The spring-loaded shut-off nozzle is a shut-off nozzle system that takes its closing force from an internal spring. When the melt pressure exceeds the spring force the nozzle opens, and when the pressure drops the spring closes the nozzle. It requires no compressed air line or machine signal.
Where is it needed?
Especially with PA 6 / PA 66 and similar materials, when the gas pressure inside the barrel rises, melt runs out continuously from a nozzle that is not a shut-off type. Moisture is the main source of this gas; that is why drying must also be checked separately. If no measures are taken, raw material is lost and hot melt running out in the open is a risk for the workers.
Technical features
The standard spring holds up to 8 bar. The specially produced spring is rated for at least 1,000,000 cycles, and the spring assembly is designed for high heat. The nozzle is resistant to materials with up to 50-60% glass fiber (GF). Its design also prevents gas from building up at the nozzle tip.
How it differs from a contact-operated nozzle
The types known as contact-operated (sliding) shut-off nozzles need to press against something in order to open. The spring-loaded shut-off nozzle has no such need; that is why purging can be carried out on the plasticizing unit at the desired point.
Gains
- Prevents raw material loss.
- Because the flow is under control, the pressure inside the barrel becomes more stable.
- Increases occupational safety by eliminating melt running out in the open.
- Allows the machine to be brought into production faster.
- The investment cost is low and it is easy to apply.
A thermocouple and heater band can be fitted for heat control. In applications where the shut-off must be timed by the machine signal, the pneumatic shut-off nozzle is preferred.
