Have you ever noticed how each type of beverage has its own unique glass? There are beer mugs, wine glasses, brandy snifters, water glasses and so forth. Red wine generally is served in a different glass from white wine or champagne, and a multitude of beer glasses are used to enhance the experience of drinking pilsners, ales, etc.
{{image2-a:r-w:200}}What do they all have in common? They are delivery devices, each designed to “feed” different types of beverages in the best way possible for that particular beverage.
The same holds true in the aggregate business as it relates to feeders. Look through a few machinery websites and one will see the diverse types of feeder available, and paired with various forms of crushers, screens, wash plants and material handling devices.
The benefits of each style of feeder are often overlooked – yet each can be a big contributor in the overall success of the plant.
If one thinks about it, the feeder is the “mouth” of the plant. Therefore, it needs to be capable of “eating” whatever “diet” the plant is on.
Obviously, each feeder type was designed to meet the unique characteristics of a particular application. While many are routinely used in a wide array of applications (especially portable configurations), understanding the operating principles, variables and limitations of each can potentially help boost efficiency as well as maintain uptime.
VIBRATING GRIZZLY FEEDERS
Most commonly used ahead of a primary crusher, vibratory grizzly feeders (VGF) are perhaps the most popular design used today.
This is primarily due to providing a dual role, both as a feeder and as a scalper to bypass or reject dirt and fines. VGFs are also popular due to a long (or wide) feed opening, which is favourable for being fed by a wheel loader. They are robust enough to accept large surges of material, and large boulders. Adjustable grizzly openings provide some control over the size of material being fed into the crusher, as well as what is rejected ahead of the crusher – thus saving crusher wear cost while boosting plant capacity.
{{image3-a:r-w:200}}It should be understood that VGF feeders rely on a vibrating mechanism to lift and throw the material down the length of the feeder pan.
Accordingly, if not enough G-forces are generated, the result can be an ineffective device that does not efficiently transfer the material or clear grizzly openings. This can be an issue with sticky material.
The ideal applications for a VGF include primary crushing plants used in shot quarry, and sand and gravel operations. They are popular in wheeled, tracked and stationary plant configurations.
ROLLER BELT FEEDERS
The biggest advantages of the roller belt feeder are 1) relatively low cost, and 2) a “positive feed” device that does not rely on vibration to move material.
Belt speeds can easily be adjusted or automated for precise volumetric metering. The loading hoppers and feeder lengths can be designed to accommodate just about any type/size of loader or excavator.
Often these machines will be equipped with hydraulic tipping grids to prevent excessive feed material from entering the system – which is especially beneficial when feeding a machine with a limited feed size.
One can expect a belt feeder to require similar maintenance to a conveyor. The rollers used are generally limited in terms of the feed size/impact that can be introduced to a belt feeder. Obviously, unlike a VGF, a belt feeder does not have the advantage of an integral scalping device.
The ideal applications for a belt feeder include sand and gravel operations, truck and railcar loaders and unloaders, and mobile wheeled and tracked screens.
APRON PAN FEEDERS
{{image4-a:r-w:200}}Similar to belt feeders, apron feeders are also “positive feed” devices that are well suited for applications where sticky materials may be prevalent.
Pan speeds can be adjusted to enable precision metering of feed. Like a belt feeder, apron feeders can be designed to any length to accommodate the desired loading device.
However, an apron feeder also provides the additional advantages of being capable of feeding material at an incline and being very robust and capable of accepting large feed sizes and heavy impact.
If properly maintained, unscheduled downtime of apron feeders is rarely an issue. As such, these devices are very popular on primary crushing plants paired with a scalping pre-screen, in mines and on mobile tracked scalping screen plants.
However, apron feeders are known for their heavy weight, a higher cost of ownership in terms of purchase price and maintenance costs, and being susceptible to spillage, which can require constant clean-up.
OTHER FEEDERS
There are several other devices that are intended to carry material from point A to point B; however, many such devices are either antiquated (eg reciprocating plate feeders) or provide a very specialised application niche (eg vibrating pan feeders).
SELECTION CRITERIA
It is always important to first understand the fundamental application principles: top size, capacity and material characteristics. These three criteria will help define the type or size of feeder that can best meet your needs in the most economical method possible.
At that point, additional variables can be weighed, including any mobility/relocation requirements, varying feed materials and so forth.
If still in doubt, write down the “diet” of your operation and then consult with both your internal and external industry peers for feeder selection advice. They will be only too happy to help you decide the best way to feed your plant.
Paul Smith is the international marketing manager for the Astec Aggregate & Mining Group.