World Grain - April 2022 - 52

MILLING OPERATIONS
Reviewing
maintenance
strategies
by Jeff Gwirtz
Milling in any part of the world is a complex business. Material
handling from receiving of wheat to the loadout or packaging
of flour and feed takes many forms, including simple
gravity flow, positive and negative pneumatic conveying systems,
belt, screw, drag, oscillating, vibratory, bucket, chain,
and tabletop conveyors.
Unit operations for cleaning, tempering, and milling, including
grinding, sifting, purification and dusters often are
positioned between material handling systems and operate
intermittently or continuously. Overlay systems including
dust collections, air make-up systems, compressed air, and air
conditioning units providing heat, cooling, and humidity control
add to the complexity of the operation. Control systems
and sensors used to direct product flow, monitor performance,
startup, shutdown or suspend operation support mill operation
and control. Success for the enterprise depends on smooth
operation of these systems to meet productivity and quality
standards.
A simple flour mill with a capacity of 300 tonnes of wheat
per day (approximately 5,000 cwts or 225 tonnes of flour
per day) may have at least as many maintenance items and
a variety of input/output devices as shown in Table 1 (page
54). The number increases with equipment complexity, level
of automation and control points monitored and controlled.
Complexity increases as mills moved from line shaft powered
rolls to individual drive rolls and rolls with individual feeder
roll motors rather than feeder rolls driven by grinding rolls.
Maintenance is critically important to ensure mill operation
is uninterrupted when operation is required to meet budgeted
demand. Unplanned downtime caused by equipment failure
is costly, increasing both fixed and variable costs. Production
staff, energy and associated variable costs realized while flour
is not being produced, as well as fixed costs, are distributed
across reduced flour production. In addition to lost produc52
tion,
the equipment failure often results in increased repair
costs that could have been avoided had the equipment not
been operated to failure.
Often a precursor of failure is reduced operating efficiency
as well as inferior product quality. Worn drive belts and
bearings may increase energy consumption while improperly
grinding or classifying mill stocks resulting in inferior quality
product. Operating to failure often increases repair cost for
example, repair of damage to a worn shaft or bearing housing
caused by a worn bearing would be avoided had the bearing
been replaced at or before bearing failure. Moreover, operating
to failure often compromises safety of the working environment.
Bearings operating to failure as in the previous
example may generate heat and/or sparks resulting in a fire or
more catastrophic grain dust explosion. Catastrophic failures
may result in extreme and costly damage to assets, injuries to
personnel, compliance, and liability issues.
So, what is your maintenance strategy today? Where are
you on your journey? Is your maintenance strategy reactive
as previously described, preventive or predictive or perhaps
somewhere in between? Where are you on the timeline?
Perhaps it may be appropriate to investigate the Society for
Maintenance and Reliability Professionals (https://smrp.org)
to gain insights into the possibilities for maintenance and reliability
improvement opportunities.
Reactive: 1970s
In the 1970s and earlier, maintenance often was based on
equipment needs or demands. Differed maintenance often resulted
in emergency repair activity, which often resulted in
collateral damage requiring considerable time and expense
to correct. In most cases, information about plant equipment,
drives and control systems was not well documented or managed.
Maintenance was relegated to putting out the fires necApril
2022 / World Grain / World-Grain.com
Where are you on your journey?
http://www.World-Grain.com
World Grain - April 2022

Table of Contents for the Digital Edition of World Grain - April 2022
