JPH0433525B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of controlling plate temperature by adjusting plate coolant flow rate in cold tandem rolling.

(Prior Art) In cold tandem rolling of high-strength steel with a thin gauge of normal steel (0.2 to 0.3 mm), the reduction rate per rolling stand is higher than that of thick gauge steel with normal steel (0.5 mm or more). For this reason, the plate temperature increases due to rolling, and heat streaks are likely to occur.

The rise in plate temperature can be suppressed by supplying coolant to the plate during rolling. However, the plate coolant flow rate must be maintained within an appropriate range. That is, if the plate coolant flow rate is too small, the plate temperature will rise and heat streaks will occur, and if it is too large, the plate temperature will drop too much and chattering will occur.

JP-A-57-156824 ``Strip temperature control method in cold rolling'' attempts to resolve the above-mentioned problems.

In the above temperature control method, the flow rate of the plate coolant is preset in association with the material of the material to be rolled, the temperature of the plate coolant, and various rolling conditions. Then, the plate temperature is detected, compared with the target temperature, and the plate coolant flow rate is adjusted according to the deviation.

(Problems to be Solved by the Invention) In the above conventional method, the plate temperature is detected. However, current temperature measurement technology cannot detect plate temperature with sufficient accuracy to control plate temperature.
Furthermore, control logic for controlling plate temperature with high precision has not yet been established.

Therefore, at present, the plate temperature is not controlled by adjusting the plate coolant flow rate.

(Means for Solving the Problems) In the present invention, the plate temperature is controlled by adjusting the plate coolant flow rate.

First, the plate temperature at the exit side of the i-th rolling stand is predicted. The plate temperature on the exit side is the plate temperature on the inlet side of the rolling stand plus the plate temperature rise in the roll bite. In the case of the first rolling stand, room temperature or a measured value is used as the board temperature on the entry side. In the second and subsequent rolling stands, the plate temperature on the entry side is determined by calculation as described later. Further, the plate temperature increase in the roll bit is the temperature increase due to rolling minus the temperature decrease due to heat transfer to the work rolls.

Next, the plate coolant flow rate at which the predicted temperature on the outlet side falls within the target range is determined. There is a functional relationship between the amount of plate coolant and the decrease in plate temperature, and this is determined in advance using the actual machine and stored in the control computer. Based on the difference between the predicted temperature on the outlet side and the target temperature, the required plate coolant flow rate can be calculated using the above function.

Adjust the plate coolant flow rate to the value determined above. The flow rate adjustment is performed by controlling the pump or the flow rate adjustment valve by a control computer.

Next, the plate temperature at the entrance side of the i+1 rolling stand is determined based on the plate temperature at the exit side of the i-th rolling stand and the plate temperature drop due to heat dissipation between the i-th and i+1-th rolling stands. Heat dissipation is
With the flow rate of plate coolant determined as above being supplied to the plate, heat transfer from the plate to the plate coolant, air, etc. occurs between the exit side of the rolling stand of the i-th stage and the entrance side of the rolling stand of the i+1th stage. Calculated as the amount of heat lost. Generally, the amount of heat transferred from the plate to the air is much smaller than the amount of heat transferred to the plate coolant, so the amount of heat transferred to the air can be ignored. Of course, heat transfer to the air can also be taken into account, and in this case, the accuracy of plate temperature control will be even higher.

Then, the above operation is sequentially repeated from the first stage to the final stage rolling stand.

(Function) Based on the temperature of the plate on the inlet side of each rolling stand, the temperature of the plate on the outlet side of that rolling stand is predicted. Then, the plate coolant flow rate is adjusted so that the predicted temperature is within the target range. Therefore, the plate temperature can be kept within a required temperature range.

(Example) FIG. 1 shows the rolling stands of the i-th stage and the i+1-th stage, and also schematically shows the change in plate temperature between the two rolling stands.

A plate coolant B is supplied to the plate A during rolling from a nozzle 3 arranged on the exit side of the rolling stand 1 to cool the plate A. Then, the plate coolant is removed from the plate surface using a draining roll 5.

The temperature of the plate increases as it is rolled, and the temperature of the plate decreases between the time it leaves the rolling stand and the time it enters the next rolling stand. The change in plate temperature will be described in more detail below.

First, the change in plate temperature due to rolling is an increase due to frictional heat generation Δθ _Fi , an increase due to plastic working heat Δθ _Pi ,
and the decrease Δθ _Di due to roll heat transfer. When the plate temperature change Δθ _i is expressed using, for example, a one-dimensional simple model, it is expressed by the following equation (1).

Δθ _i = Δθ _Fi + Δθ _Pi −Δθ _Di ……(1) Here, Δθ _Fi = 1/2 {A・WHT _i /C−Δθ _Pi /η _P }……(
2) Δθ _Pi = ηpAK _ni l _o Hi／hi／ρC ……(3) Δθ _Di ＝4λ(θ _ni −θ _Ri )√τ _di ／Cρh _ni √kπ……
(4) h _ni = (H _i + h _i )/2 ... (5) θ _ni = θ _bi + (Δθ _Fi + Δθ _Pi )/2 ... (6) Each symbol represents the following quantity.

A; Heat equivalent of work WHT _i ; Work required for rolling unit weight η _p ; Rate of thermal change during plastic working K _ni ; Average deformation resistance C _p ; Specific heat λ of plate; Thermal conductivity k; Temperature conductivity H _i ; Inlet plate thickness h _i ; Outlet plate thickness θ _Ri ; Roll temperature θ _bi ; Plate temperature at the entrance of the rolling stand τ _di ; As the time it takes for the plate to pass through the roll bite, the plate temperature θ _fi at the exit of the roll bite is , θ _fi = θ _bi + Δθ _i ...(7).

Next, the temperature θ _i of the plate cooled by the plate coolant will be explained.

Assuming that cooling by plate coolant follows a one-dimensional simple model, θ _i = (θ _fi − θ _c ) exp (−α _i / h _ni ρCτ _ci ) + θ _c ……(8) where, θ _c ; plate coolant Temperature α _i ; heat transfer coefficient of coolant on the plate surface τ _ci ; plate cooling time Therefore, if the target plate temperature after τ _ci (time to evaluate plate temperature) from the roll bite exit is _i ,
The required heat transfer coefficient α _i is expressed by the following equation (9).

α _i =h _ni ρC／τ _ci lnθ _fi −θ _C /θ _i −θ _c ……
(9) On the other hand, the heat transfer coefficient α _i is generally the plate coolant flow rate
It is a function of Q _i and coolant concentration D. That is, α _i = f (θ _i , D) ...(10) Figures 2 and 3 respectively show an example of the relationship between plate coolant flow rate Q _i and coolant concentration D, and heat transfer coefficient α _i .

Therefore, when formula (10) is solved for the plate coolant flow rate Q _i , θ _i =F (α _i , D) (11), and the required plate coolant flow rate Q _i is found.

In addition, there are cases where water is used as the coolant, and cases where water is used as the coolant.
It is broadly classified when using rolling oil emulsion. In the latter case, the cooling capacity (heat transfer coefficient) of the coolant changes depending on the concentration of rolling oil in the coolant, such as changes in the adhesion of rolling oil to the plate. Therefore, this is defined as the coolant concentration D, and this effect is included in equation (10).

The temperature θ _bi+1 at the entrance of the next rolling stand is θ _bi+1 = (θ _fi −θ _c ) exp (−α _i /h _ni ρCτ _i ) + θ _c (12). However, τ _i is the passing time of the plate between the rolling stones of the i-th stage and the i+1-th stage.

Therefore, the plate temperature θ _fi+1 at the exit of the roll bite of the i+1st rolling stand can be calculated as follows using equation (7): θ _fi+1 = θ _bi+1 Δθ _i+1 (13) Become.

In this way, the plate temperature θ _fi at the roll bite exit of the rolling stand can be sequentially determined,
Finally, the plate temperature at the outlet of the rolling stand roll bite at the most downstream stage can be determined.

Furthermore, by cooling the plate using the plate coolant flow rate Q _i determined by equation (11), the plate temperature can be kept within the required temperature range in each rolling stand.

FIG. 4 is a flowchart showing an example of the procedure for carrying out the method of the present invention.

As shown in the above flowchart, rolling conditions and plate coolant conditions are first set in the control computer. The rolling conditions include material, plate thickness, plate width, plate speed, roll circumferential speed, rolling reduction ratio, and others. Also,
Plate coolant conditions include coolant type, concentration, flow rate, etc.

Next, the plate temperature θ _b1 (usually room temperature) at the entrance side of the first rolling stand is set. If necessary, the plate temperature θ _b1 is actually measured.

Subsequently, the plate temperature increase Δθ ₁ during roll bite in the first rolling stand is calculated according to (1) to (6) above. Then, the plate temperature θ ₁ after a time τ _C1 from the exit of the roll bite is determined by equation (8). The time τ _C1 is the time from when the plate leaves the roll bite to the plate temperature evaluation position (immediately after the exit of the first rolling stand, immediately before the entrance of the second rolling stand, or a predetermined position between both stands). .

Once the plate temperature θ ₁ is obtained as described above, it is determined whether it is within the required temperature range θ _L to θ _U. If the plate temperature _θ1 is within the required temperature range,
The plate temperature θ _b2 at the entrance of the second rolling stand is calculated using equation (12). Also, if the plate temperature θ ₁ is within the required temperature range, θ ₁ = θ _LO or θ ₁ = θ _UO ,
Determine the plate coolant flow rate _Q1 using equation (12), and then reset the plate coolant flow rate to the newly determined value.

Thereafter, the above procedure is repeated until reaching the most downstream rolling stand.

If a drain roll is installed as shown in Figure 1, the plate temperature can be controlled by dividing the cooling zone into two: from the roll bite exit to the drain roll, and from the drain roll to the entrance of the next rolling stand. You can calculate it.

Here, a specific example of plate temperature control according to the present invention will be explained.

Rolling was carried out using a cold tandem mill consisting of five rolling stands. Moreover, the rolling conditions are as follows.

Material: Ordinary steel sheet thickness: 2.7mm Product sheet thickness: 0.5mm Sheet width: 1190mm 5th rolling stand rolling speed: 1438m/min Roll diameter: Work roll 550mm Back-up roll 1450mm When the sheet coolant flow rate is constant and this The plate temperature was measured when the plate coolant flow rate was adjusted by the method of the invention. In the former case, the plate coolant flow rate is 20/min for all stands. In the latter case, the rate is 20/min for the first and second rolling stands, and 50/min for the third to fifth rolling stands.

FIG. 5 is a diagram showing actually measured values of plate temperature during the above rolling. As is clear from this diagram, when the plate coolant flow rate is not adjusted, the plate temperature is
The tolerance value is exceeded in the stands after the rolling stand. However, according to the method of the present invention, the plate temperature is kept below the allowable value.

Although the above embodiment describes plate cooling using only plate coolant, the plate temperature can be controlled with even higher accuracy by considering cooling using air as described above. In this case, as the heat transfer coefficient, for example, the heat transfer coefficient α _i of the plate coolant
is multiplied by a coefficient that takes into account cooling by air. The above coefficient varies depending on the composition of the plate coolant, plate speed, atmospheric temperature, etc. For example, 1.04
It takes a value of ~1.09.

(Effects of the Invention) As explained above, according to the method of the present invention, the plate temperature can be controlled with high accuracy. Therefore, the plate temperature will not be too high to cause heat streaks in the product, or too low to cause chattering.

[Brief explanation of drawings]

Figure 1 is a diagram schematically showing the rolling stands of the i-th stage and the i+1-th stage and changes in plate temperature between the two rolling stands. Figures 2 and 3 are diagrams showing plate coolant flow rate Q, coolant concentration D, and heat FIG. 4 is a graph showing an example of the relationship with the transfer coefficient α _i , FIG. 4 is a flowchart showing an example of the procedure for carrying out the method of the present invention, and FIG. 5 is a diagram showing an example of actual measurement of the plate temperature during rolling. be.

Claims (1)

[Claims] 1 In a method of controlling plate temperature by adjusting the plate coolant flow rate, the plate temperature at the outlet side of the i-th rolling stand is predicted based on the plate temperature at the inlet side of the i-th rolling stand and the plate temperature rise in the roll bit. Then, determine the plate coolant flow rate at which the predicted temperature is within the target range, adjust the plate coolant flow rate to the determined value, and then adjust the plate temperature at the outlet side of the rolling stand of the i-th stage and the rolling of the i-th stage and the i+1 stage. A plate in cold rolling, characterized in that the plate temperature at the entrance side of the i+1 stage rolling stand is determined based on the plate temperature drop due to heat dissipation between the stands, and the above operation is sequentially repeated from the first stage to the final stage rolling stand. Temperature control method.