1. Source Control: Ensuring Quality Raw Materials and Feeding
Strict Raw Material Pretreatment: After mixing, PVC resin powder and other additives may contain impurities. It is recommended to install a sufficiently fine screen before the feed inlet to physically intercept large particles. If recycled material is used, ensure its cleanliness to prevent impurities from clogging the die head.
Stable Feeding: PVC powder has poor flowability and is prone to "bridging" in the hopper, leading to feeding interruptions. Anti-bridging devices or equipment with forced feeding systems can be used to ensure smooth material flow. Additionally, the feeding speed must be matched to the extrusion speed. Excessively fast feeding can cause material to accumulate in the barrel, and unplasticized material that cannot be discharged in time will result in blockages.
2. Melt Conveyance: Optimizing Barrel and Screw Management
Inside the barrel, improper temperature settings can also cause blockages. For example, if the temperature in the rear section of the barrel is too high, the PVC will melt prematurely before reaching the vent, causing the material to fill the screw grooves and block the vent channels. You need to ensure, based on the screw design, that the material is fully melted only when it reaches the vent. A practical troubleshooting tip is to try raising the temperature in Zones 2 and 3 of the barrel by 5–10°C, or lowering the temperature in Zone 1 by 10–20°C, to balance the conveying capacity between the front and rear sections.
3. Exhaust Gas Discharge: Preventing Material Spillage and Blockages at the Vacuum Outlet
The vacuum outlet is another common area prone to blockages. Material "spills" out of the outlet and clogs the piping, typically due to the following reasons:
Screw Configuration Issues: Mismatched conveying capacities between the first- and second-stage screws result in insufficient feed to the second stage, causing material to flow back into the outlet.
Inappropriate process conditions: Such as excessive die resistance or overly fine filter screens.
Design flaws in the vent port: An improperly sized opening or an ill-conceived structure can cause melt to accumulate there.
4. Die Setting: Ensure unobstructed flow between the die head and the sizing sleeve
Blockages in the die and sizing sleeve directly affect the forming quality of the pipe.
Die Head and Filter Screen: The filter screen (screen changer) inside the die head is a critical filtration component that is prone to clogging from impurities or decomposed materials. Regular inspection and cleaning of hard-to-reach areas within the die head are necessary, as these spots are prone to accumulating decomposed material, forming sludge that can block the flow channels. Additionally, maintain stable pressure before and after the filter screen; a sudden pressure spike is typically a sign of clogging.
Sizing Sleeve: This is critical for shaping and cooling and is also highly prone to clogging. The main causes include:
Scale and Impurities: The small vacuum holes on the sizing sleeve (typically 1–2 mm in diameter) are easily blocked by scale or impurities, resulting in uneven vacuum levels.
Accumulation of Precipitates: Low-molecular-weight substances in the PVC formulation can precipitate and accumulate in the grooves on the inner wall of the sizing sleeve, affecting the surface finish of the pipe.
Uneven cooling: Blocked cooling channels can cause localized overheating, causing the material to stick inside the sizing sleeve.
In summary, the key to preventing blockages in PVC pipe production lies in: proper raw material pretreatment, stable feeding, precise temperature control, unobstructed vacuum, clean cooling water, unobstructed sizing sleeves, and regular, thorough cleaning.