VSIs

Jul 3, 2001 12:00 PM, Dan Brown

More than ever, vertical shaft impact crushers (VSIs) are proving to be a valuable solution in aggregate processing circuits. Manufacturers report rapidly increasing sales of VSIs for several reasons.

One factor is Superpave, which imposes tighter specifications for aggregate cubicity and soundness. VSI crushers are well-suited to provide such products. Secondly, cubical stone products are better for all types of concrete because they achieve higher strengths and savings in cement content. What's more, VSIs "have a lower purchase price, lower installation costs and no greater operating cost than the traditional compression crushers such as cones, even in hard abrasive rocks such as granite," said Damian Rodriguez, general manager of Remco.

Notably, tighter specifications and new demand have heated up the competition among VSI manufacturers. And in some cases, this competition has pitted VSI proponents against cone crusher makers in the battle for customers.

In the past, some aggregate producers have regarded VSI crushers as iron-eaters or low-production, problematic machines. Recent years, however, have seen the reputation of VSI crushers improve considerably, said Jerry Heckert, manager of application engineering for the Crushing and Screening Equipment Division, Svedala North America.

"With the advent of Superpave, people have found that the VSI is a great tool to achieve the shape requirement of the flat and elongated limitation," said Heckert. "A lot of plants are adding a VSI to meet the shape requirements of Superpave."

Why can VSI crushers produce a more cubical product than cones? Cone crushers work by compression and mainly use cleavage fracture to reduce the stone to smaller particles, said Tim Harms, applications specialist at Kolberg-Pioneer. By definition, he said, cleavage fracture occurs when the energy applied is just sufficient to load comparatively few regions of the particle to the fracture point. Some aggregate is highly planar, and when energy is released along those planes a flatter product is produced.

By contrast, a VSI crusher uses stored energy by giving the aggregate velocity to achieve a shattering fracture rather than a cleavage fracture. "The energy that the material carries to the impact area is released in all directions," said Harms. "The cone and VSI can work very well together," he added. "Cones are well-suited for larger feed sizes, and then you can follow the cone with a VSI to meet limitations on flat and elongated particles."

Or, you can run a VSI side-by-side with a cone crusher. "You will get less flat and elongated product from the VSI," said Harms. "You can use the more cubical product of the VSI to blend with the cone's products."

Another benefit: in cases where manufactured sand will help meet asphalt specifications, a VSI can fill the bill.

If a VSI crusher replaces a cone in the third stage of the plant, said Remco's Rodriguez, "a little rethinking of the circuit is in order." He offered the following ways to avoid problems:

- Ensure that the available screening area is sufficient to handle the higher capacity of the VSI crusher. A VSI generally produces a finer gradation than a cone and sufficient screening area is necessary to take advantage of the additional production.

- Run the VSI crusher at or near its full motor-power capacity. "Dribble feeding a VSI crusher is a big operating error," said Rodriguez. It increases wear cost due to low wear-part utilization and causes erratic product gradings. Controlled and constant feed rates are essential to maximize VSI performance. "Often this places a demand on operating personnel to sharpen their skills in maximizing the upstream performance of the plant to make sure it can keep up with the VSI's capacity," Rodriguez said.

- Select the right VSI crusher for the job. VSIs are available in a broader range of configurations than cone crushers, and a producer must learn the finer points of VSI selection and application.

Often, producers try to achieve too much reduction with a VSI. "Folks try to take one VSI and reduce 6- to 8-in. stone down to asphalt sizes of 5/8- or 1/2-in. minus," said Harms. "Generally, VSIs are most economically applied at the smaller end of secondary and tertiary stages of a plant. A common error is violation of recommended feed sizes for the crusher configuration."

Finding the right configuration Manufacturers offer an ever-increasing number of crusher sizes and configurations. There are three basic types of VSI crushers:

- autogenous - rotor and rock shelf, relying on rock-on-rock impact;

- semi-autogenous - rotor and anvil ring, or shoe table and rock shelf; and

- standard - shoe table and anvil ring, which uses rock-on-steel impact.

It is important to use the right crusher configuration for the type of rock you're crushing. "We see applications where producers are running autogenous - using a rotor and rock shelf in limestone - where they should be running a shoe and anvil machine to achieve more production," Harms said. "Plus, a shoe and anvil machine will produce less waste fines (100 and 200 mesh) in limestone. Conversely, we've seen people run a shoe-and-anvil machine in sand and gravel, or abrasive shot rock - where it would be more economical to run an autogenous machine."

Canica-Jaques Crusher Manufacturing Co. offers several new features on its crushers:

- Shoes and anvils made of a new ceramic material, which the company calls a high alloy. Canica-Jaques President Jim Peterson said the new ceramic lasts two to three times longer than the 28% chrome alloy normally used in shoes and anvils. The new material lowers finished cost per ton working in up to 8-in. top size material.

- An auxiliary control box that includes an rpm gauge, a vibration detector, hour meter, oil-system starter and conveyor starter as standard equipment.

- Larger crushers include a 5-ton electric jib crane and hoist as standard equipment.

- An upgraded autogenous rotor, for hard rock applications, that can take up to 3-in. top size.

- A new dust-control system that uses air and water to apply a mist on the discharge conveyor.

One of the company's leading features is its patented vaulted anvil system. The anvils drop into the ring, and because of the angle of rock impact, "you get longer wear life of the parts," said Peterson. Plus, Canica's Model 155 crusher can take 12-in. feed and is rated at 1,000 tph, which Peterson said ranks as the industry's largest feed size and tonnage rate, depending on material.

Cedarapids offers three models of VSIs: the 1800, rated at 150 to 200 tph; the 2100, rated at 250 to 400 tph; and the 2600, rated at 250 to 650 tph. All three are rock-table-and-anvil machines. Rock shelves are offered as an option on the two smaller units, the 1800 and the 2100. The 2600 has four shoes, and the other two machines can have three, four, five or six shoes.

Cedarapids' VSIs can be driven either by electric motors and V-belts or by a diesel engine through a pinion gear located at the bottom of the vertical shaft, said Dave Slaughter, applications engineer for crushing and screening. All three of Cedarapids' VSIs can be mounted on portable chassis, and all three have hydraulic lid lifters. A jib crane to lift the anvil out is an option.

Cemco makes a variety of open shoe tables and patented SuperChipper rotors. Each crusher can accommodate several different rotor, shoe table, anvil ring and autogenous rock shelf configurations.

New at Cemco is the Model AEV-110 VSI crusher. With an initial rated capacity of 600 to 1,500 tph, the machine was undergoing factory testing in the fall. The AEV-110, or Turbo 110, is the world's largest VSI crusher in terms of through-put capacity, according to the company.

"It increases production, requires lower maintenance, provides a lower wear cost and allows internal components to be specifically tuned for a more exact gradation, all the while reducing dust emission," said Neil Hise, Cemco president. The company expects to introduce the machine around the turn of this year.

When fitted with a rotor, maximum feed size for the Turbo 110 will be 4 in.; with a shoe table, 7 in. The version under testing has three shoes. The impeller table diameter is 48 in. Drive motors on the Turbo 110 are installed at the same end of the crusher frame to substantially reduce cyclic vibration and extend bearing life, Hise said.

Impact Service Corp. (ISC), developed a new double-pocket impeller shoe that, according to President Ken Warren, increases wear life as much as 200% compared to ISC's conventional wear parts. "We uniquely repositioned the pockets and added mass to the impeller shoe casting," he said.

The new double-pocket shoe allows ISC's VSIs to take a larger feed size, extend the wear life of the parts and maintain a comparable product gradation to what the existing solid shoe produced, according to the company. Whereas ISC's older pocket shoe could take up to 1 1/2-in. feed size, the new double pocket shoe now can take 2 1/2- to 3-in. feed size.

"We've been developing an all-new larger VSI," said Warren. With a rated feed size of 8 to 10 in., and a 130-in. diameter on the main tub frame, ISC said the new Model 130 VSI will be physically the largest ever made in the world. "We've rated it at 1,000 tph initially," said Warren, "and it's going to weigh close to 100,000 lb." The first model is sold and was expected to be running in a plant in early October.

Kolberg-Pioneer makes five models of VSI crushers with rated capacities ranging up to 300 to 500 tph on two models. Three configurations - standard, semi-autogenous and fully autogenous - are available on the Model 1500, the 2500 and the 4500. "We have plans to develop a rock shelf and rotor for the Model 82, but for now it is a standard shoe-and-anvil machine," Harms said.

Kolberg Pioneer continues to market its hybrid rock shelf, which combines fully autogenous and semi-autogenous (rock-on-steel) crushing methods. "It's a cross between the traditional rock shelf and a clustering of anvils," said Harms. "We've experienced a 30% increase in production efficiency at a given sieve size when compared to traditional, fully autogenous rock shelves.

With the hybrid shelf, rock leaves the rotor at high velocity and a portion of it is driven upward, past the slope of material retained on the shelf. That rock positions itself in front of the anvil, according to Kolberg-Pioneer, effectively providing a wear face. Material exiting the rotor strikes a protective layer of rock, which is backed by a steel anvil. The effect is to extend anvil life and increase crushing action in the chamber, the company said.

"It's like a boiling action," said Harms. "The material slides upward and cascades back down between the rotor and the shelf."

Remco offers 20 models of VSI crushers: 10 SandMax models and 10 RockMax models. Both rock-on-rock and rock-on-anvil designs are available. Six machines are convertible and are sold in both autogenous and rock-on-anvil styles.

Remco said it leads the industry in terms of the number of models and configurations. The company's drive-power range is from 50 to 1,500 hp and the capacity range is from 40 tph to more than 1,000 tph. Remco's ST models feature the latest in hydraulic design for fast, easy access to the rotor and crushing chamber for inspections and repair, the company said.

Remco offers accessories such as supports, skid mounts, portables, dust-collection systems, service monitors, discharge chutes and operators' platforms. The feed range for Remco VSIs is from 4 to 5 in. for larger models and 2 to 3 in. for smaller units.

Svedala offers an autogenous machine with a patented feed arrangement to the crushing chamber. "Essentially you cascade virgin material into the rotor discharge stream," said Svedala's Heckert. "Additional crushing occurs when feed material is injected into the stream of discharge. No additional horsepower is required, and because the material does not go through the rotor there is no additional wear or wear parts cost.

"That allows you to vary the gradation of the crusher discharge to meet many specifications," said Heckert. "The more material you cascade into the discharge stream, the coarser the product; the less you cascade the finer the product."

Heckert said the cascading feature allows an operator to vary product gradation by plus or minus 20% from a neutral gradation. "Normally you can cascade from zero to about 15% without changing the product gradation. If you cascade 50%, you will coarsen your gradation and your cost per ton of material is dramatically reduced," he said.

Svedala offers seven models of VSIs with horsepower ranging from 10 hp. to the largest, the XD120, at 1,200 hp. Normal feed size ranges as large as 3 in.

Texas Crusher Systems makes what it calls an Autobalance Impact Crusher. It is a closed-rotor machine with three port holes on the sides of the rotor and a rock shelf. "The crusher is about 95% autogenous," said Eileen Thrasher, administrative manager and part owner of the company. "Autobalance in the name refers to an automatic balancing system in the crusher's rotor that offsets an imbalance in material. The main wear parts are at the ports of the rotor and those are protected by tungsten carbide pins."

Crusher output varies, depending on the horsepower applied. The crusher can operate effectively from about 100 tph with 200 to 300 hp to a maximum of 575 tph with 600 hp, according to the company.

The basic advantage of Texas Crusher's machine is its low wear parts cost per ton of material put through the crusher, said Thrasher. "We think ours is averaging 5 cents per ton for wear parts - and that's running with 2- to 2 1/2-in.-minus feed, taking it down to 1/2-in. minus in pretty hard, abrasive rock."

Texas Crusher's machine can run for three to four months in hard, abrasive material before the wear pins need replacing, said Thrasher. And in rock that is less abrasive, with less silica content, the crusher has run 15 months, using the same wear parts and with consistent use in the Sacramento, Calif., area, she said.

Education is the route to success with VSIs, according to Remco's Rodriguez. "There are lots of benefits to be gained with VSIs if you educate yourself," he said, "but you're going to have a pretty painful experience if you don't learn the right ways to select, install, operate and maintain these machines."

VSI crushers are different from cone crushers, according to Damian Rodriguez, general manager of Remco, and require special consideration:

- VSIs require drive motors that are designed for severe duty and vertical mounting.

- VSIs are designed for constant, full-power load operation. Operating them at low feed rates or with interrupted feed conditions detracts from their performance.

- VSIs require more frequent inspection intervals than cone crushers due to the smaller and lighter weight of the wear parts. Regular inspections ensure a better managed maintenance schedule.

- VSIs, due to their balanced operation, can be installed on lighter fabricated supports and do not require massive concrete footings or steel structures. VSIs can easily be installed on old cone crusher structures.

- VSIs have lighter lift requirements for servicing than a comparable-capacity cone crusher. Typically, a 3-ton service hoist provides sufficient lifting capacity to service a VSI; a 20- to 40-ton crane typically is required to service cone crushers.

- VSIs require control or elimination of rogue oversize in the feed. Cone crushers are more tolerant of oversize stone.

- VSIs are more tolerant of fines and unclean feed. Cone crushers tend to pack when fines, soil or other contaminants are introduced with the feed.

- VSIs perform well with smaller feed sizes. Cone crushers have difficulty when the feed size is below 11/42 in. VSI users can help make the crusher installation a success by attending to the following items.

1. Know your rock. Be familiar with its characteristics. Know its abrasives content (silicates and alumina as a percent) by performing a chemical analysis, if necessary. Note wear rates on existing equipment such as compression crushers and vibrating screens.

2. Know crushing costs for present equipment. A good measure of future metal wear cost for any VSI is what the present equipment costs. Determine wear cost on tons of finished product, not on crusher feed rate.

3. Evaluate VSI models for maintenance simplicity and operating interval between service shutdowns. Inspect machines operating in similar service and the manufacturers' technical support.

4. Plan installation of the VSI as a project involving the whole plant. The VSI can only be as successful as the environment in which it operates. The best crusher will fail in a poor circuit with poor operating procedures and lack of maintenance expertise.

5. Educate operating and maintenance personnel on the crusher's requirements.