Flow marks are a phenomenon in which a pattern of the flow tracks of the molten plastic remains on the surface of the molded product. Depending on the extent, these can become defects in the case of molded products in which their external appearance is an important aspect of quality, such as in the case of home electrical appliances, containers for cosmetics, etc.

Flow marks are caused because there is a difference in the extent to which the cooling takes place upon contact with the surface of the mold at the front end of the plastic when the molten plastic is flowing inside the cavity of the mold.

The following countermeasures can be considered in order to avoid flow marks.

(1) Countermeasures related to molds

	1.	Set the cavity surface temperature a little higher.
	2.	Widen the gate.
	3.	Widen the runner.
	4.	Acquire sufficient cold slag.

(2) Countermeasures related to the injection molding conditions

	1.	Increase the injection pressure.
	2.	Increase the injection speed.
	3.	Acquire sufficient volume and increase the cushion amount.
	4.	Increase the dwell time.
	5.	Increase the dwell time.
	6.	Increase the plastic temperature.

(3) Countermeasures related to the design of the molded product

1.

Make variations in the wall thickness of the molded product small.