Impactors

Impactors

Impactors are built for maximum reduction in single-stage crushing in hard stone, secondary aggregate, and primary or secondary asphalt and concrete recycle applications. They are engineered for high reduction rates and high yield, each model features high-chrome alloy hammers that provide longer wear life due to their inherent abrasion-resistant characteristics. Additionally, rotors are hard-surfaced in critical wear areas, and also thermal-stress relieved. Rotor assembly is dynamically balanced at the optimum RPM for smooth operation.

Design

Typically, a cascade impactor is made up of a number of classification stages consisting of a nozzle and an impaction plate arranged. In each stage an aerosol stream passes through the nozzle and impinges upon the plate. Particles in the aerosol stream having a Iarge enough inertia will impact upon the plate, and smaller particles will pass as an aerosol onto the next stage. By designing each successive stage with higher aerosol velocities in the nozzle, smaller diameter particles will be collected at each stage. Particles too small to be collected in the last stage are generally collected on an after-filter.

Operation

It has been shown that an impactor has the ability to sharply classify particles into distinct ranges of aerodynamic size. In some applications, forces other than those due to inertia, such as gravity and electro statics, may affect the collection characteristics. There may also be some effects from surface roughness in the nozzle and the wall thickness at the nozzle exit. These effects are generally small. However, the effects of inlet losses, interstage losses, and particle reentrainment from the impaction plate may be considerable and should be minimized.

Inlet losses

As is the case with any size analyzing instrument, the efficiency with which the impactor inlet is sampling the aerosol partic1es must be known before accurate size distribution and particle concentration data can be obtained. Although the efflciency for sampling from calm air environments may be high one should determine the sampling for typical cross-wind velocities. If the impactor is to sample from a moving air stream such as in ducts and stacks, isokinetic conditions at the inlet will aid in efficient sampling of particles.

Interstage losses

Particle losses in an impactor, generally referred to as wall losses or interstage losses, is the deposition of particles on surfaces other than the impaction plate. Currently, no theory exists to predict these losses, and thus, they must be determined experimentally.

Common Types

• Horizontal Shaft Impactors
• Vertical Shaft Impactors

Features

• Compact Size
• Rugged Construction
• High Performance
• Efficient Operation