an apparatus for forming the edge of containers of synthetic thermoplastic material which are open at the top and terminate in an outer flange which is arched upwards from the top and then extends downwards . the apparatus includes an edge moulding unit having four groups of three female moulds and the same number of male moulds , a rotating plate for the female moulds designed to rotate step - by - step to cyclically carry each group of moulds from a charging position , through a moulding position to a discharge position and a cooling position . a feed device having one or more groups of parallel heated screw - threaded rotating rollers are provided , each engaging a portion of the flanges of a sequence of containers in order to heat them and transfer the same from a stock of containers to the charging position . compressed - air - nozzles are arranged to cause the container to move from the feed device to a female mould .