Torbjörn Idhammar, President, IDCON INC
How to Document Cost-Effective Maintenance Tasks: Part 7
Part 6, “Components” covered going out in the plant to the hydraulic unit to collect information. The next step is to select the maintenance method so we can start documenting the Preventive Maintenance actions that need to be done to the hydraulic unit.
Maintenance Method Definitions
Operate to Breakdown: The equipment is run until it breaks down.
Fixed Time Maintenance: The replacement of parts or equipment on a fixed/scheduled frequency.
Condition Based Maintenance: The problem is found and fixed at the time when it is discovered.
It is a common assumption that Condition Based Maintenance is always the most cost effective. While this is commonly the case, it is not always true.
How to Choose a Maintenance Method
The following is an overview of how to choose a Maintenance Method using a motor on the hydraulic unit as the example component:
Operate to Breakdown
When deciding if Operate to Breakdown is the most cost-effective maintenance method, the consequence of operating to breakdown must be determined. In the case of this motor, if it runs to breakdown, the hydraulic unit and the log ladder (pictured below) that it feeds will stop running.
This will cause a production break resulting in $7,000 to $8,000 lost profit per hour. This maintenance method can be ruled out for this motor.
Fixed Time Maintenance
Fixed Time Maintenance can be used when the life of the equipment or component is known.
In this case, the life of the motor is not known precisely. There may be an average life known for the type of motor, but the life of a motor can vary from four to twenty years depending on the environment it is kept in, how well (or poorly) it is maintained, etc. so we don’t know the exact life of the motor.
Because the life of this motor cannot be determined exactly, this maintenance method can be ruled out for this motor.
Condition Based Maintenance
By process of elimination alone, Condition Based Maintenance is the maintenance method that will be used for this motor.
In most cases, asking these simple questions (What is the consequence of operate to breakdown? Is the life known?) is enough to correctly select a maintenance method, but occasionally it is necessary to perform a financial analysis to decide between the three choices. Learn more about that in this video.
Some components may benefit from a combination of Fixed Time Maintenance and Condition Based Maintenance. When using both, the condition of the component can be checked as well as replacing the component after it has been run for a specified period of time.
Preventive Maintenance vs. Preventive Maintenance Program
Preventive Maintenance and Preventive Maintenance Programs are not exactly the same. Preventive Maintenance is any action that can prolong life and predict a failure early. This action may not be a repetitive action.
Repetitive actions are what make up the Preventive Maintenance Program, while all actions (including repetitive) that prolong life and predict failures early are considered Preventive Maintenance.
Therefore, all PM actions are considered Preventive Maintenance, but are only considered part of a Preventive Maintenance Program if they are repetitive.
Design for Reliability, Inspectability, and Maintainability
Designing for reliability, inspectability, and maintainability should be done before the equipment or component is installed.
For example, if a new motor were to be installed, actions can be taken to facilitate Preventive Maintenance and prolong life. These actions include but are not limited to:
- Ensuring that the component is accessible for easier inspection.
- Ensuring that the component is correct and works best for the equipment.
- Ensuring that the component is installed correctly so that it can be balanced and aligned.
Along with these actions, continuous actions such as operating the motor correctly and updating the operator instructions with specific directions for correct operation are helpful behaviors to prolong the life of the component or equipment.
Another way to prolong life that may not be on a scheduled basis is using Design Out Maintenance. An example of this is to use sealed bearings in the place of lubricated bearings to remove the need for lubrication.
Select the Most Cost-Effective Maintenance Method
Sometimes, you may go through the steps, select Condition Based Maintenance, and then find that it cannot be done because there are technical restrictions or because the component is not accessible. Many times, this is caused by a guard blocking the component. In this case, the only choice may be to Operate to Breakdown. In this case, the guard may need to be redesigned or remote sensors removed to allow for inspections – there are different options for solving the problem.
Of course, the best choice is the most cost-effective Maintenance Method, but if you are forced to Operate to Breakdown, the job to repair or replace should be planned (but can’t be scheduled because when the breakdown will occur is unknown), and the parts and tools should be kitted and ready before the breakdown occurs.
Simply going through the thinking process of selecting the most cost-effective Maintenance Method will help maintain a solid Preventive Maintenance Program because it will be based on logic and what is most cost-effective as opposed to every department setting up a separate Preventive Maintenance System.
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