Speeds for the efficient operation of polishing wheels generally fall between the limits of 6,000 to 8,000
surface feet per minute when glue is the adhesive used. At higher speeds, because of overheating, the
glue tends to break down although polishing wheels set up with cement can safely withstand this heat up
to 9,000 surface feet per minute.
With too low a speed, the abrading operation is slowed down and, in addition, there is a tendency for
the abrasive to be ripped out of the wheel. On certain metals susceptible to physical changes because
of overheating, the ability of the adhesive to withstand heat is not the limiting factor but rather the heat
tolerance of the metal.
POST WHEELS AND FLEXIBLE POLISHING:
In the polishing coatings, described above, dry abrasive grain is fastened onto the coating of adhesive
covering the polishing medium. Although the adhesive covers the lower part of the individual abrasive
particle to grip it properly, a large proportion of the area of this abrasive grain is exposed free and
uncoated.
This open feature on the polishing face is highly desirable in many instances, particularly where fast
cutting is desirable. However, in a number of fine polishing operations, it is more desirable to have a
closed surface that is obtained by having intimate mixtures of the abrasive gain and the adhesive.
Paste wheels, where the melted glue is thoroughly mixed with abrasive and the mixture then troweled
onto the face of the polishing wheel in multiple coatings. These have long been used in the cutlery
industry particularly for double header polishing on steel knife blades. Silicate cements have also been
mixed with abrasives for similar purposes. Special techniques have been developed so wheels of this
type can be built up by frictional transfer of greaseless compound applied to the polishing wheel as it
revolves on the spindle of the polishing arbor.
APPLYING THE ABRASIVE
Flexible polishing wheels of this type are headed up by the following procedure:
A glue-base sizing material in bar form is brought to the revolving wheel, pressure is applied, and the
power is shut off. During deceleration the sizing coat is melted and flowed onto the surface of the wheel.
The motor is then turned on and off to start drying at less than full speed. It is finally run at full speed for
about two minutes or until the sizing coat is no longer sticky to the touch.
The bar of greaseless compound, also glue-base, is applied in the same manner with pressure when
the power is shut off. During deceleration the heavy coating of greaseless compound is melted and
transferred to the wheel with sufficient frictional heat, so the layer of greaseless compound is firmly
bonded to the sizing coat.
This coating is dried in the same manner as mentioned for the sizing coat and for approximately the