QUESTIONS I. What are the differences between adiabatic heating and thermal heat
ID: 702953 • Letter: Q
Question
QUESTIONS I. What are the differences between adiabatic heating and thermal heating as appl extruders and why are both important? 2. Discuss why the compression zone of a nylon-type screw is so much shorter than the 3. Discuss the temperature profile shapes normally used for nylon and polyethyl 4. Describe a spider die. What adjustments are typical and how are they made compression zone in a polyethylene-type screw. purpose screw. Which is higher in actual value? What are the slopes of each? 5. Discuss three operational steps that can be taken to reduce the thickness of an ex truded part. 6. Explain the effect of molecular weight distribution on extrusion. 7. Discuss the relationship between the melt temperature and the location of the frost line in blown film manufacturing. 8. Discuss why melt pumps are rarely used with twin-screw extruders. 9. During the operation of an extruder in making thin-walled tubing, several defects have been encountered that appear to be small globules of resin. Investigation of these glob- ules reveals that they will soften but not melt when heated. Explain what these glob- ules might be and suggest two possible remedies for eliminating them. 10. Ecpiain why outside-diameter dimensional control is easier than inside 11, why do the cross-sectional shapes of the die orifice and the final (cooled) extruded part 12. Assume you are working for a custom extrusion company that uses many dies, -diameter di- mensional control for extruded pipe. sometimes differ? resins, and many colors. To keep costs down, your company generally buys naturalExplanation / Answer
1) Adiabatic heating in extruder is the heat generated due to compression of the extruded material. The shaft or screw of the axtruder does work on the material/polymer to compress it. This causes churning and compression of the material, high friction with the walls and other complex phenomenon which cause heat generation.
Thermal heating is external heating provided to the extruder by means of heating coils, steam or warm water. This is required to maintain the temperature and hence flowability (desired viscosity) of the material. If the material gets too cold, it may choke the extruder.
2) Compression section helps in removal of gases and air from the molten material. The length of the compression section in an extruder depends on the material/polymer to be extruded. For crystalline polymers generally a very short compression section is required in the design.