12 tips to maximize cone crusher productivity

1. Operate at a consistent closed-side discharge setting (CSS)

In order to gain a consistent aggregate quality, quantity and uniformity and achieve a balanced circuit, employees should operate cone crusher at a consistent closed side discharge setting. It will result in less production and more over-sized aggregate, if the crusher is operated at a wider-than-optimum setting, even if done only temporarily. In addition, over-sized product almost always causes issues in the circuit flow.

An example regarding the effect that crusher setting has on the product gradation is as follows, if the target crusher setting is 3/8 in. (10mm) yet the setting is not checked and it wears open to 1/2 in. (13mm), then the end result is a 15 percent decrease in the minus 3/8-in. (10mm) material size. There is a significant decrease in cone crusher productivity. If crushers are not being operated at consistent close side settings, many aggregate producers lose some of their revenue – and the size of the amount could really surprise them. Therefore, it is good to check the crusher’s setting on a per shift basis.

2. Operate at a consistent “choke fed” cavity level

The product will have an inconsistent shape and the production rate will be inconsistent, if the crusher is being operated at different cavity levels during the shift. When operating at a low cavity level, also known as half cavity, the product gradation will be much coarser. This level makes the product particles flatter and more elongated. A proper choke-fed cavity level should be pursued as it will increase crusher throughput tonnage and result in a more cubical product – especially with tertiary (short head) crushers that make the most of the producers’ salable products.

3. Avoid trickle feeding the crusher

Try not to trickle feed a cone crusher. In addition to causing poor cone crusher productivity and product shape, trickle feeding has an impact on bearing alignment within said crusher. A crusher should be operated above 40% but below 100% rated horsepower in order to maximize cone crusher productivity and to have a proper “loaded bearing alignment”. An optimal power range is to operate between 75%-95%. Operating a crusher above 110% rated power can cause premature crusher failure.

4. Make sure the feed is evenly and vertically distributed

Try to direct the incoming feed material so that it is distributed vertically into the center of the crusher. This will ensure that all sides of the crushing cavity remain evenly filled. If the feed is directed somewhere else other than the center, it will cause over-sized product, more flat and elongated product particles and a low crusher throughput tonnage.

In this situation, the operator will typically tighten the crusher setting in an attempt to produce a smaller product size, which can cause an over-load in the form of adjustment ring movement on the side that is heavily loaded. Over time, in this condition the adjustment ring can become tilted on the main frame and it can cause a bigger loss in productivity. With correct feed distribution, maximum crusher capacity, more consistent product uniformity, significant reduction of the adjustment ring action, minimum pressure on the bearings, reduction in energy consumption and even wear of the liner can be reached.

5. Make sure the feed is not segregated

The feed material entering the crushing cavity should not be segregated but should be well mixed and homogenous. The feed can become segregated when bigger stones are directed to one side and smaller ones to the opposite side of the crushing cavity. In this case, the smaller stones will have a higher bulk density which can cause a condition called “packing” or “pancaking”.

Packing makes the adjustment ring move on the side of the crusher where smaller stones are, and this movement forces the operator to open the crusher setting. Opening the crusher setting eliminates the over-load condition but it will cause oversized product because of the setting increase. Also, if the feed becomes segregated and if the adjustment ring is jumping or bumping, the ring can become tilted which leads to even a larger loss in cone crusher’s productivity.

6. Minimize surge loading for a more efficient circuit

Surge loading has a bad effect on the production of any crusher. Surge piles or feed hoppers along with variable speed feeding devices can be used to provide a better and more consistent feed control to the crusher. This makes it possible for the operator to run the crusher at a very consistent and stable cavity level. Cone crusher productivity can be easily increased by a minimum of 10 % by having better feed control. It can be achieved by using surge piles, hoppers and variable speed feeding devices such as belt conveyors or vibrating pan feeders.

7. Know the cone crusher’s design limitations

There are a few design limitations in each cone crusher: the volumetric limit, the horsepower limit and the crushing force limit.

Volume limit

Regarding the volume limit, each crushing cavity has a volumetric limit that determines maximum throughput and a choke-fed crusher is operating at its volumetric limit. The volume limit is exceeded when feed material overflows the top of the crusher.

Horsepower limit

As for the horsepower limit, each crusher has been designed to operate at a maximum power draw, and power draw will increase as the feed rate increases and as the feed material is crushed finer. The horsepower limit has been exceeded when the crusher draws more power than it is rated for.

Crushing force limit

Lastly, we must not forget about the crushing force limit of the crusher and as with the horsepower limit, crushing forces being applied between the mantle and bowl liner increase as the feed rate increases and as the feed material is crushed finer. The crushing force limit of the crusher has been crossed when the adjustment ring jumps, bumps, bounces, wiggles or moves on top of the main frame.

An “ideal” operational condition would exist when the crusher is operating at its volumetric limit while still being slightly below both the horsepower limit and crushing force limit. Operating any crusher “outside” of its designed parameters with either excessive power draw or with excessive crushing force results in a very serious crusher over-load. These over-loads create something known as “fatigue damage” which is permanent, irreversible and cumulative. Without a doubt, frequent over-loads will shorten the life cycle of any cone crusher. 

8. Operate within the crusher design limitations

If you find the crusher operating in a crushing force over-load condition (ring movement) or a power over-load condition (excessive power), open the crusher setting slightly, but try to stay choke fed. The benefit of staying choke fed is that there will still be rock-on-rock crushing and grinding taking place in the crushing cavity. This helps to maintain good cubical product shape even though the setting is slightly larger than optimum.

The other option of course would be to decrease the feed rate to the crusher. The disadvantage of this option is that product shape would typically suffer. Most common reasons for adjustment ring movement or excessive power draw are tramp events, poor feed distribution, segregation of the feed, too many fines in the feed, high moisture content, wrong mantle and bowl liner being used. It is also possible that the operator is simply trying to operate at an unrealistically small closed side setting.

9. Monitor and maintain a proper crusher speed

The crusher will slow down and the belts will slip when proper drive belt tension is not maintained. This will cause unbelievably high power peaks at a very low crusher throughput tonnage. Improper or neglected drive maintenance will result in a high-horsepower consumption at a low crusher throughput tonnage. This inefficient use of connected horsepower will cause a higher than normal energy cost per ton of material crushed.

A speed sensor can be used to monitor the crusher countershaft speed and will send a “warning signal” of a slowing crusher to the PLC or it could be wired to simply turn on a “warning lamp”. When a warning is detected, the maintenance department can be dispatched to re-tighten the drive belts. When a speed sensor is used, drive belt life is extended, and proper production levels can be maintained.  

10. Determine the percentage of fines in the feed

"Fines in the crusher feed" is defined as material entering the top of the crusher which is already equal to or smaller than the crusher's closed-side discharge setting. As a rule of thumb, the maximum number of fines in the crusher feed should not exceed 25 percent for secondary crushers or 10 percent for tertiary crushers. When there is an excessive quantity of fines in the feed, it is typically the result of a vibrating screen problem. This problem could be because the screen is insufficient in size or a screen which is properly sized but is inefficient in operation.

Re-crushing and re-handling product size material due to vibrating screen, inefficiencies due to the way the screen is originally set up or due to improper vibrating screen maintenance will lead to an excessive quantity of “fines in the crusher feed”. This in-turn will lead to inefficient use of connected crusher horsepower and a higher energy cost per ton of material crushed.

11. Limit the height and the speed from which the feed material drops

Three feet, or one meter, is the maximum distance from which the feed material should fall from into the top of a small to mid-size cone crusher. When the feed material drops from a much greater distance than it should, the stones tend to slam into the “V” shaped crushing cavity with such velocity that it subjects the crusher to shock loads and extremely high stress levels. This situation is called “high-velocity wedging”. High-velocity wedging can result in power over-loads or force over-loads, or both. This action puts undue stress and strain on the crusher components and results in increased maintenance repair costs and poor crusher productivity.

Also, controlling the speed of the material that reaches the crusher is very important. When the material falls from a high height, some material can pass through the open side of the crushing chamber and others only crush in the end of the chamber, reducing the efficiency and causing adjustment ring movement, resulting in severe damages in the bronze liner on the main frame seating surface and the main frame pin bushings. Additionally, it can result in premature damage of the tramp release cylinders. In order to avoid those problems, the feeding material speed should be reduced, with steps in the chutes or stone box, reducing the fall height.

12. Remove the fines or sticky material

A vibrating screen positioned before the crusher is used to remove the fines or sticky material from the feed stream before it reaches the crushing chamber. This will help to avoid the “packing” or “pancaking” of the feed material within the crushing chamber, which also causes the jumping or bumping of the adjustment ring and inefficient operation. Keep in mind that the vibrating screen needs to be sufficient in size and efficient in operation for it to work successfully.

The original version of this blog post was first published by Pit&Quarry.