Calibration of K Bars

Due to the high quality of stainless steel wire used in the manufacture of RK meter bars, the chosen wire diameter is very accurately controlled within extremely close tolerances.

It will therefore be found in practice that any NEW RK meter bar will produce virtually identical surface coatings to any other NEW bar wound with the same wire size.

However, after numerous cycles of operation, wear will have taken place on the wire which will effectively reduce its diameter and therefore reduce the resultant coating film thickness produced.

In those cases where coating weight (or colour density) is critical, for example when the test is used in conjunction with computer colour matching, it is essential that bars are recalibrated at regular intervals to ensure consistent test results.

CALIBRATION PROCEDURE SELECTING A STANDARD BAR

1. Use a minimum of 4 NEW bars and make 3 or 4 drawdowns with each bar using your selected coating mix and substrate. Measure these instrumentally and first establish that the repeatability is acceptable for each bar. Secondly establish the average density or coat weight for all bars. Lastly, plot each bar against the average.

Select a bar that is slightly below average density - but within your tolerance. This will be your calibration standard.

2. Establish an allowable tolerance, relative to the above average result, that is acceptable for your particular product.

3. This standard bar should now be labelled and kept as the "standard" bar and only used for making 3 or 4 further drawdowns for comparison with bars that are being

calibrated. Calibration intervals may be as short as one month for the highest accuracy with fine wires.

It should be remembered that, in addition to wire diameter changes, the following items can all cause changes in film thickness applied and that each of these must therefore be constant when making comparisons for calibration purposes.

A. Type of substrate used

B. Coating mixture - type, viscosity, solids content.

C. Coating speed.

D. Type of coating bed.