Demolding temperature

Cycle time low stresses permit hotter demold temperature. 

Te[K] = demolding temperature (assumed temperature at the molding s center, at which it is to be removed)... 

A rule of thumb formula for calculating cooling is given in greater detail in Lesson 7.5. The formula employs variables of the melt temperature, wall temperature, demolding temperature, as well as the plastic material s thermal... 

Shear stress distribution Quality of part tendency to distort. Quality of part tendency to crack. Cycle time low stresses permit hotter demold temperature. 

When a material is sufficiently heated and the drawn part has everywhere the same demolding temperature, the drawn part will have equal process shrinkage. However, this is a problem because of the different demolding temperatures, mainly because of the different wall thicknesses of the drawn part. 

For the most part, the edge and the bottom areas are thicker and the side wall thinner. The different demolding temperatures have different process shrinkages. The thicker areas have a higher process shrinkage. 

The molded parts have to be cooled until the foam pressure is mostly released so they can be demolded without any uncontrollable expansion. Typical demolding temperatures are about 80 to 85 °C for PS-E and about 70 to 80 °C for PP-E. 

In the transfer technology, filling and fusion of the molded part is done in a hot mold. Afterwards, the uncooled molded part is transferred to the cold mold and is then cooled to demolding temperature. This procedure also reduces the energy consumption because the mold is not cyclically heated and cooled. The disadvantage is that two molds are used at the same time, so higher investment costs occur. The quality of the molded part is also lower than in conventional processes. 

FIGURE 2.79 Relative cooling time change as a function of mass, cavity, and demolding temperature... 

To facilitate the demolding, the three-way tap is switched over to vacuum. Should back formation of the contour be necessary after demolding, compressed air can be supplied via the third path. Precondition for this is a demolding temperature of 40 to 50 C. 

Adhesion to hot metal surface demolding temperature, distortion N Y N... 

Figure 3. Demolding temperature distributions - PA6 vs. metal/polymer blend (Tmou = 80 °C)...

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