Exploit.
The next step of a shutdown is
to maximize the use of the key mechanics as much as
possible. When the machine is down for 24 hours a day,
the local workforce isn’t scheduled for even half of
that downtime. However, if the machine is scheduled to
be down for 12 hours or less, then the key mechanics
can work for the majority or all of the planned
downtime. This kind of scheduling improves both the
use of the key mechanics and their work ratio relative
to the length of machine down-time. It is equivalent
to having a brief maintenance time put into the
regular production schedule and executed as if it was
a product run. If you stop the machine for the length
of a shift, or less, then almost everyone has the
opportunity to complete one shift of maintenance work
without leaving the job site for rest. This concept is
called maintenance linestop.
The chronology of an ideal
maintenance linestop might have the following
schedule. The machine shuts down at 7:00 A.M. and is
left threaded with non-product slack web. This process
may take 30 minutes. Maintenance begins executing a
priority work list at 7 A.M. beginning with periphery
equipment while the machine is threaded with
non-product web.
They complete as much work as
possible and taper down the job size near the end to
be completed at 5:30 P.M. The next steps are clean-up
and machine prep, followed by conveyance checkout;
these take approximately 90 minutes. The machine
startup with product is conducted at 7:00 P.M.
Allowing 0.5 hours for lunch, the amount of work time
a key mechanic has available is about 9 work hours,
providing a work hour to linestop downtime ratio of 75
percent.
|
9
work hours
12 hours total |
=.75 or 75% |
This maintenance linestop approach
is advantageous for low-risk, short-duration tasks that
do not alter the existing process. It is perfect for
both periodic maintenance (PM) and predictive
maintenance (PdM) jobs as well as for modular
replacement of bench tested (certified) subassemblies,
which engages a spare part strategy.
For example, assume that twelve
identical pumps are used in the machine and two spare
pumps are stocked. Assume removing and replacing each
pump requires 30 minutes and that rebuilding and testing
a pump requires one hour.
With two long shutdowns, an annual
PM strategy might be to overhaul five pumps during each
shutdown by disassembly, replacing parts, reassembly,
replacement and realignment in the machine, as well as
modular replacement of one spare pump each shutdown.
This approach saves one spare pump for infant mortality.
