Roll Hardness
Doctors and doctor blades should be treated with respect and caution to avoid the risk of serious injury.
Doctor blade material selection and blade thickness are primarily determined by the roll material and roll hardness.
Soft rolls (over 10-15P&J) generally use either 0.117" or 0.250" thick blades. This reduces the risk of the blade digging into the cover and causing damage.
A hard roll generally uses a thinner blade ranging from 0.035" to 0.080" thick. Final thickness selection is determined by weighing several factors. While thinner blades often clean the roll more efficiently (similar to a sharp knife), added thickness can often improve blade life since the additional material can slow wear.
Bevel Angle
Most doctor blades are supplied with a 45-degree bevel with a land area. Bevel angles are measured as indicated below. Forming section doctors and most dry end doctors perform well with this standard bevel angle. Proper bevel angle is most critical in the press section and sheet shedding doctors.
Soft rolls may require a blunt bevel to reduce the risk of roll damage. Hard rolls allow for greater latitude in selecting a bevel angle. Sharper angles may improve roll-cleaning efficiency. However, note that sharper bevel angles decrease surface area at the blade tip, and this may result in rapid initial blade wear.
Essco has developed several unique blade bevel solutions that can enhance press doctor efficiency. Specific angles can also be supplied to improve sheet shedding and directional control. Contact Essco or your representative to discuss your specific application.
Fasteners
Essco offers a complete range of blade fasteners to suit any blade holder.
A doctor blade should never be installed in a holder for which it was not designed. An incorrect blade could fall out of holder during operation, with significant risk for injury and machine damage.
Every doctor blade is designed to fit in a specific type of blade holder. Doctor blades are engaged in each type of holder by fasteners attached to the blade.
Each holder type has its own specific fastener requirements. Fasteners must be correctly sized and installed to specific specifications. Spacing of fasteners is also dependent on whether a blade can be installed in the holder from the machine aisle (END REMOVAL) or whether it must be dropped into the holder from the leading edge (FRONT REMOVAL).
Blade holder type may affect the thickness of the blade that can be used. KF-type blade holders generally accept blades up to 0.117" (3mm) thick. ETUniform and other manufacturers' pneumatic type holders are designed for a specific thickness, based on the roll hardness at time of installation.
Use of a thicker synthetic blade can be often accomplished by supplying a blade with a machined back edge or an attached backing blade. In some cases, it may be necessary to install a new pressure plate assembly.