Author Question: Assume you are working for a custom extrusion company that uses many dies, many resins, and many ... (Read 52 times)

HCHenry · **on:** Aug 19, 2018

Assume you are working for a custom extrusion company that uses many dies, many resins, and many colors. To keep costs down, your company generally buys natural (uncolored) resin. You must buy a new extruder and have two choices, one with L/D of 20 and one with L/D of 30 . Which machine would you buy? Why? Give two disadvantages of the machine you chose.

What will be an ideal response?

Question 2

Discuss why melt pumps are rarely used with twin-screw extruders.

What will be an ideal response?

Question 3

Discuss the relationship between the melt temperature and the location of the frost line in blown film manufacturing.

What will be an ideal response?

tuwy · **Reply #1 on:** Aug 19, 2018

Answer to Question 1

L/D 30 for better mixing quality. Disadvantages: heats the material longer, takes longer for the material to get through the machine, more material is wasted in changeovers.

Answer to Question 2

The purpose of the melt pump is to insure that a specific and dependable amount of material is moved through the equipment downstream of the melt pump. It is a positive displacement pump. The action of a twin screw extruder is also that of a positive displacement pump, although not as positive as a melt pump.
Nevertheless, the action of both is similar and, therefore, not needed together.

Answer to Question 3

As the temperature of the melt increases, the frost line rises farther up the bubble, that is, it gets farther away from the die. This is because the frost line is the point of crystallization of the resin and, with a higher melt temperature, the time required for the melt temperature to fall to the crystallization temperature will be longer.