Hot runner nozzle
The nozzle is a key element of the hot runner mold. To maintain the molten state of the plastic in the nozzle, it must be as perfect as possible insulated, and some nozzles also need internal or external heating. The cavity needs to be cooled. The temperature difference between the two is usually 100-200°C, so the nozzle design should first meet the heat balance requirements. It is necessary to avoid solidification and clogging caused by too much cooling material in the nozzle, and to avoid casting or drawing or even thermal decomposition of the plastic due to overheating. Secondly, thermal expansion caused by temperature difference should be considered. Again, pay attention to the leakage of the melt, which will cause flashes and affect the normal work.
Commonly used hot runner nozzle structures:
external heating
Internal heating
Spring Needle Valve
1) Structural forms of various hot runner nozzles
①Flat nozzle
Straight gate form
Split gate flat nozzle form
• Point gate form
Several forms of single gate flat nozzle
②Point gate nozzle
Single gate point nozzle form and split gate point nozzle form
③Valve nozzle
cylinder, oil cylinder
④Special nozzle
One-core multi-head type and multi-core multi-head type
2) The heating method of the nozzle
①External heating nozzle
The heat source comes from the heating ring around the nozzle. The melt flow resistance in the nozzle is small and the length is not limited. Due to structural constraints, the temperature at the gate at the front of the nozzle is relatively low. Due to the temperature difference, the heat balance is not easy to control. The heat utilization rate of the externally heated nozzle is low, and there must be a heat insulating air gap of 3 to 5mm around the heating ring.
Contact nozzle multi-cavity hot runner injection mold
1-Fixed mold floor; 2-Cushion block; 3-Stop pin; 4-Plug; 5-Heater; 6-Hot runner plate; 7-Side support plate; 8-Direct contact nozzle; 9-Heating circle; 10-fixed model cavity plate; 11-moving template
②Inner heating nozzle
The heat comes from a heating rod in the center of the shuttle. The heating rod power can be adjusted by voltage. The melt channel gap around the shunt shuttle is generally 3-5mm. The gap is small, the flow resistance is large, and the heat dissipation is fast; the gap is large, and the radial temperature difference of the melt is large. If the nozzle is longer, an electric heating coil is required to assist external heating.
The temperature of the internally heated nozzle can be effectively controlled because the high-temperature conical tip extends into the gate.
Internal heating hot runner nozzle
1-Fixed template; 2-Nozzle; 3-Taper tip; 4-Splitting edge; 5-Heating rod; 6-Insulation layer; 7-Cooling water hole.
3) Needle valve nozzle
A needle-shaped spool that can be opened and closed is placed in the nozzle to make the gate a valve. The injection packing phase is on; the cooling phase is off. The diameter of the gate can be increased, which avoids the clogging of foreign matter, and prevents the casting and wire drawing of the gate melt. Suitable for various viscosities, especially low-viscosity plastics.
The opening and closing of the spool can be driven by melt pressure or hydraulic pressure.
Spring Needle Valve Hot Runner Nozzle
1-fixed mold bottom plate; 2-hot runner plate; 3-pressure ring; 4-compression spring; 5-piston rod; 10-heat insulation layer; 11-heating ring; 12-nozzle body; 13-nozzle head; 14-fixed mold cavity plate; 15-release plate; 16-core
Forming characteristics of valve nozzles:
•No sprue marks are left on the surface of the product, and the surface of the sprue is smooth.
•Ability to use larger diameter gates to speed up cavity filling. Reduce injection pressure and reduce product deformation.
•Prevent the phenomenon of wire drawing or casting at the gate when opening the mold.
•When the screw of the injection machine moves back, it can prevent the molten material in the mold cavity from flowing backward.
• It can cooperate with the sequence control to reduce the product weld marks.
