Many users will mistakenly think that the density of foam is achieved by adjusting
the mixing ratio of polyurethane spraying machine, although this is also a way,
but it is not the most economical and efficient.
Most rigid polyurethane foams and flexible foams use either the water-blown system
or the 141B system. Suppose you are using a water foaming system for spraying.
For most rigid foams, Part A is the polymeric isocyanate, or PMDI, commonly
referred to as "isocyanate.". Part B contains one or more polyols, plus a
surfactant (s), possibly some other cell control agent, a catalyst (s) and water.
The water in the polyol reacts with the isocyanate radical (-N: C: O) to initially
form carbamic acid, a thermally unstable intermediate.It decomposes spontaneously
to form amines (which react further with the heteromorph), heat, and carbon
It's the carbon dioxide that makes the bubble. The density of the foam is
primarily controlled by the amount of water in the polyol, which in turn controls
the amount of carbon dioxide produced. More water = less density and vice versa.
This is roughly defined by the formula: percent water = 3.706D ^ -1.126
. . . Where D is the density in kilograms per cubic meter. Factors and exponents
vary from system formulation to system formulation.
If you know the density, enter that number to get an approximation of the water
content in the polyol. Then enter the density you want and calculate how much
water you need to add (the difference between the two values) to get the desired
Another thing to consider is that 1 part of water reacts with ~ 15 parts of
isocyanate. This means that when you add water, the index goes down. You can find
the definition of the index in my other post. This means that when you add water,
you usually want to adjust the ratio -- add more iso-alcohol -- to compensate for
the iso-alcohol used in the water: the isocyanate reaction,It can no longer react
For example: if you mix 200 grams of each polyol and iso-alcohol, then add 0.5
grams of water and 7.5 grams of iso-alcohol to keep the index constant. I believe that when you see this, you either understand or are "dizzy".
It doesn't matter, you just have to tell your ingredient supplier "Hey
friend, I need a lower density foam"