What does Cadno measure?
Cadno measures variation in diameter across the roll barrel (profile). It does NOT measure absolute diameter, ovality/eccentricity, or surface roughness!
How operator sensitive is Cadno?
In stark contrast to manual micrometers, 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.
How are deviations in measurement taken care of?
The measuring calliper is supported by a four or six 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 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 microns. 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 then any error in profile reading is less than a micron.
What is the reproducibility of the Cadno under the same conditions?
We claim an accuracy of about 5 microns. 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. 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.
Does Cadno measure taper (diameter difference at opposite ends of the roll barrell)?
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!
Does Cadno mark the roll?
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 clear 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.)
Does the Cadno calliper measure the diameter of the roll?
No. The instrument is pre-configured to the nominal diameter of the roll being measured and thereafter measures variation in diameter across the barrell. Cadno does not measure the absolute diameter of the roll.
Is it possible to measure roll ovality or eccentric with Cadno?
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.