ã€China Aluminum Network】 Technology for the thickness of powder coatings. It outlines the working principles and test methods and standards of related industries.
I. Overview
The film thickness measurement should be the normal work of all powder coating personnel (Figure 1). Regular measurements help control material costs, manage coating efficiency, and maintain surface quality. Powder coating manufacturers recommend target film thickness ranges that enable coatings to achieve better performance characteristics and these parameters meet customer expectations.
The thickness of the film before and after curing can be measured with several different instruments. See for example Figure 2. Each powder coating operation should know what equipment is available and how to use it.
Second, the necessity of measuring the film thickness
Film thickness can be said to be a more important measure in the application and inspection of protective coatings. The powder coating is designed to be coated by the thickness range specified by the manufacturer to achieve its intended function. Many object coatings have object and appearance properties that are directly affected by the dry film thickness (DFT). DFT affects the color, gloss, surface profile, adhesion, flexibility, impact resistance and hardness of the coating. If the film thickness is not within the tolerance, the assembly of the assembled assembly will also be affected.
Accurate measurement of coating thickness also has other benefits. Whether it can meet the requirements of the International Organization for Standardization (ISO), product quality or customer requirements for process control, companies need to confirm coating quality to avoid spending money on rework products. By checking their application equipment, they ensure that the application's coating meets the manufacturer's recommendations.
The applicator must apply the powder coating evenly and according to the product specifications. Applying an oversized DFT is not only wasteful, but there is a potential risk of incomplete curing and can greatly reduce the overall performance of the coating system. High film construction usually results in low bond strength. The coating is easily peeled or broken from the substrate. Regular inspections can reduce internal rework and the number of customer returns due to processing defects.
Third, meet the standard
The thickness of the powder coating is measured according to the test using different measurement methods before or after the powder is cured. The American Society for Testing and Materials (ASTM) has a series of standards that describe these technologies.
The D 4138 test method describes a destructive measurement method for testing a solid substrate with a slicing instrument.
D 7091 procedure describes the use of magnetic thickness gauges and
Eddy Current Thickness Gauge for Nondestructive Measurement of Metal Substrates. D6132 Test Method Describes Ultrasonic Thickness Gauge
Non-destructive measurement method for measuring non-metallic substrates.
The D 7378 standard describes three methods of measuring the thickness of a prepared pre-cured powder coating to predict the thickness after curing.
Fourth, the film thickness measurement summary
Film thickness measurements can be performed before or after curing and crosslinking. The type of substrate, the thickness range of the coating, the size and shape of the coating, and the economics of the job determine the measurement method used.
In uncured powder coatings, the height measurement can be measured with a powder comb and an electronic meter using a dedicated powder probe. Since the thickness of the powder coating during the curing process will be reduced, the reduction factor is determined to predict the cured DFT. In addition, ultrasonic instruments measure the uncured powder without contacting the surface and can automatically predict the cured thickness of the powder.
After curing, various handheld devices can perform direct DFT measurements on the coated portion. These non-destructive thickness measurement instruments are selected based on the type of substrate, magnetic induction, eddy current or ultrasonic principle. Less common methods include micrometric measurements, destructive dry film methods such as cross-sections, and weight (mass) measurements.
1, the standard unit of measurement
The normal unit of measure used in the United States powder thickness measurement is mil; 1.0 mil is equal to one thousandth of an inch (1/1000 inch). If the manufacturer's specified thickness is 2.0 to 5.0 mils, the final cured thickness of the powder should be between 0.002 inches and 0.005 inches. The measured metric units are called micrometers (micrometers); 25.4 micrometers is equal to 1.0 mils.
The applicator must apply the powder coating evenly and according to the product specification sheet. This provides a big benefit of the specific powder specifications. Most thickness inspection specifications apply to the cured thickness of the powder, so we have seen different thickness measurement techniques appearing.
2, cured film thickness measurement
The micrometer is one of the original instruments used to detect DFT and is still used today. It has the advantage of measuring any coating/substrate combination, but there are disadvantages that require simultaneous measurement of bare substrate thickness. Two measurements must be taken: one at a time and one at a time. The difference between the two readings, height change, is the coating thickness.
There are two destructive techniques that can also be used. One is to observe the clad portion in the cut section by microscopic observation and measure the film thickness. The other is to view a geometric cut through a cured coating using a zoom microscope. This method should be used when inexpensive, lossless methods cannot be used, or when non-destructive results require confirmation.
The more common method of measuring the thickness of a solidified powder is to use an electronic DFT meter. They are handheld, easy to operate, and relatively low cost. They choose the principle of magnetic induction, eddy current or ultrasonic according to the type of material.
When the part is made of steel, a mechanical meter can be used. It uses longer magnets and a calibration spring. The device measures the force required to pull the magnet from the coated steel surface. Magnetic pull gauges are rugged, simple to operate, inexpensive, portable, and often do not require any calibration adjustments. They are a more appropriate and economical alternative in some production situations that require only a few readings.
Due to its simplicity, versatility, accuracy, and record keeping features, electronic DFT measurement instruments are very popular choices for large and small powder operations. They use magnetic induction to measure steel substrates and use eddy currents to measure other metal substrates. Sometimes two principles are gathered in one instrument. The results of the test are displayed directly on an easy-to-read LCD. A variety of probes can be used to measure irregular shapes or accurately measure very thin or very thick coating systems.
Non-metallic substrates such as coated plastic or wood require the use of ultrasonic pulse technology. This provided a possibility that the industry could not perform non-destructive quality control at a reasonable price. One benefit of this measurement technique is the possibility of measuring the individual layers in a multilayer coating system.
3, pre-cured film thickness measurement.
The measurement methods discussed so far have used powder thicknesses after partial curing. It is also possible, and in some cases even more desirable, to measure the coating immediately after preparation to predict the thickness of the cured powder coating.
If the coating is improperly applied, the correction has dried or chemical curing requires expensive additional labor time, which may lead to contamination of the film and may introduce problems with adhesiveness and the integrity of the coating system. Measuring the film thickness during the preparation can determine if the applicator needs to be corrected or adjusted immediately.
4, dry powder measurement.
Although most powder coating specifications specify a target thickness for curing, this can determine whether the applied powder conforms to the thickness specification before final curing and cross-linking.
There is a good reason to require an accurate cure DFT forecast, especially on the move line. Depending on the length of the oven, the number of parts to be cured, and the time required for the curing process and the time to manually measure the DFT value after curing, there is a considerable amount of time before the operator can make necessary modifications to intervene in the application process. The delay time.
If a coating defect is found, a significant portion of the coating has to be reworked in a fitting ring, or if the cost of rework is too high, they may even have to be discarded. For certain operations, these disadvantages are not acceptable for meeting the requirements of modern machining programs.
Measuring the powder in the pre-cured, pre-gelled state ensures the correct cured film thickness. This allows the application system to be set up and fine-tuned before curing. In turn, this will reduce the amount of waste and overspray. Accurate predictions can avoid stripping and recoating, which may lead to adhesion and coating integrity problems.
The ASTM D 7378 standard describes three procedures for measuring coated powder coatings:
A. Hard metal gap (comb) meter
B. Electronic coating measuring instrument with special powder probe
C. Non-contact ultrasonic instrument
Metal gap gauge. The instrument manually measures the thickness by manually dragging the coated powder. Similar to the operation of the wet film thickness gauge, the powder height value determined by the instrument is the number of the tooth with a mark, and the higher numbered tooth with the powder adhered to it and the unmarked one, no powder adhered to it. The height between the second highest tooth. These simple tools are cheap but only accurate to a few mils. The measurement can be performed on a suitable rigid substrate, but the mark will be marked in the powder that is not covered when the powder flows during the curing process.
Electronic measuring instrument. Use a dedicated powder probe instrument to measure the thickness of the coated powder. The micro-needle built into the probe penetrates the powder coating onto the substrate. The probe is then pressed manually on the surface of the powder layer to measure the thickness. This method is only suitable for flat metal substrates and may leave traces on the final product.
The above two methods are only used for the measurement of the height of the uncured powder coating. However, as previously mentioned, most of the thickness specifications often refer to the thickness of the cured powder. Since powder coatings usually decrease in thickness by up to 50% during the curing process, these two steps require the creation of a reduction factor for each specific coating powder to predict the cured film thickness. The reduction factor is determined by measuring the thickness of the solidified powder coating at the same position of the uncured powder that has been measured, and then subtracting the two before and after the measurement.
Non-contact ultrasonic meters. Method C of ASTM D 7378 describes a relatively new type of instrument that has rapidly become a popular solution for dry powder thickness measurement. It is an ultrasonic instrument that can be non-destructively measured on uncured powder to predict the DFT value at the end and does not leave any trace of the finished product.
These instruments are hand-held and battery-powered and can be used right out of the box for most powders. Their simple operation and electronic design features allow them to be used quickly and efficiently by line operators.
Non-contact is a decisive advantage of the coating thickness gauge with no damage. This means that after the measurement, the measured components can be reintroduced into the ongoing process.
Fifth, the accuracy of film thickness measurement
These instruments are simple to operate, and a discreet user should verify their operation regularly, especially when complying with international ISO standards. These three steps ensure better accuracy.
1, calibration
Coating thickness gauges are usually calibrated by a device manufacturer in a controlled environment. The calibration certificate display can be issued to a national metrology agency. There is no standard time interval for recalibration, nor is it a requirement, but a standard time interval can be established based on experience and work environment. The 1-year calibration interval is a typical frequency proposed by many instrument manufacturers.
2, verify
This is an accurate check of the user with known reference standards. This quick check ensures that the instrument is measuring properly and the user is operating it correctly. For many meters, accuracy can be verified by measuring plastic gasket or epoxy coating standards with distribution values ​​that can be traced back to national metering agencies.
3, adjustment
The adjustment, or calibration adjustment, is the act of proofreading the thickness reading of the gauge to match a known reference sample in order to increase the accuracy of the particular coating of the gauge within a particular portion of its measurement range. This operation is rarely required in the powder coating industry because the acoustic properties in powder coating materials do not change much.
Six, coating quality control
In today's highly competitive environment, customers often choose a processing company with a solid quality control system. By investing in a simple system that records and analyzes DFT results, powder applicators can study trends, reduce costs, and provide customers with strength data that reflect the parameters they can meet to retain customers.
A quality assurance (QA) program refers to the development of a simple program that requires a certain number of thickness measurements at the same location in each section. By recording all the values, then periodically perform the change analysis and take the necessary corrective actions.
Manual data collection through pens and paper is not only time-consuming and error-prone but also adds significant cost to the coating project. Thickness gauges with measurement result storage eliminate this risk. The ability to automate readings is a good way to keep costs within control and reduce human error. In digital format, data can be easily stored, reported, and exported.
Ultra Plantâ„¢ Grow Light offers One Chip Technology aimed to meet your indoor growing expectation such as improve plants' quality, increase yield, or better the margin, etc., all for helping you realize a higher return on your crops.
Ultra Plantâ„¢ Grow Light is combined our advanced All-In-One technology with patented optical design and customized light full spectrum supported from our experienced LED engineers, plant specialists and other partners working on horticulture.
From Ultra Plantâ„¢ APP, you are able to schedule the growing process including photoperiod, brightness and spectral in advance. The lighting system will help you grow smarter, easier and better.
Ultra Plantâ„¢ is the most versatile horticultural grow lighting fixture for indoor plants with flexible full spectrum, brightness control and uniform, wider light distribution, suitable for top lighting of all types of crops. No matter it applies to anywhere for any crop, Ultra Plantâ„¢ can do perfect work for you.
Grow Light On Seedling,Seedling Grow Lights,Seedling Led Grow Lights,Best Grow Light On Seedling
Feton Corporation , https://www.ultraplantled.com