Characteristics and advantages of Hot Runner as compared to Cold Runner

Hot runner system is the great widely used plastic forming system. Mainly depend on the heating device and the electric temperature control. Makes the melt plastic would not be curdle, Let the plastic filling into the mould cavity. Under the without injection pressure circumstance, the melt plastic would not flowing automatic, and also would not appear drawing and over flow during the plastic product ejection. So the hot runner mould also called no runner or little runner mould.

1.  Hot runner and cold runner compared advantage 

A.  Cold Runner:

• During the injection filling process, as the front of the melt plastic energy lost, the surface of the melt plastic would be curdle. And also would make the injection pressure loss bigger; affect the injection machine using life directly.
• During the injection filling process, as the front of the melt plastic energy lost, the surface of the melt plastic would be curdle. Make the plastic temperature not uniform which filling into the mould cavity. This may lead to the plastic appear   splay mark, weld line, warped, sink marks, short of filling and a serious problem,  after forming to plastic product. Makes the plastic product can not reach the requirement.
• Because of the cold runner existing, urge some factory set special waste secondary processing equipment. Cause the waste of the human resource and the material resource.
• Some mould structure gate can not separate automatically with the plastic product. Request to add the processing of clip vestige. Low automation degree.
• Long time mould cooling, long time filling, make the low production efficiency.

B.  Hot Runner:

• After heating, the hot runner temperature, injection machine charging barrel temperature and injection nozzle temperature are almost equal. Avoid the plastic curdle phenomenon appear in the runner. And the injection pressure waste will be smaller. 
• After forming, high quality appearance. Because when the plastic inject to the cavity, the temperature, pressure and the density is uniform. After forming, the plastic inside pressure is small. Little shape change and stable dimension.
• Without waste material, save the material, save the resource and cost.
• Mould quick cooling, quick filling, short molding cycle and high production efficiency.

2.  Hot runner mould characteristic:

• The temperature range of the melt plastic is widely. when in low temperature, the liquidity is very good. At high temperature provide with the heat stability.
• Sensitive to the pressure. No pressure without flow, but if forcing flowing instantly.
• Good thermal conductively. Heating quick and cooling fast.

3.  Hot Runner Mould disadvantage:

• Since the hot runner system contain the heating system and the manifold system, request to occupy large space. So the total height of mould must to enlarge, add the mould cost directly.
• Heat losing seriously, hard to control.
• After heating will lead to serious thermal expansion.
• Hot runner system price is expensive, increase whole mould price.

4.  Some questions need to awareness when design the hot runner

• Because after heating will lead to thermal expansion, between hot runner system and the mould, we suggest leave enough space for thermal expansion.
• Hot runner and mould should avoid large area to connect.
• Because serious heat losing, so please add an insulation base plate between mould and injection machine, to reduce the heat lose. Insulation base plate must be insulation material. Commonly like the Bakelite plate, all kinds of plastic plate or fiberglass and etc.