What is a spray lines?

The melted resin flows in the form of a jet stream. When flowing from a narrow place to a wide area, if the flow rate is on the fast side, it sometimes flies out in a band and flows without touching the mold. It is called a spray lines. Depending on how the spray lines is expressed on the surface of the finished product, some are banded and some are foggy, but the reason is the same.

The cause of the formation of spray lines

(1) The gate size is too small

The biggest cause of spray lines is gate size. The smaller the gate, the more force it flies out and the more severe the spray lines. The gate is small because it means that the pressure at the gate is higher and the speed is faster.

(2) The injection speed is on the fast side

With the same gate diameter, the faster the injection speed, the more severe the spray lines.

(3) High viscosity/low fluidity

  a.With the same gate diameter and injection speed, the higher the viscosity of the resin (the lower the fluidity), the more severe the spray lines.

   b.The conditions that affect the increase of viscosity are as follows:

   c.The temperature of the resin is low

   d.The mold temperature is low

   e.Material viscosity

   f.The holding pressure is low

To a certain extent, holding pressure can make the spray lines too inconspicuous. Conversely, if the holding pressure is not applied sufficiently, the spray lines will be noticeable.

Solutions for spray lines

(1) Try increasing the gate size

Check if you can change the gate size. Jetting can be eliminated by changing the gate size. Short, wide gate runners are preferred, and fan-open and angled designs are also effective.

(2) Try changing the gate location

Check to see if you can change the gate location. spray lines are basically created due to the great force with which the resin flies out. And the more open the target space that flies out, the more serious it is. However, if the resin flying out of the gate hits the wall quickly, the spray pattern can be eliminated.

Even if it is not possible to change the gate position, it is expected that the same effect can be achieved if something such as a needle or wall can be placed additionally on the front side of the gate in the product cavity.

(3) Try to lower the injection temperature

Try lowering the injection speed setting. The countermeasure is to use multi-segment injections and only slow down the velocity (rather than overall reduction) as it passes through the gate.