Converting Mix Ratio by Weight to Mix Ratio by Volume

  1. The Mix Ratio of a two part resin
    system is extremely important in achieving a proper cure. Epoxies,
    Polyester, & Vinyl Ester Resins use a chemical reaction between a
    resin and hardener which have a ratio that determines the relative
    proportions in which the two substances react for this reaction. This
    ratio can vary from product to product and is reported on each Technical
    Data Sheet.
  2. Why Is It Important? An error of no
    more than +/- 5% from the mix ratio is a good guideline. Larger errors
    in the mix ratio can allow un-reacted components to remain within the
    resin and may lead to an increase in outgassing, a decrease in Tg and
    decreased resistance to chemicals and moisture.
  3. For some processes, however, a
    customer may find it more convenient to measure and mix by volume rather
    than weight. Using the reported mix ratio by weight to mix by volume
    can cause products not to cure properly.
  4. How To Convert
    The volumetric mix ratio can easily be determined from the weight mix
    ratio by using the specific gravities of each component also reported on
    each data sheet. Specific gravity is a unitless quantity defined as the
    ratio of the density of a material to the density of water. Because
    water has a density of approximately 1 g/cc, the specific gravity can be
    considered the density in units of g/cc for the purpose of these
    calculations.

    Consider
    INF-114 & INF-210 where the mix ratio by weight is 3.65:1, and
    specific gravities are 1.14 for Part A and 0.94 for Part B.

    Divide the number of weight parts by the respective density:
    Weight parts PART A = 3.65 g = 3.20 cc
    Specific gravity PART A 1.14 g/cc

    Weight parts PART B = 1 g = 1.06 cc
    Specific gravity PART B 0.94 g/cc

    This yields a volumetric mix ratio of 3.20 : 1.06, which can then be
    normalized to a more convenient ratio. To create a ratio in the form of
    100:b, divide the volume parts of Part B by the volume parts of Part A
    and multiply the result by 100.
    Volume parts PART B X 100 = 1.06 cc X 100 = 33.1
    Volume parts PART A 3.20 cc

    This yields a volumetric mix ratio of 100 : 33.1 The ratio can also be
    normalized to the form a:1 by dividing the volume parts of Part A by the
    volume parts of Part B.
    Volume parts PARTA = 3.20 cc = 3.01
    Volume parts PART B 1.06 cc

    This yields a volumetric mix ratio of 3.01 : 1