Hi.During the last blown film production of PVC, material degradation was noticed, however, machine was not fully purged prior to shutdown. upon heating-up for cleaning, stuck-up material was found and even after hours of purging,a portion of the die does not allow material to pass through. we dismantled but had difficulty removing the mandrel from the die body. the mandrel was stuck to the die body. please suggest other ideas on how to solve the problem. Thanks