The thickness testing method and standard of powder coating technology process

It outlines how it works and the testing methods and standards of the relevant industries.
is called powder coating Powder coating: Coating powder coating made from powder coating is a new solvent-free 100% solid powder coating. It has two main categories: thermoplastic powder coatings and thermo-cured powder coatings, which
in
. Coatings are made from special resins, pigments, curing agents and other additives, mixed in a certain proportion, and then prepared by thermo-extruded and crushed screening processes. They are stable in temperature, storage is stable, electrostatized sprayed or fluidized bed immersion, and then heated baking melt curing, so that the formation of a flat and bright permanent coating film, to achieve decorative and corrosion-proof purposes.
characteristics: 1, the product is not toxic, no solvents and no volatile toxic substances, so no poisoning, no fire, no "three waste" emissions and other public hazards, in full compliance with the requirements of the national environmental protection law.
2, high utilization rate of raw materials, over-sprayed powder can be recycled, utilization rate of more than 99%.
3, after the coating pre-treatment, a one-time construction, without the need for the bottom coating, you can get enough thickness of the coating film, easy to achieve automated operation, high production efficiency, can reduce costs.
4, coating dense, adhesion, impact strength and toughness are good, corner coverage is high, with excellent chemical corrosion resistance and electrical insulation performance.
5, powder coating storage, transportation safety and convenience. Powder spraying construction process and requirements: the so-called powder electrostectrulation spraying is the use of high-voltage electrostectrectration corona electric field principle. The high-pressure negative is connected to the metal conduction mark of the head of the spray gun, and the ground of the sprayed work piece forms a positive pole, which makes a strong electrostation field between the spray gun and the work piece. When the compressed air as a carrying gas, the powder coating from the powder barrel through the powder pipe to the gun's conduction rod, due to the conduction rod connected to the high-pressure negative electrode generated by the corona discharge, in its vicinity produced a dense negative charge, so that the powder on the negative charge, and entered the electrostature field with high electrostatist intensity, in the static electricity and carrying gas under the dual action, the powder evenly flew to the surface of the grounding parts to form a thick and uniform powder layer, and then heating into a uniform coating.
Coating construction process before processing a dry removal of water one spray one inspection one baking one inspection a finished product construction requirements general powder spray construction requirements
(1) in order to make the special properties of powder coating to give full play to and extend the service life of the coating film, the surface of the coating first strict surface treatment
(2) spraying, the coating must be completely grounded to increase the spray efficiency of powder coating.
(3) for the coating with large surface defects, should be scraped conductive putty, to ensure the smoothness and smoothness of the coating film
(4) after spraying objects need to be heated and cured, curing conditions based on the technical indicators of powder products, but must fully ensure its curing temperature and time, to avoid insufficient curing caused by quality accidents.
(5) powder immediately after inspection, if found defects should be treated in a timely manner, if cured after the discovery of defects, its scope is small only local without impact, the surface decoration of the coating, can be diluted with the same color powder with acetone for repair, if the range is large and affect the surface quality, then sandpaper polished, then sprayed once or with paint remover coating, and then re-powder.
(6) recycled powder must be screened to remove debris, according to a certain proportion of the new powder mixed effect. (7) Powder barrels, powder spray rooms and recycling systems should avoid contamination of other different color powders, so every time the color change must be blown clean.
2, art-type powder spray construction requirements: art-type powder, with beautiful, strong three-dimensional sense, decorative effect and so on, but its construction process requirements are strict.
(1) when spraying powder input pressure should not be too large, generally controlled at 0.5-1. 5kg/cm2 is good. Too much air pressure can cause poor pattern clarity or produce some hemp points. Static voltage should not be too high, generally controlled at around 60-70Kv. The voltage is too high, which causes the powder attached to the surface of the work piece to bounce back into a puddle. Defects such as poor leveling.
(2) spray powder should pay attention to ensure the thickness of the coating film, generally controlled between 70-100 m can be conducive to the formation of obvious patterns and larger patterns, coating thin pattern is not obvious, and the pattern is also small, at the same time there will be defects such as hemp dew bottom
(3) curing must be baked according to the prescribed temperature and time. If the temperature is too low for too short a time will cause the powder shape is not patterned, and the mechanical properties due to curing is not complete also greatly reduced. In addition, due to the particularity of the art-type pattern powder production process, after re-spraying with recycled powder, its pattern will be smaller or less obvious changes, so it is generally recommended that the recovery powder of art-type powder should not be used. It must also be tested for use. From the above point of view, although its construction requirements are more stringent, but I believe that the coating process as long as a better grasp of the above factors, will certainly achieve the ideal satisfactory results. The storage and access of powder coatings
1, away from the source of fire, to avoid direct sunlight, should be placed in a well ventilated, temperature below 35 degrees C.
2 and avoid storage in places susceptible to contamination from water, organic solvents, oils and other materials.
3, powder paint after use do not feel free to expose in the air, should be at any time to cover or tighten the mouth of the bag to avoid mixed debris.
4, avoid long-term contact with the skin, adhere to the skin powder with soapy water rinse clean, do not use solvents. The safety of the coating construction site and the equipment used in the coating operation should be well grounded to eliminate static electricity.
2, avoid the grazing machine unprovoked discharge phenomenon
3, powder spray room, the concentration of floating dust as far as possible to control below the safe concentration, to avoid the risk of dust fire explosion.
, Overview
thickness measurement should be the routine work of all powder coaters (Figure 1). Regular measurements help control material costs, manage coating efficiency, and maintain surface quality. Powder coating manufacturers recommend that coatings achieve the target film thickness range with optimum performance characteristics and that these parameters meet customer expectations.
the thickness of the powder film before and after curing can be measured using several different instruments. See Figure 2, for example, that each powder coating operation should know what equipment is available and how to use it.
, the need to measure film thickness
film thickness can be said to be the most important measurement in the application and inspection of protective coatings. Powder coatings are designed for coating in a thickness range specified by the manufacturer to achieve their desired function. The object and appearance properties of many finished coatings are directly affected by 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 tolerance, the installation of the coated assembly will also be affected.
other benefits of accurately measuring coating thickness. Whether process control can be performed to meet the requirements of the International Organization for Standardization (ISO), product quality or customer, companies need to confirm coating quality to avoid spending money on rework products. By checking their application equipment, they ensure that the applied coating complies with the manufacturer's recommendations.
applyer must apply powder coating evenly and in accordance with the requirements of the product specifications. Over-coated DFT is not only wasteful, but also risks incomplete curing and significantly reduces the overall performance of the coating system. High membrane construction usually results in low bonding strength. The coating is easy to peel off or crack from the substrate. Regular inspections can reduce the number of internal reworks and customer returns due to processing defects.
, standard
powder coating thickness measurement is based on the test is before or after the powder curing to use different measurement methods. The American Society for Social Testing and Materials (ASTM) has a range of standards for describing these technologies.
D 4138 test method describes a destructive measurement method for testing a solid substrate with a stying instrument.
D 7091 procedure describes non-destructive measurement methods for measuring metal substrates using magnetic thickness gauges and
vortex thickness gauges. The D6132 test method describes a non-destructive measurement method for measuring
non-metallic substrates with an ultrasonic thickness gauge.
D 7378 standard describes three methods for measuring the thickness of a prepared pre-cured powder coating to estimate the thickness after curing.
, membrane thickness measurement,
thickness measurement can be done before curing and cross-linking. The type of substrate, the thickness range of the coating, the size and shape of the coating and the economics of the operation determine the measurement method used.
in unculated powder coatings, height measurements can be made using powder combs and electronic measuring meters using dedicated powder probes. Since the thickness of the powder coating decreases during the curing process, the reduced factors are determined to predict the DFT after curing. In addition, ultrasonic instruments measure un cured powder without touching the surface and automatically predict the curing thickness of the powder.
, a variety of handheld devices can be used for direct DFT measurements on the coating section. These non-destructive thickness instruments are based on the type of substrate to choose whether it is magnetic induction, electric vortex, or ultrasonic principle. Less common methods include micron measurements, destructive dry film methods such as cross-slices, and weight (mass) measurements.
1, the standard unit of measurement
the normal standard unit used in the measurement of powder thickness in the United States is the millil; If the manufacturer specifies a thickness of 2.0 to 5.0 mils, the final curing thickness of the powder should be between 0.002 inches and 0.005 inches. The metric units measured are called microns (microns);
the coating device must be applied evenly to the powder coating and in accordance with the product specifications. This provides the best interests of a particular powder specification. Most thickness detection specifications apply to the curing thickness of powders, so we are seeing the emergence of measurement techniques for different thicknesses.
2, curing film thickness measurement
gigm scale 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 it has the disadvantage of requiring simultaneous measurement of the thickness of the exposed substrate. Two measurements must be made: one contains the coating and the other does not. Two readings, the difference between the height changes, are the thickness of the coating.
two destructive technologies are also available. One is to observe the cladding part of the cut-off section through a microscope and measure the thickness of the membrane. The other is to view a geometric cut using a zoom microscope through a cured coating. This method is required when inexpensive, non-destructive methods cannot be used, or when non-destructive results need to be confirmed.
most common way to measure the thickness of cured powders is by using an electronic DFT meter. They are handheld, easy to operate, and relatively inspensive. They select magnetic induction, eddy current, or ultrasonic principles depending on the type of material.
a mechanical meter when the part is made of steel. It uses a permanent magnet and a calibration spring. The device measures the force required to pull the magnet from the coated steel surface. Magnetic pull-out meters are rugged, easy to operate, inexpensive, easy to carry, and usually do not require any calibration adjustments. They are a more appropriate and economical alternative in some production situations where only a few readings are required.
electronic DFT measuring instruments are a popular choice for large and small powder operations due to their simplicity, versatility, accuracy and record-keeping capabilities. They measured steel substrates using magnetic induction principles and other metal substrates using eddy current principles. Sometimes two principles are set in one instrument. The results of the test are displayed directly on an easy-to-read liquid crystal display (LCD). A wide range of probes are available for measuring irregular shapes or for accurately measuring very thin or very thick coating systems.
ultrasonic pulse technology is required for non-metallic substrate measurements such as coated plastic or wood. This provides a possibility that the industry could not previously conduct non-destructive quality control at a reasonable price. One benefit of this measurement technique is that the possibility of each layer is measured in a multi-layer coating system.
3, pre-curing film thickness measurement.
methods discussed so far have been used in partially cured powder thickness. It is also desirable, even in some cases, to measure the coating immediately after preparation to predict the thickness of the cured powder coating.
If the coating is improperly applied, correction that has dried or chemically cured requires expensive additional labor time, which can lead to membrane contamination and may introduce adhesive and coating system integrity issues. Measuring the film thickness during preparation determines whether the coater needs to be corrected or adjusted immediately.
measurement of 4, dry powder.
most powder coating specifications specify the target thickness for curing, this allows you to determine whether the applied powder meets the thickness specifications before final curing and crosslinking.
there are good reasons to need an accurate curing DFT forecast, especially on moving lines. Depending on the length of the oven, the number of cured parts, and the time required for the curing process and the time it takes to manually measure the DFT value after curing, there is a fairly sufficient delay before the operator intervenes in the application process to make some necessary modifications.
if coating defects are found, considerable coating parts have to be reprocessed in a dressing ring, or if the cost of reprocessing is too high, they may even have to be discarded. For some operations, these disadvantages are unacceptable in meeting the requirements of modern processing procedures.
the powder at pre-curing, pre-gel status to ensure proper curing film thickness. This allows the application to be set up and fine-tuned before curing. This, in turn, will reduce the amount of waste and excessive spraying. Accurate prediction avoids peeling and recoated, as this can lead to adhesion and coating integrity problems.
as the ASTM D 7378 standard describes three procedures for measuring the coating of powders:
A. Hard metal notch (comb)
B. Electronic coating measuring instrument
C. non-contact ultrasonic instrument
metal notch meter with special powder probe. The instrument manually measures thickness by hand dragging over coated powder. Similar to how the wet film thickness meter works, the instrument determines the height of the powder between the highest numbered tooth with a mark and the second highest tooth with powder glued to it and the second highest tooth with no mark that no powder adheres to it. These.