Process Feeding and Dosing for PVC Compounding Facilities

In PVC compounding processes, product quality is directly related to the correct storage of raw materials, their precise dosing, and stable feeding into the mixer and extruder. VOLDE offers process feeding and material handling systems for PVC and mineral-filler-based compound production facilities — spanning from raw material intake to the packaging of the granular product — together with engineering, automation, and equipment manufacturing. The controlled management of PVC resin, calcite, and additive systems; hot/cold mixer lines together with extruder feeding units; and the pneumatic transfer of granular product all operate reliably under a single automation infrastructure

| PVC and Calcite Storage

The main raw materials used in PVC compound production generally consist of high-volume bulk solid materials such as PVC resin (particularly S-PVC types), calcite (CaCO₃), recycled PVC regrind, and various mineral fillers. The K-value, particle size, and flow properties of the PVC resin used play a determining role in the design of process equipment. Likewise, filler types with different micron sizes (e.g., coated or uncoated CaCO₃ in the 2–10 µm range) can be used on the calcite side. Depending on facility capacity and logistics structure, these raw materials are stored in high-capacity silos, big-bag discharge stations, or bag dumping bins.

In VOLDE systems, silo volume and geometry are determined through engineering calculations, taking into account the flow behavior of the PVC resin, the fine particle structure of calcite, and process capacity. Flow-assisting cone angles, vibration or flow aids, and suitable discharge equipment are used to minimize the risks of bridging and segregation. Raw materials are taken from silos or discharge stations and transferred to hot-mixer feed bins via vacuum pneumatic conveying systems, dense-phase transfer lines, or mechanical screw conveyors.

| Controlled Feeding to the Mixer

The intermediate bins used for hot-mixer feeding typically operate integrated with gravimetric or batch weighing systems. This allows PVC resin, calcite, and other main raw materials to be automatically weighed and fed into the mixer at the ratios specified in the recipe. All discharge and transfer points are supported by silo-top jet-pulse filters, bin filters, and central dust collection systems. Thanks to this closed-system approach, dust emissions are kept under control, while raw materials are protected from moisture and environmental effects, guaranteeing process stability and operator safety.

| Precise Weighing of Powder and Liquid Additives

PVC compounding recipes consist of numerous low-ratio components such as stabilizers, lubricants, impact modifiers, pigments, and process aids. Adding these additives in the correct quantity and in the correct order to the process is critical for both dry-blend quality and extruder performance. In VOLDE additive dosing systems, powder raw materials are typically brought into the system from filtered bag dumping bins or small big-bag stations. From there, materials are transferred to gravimetric weighing bins via screw feeders or vacuum pneumatic conveying. Depending on the recipe requirement, the systems can operate on a coarse- and fine-feeding principle, ensuring both high speed and high dosing precision. Once weighed, the additives are discharged into the automatic hot mixer as a batch, and every dosing step is recorded via SCADA.

Plasticizers, liquid stabilizers, and other liquid additives used in PVC formulations are brought into the process within the facility via a separate liquid dosing and weighing system. In VOLDE systems, liquid raw materials are typically stored in process tanks, then transferred to dosing tanks mounted on weighing cells, where they are precisely weighed to the quantity specified in the recipe. Once weighed, the liquid additives are fed into the hot mixer in a controlled manner via the automation sequence and recorded as part of the batch recipe

| Extruder Feeding

The dosed PVC resin, mineral fillers, and additives are homogeneously mixed in high-speed hot mixers. The product is then transferred to cold mixers operating at a controlled temperature, resulting in a stable dry blend suitable for extruder feeding.

The most commonly used equipment in PVC compound production are co-rotating or counter-rotating twin-screw extruders. These extruders are preferred for the homogeneous plasticization of high-filler-content PVC formulations. At the extruder outlet, the product is typically converted into granular form via strand pelletizing or underwater pelletizing systems.

VOLDE systems enable the granules coming from the extruder outlet to be conveyed to intermediate silos via pneumatic or mechanical transfer lines, and then packaged via 25 kg bag filling machines or big-bag filling systems. The entire facility — from raw material to final product — is controlled by a PLC-SCADA-based central automation system. This infrastructure makes it possible to reliably manage a large number of recipes, record traceable production data, and minimize operator errors.