Shrinkage of plastic raw materials : a comparative study of mould

Abstract EN

In plastic engineering, the mould design is considered a complex process or an art, due to the polymers used their differences and changes in properties, as well as other factors like shrinkage of the materials.

An Important point in mould design considerations is to use real and actual values of shrinkage in the early stages of design to avoid any design errors and produce an economic template.

Some containers produced locally leaks the liquids, which causes inconveniences for the users.

This problem is attributed to unspecified data of raw material shrinkage.

In this work, five samples made of polypropylene PP113 bought from the local market (Khartoum petrochemical company), and another five samples made of low-density polyethylene (LDPE), produced by SABIC of Saudi Arabia were moulded using ISO 294 test mould of dimension 60x60x2mm.

The shrinkage for the test samples was measured according to test specifications.

The averages shrinkage for samples made of PP113 was found to be 1.88, and that for LDPE was found to be 0.84.

The experimental results were compared to a simulation results obtained using Visi-12.2, and MoldFlow-Mpi Ver.

5.1 software, which often used for studying and analyzing the behavior of plastic materials in moulds cavities.

For Visi-12.2 software, the longitudinal shrinkage was found to amount of 1.25, for PP113 material, and 2.50 for LDPE material.

For MoldFlowMpi Ver.

5.1 software, the longitudinal shrinkage was found to be 1.003 for PP113 material, and 2.21 for LDPE material.

The study concluded that, there is a notable difference between the values of shrinkage obtained practically and that built in the software’s libraries, and thus for precision parts practical shrinkage tests are inevitable.