The present invention relates to a stirring device for liquid material, which circulates and stirs liquid material such as plastic material. More specifically, the invention relates to a stirring device wherein a return pipe (i.e. an outlet pipe) is inserted in a stirring tank and a feeding pipe (i.e. an inlet pipe) is connected to bottom portion of the stirring tank so that liquid material withdrawn from the stirring tank through the feeding pipe is returned to the stirring tank via the return pipe.
In a molding device to mold foamed polyurethane products, for example, polyol and isocyanate are put in separate stirring devices and then stirred while circulated between the stirring device and an injection device respectively. Such a stirring device of the prior art, used in a plastic molding device, as shown in FIG. 1 comprises a stirring tank 21, a stirring blade 22 driven to rotate at the center within the stirring tank 21, a return pipe 23 inserted in the stirring tank 21 from above for introducing a circulated liquid material into the tank, and a feeding pipe 24 connected to the bottom portion of the stirring tank 21, so that the upper opening of the stirring tank 21 is sealed, a pressure air pipe (not shown) is connected to the upper side and the stirring is performed under pressure in the stirring tank 21.
In this construction, however, since the return pipe 23 with its opening end directed downward is arranged in the stirring tank 21 and the liquid material of large flow rate flows towards the bottom portion of the stirring tank 21a, large convection in the vertical direction is produced within the stirring tank 21 and the liquid surface is swollen significantly, whereby the air content in the liquid material starting material for the foamed polyurethane becomes excessive and cannot be controlled suitably.