When you need high-precision dosing for extrusion and plastic injection molding, you will want to install a gravimetric blender onto the line. This piece of equipment can decrease blending variability from overdosing colorants and additives by allowing plastics processors to measure materials accurately. Let’s examine how gravimetric blenders provide blend accuracy even when there are bulk density variations among materials.
A Breakdown of the Gravimetric Blender Process
A gravimetric blender can deliver blend accuracy because each material is weighed before being dropped into the mixing chamber. If the amount of an additive, for example, is off, the control system will note the difference and then adjust the measurements for the other resins to maintain the proper concentration of each material relative to one another.
The process begins by dispensing materials into the material hoppers. This can be done by hand or by a hopper loader. Next, the processor sets the recipe percentage for each material. The vertical valves attached to the hoppers will drop the ingredients into the weigh bin based on these settings. Once the load cell determines the batch is ready, the pneumatic cylinder will send the batch to the mixing chamber. Then, the mixer blends the batch. Finally, the mixture is emptied from the blender.
Across each batch, the gravimetric blender system will adapt to variabilities of materials, such as pellet size or regrind—this process control results in higher-quality, similar end products batch after batch.
Types of Gravimetric Batch Blenders
Gravimetric blenders can be either loss-in-weight or weight-saving. Loss-in-weight gravimetric blenders are used when weighing materials into the system, while weight-saving blenders are used when weighing out.
With the loss-in-weight dosing dispenser, the weight of the material is measured as it enters the hopper. Once this weight decreases to a certain level, more of the material is automatically added. This allows for continuous dosing.
Weight-saving dispensers are often used for batch dosing of bulk products. Gravimetric weight-saving blenders can be combined with volumetric dosing dispensers. This type of blender allows for continuous flow at the hopper.
The type of gravimetric blender you will need will depend on the specific application and the desired flow rate.
Improve Processes with Gravimetric Blenders
The right gravimetric blender can help you achieve quality and repeatability within your plastics injection molding and extrusion processes. And, overall, this will reduce material costs and improve your bottom line.
If you’re ready to improve dosing accuracy and end-product quality, get in touch with Plastrac. We have a variety of gravimetric blenders, including the Auto-Disc GF-202 Model, as well as hopper accessories to boost plastics processing.
