INTERPRETATION OF THE RESULTS.

There are a number of different factors which can effect the way in which the roll surface elongates, or compresses. To analyze the results there needs to be some estimation of the effects of each of these factors. These strain effecting factors are as follows:

a) Roll extension. b) Roll profile change.

c) Ground slot profile results. %•

d) Roll bending. a) Roll extension.

The extreme loads applied and low level of metal to metal co-efficient of friction may mean that the roll elongates. This elongation would be measured as strain on both the horizontal gauges and the undercut roll gauges.

The plots showing the horizontal gauge results for different loads (Figure 29) show that the effects of roll extension are small. The individual plots are not displaced from each other and only the peak strain values are affected. If the extension effects were large then the plots should be displaced from eiach other by amounts relating to the applied load.

b) Roll profile change.

A loaded work roll will change its profile along its length, and through its cross section. The manner with which the profile changes is related to the roll material properties, profile, the load applied, and the manner of support. Estimates of the profile change are shown in Figure 35.

Any differential loading of a work roll along its length will cause a longitudinal profile change. This variation in profile will affect the roll surface geometry and hence the strains recorded.

Alterations in roll profile would be expected at points of loading alterations. There is no means of isolating these effects from roll bending.

There are two areas to consider with cross sectional roll profile changes. These are, the strains caused by the changing roll radius, and those caused by direct compression. If a cuboid block was loaded, then from Poissons ratio effects, the strains in the direction of load should be three times that in the plane at right angles to the load. Measurements of horizontal and vertical gauge strains show the stress in the direction of load to be one third those in the plane at right angles to the load. One explanation for this is that a high degree of geometry change and compression occur at the same time, hence corrupting the results.

c) Slot edge effects.

Since the gauges on the undercut roll are sunk into recesses, and the load is applied around these, then the behaviour of the slots affect the strains experienced.

Whilst loading the undercut roll through a level mill set up, that is with all rolls ground parallel, a static strain level of 210/dE is seen (Figure 34c). When loading the horizontal gauged roll in the same manner a strain value of 75/xE is seen. If elongation alone was being measured then these results would be similar. The slots must have an effect on the strains measured. These effects are shown to be consistent, and so can be taken into account when analyzing the results.

d) Roll Bending.

This can be broken down into two areas: i) Horizontal roll bending.

ii) Vertical roll bending.

i) Horizontal roll bending.

Typical plots show that between the right and left of the work roll opposing strain

patterns, or separated plots, occur. The plots cross over at the mill centre. This type of plot is indicative of bending. The position of the gauges means that horizontal bending and not vertical is recorded. It has been shown that the strains are recording either roll profile changes, or roll bending or a combination of these.

The arguments in favour of roll bending occurring are:

- The consistent strain pattern for different loading conditions. - The difference in strains between the right and left of the mill.

- The crossing over of the strain plots from the front to the back of the mill. - The parallel plots recorded when loading the roll through the flat ground roll

cluster.

ii) Vertical roll bending.

The roll bending strains measured by the undercut roll show the vertical bending of a work roll. The high strains measured next to the taper transition of the first intermediate roll show that bending is occurring.

The strains measured are large compared to the roll extension and slot edge effects (Figure 34c).

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Strains are highest at the point of contact with the first intermediate roll taper transition. The taper transition is at the front of the mill with the roll in the top half and vice-versa. This lack of symmetry is shown by the strain plots. There is asymmetry between the top and bottom and between the left and right of the mill.

Loaded mills experience flexing, this flexing is translated into work roll bending. Using the undercut roll this flexing can be found. From the results taken with a parallel ground roll mill set up (Figure 34c) a slight curving of the plots is revealed, this indicates the •amount of mill flexing. The strains recorded are lower at the centre than the sides of the

mill. There is evidence that there is slightly higher mill load at the back (drive) side of the mill.

Comparing the plots of the flat ground roll mill set up (Figure 34c) and typical results of undercut roll strains there is a levelling out of the plots at the centre of the mill which coincides.