It is our experience that too many people lean towards too late, the optimum time to change a liner really depends on how much money you are prepared to lose to production losses to get the maximum use out of a wear component.
The first condition that is optimum is that the liner change happens when you planned it. This gives you the opportunity to have all of the required parts on hand before starting. This also allows you to perform other maintenance work on other equipment when the change is being conducted. These days it’s tough to get screen media and manganese on a moment’s notice and you will need to plan things if you need to rent a crane.
The second condition is changing the liner before you start to suffer significant production losses. On top adjust/screw adjust cones this is especially true as the feed size starts to shrink pretty dramatically as soon as you get to the last 1/3 of life and as you near the end the feed size can get very small, losing as much 30% of feed size. This is less of an issue with hydrocones as the feed size remains constant throughout the life of the manganese.
You should have a pretty good idea when you will need to change manganese and be able to have all of the parts on hand prior to needing to change. By having an accurate belt scale, you can know to the day when your production starts to tail off to the threshold and schedule the change immediately.
What is the threshold for a liner change? We believe the maximum threshold for a liner change is as follows: Change your liners no later than a 10% decline in production.
Production rate: 200 tons per hour of sellable? minus Crush Margin $2.50 per ton hours per day 10 production hours per day.
Therefore a 10% reduction in production results in a loss of $2,000 per day in gross profit. All of the other fixed and “variable” costs of labor and fuel keep adding up at the same rate. At $10,000-12,000 per week it doesn’t take too long to rack up serious losses, in two weeks you could afford at least two new sets of liners!
Some may say that times are tough and we can’t sell everything we can produce so why not get the last ton out of that set of manganese? If you conduct four liner changes per year and you delayed each change by two weeks, you add forty four hours of operation time to your season, that’s a whole week of wages and fuel!
Simple, have an accurate belt scale, plan your liner change and do it no later than when you notice a 10% decline in production. When do you change cone liners?
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