Cost-effective aggregate production begins with employees who are knowledgeable about the maintenance requirements and operational parameters of the cone crushers they operate. There are certain proven methods and practices industry experts use to ensure a smooth crushing operation. This article presents key tips that will help you maximize your cone crushing operation.
1. Operate at a consistent closed-side discharge setting. Producing a consistent product quantity, quality, uniformity and attaining a balanced circuit begins with operating the cone crusher at a consistent closed-side discharge setting. If a crusher is allowed to operate at a wider-than-optimum setting for even a short period of time, the result will be less product and an increase in oversized material.
Keep in mind that oversized product almost always creates circuit flow problems within the aggregate plant. An example of the effect that crusher setting has on the product gradation is as follows: If the target crusher setting is 3/8 in. (10 mm) but the setting is not checked and it wears open to 1/2 in. (13 mm), then the end result is a 15 percent decrease in the minus 3/8-in. (10 mm) material size. This is a substantial decrease in productivity.
Most aggregate producers would be amazed at the revenue lost each year due to the simple fact that crushers are not being operated at consistent closed-side settings. The crusher setting should be checked on a per-shift basis.
2. Operate at a consistent “choke-fed” cavity level.If a crusher operates at varying cavity levels throughout the shift, the result will be an inconsistent product shape and inconsistent production rate. Operating a cone crusher at a low cavity level (half cavity) will result in a significantly coarser product gradation, and this low cavity level will also produce more flat and elongated product particles.
Efforts should be made to operate the crusher at a proper choke-fed cavity level, as the favorable end result will be increased crusher throughput tonnage and a more cubical-shaped product. This tip is particularly important for the tertiary (short head) crushers in the circuit, as they produce the vast majority of an aggregate operation’s salable products.
3. Do not trickle feed the crusher. Trickle feeding a cone crusher should be avoided because it not only results in poor productivity and poor product shape, but it can also adversely affect bearing alignment within said crusher. Due to the operational characteristics of a cone crusher, when crushing, it should never be operated below 40 percent rated horsepower. To obtain a proper “loaded bearing alignment” and to maximize productivity, the crusher should be operated above 40 percent rated horsepower yet below 100 percent rated horsepower of the drive motor.
A power draw of 75 to 95 percent is a great target range to stay within while crushing. Excessive power peaks, particularly above 110 percent rated horsepower, should be avoided as this could lead to premature crusher failure.
4. Ensure the feed is evenly distributed. The incoming feed material should be directed on a vertical plane into the center of the crusher. When the incoming feed is not directed into the center of the cone, one side of the crushing cavity could be quite full while the opposite side of the cavity could be low or empty. This will always result in a low crusher throughput tonnage, the production of more flat and elongated product particles and oversized product.
This typically prompts crusher operators to tighten the crusher setting in order to get the crusher to make the smaller product size that they are trying to produce. This in turn can result in an overload condition in the form of adjustment ring movement on the side of the crusher that is heavily loaded. Over the long term, this can cause the adjustment ring to become tilted on the main frame, resulting in an even larger loss of productivity.
5. Ensure the feed is not segregated. All incoming feed material should be well mixed and homogeneous. A segregated feed condition exists when large stones are directed to one side of the crushing cavity and small stones are directed to the opposite side.
The side of the crusher receiving the small stones will have a higher-than-normal bulk density, and this can lead to something known as “packing” or “pancaking.” This in turn leads to adjustment ring movement on the side of the crusher receiving the smaller feed stones. Adjustment ring movement forces the operator to open the crusher setting to avoid this overload condition. This results in the production of oversized product due to the increase in crusher setting. In addition, segregated feeding and the resultant adjustment ring movement can lead to a tilted adjustment ring, resulting in larger loss of productivity.
6. Minimize surge loading for a more efficient circuit. Surge loading of any crusher is a “production enemy.” 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 allows the operator to run the crusher at a very consistent cavity level for extended periods of time. Providing better crusher feed control for the cone crusher through the use of surge piles, hoppers and variable-speed feeding devices such as belt conveyors or vibrating pan feeders can easily increase crusher productivity by a minimum of 10 percent.
7. Understand the design limitations of the cone crusher. Every cone crusher has three design limitations. These are the volume limit, the horsepower limit and the crushing force 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. As for the horsepower limit, each crusher has been designed to operate at maximum power draw, and power draw will increase as the feed rate increases and as the feed material is crushed finer. The horsepower limit is exceeded when the crusher draws more power than it is rated for.
Lastly, don’t forget about the crushing force limit of the crusher. 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 is exceeded when the adjustment ring bounces, wiggles or moves on top of the main frame.
An ideal operational condition exists 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 excessive crushing force results in a very serious crusher overload. These overloads create something known as “fatigue damage,” which is permanent, irreversible and cumulative. Without a doubt, frequent overloads 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 overload condition (ring movement) or a power overload condition (excessive amperage), open the crusher setting slightly, but try to stay choke fed. The advantage of staying choke fed is the fact that there will still be rock-on-rock crushing and grinding taking place in the crushing cavity. This helps to maintain good cubical product even though the setting is slightly larger than optimum.
The other option, of course, is to decrease the feed rate to the crusher. But the downside is that product shape tends to suffer. Typical 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 or simply trying to operate at an unrealistically small closed-side setting.
9. Monitor and maintain a proper crusher speed. If proper drive belt tension is not maintained, the belts will slip and the crusher will slow down. A slowing crusher will cause incredibly 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, and this inefficient use of connected horsepower will result in a higher-than-normal energy cost per ton of material crushed.
A speed sensor can be used to monitor the crusher countershaft speed, which will send a warning signal of a slowing crusher to the programmable logic controller, 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 due to the fact that the screen is insufficient in size, or a screen that is sufficient in size yet is inefficient in operation. Re-crushing and re-handling product size material due to an insufficiently sized screen, inefficiencies due to the way the screen is set up or due to improper vibrating screen maintenance will lead to an excessive quantity of “fines in the crusher feed.” This will lead to inefficient use of connected crusher horsepower and a higher energy cost per ton of material crushed.
11. Limit the height from which the feed material drops. The maximum distance from which the feed material should fall from into the top of a small to mid-size cone crusher is 3 ft. When the feed material drops from a much greater distance, 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 referred to as high-velocity wedging, and it can result in power overloads or force overloads – or both. This action puts undue stress and strain on the crusher components, and it results in increased maintenance repair costs and poor productivity.
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