DISCUSSION

Actually, we unable to run this experiment yet because of insufficient silicone rubber and the

new silicone rubber that laboratory received from supplier was different in concentration for

this experiment. Thus, the laboratory advisor will call us to perform this experiment if the

right material are available. So, in this experiment we will discuss about the defect on the

product from the other's group because of using new silicone rubber.

There are many types of defect on silicone mould which are:

1) Entrapped Air

Air entrapped in the mould or in the silicone rubber may produce soft, discoloured

areas on the surface or in the cross section of the mould part, due to incomplete

vulcanization. This is because some of the vulcanizing agent is lost reacting with air.

2) Scorch

Premature vulcanization occur before the flow of silicone rubber in the mould is

completed. The poor mould flow result in distorted or incompletely formed parts.

Scorch may be caused by hot spots in the mould, by moulding at over high

temperature, by over length of time between start of mould that substantially reduce

the rate flow.

In order to prevent scorch, make sure the mould cavity is uniformly heated and if

possible, use a vulcanizing agent with a higher reaction temperature.

3) Surface Discoloration

It results from excess build up of mould release agent in the mould cavity.

To prevent it, we need to clean the mould as often as necessary and keep the performs

clean.

4) Backrinding

Distortion of mould product at the mould parting line.

May be caused by burns or roughness of the mould parting edges a warped mould that

does not close completely.

To produce the silicone mold, we need to consider the parameters used in this process. The

parameter involve are mold size, mixing ratio of hardener and quantity of silicone and

hardener. To produce a good quality mould, all the parameters should be calculated correctly

especially for the mixing ratio of hardener. If too much hardener poured in mould, it will

produce bad quality mold and more defect occur on mould.