determination of doctor angle
DESCRIPTION
A simple and quick method for determination of angle of doctor blade on any roll.TRANSCRIPT
Importance of Angle MeasurementImportance of Angle Measurement
� Doctor angle plays a significant role in getting proper doctoring results. Too steep an angle can damage the roll surface and/or doctor blade itself, while too little and/or doctor blade itself, while too little an angle may result in inadequate cleaning of roll surface.
February 2014 2Determination of Doctor Angle
A Simple ApproachA Simple Approach
� The objective of this presentation is to show a simple, very simple tool to determine angle of doctor blade on any roll.roll.
� However, it is always recommended to get a proper doctor angle measuring device from some good supplier.
February 2014 3Determination of Doctor Angle
Items RequiredItems Required
� Two templates similar to these indicated.
(You may use two identical visiting cards for this.)
� Scissors.
February 2014 4Determination of Doctor Angle
Step OneStep One
� Cut these along dotted lines.
February 2014 5Determination of Doctor Angle
Step TwoStep Two
� You will get shapes as under-
Template A Template B
February 2014 6Determination of Doctor Angle
Template Template A PositionA Position
Hold template A in such a way that its one corner touches the desired roll at the point of doctor blade, and the line indicated in red color in aligns the doctor blade.
February 2014 7Determination of Doctor Angle
Template B PositionTemplate B Position
Hold template B in such a way that its one corner touches the desired roll at the point of doctor blade, and the other corner touches the roll.
February 2014 8Determination of Doctor Angle
MeasurementMeasurement
Place both templates as shown in the figure, and measure overlap angle on template B. The overlap angle is the doctor angle (almost) for larger size rolls. However, there would be a minor error for smaller rolls which needs to be corrected as shown in next slides.
February 2014 9Determination of Doctor Angle
Scaling Scaling of Template Bof Template B
25 24 23 22 21 20 19
| | | | | | |
For ease, the top side of template B can be scaled as shown in figure above.
Whenever you need to measure angle of any doctor blade, just measure directly from these, compensate for correction factor, and get the correct angle immediately.
February 2014 10Determination of Doctor Angle
Determination of Error AngleDetermination of Error Angle
Error Angle
It can be shown that the error angle isA function of roll diameter and template Length.It can be given as e’ = Sin-1(L/D)Where,
L is template length andD is roll diameter.
February 2014 11Determination of Doctor Angle
Error Due to Template BError Due to Template B
� The error caused by the limitations in design of Template B decreases with increase in roll diameter. Some typical values are as indicated for template length values are as indicated for template length of 75mm-
◦ Roll Dia. Error Example
◦ 750mm 5.7˚ Press Roll
◦ 1500mm 2.9˚ Dryer
◦ 4250mm 1.0˚ 14’ Yankee
February 2014 12Determination of Doctor Angle
Correction of ErrorCorrection of Error
� The error, though it is a minute one, can be added to the measured angle value to get the correct doctor blade angle.
February 2014 13Determination of Doctor Angle
Measured AngleMeasured Angle
� Doctor angle can be expressed in two ways.
◦ With reference to radial line (BSI), and
◦ With reference to tangential line (ASTM)◦ With reference to tangential line (ASTM)
� This method gives angle along tangential line.
� To get angle along radial line, just subtract the angle computed from 90˚.
February 2014 14Determination of Doctor Angle
Angle MeasuredAngle Measured
� After you have got the running doctor blade angle, you may check with the supplier guidelines whether it is correct or needs to be altered.or needs to be altered.
February 2014 15Determination of Doctor Angle
Happy Doctoring!
Please send your comments and feedback to:
February 2014 16Determination of Doctor Angle