| Monitors cure conditions |
| Monday, 19 October 2009 00:00 | |||
|
When powder coating it is essential that the curing process is monitored so that a quality finish is produced, as Elcometer explains It is critical to the final appearance and service performance of a powder coating that the temperature and time for the oven curing process are sufficient to achieve a full cure. The oven temperature/time profile is influenced by the thermal loading of the oven and therefore it is not sufficient to set the oven zone controllers to an appropriate temperature value and expect the temperature/time requirements to be met. An unsatisfactory cure results in a significant reduction in the quality of the final coating in terms of gloss, colour and adhesion. Too high a temperature can burn the coating and too low a temperature or insufficient time at the required temperature results in an incomplete cure.
The data-logger uses a menu-driven operating system to make it simple and quick to operate, with easy-to-follow instructions shown on a large easy-to-read display. The data-logger displays the result of every stored reading showing the maximum temperature and the cure-index figure, percentage and pass/fail indication either as a value or represented graphically. The data can be printed on any HP printer using an optional link or the readings can be analysed in more depth by downloading the data via the USB data cable to a PC running the very powerful support software supplied with the Elcometer 215. The Download Logger Wizard makes the data transfer very easy and the User Setting Wizard allows additional fields such as sample rate, paint type, temperature units, cure specification, probe names, date and time to be added to the report. The Outgoing Mail configuration enables any report generated from the logged data to be e-mailed and the reports can be customised to include the company name, address, logo and website. A typical screen is shown in figure 2..
The software has been designed specifically for the powder and paint cure processes and there is an immediate confirmation that the paint has been cured successfully or not by reference to a cure specification in terms of temperature and time as provided by the paint manufacturer. The software is available in five languages, English, French, German, Spanish and Italian. The effectiveness of the cure process and the quality of the final coating can be assessed using a set of portable test instruments either directly on the coated component or on a coated test panel that has passed through the oven cure process with the components. The most common parameters that will be assessed against the coating specification are coating thickness, gloss, colour and adhesion. The Elcometer 456 Mk 3 family of Digital Coating Thickness Gauges have unique features to make coating thickness data collection and analysis easier and quicker to facilitate the reporting of inspection results. Figure 3 shows an Elcometer 456 Coating Thickness Gauge. The Bluetooth connectivity within the Standard and Top versions of the gauges allows wireless communication of readings data over a distance of up to 15 metres to a PC using ElcoMaster Software. ElcoMaster Software is the Coatings Data Management Tool, supplied as standard with Standard & Top Models of the 456 Mk 3 gauges. Included as part of ElcoMaster suite of programmes is ElcoMaster Mobile software allowing readings to be sent directly to data devices such as PDAs & mobile phones by the gauges making remote communication easier. ElcoMaster also offers features for analysing data, for reporting and for archiving data for future analysis or comparison. The Elcometer 456 gauges have an enhanced data output specification with RS232 data output available on Basic models as well as Standard and Top models. The Elcometer 456 Mk 3 gauges now offer a softkey lock feature. When enabled, the softkey menu items disappear from the screen as readings are taken and only reappear when a softkey is pressed. This allows the individual readings to fill the entire screen height – this large font enables easy viewing of the values. With the established comprehensive range of probe options for thickness measurement on either steel or non-ferrous metal substrates that allow different thickness range options from miniature probes with 500 µm range to large range probes capable of measurement up to 25 mm the 456 Coating Thickness Gauge will meet all coating thickness measurement requirements. Gloss assessment of the coating after cure is carried out using an optical measurement where light is directed on to the surface at a fixed angle and the amount of reflected light at the same angle is detected relative to the light reflected from a smooth, polished, black glass reference standard. This standard is nominally 100 Gloss Units (GU). A high gloss surface will have a value in the 80 to 100 GU range and a matt surface will have a value in the 0 to 10 GU range. Different gloss angle measurements are used depending on the gloss level expected. In the range 10 – 70 GU the 60° angle Glossmeter is recommended. For surfaces expected to be above 70 GU, for example those typical of the automotive coatings, the gloss is best measured using a 20° Glossmeter and for matt surfaces below 10 GU and 85° angle is used. Elcometer offer two Glossmeters, the Elcometer 406L single angle (60°) or dual angle (20/60°) Glossmeter and the Elcometer 407 triple angle (20/60/85°) Glossmeter. Elcometer Novo-Soft™ software supports both of these Glossmeters and allows data to be downloaded for analysis, reporting and storage. Figure 4 shows the Elcometer 407 Glossmeter. Colour is strongly influenced by the oven cure process and where consistency from batch to batch is important colour measurement is very important. Elcometer offer the simple to use Elcometer 6210 RAL Colour Charts for comparative colour assessment supported by the Elcometer 6300 Colour Assessment Cabinets and the Elcometer 6075 group of Portable Sphere Spectrophotometers for fast and accurate colour measurement. The sphere spectrometer is a lightweight and compact portable colour measurement system with a diffuse/8° spherical optical geometry that produces a colour fingerprint for the surface being measured and allows this data to be calculated for several colourmetric systems such as CIE L*a*b. Adhesion for powder coatings is generally assessed using the cross hatch adhesion test as defined in ISO 2409 and ASTM D3359 Method B. Both these methods use a matrix of cuts through the coating to the substrate at right angles to define a set of squares. The adhesion is determined as a rating by assessing the damage to the coating with zero damage being ISO rating 0 (ASTM rating 5B) and greater than 65% damage being the ISO rating 5 (ASTM rating 0B). These tests also reference the use of adhesive tape to remove the damaged squares from the substrate and the Elcometer 107 Cross Hatch Cutter Kits are available as ISO 2409 versions or ASTM D3359 versions with the appropriate tape and a selection of cutters as defined in the appropriate test methods. The ISO 2409 method specifies 1 mm spaced cutters for coatings up to a thickness of 60 µm and 2 mm spaced cutters for coatings with a thickness from 60 – 120 µm. The quality of the finished powder coating requires a well controlled oven cure process and the oven data logger allows the oven to be set up correctly to achieve the correct temperature and time profile to ensure the correct cure conditions for all oven loading. Completed coatings can be checked for thickness, gloss, colour and adhesion using test methods defined by national and international test methods, with software backup to present test reports to clients in a professional and efficient manner.
|
The recently updated Elcometer 215 Oven Data Logger is an easy-to-use, battery powered temperature data recorder that uses up to six K-type thermocouple probes to monitor the cure process, as the coated item and the data logger pass through the oven together. A variety of probes are available for measuring surface or air temperatures and the data-logging interval for the readings can be set from 8 readings per second to 1 reading per hour by the User. With a capacity for storage of up to 260,000 readings or 8 production runs, the Oven Data Logger provides the ability to set up and control the cure process no matter what components are passing through the oven. At the very least the Oven Data Logger should be used at the start of the working day to ensure that the cure conditions are satisfactory.
LEFT: Figure 1- The Elcometer 215 Oven Data Logger
LEFT: Figure 3- Elcometer 456 Coating Thickness Gauge With Bluetooth Connectivity to a PDA
