Although past investigations have been conducted to determine crushing relationships, no program which covered a broad range of crushing conditions had been conducted. The previous studies appear to concentrate on small segments of the overall picture and did not fullfill our desired information objectives. Due to the broad range of variables utilized in a production size crusher, is believed to be the most comprehensive study of its kind as of this date.
The principles developed by the Symons brothers in 1925, when they patented the cone crusher as we know it today, are still being used in the machine known as the Symons Cone Crusher. During the development of this novel crushing concept, a technique known as the fall of material (called the Bouncing Ball Theory by some) was used to determine an idea as to the proper head angle, eccentric and speed of eccentric rotation. The final variables used for the Symons Cone Crusher design were, therefore, the logical conditions to start with and use as a reference against which other variables could be compared.
Other tests, conducted in the field and at the MRTC, have confirmed that the eccentric speed should not be reduced below the speed normally used. Similar tests have indicated that the eccentric throw should not be increased significantly above that normally used. It was logical, therefore, that the speed and eccentric should be given significant increases and decreases, respectively during a testing program. The head angles selected were based upon the range of cone crusher head angles being used. It is believed that the majority of the crushing variables used by the various cone crusher manufacturers are covered by the variable ranges selected.
Five hundred tons of 3 (76.2mm) x 1 (31.7mm) limestone was purchased from a limestone quarry near Milwaukee for use as the test material. All the material was obtained on the same day from the same part of the quarry to minimize fluctuations in material characteristics during the test program. Due to the large number of tests (135), no repetitive testing was thought to be necessary.
The material was fed to the crusher at a rate which would either utilize the total horsepower available or fill the crusher cavity. Normally, the horsepower was the limiting factor with the (6.35mm) and 3/8 inch (9.53mm) settings while the cavity capacity was the limiting factor at closed side settings above the 3/8 inch (9.53mm) value.
After either of the two criteria were obtained, the crusher was run until steady operating conditions were achieved. The crushing circuit was then stopped and a belt sample taken. After being weighted, this sample was split to a size convenient for screen size analysis.
Closed side settings were determined by passing a lead slug approximately 2 inches (50.8mm) thick through, the crusher prior to starting the test. This slug was then measured and the value recorded as the crusher setting for that test.
The data from all 135 tests were simultaneously supplied to a canned statistical package known as S.P.S.S. for the equation development. The S.P.S.S. package used was supplied by the Control Data Corporation (CDC) program library. Using a stepwise regression procedure resulted in an indication of each variables importance in relation to the dependent variable, horsepower. Stepwise regression results in each independent variable being entered according to the respective contribution of each to the explained variance (the variability of the dependent variable explained by the regression line)
The R value indicates how well the regression equation fits the sample data. The R value is obtained by dividing the regression sum of squares by the value for the regression sum of squares plus the residual sum of squares. The regression sum of squares being the amount of variation in the independent variables associated with the regression on the dependent variable. The residual sum of squares is the variation of the independent variables not associated with the regression of the dependent variable. This variation is due to the variation in sample data.
C.S.S. = Closed side setting (inches) Eccentric = Eccentric throw (% of normal) Head Angle = Head Angle in degrees from horizontal Speed = Linear Speed in ft./min. of the closed side setting at outermost point of liner Horsepower = Dependent Variable being predicted
The closed side setting therefore accounts for an explained variance of 43%; the eccentric 22%; the head angle 13%; and speed 1%. The R value of .79 indicates that an unexplained variance between the equations developed and the data of 21% exists.
Each of the above were represented by an equation containing the C.S.S. for each eccentric value at the head angle selected. Tables 1-2 show the R values for capacity and horsepower. In nearly all cases the R values for each eccentric value are excellent. Obviously the change in eccentric has a large effect for each head angle as evidenced by the excellent R values developed for the individual eccentrics and the relatively poor R obtained by combining all data for each head angle and developing an equation. This relationship holds true for both the capacity and horsepower predictions.
In tables 1-2 the column labeled Correlation at the 95% confidence level indicates whether a null hypothesis (H0: the values obtained were from a population for which no correlation existed) can be rejected. If a yes is indicated, you can be 95% confident (statistically) that the information used came from a population of data for which a correlation exists. In all but one case, we were able to reject the null hypothesis. Only the correlations obtained from the equations developed using log transformations are presented as the log transformation resulted in the best R values.
Scattergrams for each head angle and eccentric were generated from the equations developed to indicate the predicted horsepower and capacity versus closed side setting. These scattergrams are presented in Figures 1 through 6. Figures 1 through 3 indicate the effect of head angle and eccentric for horsepower consumption versus closed side setting. Figures 4 through 6 show the effects of the same variables on crusher capacity.
Regardless of head angle, eccentric throw, or speed, the closed side setting had the greatest effect on capacity and horsepower. As the closed side setting decreases the capacity decreases and the horsepower increases both changing based upon separate mathematical relationships. It would be logical to assume, therefore, for any given crusher, that an increase in closed side setting will increase capacity (up to the point where the cavity will not accept additional material) and decrease horsepower. There are practical limitations however. We cannot arbitrarily increase the closed side setting (C.S.S.) if we wish to maintain a maximum product top size. At the other extreme there is a physical limitation on how small the setting can be before the mechanical integrity of the crusher in question is violated.
Obviously, we must therefore look at the next variable which contributes to the process. The eccentricity, once again regardless of head angle or speed, has a very significant impact on a crushers capacity. As the eccentricity of the movable crushing member increases, the capacity rapidly increases. (See Figures 4-6) The eccentricity also controls, for any head angle, the horsepower consumption (do not forget the influence of C.S.S.) as shown in Figures 1-3. The horsepower draw will also increase significantly as the eccentricity increases.
It is apparent at this point that for a given closed side setting and head angle that the larger eccentric throws will produce the largest capacities and horsepower consumptions. While it is valid to assume that the amount of work done is related to the horsepower consumption, this assumption is only good up to the point where the added horsepower no longer is doing useful work, but rather is being absorbed in the crushing and supporting structures. Several examples of this wasted horsepower are adjustment ring movement or as seen in a different design the head moving away from the fixed crushing member. It is important therefore, to add horsepower only as long as the work is being done on the material and up to the point where the structural integrity of the machine is not being violated.
The next variable of importance (as per the stepwise regression) is the head angle. It is apparant that as the head angle increases, for a given setting and eccentric, that capacity and horsepower also increase. It has been previously established that a large eccentric is important. A large eccentric coupled with the 60 head angle resulted in a horsepower level far above the maximum acceptable limit at the smaller C.S.S.
An inspection of Figure 3 shows the detrimental effect of the 60 head angle large eccentric on horsepower consumption. In this instance the horsepower draw was high and erratic at the smaller settings. This situation caused a reduction of feed to the cavity to bring the horsepower within acceptable limits. Obviously the head angle must be something less than 60 if we are going to be able to fully utilize the whole crushing cavity at the rated machine horsepower. At the present time there is not enough information available to select the optimum head angle. Another test program concentrating on a broader range of head angles at a large eccentric is needed.
As we have seen, speed increase has been the least contributor to the explained variance. No effect was seen in regard to horsepower consumption. There is some indication that an increase in speed will reduce the crusher capacity (regardless of eccentric or head angle).
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HS Series Symons Cone Crusher is widely used in the metallurgical industry, construction materials industry, road building industry, chemical industry and silicate industry. It is suitable to crush ores and rocks with medium hardness and medium hardness above. It has features of strong crushing force, reliable structure, high efficiency, high capacity, low operating cost, easy adjustment, economical to use and so on. Also symons cone crusher uses the compensating lubricating grease sealing, it can avoid lubrication oil being polluted by dust, so that all parts work reliably and have a long operating life. The safety insurance system of cone crusher uses several spring sets, so the matter and iron ore are down from the crushing cavity and do not damage the crusher, simply and reliably. The safety system uses dry oil and water as two kinds of sealed formation to make plaster powder and engine oil separate to make sure reliable performance. The cone crusher has standard type and short head type, the standard type is suitable to medium size and the short head type for medium and fine crushing.
HP Series Multi-cylinder Hydraulic Cone Crusher is one of advanced cone crushers in China, which is developed and manufactured by our company. The machine is one kind of high-class product combined with mechanical technology, electrical technology, hydraulic technology and advanced crushing technology. The machine adopts high strength casting-steel frame, alloy forging main shaft and high precision straight bevel gear driving structure, combined with multi-chambers selection and automation control system, which fulfills the performance and advantages. It can be widely used in secondary and fine crushing work for all kinds of hard materials and rocks to meet customers' various needs for crushing.
DP Series Single Cylinder Hydraulic Cone Crusher is one of advanced cone crusher in China, which is developed and manufactured by our company. The machine is one kind of high-class product combined with mechanical technology, electrical technology, hydraulic technology and advanced crushing technology. Not only provides the features of high reliability, but also with the features of high crushing efficiency, low operation cost, good shape of the end products. The machine adopts high strength casting-steel frame, alloy forging main shaft and high precision arc-shaped spiral gear driving structure, combined with multi-chambers selection and automation control system, which fulfills the performance and advantages. It can be widely used in secondary and fine crushing work for all kinds of hard materials and rocks to meet customers' various needs for crushing.
PY Series Spring Cone Crusher is suitable to crush all kinds of ores and rocks with medium hardness and above. It has features of reliable structure, high efficiency, high capacity, low operating cost, easy adjustment, economical to use and so on. Spring system plays the role of overload protection, which will enable the exotic materials or steel piece to pass through the crushing chamber without any damage to the machine. It adopts grease seal to isolate dust and lubricants, therefore ensure its reliable operation. According to customer demand, respectively, using standard type, medium type and short head type for coarse crushing, medium crushing and fine crushing operation.
The portable cone crusher plant is consist of stable and sturdy chassis, efficient cone crusher, screening equipment, belt conveyor, electric motor and electrical control system, and optional hydraulic auxiliary system, environmental dust removal system, maintenance platform and other components. Cone crusher is optional by curtomers' requirements, which can be spring cone crusher, symons cone crusher, multiple or single cyliner hydraulic cone crusher.
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Crusher Plant Crusher plant is a complete aggregate crushing processing, which can be divided into the jaw, impact, cone crushing plant, portable mobile crushing station, quarry crushing plant. Crushing materials that include rock, puzzolana, gravel, limestone, coal, iron ore, construction and demolition wastes, and other mineral raw materials.
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 operations 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.
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, dont 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 crushers 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.Get in Touch with Mechanic