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Plastic Extrusion Defects and Solutions

Views:900 Publish Time: 2021-11-11 : Louis Lu

Plastic Extrusion Defects and Solutions

Overview of plastic extrusion defects and solutions

Plastic extrusion is a continuous high-volume manufacturing process. A thermoplastic material (powder, pellets, or granulates) is homogeneously melted and then forced out of the shaping die through pressure. 

The majority of the extrusion processing steps occur within the machine. Due to the complexity of the processing method, plastic extrusion defects will eventually occur.

In this article, we will mainly discuss the common defects in extruded products and how to improve the process.

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The main plastic extrusion defects

To ensure the quality of extrusion manufacturing, the operator needs to identify, control, and monitor all quality parameters.

There may still be several extrusion defects even with a stable process. The common defects in extrusion process are due to three main causes: mold design, material selection, and processing. Most failures appear during the processing stage. Here, we have listed some of the most common defects in extrusion process:

lImproper system engineering: This category comprehends many different problems, such as utilizing the wrong clamp, overly tight clamp, improper die setting, use of incompatible fire caulk, and contact with the outside pipe with incompatible material. Improperly carrying out operations may lead to chatter marks and centering defects in extruded products.

lImproper operation: The improper operation will cause uneven surface thickness. The result may be caused by exposure to freezing temperatures without freeze protection, over-pressurization, or pulsating water pressure.

lResin defects: Resin flaws result in blowholes formation on the product. The extrusion defect can be attributed to poorly distributed filler, foreign contamination, and improper mixing of resin and additives.

lImproper material addition: This extrusion defect occurs when materials absorb moisture from the air, eventually causing bubbles on the surface.

lSurging: Surging is a cyclical product thickness variation in the direction of extrusion. The surge cycle time is typically between 30 seconds and 3 minutes.

lPoor mixing: This flaw will lead to clogging the extrusion defect. The screw cannot be run faster because poor mixing will cause the material to have a striped surface, parabolic ridges, and particles of undispersed additives.

lMelt fracture: Melt fracture refers to fine ridges or rough surfaces when the melt comes too fast from a thin die. 

l Overheating: The defect may produce degradation, making dimensional control and sizing difficult. Overheating may limit the rate when the take-off cooling is limited.

l Moisture absorption: The situation will cause a pattern of dotted lines, long bubbles, and pits on the surface. A moisture level of 0.1% is usually low enough to avoid such visual problems.

l Trapped air: A trapped-air surface will show bubbles and pits on the material. This extrusion defect occurs because of air going through the machine when operating at high speed.   

Suggestions on how to improve the process of plastic extrusion

l Preventative measures for extrusion defects

The maintenance staff should solve certain issues before acting on specific defects in extruded products. It is important to diagnose plastic extrusion defects quickly and accurately to minimize production downtime or off-quality product.

Here, we share some of the preventive measures for extrusion defects you may adopt:

1. Operators should fully understand the extrusion process:

The incorrect operation may damage the extruder, and the product will appear to be of poor quality. Serious accidents will occur when extruders are not operating properly. First, people who run extrusion equipment must receive comprehensive training to prevent defects in the extrusion process.

2. Collection and analysis of historical data:

The data to be collected include processing information from the extruder (temperatures, pressures, motor load, line speeds, barrel dimensions, screw dimensions) and information about the material.

3. Material storage:

The material should be stored in a clean, dry area without being affected by extreme temperature variation. 

4. Regular inspection of equipment and instruments:

 Equipment instruments used to monitor temperature, pressure, RPM, and amperage should be calibrated twice a year in case the data change over time.

5. The condition of the equipment

Maintenance records should be kept to assess the machine's situation. Extruder screws and barrels will wear over time. The operator should regularly measure the internal diameter (ID) of the barrel and the outer diameter (OD) of the screw to predict the life of the components.

To prevent extrusion defects and improve the process of plastic extrusion, all procedures above need to be paid much attention to in the daily use of equipment and instruments.


Solution to plastic extrusion defects

When plastic extrusion defects appear with a normally stable process, the technician usually troubleshoots by detecting current conditions.

In solving the extrusion defect, the first step is to examine the equipment components of the manufacturing process. The following list is the main variables that need to be examined:

1. Melt pressure and temperature

2. The temperature of the barrel and die

3. Heater and cooling power

4. Speed of the screw and the line

5. The motor load in amps

6. Die wear or improper design


After examining the above variables, the following steps are some solutions to remedy the defects in the extrusion process:

1. Use the digital temperature sensor and pressure gauge

2. Adjust the die setting

3. Exact addition of resin material

4. Increase rpm back pressure for better mixing

5. Altering or replacing the screw

6. Installing a gear pump between the extruder and the die

7. Maintain the speed of the extruder


 

Why Choose Boyu

 

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Boyu Plastic Machinery is a professional plastic extrusion machine manufacturer. Our company was established in 1998 and had over 20 years of plastic extrusion experience.  

We specialize in the PVC Flooring Extrusion Production Line, and we are also acclaimed as the leader of SPC floor equipment.

We have professional technical support with more than 90 international and national technical patents. Boyu has rich theoretical knowledge and practical experience in preventing plastic extrusion defects and making solutions.

We are looking forward to becoming your reliable business partner, contact us!


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