Analysis of coal log ram extrusion

Ram extrusion of coal logs was studied for the purpose of coal log pipeline transportation of coal. Due to the existence of wall friction and contraction of the die (mold) cross-sectional area, high pressure may be needed to cause the flow of coal through the die. One common problem of ram extrusion is the predetermination of the extrusion load. In this study, equations are derived to predict the pressure drop inside a conical die under static conditions. It was found that the extrusion area ratio, the Janssen constant (i.e. the radial-to-axial stress ratio), the contact friction coefficient, and the cone angle all contribute to the extrusion load. Experiments were carried out on a conical die using a bituminous coal. There was less than 10% difference between the experimental results and the theory. It was also found that the Janssen constant approaches a constant when the compaction pressure is high. Water content, binder, and lubricant all affect the force transmitted to the wall and the contact friction coefficient.