World Grain - April 2022 - 54

MILLING OPERATIONS
Table 1
Example of maintenance items
and I/O in a 300-tonne-per-day mill
Maintenance
Item
Motors
Belts
Bearings
Gear Reducers
Air Control
Valves
Air Cylinders
VFD
Table 2
Number Measurement
Input/Output
160
274
686
56
81
144
26
Amperage
Pressure
Temperature
Flow rate/Level/Presence
Motion
Alignment/Position
Stress/Strain/Load/Yield
Emerging and developing preventive
maintenance technologies
* Infrared analysis
* Thermographic
* Motion amplification * Vibrational analysis
* Motor circuit analysis * Ultrasonic inspections
* Precision alignment
* Dynamic balancing
essary to keep the plant in operation. Monitoring often was
limited to sight (vision), hearing (auditory), smell (olfactory),
taste (gustatory), touch (tactile) and vestibular (movement and
balance sense).
Maintenance store rooms were filled with materials and parts
that may or may not be required resulting in non-productive
financial investment and poorly controlled inventory. Some
mill's maintained " bone yards " of used equipment, including
motors and drives in various states of condition that would be
used in emergencies to keep the facility operating. Maintenance
costs were significant yet failed to provide for plant operation
meeting budgeted levels of performance. Often, the budgeted
performance level or productive run time was set based on the
ability of keeping the plant in operation. Improvements were
planned but often fell short.
Preventive: 1990s
Maintenance employees started to realize
the best way to address a problem
is to prevent the problem from occurring.
Time to failure was recognized
as a factor and considered in the development
of early preventive maintenance
activities based on equipment
maintenance requirements. As a result,
inspections at planned time intervals
combined with parts replacement prior
to failure became more prevalent.
More information about plant equipment,
drives and control systems was
being documented and managed in
54
April 2022 / World Grain / World-Grain.com
spreadsheet or databases to develop a schedule and strategy.
Unfortunately, some schedules were adhered to without a
much closer examination of costs or impact. For example,
positive displacement blower oil may have been changed on
a time schedule independent of oil condition. Disposing of oil
with remaining time in its lifecycle was a waste of resources
and included the cost of oil, disposal costs and labor.
Nonetheless, this was the beginning of preventive maintenance,
which became more refined as it transitioned into a more
advanced approach to preventive maintenance in the 2010s.
Preventive: 2010s
Planning of preventive maintenance activities became more
condition-based but easier to handle with the use of computers
and development of Computerized Maintenance Management
Systems (CMMS). Even greater amounts of information
about plant equipment, drives and control systems were being
documented and managed by CMMSs.
The systems were able to develop inspection, maintenance
and repair schedules, including identification of material requirements,
skill crafts required, safety issue and personal
protective equipment requirements and time allocation. Work
orders could be issued, assigned and status monitored.
Storage rooms became leaner, smaller, neater, with inventory
more well managed. As preventive maintenance in the
2010s progressed, it was not only based on equipment but also
the use of sensors and devices considering time, failure, and
condition of equipment in operation.
For some millers in older plants, the use of CMMS presents
a significant challenge due to the need for equipment and drive
information input and personnel support required to realize system
potential. With newer construction, perhaps the information
was more readily available but still required verification as
plans and reality often intersect during installation and startup.
New preventive maintenance methodologies emerged inAs
the " heart " of the milling process, roller mills must be
properly maintained to ensure profitability.
Source: Jeff Gwirtz, Photo courtesy of Bühler
http://www.World-Grain.com
World Grain - April 2022

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