(64d) Modeling of Foam Flow From Adjacent Pour Regions in Reactive Polyurethane Foaming

Molding of flexible polyurethane
foam starting from a reacting mixture of polyol,
water and isocyanate is a fast process where the
structure is formed in a matter of minutes.  The blowing reaction usually proceeds much
faster than the crosslinking reaction: the reacting foam attains gel
consistency well before the gel conversion of the crosslinking reaction ? see
Mora et al. (1991).   There is
considerable literature on numerical simulations of the expanding and reacting
flow ? see e.g. Bikard et al. (2007). However, predictions
of unfilled regions near the end of fill were found to be inconsistent with
observations in molding of seat cushion foam.

The object of this paper is to track the approach and
merging of foam flow fronts from adjacent and separate pour regions in a
rectangular mold cavity (see example in Figure). Numerical simulations were
carried out by using the VOF method and the finite element software FLUENT with
the help of user defined functions for the time varying density and viscosity
of the foam.  As a first step, foam flow patterns were obtained for the
rectangular mold filling case reported by Mitani and Hamada (2003) with their specifications
on density and viscosity and our results were found to be consistent with their
results. Next, the flow field near the merging fronts was investigated for
varying distance between pour regions. This was done at first with time varying
but Newtonian viscosity for the expanding foam and then with a different
viscosity function near the approaching fronts. 
In particular, conditions that locate an air pocket in the merging
region were identified.

Bikard, J., Bruchon,
J., Coupez, T., Silva, L., ?Numerical simulation of
3D polyurethane expansion during manufacturing process,? Coll. Surf. A 309, 49-63 (2007)

Mitani, T. and Hamada, H., ?Prediction of
flow patterns in the polyurethane foaming process by numerical simulation
considering foam expansion,? Polym.
Eng. Sci. 43 (9), 1603-1612 (2003)

Mora, E., Artavia, L.D., Macosko, C.W., ?Modulus development during reactive polyurethane
foaming,? J. Rheol., 35 (5), 921-940 (1991)

Adjacent pour regions
in a rectangular mold cavity at the start of expansion