- Buyer's Guide
Do you listen to your motors complaining about overload? Do you see your pump packings crying a flood? Do you hear your bearings whine about contaminated lubricants? Do you notice your steam system coughing excessive condensate and complaining about strained elbows?
There are two types of people in mills. There are people who notice when
equipment show signs of distress, and people who don’t. We often call people who
don’t see the signs of distress in equipment “mill blind” people. The mill
blindness may not be intentional, but rather a product of being so used to the
environment that poor equipment condition just isn’t noticed. Let us supply you
with a small informal mill blindness test.
Below are a few examples of mill blindness that we often see in pulp and paper mills. Most of you have at some point seen these equipment problems before, but ask yourself, are we accepting these conditions or are the problems corrected in our mill?
Basic condition monitoring
Leaking rotary joints are so common in many mills that they have become accepted over the years. It’s not unusual for new employees in a paper machine area to be told that leaking rotary joints are normal, and that leaks can’t be detected before steam is coming out of the joint.
Steam joints often leak when the carbon ring wears inside the joint. The carbon ring is designed to wear and start to leak after wearing a certain amount. The wear in most joint designs can easily be measured since the carbon ring is spring-loaded and two surfaces of the joint moves as the carbon ring wears. For example, a certain Valmet model requires carbon ring change when the distance – (a) in Figure 1 – wears to 0.59 inches (15 millimeters). Many Johnson joints have a pin to indicate the amount of wear on the carbon ring.
Figure 1. Valmet steam joint.
Spare parts storage can have a huge impact on the level of planning and scheduling of maintenance jobs and the reliability of equipment. But, we often forget the direct reliability impact of incorrect management of spare parts.
Some spares are perishable goods, mostly components with rubber or plastic material such as belts, couplings and O-rings. For example, the commonly used orange peel coupling has a “best before date” when purchased. They are designed to last five to six years whether in use or stored in the store room. It is common to find couplings five years and older in stores even though their life already is exceeded.
Bearings should be wrapped and sealed in order to avoid contaminants in the bearing. It’s not uncommon to find bearings unwrapped and dusty in a store room.
Mill sites often have a small vibration in the store room from surrounding equipment. When bearings are fixed in the same position, the vibration causes fatigue damage inside the bearings, because the bearing balls keep “tapping” the outer bearing race. Shafts on stored motors should therefore be turned a quarter turn on a periodical interval to reduce the damage. Take a look in your storeroom. Are motor shafts of motors turned by storeroom personnel?
Figure 2. Top, bearing stored without protective
Bottom an “orange peel” coupling with manufacturing quarter
and year on the sticker to indicate perishable date.
Torbjörn (Tor) Idhammar is partner and vice president of reliability and
maintenance management consultants for IDCON Inc. Michael Lippig is the business development manager. Tor's primary responsibilities
include training and implementation support for preventive maintenance/essential
care and condition monitoring, planning and scheduling, spare parts management,
and root cause problem elimination. He is the author of “Condition Monitoring
Standards” (volumes 1 through 3). He earned a BS in industrial engineering from
North Carolina State University and an MS in mechanical engineering from Lund
University (Sweden). Contact Tor at 800-849-2041 or e-mail email@example.com.