Feeders are an important part of material handling systems. They control the flow of the materials, helping to expedite and control operations in a variety of industries. One question that comes up frequently is whether it is better to use an apron feeder or a vibrating feeder. There are the pros and cons to each type of feeder, and often the best option will depend on how the feeder is to be used.
Apron feeders are well suited for applications where large tonnages of material will be moved, and are also ideal for situations where severe impact loading is expected. These feeders are also ideal when rough or abrasive materials are being processed, such as commonly is the case with ore and rock.
Using an apron feeder provides a steady feed, as well as a sturdy one. These feeders are perhaps the most durable in the business, and are also versatile enough to work with materials that are wet, frozen, clayish or sticky. Excellent feed control with a variety of materials and long-term reliability make apron feeders so popular in many mining operations.
Vibrating or vibratory feeders are able to accommodate a wide variety of materials and particle sizes. These feeders are well suited for use with both heavy and abrasive materials, and are a good option for sorting a variety of different materials. This is commonly the case with gravel and stone-crushing operations, where different sized stones may need to be handled and processed differently.
Vibrating feeders may not be ideal for materials that are very fine, however. Materials that are sticky also may not work well with vibratory feeders as the material may build up in the pan.
First let’s define what feed equipment is not. Material feeding equipment, also called powder dosing equipment, is not a conveying system. Mechanical conveyors, such as screw conveyors (also called auger conveyors) and vibratory conveyors, typically consist of one inlet and an outlet purely for the purpose of moving material from point A to point B over longer distances. They usually run at a fixed rate and move material downline at a constant throughput measured in pounds or kilograms per hour.
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In contrast, feeding equipment is used in situations where more control and precision of the material flow rate is required. Also, screw feeders and vibratory feeders are not for moving material over longer distances, rather they are used to dose material from a hopper or IBC tote into a packaging line, or possibly a powder mill. They are much smaller than mechanical conveyors consisting of an integrated hopper, agitator, small tube or flat bed and a variable frequency drive. The integrated hopper is necessary for feeding equipment because a constant head load must be maintained for proper operation. The speed can be controlled on feeding equipment via a VFD, to allow slower and faster feed rates.
If your process requires repacking the processed material into 25 – 50 kg paper bags, and you need to be certain you’re not over or under packing the container, feeding equipment is the way to go. Similarly, powder mills cannot run on a head load or be slug fed, they perform at their best while running under a steady and consistent feed rate.
So now that we understand how feeders are used and various material characteristic categories, let’s put both of those components together and define what feed equipment will work best. Screw Feeders use a built-in hopper with stirring agitator that flood feeds a tubular channel. Within the tube is a small screw that pushes the product through an outlet into the downstream process. There are several designs for the small auger within screw feeders such as: pigtail screws, ribbon screws, and screws with a drive shaft.
Screw feeders offer a good deal of precision, in some instances dosing at an accuracy of -/+ 1-2 grams. They are a common type of feeder as they fit most applications, except in instances of materials that are friable or heat sensitive.
Vibrating feeders have a similar build (hopper and tubular structure unit) but instead of a screw, shaker motors are attached to the unit and the structure is supported by spring coils, to allow the unit to vibrate. A very minimal angle will allow the unit to shuffle the material down the feed bed into the downstream process. The feed rate can be controlled by increasing or decreasing the vibration amplitude and frequency. The shuffling action helps preserve the integrity of the materials, or avoid unnecessary wear and tear in the case of abrasive materials. Therefore, whenever dealing with materials that are either friable, temperature sensitive or abrasive, vibrating feeders are the way to go.