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The “Culprits” Behind PVC Screw Breakage and Countermeasures
Views: 62526 Author: Site Editor Publish Time: 2025-02-12 Origin: Site
Screw Breakage in PVC Extrusion: Causes and Preventive Measures
In the PVC extrusion industry, screw breakage is a common issue that severely impacts production efficiency and product quality. Screw breakage is generally categorized into normal wear breakage and abnormal breakage. This article analyzes the causes of both types and provides preventive measures.
I. Screw Processing and Materials
1. Material Selection
Barrel Material: Cr12MoV (SKD61 alloy steel) and 38CrMoAlA.
Screw Material: 38CrMoAlA is typically chosen.
2. Heat Treatment Process
Barrel: Tempering is used to homogenize the internal structure and improve the metallurgical grade. Two-stage alloy steel parts undergo overall quenching, achieving a hardness of HRC60 after quenching.
Screw: The final heat treatment is surface nitriding, with a nitriding depth of 0.5–0.7 mm. Large companies can achieve a nitriding depth of over 0.6 mm.
3. Bimetal Processing Methods
Metal processing methods generally include:
Forging for large parts
Casting for small parts
4. Service Life
The service life of the screw is related to the filler content:
Filler Content
Service Life
≤100 parts calcium
1–2 years
100–200 parts calcium
~1 year
200–300 parts calcium
6–8 months
>300 parts calcium
3 months
II. Influence of Screw Structural Characteristics on Pipe Processing and Mechanical Properties
1. Requirements for Screw Structure Based on Filler Content
<80 parts: High-calcium screws with reduced feed and metering section flight gaps.
<30 parts: Feed mixing section and compression section combined, with larger metering section flight gaps.
2. Impact of Low-Filler and High-Filler Screw Structural Changes
Different formulations require different screws. The amount of lubricant affects plasticization and flow performance.
3. Impact of High-Filler Production Formulations
High-filler formulations significantly increase wear on barrels and screws, reducing service life to typically 5–6 months.
III. Relationship Between Extruder Gearbox and Screw/Barrel Clearance
Clearance specifications for different models:
Model
Axial Clearance
Single-Side Clearance
Front Clearance
55/110
1.5 mm
0.75 mm
0.25 mm
65/132
2 mm
1 mm
0.25 mm
68/146.5
2.5 mm
1.25 mm
0.30 mm
80/156
3 mm
1.5 mm
0.35 mm
80/173
3 mm
1.5 mm
0.35 mm
92/188
2.8 mm
1.4 mm
0.4 mm
IV. Relationship Between Barrel-Screw Clearance and Product Processing/Plasticization
Increased clearance: Higher backflow, poorer plasticization, increased screw wear, and shorter service life.
V. Analysis of Normal Wear Breakage and Abnormal Breakage of PVC Screws
1. Normal Wear Breakage
Screws are consumables during extrusion. Their lifespan is related to calcium powder content. Light calcium extends screw life compared to heavy calcium.
2. Abnormal Breakage
Cause
Solution
Gearbox bearing damage: Caused by aging or quality issues.
Replace bearings.
Insufficient heating temperature: Due to wiring issues or damaged heating rings.
Check wiring or replace heating rings.
Material interruption during production: Caused by bridging in the hopper or delayed feeding.
Install a hopper agitator.
Formula error: Caused by mistakes in ingredient mixing.
Follow the formula strictly.
Foreign objects in raw materials: Foreign objects causing screw jamming.
Place strong magnets at the feed inlet.
VI. Summary
Most screw breakages are caused by the reasons mentioned above. Regular inspection of the gearbox, ensuring adequate heating temperature, avoiding material interruptions, strictly following formulas, and preventing foreign objects in raw materials can effectively reduce the risk of screw breakage.
Most screw breakages are caused by the reasons mentioned above. Regular inspection of the gearbox, ensuring adequate heating temperature, avoiding material interruptions, strictly following formulas, and preventing foreign objects in raw materials can effectively reduce the risk of screw breakage.
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The bright full moon carries our sincere regards. On this beautiful Mid-Autumn Festival, Ningbo Superior Machinery wishs all partners and friends good health, happiness and a joyful reunion with your families.
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