A: Todd D. Messmer, Schenck Process, says:
When selecting a feeder, weighbelt feeders are often overlooked. There are several reasons to use a weighbelt feeder in your process. Using the following list of questions and answers can help you determine if a weighbelt feeder is the ideal solution for your application.
What’s your material? The first important factor to consider is what material type needs to be fed. If the material is friable (can be easily broken) and the end product’s physical shape can’t be damaged, one of the first feeders to consider is a weighbelt feeder. Cereals, pet food kibble, granola components, and raw vegetables are examples of materials that are ideal for a weighbelt feeder because this equipment is gentle on friable materials. Other than the moving belt, a weighbelt feeder typically has no other moving parts, such as feed screws or internal agitators, coming into contact with the material.
If the material size is larger than a powder or a granule, for example wood strands going into a dryer in an oriented strand board (OSB) process or cement clinker going into a grinder, a weighbelt feeder would also be recommended.
What’s your feedrate requirement? Certain feedrates are well suited for weighbelt feeders. A gravimetric screw feeder with a 6-inch feed screw typically has a top-end feedrate of 1,000 cubic feet per hour. If the customer requests rates in standard or metric tons per hour, the use of a weighbelt feeder may be required. Weighbelt feeders are very flexible for high-feedrate applications because the has the flexibility to be sized with belts and increasing belt speed or material bed depth.
How much room do you have to install a feeder? A continuous gravimetric screw feeder typically requires a dedicated refill hopper above it for replacing material as the feeder hopper empties. The feeder’s feedrate will determine what refill hopper size is necessary. Oftentimes, there isn’t enough room to install both a feeder and a refill hopper. One unique feature of a weighbelt feeder is that the entire feeder doesn’t get weighed. The weighing portion of the feeder is offset from the infeed. This feature equates to a low-profile piece of equipment that can be “shoe-horned” into tight spaces. The offset weighing area provides an opportunity to flood feed, continuously refill a hopper attached to the weighbelt feeder, or both. You wouldn’t be able to continuously flood feed a gravimetric feeder, as the load cells would be in an equilibrium state as material is fed into the equipment as soon as the material is fed out. This makes the weighbelt feeder a great choice to place under a storage bin that might be continuously refilled during the process.
What’s your application? Another example of a weighbelt feeder application is when a material needs to be conveyed horizontally from point A to point B while being weighed in the process. Weighbelt feeders come in several standard lengths, offering many options for centerline-of-infeed to centerline-of-discharge requirements, whereas the screw feeder’s centerline-of-infeed to centerline-of-discharge is much more limited.
When is a weighbelt not recommended? After taking a close look at the material and its characteristics, you must determine if it’s floodable, dusty, adhesive, or cohesive. Floodable materials can flood through the weighbelt feeder without the feeder even running. Weighbelt feeders perform best when a uniform material depth can be profiled across the belt. The material must be stable and not moving as it goes over the weighed area of the belt. Custom infeeds with special baffles, curtains, or both may need to be designed to prevent flooding and assist with profiling the material.
Feeding dusty materials on a weighbelt feeder generally will require more housekeeping. As the dust accumulates on the weighbelt feeder’s head and tail pulleys, you may start to see belt tracking and slipping issues occur. If this is the case and a weighbelt feeder is the only option, then be sure it’s equipped with all the features to assist with housekeeping. Items such as self-cleaning pulleys or drag-out conveyors can help. You also want to make sure that the weighbelt feeder can indicate if there’s a belt-slip or off-track problem. Sensors and limit switches are available as options.
Certain adhesive materials can be self-cleaned off the belt using scrapers, but if the material is cohesive, meaning it sticks to itself, then material testing should be done to determine if the weighbelt feeder can positively extract and profile the material out of the infeed shear gate. Always ask to test your material if you’re unsure. Other than the cost of shipping the material to and from the test lab, most companies will test your material for free.
If you’re interested in a weighbelt feeder, speak with an application engineer who should be able to determine if a weighbelt feeder is right for your application.
Schenck Process, Whitewater, WI, provides solutions for measuring and process technologies in industrial weighing, feeding, conveying, screening, and automation, as well as air filtration technology.