Surface World December 2018 Surface World Magazine December 2018 - Page 56

TESTING & MEASUREMENT The methods all have their limitations. The comparator is subjective test and does not provide a numerical result. Replica tape provides a value for the maximum peak to valley height within the small sample area tested. Accuracy depends on the tape not being affected (primarily crushed) by the operator or the anvils of the dial gauge during the measurement process. The replica tape reader enables a user to gleen more information from replica tape than just the maximum profile depth and the result obtained has been shown to be similar to the Ra and Rz values obtained by a Surface Roughness Gauge. The Profile gauge, digital or otherwise, can give 2 different values depending on whether the user takes the maximum or the average of the 10 readings per measurement. It has been shown that using the average of the maximum values correlates more closely to replica tape readings, however the average of the mean gives a more representative characterisation of the surface. The latest scanning development gives the option to measure either profile depth or equivalent roughness parameters at a much improved speed and together with the ability to save data and connect with a PC to download the data is the more flexible and fastest option. Surface Roughness Gauges have the ability to provide much more data than all of the previously mentioned methods, but these gauges are not primarily field instruments and are very delicate. The data provided is more aligned to machined surface finishes and not merely a profile depth and as such they are designed to measure much lower profiles as they are looking for minor imperfections in surfaces. If they are to be used then the correct design of stylus and arm should be used to ensure more relevant measurements are made. Ultimately the inspector is likely to have no choice as the method to be used will be specified relative to a Standard and the Standard will define the equipment to be used, but it appears that Profile depth is currently the most required value. Telephone: +44 (0) 161 371 6000 Email: Visit: Wherever there are painted surfaces Automotive industry, car paint shops, corrosion protection, façade construction – all share the need to check and document paint coating thicknesses for a variety of reasons from safety to maximising cost effi ciencies. Fischer explains how its latest digital pen-like pocket instrument is probably one of the easiest and effective devices currently on the market. There are three key industry applications when it comes to measuring painted surfaces; and each one centres on quality control. ‘Incoming goods’ is one, where products manufactured overseas may have had different or less stringent quality control standards applied. In this situation, it becomes necessary for a testing laboratory to take the paint thickness measurement and check it against required UK standards DIN EN ISO 2360, ASTM D7091, DIN EN ISO 2178, DIN EN ISO 21968. ‘Quality assurance’ is another large application area, particularly in car production Inspection of a storage tank and in car paint shops where samples are measured during the assembly process. ‘Inspections’ is a huge application field as it covers corrosion protection and construction, where fast and reliable paint thickness measurements need to be taken on site. selects the right mode. In the second case, the device measures both ferrous and non-ferrous metals, as well as anodised layers on aluminium, using the phase sensitive eddy current method. Fischer’s new device has answered user issues like ‘I’m not sure what kind of substrate I’m dealing with’ or ‘I need to measure magnetisable substrates such as steel or iron as well as and non-magnetic metals like aluminium’. The answer to both is ‘yes’, in the first case, the device automatically detects the substrate and then Rigorous testing Bearing in mind some of the more exposed environments in which paint thickness testing is required, the digital pen-like device was developed with a rugged housing to protect the smart electronics inside. Safe within its IP65 housing, water, dust and corrosive CONTINUED ON PAGE 56 54 DECEMBER 2018 twitter: @surfaceworldmag