Answer to Question 1
Nylon melts over a much narrower range than polyethylene. Since the purpose of the compression zone is to melt the polymer, the distance to do the melting need not be as long with the more easily melted nylon.
Answer to Question 2
Spider dies are used to make hallow parts, such as tubes and pipes. The inside diameter of the die decreases gradually and smoothly from the inlet of the die to the land. The land is the final output zone and in this zone the inside diameter of the die is constant. The mandrel inside the die