Proportioning ingredients by the batch method is the simplest, oldest and most straightforward approach to formulating a plastics recipe. Whether performed manually or by one of today’s fully automated batching systems, the principle is the same: A recipe’s components are weighed out according to pre-specified proportions of desired total batch weight, combined and then mixed prior to further processing.
Depending on specific need, batch blending may or may not include all recipe components, may or may not include a resin component at all, or may include a reduced level of resin sufficient to pelletize the mixture in the form of a concentrated blend of additives, colorants or the like. Additionally, again depending on need, batch blending may be performed on- or off-line.
Illustrated here is a typical automated batch blending configuration:
In this approach batch components are introduced sequentially, one after another into a weigh hopper. According to recipe specifications, the weigh hopper senses when the required amount of a particular ingredient has been added, stops the flow of that ingredient, and starts the flow of the next, sequentially layering ingredients in their proper proportion until the recipe is complete. The batch is then discharged to a mixer and further processing.
Advantages, Limitations and Considerations
- Low cost due to a single, central weigh system and the use of volumetric devices for ingredient addition
- Lengthy formulation time due to sequential introduction of ingredients
- Lower proportioning accuracy on minor (typically more costly) ingredients due to relatively large capacity weigh hopper
- Layering of ingredients necessitates post-proportioning mixing