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Experiment 3 : To test the bending of two materials having different coefficients of expansion.
Apparatus and Materials Required : OHP sheet 0.2 mm, Foam sheet 2 mm, heat gun temp 400-550 deg.C, OTG 100-250 deg.C, thread to tie, fevikwik gel as adhesive.
Procedure :
Combination of two materials and observing the change in form on the application of heat. Use adhesive at different points on the surface and heat. Use adhesive entirely on the surface between two sheets. Use thread to tie materials without adhesion.
Heat will be applied at different temperatures and time will be observed. Heat from a heat gun applied and observed changes. Heat from an OTG applied and observed changes.
Copy of VID20200819131955.mp4
0.2 mm OHP sheet and 2 mm foam sheet was and stuck with glue only at the edges.
The temperature with a heat gun was 550 degrees Celsius for a period of 1 min.
Result - The sheet begins to bend instantly wherever the heat is applied because of high concentrated heat. The bending is uneven across the surface.
Plastic has the ability to contract and crumple whereas the foam sheet does not easily, and gets pulled in the direction of the bending plastic.
0.2 mm OHP sheet and 2 mm foam sheet was and stuck with glue only at the edges.
The temperature in oven was 250 degrees Celsius for a period of 2 mins.
Result - The sheet begins to bend gradually, takes the form of a vault at first and then flattens again and finally crumples and takes the form of an uneven four sided vault.
0.2 mm OHP sheet and 2 mm foam sheet was stuck to each other in a grid of 20 mm.
The temperature in oven was 250 degrees Celsius for a period of 1 and 2 mins resp.
Result - As the grid makes the sheets as one piece. The resulting form becomes a vault after a minute of heating and crumples parallel to the grid after 2 minutes of heating.
Another experiment gives a vault form on heating for a minute and flattens after it is cooled down. On flattening the plastic bends perpendicular to the grid.
0.2 mm OHP sheet and 2 mm foam sheet was tied at the corners with a thread.
The temperature in oven was 250 degrees Celsius for a period of 2 mins.
Result - As the sheet is detached from the foam piece, the plastic does not pull the foam sheet towards itself but becomes deformed.
The foam is not affected much and instead being harder than plastic, retains its shape and tends to bend the plastic.
0.2 mm OHP sheet and 2 mm foam sheet was tied at the corners with a thread.
The temperature with a heat gun was 550 degrees Celsius for a period of 1 min.
Result - As the sheet is detached from the foam piece, the plastic does not pull the foam sheet towards itself but becomes deformed.
The foam bends uniformly with the plastic and almost takes its shape.
0.2 mm OHP sheet and 2 mm foam sheet was stuck to each other with adhesive covering the entire surface.
The temperature in oven was 250 degrees Celsius for a period of 2 mins.
Result - The sheet material of the plastic crumples on the side of the foam this type and becomes brown because of the burnt adhesive.
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