The thought of unscheduled plant downtime during the height of the production season is enough to keep operators lying awake at night. This is an unfortunate reality if a plant's major wear components are ignored. Big wear items — those that take several days or weeks to properly repair or replace — unexpectedly going down during the paving season can lead to a long downtime period, halt paving activities and cost producers tens-of-thousands if not hundreds-of-thousands of dollars. A well-planned service program should be an extension of a well-organized inspection program that is conducted throughout the year.
When developing an inspection program, the first place to start is to review the manuals that are shipped with the plant. Inspection guidelines are given in the maintenance and lubrication guides supplied by the manufacturer. The manuals will call out the wear items and give producers a check list to follow.
The guides will also give the estimated service life for major wear components, based on the number of tons produced by a plant. Over a period of time, operators will also be able to spot the little warning signs that signal potential problems with a certain plant component. For example, particulates starting to escape the baghouse are a clear indicator that the bags will soon need replacing.
Preparation for repairing or replacing the big wear items with long service times begins during the paving season with routine inspections, and companies should be prepared to make the repairs during a scheduled downtime.
Common wear components
The primary concern that big wear items pose for producers is the time they take to service. This is why these components are left to the winter season for repair or replacement. It is not essential that the wear item be to the point of failure before replacing. Savvy producers will attend to components that are questionable as to whether or not they will make it through another paving season. They know that it is much less costlier to service a questionable component than it is to suffer an expected downtime event during the height of the season.
For the drum, producers can inspect the drum liners, shell, and flights, especially the veiling flights. The area between the material inlet and the asphalt injection point is where the majority of the wear occurs. Liquid asphalt serves as a lubricator and, therefore, reduces wear on the flights past the injection point. When planning for drum wear, producers must keep in mind the type of aggregate being used in the mix designs.
Manufacturers recommend the burner's blowers and exhaust fan should be balanced once a year, and the winter months are a good time to do this. At the same time, inspect all of the burner's safety devices, i.e. shut-off valves, and immediately replace any questionable components.
Another high wear, big ticket item that should be serviced is the drag conveyor. The drag chain, flights and floor are all subject to wear throughout the paving season. A tip when servicing the drag conveyor — lay the conveyor on the ground when working on it. It's safer, and it saves the crew time, since it eliminates the need to constantly go up and down when replacing parts.
To enhance loading safety, any wear uncovered in the silo cone liners should be addressed during the shutdown. The cone area withstands a great deal of weight from stored asphalt and properly servicing the liners will help to avoid a catastrophic event.
Wintertime is also a good time to rebuild large plant gear boxes. Drive gears for the drums, drag chains and pugmills serviced during the off season will limit the possibility of unscheduled downtime during the paving season. Oil samples taken throughout the paving season will aid in the detection of gear boxes that need to be rebuilt.
The production shutdown is also the time to perform thorough inspections of items that don't typically get checked during the paving season. Items such as the ductwork, cyclone/pre-cleaner and drum shell thickness should be inspected for wear and repaired as required. In addition, replacement of baghouse bags and repairs to silo transfer conveyors should be made during a scheduled shutdown.
Drive sprockets and chains may need replacing throughout the paving season, and maintenance crews should make a template of a new sprocket for fast wear inspection. More than a quarter-inch wear means it needs to be replaced.
Finally, don't forget about the controls. The computer controls are the quickest items to become obsolete on a plant. Unfortunately, many producers don't find out that their controls are obsolete until a problem occurs. Then it is a more costly problem to fix.
Frequent maintenance approach
For producers who do not have the luxury of shutting down for a month or more to repair wear items, they must schedule multiple shorter-duration downtime periods throughout the year. This makes the routine plant inspection all the more critical. These examinations must flag those components that need replacement, and the maintenance crews must have the repair parts on hand prior to the scheduled downtime period.
It's essential for a producer's longevity in the business to keep a well maintained asphalt plant. Routine inspections, scheduled downtime and keeping inventory of wear parts will keep a producer operating efficiently and profitably, minimizing the potential for unscheduled downtime.