With the margin of error being so low, precision is of the utmost importance when it comes to feeding plastic pellets or powder into a material blender. Whether you’re using injection molding or extrusion molding processes, you will need to carefully select a feeder for your processing equipment to avoid problems due to incorrect measurements later on. You should ask yourself the following four questions to determine the right feeder for your material and application.
What Is Your Material Like?
Is your material in pellet or powder form? The answer to this question can greatly determine the type of feeder that works for your application.
For pellets, you will need to consider the size and shape of the pellets. Are they square, round, rectangular, or flat? Is the size of the pellets consistent? If the shape and size of the pellets vary significantly for your material, you may have a more challenging time achieving consistent end products, especially when you use a low-rate feeder.
For powdered materials, particle size really isn’t a consideration. However, you will need to think about the flowability of the material. If it is likely to stick or clump, you will want a feeder that uses flow aids to ensure accuracy across every batch.
In addition to knowing whether your material is in the shape of a pellet or powdered form, you need to consider the following information about your material when selecting a feeder:
- Bulk density
- Flowability
- Particle size
Do You Need Your Feeder for Batching or Blending?
Now that you’ve evaluated the type of material you will be using, you need to think about what you expect the feeder to do. Will you use it for batching or blending?
With batching, you will need to control the flow of materials based on a predetermined set point or batch amount. For example, you would use batching to set a specific weight of an ingredient that goes into a mixture.
With blending, you will stop and start flow based on a predetermined flow rate rather than a batch amount. With this process, flow is often continuous.
If you plan on using your feeder for batching or blending, you will typically want to choose a volumetric or gravimetric feeder.
Would a Volumetric Feeder Work in Your Application?
Volumetric feeders are set according to a specific speed or rate and come in various types, including rotary valves, belts, and screw conveyors. These feeders are easy to use and low-maintenance because they do not need to be calibrated based on the material used. For this reason, they are often cheaper than gravimetric feeders, but they are also less accurate because they are not taking into account the specific material. Anything from the moisture content of the air to the environmental temperature can change the material’s density, throwing off the entire process.
Should You Choose a Gravimetric Feeder Instead?
A gravimetric feeder measures the weight of the product flowing through the system to control the material’s flow rate. In this way, it can produce more accurate results than a volumetric feeder.
There are two common types of gravimetric feeders: the loss-in-weight feeder and the weigh belts. The loss-in-weight feeder features a delivery device, a hopper holding the product to be fed into the system, and a weighing mechanism. As the product leaves the feeder, the loss-in-weight is measured, and then more of the material is delivered to the feeder. The weigh belt consists of a conveyor belt and feed delivery system, such as a hopper. The material is consistently fed onto the belt based on belt speed and weight.
The Feeder That’s Right for You
As you can see, a significant number of factors play a role in determining the type of feeder that is right for your application. In general, if cost is a significant concern for you, then a volumetric feeder would be the best economical choice. However, if the quality and accuracy of the finished product are more important to your application than the cost of the equipment, you should choose a gravimetric feeder.
If you’re still on the fence about which feeder is best for your plastic material and application, get in touch with a representative at Plastrac. We would be happy to help you determine which volumetric or gravimetric feeder is right for you. We can also get you set up with the best blenders and hopper loaders for plastics manufacturing. Contact us today to learn more!
