Defelsko manufactures handheld, non-destructive ultrasonic Thickness Gauges designed for the non-destructive measurement of dry film thickness of coatings on wood or other wood-based products. Many factories now use this non-destructive technique for quality monitoring programs.
Two models for wood coating measurement:
1. PosiTector 200 B1 (standard type) is economical and commonly used to measure the thickness of the total coating system.
2. PosiTector 200 B3 (advanced type) can simultaneously measure the total coating thickness and the independent thickness measurement of up to 3 layers in a multi-coating system. It is also capable of outputting plots that facilitate detailed analysis of coatings.
Application 1: Measuring Total Coating Thickness
Some wood finishes are applied in layers to achieve their desired goals. The positector 200 B1 is the ideal solution when the user only needs to know the final total coating thickness.
The PosiTector 200 is ready to measure most ready-to-use wood coatings. It has a measurement range of 13-100 microns (0.5-40 mils) and is suitable for measuring polymer coatings such as paints, primers, UV-curable coatings, acrylics, powder coatings, etc. No calibration adjustments are required for most tests, it features mil/micron unit switching, and it has a large, thick, impact-resistant polycarbonate display.
For those familiar with magnetic coating Thickness Gauges, using an ultrasonic coating Thickness Gauge is convenient and intuitive. The measurement method is simple and non-destructive.
Application 2: Measuring the finish of a guitar
A good example is the use of the PosiTector 200 B1 to measure the total thickness of multiple coatings in a musical instrument manufacturing process.
Lacquer is applied to a guitar base (usually wood or graphite) to achieve a glass-like sheen that reveals the beauty and luster of the wood. The scratch-resistant hard varnish protects the wood from moisture, chemicals and damage while optimizing the acoustic resonance of the instrument.
The methods and benefits of ultrasonic thickness testing of guitars are discussed in a separate article.
Application 3: Measuring veneers and composite laminates
Thickness measurements are not limited to natural wood. Some of today's modern materials are a combination of synthetic and natural materials. In carpentry, veneer is thin slices of wood usually glued and pressed to a core board (usually wood, particle board or MDF) used to produce flat panels such as doors, cabinet top and side panels, parquet floors and furniture Component. Composites with wood veneer surfaces are increasingly used in aerospace, underwater and automotive structures.
The surface of wood or wood products is often coated with a polymer coating, the thickness of which can be easily measured with the positector 200 B1.
Application 4: Measuring Rough Surface Coatings
Coatings on rough surfaces are challenging for any measurement method, and ultrasonic testing is no exception. The positector 200 Thickness Gauge is designed to handle these situations.
At the microscopic level, the thickness can vary (see Figure 1). Meaningful thickness measurements are best obtained by taking multiple measurements at the same general location and then averaging the several test results.
Figure 1 Plywood coating on rough surface Figure 2 Couplant filling the gap between probe and coating
On rough surfaces the positector 200 usually measures the thickness from the top of the coating peak to the substrate. The distance shown in Figure 2.
The couplant fills the gap between the probe and the coating to assist the penetration of the ultrasonic wear into the coating.
Severe roughness will cause the gage to display a low thickness value (distance #2). This is because the echo is stronger from the couplant/coating interface than the coating/substrate interface. The PosiTector 200 has a unique user adjustable set range feature to ignore rough echoes.
image 3
To obtain meaningful thickness measurements of rough surfaces, the memory mode of the PosiTector 200 (Fig. 3) is used to calculate the average value.
Application 5: Measuring powder coatings on medium density fiberboard (MDF)
Medium-density fiberboard, or MDF, is a solid wood product made from wood particles mixed with synthetic resins. Powder coating is a dry process using fine particles of pigments and resins, which are electrostatically blasted onto MDF. The charged particles adhere until the heat and energy process melts the charged particles and fuses them into a solid, flat coating.
MDF is suitable for powder coatings due to its low porosity and uniform surface. MDF products include office furniture, kitchen and bathroom cabinets, doors, storage and displays, as well as DIY furniture for the office and home.
These single coat applications typically range in thickness from 3 to 9 mils, which can be easily measured with the PosiTector 200 B1. For the rough surfaces mentioned above, the PosiTector 200 has a unique user-settable range feature that ignores rough echoes. And together the storage mode is used to display the average value of a series of measurement results. Large-screen LCD display can display the number of measurements, standard deviation, highest and lowest readings.
图4 在这个例子中，已经采取了10次测量。最后一次测量值显示为18.2密耳，另外还有显示10个读数的标准偏差和最大值/最小值。平均值为18.26毫升。
应用6：厚的聚酯类聚合物
聚合物涂层应用于木质材料，如中密度纤维板（中密度纤维板、胶合板、纤维板、刨花板）提供一个美观耐用的涂层表面。全行业已围绕聚合物涂层使用发展。例如，聚酯型granicoat®（图5）喷洒在木材表面如便携式自助餐桌、厨房台面、浴室面盆，以及桌子和吧台。
图5 测量granicoat厚度
对这些厚涂层测试，建议使用positector 200 C3。它的测量范围为50~3800微米（2~150密耳），是厚度涂层的称心测厚工具。它的图形模式在确定薄的引物和其他难以区分层的厚度是非常有优势的。
图6（左）和图7（右）
图6显示了在当图形模式开启进行测量时，仪器液晶显示屏显示的内容。既有测量的厚度值又有显示回波“尖峰”，“峰”的图形表示。有趣的是，一个较小的峰也可以看到。虽然它太微弱了而不能自动测量，一个绿色的光标可以放置在手动测量的顶部。
图7中的绿色光标告诉我们显示的峰值是4.4密耳厚。
应用7：干胶
有许多类型的木材粘合剂。湿胶不能通过超声波测量因为positector 200探头在测量时需要接触被测材料的表面。然而，干胶和其他单一涂层一样，可以由positector 200 B1的测定。
应用8：多涂层应用中单个层厚度的测量
PosiTector 200 B3能够同时测量总涂层厚度和多涂层体系中最多达3层的独立厚度测量。它也能够输出有助于详细分析涂层系统的图解。
图8
在上面的例子中，层1是1.5密耳厚。层2是1.5密耳厚。总厚度为3密耳。图形液晶显示两个“峰”，代表两个材料接口。进行两步骤过程调整仪器来用于多涂层测试。
应用9：其他非常适合于超声检测涂层厚度的应用
UV-curable coating for hickory wood Water-based acrylic primer for plywood Factory primer for untextured formed hardboard
UV curable paint on unfilled maple wood Roller coat acrylic on cardboard Spray paint on oak
Filler/Foundation/Good Cover
Application A: Coatings with large, solid particles
The PosiTector 200 probe contains an ultrasonic transducer that sends ultrasonic vibrations to the coating. This vibration travels through the coating until it encounters a material with different mechanical properties - usually the substrate. The vibration is partially reflected at this interface and propagates back to the transducer.
Figure 9
For good accuracy, the ultrasonic vibrations need to pass smoothly through the coating. Large solid particles such as sand will deflect the vibration and prevent a clear echo back to the transducer. Therefore the positector 200 cannot reproducibly measure these applied coatings.
Application B: Wood Stains
Wood stains are a subcategory of paints. It consists of a "vehicle" of pigment suspended in a solvent and binder (alkyd, linseed oil, acrylic, polyurethane, lacquer or resin). It is configured to add or transport pigment into the pores of the surface rather than creating a film on top of the surface.
The PosiTector 200 is designed to measure the thickness of the film formed on the wood surface, which penetrates the wood fibers to seal and protect the wood, and cannot be measured ultrasonically.
Remarks: This article comes from Defelsko and is professionally translated by NBCHAO Mall. The source must be indicated when the translation is reproduced.
