Cold flake suppression method

A cold flake suppression method for suppressing occurrence of cold flakes in an injection molding device, which comprises a sleeve of a cylindrical shape, a tip slidable in an axial direction within the sleeve from one end of the sleeve to the other end, a sprue guide portion which is disposed at the other end of the sleeve and in which a molten metal pressed by the tip in the sleeve and pushed out from the sleeve moves, and a molding die into which the molten metal moving through the sprue guide portion is injected to mold a product, the cold flake suppression method comprising:

• a contact area estimation step of estimating a contact area between the sleeve and the molten metal per unit time;
• a total contact area estimation step of estimating an integrated value of the contact area per unit time estimated in the contact area estimation step;
• a shape determination step of determining a shape of at least one of the sleeve and the sprue guide portion so that a cold flake index is equal to or less than a predetermined value;
• and
• a cold flake index estimation step of estimating the cold flake index, which is a value obtained by dividing a total contact area estimated in the total contact area estimation step by a volume of the sprue guide portion.