Table of Contents
Introduction
- Blown film extrusion is a technology that is the backbone of the packaging industry. It is the process that makes plastic films that are used in bags, wrappers, and laminates. But, to produce a high-quality film, it is important that the thickness is uniform. Therefore, scanners are used for real-time thickness measurement and quality control. Two key technologies—beta gauge scanners and capacitance scanners—are used to accurately check the thickness in blown film extrusion. This is where scanners come into play—they are devices that monitor and control the thickness of the film.
- In this blog, we will explain how these two scanners work, their advantages and limitations, and which scanner will be right for your extrusion process.
What Are Scanners in Blown Film Extrusion?
- In blown film extrusion, scanners are devices that measure and control the thickness of the plastic film. These machines rotate or oscillate around the film bubble and check the thickness at each point. The main job of scanners is to ensure that the thickness of the film is uniform everywhere—neither too thick nor too thin.
Why are scanners important?
- Quality Control: Uniform thickness improves the film’s strength, durability, and appearance.
- Material Savings: If the thickness is too much, extra material is wasted, and if it is less, the film can be weak. Scanners control this and optimize the material so that there is no thickness variation.
- Cost Efficiency: Consistent thickness reduces the production cost because if there is no uniform thickness, more material will be used at the place where there is more thickness, which can increase the cost of the product. Scanners are used to prevent this.
Types of Scanners
Blown film extrusion uses Beta Gauge and Capacitance Scanners for real-time monitoring, allowing film thickness to be continuously measured and adjustments to be made immediately.Mainly two types of scanners are used in blown film extrusion:
- Beta Source Scanner: It measures the thickness of the film using radioactive beta particles.
- Capacitance scanner: it measures the thickness of the film by detecting changes in capacitance.
How do scanners work?
- Scanners move around the film bubble using a rotating arm or oscillating system. At each point, they measure the thickness and send the data to the control system. If the thickness is too low or too high at any point, the control system automatically makes adjustments.
Key Features of Scanners
Non-Contact Measurement:
- Scanners measure film thickness without touching the film, which does not damage the film.
Real-Time Monitoring:
- They provide real-time data, which allows operators to make quick corrections.
High Precision:
- Scanners accurately measure film thickness down to microns.
Beta vs. Capacitance Scanners: Key Differences
Beta Source Scanner:
1. Working Principle
- Measures the thickness of the film using beta particles (radiation).
- Beta particles pass through the film, and the detector measures their intensity.
- Uses a radioactive source (typically beta or gamma radiation) to measure film thickness.
2. Thickness Range
- Ideal for thin films (microns to 0.5 mm).
- Provides high accuracy in very thin films (below 50 micros).
3. Advantages
- High accuracy and reliability in thickness measurement.
- Suitable for a wide range of materials and thicknesses.
- Can measure multiple layers in co-extruded films.
4. Material Dependency
- Material independent: Works with all types of material as it does not come into contact with the film and only emits beta particles and measures thinness.
- Gives accurate results on polymers, metals, and coatings.
5. Environmental Sensitivity
- It is less affected by humidity, temperature, and dust because its source is fully covered.
- Since it is a radiation source, it is also harmful, so it is used by keeping it in a fully covered box.
- Because of this, it remains stable in every environment, and humidity has no effect on it.
6. Safety and Handling
- Beta-source scanners use radioactive materials, and radioactive materials emit radiations such as beta and gamma, which are harmful to our bodies, causing safety concerns.
- It requires licensing and regulatory compliance.
Capacitance Scanner:
1. Working Principle
- Thickness is measured by detecting changes in capacitance (an electrical property).
- The film acts as a dielectric material and the sensor detects changes in capacitance.
2. Thickness Range
- Capacitance scanners are used to measure thick films because the accuracy of capacitor scanners is good for thick films.
- The accuracy is less in thin films, especially below 50 microns.
3. Advantages
- No radioactive materials, making it safer and easier to operate.
- Faster scanning speeds compared to radioactive systems.
- Lower maintenance and operational costs.
4. Material Dependency
- Material dependent—depends on the dielectric properties of the film. If the material is sticky, then there is a lot of problem in scanning because the scanner keeps sticking to the material.
- If the dielectric properties of the material change, then accuracy is affected.
5. Environmental Sensitivity
- It is easily affected by humidity, temperature, and dust. Because it is an open source project that is in contact with the bubble.
- Frequent calibration and adjustments are required.
- Accuracy may be affected by film moisture content or environmental conditions.
6. Safety and Handling
- No radioactive materials—safe and easy to handle.
- No special safety measures are required.
- If safety, cost, and ease of use are top priorities, a Capacitance Scanner is a good alternative, especially for thin films
Conclusion
- The beta source scanner is perfect for thin films and provides high accuracy, but it uses radioactive materials, which raises safety and cost concerns.
- The capacitance scanner is better for thicker films and is safer and more cost-effective, but it is less accurate with thinner films and is easily affected by environmental factors.
- Your scanner choice will depend on your specific application, film thickness, and budget. Both scanners have their pros and cons, and it is important to understand them well to make the right decision.
Note:
FAQ for Beta and Capacitance Scanners
What is the main purpose of scanners in blown film extrusion?
- Scanners are used to measure and control the thickness of the film during the blown film extrusion process. They ensure that the film has a uniform thickness, which is critical for product quality, material savings, and cost efficiency.
Are Beta Source Scanners safe to use?
- Beta Source Scanners use radioactive materials, which require strict safety protocols and regulatory compliance.
- While they are safe when handled properly, they pose potential health risks if not managed correctly.
How do I choose between Beta and Capacitance Scanners?
Your choice depends on:
- Film thickness: beta for thin films, capacitance for thicker films.
- Material type: Beta is material-independent, while capacitance works best with consistent dielectric properties.
- Budget: Capacitance is more cost-effective.
- Safety concerns: capacitance is safer as it does not use radioactive materials.
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