PVC mixing glossary

Hard or soft lumps formed in the dry blend when resin, filler or liquid additives stick together. Typical causes are liquids added too fast or at the wrong temperature, insufficient cooling, moisture or worn blades. Lumps cause uneven extruder feeding and surface defects, so they are prevented with correct addition sequence, proper cooling and screening.

A batch is the quantity of blend prepared in one mixing cycle, expressed in kg; hourly output equals batch weight multiplied by the number of batches per hour. According to the catalogue, EPM-H models handle 150–500 kg per batch and EPM-V models 100–200 kg, with typical operation at 4–6 batches per hour. The right batch weight is chosen from the extruder's hourly consumption and the bulk density of the formulation.

Bulk density is the mass of a powder per unit volume including the voids between particles (g/l or kg/m³); it determines how many kg fit in the mixer vessel and how efficiently the extruder is fed. Flowability is the ability of the powder to flow freely through silos, hoppers and feed throats without bridging. A well-prepared and properly cooled dry blend has higher bulk density and better flow.

A compound is dry blend that has been melted and homogenised in an extruder or kneader and then pelletised. It is common for cables, hoses and injection-moulded parts and is easier to transport and store. While dry blend is fed directly to profile and pipe extruders, compounding also starts with a well-prepared blend.

A mixer that cools hot dry blend discharged from the heater mixer by gentle agitation in a vessel with a water-cooled jacket. Its job is to bring the blend down to a safe storage temperature, typically around 40–50 °C for rigid PVC, without lumps, condensation or additive degradation. The cooler is sized larger than the heater so it can take a full hot batch comfortably.

The temperature at which the heater mixer discharges the blend to the cooler, one of the most important settings for dry blend quality. For rigid PVC formulations it is typically around 110–120 °C; too low leaves additives poorly absorbed, too high can cause discolouration and consume stabiliser. The correct value depends on the formulation and the raw material supplier's recommendations.

A free-flowing powder made by mixing PVC resin with stabiliser, lubricants, filler, pigment and, if required, plasticiser in a heater–cooler mixer. The additives are distributed evenly onto and into the resin particles so that the extruder is fed consistently. Dry blend quality depends on the formulation, addition sequence, discharge temperature and cooling conditions.

The continuous, controlled transfer of prepared dry blend from an intermediate silo to the extruder hopper. It is usually done with a flexible screw conveyor or vacuum conveying and runs automatically from a level sensor in the hopper. Because irregular feeding causes pressure and dimensional fluctuations in extrusion, the feeding line should be planned together with mixer capacity.

The most common filler in PVC formulations is finely ground, usually surface-coated calcium carbonate (CaCO3). It reduces cost, increases stiffness and influences processing; its loading varies with the product. Highly filled formulations increase bulk density and dusting, so accurate dosing and good dust filtration become more important.

A simple, economical conveyor that moves powders and pellets in a closed system by means of a spiral rotating inside a flexible tube. It is widely used over short and medium distances between silos, mixers and extruders. Its enclosed design limits dust; for long distances and multi-point lines, vacuum conveying may be a better fit.

A soft starter ramps up the motor voltage at start-up to limit inrush current, but does not allow speed adjustment during operation. A frequency inverter also gives a smooth start and additionally allows stepless speed control to suit the formulation and mixing stage. The choice depends on recipe variety, the plant's power supply and budget.

In a heater mixer the blend is heated not by an external heater but by friction between the high-speed blades and the powder and by particle-to-particle impact. The heating rate depends on blade geometry, tip speed, batch fill and formulation. Worn blades or the wrong fill level therefore lengthen the cycle and directly reduce hourly output.

As temperature rises during mixing, the porous resin particles absorb plasticiser and liquid additives, after which the blend becomes dry and free-flowing again. True gelation (fusion) takes place later in the extruder or calender under heat and shear. Overheating in the mixer can cause premature gelation and lumps.

A dosing method in which material is measured by weight, using load cells, rather than by volume. Because it is not affected by changes in bulk density, it improves recipe accuracy and batch-to-batch repeatability. It also prevents overdosing of expensive additives and makes record keeping easier.

A vertical mixer with a high-speed blade assembly at the bottom that heats the blend by friction. Resin and additives are homogenised here, liquids are absorbed, and the blend is transferred to the cooler once it reaches the set discharge temperature. Blades, shaft seals and the discharge valve are the main parts needing regular maintenance.

The standard equipment for PVC dry blend production, in which a heater mixer and a cooler mixer work together as one system. The blend is first heated by friction in the heater and then brought down to storage temperature in the cooler; since both run in parallel, one batch cools while the next is prepared. The cooler can be of vertical or horizontal design.

A general name for mixers with high blade tip speed that produce intensive mixing and frictional heat in a short time. In the PVC industry the term usually refers to the heater (turbo) mixer; the same principle is used in applications such as colour concentrates and metallic bonding. Unlike slow mixers such as ribbon or planetary types, it transfers energy to the material within a short cycle.

A polymeric additive that reduces the brittleness of rigid PVC and improves impact strength, especially at low temperatures; acrylic (ACR) and CPE types are common. It is a key component in window profile and some pipe formulations. It is supplied as a powder and must be distributed evenly in the mixer, typically early in the cycle after the resin.

A dust collector that captures dust from mixers, silos and conveying lines with bag or cartridge filters and cleans them automatically with pulses of compressed air. It keeps the workplace clean and reduces material loss by returning collected dust to the process. Filter selection depends on the type of dust, air flow and line layout.

A number calculated from solution viscosity that indicates the average molecular weight of a PVC resin. Lower K-value resins flow more easily and suit injection moulding and thin products; higher K-values give better mechanical properties and are used for pipes, profiles or plasticised products. The K-value also affects how the resin absorbs plasticiser and therefore the mixing conditions.

A sensor that converts applied force into an electrical signal and forms the basis of weighing systems. Mounted under dosing hoppers and weigh bins, it measures material weight and makes gravimetric dosing possible. Accurate readings require regular calibration, isolation from vibration and connections that do not put load on the weighed vessel.

A continuous gravimetric feeder in which the feeder itself is weighed constantly and the flow rate is controlled from the measured weight loss per unit time. It is used in continuous processes where additives or filler are fed directly to the extruder. Unlike batch weighing, it holds a target rate in kg/h continuously.

Additives that reduce friction between polymer chains (internal lubricants) and sticking of the melt to metal surfaces (external lubricants) during processing; paraffin, PE wax, stearic acid and stearates are common examples. The balance of internal and external lubrication directly affects fusion rate, surface finish and extruder load. Many lubricants melt and coat the resin within a certain temperature range in the mixer, so the addition sequence matters.

A process in powder coating manufacture in which metallic or pearlescent pigments are bonded to the surface of the paint particles by mixing under controlled heating. This prevents separation of pigment and powder during application and keeps shade and appearance consistent. Temperature must be controlled very precisely, otherwise the powder can agglomerate or pre-cure.

Water in raw materials or in the blend, which enters mainly with fillers and hygroscopic additives. Moisture can cause bubbles, surface defects and lumps in extrusion, so venting it as vapour from the heater mixer is important. Storing warm blend that has not been cooled enough, or contact with cold surfaces, can also lead to condensation.

Pigments are powder additives that give PVC colour and opacity; titanium dioxide (TiO2) is the most common for white products. A masterbatch is a concentrated dispersion of pigment in a carrier, supplied as pellets or powder, which makes dosing easier. Because they are used in small amounts, accurate weighing and good dispersion are critical for colour consistency.

A mixer in which the agitators rotate on their own axes while also orbiting around the vessel. This motion sweeps the whole vessel and mixes high-viscosity pastes, putties and plastisols without dead zones. It is chosen for viscous products rather than for powder dry blend production.

Additives, usually liquid, that make PVC soft and flexible; DOP (dioctyl phthalate) and its phthalate-free alternative DOTP are the best-known examples. They are used at high levels in flexible products such as cables, hoses, films and tarpaulins. Adding them at a controlled rate once the resin reaches a suitable temperature is important for absorption and flowability.

A suspension of paste-grade (emulsion) PVC resin in plasticiser that is fluid at room temperature. It is applied by coating, dipping or casting and gels into a solid, flexible film when heated. Being a viscous product rather than a dry powder, it is prepared in planetary or dispersion-type mixers.

An additive, usually a high-molecular-weight acrylic, that accelerates fusion of PVC and increases melt strength. In rigid PVC extrusion it gives a more homogeneous melt, better surface finish and a more stable process. It is a powder and must be distributed evenly in the dry blend together with the other additives.

The white powder base material produced by polymerising vinyl chloride; suspension-grade resin (S-PVC) is used for most profiles, pipes and cables. The resin cannot be processed on its own and must be mixed with stabiliser, lubricants and other additives into a dry blend. Its particle structure, porosity and K-value determine how it behaves in the mixer.

The formula defining the type and proportion of each raw material in a PVC blend, usually expressed per 100 parts of resin (phr). It is set by the producer and raw material suppliers according to product type, processing method and target properties. In automated mixing lines, recipes are stored in the control system, which runs the dosing and mixing steps accordingly.

A low-speed mixer in which inner and outer helical ribbons, pushing in opposite directions inside a horizontal U-shaped trough, convey and blend the material. It is suited to gentle homogenising of powders and granules, cold blending and pre-storage blending without generating heat. Since it produces no frictional heat, it cannot replace the heating stage of PVC dry blend production.

Rigid PVC (PVC-U) contains no or very little plasticiser and is used for rigid products such as profiles, pipes and cable trunking. Flexible PVC (PVC-P) contains a high proportion of plasticiser and is used for cables, hoses, films and tarpaulins. The two types require different mixing temperatures, liquid dosing arrangements and cooling conditions.

SPC (Stone Plastic Composite) is flooring with a rigid core made of PVC and a high proportion of calcium carbonate filler. LVT (Luxury Vinyl Tile) is a more flexible vinyl covering built from plasticised layers. Especially for SPC, the high filler content makes accurate weighing, good dispersion and dust control key requirements for the mixing line.

The essential additive that prevents PVC from degrading (releasing HCl and discolouring) at processing temperatures. Lead-based systems have largely been replaced by calcium-zinc (Ca/Zn) and organic-based lead-free stabilisers. Stabilisers often come as a "one-pack" combined with lubricants and are added with the resin at the start of the mixing cycle.

A system that moves powder or pellets through closed pipes in an air stream created by a vacuum pump or blower. It offers flexibility over long distances, with height differences and in plants that feed several extruders. Conveying velocity and filter selection should suit the material so that the blend does not segregate.

A dosing method in which material is metered by volume, for example by screw speed or chamber volume, rather than by weight. It is simple and low-cost, but the actual quantity changes whenever bulk density or flow changes. It therefore needs regular calibration, and gravimetric systems are preferred for precise formulations.

A composite made by combining wood flour or fibre with a polymer such as PVC or a polyolefin, used for decking, panels and profiles. Because wood flour absorbs moisture, removing moisture before and during mixing is critical. Its low bulk density and fibrous nature must be considered when choosing mixer fill level and the feeding system.