow condition is made impossible. Thus, with the closed-type nozzle header construction, it is necessary to give considerations so as to reinforce the external sealing of the nozzle header and prevent the entry of airfrom the supplied water.

It is a primary object of the invention to provide a flat laminar flow nozzle header so designed that a flat laminar flow suitable for use in the cooling of high-temperature flat-rolled steel products, etc., is produced uniformly in the product width direction with a wide flow control range.

It is another object of the invention to provide such flat laminar flow nozzle header so designed that the flat laminar flow always impinges at the same position on every high-temperature flat-rolled steel product to be cooled.

It is still another object of the invention to provide such flat laminar flow nozzle header so designed that the width of the flat laminarflow is adjustable in correspondence with the width of every steel product to be cooled.

It is still another object of the invention to provide such flat laminar flow nozzle header so designed that if a high-temperature steel product to be cooled has a temperature distribution in its width direction, the flow rate of the flat laminar flow is varied in the product width direction in accordance with the temperature distribution.

In accordance with one phase of the invention, the flat laminarflow nozzle header of the invention includes a water tank, a flat water channel provided at the upside of one side wall of the water tank and a water pipe arranged inside the water tank whereby the cooling water in the water tank overflows the side wall, passes through the water channel and falls in the form of a flat laminar flow from the forward end of the channel.

In accordance with another phase of the invention, the flat laminarflow nozzle header is constructed so that a baffle plate having a slightly greater width than the plate channel is vertically arranged in front of the flat-plate channel such that its furnace lies perpendicular to the plane of the water channel and the water wall from the water channel impinges on the baffle plate thus causing it to take the form of a downward laminar water wall.

In accordance with still another phase of the invention, the flat laminarflow nozzle header is constructed so that a pair of side walls are provided at the forward end of the flat water channel so as to be movable in the flow width direction and the width of the flat laminar flow is adjusted in correspondence to the width of a high-temperature steel product to be cooled.

In accordance with still another phase of the invention, the flat laminar flow nozzle header is constructed so that a pair of adjusting liners are formed symmetrically with respect to the flow width direction and arranged to be slidable from the side walls of the flat water channel toward the center thereby making the bottom portion of the water channel deep at the center and shallow at the sides.

In accordance with the basic idea of the invention, by virtue of the above-mentioned construction of the header of the invention, not only the water wall falling from the forward end of the flat water channel takes the form of a laminar flow but also, in particular importance, the water surface of the cooling water is not disturbed. Generally, in the case of the conventional header, the cooling water within the header is caused not a little to take the form of a turbulent flow under the influence of the dynamic pressure of the supplied water and the water surface of the cooling water is also disturbed. The occurrence of such disturbance makes nonuniform the flow distribution of the nozzle in the product width direction.While it is conceivable, as a means of preventing such disturbance, to increase the volume of the header to such an extent that the dynamic pressure of the supplied water is decayed and the water surface is not influenced, this makes the header construction large in scale and hence its installation on the line or the like is difficult. However, these deficiencies are easily overcome by the method of this invention in which the cooling water overflowing the header is caused to fall from the flat water channel having a horizontal flow path adapted to flow the cooling water substantially horizontally.Even if the water surface of the cooling water is disturbed within the header, the overflown cooling water is rectified by flowing horizontally through the flat water channel and thus the water curtain of the laminar water wall falling from the forward end of the flat water channel is provided with a uniform thickness in the product width direction.

Since this flat water channel is of the open-type having its top opened to the atmosphere, contrary to the conventional slit nozzle, the minimum flow rate is not determined by the gap of the nozzle and the flow rate can be freely adjusted within a range of 0 to 5 m31min.m by the single header thereby considerably increasing the control range of cooling capacities.

By virtue of the above-mentioned construction, the flat laminar flow nozzle header of the invention has great effects as summarized hereunder.

(a) The thickness of a flat laminarflow impinging on a high-temperature flat-rolled steel product to be cooled is uniform on the product width direction.

(b) The flow rate of the flat laminar flow can be controlled over a wide range of values.

(c) The flat laminar flow can be used to fall and impinge at a given position on every product to be cooled.

(d) The width of the flat laminar flow can be adjusted in correspondence to the width of a product to be cooled.

(e) The flow rate can be controlled in correspondence to the width-direction temperature variation of a product to be cooled.

In the drawings:- Figure 1 is a longitudinal sectional side view of a conventional flat laminar nozzle header.

Figure ib is a perspective view of the nozzle header of Figure 1.

Figure 2 is a graph showing the relation between the slit gap and flow rate and the laminar flow area in the conventional nozzle header.

Figure3a is a longitudinal sectional side view of a flat laminar flow nozzle header according to the invention.

Figure 3b is a sectional view taken along line lli - ill of Figure 3a.

Figure 4 is a graph for obtaining the length L of the horizontal flow path.

Figure 5 is a longitudinal sectional side view of another embodiment of the invention.

Figure 6 is a longitudinal sectional side view of another flat laminar flow nozzle header having a baffle plate.

Figure 7 is a diagram for explaining the path of a water wall.

Figure 8 is a diagram for explaining the position of the baffle plate.

Figure 9a is a diagram for explaining the position of the baffle plate.

Figure 9b is a diagram for explaining the position of the baffle plate.

Figure 10a is a front view of another flat laminar flow nozzle header having movable side plates.

Figure 10b is a plan view of Figure 10a.

Figure 1 la is a front view of another flat laminarflow nozzle header having adjusting liners.

Figure 1 is a longitudinal sectional side view of Figure 11a.

Figure 12a is a side view of the adjusting liner in stil another embodiment of the invention.

Figure 12b is a side view of an adjusting liner according to a modification.

Figure 13 is a partial sectional view showing still another embodiment of the invention having a plurality of adjusting liners on each side.

Figure 1a shows a conventional open-type flat laminar flow nozzle header 1 and Figure 1b shows a conventional closed-type laminar flow nozzle header 10. In the former, cooling water 5 is supplied into a water tank 2 through a water pipe 3 having a large number of feed openings 4 and the cooling water 5 is discharged from a nozzle 6 to fall as a water wall 7. In the case of the latter, cooling water 5 is supplied into a water tank 12 through a water pipe 11 and the cooling water 5 is discharged from a nozzle 13 to fall as a water wall 14. In each of the two nozzle headers, the gap t of the nozzle 6 or 13 determines the minimum and maximum flow rates for maintaining a laminarflow. Figure 2 is a graph showing the circumstances, in which the abscissa represents the gap t(mm) and the ordinate represents the delivery flow rate F(m3/min.m).As will be seen from the graph, the range is relatively as small as about 5 times in terms of the maximum/minimum ratio. Also, since it is difficult to form the gap t of the nozzle uniformly all over the width direction, the flow rate Ovaries in the width direction and this has a detrimental effect on the uniform cooling of a steel product to be cooled.

Figures 3a and 3b are respectively side and front views of an embodiment of the present invention. As shown in the Figures, a flat water channel 23 having substantially a horizontal flow path is arranged at the upside of a side wall 22 of a water tank 21 of a header 20 and cooling water 26 is supplied through a water pipe 24 formed with a large number of outlets 25 in its lower surface. Thus, when the cooling water 26 overflows the side wall 22 so that it is passed through the flat water channel 23 and discharged from its forward end, a laminar water wall 27 is obtained.

Then, as regards the required length L of the horizontal flow path, the results of various experiments have shown that in order to keep the variation of the product width-direction flow distribution given by the following equation (1)5% or less, maximum distribution variation = maximum flow-minimum flow flowdlstnbutlonvarlatlon= average flow x 100 (I) the minimum required length L is given by the following equation L = 25 x Q-7 (2) where L = the length of the flat water channel, mm Q = the flow rate, m3/min.m These maximum flow rate, minimum flow rate 0, etc., were measured such that in the case ofthe nozzle width direction length of 2,500 to 5,000 mm, for example, the length was divided into unit widths of 100 to 200 mm in the nozzle width direction and the falling water quantity per unit width from the nozzle was received by a suitable bucket thereby making the measurement.

Figure 4 is a graphical representation of the equation (2). If the length L of the horizontal flow path is in the region above the curve Z, it is possible to obtain a flat laminar flow which keeps the variation of the flow distribution in the product width direction 5% or less and this flat laminar flow is much superior to that of the conventional header. Thus, the length L should preferably in the range that satisifies the previously mentioned relation.

Figure 5 shows another embodiment of the invention which differs from, the first embodiment in that the position of the flat water channel 23 provided at the upside of the header side wall 22 is selected on the inner side of the header 20 as shown in the Figure. Also, the same effect can be obtained by selecting the mounting angle of the horizontal flow path to the horizontal direction to be within a range of t 15 degrees.

Figure 6 shows still another embodiment of the invention which differs from the flat laminar flow nozzle header of the first embodiment in that a baffle plate 31 is positioned in front of the flat water channel 23 of the header 20 and the water wall 27 falling from the forward end of the flat water channel 23 is impinged on the baffle plate 31 thus causing it to fall as a downward laminar water wall 32.

Generally, if the header 20 shown in Figure 6 is not provided with the baffle plate 31, the water wall 27 from the header 20 falls describing, as shown in Figure 7, a parabolic path which varies in dependence on the flow rate or the amount of water supplied from the flat water channel 23 and a position Pat which the water wall 27 impinges on a high-temperature steel product varies in dependence on the amount of water. Thus, in this embodiment the baffle plate 31 is provided to correct the falling direction of the water wall 27.

In other words, in Figure 7 the distance X between the nozzle forward end and the position P at which the falling laminarwall 27 impinges on the surface of a steel product 33 to be cooled is given by the following equation if the height from the steel product surface to the nozzle header is H(m), the nozzle flow velocity is VO(misec) and the acceleration of gravity is 9.8m/sec2, provided that the value of H is selected 2.5 m or less X(m) = 2 Vo2.H (1) 9,8 With H=1.5m, if the cooling water quantity Q is varied within the range of 0.3 to 2.5 m3/min.m, then the position of the point P orthe distance X varies by an amount within 350 mm.

Generally, where a high-temperature flat-rolled steel product is to be cooled, the upper and lower surfaces of the steel product are cooled simultaneously for reasons of preventing the occurrence of cooling strain, ensuring the uniformity in quality of products, etc. In the case of the hot rolling run-out table cooling, if the cooling water impinges on the upper and lower surfaces of a steel product at different points for the reasons mentioned, there is a problem of deteriorating the passing performance of the steel product and therefore it is not desirable for the impinging points of the laminar water wall on the steel product to shift in dependence on the flow rate.Also, where the outer surface of a steel pipe is cooled by the laminar water wall, any variation in the distance X makes it impossible forthe laminar water wall to impinge at the apex of the steel pipe and this is inconvenient from the standpoint of cooling effect on the steel pipe. While it is conceivable to overcome this deficiency by providing a device which shifts the position of the nozzle header back and forth in dependence on the flow rate of water, this is still disadvantageous from the standpoint of equipment cost and maintenance.

The present embodiment provides a nozzle header which overcomes the foregoing deficiencies and which has no danger of changing the falling point of the laminarwater wall with a change in the flow rate of water.

Then, in order that the water wall 27 discharged from the forward end of the water channel 23 may be impinged on the baffle plate 31 to obtain the desired laminar water wall 32, it is essential that the values of A, B and C in Figure 8 satisfy the condition of the following equation (2) A(m) ' Dmax (m) (2) Dmax = D(m) at maximum flow rate 9.8x 9.8 x A2 Qmin ~ Q rnin (3) 2 min Qmin = minimum flow rate, m3/sec.m Dmin = D(m) at minimum flow rate By satisfying the equations (2) and (3), it is possible to always cause the laminar water wall 32 to impinge at the same point on the surface of every steel product.However, if the value of D is greater than the value of A, the thickness of the falling water wall becomes equal to the value of A so that not only the falling water wall is accelerated thus failing to remain laminar any longer but also it is impossible to obtain the desired cooling rate. As a result, it is necessary to select the value of A to be at least equal to or greater than the value of Dmax corresponding to the designed maximum flow rate of water.

Also, where the water flow rate 0 is high, the value of D is increased and the initial velocity V0 of the water wall from the forward end of the water channel 23 is naturally increased. As a result, the forward end of the parabola described by the water wall impinges on the baffle plate 31 and it falls as a laminarwaterwall in the vertical downward direction as shown in Figure 9a.Contrary, where the water flow rate W is low thus decreasing the value of D and the initial velocity V0 of the water wall from the forward end of the water channel 23, if the length of the baffle plate or B is small, as shown in Figure 9b, the parabola described by the water wall does not impinge on the baffle plate 31 thus failing to obtain the desired laminar water wail whose impinging position on the steel product has the desired distance A to the forward end of the water channel 23. Thus, the height B from the lower end of the baffle plate 31 to the upper surface of the water channel 23 must satisfy the equation (3).

Figures 10a and 10b show still another embodiment of the flat laminarflow nozzle header according to the invention which is adapted to vary the width of a water wall. Figure 1 0a shows its front view and Figure lOb shows its plan view. More specifically, in the Figures mounted on the bottom plate of the forward end of a flat water channel 23 are a pair of side walls 41 each formed into an L shape by a lower flange 42 and a water sealing gasket 43 adhered to the bottom of the flange 42. A rod 45 of a cylinder 44 is connected to the back of each side wall 41 and the cylinders 44 are actuated so that the rods 45 are moved forward or backward and the distance 1 between the side walls 41 is expanded or contracted uniformly on each side over the bottom plate of the flat water channel 23.With the nozzle header of this embodiment constructed as described, by virtue of the fact that the width of a water wall 27 can be varied by moving the pair of said walls 41 arranged on the flat water channel 23 through the operation of the cylinder 44, it is possible to discharge the optimum laminar water wall for cooling purposes even in the case of high-temperature steel products of different widths to be cooled and this is very effective in improving the cooling effect of this header. While, in this embodiment, the cylinders 44 are used as driving mechanisms for the pair of side walls, the invention is not limited to the cylinders 44 and any other ordinary mechanisms such as screw mechanisms may be used.

Also, to make the water sealing of the side walls 41 more complete, each of the side walls 41 should preferably be provided with a slide guide.

Figures 11 a and 11 b are respectively a front view and longitudinal sectional view of still another embodiment of the invention comprising a flat laminar flow nozzle header having adjusting liners. Generally, when a heated flat-rolled steel product just emerging from a rolling mill or a heat treating furnace is subjected to a cooling heat treatment such as an accelerated cooling quenching, the control of the desired cooling stopping temperature in response to a change in the temperature of steel products introduced into a cooling equipment or the control of the cooling rate during the cooling operation is effected for every product size.A flat laminar flow (laminar water wall) having a large cooling capacity and providing uniform cooling in the product width direction is suited for such cooling and it is used in the hot rolling run-out table cooling, the thick plate controlled cooling equipment, etc.

However, no matter how a slab has been heated uniformly, the slab is formed into a plate by subjecting it to the rolling pass several times and therefore the width-direction temperature distribution of the plate is such that the plate ends are lower in temperature than the plate central portion by several tens degrees. This is caused by the fact that the cooling due to a fin effect and the heat dissipation from the sides take late at the plate ends and the temperature drop in these portions is accelerated. In the case, for example, of a flat steel product of 3.2mm thick at the point of just emerging the final finishing stand of a hot rolling line, the thus obtained temperature distribution on the product width direction shows a temperature difference of about 70"C between the end portions and the central portion.Also, in the case of cooling a steel product which has been heated in the form of flat steel in a heating furnace, more or less time is required during the transport from the heating furnace to the cooling unit so that a temperature difference is similarly caused between the end portions and the central portion, although the amount is small as compared with a case where the product is cooled following the completion of its rolling.

If the laminarflow cooling is performed under these circumstances, the cooling of the end portions proceeds in advance of the central portion. As a result, even if the flat laminar flow having a uniform flow distribution in the product width direction is used, the end portions will unavoidably be cooled excessively so that it is difficult to cool the product uniformly in the product width direction and this causes the occurrence of cooling strain and nonuniformity in quality. The present embodiment, shown in Figures 1 1a and 11 b, has been made with a view to overcoming this deficiency.

In this embodiment, a flat water channel 23 is arranged at the upside of the whole side wall 22 of a header 20 to form a horizontal flow path 51 and a window 54 for receiving an adjusting liner 54 is formed at the lower part of each walls 52 of the flat plate channel 23. The adjusting liners 54 are inserted through the windows 53 along the bottom surface of the flat water channel 23 so as to be arranged symmetrically such that the horizontal flow path 51 is deep at the center and shallow at the left and right sides. In the figure, the numeral 55 designates a gasket adhered to the lower surface of each adjusting liner 54, and 56 a sealing member fitted in each receiving window 53 to slidably contact with the upper surface of the adjusting liner 54. The side of each of adjusting liner 54 is formed so as to closely contact with the inner side of the receiving window 53.In this way, the receiving window 53 and the adjusting liner 54 provide a watertight structure.

The operation of this embodiment will now be described. The flow crown in the product width direction of the header 20 is provided in the following way. In other words, when the adjusting lines 54 are inserted symmetrically through the receiving windows 53 of the side walls 52 of the flat water channel 23, the horizontal flow path 51 formed by the flat water channel 23 becomes deep at the center and shallow at the left and right sides. Thus, the flow rate is high in the central portion and the flow rate is low in the end portions.As a result, by causing the cooling water to fall from the forward end of the flat water channel 23 having the preliminarily adjusted flow rate, the resulting falling water wall 57 takes the form of a flat laminar flow having a flow crown in the product width direction and it falls onto a hot flat steel passing below the flat laminar flow 57 perpendicularly thereto thereby cooling the flat steel. However, since the temperature distribution of the hot flat steel shows that the central portion is high in temperature than the end portions, the flow crown of the flat laminarflow 57 can be adjusted in correspondence to the temperature distribution so that the end portions of the flat steel are prevented from being cooled excessively and the flat steel is cooled uniformly.

Also, the adjusting liners 54 of the same thickness all over its whole length may be replaced with wedge adjusting liners 56 as shown in Figure 12a or crown adjusting liners 58 as shown in Figure 12b and alternatively adjusting liners 60 may be arranged in steps as shown in Figure 13 thereby obtaining any desired flow distribution in the product width direction.

Claims (6)

1. A nozzle header for producing a flat laminarflow comprising: a water tank; a flat water channel arranged at an upside of one of side walls of said water tank; and a water supply pipe arranged within said water tank.

2. A nozzle header according to claim 1, wherein a baffle plate having a width slightly greater than that of said flat water channel is vertically arranged in front of said water channel such that a surface of said baffle plate crosses a plane of said water channel at right angles.

3. A nozzle header according to claim 1, wherein said flat water channel includes a pair of side walls movable in a flow width direction on a bottom plate of said flat water channel.

4. A nozzle header according to claim 1, wherein a pair of or a plurality of pairs of adjusting liners are symmetrcially arranged in a flow width direction so as to be respectively slidable from a pair of side walls of said flat water channel toward the center thereof whereby a bottom portion of said channel is deep at the center and shallow at the sides thereof.

5. A nozzle header according to claim 1, wherein said flat water channel has a minimum required length L expressed by the following equation L = 25 x 01.7 where L = the minimum required length of the flat water channel 0 = flow rate (m3/min.m).

6. A nozzle header substantially as hereinbefore described with reference to, and as illustrated in, Figure 3, or any one of Figures 5,6 and 10- 13 of the accompanying drawings.