When ground parts start
to rust, the first reaction is to increase the coolant strength. This usually
starts a vicious cycle of increased abrasive wear and parts out of tolerance,
with the subsequent changes in abrasive specification and new trials.
Rust is caused by low
pH, (refer to the technical report of pH) poor coolant control and the depletion
of rust inhibitors from the coolant.
Rust can also be
caused by:
1. A Slow Drying Rate.
Anything that can be done
to speed the rate of drying will help. Rack the parts, reduce the tote box
loads or move parts to a warm, dry area.
2. Bacterial growth
of acids in coolant.
Bacteria cause the formation
of acids in the coolant solution, which will lower the pH. When coolant becomes
foul, it must be changed completely.
3. Suspension of fine
metallic particles in the coolant.
As an example, fine iron
oxide is introduced when grinding rusted parts. When these particles are deposited
on a freshly ground surface, a galvanic cell is formed, which will start electrolytic
corrosion.
With proper care and control,
rust can be eliminated without upsetting the operation.
