UA32113U - Method of descaling of hot-rolled steel strips - Google Patents

Abstract

A method of descaling of hot-rolled steel strips relates to the branch of technology, namely to the rolling production, and it can be used for removal of slag from hot-rolled steel strips.

Description

The useful model refers to the field of engineering, namely to rolling production and can be used for cleaning hot-rolled steel strips from scale.

A known method of hydro-mechanical scale removal from a hot-rolled strip, in which the scale is destroyed (knocked down) by the impact of water jets flowing out under a high pressure of 20...60 MPa | Mikheev V.A., Pavlov A.I.

Hydroblasted slag! in rental shops. - M.: Metallurgy, 1964. - 107 p.).

There is also a known method of removing scale from hot-rolled steel strips, chosen as a prototype, according to which scale is cooled by laminar jets of low-pressure water, less than 0.01 MPa. Upon sharp cooling, the scale becomes brittle, cracks and, under the influence of thermal stress, separates from the metal base (Yamaguta, Nakao, Masakazu, Takatsuka, Kamiro, etc., K.k. Kobo szykose. Application 57-124516, Japan. Application. 01.23.81 , Me56-9503; publ. 03.08.82, MKY B21845/06).

General essential features of the known method and the one that is claimed are the supply of laminar jets of low-pressure water that cool the scale.

However, when using the known method, a vapor film with high thermal (and electrical) resistance can form between the low-pressure laminar flow and the heated metal surface, which prevents the contact of the liquid with the heating surface and the transfer of energy to the liquid. The known method does not allow controlling the nucleation of the steam film and does not provide for the possibility of transition from film boiling to bubbling mode of boiling, which does not ensure high-quality scale removal.

The useful model is based on the task of improving the method of removing scale from hot-rolled steel strips by optimizing the main technological parameters.

The task is solved due to the fact that the bubble boiling mode is continuously maintained on the surface of the scale, which is one of the most advanced methods of cooling the heating surface.

In the proposed method, in the process of its implementation, the bubbling mode of boiling is continuously monitored and in the case of the formation of a steam film, the water outflow pressure automatically increases, the jet becomes turbulent, and under the action of increased pressure and turbulent pulsations, the steam film is destroyed and the bubbling mode of boiling is restored.

To control the bubbling mode of boiling, a constant electric current is passed through the water jet, which, at the moment of generation of steam bubbles and periodic changes in electrical resistance at the water-scaling boundary, induces in the induction coil a variable component of the electric current, the frequency and amplitude of which determine the bubbling mode and intensity heat transfer

The essence of the useful model is explained by the drawings, which show: - Fig. 1 - a device for implementing a method of removing scale from a hot-rolled strip; - Fig. 2 - a graph of the dependence of the first critical point of the heat flow dkri on the pressure P and water temperature.

The proposed method is carried out in the following way. Water under pressure Po from the collector 1, located in the longitudinal direction of the strip 2, through the controlled throttle 3, is fed to the collectors 4 with nozzles 5 located in the transverse direction of the strip 2. The central nozzle 5 of the collectors 4 is supplied with an induction coil 6, with the help of which fix the boiling mode on the scum surface. To do this, an electric current is passed from the direct current source 7 through the limiting resistor 8 and the water jet 9. If a steam film with a stable and high electrical resistance appears on the surface of the scum 10, the signal in the induction coil 6 disappears and a command is sent to the throttle 3, which increases the pressure P of the outflow of the jet 9. As the pressure of the outflow of the jet on the surface of the vapor film increases, the speed increases and turbulent pulsations of the forced movement, the saturation temperature increases and the surface tension coefficient decreases, which contribute to the destruction of the vapor film and the transition to the bubble boiling regime.

Steam bubbles, breaking away from the heating surface, contribute to the periodic contact of water with the heating surface. The average frequency of separation of steam bubbles is 1-62 1/s. Approximately according to the same law, the electrical resistance at the water-scale separation boundary changes, which induces an alternating current in the induction coil 6

EDS. The amplifier 11 amplifies the variable EMF, and the limiting device 12 equalizes the output signal of the amplifier 11 with the reference voltage Eop, and the regulator 13 increases the opening of the throttle 3, increasing the water outflow pressure until the output signal of the amplifier 11 becomes more than Eop, that is, the bubble mode appears boiling.

Example. Furnace slag was removed at site 2000 of the Novolipetsk metallurgical plant. An experimental and industrial device was made, which accommodated three collectors with nozzles placed in the transverse direction of the workpiece. The device was placed above the roller conveyor and connected to the 14 MPa high-pressure hydraulic scale remover operating at state 2000 through a regulating valve, the pressure at the outlet of which was measured by a manometer.

The workpieces heated to a temperature of 11007C were passed through the device at a speed of 0.5 m/s. The boiling crisis was observed visually by red-hot spots that appeared on the surface of the workpiece. It was established that the transition from film to bubbling mode of boiling is observed at the outflow pressure of water P-0.7MPa, which corresponds to the first critical point of the heat flow Dkri-7.8MW/m: (see Fig. 2). It was also determined that for the removal of furnace scale, it is sufficient to ensure an outflow pressure of P-0.7 MPa and a water consumption of 200 l/s with a power consumption of 140 kW. A higher quality of cleaning was noted in comparison with those functioning at state 2000 with hydraulic scale beating with water under high pressure, the consumer power of which is 1700 kW.

The use of the proposed method allows you to improve the quality of the surface being cleaned, reduce energy costs for hydraulic cleaning, and also use inexpensive and reliable low-pressure pumps and hydraulic equipment for scale removal.

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Claims (1)

The method of removing scale from hot-rolled steel strips by supplying laminar jets of low-pressure water, which is characterized by the fact that the process of bubbling mode of boiling on the surface of the strip is established by turbulating the jets of water by increasing the pressure, which is continuously controlled in automatic mode by passing a constant electric current, which at the moment of generation steam bubbles and periodic changes in electrical resistance at the water-scale separation boundary induces in the induction coil a variable component of the electric current in terms of frequency and amplitude.