RU1838012C - Method of cooling of moving plates - Google Patents

Description

The invention relates to metallurgy, in particular to rolling production with cooling of rolling steel.

The aim of the invention is to increase the level of mechanical properties of steel and to reduce the different grain sizes of rolled products by increasing the cooling rate.

In a method involving the creation of a cooling zone by supplying water jets to its upper surface with a water flow rate at the beginning of the cooling zone by 20%, exceeding the average flow rate and with its uniform decrease at the end of the zone to a value of 20% below the average flow rate, create a cooling zone simultaneously with the upper cooling the lower surface of the rental by applying air jets to it, while the flow of water to the lower.

the cooling zone is set at the beginning of the zone equal to (1.0 ... 1.2) the initial flow of water to the upper cooling zone with a uniform increase in the length of the cooling zone until the end of the zone reaches (2.0 ... 2.2) the final flow water to the upper cooling zone at the end of the zone, keeping the rate of flow of the jets to the lower zone constant over the entire length.

The technical essence of the implementation of the proposed method is as follows. The rolling stock moving along the rolling table is subjected to two-way cooling by water-air jets. On the upper surface, due to the change in water flow rate and flow rate of the jets along the entire length of the cooling zone, a high heat transfer rate is maintained. At the same time, conservation

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the constant ratio of the flow rate of water for cooling the upper and lower surfaces, in view of the decrease in the flow rate of water for cooling the upper surface along the length of the cooling zone, is irrational, since the heat transfer conditions on the lower surface differ from the heat transfer conditions on the upper surface. There is no accumulation of a layer of liquid on the lower surface, separated from the hot rolled surface by a steam film, which reduces the heat transfer rate, and therefore, it is not necessary to increase the jet energy to destroy this film. In this case, the interaction of water with the cooled surface is short-term, there is no possibility of involvement in heat transfer previously supplied to the cooling water.

It is also irrational to maintain a constant flow rate of water supplied to the lower surface along the length of the cooling zone. The heat transfer coefficient during water-air cooling in the temperature range at which heat transfer occurs after rolling (750 ... 000 ° C) remains almost constant (ct 2000 ... 2500 W / m2K) and depends only on the flow of components for cooling and their conditions supply, - At the same time, a decrease in the temperature of rolled metal during convective heat transfer causes a decrease in the heat flux from the surface to be cooled along the length of the cooling zone, thereby reducing the efficiency of water use in this section.

Thus, to compensate for the uneven cooling conditions of the upper and lower surfaces, it is necessary to increase the water supply to the lower surface along the length of the cooling zone. It has been analytically and experimentally established that with an optimal flow rate of water for water-air cooling, it is sufficient to supply 10% less at the beginning of the cooling zone, and 10% more than the average water flow rate at the end of the cooling zone of the lower surface. Therefore, with a decrease in water flow along the length of the cooling zone of the upper superfluid within the limits specified in the prototype, and the above increase in water flow along the length of the cooling zone of the lower surface, the ratio of the water flow to the upper and lower cooling zones at the beginning of the zone is (1 , 0. ,, 1,2) and increases uniformly to (2.0 ... 2.2) at the end of the cooling zone.

Reducing the ratio below 1.0 at the beginning of the cooling zone and 2.0 at the end of the zone for minimum thickness

rolled strips leads to insufficient cooling of the lower surface and a decrease in the level of mechanical properties of steel in this part of the rolled product.

Exceeding the ratio of more than 1.2 at the beginning of the cooling zone and 2.2 at the end of the zone leads to overcooling of the lower surface, annealing of the lower layers of the car and an unreasonable increase

water consumption.

In more detail, the technical essence of the proposed solution can be represented by the example of a specific implementation of the method under the conditions of production of rolled products on universal broadband mill 800 OKHMK. Let us consider the cooling of a strip made of 09G2 steel with a thickness of 16 mm (with a rolled assortment of strips from 6 to 25 mm thick) with an initial temperature of 950 ° C, moving along the rolling table at a speed of 2 m / s. In order to cool the upper surface, sections are used with nozzles located above collectors parallel to the direction of rolling movement of the collectors and creating a forced cooling zone due to the supply of water-air jets. At the same time, 60 m3 / m

h of water with a uniform decrease in flow rate along the zone length up to 40 m / m h. For cooling the bottom surface, an arrangement between the transport rollers of the section is used, which have an individual cooler supply, with the nozzles perpendicular to the rolling movement of the nozzles for supplying air jets. With an average specific water consumption for cooling the lower surface of 80 m3 / m2 h, at the beginning of the zone

cooling is supplied at 72 m3 / m2 h, with a uniform increase to 88 m3 / m2 h at the end of the zone. The increase in flow can be carried out both continuously and stepwise, which is easier to implement in practice.

Thus, the ratio of water flow for cooling the upper and lower surfaces of the strip at the beginning of the cooling zone is 1.2 and at the end of the cooling zone 2.2. Moreover, on the upper and lower surfaces of the strip, a uniform decrease in temperature is achieved by 10 ... 120 ° C, which leads to the preservation of uniformity in thickness and an increase in the level of mechanical properties by 10 ... 15%,

Claims (1)

The claims A method of cooling a rolling sheet metal, including creating a cooling zone by supplying water jets to its upper surface with a water flow rate of 20% at the beginning of the cooling zone 51838012 b exceeding the average flow rate, and with equal to the beginning of the zone 1.0 ... 1.2 of the initial flow rate by decreasing it along the length of the cooling zone of the cooling surface of the upper surface from laziness to a value at the end of the zone by 20%, a uniform increase in length to - less than the average water flow rate, from the number of degrees at the end of the zone of magnitude equal to u and so that additionally create 52.0-2.2 of the final flow rate of the cooling zone, the cooling zone of the lower surface of the upper surface, while by supplying water-air flow to it in the cooling zone It jets, the water flow rate in zone COOLING surface kept constant by the length of the lower surface of spinning ustanavlivayutvsey.