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实验室测量是质量控制的第一步 许多塑料薄膜的生产商和买家出于购买或质量的考虑会想要测量薄膜的厚度。 平均厚度可以用密度，重量和一片薄膜的横截面来测量。 为了得到薄膜的可变性，您需要测量薄膜上不同的点来观测薄膜的变量。
ASTM 标准 D6988 描述了利用净重卡尺
Additionally, a surface finish on a film will typically give a micrometer an error. Usually it will skew the reading high because the device will rest of the peaks of the rough surface.
For most plastic films and especially thin films, non contacting gauging is the method of choice to get an accurate and quick reading. Many capacitance gauging systems are set up as profilers, such as SolveTech’s PR2000 Precision Profiler. Profilers are helpful because they can provide a picture of the film thickness across the web or in the machine direction. You can bypass the calipers by calibrating based on the average thickness of a strip. This is known as the gauge by weight method and it is built into the PR2000 software.
Capacitance is the preferred method for the following reasons:
Capacitance technology will tell you the overall thickness of the material you are trying to measure. However, coating thickness can still be measured if you are able to measure the material before the coating is applied and after the coating is applied. You can then do a subtraction of the before and after to get the delta.
There are other technologies on the market that can be helpful when trying to read individual film layers using NIR for example. Capacitance has a drawback in that it can’t measure conductive materials and it can also be sensitive to variation in moisture levels.
Measuring on line is a great tool for monitoring your quality in real time. Catching an error can help reduce waste and improve the products you are producing. Additionally, producers can sometimes down gauge their average thickness if they produce a more uniform film. A thin spot in the film is like the weakest link in a chain, so if it is eliminated, the film becomes stronger overall. Down gauging can save some producers a great deal of money in material costs.
In many cases, live feedback control is used to help make automatic adjustments to the extruder. Contact gauging is typically not practical in this case due to the high speed of the line, so non contacting methods have been widely adopted.
It is important to understand some key concepts for on line gauging, and different processes will have some different needs. You can measure both in the machine direction and in the cross web direction. Cross web measurements are more typical, but machine direction gauging is gaining in popularity.
There are several styles of blown film production equipment: no rotation, and oscillating die, and an oscillating haul off.
For on line gauging, there are two basic methods, on the bubble gauging, and gauging after the lay flat. To learn more, read our article “The Impact of Thickness Gauging on a Blown Film Plant”
On The Bubble
Thickness gauges that measure on the bubble are used to provide the thickness of the film as it is being produced. They typically use a capacitance based technology, although it is different the technology SolveTech uses for it’s capacitance gauging systems. These systems scan the bubble using a circular slide and give a relative measurement, meaning that they measure the variability across the web. They have difficulty measuring absolute thickness because they have trouble holding calibration.
They are however popular on many blown film lines because they can provide feed back control to the die. If the density is known, they can use gravimetric control to calculate the average thickness. However, in practice, the exact density is not always known or entered correctly, and the dimensions of the bubble also have to be considered. Some blown film companies also find these machines to be complex to operate and maintain.
After the Lay Flat
A simpler and lest costly approach is to measure the thickness after the lay flat, meaning after the bubble is collapsed. SolveTech’s BF200 measures material after the lay flat using a spot along the edge or both edges. If either the die or the haul off is rotating, the system can map the entire bubble by measuring one point along the edge. This is because the bubble profile will rotate through this one point over time, and the rotation speed can be tracked.
Besides being simpler to operate and more economical, these systems are easily retrofitable to existing blown film lines and can hold calibration for an absolute measurement.
The disadvantages are that there is more process time between the creation of the material and when it is measured, and if there is no rotation on the line, you can not get a bubble profile. There can also be some challenges when doing feedback control when using a oscillating haul off. This is because twisting of the bubble can distort the profile.
Overall, these systems have been widely adopted, and SolveTech is a leader in this area with well over 150 installed.
For cast film, producers will often measure thickness across the web and make adjustments to their die accordingly. For wide webs, many customers will use a scanning gauge of some kind. Scanning gauges take a measurement head to scan it back and forth across the web to create a thickness profile. Some typically technologies include x-ray, gamma backscatter and beta ray gauges. There are also some capacitance based technologies and optical technologies that are used. For measuring a coating thickness, NIR or Near Infrared is popular.
For narrow webs less than 60 inches, many producers use a C Channel capacitance gauging system. SolveTech offers our unique Multichannel which does not scan and instead offers full and contact coverage of the web using multiple channels. This system has been widely adopted as the standard in narrow web since it has superior performance to the other scanning gauge technologies, and it can give a high percentage of coverage.
Biaxial Film is stretched in two directions. Therefore, along with measuring the cross web like in cast film, it may be important for the producer to measure the thickness variability in the machine direction. This is a SolveTech specialty due to our unique gauge design, and for more information, you can visit our page on machine direction gauging.
In summary, there are several methods available to measure plastic film thickness, and the one you select depends on your need and process. You can learn more about what thickness gauging can do for a blown plant here.
For more information on thickness gauging for plastic film, please contact us at firstname.lastname@example.org and we would be happy to answer your questions.
How to Measure Plastic Film | Plastics Film Thickness Gauging | Measure Plastic Film Thickness