Last week we introduced some fundamental concepts related to spray foam chemistry and discussed what is actually happening when the two part systems are mixed together. To continue the discussion of processing SPF we are going to talk about the chemical flow through the system, external conditions and targeted processing conditions.
So following the spray setup backwards, you know the liquid that is spray applied to the substrate, from the spray gun, flows down a 200 to 300 foot heated and pressurized hose, from the proportioning unit, that is feed supply chemical from a drum using drum pumps. The chemical reaction that occurs on the wall can create good foam or not so good foam. And, there are many factors that affect the performance and physical properties of this foam application, including the ambient air temperature and relative humidity, the surface temperature and the starting temperature of the chemical in the drums. The combination of these factors affect the speed of the reaction and the timing of the foam evolution, resulting in our final foam.
These chemical reactions are exothermic, meaning they generate heat, and they are temperature sensitive. The overall temperature ranges can have a dramatic effect on the performance of the product, in particular, cold chemicals means a slower reaction time and less expansion, thus a lower than optimum yield, and overheated chemicals means a faster reaction time, possible shrinkage, thus a lower than optimum yield. An SPF contractor is in the business of manufacturing foam plastic from liquid chemicals, to provide an insulation solution for their customer; so optimizing application, processing, and, in turn yield, is critical to the bottom line.
An SPF applicator’s goal is to be skilled enough to read and modify the processing temperature and pressure of the proportioning equipment, to compensate for the external conditions, and manufacture good quality foam on site. It is highly recommended, and can prove very useful, to monitor and record these external conditions and equipment processing parameters on a daily basis, in a job site report, to track changes and possibly predict optimal starting points based on prior processing history. Make sure to refer to the appropriate manufacturer’s product data for an acceptable range for external conditions and recommended processing parameters.
Now that we know the purpose of the proportioning equipment is to compensate for external conditions so an applicator can create good quality foam, stay tuned over the next few weeks as we discuss processing open cell and closed cell SPF.
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