Quiz #3 ME 330.3 Manufacturing Processes 2017/2018 Term 1

Quiz #3 ME 330.3 Manufacturing Processes 2017/2018 Term 1

Time:20 minutes

Name: ______Student Id:______

1. Explain what p is in the equation below. Is p an independent variable or dependent variable? Why? [20]

The p is the pressure at the head of the extruder and p is a dependent variable. This variable is the result of other variables such as the rotational speed of the screw bar.

1. Explain the phenomenon of die swell in plastic product fabrication and the underlying reason behind this phenomenon. [10]

The material tends to recover to its original state. The underlying reason is that the material shows a viscoelasticity behavior.

1. Explain the die characteristic curve in the context of the plastic extrusion process. [10]

The die characteristic curve represents a relation between the pressure in the fluid at the exit of the die and flow rate of the fluid. To the whole system of the extrusion process, the die serves a resistance to the flow movement driven by the extruder, and it gives the allowable rate of the flow that can pass the die.

1. Explain the extruder characteristic curve in the context of the plastic extrusion process. [10]

It describes the relation between the head pressure and flow rate at the gate nearly prior to the die.

1. Explain the concept of operating point in the context of the plastic extrusion process. [10]

The operating point in this case is described by two variables that are: the pressure in the fluid which is located in the interface between the die and extruder. The operating point reflects the actual situation of the process, and in the context of the extrusion process, this means that actual pressure in and flow rate of the fluid. For the extrusion process, the operating point is then determined by the balancing of the die characteristic curve and the extruder curve, and in particular, the intersection point of the these two curves is the operating point.

1. Explain the concept of the operating or process parameter and list two operating parameters in the context of the plastic extrusion process. [10]

The process parameters are parameters that describe the process, e.g., the speed of the screw bar in the plastic extrusion process, the determination of the process parameter must be in the occasion when the system is in operation.

In the plastic extrusion process, the speed of the screw bar is a process parameter and the viscosity of the fluid is another process parameter.

1. List two benefits of plastics materials in terms of production as opposed to metal materials. [10]

(1) Less energy required.

(2) High corrosion resistance.

1. Explain the role of breaker plate in the extruder. [10]

To strengthen the material by making the micro-structure more regular.

1. Explain the major difference between two-plate mold and three-plate mold in injection molding. [10]

One major difference is that three-plate mold will allow for the gate to be on the top side of the mold instead of the side of the mold (which is the case for two-plate mold), and this will allow the flow more uniformly distributed.

1