Density of Melt
Sensitivity | Availability | Datasheet Category | Cool Time Relationship |
|---|
Low | Low | Physical Properties | Direct Variation |
Density of Melt for a given material is the density of the material in its molten state (which can differ significantly from its density when solid--polymer molecular chains expand when heated, reducing density). Cooling time increases as Density of Melt increases.
Values for Density of Melt are typically obtained through experimentation. The range of typical values is small (0.9-2.2 g/cm3).
In the material specification,
Density of Melt may appear in the Physical Properties category. For certain materials, you may have difficulty finding information on
Density of Melt values. See
Estimating Density of Melt. Note that accuracy of this value is less important than accuracy of values of
Eject Deflection Temp,
Mold Temp, and
Melting Temp.
Estimating Density of Melt
If you want to add a new material to your Digital Factory, and you cannot obtain Density of Melt from a material’s specification, you may be able to estimate the value based on solid density or Density of Melt for a similar base polymer. The following considerations may help you formulate your estimate:
• Semi-crystalline polymers tend to have higher melt (and solid) densities than amorphous polymers.
• Amorphous and semi-crystalline materials behave differently when heated:
o For amorphous polymers, Density of Melt is typically 90% of solid density.
o For semi-crystalline polymers, Density of Melt is typically closer to 80% of solid density.
(For information on which materials are semi-crystalline and which are amorphous, see
https://www.iapd.org/Documents/Members%20Only/iapd_rectangle.pdf. Note that URLs may change.)
• Glass fiber fillers typically increase Density of Melt.
If you know the Density of Melt for the raw polymer, you may be able to calculate composite Density of Melt as a weighted sum:
1 For each component of the mixture, find the density, D1, D2, …, Dn.
2 Find the fraction, F1, F2, …, Fn, of the mixture accounted for by each component. For example, if a compound contains 30% glass fiber and 70% polymer resin, the fractions are 0.3 and 0.7.
3 Estimate Density of Melt for the mixture as the weighted sum (F1 * D1) + (F2 * D2) + … + (Fn * Dn).