during mold opening, the well can pull the slug off the spure bush. The diameter of a cold-slug well should be larger than the larger diameter of the spure, while it’s length should be about the same as the larger diameter of the spure, to promote the material flow.
What’s the cold slug? It’s the small nub of plastic that cools and solidifies inside the nozzle tip during the cooling phase of the injection cycle. This occurs because—while the nozzle is heated—the tip of the nozzle is pressed against the cold, water-cooled mold steel.
Why is sprue needed?
In many cases it controls the flow of material into the mold. During casting or molding, the material in the sprue will solidify and need to be removed from the finished part. It is usually tapered downwards to minimize turbulence and formation of air bubbles.
How do you fix injection molding problems?
Redesign the mold with wider channels or gates for better flow. Increase injection speed or pressure or choose a thinner base material to improve flow. Increase mold temperature to prevent material from cooling too rapidly. Add additional air vents or enlarge existing vents in the mold to allow trapped air to escape.
How do you prevent flow marks?
Countermeasures
Increase the amount of material feed.
Install a screw with a back-flow check valve.
Increase injection pressure.
Raise the cylinder temperature setting.
Make sure there are no severed lines to the heater.
Make sure the nozzle is not clogged.
Increase injection speed.
Where does cold slug in injection molding come from?
Loading… A cold slug happens near the tip of the nozzle, where the nozzle is pressed against the (relative to the temperature of the plastic) is colder and therefore not fully molten. Follow good design for the material being used and use the appropriate nozzle for the material being use.
Why is the cold slug at the tip of the nozzle?
The cold slug that forms at the nozzle tip is actually kind of handy in that it can act as a small plug to prevent drool during ejection. The problem is that during the next shot that little nub of cold plastic has to go somewhere, and you’d rather it not go into your part!
Can you put a cold slug in a cold runner mold?
If you get a cold-runner mold in your shop and there’s no cold slug well, insist that one be put in. It’s generally a cheap and simple mold modification, and one that could save you a lot of headaches. Over the past decade, soft-touch overmolding has radically changed the look, feel, and function of a broad range of consumer products.
What should I do if my injection molder is clogged?
Raise the nozzle temperature, too. Make sure there are no severed lines to the heater. Make sure the nozzle is not clogged. If the nozzle clogs frequently, raise the mold temperature or shorten the cycle time. Raise the mold temperature. Increase the mold gas release. Increase gate cross section surface area. Increase the molded product thickness.