A Terex Company. HSI Primer

Transcription

1 I. Introduction The intent of this primer is to help you better understand HSIs, and the applications they fit in best. Cedarapids HSIs are a good fit in many applications: Behind jaw and impactor primaries Providing secondary reduction before hammermills, cones, and VSIs As stand alone units in rock or recycle Sometimes are applied as tertiaries. The "how" and "why" is in this primer. Knowing the desired product size, tonnage, the intended feed size, the rock type with it's abrasiveness and friability, any constraints of the application, like available power or screening, will help you work through this primer to successful applications. It is intended as a resource to refer back to. II. Good Applications Given the right application, Cedarapids HSIs offer many advantages over other methods of crushing, if the model size, rotor configuration, impeller bar metallurgy, and rotor speed are correctly selected. A brief look at their merits: High tonnage Low capital investment Very portable Good versatility to make a variety of products. Cubical particle shape achieved without process controls. Accepts feed sizes in rock from 6" maximum to 22" maximum. Accepts raw concrete and asphalt recycle feed. Specific to production requirements, HSIs excel at solving circuit problems and at making certain product sizes. The most common applications are: Solving secondary circuit feed size problems of cone crushers when larger jaws are opened up for maximum capacity. Single crusher or two crusher circuits in recycle of concrete or asphalt. Producing a controlled blend of concrete rock, chips and manufactured sand. Producing a maximum amount of concrete rock and larger products with minimum fines. Soft stone elimination (beneficiation). Shaping. Chart 1 shows a rough comparison of how the HSI compares in each of seven applications. Of course this isn't the whole story, initial investment, ease of portability, and the rock's abrasiveness may need to be considered. Chart 2 looks at the HSI versus other types of crushers from the standpoint of rock abrasiveness. Chart 3 looks at the suitability of different crushing chamber metallurgies for different applications. For rocks of very high abrasion, the HSI is only occasionally used. Section V gives a more in depth description of how Cedarapids Inc. can help you evaluate rock samples to determine relative abrasiveness. In Section IV we will look at the controls available to the producer to give the Cedarapids HSI and the applications listed above the best possible fit with each other, including: How rotor speed and rock velocity to the rotor combine to affect rotor penetration. Application differences of the three and four bar rotors. How critical it is in some applications to keep a good bar profile. Apron adjustments for both primary and secondary aprons (5/00) Page Cedarapids, Inc.

2 Product Secondary (takes up to 22" feed from primary jaw) HSI Cone Secondary Gyratory VSI Mill Primary Recycle Secondary Recycle Concrete Rock / Chips / Manufactured Sand Concrete Rock & Larger Products Base Shaping Good Fair Poor Chart 1 - Comparison between crushers in different applications 5 4 Abrasion HSI Cone Secondary Gyratory VSI Roll Chart 2 - Comparison between crushers versus abrasiveness of material (5/00) Page Cedarapids, Inc.

3 = Suitable Choice = Best Choice Large-Feed Secondary Monoblock / Chrome Aprons & Chrome Bars Monoblock / Chrome Aprons & Tool Steel Bars Primary Recycle Secondary Recycle Concrete Rock / Chips anufactured Sand Chrome Aprons and Chrome Bars M Concrete Rock and Larger Products Base Shaping Chart 3 - Suitability of Crushing Chamber Metallurgies for Crushing Applications III. How Rock Is Affected By Impactors You've probably noticed that in our Cedarapids pocket handbook we print expected gradations for cone crushers that change only with differences in the closed side setting of the crusher. No difference is attributed to different rock types. Impactors differ. In virtually every impactor a friable rock will crush to a different gradation than a tougher more resilient rock, even at the same apron setting and rotor speed. Since this difference exists, to help you get the crusher and the application matched up right, we've included Chart 4 for a typical comparison of crushed output gradations of friable and tough rock types. Note that this difference in how rock is affected can help you too: As shown, it also opens doors to applications not suitable for compression crushers. Friability In impactors friable rocks crush more readily than tough rocks. So having an accurate way to determine the friability of your rock is critical. Some rock types have high compressive strengths, like obsidian, but are brittle and shatter easily in impactors. Therefore while compressive strength is very relevant to some crushers, it may not help in evaluating an impactor's suitability. Toughness is more critical for impact applications. A few measures of toughness are 1) the ASTM D- 3 Test for Toughness; 2) ASTM C-13 Loss Angles Abrasion Test; 3) comparing gradations from Burbank Tests. Charts 5a and 5b show the first two with their affect on the maximum recommended feed sizes to the HSI. Use Chart 5c if you do not have data from either test. Find the category of rock type that you will be crushing and use your judgment of whether it is on the tough or friable end of that scale. Then you can get an idea of what feed size you could expect the HSI to accept while working within rated capacity. Across the scale, tougher materials result in a much smaller recommended feed size. This variance is typical from softer rock to hard rock applications, so the HSI is designed to be adaptable to either extreme. Do not confuse toughness with abrasiveness. For example some granites are high in abrasion, but as friable as a medium tough limestone. Clearly not all the materials shown on Chart 5c are suitable for impactors, the point is that evaluating any application requires sorting out relevant data from irrelevant. See section V for more on material testing (5/00) Page Cedarapids, Inc.

4 Recycled Concrete Percent Passing Medium-Hard Limestone Basalt 0 #200 #100 #50 #30 #16 #8 #4 3/8" 3/4" 1-1/2" 3" Square Opening Screen Chart 4 - Output Gradation from HSI Crushing Material of Different Friability Recycled concrete is more friable than most rock types. In addition, the user is dealing with slabby material, which affects it's apparent friability, and the maximum recommended feed size. As the slab thickness decreases, the impactor has an easier time biting off chunks from a larger slab, so the overall maximum feed size of any one piece is increased. Chart 6 shows this relationship as a guideline. Soft Stone Elimination This difference between tougher and more friable types of rocks allows impactors to help "beneficiate" a rock supply, or improve it. The trick is to select a rotor speed that does not blow all the tougher rock apart, but does a good job of exploding the softer stone down into smaller fractions. Then screening can effectively separate it from the harder stone. Each application requires some experimenting with rotor speed. It may not cause a complete elimination of soft stone, but when producing concrete rock, this can contribute to a higher quality product. When producing asphalt material, experience has shown that impacting rock improves the freeze-thaw test results (lowers the results of sodium sulfate or magnesium sulfate tests). Product Shape Impacting is universally accepted as a way to improve particle shape. Certainly some rock types tend to break more cubical than others, but given the same rock type, impacting tends to give more equidimensional particles. Impacting can improve flat and elongated test results by as much as 70%. Follow these rules of thumb for the best particle shape: Lower the reduction ratio slightly and recirculate more rock back to the crusher. Keep the crusher as full as possible. Secondary rock-on-rock collisions help even in secondary/ tertiary impactors. If impactors and compression crushers will both be used in the circuit, use care to select the right sequence of crushers and screens, and where to take products off. In other words, an impactor can help shape up material at either the secondary or tertiary stage, especially if products are taken off at the screen right after the crusher (5/00) Page Cedarapids, Inc.

5 24" 22" 20" 18" 16" 14" 12" 10" ASTM D-3 Toughness Test Chart 5a - HSI Feed Size vs Toughness of Rock Using ASTM D-3 Toughness Test Data 24" 22" 20" 18" 16" 14" 12" 10" ASTM C-13 Los Angeles Abrasion Test Chart 5b - HSI Feed Size vs Toughness of Rock Using ASTM C-13 Los Angeles Abrasion Test Data (5/00) Page Cedarapids, Inc.

6 24" 22" 20" 18" 16" 14" 12" 10" Granite Gravel Dolomite Quartzite Trap Rock Limestone Basalt Increasing Toughness of Rock Chart 5c - HSI Feed Size vs Toughness of Rock Using Material Type 16" 14" Thickness of Slab 12" 10" 8" 6" " " 0" Square Feet of Face of Largest Slab Chart 6 - HSI Recommended Top Feed Size in Recycled Concrete at Rated Capacity (5/00) Page Cedarapids, Inc.

7 Material: Limestone Breaker Apron Settings: Primary 2" Secondary 1" Ft/Min RPM 50" Rotor 60" Rotor % Passing Ft/Min 6500 Ft/Min 5300 Ft/Min 3900 Ft/Min M 100M 50M 30M 16M 8M 4M 3/8" 3/4" 1-1/2" Square Opening Screen Chart 7 - Variations in Output Gradation by Varying Impeller Speed IV. Variables You Can Control To Meet Your Requirements This section covers some options the producer has to meet his or her aggregate size requirements. It touches on what options can help to reduce wear costs, but see section VII for a further discussion of controlling wear costs. Impeller Speed Chart 7 gives an idea of the variation in crusher output gradation that the user can accomplish in one rock type by varying the rotor speed. Tougher rocks may crush coarser than this, and more friable rocks may crush finer, but regardless of rock type, varying the rotor speed can cause a broad change in output gradation. Rules of thumb: For a finer product, increase rotor speed. For a coarse product, slow the rotor speed. Faster rotor speeds consume more horsepower per ton of crusher throughput. Faster rotor speeds will cause more wear cost per hour. Faster rotor speeds cause more dusty air to escape from the crusher. A faster rotor speed will increase gross crusher throughput with good rotor penetration, but can decrease gross throughput with improper rotor penetration. Understanding The Benefits of Proper Rotor Penetration Three variables have great interdependence and they all add up to proper rotor penetration. The three are rotor speed; feed size; and how fast the material is traveling when it enters the rotor. Ideally for proper rotor penetration, first set the speed of the rotor to make the desired gradation, then drop the rock from the correct height so that the feed size you (5/00) Page Cedarapids, Inc.

8 Rotor Speed Assumptions: 3-bar impeller, material rolling down chute, 45-degree feed chute and initial velocity - 0 fpm ' 2' 3' 4' 5' 6' Feed Height Chart 8 - Approximate Feed Height for Proper Penetration are working with penetrates in front of the face of the bar to the correct distance. See Chart 8. This is easier said than done, but coming as close as you can will reward you with a more desirable output gradation at a more economic wear cost. Understandably if the crusher is fed by a VGF on a portable plant, you are not going to change the drop height of the rock significantly, if at all. But in stationary installations or when the crusher is conveyor fed, and the velocity of the feed can be controlled, doing so can net you more tons of desirable product. Chart 8 gives a guideline of what drop distance you may want to consider when installing an HSI. It shows a curve comparing rotor speed to feed height. Note that this chart is arranged based on all the assumptions written above it. If the feed chute is steeper than 45, or the rock drops straight onto the rotor, the rock will have greater velocity than if it rolls down a 45. Please use this only as a guide. If your feed size is small, say 6 to 8" maximum, you would use the upper part of the curve. If your feed size is very coarse, say a maximum of 20" and minimum of 6", you should use the lower part of the curve. That is because larger feed should penetrate a bit further in front of the impeller bar. Rock velocity that is either too fast or too slow can cause problems. Anytime you vary rotor speed, watch for differences in the wear patterns on the impeller bars, the primary apron, and the discs of the rotor fabrication. Material that is entering the crushing chamber at too high a velocity will cause unusual wear on the rotor discs and the wedges that hold the impeller bars in. If this happens the best method of controlling the velocity of the feed is to lower the feed device discharge point. If this is not possible, creating a "rock ladder" of alternating steps that the rock lands on and changes direction can help. A chain curtain can help if the rock velocity only requires a small change, but be careful not to let the chains wear to the point where they could break and fall into the crusher. If the material velocity is too slow, you may experience "scuffing" of the rock against the impeller bar which will accelerate rounding off of the bar and cause the wear to concentrate on the top of the bar, generate additional fines, and can also cause the rotor to refuse feed and slow the tonnage rate of crusher throughput. The solution, if possible, is raising the height of the feed device or making the feed chute steeper. If controlling the material velocity is not an option, compromising on a practical rotor speed selection that allows proper feed entry and gives an acceptable gradation may be the best choice. Cedarapids offers the 50" HSI family in two rotor configurations, 3-bar and 4-bar. A further discussion of how this enters into the rotor speed selection is included below. With the new (1999) 50" HSI design, the user has the option of choosing a rotor fitted with rotor disc guards at extra cost. If it appears the feed drop height will cause excessive rotor penetration, and feed arrangement cannot be altered, the user should consider this option. Apron Settings Once the correct rotor speed is determined, the aprons can help significantly to control oversize, and recirculated load, in the crushed product. Closing the apron setting down (bringing it closer to the rotor) will result in less oversize. Increasing the gap (5/00) Page Cedarapids, Inc.

9 (moving the apron away from the rotor) will result in more oversize. A general rule of thumb for apron adjustment is to set the gap of the secondary apron at one to one and a half times the maximum product size for final product control. Then set the primary apron at two to three times the setting of the secondary apron, both measured from the impeller bar to apron. This rule of thumb is good to get you started. After that, the acceptability of the gradation should determine whether the secondary apron is set right. Experienced producers often adjust the primary apron to try to even the wear between the two aprons when using interchangeable liners on both aprons. Recycle is an exception to this because the primary crushing chamber receives such large material and usually needs a bit larger gap setting. Cedarapids new (1999) 50" HSI design offers as an option a hydraulic assist to significantly reduce apron adjustment time and effort. The hydraulic assist works off the hydraulic power pack included with the machine. It includes two more valves, one to operate the adjustment assist on each apron. Please see the operators manual for an operation description of this labor saving device. 3-Bar Versus 4-Bar Rotor Each rotor has applications that favor it. The 3-bar rotor is more popular, but the 4-bar may be a better fit in some applications, as shown below. If the 4-bar rotor is configured with "two up/two down," or two new bars in opposite locations, and two worn bars in the other two locations, it is in effect a 2-bar rotor. For the fastest rotor speeds, like 600 rpm and above, combined with the lowest drop heights, this may be a good alternative. Cedarapids finds that a broad range of applications suit the 3-bar rotor. Rotor speeds of 400 to 600 rpm match up well with the 3-bar rotor. The 3-bar rotor has more open area between bars than a standard 4- bar, which means that proper rotor penetration can be achieved with medium rotor speeds and a fairly low drop height, compared to the 4-bar rotor with all bars at the same profile. Most applications call for production of rock and chips, not maximum fines, and thus medium or slow rotor speeds are desired. Feed drop distances of as little as 30", or as much as 12' have also been used with the three bar rotor. For applications with very slow impeller speeds, or very fast rock velocity that cannot be changed coupled with medium rotor speeds, the 4-bar rotor with all bars in the "up" position may be best. This configuration has been successfully applied with rotor speeds as slow as 320 rpm, up to 400 rpm. If the rock is being dropped from a substantial height, and the velocity cannot be slowed, the 4-bar rotor offers the chance of decreasing rotor penetration without speeding the rotor up past the desirable rpm. Bar Profile In applications where the HSI is used as a finish crusher, especially when making chips, the importance of bar profile cannot be overstated. Keeping a good "edge" on the bar can improve production rates by as much as 50%. This assumes that the apron settings and rotor speed have already been put to the proper adjustment. Section 4 of the operators manual offers a description of when to change bars in normal secondary applications, but in this application when the bars have rounded over to the point where production has fallen off to an unacceptable level, the bars should be turned. Cedarapids utilizes a four-turn bar which will give the best utilization possible in this circumstance. The utilization of the bar will change some when following that guideline. Users generally achieve from 35% to 45% utilization, but in the circumstance of having to keep a bar profile at optimum, and consequently turning the bar more often, you will likely achieve less than 35% metal utilization. Adjustable Stripper Bar All Cedarapids HSIs are equipped with an adjustable stripper bar as standard. The main purpose of the stripper bar is to slow the air circulation in the (5/00) Page Cedarapids, Inc.

10 crusher, so it is more often a wear reducing feature. For rock applications we recommend the stripper bar be adjusted to about 3 8" to 1 2" from the impeller bar. This setting is more important for applications with the circuit closed at less than 2" due to the fan affect and the tendency to carry smaller stones in the air in front of the impeller bar. The stripper bar is very effective at restricting air movement around the rotor, and thus reducing the tendency to sandblast the wear liners and impeller bars. As the edge of the stripper bar wears, it can be moved forward to keep the adjustment correct. The new HSI design incorporates a stripper bar which is much easier to use and more durable in recycle applications. In most recycle applications, we recommend that the stripper bar be backed away from the rotor to at least 1" to 1-1 2". More is better. This is to allow room for any pieces of metal that may wrap on the rotor to pass around without damage to the stripper bar assembly. However the huge variation in recycle applications make this a rule of thumb and not an absolute. If the user is recycling asphalt, the lack of steel does not make this as critical (5/00) Page Cedarapids, Inc.

11 V. Analyzing Rock's Suitability For Impacting Relative Abrasiveness of Rock Types Chart 9 shows a variety of rock types all compared to a common scale of abrasiveness. Put into perspective you can see that a rather "abrasive" limestone may be lower in abrasiveness than a medium abrasion basalt. Cedarapids HSIs are applied in most abrasive ranges. The availability of different apron and impeller bar metallurgies gives the operator the ability to choose the right mix of abrasion resistance and durability. For example, crushing medium to medium high abrasion rock would call for chrome bars and chrome liners. But crushing concrete recycle as a stand alone unit with the same abrasiveness of rock in it might call for 5" chrome (or even tool steel) bars and a manganese or tool steel apron. See Chart 10 for an approximation of the abrasive ranges each bar/apron combination is suitable for. As the rock supply's abrasiveness increases, the impeller bar life decreases. In low abrasion rock impeller bars may last over a million tons. Conversely, in recycle of concrete that was originally produced with abrasive rock, the bar life would be much shorter, possibly as low as 15-30,000 tons. Concrete And Asphalt Recycle Trying to calculate expected abrasion from either recycled concrete or asphalt is more difficult than with a single rock source because the virgin aggregates in the concrete or asphalt come from a variety of sources. This variance makes accurate part life estimating difficult, but some generalizations can be made: IGNEOUS Granite Rhyolite Andesite Basalt SEDIMENTARY Shale Limestone Dolomite Sandstone METAMORPHIC Quartzite Slate Hornfels Serpentine Chart 9 - Rock Types on a Scale of Abrasiveness (5/00) Page Cedarapids, Inc.

12 Monoblock / Chrome Aprons & Chrome Bars Monoblock / Chrome Aprons & Tool-Steel Bars Chrome Aprons & Chrome Bars Very High High Medium Medium Low Low Chart 10 - Select Crushing Chamber Components According to Abrasiveness of Rock If most rock supplies in the area are commonly abrasive, the recycled materials are likely to be the same. Same is true for low abrasion rocks. Pre-processing recycle to bring the lump sizes down, and/or taking out some of the metal contaminant can lower wear cost by allowing the use of more abrasion resistant liners. Use the most abrasion resistant metallurgy you can while still controlling part breakage. Calculating Wear Estimates Cedarapids' test lab can take a great deal of the mystery out of this determination. Over the years we have compiled thousands of test reports to rely on for comparative data of different rocks and minerals. More important is the interpretation of the test data. Silica content has universally been considered the best guideline of abrasiveness. We have found that other factors enter the equation, like the moisture content, rotor speed, and the tonnage to the machine. We can also perform a true impact abrasion test called a "Burbank Test". Taken as a block of information to be used together, the chemical analysis and the pertinent data from the application can be used with the Abrasion Index Number (AIN) from the Burbank Test. This method is not foolproof, but it does help us estimate expected part life more accurately. Consult the Cedarapids Pocket Handbook for some categories of test data that are relevant to applying an HSI successfully, such as Mohs hardness, chemical analysis, and the Burbank test. Any information is a help and usually the more the better. The results and the estimate are only as accurate as the information we begin with. Sample integrity is absolutely critical, and having good data about the application increases the accuracy of estimates (5/00) Page Cedarapids, Inc.

13 VI. Power Requirements Two factors determine most of the horsepower requirement for an HSI: Rotor speed and gross throughput tons. Chart 11 shows an approximate relationship between rotor speed and horsepower required per ton. This guideline can then be multiplied by the gross throughput tonnage for an approximate overall horsepower required. Caution should be used, as there is some slight variation between rotors. Different rotors have different amp draws running empty due to inertia and air flow variances, giving a slightly different starting point for the power curve. HP Per Ton of Crusher Throughput ROTOR SPEED Chart 11 - Calculating Horsepower Requirement Today's sophisticated electronic starters allow longer "soft start" ramp up times, which means smaller electric motors can start the HSI even with it's high inertia ratings (WK2). If these type starters are used, the motor can be sized for the crusher throughput tonnage, and not for starting. However, in the case of a diesel engine, the engine may have to be sized for starting the HSI. Horsepower of the engine is not as critical as is the low rpm torque, when using a conventional clutch. VII. Controlling Wear Impacting is usually associated with higher wear part costs than the manganese cost in a cone crusher. But considering the low initial investment cost of an HSI with it's high production rate, in medium or low abrasion rock the HSI may actually improve the overall plant cost per ton. Each application deserves a careful analysis including all owning and operating costs. Once the HSI is installed the user does have ways to control wear. The strategy for controlling wear should include the following: Use the slowest impeller speed possible while still producing a desirable gradation. Achieve proper rotor penetration for proper bar wear. See Section IV. Use impeller bars with as high an abrasion resistance as possible without experiencing excessive breakage. Example: 4" high chrome bars break occasionally, and 5" tool steel works fine but the wear is high, try 5" chrome bars because they have greater strength due to the thickness, yet offer the abrasion resistance of the high chrome bar. Use an efficient vibrating screen ahead of the crusher to scalp out fines and product sized material. Reduce or eliminate water with the feed. More water usually means more wear to parts such as bars, apron liners and side liners. Water causes fine particles to cling to coarse particles, making the coarse particles more abrasive. Keep feed properly distributed across the width of the rotor. Letting the feed run to the center of the rotor will cause a dip in the bar wear edge, and can make apron and stripper bar settings difficult to measure. Keep the stripper bar adjusted to the proper distance from the rotor. Assures that airborne fines don't sandblast the wear parts. Generally rock applications require a stripper bar setting of about 3 8" to 1 2". In primary recycle applications adjust the stripper bar so that it is at least 1-1 2" away from the bar (5/00) Page Cedarapids, Inc.

14 VIII. Balancing a Circuit Perhaps the greatest cost savings the HSI offers in plant renovation is when the user needs to increase his plant capacity, but hesitates to spend the high dollars required for a larger jaw crusher. Say the user has a 4248 jaw, but it is set at 6" to properly size the feed for the cone(s) that follow it as secondaries. The user has no choice but to keep this setting due to the feed size restriction of the cones. Instead of replacing the jaw with a larger one (at considerable expense) putting an HSI of the proper capacity in as a secondary allows the operator to open the existing jaw up, enjoy a much higher capacity. See Charts 12, 5a, 5b and 5c. The HSI is not so feed size sensitive, and the investment in crushing equipment far less. But don't forget to increase the screening capacity to handle the higher tonnage. The most common circuit balance problems occur in secondary and tertiary positions. Since HSIs are notoriously high tonnage capacity, the need for screening often increases. The gross throughput capacity of the HSI remains more constant through speed variations, and when making different size products, so the screening demands can go up substantially compared to most compression crushers. Quality circuit design takes into account many variables. For example, when the parts begin to wear, the output gradation from the HSI will change somewhat. That changes the recirculated load (if the circuit is closed), and the demands on screening and support equipment. Again, if the screening is at capacity, there will be no left over capacity to absorb this. If the HSI is in open circuit, the load on any 5064 Crusher 5048 Crusher 20" 16" 12" 8" 4" 20" 16" 12" 8" 4" TPH TPH Note: Capacity will approach upper curve with even-graded, non-slabby material fed well-centered in the chute, no surges, sufficient power, etc. Capacity will approach lower curve with slabby, gap-graded material, off-center feed, insufficient horsepower, etc. Chart 12 - Throughput Capacity vs. Feed Size (5/00) Page Cedarapids, Inc.

15 crushers following it will increase. So if they are at capacity when the HSI has new parts, the balance could be affected when parts wear. Balancing an entire circuit requires analysis of the primary, secondary, and tertiary crushers, along with the screens at each stage, to assure a good match of capacity and the ability of each to prepare an acceptable size for the next machine. But one rule can help in virtually all instances: Make your crushers the bottleneck! Screens still do a great job when underfed, but most crushers do a better job when fed near capacity. Since crushers cost more than screens, letting the crushers work at their capacity maximizes your efficiency of investment! (5/00) Page Cedarapids, Inc.