The invention also relates to a device for use when applying the inventive method, and particularly for registering move- ments in the roller guide that can be later used in the moni- toring process.

Rod or shapes are often rolled in a plurality of roll units co-ordinated in a rolling line with the various roll pairs arranged close together, said rolls being arranged in the rolling line in such close relationship as to make visual inspection of the rolling sequence between the roll pairs impossible to carry out. It is also possible that parts of the rolling line are enclosed in a protective casing in order to prevent cooling water from splashing from the rolls into the surroundings, among other things, which also makes in- spection of the rolling result between the roll pairs impos- sible to carry out.

Consequently, the rolling result cannot be assessed until the rod/shape has left the rolling line, and then solely by a visual examination of the rolled product leaving said rolling line. If an adjustment needs to be made, it may be necessary to stop the rolling process so as to enable a manual adjust-

ment to be made to one of the rolls, for instance. Hitherto, no method has been proposed by means of which a maladjusted roll in a roll unit can be determined directly. Instead, the adjustment has been made essentially with a starting point from past experiences of the machine operator and the adjust- ment is normally made at the place where the adjustment is expected to give the intended result.

Accordingly, the object of the present invention is to pro- vide a method and means which enable the distance between the rolls of respective roll units to be monitored during a roll- ing operation and as a consequence thereof also to be ad- justed, so as to obtain a rolled product of high and uniform quality.

The aforesaid objects have been achieved with a method and means having the characteristic features set forth in respec- tive associated Claims.

The invention is based on continuously sensing vibrations in the roller guides and analysing their frequency and possibly also their amplitude, so that changes in certain frequencies can be used to give an indication of the state in the roll pair that precedes the roller guide and possibly also in the roll pair that lies downstream of the roller guide in the feed direction of the stock.

The invention will now be described in more detail with ref- erence to non-limiting embodiments thereof and with reference to the accompanying drawings, in which Fig. 1 illustrates from above a roller guide for a roll pair provided with reg- istering means for application of the inventive method when rolling round rod; Fig. 2 is an end view of the roller guide

shown in Fig. 1; Fig. 3 is a schematic illustration of part of a roll line having eight roll pairs in which the inventive method can be applied; and Fig. 4 is an example of a vibra- tion level curve obtained with different adjustments of pre- ceding and following roll pairs in a rolling line.

Fig. 1 illustrates a typical roll guide for use in rolling mills or lines and having an infeed end 2 and a guide end 3.

The guide end 3 typically includes two grooved and rotatable rollers 4 and 5 which guide the stock 6 therebetween during the rolling process (see Fig. 2). The rollers 4 and 5 are carried by arms 7,8 fixed to the holder 9 of the roller guide.

Vibration sensors 10 and 11 are each screwed into a respec- tive roller arm 7,8 and protected by a protective casing 12 attached to the holder at the guide end 3 of the roller guide. The vibration sensors 10 and 11 are adapted to sense vibrations in the arms 7 and 8 and are connected by signal cables to an electric contact 13 to which a signal cable (not shown) can be connected for conducting said signals to a processing unit, for instance to a computer equipped with software for automatically analysing the signals incoming from the sensors 10 and 11.

A rolling line, or rolling mill, can include a plurality of mutually sequential roll pairs where each alternate roll pair rolls the rod to an oval shape and each other alternate roll pair rolls the rod to a round shape. Fig. 3 is a highly sche- matic illustration of an example of part of such a rolling line that includes eight roll pairs 14,15,16,17,18,19, 20,21, of which the roll pairs 14,16,18 and 20 roll the rod to a round shape while the roll pairs 15,17,19 and 21

roll the rod to an oval shape. The chain line 22 drawn in Fig. 3 indicates the rolling line through which the rod is moved during a rolling operation. A roller guide 1 is pro- vided upstream of each of the roll pairs 14,16,18 and 20, i. e. the roll pairs that roll the rod to a round shape. Al- ternatively, one such roller guide can be provided at each roll pair in the rolling line. All of the roller guides 1 will conveniently be provided with vibration measuring means that enable the inventive method to be applied. The rolls of respective roll pairs can be adjusted relative to each other in a known manner, such as to enable the distance between the rolls of a respective roll pair to be either increased or decreased, because of wear on the rolls on the one hand and also because of differing qualities of the material to be rolled on the other hand.

When the vibration measuring means are used to monitor the state of the rolls, vibrations occurring in the arms 7 and 8 of the roller guides are analysed by frequency analysis. In the case of frequency analysis, vibrations deriving from normal rotation of the rolls, the frequencies of which can be established when the speed at which the stock is advanced and the width and diameter of respective rolls is known, can be sorted out from the analysis and changes in other, selected, frequencies can be used as a measurement of the load on the roll pair concerned. Frequencies deriving from other control points in the rolling line or rolling mill can be analysed and excluded from the analysis during operation of the plant. By studying the frequency changes obtained with a given roller guide as a result of a change in the distance between the rolls of a preceding and following roll pair respec- tively, it is possible to obtain for each roller guide threshold values corresponding to certain frequencies and to

allow these threshold values to provide an indication as to whether or not the rolls function in the manner intended.

Trials have been run in which it was observed that changed results are obtained both in the event of a change in the distance between the rolls of the roll pair that preceded the roller guide and also in the event of a change in the dis- tance between the rolls of the roll pair that followed the roller guide concerned. Fig. 4 is a diagrammatic illustration that shows how the vibration level (in this case the accel- eration) changes in a roller guide at the selected frequen- cies as a result of a change in the distance in the preceding roll pair (F) and also in the following roll pair (E). In the diagram, there is shown at 0 the vibration level in a normal setting of the roll pairs, and with-and + there is shown the vibration level when the distance between the respective pairs of rolls decreases and increases respectively. In addi- tion to acceleration, the vibration measuring process can also be carried out with respect to speed or movement.

After manually testing the rolling mill or rolling line and carrying out a frequency analysis for each of the roller guides and their rollers with a change in the setting of the distance between the roll pairs upstream and downstream of respective roller guides, there can be established threshold levels at which there is delivered a signal indicating that an adjustment needs to be made. Those frequencies that origi- nate from rotation of the rolls and the advancement of the rod can then also be sorted out in the frequency analysis.

This can be readily achieved with the aid of computer tech- nology. For instance, the values that caused the signal to be sent can be presented on a computer screen and therewith

enable the roll pair requiring adjustment to be manually adjusted.

Data obtained from the aforedescribed frequency analysis can also be presented by continuously presenting the vibration levels of respective sensors on a computer screen in the form of stack diagrams, where different vibration levels are given in different colours so as to enable deviations from a normal state to be easily observed.

When a frequency analysis has been made and the basic setting values have been obtained in accordance with the aforegoing, the processing computer may be coupled to means for setting the respective roll pairs in the rolling line.

The vibration sensors used may conveniently be piezoelectric accelerators that sense all movements, in this case their own movement and also movement of the rollers and the arms, and that deliver a signal whose strength is proportional to the acceleration. The vibration sensor retailed under the desig- nation 353 B67 by Piezotronics Inc., U. S. A., is an example of one type of vibration sensor that can be used to this end.

In addition to being used for the aforesaid purpose, the vibration sensors may also be used in a known manner to de- tect wear in the roll bearings. This enables faults to be detected and an alarm raised with the same equipment as that used to monitor the distance between the rolls, therewith enabling unplanned interruptions in operation to be prevented when the faults are detected in time. The inventive method can also be applied to detect faults in the setting of the roll pair per se and also in relation to said roll pair, and also enables direct damage to a roll caused by a fault in the rolled material to be detected. Other faults in the roll unit caused by wear on the rolls and the rollers can be detected by monitoring changes in the frequencies generated by said rolls and rollers.