8.1 Introduction

This Chapter deals with the first stage of the injection in a cold chamber machine in which the desire (mostly) is to expel maximum air/gas from the shot sleeve. Porosity is a major production problem in which air/gas porosity constitutes a large portion. Minimization of Air Entrainment in the Shot Sleeve (AESS) is a prerequisite for reducing air/gas porosity. This can be achieved by moving the plunger at a specific speed also known as the critical slow plunger velocity. It happens that this issue is related to the hydraulic jump, which was discussed in the previous Chapters (accidently? you thought!).

The ``common'' model, also known as Garber's model, with its extensions made by Brevick<sup>1</sup>, Miller<sup>2</sup>, and EKK's model are presented first here. The basic fundamental errors of these models are presented. Later, the reformed and ``simple'' model is described. It followed by the transient and poor design effects³. Afterwards, as usual questions are given at the end of the chapter.