I am using u-pvc injection molding for pvc pipe fittings.

When running a male addoptar which weight about .05 kg we are observing burning in the end of injection, what its cause?

In such cases, the cause is degraded material. PVC most often degrades whenever it either stagnates in the nozzle or adaptor or remains in the barrel too long.

PVC molders often have a habit of increasing the back
pressure above what is necessary to create a consistent melt. This tends to promote degradation and burning of the material.

-Andy