PVC and Calcite Storage and Process Feeding Silos

PVC & Calcite Silos are designed for the safe storage of fine powder raw materials with very different flow characteristics — such as PVC resins and calcite (CaCO₃) — and for controlled feeding into dry-blend, dosing, or extrusion lines. The low bulk density and electrostatic tendency of PVC powders, together with the high density and compaction-prone nature of calcite, require specialized engineering. VOLDE handles not just silo manufacturing, but the entire system — including filling, ventilation, flow control, and pneumatic conveying — from a single source

| Capacity and Material Selection Suited to Process Consumption

In PVC processing facilities, silo capacity is determined based on mixer feeding speed, daily production plan, and logistics strategy. VOLDE manufactures PVC or calcite silos of up to 150 m³ in one-piece construction, and offers modular or multi-silo solutions for higher-capacity requirements.

The body material and interior design are selected according to the product's chemical and physical properties:

• Painted carbon steel (standard industrial applications)
• Stainless steel (facilities with corrosion, moisture, or cleanliness requirements)
• A smooth interior surface design that reduces product sticking
• Structural strength and safety equipment for high fill rates

PVC resins are typically materials with a particle size of 100–180 µm, low bulk density (0.45–0.65 t/m³), and a high tendency to generate dust during flow. Calcite, on the other hand — in micronized or coated types — has a much higher density (0.8–1.2 t/m³) and is prone to compaction and bridging. For this reason, using separate silos for different products in the same facility provides a significant advantage in terms of dosing accuracy and operational safety.

Silos ⇢

| Discharge Design Optimized Against Flow Problems

The most critical factor determining silo performance for fine powder raw materials is the discharge zone. Micronized calcite in particular can easily bridge at the conical outlet, while PVC can exhibit channel formation (ratholing) during flow. VOLDE silos are equipped with flow-assist equipment according to the product properties:

• Vibrating, controlled flow initiation with a bin activator
• Homogeneous discharge via a pneumatic fluidized bottom
• Product-specific cone angle and outlet geometry design
• A silo-top jet pulse filter for air venting during filling

This structure prevents dead-zone formation in the silo, ensuring that the entire product volume operates as usable active capacity. It also prevents segregation and density variations, allowing proper feeding to the process equipment at the silo outlet.

Silo Discharge Systems ⇢

| Silo Filling, Filter, and Pneumatic Conveying Solutions

VOLDE does not design the silo as a standalone piece of equipment, but as the central storage and distribution point of the process. For this reason, filling, discharge, and conveying systems are engineered together. The filter located on top of the silo captures the air-dust mixture generated during filling, preventing environmental emissions and balancing the internal pressure of the silo.

At the silo outlet, depending on the application, the following solutions are used:

• Rotary valve + vacuum pneumatic conveying systems
• Rotary valve + pressure (blow) conveying lines
• DENSPLUS dense-phase conveying with low speed, minimum wear, and product breakage
• Controlled transfer to mixer feeding, dosing systems, or intermediate bins

Dense-phase conveying significantly reduces product degradation, segregation, and pipeline wear, particularly for PVC and filler minerals. Thanks to low air velocity, energy consumption is also reduced and the system operates more quietly.

Silo Filling ⇢ Dense Phase Conveying ⇢