JPS5939408A - Method for preventing thrust in rolling mill - Google Patents

Abstract

PURPOSE:To reduce the friction coefficient and thrust between rolls, and to prevent bearing troubles, by shifting the timing of stopping the injection of a rolling oil during the idle time after a rolling material runs out of the rolls. CONSTITUTION:The period of feeding a rolling oil into an idle time is prolonged by 5 and 20 seconds even after the tail end of a rolling material runs out of rolls, and also the rolling oil sticking to the rolls is washed out by a roll cooling water, before the following material is bitten by the rolls, to increase friction coefficient. At that time, if said timing is prolonged by 25 seconds till the feed of oil is made off, the effect for washing out the oil is reduced, and slip is caused when the following material is bitten.

Description

[Detailed description of the invention] By applying rolling oil, which has been used only for prevention, during roll kissing during idle time, the thrust force during rolling roll kissing can be reduced, thereby preventing bearing troubles caused by thrust. .

As is well known, when rolling steel strips using a continuous hot rolling mill, in the case of thin steel strips, the work rolls are kept in contact with each other and rotated during idle time to improve the accuracy of the strip thickness.
Kiss roll rolling is commonly practiced.

When we investigate the frequency of bearing troubles in continuous hot rolling mills, we find that they are concentrated in thin materials that undergo kiss roll rolling, as shown in Figure 1. In addition, if the rolling mill is used for a long time and the play between the roll chock and the work roll chock becomes large, minute crosses may occur between the rolls. Ru. If a kiss roll is performed in this state, a thrust force will be generated between the rolls.

This can lead to bearing seizure. On the other hand, the roll cross rolling method (Japanese Unexamined Patent Publication No. 556
490'8), even if the above-mentioned kiss roll rolling is performed, the same thrust occurs and the same problem occurs.

Therefore, the relationship between the cross angle and thrust force was investigated using a model mill using the above roll cross rolling method.

Figure 3 shows the experimental results for determining the thrust coefficient in a kiss roll state. Even if the cross angle is slightly increased, the thrust coefficient (μT - thrust force/kiss roll load) increases rapidly, reaching a maximum of μT = 30%. I understand. Figure 4 shows the relationship between the bearing heat generation limit and the thrust coefficient. From the figure, it is clear that in order to suppress the generated thrust within the bearing seizure prevention range, the inter-roll thrust coefficient must be kept below 10%. I understand. The basic factor in the generation of thrust force during roll kissing is the frictional force caused by the opposing blades between the rolls as they cross the rolls. Therefore, the inventors believe that reducing the frictional force leads to reducing the thrust. Therefore, as a countermeasure, we considered a method using oil lubrication.Figure 5 shows that the effect of oil lubrication was not as good as the inter-roll thrust coefficient, and the thrust coefficient, which was about 30 when not lubricated, was reduced to less than 10%. Therefore, oil lubrication is considered to be an effective method for preventing bearing seizure, but in the conventional hydraulic rolling sequence, as shown in Fig. , the bottom puller is drained of oil before (a) (JP-A No. 46-1353).During idle, there is no oil between the rolls, resulting in an unlubricated state.Therefore, in such a sequence, during idle time It was not possible to completely prevent the occurrence of thrust caused by kiss rolls, and bearing troubles could not be prevented.

Therefore, in the present invention, as shown in Fig. 6 (■), the timing of stopping the injection of Vc1 rolling oil is maintained at an appropriate (b). We have completely discovered that it is possible to reduce the coefficient μT. Figure 7 shows the complete relationship between the rolling oil off timing and the thrust coefficient. The time taken before and after the plate bottom removal was taken at the off-timing, and the thrust coefficient was calculated by performing a kiss roll at idle after turning off the oil and measuring the slip torque just before the next material was bitten. The figure shows that in conventional tail removal, the previous oil off timing caused about μT=30% at idle, but by shifting the oil off timing until later, μT'(
It can be seen that it can be reduced by 5.

This is thought to be due to the fact that by adjusting the oil-off timing, the amount of oil remaining on the roll surface increases and the thrust coefficient decreases. Also, from the example in Figure 7.

It can be seen that in order to lower the roll-to-roll thrust coefficient during idle to a factor of 10 or less, it is necessary to wait at least 5 seconds after the oil-off timing.

However, due to the problem of slippage when the next material is caught in the board, it is not possible to limit the oil off timing. From this experiment, it was found that if oil is injected for more than 20 seconds after tail removal, a slip phenomenon of the next material will occur, so it is desirable to set the oil injection off timing to 1d20 seconds or less. After draining the oil, the oil is washed away with roll cooling water.

It is thought that if the washing is not carried out for 20 seconds or more, the next material will slip. Therefore, as an operating condition for preventing flipping, it is preferable to turn off the hydraulic pressure for at least 20 seconds before the extension material is bitten. In addition to the treatment for increasing the coefficient of friction of oil using roll cooling water, any method such as the Wino ξ one-way method or the )-on-off method can be implemented.

As can be seen from the above examples, in the case of the conventional method.

Although there is no slippage due to biting of the next material, the thrust force during kiss roll is large and bearing seizure problems occur frequently. On the other hand, as shown in Comparative Example 1, the method of turning off the oil at the same time as the end of the plate comes off, although a slight reduction in bearing seizure troubles can be seen, the effect is insufficient.

However, by extending the oil-off timing to 5 seconds and 20 seconds during the idle time as in Examples 1 and 2 of the present invention, the bearing seizure problem is greatly reduced.In particular, if the oil-off timing is extended by 20 seconds, the bearing seizure problem is reduced. decreases dramatically. However, as shown in Comparative Example 2, if the oil-off timing is extended too much (25 seconds), the effect of washing the oil with roll cooling water is small, and slipping occurs when the next roll is bitten.

Next, Example 3 of the present invention shows the case of roll cross rolling (kiss roll cross angle 1.5 degrees) shown in FIG.
The best effect was obtained by taking the same measures as in Example 2 of the present invention.

Based on the above, conventional ■ Load reduction during rolling (labor saving effect)
■Hydraulic rolling, which has been applied to prevent roll roughness, can now be applied as a new application to reduce thrust during roll kissing.It also takes into account slip prevention when primary material is caught. The operating conditions for oil injection timing could be established.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between plate thickness and bearing failure frequency, Figure 2 (B) is an illustration of the n-roll cross rolling method, and Figure 3 is a diagram showing the relationship between roll cross angle U and thrust coefficient during roll kissing. Figure 4 shows the relationship between the bearing heat generation limit and the thrust coefficient. Figure 5 is a chart showing the relationship between roll cross angle and thrust coefficient when rolling oil is applied during roll kissing, and Figure 6 (
A) (B) n A chart showing the timing of oil injection according to the conventional method and the method of the present invention, FIG. 7 is a chart showing the relationship between the oil off timing and the thrust coefficient, and FIG. 8 shows the oil injection timing in the example. This is a diagram. 1st J Atsushi 2m (A) (B) Me 3 Figure 84 Figure ct-Nob riJk-@ (rpm) Raku 5 Entori Figure 6

Claims (1)

[Claims] (II) In the kiss roll rolling method, in which the rolls are kept in contact during the idle time after the material to be rolled passes through the rolls, rolling oil is continued to be supplied to the rolls even after the rear end of the material to be rolled passes through the rolls. A method for preventing thrust in a rolling mill, characterized by reducing the coefficient of friction between rolls and increasing the coefficient of friction of rolling oil adhering to the rolls before the next material is bitten.