In injection section of injection process, filling speed plays a leading role. According to needs of product quality, different speeds of 1-5 or more stages can be set. Generally, one segment of product is sufficient, and a more suitable speed is set according to arm thickness of product. Speed of thin-walled product is faster, and speed of thick-walled product is slower. Ordinary gears are better between 20% and 50%. If it is too fast, it is easy to cause poor exhaust or poor front, and if it is too slow, it is easy to cause poor flow or insufficient filling.

Above statistical analysis methods can be applied in practice.

From nozzle to front of gate, since this section is all about nozzle position of runner, requirements are not high, and it can be done a little faster. If it is too slow, it will solidify and increase resistance. Area shown in Figure 1 below;

 

When melt flows through gate, because gate is smaller than runner and wall thickness of product is smaller, it is compressed from runner to gate, and melt is released from gate to cavity to produce an expansion effect. Filling speed in the area near gate should be appropriately slower, as shown in Figure 2 below;

 

From area near gate to before cavity is full, all are product positions. At this stage, while considering apparent quality of product, it is more important to consider exhaust status of cavity. On the premise that there is no problem with exhaust, speed should be appropriately faster, otherwise it should be as slow as possible. Area shown in Figure 3 below;

 

Before cavity is full, pressure of cavity rises sharply, and most of gas is also discharged from PL surface, ejector pin position, slider and exhaust groove, etc., but a small part of gas is forced to accumulate in this position , at this time, filling speed must be as low as possible, or switch to pressure maintaining project, as shown in the area shown in Figure 4 below;

 

Nozzle is a key element of hot runner mold. To maintain molten state of plastic in nozzle, heat insulation must be as perfect as possible. Some nozzles also need to be heated internally or externally, while cavity needs to be cooled. Temperature difference between the two is usually 100-200℃, so nozzle design should first meet heat balance requirements. It is necessary to avoid solidification and clogging caused by too much cooling material in nozzle, and to avoid casting or drawing or even thermal decomposition of plastic due to overheating. Secondly, thermal expansion caused by temperature difference should be considered. Again, pay attention to leakage of melt, which will cause flashes and affect normal work.

 

Commonly used hot runner nozzle structures:
External heating
Internal heating
Spring Needle Valve

 

Straight gate form

 

Split gate flat nozzle form
• Point gate form

 

Several forms of single gate flat nozzle

 

Single gate point nozzle form and split gate point nozzle form

 

cylinder, oil cylinder

 

One-core multi-head type and multi-core multi-head type