By Nick Mike, NGM Tissue Consulting, LLC
THE PROBLEM: Unexplained breaks, picks and yankee coating issues.
SOLUTION: Use a GONIOMETER to measure doctor blade wear angles.
The GONIOMETER is a neglected but very important tool for diagnosing doctor blade issues in tissue mills. The GONIOMETER measures the wear angle of the doctor blade. This is different than the wear pad. The wear angle of the doctor blade is identical to the doctor tip angle. See diagram below. Why is this measurement important? If the wear angle is not uniform in the cross direction there is nonuniform pressure and attack at the sheet/coating interface by the blade. This could allow more or less yankee coating to be taken off or interfere with the sheet matrix. If the doctor blade is pressing lightly in one spot the tip can pick the sheet. If its pressing too hard, it could be removing too much coating and allowing the blade to contact the yankee surface. This can cause corrugation to the reel or damage to the yankee.
In this example there is a high front edge wear angle on the front and the low wear angle around 30 and 112 inches. This high reflects not enough blade pressure and the low at 24 and 112 inches indicates there is t00 much blade pressure.
The goniometer works by directing a light source on a flat used blade. As the light source is rotated, the brightest flash is the point where the blade angle is perpendicular to the light and can be measured on a protractor scale on the unit. A Vernier sub scale allows the measurement to accurately measure up to on tenth of a degree. More advanced goniometers can incorporate an electronic inclinometer for direct digital readouts.
Nick Mike of NGM Tissue Consulting, LLC can be reached by calling 603-616-8931, or by email at firstname.lastname@example.org.