QC Automation Insight

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Technology Spotlight: Confocal Imaging Method for In-Line Bottle Wall Thickness Measurement

An alternative to terahertz wall thickness at-line or lab testing system is the GP Resources, LLC  Lateral Chromatic (Confocal) Imaging WTS technology. It has the advantage of testing 100% of translucent plastic bottle line production at line speed of bottles (up to 10,000 measurements per second speed). Using this Patented Line Confocal Imaging method, the surface is illuminated by a near infrared light source integrated with customized optics that focuses different colored lines of light split to focus on the inner and outer walls of the bottle. With its proprietary optics/software this imaging system then reads the distance between these outer/inner wall light beams and automatically adjusts for the bottle distance from centerline while also correcting for any bottle tilt from nominal on the conveyor. The result is to optimize the individual wall thickness repeatability that otherwise would be impacted by the bottle wall test read location varying from a minimal location on the conveyor line. A thickness measurement accuracy of +/- 0.0008″ with +/- 0.0006″ repeatability is achievable. Once the software calculates the actual thickness data, it is then sent to the integrated 24” touch CRT screen for operator review. This technology thus provides ability to measure individual wall thickness versus other older technologies on the market that employ Infrared and light intensity vision based technologies that average the walls 180 degrees opposite each other to provide a nominal wall thickness on a bottle from the two walls instead of the Confocal Imaging providing individual wall thickness measurements on the walls 180 degrees from each other.

For more information on this technology, contact TeTechS Inc.

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The pros and cons of different non-contact methods for measuring thickness in the coating industry

Advanced technologies are used in non-destructive methods to measure the thickness of coatings and films without damaging the test sample. The thickness of the coating can be determined by using optical light, electromagnetic waves, or ultrasonic waves to probe the sample. Some of the non-destructive methods for measuring the thickness of paints and coatings include:

Magnetic and electromagnetic inductive methods are used to measure the thickness of electrically non-conductive coatings and films on magnetic and non-magnetic metallic substrates. Magnetic and electromagnetic methods can accurately measure the thickness of coatings and paints on most metals, but they are not suitable for non-ferrous metals. Eddy current methods are commonly used to measure the thickness of paint on non-ferrous metals.

Transparent coatings and paints on reflective and transparent substrates are typically measured using optical methods in transmission mode . Ultrasonic methods are used to detect the reflected wave by applying ultrasonic vibration to the paint. The travel time is recorded and by knowing the speed of ultrasonic vibration inside the material, the thickness is calculated. Total coating thicknesses can be measured using ultrasonic thickness measurement gauges, which have a measuring range of typically 13 to 1000 microns.

Terahertz waves, a form of light with a wavelength that falls between microwave and infrared, are the power source of terahertz metrology solutions. Terahertz time-of-flight measurement technique is ideal for multi-layer thickness measurement in reflection mode for paint and coating applications. The layer thickness is calculated based on the speed of terahertz waves in the material, hence it is a “true thickness” with no on-going calibration required. Terahertz waves pass through both opaque and transparent materials, so unlike optical methods, there is no transparency limitation on paint and coating. Unlike magnetic and eddy current methods, there is no limitation on the electrical or magnetic properties of the substrates. Another advantage of the terahertz time-of-flight method is that it can accurately measure the thickness of each individual layer of a multi-layered coating.

Another area in which the terahertz time-of-flight method prevails is in measuring paint on plastics. The automotive industry has led to a significant increase in the use of plastics in various industries over the last few years. Plastic parts often need to be painted for various reasons, such as improving their appearance, producing parts with matching colors, and improving the stability of plastic surfaces. The thickness of paint on plastic can be accurately measured using the terahertz time-of-flight method.

8 reasons why plastic bottle manufacturers should use terahertz for their wall check quality control

Until now, plastic bottle and container manufacturers have been limited by labor intensive (and in many cases destructive) thickness measurement quality control practices. Techniques such as Hall effect gauges, which are manual and contact-based, have poor gauge repeatability and reproducibility, and can only measure overall wall thickness– something that is insufficient when a multi-layer structure is involved. Cutting and measuring oxygen barrier layers is another ineffective technique, as it is both destructive, wasteful, and prone to human error.

Here are 8 reasons why now is the time for plastic bottle and container manufacturers to adopt terahertz-based automated measurement solutions for their bottle wall thickness and barrier layer thickness measurement quality checks:

1. Measures opaque and transparent materials (HDPE, PP, PET, etc.)

Unlike optical measurement techniques that limit their use to transparent materials, terahertz-based measurement gauges can measure any type of plastic polymers, even those with opaque properties.

2. Measures overall wall thickness

The true thickness measurement is achieved by utilizing the time-of-flight principle to measure the wall thickness of the bottles. Optical measurement gauges use material absorption to calculate wall thickness values, which is an indirect thickness measurement technique that requires on-going calibration.

3. Measures EVOH barrier thickness

Unlike optical measurement gauges that only measure overall wall thickness of the samples, a terahertz based measurement gauge can measure the thickness of the oxygen barrier layer separated from the outer and the inner layers.

4. Optimizes expensive EVOH resin usage

Manufacturers can avoid resin overuse by optimizing the amount of resin used in production with high-precision measurement data on the expensive EVOH barrier layer.

5. Frees up staff time for higher value tasks

An automated walk-away solution handles the tedious and time-consuming task of bottle wall checks, allowing the operator to focus on more important tasks.

6. Improves on employee safety

The cutting of samples for barrier checks is a significant safety risk for employees and can be a source of liability for employers. This risk is completely eliminated by a non-contact barrier thickness measurement solution.

7. Brings high quality data into the process

Manually collected measurement data is susceptible to human error, making it less reliable. Measurement data collected by an automated system with low gauge R&R provides high-quality data for the production process.

8. Measures a full batch of samples in a cycle

A full cavity shot of bottle samples can be measured in one cycle with an automated and hands-free measuring system. The measurement data for the entire batch is recorded and automatically saves to the database for analysis and reporting purposes.