In this article Jason discusses best practices when feeding a crusher.
Factors needing consideration when setting the primary crusher feeder speed and loading of the feeder
How much material can the rest of the crushing circuit handle ? Could it cause spillage or an overload situation in the rest of the circuit?
The type and size of the feed material (ROM) that is being loaded into the feeder hopper.
Is the crusher sitting on level ground ?
Is there a lot of fines? Is there no fines?
Is the material wet?
Is there a high percentage of clay?
Is there contaminants like steel or timber in the feed?
If your material has these properties the feeder speed will need to be adjusted accordingly or you could overload the rest of the circuit or cause blockages. Then it becomes time to get out the shovels and start digging and I haven't met anyone yet that loves digging out a bogged crusher or screen.
Different operators will feed at different speeds and with a variety of bucket fill levels resulting in different amounts of material in the hopper. This greatly affects the speed that the material moves in the feeder.
The higher the moisture content of the feed material, the slower the material moves and will cause build-up and further slow production. Adjustments will need to be made during the shift if the material changes from dry to damp/wet. This must be monitored.
Clay or rocks jammed in the grizzly/bofor bars will cause the material flow to slow dramatically and build-up in the fines chute that will also cause serious damage if not cleared regularly.
The plant will always be more productive with an even constant feed of material. It is critical that the material is loaded to the back of the hopper to give the grizzly or pre-screen the best chance of removing the fines, resulting in higher production and less wear.
Feeding the crusher
Always check that the crusher is on level ground with no cross fall or you will get uneven feed, cause uneven wear and potentially damage the crusher.
If the crusher is setup on ground that is facing uphill, the feeder will have to work harder to move the material. Flat or a 1-2 degree downhill angle is acceptable.
It is preferable to feed with an excavator and easier to achieve proper crusher feeding than with a wheel loader tipping side on. If loading with a wheel loader it is preferable to install hopper extension wings and feed from the rear. This gives the feeder a chance to remove the fines instead of getting a huge surge of material onto the grizzly / pre-screen from the loader feeding side on.
When feeding an impactor with an excavator always feed from the side or on an angle – never directly behind to avoid being hit by ejected material. When loading from the rear of an impactor it is important to ensure that the crusher chains and rubber curtains are well maintained to reduce the possibility of rock being ejected backwards at the operator’s cab.
Do not push the material forward in the feeder. This will overload the grizzly and the crusher as the thickness of material keeps changing and every time the feeder stops due to high engine load, you lose production.
For best results you need consistent, even feed into the hopper.
Do not fill the feeder to capacity - constant steady feed rate will always result in higher production over the day, week or month.
Do not drop large rock onto the hopper wings – place it on top of the material on the feeder floor.
Do not try to force large rocks into the crusher with the bucket or ripper tine. This can result in catastrophic damage. Better to remove them safely using the correct tools or lifting gear.
An excavator on a decent loading pad can watch more closely what is in the feeder and can see what has or is about to come out of the bucket. An excavator operator has a better chance of seeing an over-size rock or tramp metal than a wheel loader operator. If the crusher is fitted with a radio remote the operator can switch the feeder off to minimise the issue.
An excavator operator can also monitor build-up on the feeder floor better than a wheel loader operator.
Always keep a bed of material on the floor of the feeder to provide a cushion against large rocks directly hitting the feeder. Doing this can also help with stopping bigger rocks getting jammed just off the floor of the feeder. Big rocks hitting the floor will result in reduced feeder life and will increase wear.
The grizzly needs to be regularly monitored to check for build-up and with damp clay material, the gap between the feeder and the hopper wings needs to be monitored or a lot of vibration will be transferred from the feeder to the hopper wings resulting in damage to both. This can also result in vibration being transferred to the rest of the machine and cause further damage.
The crusher bypass chute needs to also be checked regularly. If the chute is blocked, the feeder operation will slow due to the extra weight, more fines will enter the crusher resulting in high engine loads, increased wear, higher fuel burn and will transfer vibration from the feeder to the chute resulting in cracks or damage to the feeder and the chute itself.
In summary to ensure the highest production and the least maintenance, ensure that the crushers and screens are always;
on level ground
fed at a constant smooth rate
monitored for build up on the feeder and grizzly / pre-screen
adjusted to compensate for changes in feed properties from fine, coarse, dry or wet
fed with no over size rock or concrete that will cause issues - pre-treat properly
Written by Jason MacDonald, Product Manager - Crushing and Screening at Onetrak Pty Ltd