The narrow neck press and blow (NNPB) process was introduced to gain better control over glass distribution in the container. The improved control over glass distribution has enabled significant reduction in glass weight of up to 33% without adversely affecting the mechanical performance of the container. A key component in the process is the plunger, used to form the cavity in the parison during the forming stage. The function of the plunger is to evenly distribute the glass within the blank mould cavity and to aid the removal of thermal energy from the internal surface of the parison. Whilst there has been considerable attention given to the requirements of the glass, eg viscosity, gob weight, temperature and homogeneity, there has been little attention given to the plunger material, cooling system and the plunger operating environment.
