In some instances, the trucks delivering crushed stone to the asphalt producers are the same trucks leaving potholes and ruts in the road. The problem, however, is not the trucks. It's inadequate roads, which led to Superpave, a higher-standard specification for road material.

The Federal Highway Administration and American Association of State Highway Transportation Officials corroborate to create national standards requiring crushed stone with higher cubicity. The state DOTs conform to the best of their ability. In 1998, 37 states had adopted some standard for Superpave, and the push is for all 50. It's important for aggregate producers to conform if they want a bigger slice of federally funded highway projects. And conforming to new standards often means new equipment.

Most compression crushers produce sliver- and pancake-shaped stone that ruts easily in asphalt roads. As more quarries conform to the higher standards, more are considering vertical shaft impactors. VSIs produce the cubical stone ideal for Superpave.

Cemco President Neil Hise, a VSI producer, says Mother Nature produced the stone with natural fissures that split into a cubical-crystalline shape that fits together perfectly. And a VSI splits the stone along these fissures. Hise says Superpave will withstand the rut-making 80,000-lb trucks with steel-belted radial tires.

“We've got to put more (cargo) on the road with more weight so we can get from place to place with more goods and make more profits,” Hise says. “That's the name of the game.”

Hise says that most Superpave specifications require a cubicity ratio of 5 to 1, and many states are going to 3-to-1 ratio. As the specs tighten, the need for proper equipment is growing.

A VSI is designed for secondary, tertiary and quaternary crushing. It provides higher throughput when combined with compression or horizontal shaft impactors.

When material enters through the vertical shaft, the impeller shoes or closed autogenous rotor turns at a 90-degree angle, using centrifugal force to throw it against a ring of anvils or rock shelf. VSIs can produce material much smaller than traditional horizontal shaft impactors. There also is a higher throughput and fine reduction is greater than in horizontal shaft impactors. But maintenance costs are higher because of sliding wear on the impeller shoes, Hise says.

Initially, many producers are intimidated by the maintenance requirements because of the number of parts in a VSI. But in reality, the maintenance takes five to 10 minutes each day to inspect castings for wear, he says.

To reduce downtime, Hise advises changing castings between shifts or after hours. It helps to have spare rotors, anvil rings and shoe tables. It also pays to match odd castings into pairs or sets. Hise says this will maximize the use of the castings for the most return on the investment.

When a part needs to be replaced, Hise says it can be done in a matter of hours at the site. But, there are several parts to replace including shoes, shoe tables and 16 to 26 anvils. Hise says anvils can weigh as much as 350 lb in the humongous machines, but parts for the average machine are manageable by hand. The smallest VSI weighs 4,500 lb, and the largest is 69,000 lb.

“They all have a vertical shaft, they all have bearings, and they all throw rocks,” Hise says. “It's how you cross the pieces and maintenance and speed that makes the difference.”

The amount of possible internal configurations, however, allows operators to alter the machine to produce multiple grades. Shoes can be added to make smaller material or removed to make the product coarser. Changing the size of the rotor changes the throw distance, which also affects gradation. Also, if the material that enters the impactor is large it will break smaller because of basic physics.

But there is a downside to the physics of a VSI, Hise says. A VSI is similar to a large fan. Free flowing air gets stirred up inside, creating dust. “The greener our country becomes, the more in jeopardy you are from dust. Dust collection is in your future,” Hise says. “They are dust makers, but they can readily have that dust eliminated.”

A simple solution is to add a dust collector. Another is to reduce the airflow by installing air shims on the hopper to prevent fugitive dust.

Adding moisture to the material also is an option, but it should be done with caution. Hise says a small amount of water is fine, but large amounts can decrease crushing efficiency. If the material becomes damp it could cause screen blinding downstream.

Another hazard to VSIs is metal. It can break rotors, shoes and anvils. “Think very seriously about investing in a magnet or a metal detector.”

One way to increase efficiency is by decreasing the rotor's speed, which decreases power consumption and wear rates. Hise says to run VSIs as slow as possible to produce the desired size. Adjusting the throw distance with special anvil rings also increases production.

Another way to ensure machine efficiency is developing a working relationship with reliable equipment manufacturers. “Our industry is relationship driven,” Hise says. “That's the first thing that they're selling you.”

A crusher is not a used car. You can't afford to buy a lemon from a fly-by-night operation, Hise says. Know the company will be there for technical and mechanical support in the future. Pick a company with a good reputation because the crusher is one of the biggest investments that a quarry can make.