Chloe Zhang
Measuring the thickness of plastic is an important process in the plastic industry. It ensures product quality, complies with regulations, and optimises production processes. There are several methods for measuring plastic thickness, including contact and non-contact measurements. Contact measurement involves physically touching the plastic surface with a gauge or micrometer, while non-contact measurement uses sensors or lasers to measure the distance between the sensor and the plastic surface. Micrometers are inexpensive and simple to use, but they have limitations when measuring thin plastic films, as they may not provide accurate readings. Other methods, such as ASTM standards and ultrasonic measurement, are also used to measure plastic thickness accurately and efficiently. Understanding and controlling the thickness of plastic films are crucial for manufacturers to meet quality standards and customer specifications.
| Characteristics | Values |
|---|---|
| Standards | ASTM standards: E252, D6988, D8136 |
| Units | Micron, mil, gauge, millimetres |
| Methods | Contact, non-contact, ultrasonic, online, offline |
| Instruments | Micrometers, thickness gauges, calipers, capacitance gauging systems, profilers |
| Applications | Quality control, compliance with regulations, process optimization, product development |
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What You'll Learn
Contact vs non-contact measurements
Contact and non-contact measurements are two of the three main ASTM standards for measuring the thickness of plastic film. The average thickness of plastic film can be calculated using the density, weight, and cross-sectional area of a piece of film using gauge-by-weight. However, to get film thickness variability, multiple points along the film must be measured to determine the variance in thickness.
Contact measurement involves physically touching the plastic surface with a gauge or micrometer. This method provides accurate and precise measurements but can be time-consuming and requires skilled operators. Micrometers are inexpensive and easy to use, but they have limitations when it comes to measuring thin plastic films. The precision of a micrometer gets worse as the film gets thinner, and thin films under 1 mil thick are common. Contact measurements may also have bias in the reading from compressing the film.
Non-contact measurement, on the other hand, involves using sensors or lasers to measure the distance between the sensor and the plastic surface. This method is fast, can be automated, and is useful for quality control. Non-contact gauging can provide more accurate readings for thin plastic films and can be used on moving materials without causing damage. Non-contact thickness gauges are based on dielectric measurement principles, which measure the size of the electric field created by the object to determine thickness. Capacitance sensing, for example, can be used to make non-contact thickness measurements for insulating materials, including plastics.
Both contact and non-contact measurements have their advantages and disadvantages, and the choice between the two depends on the specific requirements and goals of the user.
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Micrometers
Despite these limitations, micrometers remain a valuable tool for measuring plastic thickness, especially in laboratory settings where thin films are not the primary focus. They are widely used in the plastic industry to ensure product quality, comply with regulations, and optimize production processes.
One example of a micrometer used for plastic thickness measurement is the Digital Micrometer 49-86 from Testing Machines, Inc. This device is specifically designed to test the thickness of plastic packaging films, providing essential information about their properties.
In addition to micrometers, other contact measurement tools, such as dead weight calipers, can also be employed to measure plastic thickness. However, it is important to note that the accuracy of these tools may vary depending on the thickness and surface finish of the plastic being measured.
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Thickness gauges
There are several methods available to measure plastic thickness, including contact and non-contact gauges, micrometers, and plastic film thickness gauges. Contact gauges are simple and easy to use, but they have some drawbacks, especially when it comes to accuracy in measuring thin films. Micrometers are inexpensive and easy to use, but they also present limitations in terms of precision and bias when dealing with thinner films. Non-contact gauges, on the other hand, provide greater accuracy and are often the method of choice for measuring thin plastic films.
SolveTech, a company with over four decades of experience in measuring plastic film thickness, offers proprietary gauging technology. They have developed the PR2000 Precision Profiler, which provides an accurate and quick reading of film thickness. Another product is the Baxlo film thickness gauge, which is designed specifically for measuring the thickness of plastic film, sheets, bags, and other materials. It has a resolution of thousandths of a millimeter and a maximum measurement capacity of 1 mm.
It is important to note that the accuracy of thickness measurements depends on the calibration and proper use of the measuring instruments. Regular calibration and operator training are essential to ensure consistent and precise readings.
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ASTM standards
When it comes to measuring the thickness of plastic film, there are three main ASTM standards:
E252 – Test Method for Thickness of Foil, Thin Sheet, and Film by Mass Measurement
This standard is often referred to as gauge-by-weight, where the average film thickness is calculated using the material’s weight, density, length, and width. While this method provides the real average thickness of the film, it is time-consuming and does not account for variability.
D6988 – Guide for Determination of Thickness of Plastic Film Test Specimens
D6988 is a global standard for determining the thickness of plastic films with a nominal thickness of no greater than 0.25 mm. It provides a comprehensive set of standards that create industry integrity, guide the manufacturing process, and improve the final product. This standard is particularly useful for plastic films such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE).
D8136 – Standard Test Method for Determining Plastic Film Thickness and Thickness Variability Using a Non-Contact Capacitance Thickness Gauge
D8136 is a precise and reliable test method that defines film variability profiling. It provides detailed profile scans that determine if the film meets average thickness and variability requirements. This standard is useful for communication between plastic film buyers and sellers, as it provides a means to characterize the thickness and pattern of thickness variability. It also eliminates issues such as dirt on the probe, slow measurements, and poor reproducibility.
In addition to these three main standards, there are other ASTM standards related to plastic film thickness, such as D7310-11, which focuses on defect detection and rating of plastic films using optical sensors.
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Converting measurements
When it comes to converting measurements of plastic thickness, there are several units to consider. Plastic film thickness is commonly denoted in gauge, millimetres, and microns. Navigating between these units can be challenging, but online conversion calculators can simplify the process.
To begin with, it's important to understand the relationship between millimetres, microns, and mils. Millimetres are the base unit for measuring thickness in the metric system. For measurements below 1 millimetre, the millimetre is further divided into 1000 parts, known as microns. So, 0.5 millimetres is equivalent to 500 microns. This conversion factor (0.5 millimetres = 500 microns) can be used to switch between millimetres and microns.
The term 'mil' is used in the USA, representing 1/1000 of an inch. This unit can be a source of confusion for those familiar with the metric system, as it may be mistaken for millimetres. To convert mils to microns, you multiply the number of mils by 25.4. For example, 1 mil is equal to 25.4 microns.
Now, let's introduce the concept of 'gauge'. Gauge is another method used to denote thickness, in plastics. The gauge number is inversely proportional to the material's thickness; a higher gauge number indicates a thinner material. To convert mils to gauge, you multiply by 100. For instance, 0.3 mils is equal to 30 gauge.
There are also ASTM standards for measuring plastic film thickness that you may need to consider when converting measurements. These include gauge-by-weight, contact, and non-contact measurements. The gauge-by-weight method involves calculating the average thickness of a plastic film based on its weight, density, and cross-sectional area. Non-contact methods, such as capacitance gauging systems, are often preferred for thin plastic films as they provide accurate and quick readings.
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Frequently asked questions
Thickness gauges, micrometers, and ultrasonic thickness gauges are all tools that can be used to measure plastic thickness.
Contact Measurement involves physically touching the plastic surface with a gauge or micrometer, while Non-Contact Measurement involves using sensors or lasers to measure the distance between the sensor and the plastic surface.
There are three main ASTM standards to consider: E252 – Test Method for Thickness of Foil, Thin Sheet, and Film by Mass Measurement; D6988 – Guide for Determination of Thickness of Plastic Film Test Specimens; and D8136 – Standard Test Method for Determining Plastic Film Thickness and Thickness Variability Using a Non-Contact Capacitance Thickness Gauge.
