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Cadno: Frequently Asked Questions

 

Please search here for the answer to your Cadno Electronic Measurement System query. If you have a query which is not answered here please contact us on support@metrologysystems.co.uk

   
 

Question 1: How are deviations in measurement caused by wheeling the instrument not parallel to the axis taken care of?

Question 2: Is it possible to measure whether the roll is not round / circular due to wear?

Question 3: Is it possible to measure eccentricity of the roll, i.e. the axis not in the centre of the roll?

Question 4: What is the reproducibility of the instrument under the same circumstances?

Question 5: What is the influence of differences in roll temperature on the measurement?

Question 6: What is the influence on a measurement when the roll temperature varies (descend) during a measurement?

Question 7: If there is influence of temperature is there a possibility to measure roll temperature and adjust for it.

Question 8:  Does the CADNO Calliper measure the diameter of the roll?

Question 9:  Does the CADNO Calliper measure taper (diameter difference at opposite ends of the roll barrell)?

Question 10:  Does the instrument mark the roll?

Question 11:  How operator sensitive is the instrument?

Question 12:  Can the CADNO Calliper measure roll surface temperature?

   
 

Question 1: How are deviations in measurement caused by wheeling the instrument not parallel to the axis taken care of?

Answer: The measuring calliper is supported by a four wheeled carriage. The contour of the wheel tyres, the position of the wheels and their angle are all designed to ensure that the carriage tracks accurately across the roll barrel. A typical hot mill work roll might be 2000mm long with a diameter of about 700mm and the departure from a perfect cylinder is usually less than 0.200mm so it can be seen that the roll itself forms part of a very accurate guidance system for the measuring calliper.

On a 700mm roll the measuring tips would need to deviate from being at opposite ends of a true diameter (longest chord) by 2mm or 2000 micron to give an error in the profile reading (variation in diameter) of 0.006mm or 6 micron. Errors due to the measurement plane not being perpendicular to the roll axis are of the same order of magnitude. Furthermore because one is looking for variation in diameter (as opposed to absolute diameter) then even if the measurement plane is not perfectly perpendicular, provided it remains at the same angle to the axis (as would be the case once any "play" in the centre bearing has been taken up) then any error in profile reading is less than a micron.

   
 

Question 2: Is it possible to measure whether the roll is not round / circular due to wear?

Answer: When the CADNO instrument has been correctly pre-configured to suit the absolute diameter of the roll under test. The calliper is supported perpendicular to the roll axis and the gauging tips are at opposite ends of a horizontal diameter. The carriage is designed to permit the calliper to be moved smoothly across the roll barrel. Variation in diameter from the start position, at which the instrument was "zeroed", is measured and recorded.

The carriage wheels are designed to prevent the instrument slipping around the circumference but there is no reason why some low friction fabric should not be placed under the wheel thereby allowing the roll to be rotated slowly under the instrument.

In "calibration mode" the display gives the actual movement of the gauging tip in micron and so the displayed reading could be correlated with the rotation of the roll barrel. (Although such a reading is possible, as far as I am aware none of our customers make regular use of the instrument for this purpose. I suspect that this is because, by the nature of their usage in the mill, the rolls wear in a very uniform way around their circumference – of primary concern is wear patterns along the barrel. )

   
 

Question 3: Is it possible to measure eccentricity of the roll, i.e. the axis not in the centre of the roll?

Answer: No- because the carriage is running along the roll surface with no reference to the axis or the journals. By far the best way of measuring eccentricity is to mount a measuring probe radial to the roll surface from a suitable mounting point on the grinding machine. (If required the CADNO measuring probe can be removed from the electronic calliper assembly and used in this way. In calibration mode the movement of the tip of the gauging probe is displayed in micron on the microcomputer based module.)

   
 

Question 4: What is the reproducibility of the instrument under the same circumstances?

Answer: We claim an accuracy of about 5 micron. If two traces are taken of the same roll and the graphs superimposed then allowing for surface roughness variations etc. the two curves lie on top of each other. An even better test is to measure the roll from left to right and print out the graph and then from the other side of the roll repeat the measurement so that the calliper is now traversing the roll in the opposite direction. If the two graphs are superimposed so that the printed sides are facing each other and then the pair are viewed against the light then the two curves can be made to lie one on top of the other by moving them vertically by twice the value of any taper present. Where accuracy’s in excess of 5 micron are required then successive traces can be taken and averaged. If, for example, 10 traces are taken then any random error present is divided by a factor of 10.

   
 

Question 5: What is the influence of differences in roll temperature on the measurement?

Answer: No significant effect. It is important to remember that the instrument is measuring variation in roll diameter. If the probe is zeroed at one end of the roll then it can be traversed across the roll in say 10 seconds or less. If the roll surface is at 100 degrees Celsius then the error is the amount the yoke would expand as a result of radiated heat from the roll surface in 10 seconds.

 

 

 

Question 6: What is the influence on a measurement when the roll temperature varies (descend) during a measurement?

Answer: See answer to question 5. It is possible to take successive scans along the barrel of a roll over a period of say 2 hours - as the higher temperature at the roll centre soaks out to the necks. The instrument is zeroed at the start of each scan in the normal way and the variation in diameter (roll profile) measured. There is a facility in the software to display the decay of thermal camber by displaying the multiple profile traces in 3 dimensions with user definable angle of rotation and colour banding.

 

 

 

Question 7: If there is influence of temperature is there a possibility to measure roll temperature and adjust for it.

Answer: As already mentioned there is no significant error due to temperature. However there is no reason why the variation in surface temperature at intervals across the barrel should not be measured using a portable temperature probe and this information recorded. We would be happy to quote for a special feature to the software to allow this temperature information to be plotted or to be used in any other specified way in conjunction with the physical measurements of roll profile.

 

 

 

Question 8:  Does the CADNO Calliper measure the diameter of the roll?

Answer:  No.  The instrument is pre-configured to the nominal diameter of the roll being measured and thereafter measures variation in diameter across the barrell.

 

 

 

Question 9:  Does the CADNO Calliper measure taper (diameter difference at opposite ends of the roll barrell)?

Answer:  Yes. If the instrument is 'zeroed' at one end of the roll barrell, then the reading at the opposite end is a true measure of the taper.  A dramatic demonstration of the accuracy of the instrument is to measure a roll from operator to drive and then remove the calliper and from the other side of the roll measure it from drive to operator.  Within a few microns, the same value of taper will be displayed - only the sign being different!

 

 

 

Question 10:  Does the instrument mark the roll?

Answer:  The standard instrument is supplied with contoured steel tyred wheels and tungsten carbide tips on the counter weight and the measuring sensor.   This option is completely satisfactory for the  vast majority of rolls and does not produce any marking of the roll surface.  For special applications, such as 'mirror finish', we can supply soft wheels and soft gauging tips (interestingly, in the cold rolling of aluminium strip, even the softest tips will disturb the coolant film sufficiently to affect the uniformity of the subsequent oxide coating and so we recommend a final light grinding pass after measurement with the CADNO system.)

 

 

 

Question 11:  How operator sensitive is the instrument?

Answer: In stark contrast to the large manual micrometer, where different operators can obtain readings as much as 100 microns apart, after a short period of training any two operators using the CADNO system will produce virtually identical profile traces.

 

 

 

Question 12:  Can the CADNO Calliper measure roll surface temperature?

Answer: No. However, a simple hand held probe can of course be used for this purpose; the data obtained can be entered into the CADNO 2000 software system along with other roll details (e.g. surface roughness, hardness etc.) for subsequent analysis.

 

 

 
 
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