SECTION 2 -BRUSH DESIGN, MANUFACTURE AND APPLICATION
Question 2:7 What Is The Purpose Of The Rubber/Fibre Pad On The Top?
It holds both wafers of a split brush together for ease of installation but it performs two other more important functions:
:1 Isolates the brush from the spring and prevents damaging current flowing through the spring. This is particularly important in constant force springs which are easily damaged by current flow and excessive heat.
:2 By far the most significant benefit results from using a cushioned pad comprising a hard fibre top plate with a neoprene or silicone mat underneath. The resilient pad allows both halves of the brush to move relatively independently over a small range which give much better contact over the full brush face, particularly when there are irregularities in the commutator surface.
In the case of solid brushes the rubber/fibre pad absorbs some of the vibrations or rapid movements in the brush like a shock absorber which maintains better brush face contact.
Sometimes the spring arm or constant force spring may press more on one wafer of a split brush resulting in uneven forces at the brush contact face and a slight step may be noticed between the wafers when the brush is removed.
This is not normally a significant problem as it tends to even out as the brush wears, however, if it causes problems from unequal current flow then a metal hammer plate can be used which supplies equal force to each wafer.
The benefits of the resilient pad are sacrificed with metal hammer plates. In some extreme cases a resilient pad can be attached to the metal hammer plate.
Question 2:8 Why Do Some Brushes Have An Insert Fitted In The Face?
The information has been drawn from experience of Morganite Taiwan Limited Application Specialists combined with a wide range of published information from major carbon supplier and motor manufacture. However, the material can not be downloaded, copied or used without written permission.
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