What Is VSI?

All roads, you might say, lead to the Vertical Shaft Impactor (VSI) because these crushers make it possible to create roadways and just about everything else. Francis E. Agnew of California patented one of the first Vertical Shaft Impactors in . His configuration stacked three VSIs atop each other to produce sand, thus starting the VSI evolution.

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Today, VSI crushers – and the folks who rely on them – have produced many configurations to include everything from the addition of cascading material into the crushing chamber, to air swept separation of lighter product. One version suspends the shaft from above like a sugar centrifuge. It’s also one of the most feature-patented crushers, so some of the things mentioned here might be unique to a single manufacturer. VSIs apply a large amount of energy to crush material and that’s why it’s one of the most versatile crusher configurations today.

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VSI Benefits

When it comes to producing materials such as aggregate for road making, VSI crushers use a high-speed rotor and anvils for impact crushing rather than compression force for the energy needed for size reduction. In a VSI, material is accelerated by centrifugal force by a rotor against the outer anvil ring, it then fractures and breaks along natural faults throughout the rock or minerals. The product is generally of a consistent cubical shape, making it excellent for modern Superpave highway asphalt applications. The rotor speed (feet per minute) controls final particle size.

The VSI’s high cubical fracture percentage maximizes first-pass product yield and produces tighter particle size distribution. It has a high-throughput capacity ideal for beneficiation (elimination of soft material). Properly configured the VSI accepts highly abrasive materials. It has simple operation and maintenance. You can quickly change product size by changing rotor speed or cascade ratio. Some models have reversible wear parts to reduce downtime. The VSI typically has low operating costs even in high-moisture applications because of reduced energy costs and low wear cost per ton.

VSI Disadvantages

There are some feed size limitations with a VSI because of the small feed area available in the center of the rotor. Tramp material in the feed such as gloves, tools, etc. can cause problems with imbalance. The high RPM and HP require careful balance maintenance such as replacing shoes on both sides of the rotor at the same time. High wear part cost may be a problem for some hard abrasive materials, but the VSI may still be the best option.

VSI Applications

Major limestone applications are for Superpave asphalt aggregates, road base, gravel, sand and cement. Industrial uses include: corundum, corundite, ferro silicon, glass, refractories, silicon carbide, tungsten carbide and zeolite. Mining applications include: bauxite, burnt magnesite, iron ore, non-ferrous metal ore, perlite and trona sulfate. VSIs are excellent for everything from abrasive materials to waste and recycling applications.

VSI Crushing Method

The VSI is typically used after a primary or secondary crusher. This makes a VSI ideal for making sand and for making coarse and medium aggregates for concrete/asphalt production.

Feed size and characteristics will affect the application of a VSI. The feed size is limited by the opening in the center of the rotor. Normally less than 5-inch material is desired, but very large VSIs can handle up to 12-inch feed. Another feature that will affect application is moisture, which can make the feed sticky. Required production capacity is the final limiting criteria. Large primary horizontal shaft impactors can output up to TPH and more. TPH is about the maximum for a VSI because of the limiting motor size and the rising G-force of a high-speed rotor, which is calculated by multiplying the radius times the square of the RPM.

Shoe configurations are many: rock on rock, groups of rollers, special tip wear parts and many others. The metallurgy of the shoes is also highly varied. Rotors can have three to six shoes. The number of shoes is typically governed by the diameter of the rotor. The larger the diameter rotor, the more openings are possible. Computational Fluid Dynamics (CFD) mathematical models are utilized to simulate the flow and collision forces to reveal solutions for lower wear cost, consistent final product, and higher energy efficiency.

The material to be crushed is fed into the center of an open or closed rotor. The rotor rotates at high rpm, accelerating the feed and throwing it with high energy into the crushing chamber. When the material hits the anvil ring assembly, it shatters, and then the cubical shaped product falls through the opening between the rotor and the anvil and down to the conveyor below.

The rotor speed (feet per minute) controls final particle size. Speeding up the rotor will produce more fines, slowing it down will produce fewer fines.

The VSI features multiple rotor/anvil configurations for various applications. From open or enclosed rotors to the tubular rotor, each machine is configured for their unique application. In many cases the rotor table, rotor assemblies, anvil ring or rock shelf are interchangeable, allowing maximum application flexibility.

Open top metal rotor shoe on metal anvil

The open top metal rotor is good for large feed or medium to very hard material, but it will work best for softer materials. It can handle medium abrasive, dry or wet, but not sticky materials. High reduction ratios are common, which are excellent for sand and gravel production in closed loop systems. Shoe shape can change the production size range. A straight shoe face design produces finer product, and a curved shoe face design produces coarser material.

Tubular metal rotor shoe on metal anvil

The tubular rotor creates higher tip-speeds, which increases first pass yield with tighter particle size distribution and also reduces the recirculation loads. One unique feature is that the rotor rotation is reversible, allowing wear on both sides of the tube. Rotating the tube itself one-quarter turn also doubles the wear.

Enclosed metal rotor shoe on metal anvil

The enclosed top plate on a rotor primarily prevents material from escaping from the top of the rotor, which could happen with an overfed open top rotor.

(Above: Rock shelf when VSI at rest. In operation, the brown rock fills the chamber to the upper roof ring. Rock impacts rock in operation.)

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Enclosed autogenous rock rotor table on autogenous rock shelf

Any time the material or rock is used as an impact wear surface the term autogenous is used. Putting a top on the rotor table and shoes allows autogenous use. During operation of the VSI, a bed of material can be designed to build up inside the rotor against each of the shoe wall segments. The bed, which is made up of material that has been fed to the rotor, extends to a wear tip. The bed protects the shoe wall segment from wear.

Concerning the rock shelf anvil, it forms a near vertical wall of material upon which the accelerated material impacts. “Rock-on-rock” crushing reduces maintenance but can require up to 30 percent of material recirculation before meeting size requirements. Also, the rock shelf anvil absorbs energy that could otherwise be used for breaking, which may reduce efficiency. More RPM may be needed to achieve the same result as a solid metal anvil.

Good for medium abrasive materials, rock-on-rock configurations of either or both rotor and anvil may produce consistent material with low-wear cost and can handle wet but not sticky conditions. Reduction ratios from 2:1 to 5:1 can be expected. It’s widely used for quarried materials, such as sand and gravel.

Due to the many configurations of the VSI feed, rotor, anvil and open- or closed- system design; testing is the only way to ensure proper application of a VSI crusher.

Summary

The VSI is one of the most versatile crushers available on the market today. Even with some limitations, like feed size and output capacity, VSI features have been and continue to be developed to maximize first-pass yields and lower operating costs. If you test your process on full-scale equipment before choosing your VSI, you won’t be disappointed.

In a vertical shaft impact crusher, the aggregate feed is introduced into a shoe or pump spinning on a vertical axis. The aggregate feed is thrown centrifugalLY against a series of anvils, pockets of aggregate particles (i.e., autogenous), or a combination thereof. Vertical shaft impact crusher(uz,es,vi)s produce a small reduction ratio and arc often used for crushing tines.

In hammer mills the impact of a fast-moving hammer on a slow-moving rock causes shattering. It can also be caused by the collision of a rock traveling at high velocity with another rock or a breaker plate. This is the concept of a vertical-shaft impact crusher.

Vertical Shaft Impact VSI Crusher



The Vertical Shaft Impactors or VSI Crusher are one type of impact crushers, which offer higher reduction ratios at a lower energy consumption. These impactors

can be considered as a ‘stone pump’ operating like a centrifugal pump. The material is fed through the centre of the rotor, where it is accelerated to high speed before being discharged through openings in the rotor periphery. The material is crushed as it hits the liners of the outer body at high speed and also due to the rock-on-rock action. These crushers are mainly used in the production of fine materials, including sand, with a good cubical shape.

A number of VSIs are available in the market. The most popular VSIs are the Sandvik’s CV Series by Sandvik Mining and Construction, Sweden, and the Barmac B and VI Series by Metso Minerals, Finland. These crushers use the impact and rock-on-rock crushing principle for size reduction, which minimise wear costs.

Sandvik’s CV range of VSI crushers are autogenous VSI crushers covering a capacity range extending to 600 tph nominally. The whole range has been designed to ensure maximum production and yield of product for the lowest possible power consumption.

Sandvik’s VSI crusher is primarily a third or fourth stage crusher. The rock-on-rock crushing principle offers two main advantages:

• product gradation remains constant, even as rotor-wear parts wear, and
• contamination rates are extremely low, as no wear parts are used to directly crush the rock.

Feed material enters the crusher via a rock-lined hexagonal feed hopper. Rotor-material feed rate is controlled by the hydraulically operated rotor throttle gate. This material falls by gravity into the feed tube, which subsequently feeds the hurricane rotor. The crusher uses a rock-lined hurricane rotor to accelerate material. This material is accelerated by centrifugal force to typically 45 to 62 m/s. The crushing chamber is lined with a solid bed of material against which the energised rotor material impacts. It is this high-velocity autogenous impaction that causes impact, cleavage and attrition of the feed material.

The computer-designed crushing chamber geometry of these crushers give improved crushing action within the chamber when combined with the Bi-Flow system. The path of the material from entry (feed hopper) to exit (discharge chute) is controlled via autogenous rock-lined pockets within the crusher. This improved design further reduces points of contact within the crusher, resulting in extremely low crusher component wear.

Sandvik VSIs have the ability to handle hard, abrasive, fine, moist, or sticky feed materials, which makes them suitable for all of applications, such as quarries and gravel plants (production of premium-shaped aggregates for concrete and asphalt); recycling (processing glass bottles, etc., to sand specification and recycling of ceramics); mines (liberation of ores for heap leaching and differential liberation of hard particles, e.g., gemstones from softer matrix); cement works (crushing cement clinker to maximise fines prior to milling); and industrial minerals (crushing of highly abrasive minerals, e.g., fused alumina, silicon carbide, zirconia, mulochite, calcined bauxite, etc.).