Paint, in various colors, paint chemistries and textures, is applied on steel substrates using continuous production. The wet painted substrate is heated after application in ovens to cure the paint and remove the solvent, so the temperature of the painted substrate alters as the process continues. This is important since the paint color also changes depending on the temperature. Most of the time two paint layers are applied, one after the other. It is also to be noted that dry film physical properties are not identical and the different paint formulations are color specific (example, dry film density, heat absorption, radioactive properties).
The substrate surface onto which the paint is applied could be Hot Dip Galvanised, Galvalloy, Magizinc or cold reduced steel, where the substrate surface is typically MB or MC according to EN10346 with a typical roughness of 0.5 - 1.5 Ra measured by a cut-off of 2.5mm. The dry paint thickness varies from 3 to 400 microns and the line speed at which paint is applied is max 150 m/min.
Color, gloss and paint thickness are critical parameters that need to be controlled tightly to ensure homogeneity and product quality. To measure coating properties samples are taken from the coated sheet, but it takes time to cut a sample from the production line and check the color, gloss and thickness using off line equipment.
The accuracy required for measurement of various parameters is the following:
The greatest challenge is also to measure accurately the in-line paint thickness of our thickest coatings - PVC 200 micron, to within an accuracy of +/- 0.5 micron. These measurements are also only spot checks so variation in properties isn't picked up till the next off-line measurement.
The production process begins without any initial testing and relies on operator experience to set up the “paint coater head” to get the correct finish. By the time the painted sample is cut at the exit of the line, any deviation from standard, affects a large amount of production that has already been made. To ensure better process control and greater consistency in product properties, it is very desirable to have an online color, gloss and thickness measurement machine, in a single device.
There are online color, gloss and thickness measurement technologies already on the market for carrying out these tests, however there is no technology/device that can carry out all these measurements together in a single unit. The ideal measurement technique should be non-destructive. Currently, the color measurement industry uses 0/45 geometry color machines. There are also various online dry film thickness machines. Examples of these are CO2 laser, Beta scatter and Laser Displacement devices. Gloss measurement techniques are currently based on EN13523-2:2014, 60°.
Solutions are invited for a machine/technology that will measure all the parameters: color deviation, gloss and dry film thickness, online & in one unit. In the first phase, this machine/technology will be deployed to measure these parameters for solid colors, followed by metallic shades and ultimately textured paint surfaces.
The solution must meet the following requirements: