July 2003
Self-contained segments and standard plant components add flexibility and cut costs.
By Bob Drake
Pegson’s 1300 Maxtrak cone crusher plant is self-contained with a belt feeder and integral hopper that can be fed from a conveyor, excavator, or a mobile primary crusher. The crusher feed chute has a level probe to ensure choke feeding of the cone.
The word “modular” has been used to describe lunar landing craft, computer hardware and software, and buildings. Recently it has been appearing with increasing frequency in descriptions of aggregate processing equipment. What does a modular crusher have in common with a lunar module or a computer program?
Webster defines module as “a preassembled, self-contained unit, usually a component or subassembly of a larger structure,” or “a standard structural component repeatedly used.” In this context, modular aggregate plants may be preassembled, self-contained process segments that can function by themselves or be connected to upstream and downstream segments to form a complete plant; or, they may be standardized components incorporated into a plant several times, in several places, in several ways.
These are not hard and fast definitions, but they provide some idea of how equipment manufacturers are approaching the concept of modular plants and components.
Continental Conveyor’s Red Line field conveyors use pre-engineered components, such as this impact bed loading section.
Self-contained segments
In many cases, it is difficult to distinguish a modular plant from a traditional portable crushing or screening plant. In fact, they often are similar. However, there are subtle differences. Most plants marketed today as “modular” are truly self contained with on-board power supplies and control systems. They can be linked with other modular segments — both in a physical sense and through automated control systems — or they can be operated separately.
Most modular plants have an integral hopper and feeder and closed-loop control system to regulate material flow to the crusher or screen, even in a secondary-type plant. Often, modular plants are flexible enough to accommodate feed by conveyor from an upstream segment when linked together, and by a loading tool (excavator or wheel loader) when operated separately.
Flexibility also is key in how modular plants connect together. Crushers, screens, and conveyors easily can be added to or taken away from the system to accommodate variable materials and product demands at different sites or at different times.
Part of the Kolberg-Pioneer/JCI Fast Pack system, this portable cone crusher plant has an on-board surge hopper/feeder with a level sensor to ensure choke feeding. A self-contained power system eliminates the need for external power, a motor-control center, and cables.
Standard components
From a manufacturer’s perspective, a modular plant may be one that contains standard components that can be assembled in different ways to fit different applications. For example, Metso Mineral’s ST-series mobile screen plants can be mounted on wheels, tracks, or skids.
On a more basic level, however, modular components may be the common pieces from which any number of complete and unique systems are designed and built. Astec Systems has constructed several stationary plants using modular tiers that are stacked to make screen and crusher towers. No two completed towers may be the same, but each component tier is identical.
This system not only saves design and manufacturing costs, but results in less time and cost during plant erection. In addition, the plant modules can be disassembled, transported to another site, and assembled in the same or different configuration.
Modular construction also is used in conveyor systems. Several manufacturers offer stackable, self-contained conveyor sections, including motors and reducers, that are easily transported to a site, then set up end-to-end to stretch the required length.
Continental Conveyor uses the modular concept for its Red Line field conveyors. Pre-engineered conveyors can be assembled in the required length and belt width by combining standard components. Components include impact bed or idler loading section, idlers and support structure, discharge drive section, and take-up section.
Superior Industries’ modular feed system comprises three 9- x 14-ft hoppers that can be separated for different applications and three 24-in. x 70-ft. stackable conveyors. Hoppers are connected and the conveyors stacked on top for one-load transport. The axle assembly and fifth-wheel hitch are removable.
Metso Mineral’s ST-series mobile screening plants (ST348 shown here) feature the company’s SmartScreen system designed to maximize screening efficiency by controlling the material feed rate, screen box performance, and start-up and shutdown. The automation system can be linked to other Nordberg mobile crushers and screens, allowing communication between machines.
Bob Drake is editor for Aggregates Manager.
Annual calibration ensures that equipment is working properly and provides protection in times of trouble.
The dictionary definition of calibration is: to determine by measurement or comparison with a standard, the correct value for each scale reading on a device.1 As an aggregates producer or blast contractor, you assess risk every day. But, have you considered the importance of, and the risks associated with the calibration of your seismograph and the accuracy that is provided?
Can your calibration provider back you up in times of trouble and provide documented evidence that the equipment was functioning within specification? Can its calibration procedures withstand independent scrutiny and be shown to be traceable to national standards for accuracy of measurement? These are important documents that in court provide tremendous support that blasting and monitoring activities are conducted professionally and competently.
Why calibration is important
The recommended interval for calibration of most measuring equipment, including seismographs, is one year. Across most of North America and many parts of Europe, regulatory authorities actually require seismographs to be calibrated on an annual basis. This requirement has been or is being adopted by several other countries around the world and some specific projects even require that seismographs be calibrated every three or six months.
Calibration is important to ensure the instrument is performing as it was designed to and measures accurately the true ground vibration and air-blast. Although seismographs are designed to be used in a rugged environment, they are still a sophisticated electronic monitoring device. Therefore, preventative maintenance becomes an important part of the annual calibration process.
Many manufacturers and their authorized calibration facilities will perform upgrades and preventative maintenance on your instruments, often free of charge, providing the units are regularly serviced. The upgrades often include product enhancements of both hardware and software and result in expanding the functionality of the equipment.
How a seismograph is calibrated
During the calibration process the geophones are mounted on a shake table with a reference sensor and excited at a specific frequency and amplitude. At this point, the sensors should be checked for the “as found” conditions of each channel. This must be performed before any adjustments have been made. These results will allow the user to assess all of the vibration records that have been recorded since the last time the seismograph was calibrated and determine the impact, if any, on these records. The seismograph is then adjusted to match the level being recorded by the reference sensor. The geophones are then checked to ensure they are within specification across the required frequency range of the equipment.
Microphones are calibrated in a similar manner. They are exposed to a sound source at a specific frequency and sound pressure level and the “as found” conditions are recorded. The microphone is then adjusted to match a reference microphone. Then, like the geophone, they are checked to ensure they meet the specifications for the required frequency range.
To ensure compliance, it is very important that all sensors are tested at several frequencies within their required range. For example, if a calibration service provider uses a device called a piston phone to calibrate microphones, the microphone is only checked at one frequency and one pressure level. This frequency is typically about 250 Hz and is at the high end of most seismographs’ frequency response.
This is not a valid method of calibration, because the single-point calibration does not provide any indication of the response at other frequencies. The seismograph may be reading high, low, or nothing at all at other frequencies within its specified frequency range.
Some models of seismographs are meant to have the geophone, microphone, and data acquisition unit calibrated as a system. Generally this allows the entire system to be calibrated more accurately. However, a limitation of instruments that are calibrated using this method is that the geophone and the microphone are matched to the acquisition unit and the sensors may not be interchangeable with other instruments, even if they are the same model from the same manufacturer, without a decrease in overall accuracy.
Other models of seismographs may have the geophone, microphone, and the data acquisition unit calibrated as independent assemblies. This type of seismograph should maintain its accuracy when sensors from compatible models are interchanged.
To help maintain the integrity of the recorded data, most seismographs have a sensor checking function. Some users may confuse the purpose of this function with that of the yearly calibration. This sensor check can provide valuable information about the sensors and their set up. If a sensor has not been installed or connected properly, the sensor check function would provide some indication of a failed sensor.
In general, the sensor check will induce an electrical pulse into the sensor that will cause the mechanical components in the sensor to move. The seismograph in turn measures this movement, just as if it was a true vibration, and the response is recorded. This response is then analyzed to make sure the sensors are operating within an acceptable range.
This is a very good indicator that the sensors and unit are working properly. However, the sensor check is not a calibration check and cannot replace the annual calibration process. The sensor check does not compare the measured result against an external traceable reference sensor, nor does it test the entire electronic circuits that are integral to the geophone response.
What the calibration certificate means
When your seismograph is calibrated by an authorized calibration facility, the facility will issue a calibration certificate. The calibration certificate provides the list of reference equipment used in the calibration process. In order for the calibration to have any validity, this reference equipment must be itself calibrated by equipment, which is traceable to a nationally recognized standard, such as the National Institute of Standards and Technology (NIST) in the United States, or the National Research Council (NRC), in Canada. The calibration certificate should also contain the model, serial number, date the instrument was calibrated, and the name of the person who performed the calibration. Should an authority question your seismograph records, this certificate is the document that provides proof of professional calibration.
The reference equipment used in the calibration process must be even more accurate than the equipment being calibrated. The reference equipment must itself be calibrated by even more accurate equipment that is traceable.
Importance of manufacturer certified calibration
There are individuals and companies worldwide that are not certified by the manufacturer to perform seismograph calibration, yet continue to do so. It is in your best interest to have your seismograph calibrated by the specific manufacturer or its authorized agents.
The key factor is the integrity of the measured record if it is ever called up as evidence in a court of law. Using a manufacturer-certified facility ensures that proper procedures are followed when calibrating your seismograph. This removes any uncertainty associated with the reliability and measurement accuracy of your seismograph. Using unauthorized facilities may cause problems in court if the reference equipment is not traceable, or if the certification documents are incomplete. In some instances, unauthorized facilities have even been found to calibrate equipment without ever updating the calibration date within the instrument. If an improper calibration date is printed on vibration records, it may call into question the validity of the report itself.
Also, if a seismograph does require repair, the manufacturer has the best experience and knowledge to find and fix the problem. They will also ensure that any replacement parts that are used meet the specifications for the equipment. Unauthorized facilities do not have access to test specifications, procedures, or parts lists, and some of these facilities may use substitute parts that do not meet the functional requirements. This can ultimately lead to inaccurate vibration levels being reported.
Calibration service providers should:
- Be authorized and trained by the manufacturer;
- Have reference equipment calibrated to a traceable standard;
- Provide copies of the calibration certificates for reference equipment;
- Record the “as found” condition as part of the calibration procedure; and
- Test the microphone and geophone sensors at multiple points within their stated frequency range.
If seismographs are serviced regularly, annual calibrations are often provided free of charge. They also provide a good opportunity for hardware and software upgrades.
Conclusion
When you send your seismograph out for its annual calibration remember to manage the associated risk. The factors listed above will help to lower your risk and provide assurances to the regulatory authority that you are proactively monitoring your vibration levels.
1. McGraw-Hill, Dictionary of Scientific and Technical Terms, Fifth Edition.
Information provided by Instantel, Inc.
VSIs Push the Crushing Envelope
Improved wear and larger and more versatile crushers help VSIs gain acceptance in aggregate operations.
By Bob Drake
Superpave specifications for aggregate cubicity served as a significant market catalyst for vertical shaft impact (VSI) crushers. Having gained wider acceptance at aggregate operations, VSI users and manufacturers now are pushing the application envelope to encompass more than just shaping or beneficiating stone.
Larger VSIs, greater flexibility in machine set up, better wear materials and component designs, and more effective dust control systems are moving acceptance of VSIs to a level closer to that of horizontal shaft impactors and cone crushers in quaternary, tertiary, and even secondary circuits.
Improved wear rates is the major story from almost every VSI manufacturer. This is accomplished through tweaking the design of feed tubes, distribution plates, rotors, and shoe tables to enhance material flow through the crusher; and through incorporation of ceramics and tungsten on high wear surfaces and in castings. In addition, manufacturers have focused on making wear part replacement easier and faster.
Flexibility is the second chapter of the VSI story. The debate about rock-on-rock vs. rock-on-steel crushers has largely been muted by development of versatile machines that can be configured — and changed — to best suit the application. In addition, larger tubs and improved wear rates are expanding the application of VSIs in secondary circuits and in hard and abrasive stone.
Dust control, long a concern with VSIs because of the volume of air they can push through the crusher, is being addressed in several ways. Air recirculation systems, strategically placed spray nozzles, and improved material feed systems are three of the methods manufacturers are using to suppress dust.
Following are brief descriptions of how various manufacturers are addressing these and other VSI design and operating issues. Additional information is available using the appropriate InfoExpress number and the link on Aggregates Manager’s website (www.aggman.com).
VSI Crushers
1. Cemco
Topping out Cemco’s line of seven VSI models are the Turbo 160 and Turbo 175. The 77,000-lb. Turbo 175 is a shoe-and-anvil machine — rock shelf is optional — with tables available to hold three, four, or five shoes. Each 136-lb. shoe is designed so that the two bolts holding it in place don’t need to hold against centrifugal and crushing forces, the company says. Speed and throw distance can be varied to maximize crusher efficiency. Throughput, a function of horsepower, has ranged from 800 to 1,300 tons per hour on two Turbo 175 machines — 800 and 1,000 hp, respectively — that have operated for more than a year, according to Cemco. The Turbo 160 has similar throughput capacities, but at 56,000 lb. is just small enough to be portable. The maximum long-side feed size in both crushers is 7 in. processing limestone. Cemco is experimenting with ceramic shoes in the Turbo 175. InfoExpress 701
2. Impact Service Corp.
Impact Service Corp.’s (ISC) newest VSI, Model 130, weighs 86,976 lb. (without power), has a 130-in.-diameter tub, and 61.25-in.-diameter impeller table assembly with 266-lb. shoes. ISC also introduced larger impeller tables on its Model 103, Model 77, and Model 82 VSIs. The impeller table on the Model 103 is 54.5 in. in diameter and features a four-bolt shoe-fastening system with the addition of a vertical lock pin recessed into the face of the shoe bracket (see inset photo). The new design can handle larger feed sizes and faster impeller table speeds, ISC says. Models 77 and 82 now have a 48.5-in.-diameter table with as many as seven shoes for maximum fines production. Larger diameter tables, which allow increased shoe spacing, reduce amperage draw per ton, allowing increased tonnage and lower costs, according to ISC. The company is in the process of developing a line of impeller shoes, anvils, and feed discs with ceramic imbedded internally for increased wear life. InfoExpress 702
3. Kolberg-Pioneer
Kolberg-Pioneer’s five VSI models can handle maximum feed sizes ranging from 2 in. to 6 in. Three of the models are available in either standard (shoe and anvil), semi-autogenous (rotor and anvil), or fully autogenous (rotor and hybrid rock shelf) configurations. The hybrid rock shelf, unique to Kolberg-Pioneer, incorporates rock-on-rock and rock-on-steel crushing. Material collects on a shelf impact area in front of the anvils, providing abrasion protection (see inset photo). The anvils back up and support this accumulated material for increased crushing efficiency, the company says. Kolberg-Pioneer’s VSIs are available with shoe tables or rotors. Rotors have 100 percent bolt-on wear parts, including replaceable carbide strips. Tables are available with pin-on or bolt-on shoes and replaceable liners. InfoExpress 703
4. Metso Minerals
Metso Minerals offers two series of its Barmac VSI crushers for applications requiring rock-on-rock or rotor-and-anvil configurations. The Barmac B-Series has a rotor and rock shelf and a hydracascade feed system to divert a portion of the feed directly into the crushing chamber, bypassing the rotor. The amount of cascading material can be adjusted manually or by an automated plant system while the crusher is operating. Other crusher adjustments include rotor speed and diameter and choice of crushing chamber cavity rings. An optional control system can monitor vibration and bearing and motor temperature. Seven B-Series models have maximum feed sizes ranging from 3/4 in. to 3 in. Four VSI models in Metso’s VI-Series accept maximum feed sizes from 1.6 in. (closed rotor) to 6 in. (open rotor). Crushing chamber configurations can, in the same frame, be changed from open rotor and anvil to closed rotor and rock shelf. Cylindrical anvils, unique to the Metso Barmac VI-Series, can be rotated when half worn. The VI-Series design reduces dust emissions by reducing and recirculating air flow within the crusher confinement hood, Metso says. InfoExpress 704
5. REMco
REMco’s RockMax and SandMax rock-on-rock lines of VSI crushers and ST/AR rock-on-anvil VSIs accept feed rates up to 1,500 tons per hour and feed sizes up to 4 in., typically in tertiary or quaternary circuits, according to the company. Machine power requirements range from 60 hp to 1,500 hp. REMco’s rotors are available in three-, four-, five-, or six-port designs with drop-in, non-bolted tungsten tips for easier replacement. Hardened AR steel replaceable top and bottom wear disks reduce the amount of repair welding on the rotor body, the company says. Four- or five-shoe tables also are available for ST/AR models. ST/AR (Swing Top/Anvil Ring) crushers have reversible anvils on a multi-position ring that can be raised or lowered to maximize anvil wear. All ST/AR models can be converted from anvil rings to rock-on-rock chambers. REMco recommends use of anvils only when materials have an abrasive content of less than 15 percent, defined as the sum of silica, alumina, and iron as a percent of the total chemical analysis of the rock. InfoExpress 705
6. Sandvik Rock Processing
Sandvik Rock Processing introduced the Merlin-VSI featuring a Bi-flow feed system and Hurricane rotor that work together to optimize crusher loading, according to the company. The Bi-flow system allows directional control of by-pass material, providing control of product gradation and reducing wear to internal components, Sandvik says. Design of the Bi-flow feed hopper and gates also reduces dust emissions, according to the manufacturer. A new rotor design has fewer wear parts that can all be changed without removing the rotor from the crusher. InfoExpress 706
7. Terex Impact
Terex combined its VSI resources from Canica and Cedarapids to form a group called Terex Impact, which focuses on VSIs and horizontal-shaft impactors. Experts in the group have about 130 years combined experience in the impact crushing industry, including with many major VSI manufacturers. Terex is in the process of introducing a new series of VSI crushers that will incorporate more than 100 new design features. The line of eight models, ranging from 15 hp to 1,200 hp, will be available in both open-shoe table and closed-rotor configurations. The largest VSI, C-3000, will handle a top feed size of 12 in. Model C-2300, to be introduced in August, will have tungsten and ceramic wear parts that the company says allows use of the standard type of shoe-and-anvil crusher in traditionally rock-on-rock applications. Tungsten wear parts allow VSIs to operate at higher speeds than with standard chrome castings, Terex Impact says. Tungsten and ceramic wear parts also are being used in its enclosed rotor designs. Terex offers an optional Crusher Management System for its VSIs that allows remote operation and monitoring by computer or PLC. The system monitors and logs lubrication and bearing temperatures, vibration levels, motor amp draw, and crusher coast-down time. InfoExpress 707
8. Texas Crusher Systems
Texas Crusher Systems offers a VSI with an automatic rotor balancing system that the company says eliminates the need to balance the rotor with each wear part change and the need to change all wear parts in the rotor to achieve balance if only one part is worn out. Other crusher features include a distributor plate that rotates more slowly than the rotor for improved wear life, material packs to minimize the number of wear parts, tungsten carbide for major wear parts, no lid or side liners, and a non-mechanical air return system to minimize dust. InfoExpress 708
VSI Wear Part Options
Wear parts play a critical role in successful application of VSI crushers. In addition to OEM parts, following are some of the replacement options available from wear material manufacturers.
Columbia Steel
In addition to standard wear parts, Columbia Steel Casting Co. custom designs VSI shoes and anvils for specific applications. The company says it often works closely with aggregate producers to evaluate wear patterns and develop reduced-wear solutions from its range of high-chromium alloy irons. InfoExpress 709
ESCO
ESCO Corp. supplies replacement wear parts for a variety of VSIs. Parts are cast from ESCO alloy 35S, a chrome white iron that the company says has good toughness with superior wear characteristics. Shoe weight is maintained to close tolerance to minimize vibration, ESCO says. InfoExpress 710
Kennametal
Kennametal offers VSI center feed disks made from its KenCast wear material in various shapes and sizes up to 21 in. in diameter. KenCast has tungsten carbide buttons imbedded in hardened steel. InfoExpress 711
Magotteaux
Magotteaux’s Xwin composite material is available in VSI shoes and anvils. Xwin, a metal matrix composite consisting of metallic and ceramic alloy, combines the hard surface of ceramic with the mechanical properties of cast iron or steel, according to the company. This makes the wear parts sufficiently strong to prevent breakage in service and provides wear resistance that is three to four times greater than chrome alloy, Magotteaux says. InfoExpress 712
Bob Drake is editor for Aggregates Manager.
Conquering Belt Wear Problems
Ultrasonic monitoring program helps Vulcan’s Carrabus Quarry improve conveyor belt selection and expense.
The ultrasonic gauge transmits soundwaves into the belt that bounce off the ply.
A new ultrasonic monitoring program being used at Vulcan Materials Co.’s Carrabus Quarry, in Concord, N.C., has led to significant improvements in the life cycle costs of conveyor belts there.
The monitoring program, offered through Goodyear Tire & Rubber Co.’s authorized conveyor belt distributors, helps the Vulcan staff evaluate wear conditions, predict the remaining life of various conveyor belts, and prove that a change in belt type was a sound investment.
According to David Statum, former plant foreman at the Carrabus Quarry and current plant manager of Vulcan’s nearby Clear Creek Quarry, the operation began looking at its belt investments approximately two years ago. Statum says that while planning a new belt purchase, he reviewed old purchase records and learned that the belt on one particular conveyor was being replaced every 11 to 13 months. “I knew we should be getting more life out of them,” says Statum. In response, he sought advice from Goodyear Technical Manager Mark Wilke.
Wilke visited the operation and used Goodyear’s ultrasonic gauge to evaluate the belt. Initially, he assessed the second belt off the primary. which runs on a steep angle with a lot of tumbling action coming from the minus 14-in. rock it transports to the screen tower. Since then, he has used it on a number of other belts at the operation.
Using an ultrasonic sensor, Wilke tests various points across the width of a belt, then moves 50 to 60 ft. up the belt for another set of readings. Accompanying software averages multiple sets of readings to eliminate anomalies. The entire process takes about five minutes to complete.
The unit, which consists of a probe that is attached to a wire running into a handheld unit, transmits a soundwave into the belt that bounces off the ply.
The readings are fed into an accompanying computer program that incorporates factors such as type of rubber, rubber thickness, temperature, and tonnage and estimates remaining belt life.
Based on the readings Wilke took at the Carrabus Quarry, he recommended a change in belt type. Rather than using a conventional Grade 2 belt, he recommended switching to a Conquest belt, which features a premium abrasion-resistant cover.
While Statum says that he was initially concerned about the cost of the Conquest, which was approximately 25 to 30 percent higher than a conventional belt, ongoing monitoring of the system has proven it to be a worthwhile investment.
“Based on the way the conveyor belt was wearing in the beginning, we were able to project an extra 50 to 60 percent life out of this belt compared to the other belt,” says Statum. “That’s just for the conveyor itself. It doesn’t include downtime to replace it or splicing, so that automatically related to cost savings.”
Statum says that following an ultrasonic monitoring session, he receives a spreadsheet that shows the date of the sample, tonnage, and recommended/estimated belt life.
“It also puts (the information) on a graph and gives you a visual of how the belt is wearing,” he adds. “What’s really interesting is that if you have a problem with a belt feeding to one side — not enough to see it visually, but enough to cause the conveyor to have tracking problems — this graph could help you see it.”
That feature not only helps with current conveyor maintenance issues, but also helps with planning for future belt investments.
For example, Statum says that the graph provides insight not previously available into future belt performance. That enables a producer to test a new belt type and see how it performs without waiting for it to wear out.
“There wasn’t a way of looking at a belt until it was worn out,” says Statum. “ This just lets you see what that cross section looks like without having to cut the belt in two and measure it.”
Based on the performance of the operation’s first Conquest belt, Statum says that the Carrabus Quarry purchased an additional Conquest belt. The ultrasonic gauge readings played a large part in that decision: “They came in with a package, made a suggestion, and were able to follow up with ultrasonics,” says Statum. “It helped prove that this was the right decision for that belt.”
“In this industry, everyone talks about cost per ton,” notes Wilke. “This is truly a way that we can start analyzing our customers’ cost per ton.”
The Bottom Line
An ultrasonic monitoring program helped Vulcan Materials Co.’s Carrabus Quarry select the best belt for operating conditions and extend belt life by approximately 50 percent.
To submit a suggestion for a Success in the Field or for more information about any of these stories, contact Aggregates Manager at 330-966-2454, Fax: 330-966-2454 or email at bob@aggman.com