Dear Arif Shahul Hameed, what is the casting hot plate temperature? May be it is too high! You can use an antiadhesion wax (mold release agent) or coat/film/sheet of PTFE (such as the case of cooking pan). My Regards

Professor Abdelkader Bouaziz ,I kept it at 70 degree,it form a layer only,can u suggest an antiadhesion wax which doesn't affect the casting process

It depends on various parameters, but the type of the polymer is the first think to consider.

https://www.sciencedirect.com/topics/materials-science/mold-release-agent#:~:text=A mold–release agent is,its removal from the mold.

thank you professor @ Abdelkader