When it comes to inventory availability, it’s important to have the
right parts in like-new condition to best support maintenance
operations. The standard used by many is the same method that the
Original Equipment Manufacturers (OEM’s) and distributors use to store
spare parts.
The location where some spare parts are stored is critical to meeting
the “ready to use” requirement. Minimizing the effects of temperature
and humidity is basic, but the protection of parts against the effects
of handling during cycle counts and normal store room movements is also a
contributor. When possible, it is favorable to have vendors keep the
spare parts on their shelves and use a “Just In Time” delivery agreement
for access. When not possible, precautions must be taken. Parts that
are not in prime condition for use are just as detrimental as no parts
at all.
Table 1 shows several types of parts kept in most warehouses or unit
locations that need special attention and the category of environmental
hazard for these parts.
Electrical Parts.
For many electrical parts, particularly parts with circuit boards,
the three main environmental hazards that need to be guarded against are
temperature, humidity and Electro Static Discharge (ESD).
During the last twenty years, the nature of electronics used in
running a manufacturing plant has changed through the use of more
advanced computer controlled equipment. This equipment relies on the
use of printed circuit boards that require a low humidity environment
with little fluctuation in temperature. Changes in temperature and
humidity can cause the micro connections between the components and the
printed circuit board to separate or warp. These components are also
subject to short circuits from small amounts of voltage, the source of
which can be as small as a micro-discharge from the person holding the
part. For this reason, these electronic parts must be kept in their
special ESD packages, usually a black bag made of non-conductive
material originally supplied by the manufacturer. These parts can be so
sensitive that even when ESD parts are removed from their special
package, the handling person should be grounded using a specially
designed ground strap to avoid ESD damage.
Figure 1 is a picture of a typical electrical assembly properly
packaged in an ESD bag and enclosed in a custom fit foam container. All
employees should be alerted to “black-bag” parts and the caution
required to keep them functional.
Belts and Hoses.
Belts and hoses are subject to degradation over time from the affects
of UV light, heat, cold and humidity. Unfortunately, there are no
black or silver EDC bags to alert users of belts and few plants
accurately date or rotate belts and hoses when aging occurs. Since many
of the hoses and belts kept in a store room are an insurance spare,
these parts may not have a high turnover. When possible, it is best to
allow the part supplier to keep these in their environmentally
controlled warehouse. This will ensure fresh parts are available for
use when needed. If not possible to keep the parts at the distributors’
warehouse, belts and hoses should be stored in an environment that is
air conditioned in the summer and heated in the winter and not in direct
sunlight. The store room should apply First In, First Out (FIFO)
stocking practices so that the oldest parts are used first. In extreme
cases, a lifecycle approach may recommend discarding and replacing dated
belts and hoses after x number of years. We also recommends the use of
flat storage wherever possible and hanging storage only with
appropriate fully supportive fixtures.
Figure 2 shows properly stored gaskets.
Electric Motors.
Electric motors offer another possibility for degradation due to
humidity, temperature extremes and vibration. All motors should be kept
in the same low humidity and stable temperature environment as belts
and hoses, but they also require regular shaft turning to avoid low
spots on the armature and coils and damage to the bearings from false
Brinelling. Motor turning can be managed through the use of tags
attached to each motor that show the last turn date similar to the
inspection date on a fire extinguisher. Electric motors with horsepower
greater than 25 should be kept heated through the use of electric
heaters. This will prevent shrinkage and expansion from the effects of
cold and heat on any metal parts that have different coefficients of
shrinkage during temperature fluctuations.
Figure 3 displays an electric motor stored in a low humidity, heated
and cooled warehouse. Note the numbers on the motor used to align and
indicate position on the shaft key way after rotation. The date and
position of rotation is also noted on the blue tag affixed to the
motor. The motor is bolted to a wooden skid to lessen area vibrations
and ease movement
Summary.
It is important to recognize many of the parts kept in a maintenance
store room can be subject to degradation and damage from the effects of
the environment and improper handling or storage techniques. Keeping
unknown defective parts on the shelf for emergencies will compound a
break down when the defective part is installed and subsequently
removed/replaced because of improper storage. Whenever possible, the
use of the distributor’s stock should be used as this stock is turned
over more frequently than the plants’ stores stock. Typically,
distributors and manufacturers are more likely to keep parts in their
stores under tight environmental and handling controls.
If keeping parts on-site, keep them on-site correctly! Hidden damage
is worse than known damage and will cost the site more in the log run.
