July 2024

PVC is a thermoplastic resin that cannot be processed on its own due to its very low thermal stability and high melt viscosity. Therefore, it is necessary to prepare an intermediate product where a variety of additives are mixed with the PVC resin to form a “dry-blend” that can be later melt-compounded or processed into a finished article. The unit operations present in the compounding of PVC involve delivering and storage of raw materials, feeding and spraying of all ingredients into a special mixer, mixing and heating the materials to create a dry-blend, then cooling and transferring the dry-blend to storage or to a conversion process such as molding, extrusion or calendering.

The goal of a compounding plant is economical production! Among other things, this means as little waste as possible and minimum reconfiguration time. The Coperion K-Tron feeding system makes this possible. An important factor is the adherence to the recipe during ramping up of the extruder and naturally also during large setpoint changes. The short-term accuracy of a high-performance extruder is a key factor for quality of the end product. In order to even be able to speak of adhering to recipes with changing operating data, one condition must be fulfilled: the mass flow must adapt to the setpoint as quickly as possible. This is only possible with advanced gravimetric control and the high sampling rate and resolution offered by Coperion K-Tron’s Smart Force Transducer weighing technology.

The design of a feeding or
pneumatic conveying system
is heavily influenced by a bulk
solid’s particle shape, size (aspect ratio) and particle size distribution as well as the particle’s
roughness, hardness (abrasiveness), and density.
In the case of calcium carbonate these characteristics vary
widely depending on the source
and production process for the
individual samples. The sieve
analysis below illustrates the
difference in particle shape,
particle size and particle size
distribution for two samples of
calcium carbonate.