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A gravimetric blender is an item of industrial equipment used in the
plastics industry The plastics industry manufactures polymer materials—commonly called plastics—and offers services in plastics important to a range of industries, including packaging, building and construction, electronics, aerospace, and transportation.
It is ...
to accurately weigh two or more components and then mix them together prior to processing in an
injection molding
Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...
machine,
plastics extrusion
Plastics extrusion is a high-volume manufacturing process in which raw plastic is melted and formed into a continuous profile. Extrusion produces items such as pipe/tubing, weatherstripping, fencing, deck railings, window frames, plastic film ...
, or
blow moulding
Blow molding (or moulding) is a manufacturing process for forming hollow plastic parts. It is also used for forming glass bottles or other hollow shapes.
In general, there are three main types of blow molding: extrusion blow molding, injection ...
machine.
There are two types of gravimetric blender.
Loss in weight
This type of gravimetric blender measures the "loss in weight" from two or more hoppers using a load cell under each hopper. Material is usually dispensed from the hoppers using a
screw conveyor
A screw conveyor or auger conveyor is a mechanism that uses a rotating helical screw blade, called a "''flighting''", usually within a tube, to move liquid or granular materials. They are used in many bulk handling industries. Screw conveyor ...
. All materials are dispensed together and the rate of dosing from each hopper is controlled to ensure the correct blend is achieved.
Gain in weight (sometimes called a batch blender)
A gain in weight gravimetric blender has two or more hoppers arranged above a weigh-pan. These hoppers contain the components which are to be mixed, at the base of each hopper there is a valve to control the dispensing of material from the component hopper into the weigh-pan. The components are dispensed one at a time into the weigh pan until the target or batch weight is reached. Once the batch has been weighed out the contents of the weigh-pan are dispensed into a mixing chamber where they are blended. The resulting mixture exits the base of the mixing chamber into the processing machine.
A typical application of a gravimetric blender would be mixing virgin plastic granules, recycled plastic, and
masterbatch Masterbatch (MB) is a solid additive used for coloring (color masterbatch) or imparting other properties (additive masterbatch) to plastics. Masterbatch is a concentrated mixture of pigments and/or additives which is manufactured by encapsulation du ...
(an additive used to colour plastics) together.
Industrial equipment