Turn Up / Down The Heat And Shoot Slow / Fast

[CNC Molds N Stuff]

Plastisol is workable in relatively wide range of conditions, and molds have a wide range of demands. 

• If you have a mold that is trapping air it may need some vents added at key locations. 
• Things you can do to improve the ability of air bubbles to rise to the parting line and get squeezed out at those vents are to raise your injection temperature and shoot slower. 
• Molds with lots of details may also need to be shot hotter and slower. 
• Don't worry about about knowing if you can shoot faster.  Your own impatience will quickly tell you when you are shooting to fast. 
• Sometimes if fine details do not fill out preheating the mold may help with that.  Often just injecting it a couple times will get it hot enough to run.

Thick baits may shrink leaving dents. 

• Colder plastisol will shrink less. 
• Holding pressure on the mold after its full may help force it to flow a few seconds longer than it would if you just move onto the next mold when its full. 
• Larger gates will flow longer than smaller gates.
• A mold cavity with a textured surface is more likely to pull in more plastisol than pull away from the cavity surface as it cools than a cavity with a smooth surface. 
• Molds designed with the cavities as close as possible to the main runner will have less heat sink cooling affect at the gate. 
• A larger runner will hold heat longer and flow longer. 

Sometimes a mold cavity will draw air in through the runner and gate leaving a hollow bait. 

• Holding pressure on the mold keeps a supply of plastic available. 
• Sometimes just topping off the mold with some plastisol poured from the injector or a cup is enough to keep feeding the cavities plastic instead of air.
• A sprue extender can sometimes increase the reservoir of plastic your cavities can draw upon before they start drawing air.   

If a mold doesn't work perfectly it doesn't mean the mold is bad.  It could be bad, but more likely if you provide it with the right injection parameters it will work better for you.  There is no magic one size fits all.  Often even a general sale mold is made to fit particular customer demands that do not make it possible to shoot perfectly no matter what.  The laws of physics always apply. 

Please post tricks you have learned to make your plastisol molds work better in the replies below.