Author Question: Describe the principle similarities and differences between RIM and low-pressure foam molding. ... (Read 119 times)

DelorasTo · **on:** Aug 19, 2018

Describe the principle similarities and differences between RIM and low-pressure foam molding.

What will be an ideal response?

Question 2

What is meant by blowing the cells open, and how can this event be controlled?

What will be an ideal response?

Question 3

Explain why open-cell structures are created when the mold expansion in high-pressure foam molding is quite rapid and why closed-cell structures occur when the molding is slower.

What will be an ideal response?

cascooper22 · **Reply #1 on:** Aug 19, 2018

Answer to Question 1

In low-pressure foam molding the mold is only partially filled and then allowed to expand to complete the filling of the mold. In RIM the mold is completely filled but the foaming occurs simultaneously with the filling of the mold. RIM also has the capability of adding a reinforcement inside and of foaming around metal inserts which would be very difficult with low pressure foam molding.

Answer to Question 2

Blowing the cells open is the conversion of closed cells to open cells by the rupturing of the cell walls. This can be controlled by controlling the amount and rate of expansion of the gas inside the cells. This control can be achieved by limiting the expansion of the mold in high-pressure foam molding. It can also be

controlled by reducing the temperature at which the foaming occurs. Other methods that limit the expansion of a gas, such as increasing the pressure under that expansion occurs, can also prevent blowing the cells open.

Answer to Question 3

Rapid expansion of the mold tends to allow the gas inside the cells to expand very rapidly and to expand to a much larger size. This large expansion can rupture the walls of the foam and change closed cells into open cells.