Coal Preparation » General
In an earlier project, C8063, prep plant managers were surveyed with regard to maintenance requirements. There was general consensus that help in understanding poly screen wear and performance would assist prep plant managers in reducing maintenance costs.
This project gave details of a study of poly screen panel materials, maintenance methods, and performance data collected from coal prep plants in QLD and NSW.
Ex-service screen panels were collected from a range of coal prep plants in the Bowen Basin and Hunter Valley. Five manufacturers produced the poly screens. The mode of failure was determined using failure analysis techniques including determination of chemical composition, physical and mechanical properties, and fracture surface microscopy.
Four failure modes were determined; three of these resulted in dramatically reduced service life.
The failure modes were identified as:
- uniform wear
- cover delamination
- overload failure
- inclusion-initiated fracture
Modes 2-4 are attributed to inappropriate procedures during poly screen panel manufacture (faulty panels) and these modes cause early failure. The faulty panels are not attributable to a single manufacturer. A section of the report focuses on how and why manufacturing defects occur in injection moulded and cast poly screen panels.
The effect of screen panel wear and failure on operational efficiency was estimated from data obtained during the project. A measurable wear parameter that is related to the eventual failure mode could be used to identify faulty panels and to optimize screen panel maintenance. The measurable wear parameter of choice is aperture open area and size distribution.
The cost of non-optimized maintenance is reflected in the variability of the poly screen panel cost per tonne at different prep plants. This cost varied from 2 cents per tonne to 9 cents per tonne, a 400% difference.
It is recommended that the screen panel manufacturers be held responsible for inadequately manufactured materials. It is recommended that screen panel manufacturers become more involved in the next phase of this work in order to address issues of quality control. It is recommended that specification should be made during purchase of "screen panels free from manufacturing faults."