A gas concentration estimation method used in an injection device for foam molding configured to melt and feed a resin by rotating a screw in a heating cylinder, form a non-filled section in which molten resin is depressurized and the heating cylinder becomes a non-filled state, and supply gas to the non-filled section such that the gas dissolves in the molten resin, the method including estimating the gas concentration in the molten resin from following equation (c1) and a passing time T, which represents a time required for the resin to pass through the non-filled section

[00001]$\begin{array}{cc}\frac{\mathrm{dC}}{\mathrm{dt}}=k\left(C^{*}-C\right)& \left(\mathrm{c1}\right)\end{array}$

where dC/dt: CHANGE RATE OF GAS CONCENTRATION IN MOLTEN RESIN [g/(m.sup.3s)] k: CONSTANT [/s] C*: SOLUBILITY OF GAS [g/m.sup.3] C: GAS CONCENTRATION IN MOLTEN RESIN [g/m.sup.3]

A molding system and a method for forming a sole structure are provided. The method includes flowing a molten polymeric material into a mold from an upstream device, receiving the molten polymeric material in a cavity of the mold, and maintaining a repeatable, uniform pressure profile as the molten polymeric material is delivered into the mold.

A foam molding method includes: moving a screw backward to take air into a heating barrel through a nozzle part in a state in which a shut-off nozzle is opened, the shut-off nozzle that opens or closes the nozzle part for injecting the molten resin and is disposed on a heating barrel; closing the shut-off nozzle and moving the screw forward, to diffuse the air taken into the heating barrel, in the molten resin in the heating barrel; feeding the molten resin forward while dispersing the air as the air bubbles in the molten resin by moving the screw backward while rotating it in a state in which the shut-off nozzle is closed; and opening the shut-off nozzle, to inject the molten resin containing the dispersed air bubbles into the cavity.

An injection device (2) of an injection molding machine (1) includes a heating cylinder (18) having a gas introduction port (30) and a screw (19), and a gas supply device (5) is connected to the gas introduction port (30). The gas supply device (5) includes a gas supply source (33) and a gas pressure regulating unit (34). The gas pressure regulating unit (34) regulates a gas pressure and supplies the gas when a gas from the gas supply source (33) is introduced into the gas introduction port (30). Specifically, the gas pressure is caused to change in a molding cycle and is increased to a high pressure in a metering process (61). That is, a pressure increasing period (71) in which the gas pressure increases at least partially overlaps with the metering process (61).

A molded foam manufacturing apparatus 1 includes a cylinder 2 in which a plasticization zone 21 where a thermoplastic resin is plasticized and melted, a starvation zone 22 where the molten resin is put into a starvation state and an injected physical foaming agent is dissolved in the molten resin, and a feeding zone 23 where the molten resin in which the physical foaming agent is dissolved is compressed and metered are provided in this order from an upstream side, and a screw 3 that is installed inside the cylinder 2 so as to be freely rotatable around an axis of the cylinder and has flights formed in a spiral shape on an outer circumference of a shaft 31, wherein a lead angle R of the flights of the screw 3 corresponding to the feeding zone 23 is set smaller than a lead angle of the flight corresponding to the starvation zone 22, and the number of pieces of the flight of the screw 3 corresponding to the feeding zone 23 is set smaller than the number of pieces of the flight corresponding to the starvation zone 22. In this way, it is possible to prevent a decrease in the flow rate of the molten resin transported in the starvation zone and the feeding sone and manufacture high-quality molded foams with high production efficiency.