Frozen layer fraction result

The Frozen layer fraction result shows the thickness of the frozen layer as a fraction of the part thickness.

The values of this result range from zero to one. A higher value represents a thicker frozen layer, a higher flow resistance, and a thinner polymer melt or flow layer. A polymer is considered to be frozen when the temperature falls below the transition temperature (Ttrans).

Note: For compression-type molding processes, this result is plotted displayed on the deformed mesh as the default setting. With this default setting, if you click through the time steps you can watch the polymer as it is compressed into the part shape. To turn it off, so that all you see is the result on the part, right-click the result, select Properties and uncheck Display on deformed mesh.

Note: The Frozen layer fraction result is an intermediate result, which is animated through time by default. The default scale for this result is from the minimum to the maximum of the entire range of the result.

During filling, the frozen layer should maintain a constant thickness in areas with continuous flow because the heat loss to the mold wall is balanced by the hot melt coming from upstream. When the flow stops, the heat loss through the thickness dominates, resulting in a rapid increase in the thickness of the frozen layer.

Frozen-layer thickness has very significant effects on the flow resistance. The viscosity exponentially increases with decreasing temperature. The thickness of the flow layer is also reduced as the thickness of the frozen layer increases.

The effect of the thickness reduction can be roughly estimated with the definition of fluidity, as with representative shear rate. The fluidity is proportional to the cubic power of the part thickness. A 50 percent reduction in part thickness reduces the fluidity by a factor of eight, or increases the flow resistance by a factor of eight. A 50 percent reduction in thickness in runners reduces the fluidity by a factor of 16.

Using this result

Ideally the part freezes uniformly and as quickly as possible. The Frozen layer fraction result is used in conjunction with the Time to reach ejection temperature result to locate problem areas in the mold. The Frozen layer fraction result can reveal the following problems in your part:

• Excessive high pressure is required to fill parts in which hesitation occurs early in the filling stage. The flow layer becomes very thin in areas of hesitation, which are filled last.
• If the Time to reach ejection temperature values for the part as a whole appear high, then general measures for reducing the excessive cycle time, such as adjusting the mold and melt temperatures, may be required.
• Areas of the part taking longer to cool indicate hot spots.

Things to look for

If hot spots occur, look for ways in which the cooling circuit design can be improved.