How to Choose vibrating screen feeder?

Author: Polly

Oct. 07, 2024

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How To Size and Select a Vibrating Screen for an Aggregate ...

Screening is one of the most important parts in aggregate production. It takes place before and/or after the crushing stage (or stages) and produces the specifications required of the final products.

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The purpose of screening is to separate a flow of aggregate particles into uniform sizes. This is accomplished by using Vibrating Screens.

What is a Vibrating Screen?

Vibrating Screens are machines used to separate aggregates by particle size by means of an exciting force applied to the machine. The vibration lifts the material, causing it to stratify, allowing the smaller material to move from the top of the depth of material to the bottom of the material, thus exposing them to the screening surface.

Types of aggregate Vibrating Screens

There are two main types of aggregate vibrating screens for dry screening applications:

Horizontal Screens
Inclined Screens

The primary difference between Horizontal Screens and Inclined Screens is the Inclined Screen uses gravity to help with the flow and conveyance of the feed material.

However, both screens offer advantages for various applications.

Inclined Screens

Inclined Screens are the most popular for aggregate applications. They are installed on an incline (anywhere from 5-45 degrees depending on the type of screen and the required cut) and employ the use of gravity to propel material down the screen. Since gravity helps to move the material, this type of screen requires low energy and low stroke.

Horizontal Screens

Horizontal Screens are run flat at zero degrees but can be inclined or declined as much as 10 degrees in either direction. Because they don&#;t rely on gravity to move the material forward, Horizontal Screens require higher energy and a larger stroke.

These types of screens are ideal for low-profile applications where height requirements are limited, which makes them a great choice for portable plants. In stationary plants, they are often used as tertiary or finishing screens. Finer screening applications can greatly benefit from this type of screen.

Known for their efficiency and reliability, Horizontal Screens offer more accurate particle sizing. The high G-forces required to move the material ensure screen plugging is virtually eliminated, allowing for more continuous open area. The flat orientation of the Horizontal Screen allows material to be retained on the screen longer for higher efficiency. It also makes them a great choice for wet screening applications.

How to select the right aggregate screen

Because screening plays such an important role in producing the required specifications of a final product, it is imperative that the right screen is selected for the job.

Vibrating Screen selection is based on the following factors:

The maximum tons per hour
A gradation of the feed material
The type and weight of material
The desired size of separation
Any surface moisture on the material
Any special operation requirements, including physical characteristics of the feed or product requirements

Sizing Vibratory Screens

Vibratory Screens come in a variety of sizes. They can range from 4&#; to 12&#; wide and 6&#; to 32&#; long. The width of the screen determines the carrying capacity of the screen deck, while the length of the screen determines the overall efficiency of the screen. Typically, the length of the screen is 2.5 to 3 times the size of the width.

Every manufacturer has its own screen sizing formula. Screens are tailored to an operation based on the following factors:

Basic capacity &#; how much material is going to pass through a certain opening
Incline &#; how much of an incline, if any
Deck &#; not all of the length of the lower decks may be utilized, as material has already traveled down some length of the upper decks before reaching the lower ones
Oversize &#; how much material should go over the deck
Half size &#; how much material is half the size of the media opening With a high percentage of half size, the probability of the material passing through the screen openings will be higher, and the screen will be that much more efficient.
Slot &#; how large the openings in the screen are
Condition &#; applies to both the feed material and the atmosphere around the plant. Is the material wet and sticky? Does it have a high percentage of clay? What is the temperature outside? Is it a wet or dry climate?
Shape &#; Round or cubical particles have a higher chance of passing through the screen openings than a flat, elongated particle that has to find just the right position to fall through
Weight &#; the density of the material
Open area &#; the more open area on the screen, the better the chance particles will find an opportunity to pass through

How many decks do I need for my Vibratory Screen?

Vibratory Screens can be configured with one, two, three or four decks. Some fine screening operations can even have as many as eight screening decks. Three decks are pretty common in the aggregate industry, but the number of screen decks depends on the number of products the site needs to make.

In a typical application where multiple products are being made, the top deck(s) of the screen makes the coarse cut, the middle deck(s) makes a middle cut and the bottom deck(s) make the fine cut.

Each screen deck is covered with screen media containing the openings for the particles to pass through. Screen media comes in many different forms, and the type of screen media plays an important role in screening efficiency.

What type of screen media is best for my Vibratory Screen?

Screen media is all about open area, or the number of openings in the screen. The more openings in the screen, the more opportunities the particles will have to pass through and the more efficient the screen will be.

However, more openings in the screen can decrease the wear life of the media. The correct screen media for an application will balance both wear life and efficiency.

Common types of screen media for aggregate applications include:

Woven wire
Polyurethane
Rubber
Hybrid

Wove wire cloth is the most consistent, versatile performing media product. It averages 50-70% open surface area in most configurations and provides the most flexibility for operations that need to make frequent media changeouts due to varying product specifications. Overall screening efficiency is good with this type of media.

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Wire media

Polyurethane is better suited for wet/wash screens and dry applications with highly abrasive materials. It provides 30-40% less open area than wire cloth; however, polyurethane offers extended wear life over wire media.

Polyurethane media

Rubber media is used for heavier, coarser materials that can damage standard wire screens. It is most often used for dry applications or abrasive materials. Rubber media has less openings than wire cloth, and therefore less throughput; however, they last much longer than wire screens.

Rubber media

Hybrid media combines wire screen with reinforced rubber or urethane strips to fit screen supports. It is highly popular in dry screening applications with high moisture materials and a high proportion of fines. This type of media works to eliminate blinding and pegging, which ends the need to stop production to clean the screen. It provides more open area than polyurethane and lasts longer than woven wire. Depending on the application, production can increase 40% using hybrid screen media.

When sizing and selecting a Vibrating Screen for an aggregate operation, be sure to provide the manufacturer with as much accurate detail about the feed material and the application as possible. From there, they can recommend what type of screen (Inclined or Horizontal) is best for the site, as well as the number of decks required and the type of screen media that will provide the best wear life and efficiency.

How To Select The Proper Vibrating Feeder Design

There are two basic designs available when selecting a vibrating (linear) feeder: electromagnetic and electromechanical. Air powered vibrating feeders are basically an alternate to the electromechanical feeders as they have the same simple brute force design concept &#; the vibratory drive is directly attached to the tray. Our challenge is to obtain as much information about the application to make recommendations or at least provide the advantages and disadvantages so the customer has enough information to make an informed decision in order to select the best possible solution for their application.

In essence, all three styles could be suitable, but it&#;s quite possible that only one of the three could be the most advantageous. The following are the basic advantages and disadvantages of these three feeders.

Electromagnetic Feeders &#; The Electromagnetic Feeders provide variable intensity with typically fixed frequency of vibrations per minute. They only require single-phase power, offer quick stopping, and are ideal for cold weather installations. However, they are sensitive to line voltage fluctuations and temperature swings, can require tuning if there are rate or load changes, require skilled maintenance, and are not suitable for hazardous areas.

Electromechanical Feeders &#; The Electromechanical Feeder design is the most versatile as the power is provided by twin rotary electric vibrators where a multitude of forces and frequencies can provide a wide range of stroke and frequency combinations. You can further enhance the flexibility of this design by controlling the twin vibrators with a VFD (variable frequency drive) which provides a quick and easy adjustment without having to manually adjust the eccentric weights. Since this design has the twin vibrators synchronizing to produce linear force, these feeders do not stop shaking immediately after power is turned off as the eccentric weights coast to a stop. A VFD with dynamic braking or a starter with a dynamic brake will end the vibration much more quickly to limit the erratic motion at shut down. This design provides the quietest operation and is less susceptible to head loads. Explosion proof vibrators are available for operation in hazardous locations.

Air Powered Feeders &#; This low-cost design is ideal for hazardous locations as the drive is an air-cushioned piston vibrator which produces linear force and can also handle high temperatures. It&#;s the simplest to maintain, and the controls are the most economical of the three in which a simple regulator that can adjust the air pressure will vary force & frequency output. While this feeder doesn&#;t require tuning, there are limitations to the physical size of the tray & feed rates, it&#;s less suitable for outdoor operation as freezing airlines are a problem and is susceptible to head load.

Consider the advantages and disadvantages outlined above to determine the best possible solution for your requirements. While this information is provided as an aid, you should always enlist the assistance of an application specialist to select the proper feeder for your application. Call or click today for more information!

Jack Steinbuch has been with The Cleveland Vibrator Company for over 36 years accumulatively. He has previous experience in the manufacturing industry as a Senior Application Engineer and has worn many hats on our team in sales and managerial capacities. Now, he&#;s in the position of General Sales Manager. With a BSCE from The University of Toledo, he is an expert in the realm of sizing vibratory screeners and feeders, and sizing vibratory drives for tables and other vibratory equipment. Understanding that customer service is crucial, Jack believes it is important to provide the proper product for every application, even if it happens to not be supplied by The Cleveland Vibrator Company.

In his off-hours, you can find Jack spending time with his family and playing with his grandchildren. He loves sports; both watching and playing, and is an avid golfer and a league bowler during the winter. He will be retiring at the end of September and hopes to spend his winters vacationing in Florida.

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