PURPOSE: To form hollows in the whole of a frame even when the frame consisting of a particularly thick synthetic resin having square continuous or incontinuous hollows is to be formed.
CONSTITUTION: One or more auxiliary chambers 9a and 9b communicated with a cavity 3 are provided. Open-close valves 11a and 11b are provided between the cavity 3 and the auxiliary chambers 9a and 9b, respectively. After melted synthetic resin is injected into the cavity 3, hollow forming liquid is put with pressure in the melted synthetic resin, and the open-close valves 11a, 11b at one side are opened so as to push out a part of the melted synthetic resin 7 to an auxiliary chamber 9 so that a hollow is formed. In the same manner, the hollow forming liquid is put with pressure in the melted synthetic resin in sequence and a part of the melted synthetic resin is pushed out to the auxiliary chambers 9a and 9b by opening the other open-close valves 11a, 11b so as to form a hollow, thereby providing hollows almost in the whole of a frame.
TANIGUCHI TERUO
MINAMI TORU
