Maximizing screen performance starts with attention to detail from day one.
A well-set screen can mean more dollars down the road, but setting up a new screening circuit involves many variables.
Producers should begin by adjusting and maintaining the screen’s operational settings to match the specific application.
“Speed and stroke are two of the major factors to fine-tune when setting up a screen,” says Ed Sauser, vibratory product manager at Superior Industries.
Proper setting guidelines
Speed and stroke work together in standard formulas designed to optimize screening efficiency for specific applications.
Generally, finer screening requires less stroke and a higher speed while coarse separation means an increased stroke and a lower speed.
The right speed ensures a material travel rate and bed depth that allow finer particles to pass through the screen. In combination with proper speed, the screen’s stroke must be set at a level that’s strong enough to prevent plugging – without risking damage to machine components.
Working closely with your screen manufacturer’s product managers and applications engineers will lead to streamlining the setup process and ensuring your screen is sized correctly for the application.
Most manufacturers use the Vibrating Screen Manufacturers Association (VSMA) formula to determine optimum screen capacity, which is the calculated capacity per square foot of screen area in tons per hour. The VSMA handbook also provides a detailed, illustrated guide for step-by-step screen setup.
Speed kills
The potential downside of higher speeds is often overlooked.
Sauser cautions that “speed kills,” as speed can compromise the life of the machine. With vibratory equipment, he says bearing life is affected exponentially by speed.
A 10 percent speed reduction – if specs are still met – can potentially double bearing life. Conversely, increasing speed by 10 percent can cut bearing life in half.
The bottom line: Don’t run vibratory equipment faster than you have to. If material is blinding or pegging, more speed is required. But if you can do the job with less speed, it’s better for the machine’s wear life.
Attention to detail
Every aspect of an application – from feed size and particle shape to moisture content, media selection and desired cut – affects screen setup and performance.
In Sauser’s experience, producers too often try to do too much with one screen or with one deck. But efficient screening is only possible when material is well distributed.
According to Sauser, bed depth on a deck should not be so deep that it causes finer particles to take too long to reach the media openings and pass through the screening surface.
As a general rule, bed depth to media opening should range from 4-to-1 to 6-to-1 at the discharge end. As an example, a 6-to-1 ratio with a 1/4-in. opening means just 1 1/4 in. of bed depth.
So, define your application thoroughly, and choose settings that support both maximum efficiency and long-term machine life.
Carol Wasson is a veteran freelance writer for the aggregates and construction equipment industries.
Related: Screening (Part 1) | P&Q University Handbook