JPS644842B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention aims to reduce thrust force during roll kissing by applying rolling oil, which has conventionally been applied only to reduce rolling load and prevent roll roughness, during roll kissing during idle time, thereby preventing bearing troubles caused by thrust. be. As is well known, when rolling steel strips using a continuous hot rolling mill, in the case of thin products, kiss roll rolling is generally performed, in which the work rolls are rotated in contact with each other during idle time in order to improve the accuracy of the strip thickness. ing. If we investigate the frequency of bearing troubles in continuous hot rolling mills, we will find that they are concentrated in thin material rolls where kiss roll rolling is performed, as shown in Figure 1. This is because when a rolling mill is used for a long period of time and the play between the back-up roll chock and the stand becomes large, and the play between the work roll chock and the back-up roll chock becomes large, minute crosses occur between the rolls. If a kiss roll is performed in this state, a thrust force will be generated between the rolls, which will lead to bearing seizure. On the other hand, even if the above-mentioned kiss roll rolling is performed in the roll cross rolling method (Japanese Patent Application Laid-open No. 55-64908) shown in FIGS. 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 can be seen that in order to suppress the generated thrust within the bearing seizure prevention range, the inter-roll thrust coefficient must be kept below 10%. The fundamental factor in the generation of thrust force during roll kissing is the frictional force caused by relative sliding between rolls due to roll crossing. Therefore, since reducing the frictional force leads to reducing the thrust, the inventors considered a method using oil lubrication as a countermeasure. Figure 5 shows the effect of oil lubrication on the inter-roll thrust coefficient, and is an example showing that the thrust coefficient, which was about 30% without lubrication, can be reduced to 10% or less. Therefore, oil lubrication can be considered as an effective method to prevent bearing seizure, but in the conventional hydraulic rolling sequence, as shown in Figure 6A, the oil is cut off before bottoming out in order to prevent the next material from biting into the plate and slipping. During idling, there is no oil between the rolls, resulting in a non-lubricated state. Therefore, in such a sequence, it was not possible to prevent the occurrence of thrust due to kiss rolls during idle time, and it was not possible to prevent bearing troubles. Therefore, in the present invention, as shown in FIG. 6B,
It has been discovered that by keeping the timing of the injection stop of rolling oil at an appropriate value b, it is possible to reduce the inter-roll thrust coefficient μT at idle without being affected by the slippage caused by the board biting of the next material. FIG. 7 shows the relationship between rolling oil off timing and thrust coefficient. The off timing was determined by taking the time from before and after the sheet bottom came out, and the thrust coefficient was calculated by performing a kiss roll at idle after the oil was turned off, and measuring the slip torque just before the next material bit. The figure shows that with the conventional oil-off timing before tail-off, μT would occur at around 30% during idle, but by shifting the oil-off timing until after tail-off, μT can be reduced.
This is thought to be because by shifting the oil-off timing, the amount of oil remaining on the roll surface increases and the thrust coefficient decreases. Furthermore, from the example shown in FIG. 7, it can be seen that in order to lower the inter-roll thrust coefficient during idle to 10% or less, the oil off timing must be set at 5 seconds or more after the end of the oil. However, it is not possible to shift the oil-off timing indefinitely due to the problem of slippage when the next material is caught in the board. From this experiment, it was found that if oil is injected for more than 20 seconds after the bottom has finished, slipping of the next material will occur, so it is desirable to set the oil injection off timing to 20 seconds or less. After draining the oil, the oil is washed away with roll cooling water, but after 20
It is thought that if the water is not washed for more than a second, the next material will slip. Therefore, as an operating condition for preventing slippage, it is preferable to turn off the hydraulic extension material for at least 20 seconds before it engages. In addition to increasing the coefficient of friction of oil using roll cooling water, any other method such as a wiper method or a burn-off method can be used.

【table】

[Table] As can be seen from the above examples, in the case of the conventional method, there is no slip due to the subsequent material being bitten, but the thrust force during the kiss roll is large and bearing seizure problems occur frequently. On the other hand, the method shown in Comparative Example 1, in which the oil is turned off at the same time as the plate ends, reduces the bearing seizure trouble to some extent, but is not sufficiently effective. 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, bearing seizure troubles are greatly reduced, and especially when the oil-off timing is extended by 20 seconds, bearing seizure troubles are drastically reduced. do. However, as shown in Comparative Example 2, if the oil-off timing is extended too much (25 seconds), the oil washing effect by the roll cooling water is small, and slips occur when the next material is bitten. Next, Invention Example 3 shows the case of roll cross rolling (kiss roll cross angle 1.5 degrees) shown in Fig. 2, and the best effect can be obtained by taking the same measures as Invention Example 2. It is being From the above, hydraulic rolling, which has conventionally been applied to reduce the load during rolling (energy saving effect) and prevent roll roughness, can now be applied as a new application to reduce thrust during roll kissing. We were able to establish operating conditions for oil injection timing that also take into account slip prevention during jamming.

[Brief explanation of drawings]

Figure 1 is a chart showing the relationship between plate thickness and bearing failure frequency, Figure 2 A and B are illustrations of the roll cross rolling method, and Figure 3 is a chart showing the relationship between roll cross angle and thrust coefficient during roll kissing. , Figure 4 is a chart showing the relationship between the bearing heat generation limit and 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 and B are charts showing the relationship between bearing heat generation limit and thrust coefficient. FIG. 7 is a chart showing the relationship between oil-off timing and thrust coefficient, and FIG. 8 is a chart showing oil injection timing in Examples.

Claims (1)

[Claims] 1 In the kiss roll rolling method in which the rolls are kept in contact during the idle time after the material to be rolled has passed through the rolls, rolling oil is continued to be supplied even after the rear end of the material to be rolled has passed through the rolls. A method for preventing thrust in a rolling mill, characterized by reducing the coefficient of friction and increasing the coefficient of friction of rolling oil adhering to a roll before the next material is bitten.