Feb 9 2009
Cellular PVC is gaining strength as the material of choice for deck systems as an alternative to natural wood materials. Cellular PVC (also called foamed PVC) compounds are gaining market share due to favourable cost, ease of processing, and weatherability. Favorable weather resistance is achieved by applying a capstock downstream in the extrusion process. This capstock can also include colouring agents.
Cellular PVC extrusion is not without problems however. The chemical reaction of the blowing agent can make dimensional control challenging, thus the need for continuous on-line monitoring for size and shape, particularly for features that affect fit and alignment, such as tongue and groove dimensions. On-line monitoring can also detect cross-sectional bowing in the board surface, a condition which negatively affects the visual uniformity of deck installations.
Key to effective on-line measurement is the laser profile sensor. The profile sensor projects a laser line across the board so that the light is reflected through precision optics and onto a CCD detector, which digitizes the profile. Once digitized, virtual software calipers are applied to capture key dimensions, which are displayed for the operator, much like a real-time optical comparator. As a result, when the extrusion process goes out of specification the operator is alerted immediately to take action necessary to regain control of the process.”
Deck board manufacturers are under increasing pressure to run more lines with fewer people. Profile360 displays are often arranged so that one operator can view the status of several lines. Real-time status can also be viewed at any PC on the factory network, so people in the production and quality teams can stay apprised of the line performance. Trend line displays permit any observer to see the dimensional values for the complete run.
Bytewise Measurement Systems are represented in the UK by Nortest.