TESTING & MEASUREMENT
Climate Monitoring for the Coating Process
The drying and curing process for paint films is very dependent on the climatic conditions under , which the paint is applied and cured . Quick and simple measurement of the relative humidity and surface temperature together with calculation of the dewpoint temperature ensures that the correct conditions for a high quality finish are achieved .
Air has the capacity to hold a certain amount of moisture as vapour , depending on the temperature . Relative humidity is the proportion of moisture in the air at a given temperature , as a percentage of the maximum amount that can be held by the air at that temperature . As air cools , the capacity to hold moisture is reduced and the relative humidity in the air will increase until the moisture starts to condense out of the air on to surrounding cold surfaces .
The dewpoint is the temperature at which condensation occurs for air with a given relative humidity . If the air can be cooled to the dewpoint then the moisture will condense out of the air . More importantly if there is a cold surface at or below the dewpoint temperature the moisture will condense on that surface as a thin film of water molecules .
When applying paint it is vital that the substrate is not only clean but also dry in order to achieve the service life of the coating system . The general rule used in the protective coatings industry is that the surface temperature must be at least 3 ° C ( 5l ° F ) above the dewpoint temperature for the surface to be free of moisture from the surrounding air .
The monitoring of climatic conditions should not be limited to determining if it is “ OK to paint ”, changes in temperatures and humidity during the cure process can result in changes to the recoat time and / or defects in the finished film .
The Elcometer 319 Digital Dewpoint meter has been designed to determine if the climatic conditions are appropriate to paint and to monitor the climatic conditions during the cure process .
Fig 1 . Elcometer 319 Digital Dewpoint Meter ( picture to the left )
These rugged Dewpoint meters quickly and accurately measure relative humidity ( RH %), air temperature ( Ta ) and surface temperature ( Ts ) and calculates the dewpoint temperature ( Td ) and the difference between the surface temperature and the dewpoint temperature ( ΔT ). Each gauge also calculates the equivalent wet and dry bulb temperatures from the measured values for the convenience of some coating inspection regimes where these parameters are required to be included in any report .
Fig 2 . The user can select which five of the seven parameters are displayed
The Elcometer 319 Dewpoint Meter has many features to make its use quick , simple and accurate , this includes Bluetooth ® wireless communication .
Available in two models ( Standard & Top ) the Elcometer 319 can be used as a hand-held gauge to measure the climatic conditions or as a stand-alone data logger to monitor conditions over an extended period of time , during the coating cure process for example . The gauge can be held in place on a steel surface for the logging process using magnets attached to the back of the gauge . When used as a data logger the gauge uses a K-type socket to utilise an external magnetic surface temperature probe to monitor the surface temperature continuously .
Fig 3 . The gauge can be held in place on a steel surface for the logging process using magnets attached to the back of the gauge .
The gauge is operated using easy to use menus , allowing the user to quickly set up features such as warning limits , backlight brightness , measurement units , etc ., and review statistics and measurement records . Standard versions have a rolling memory of the last 10 readings ; Top versions come with a memory capacity for up to 25,000 records in up to
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28 DECEMBER 2020 read online : www . surfaceworld . com