Tips to Help Ensure That Your Hot Runner Nozzle Does Not Fail

The plastic industry is one of the most profitable industries in the world. Being the third world’s largest producer of plastic, the U.S. earns over $300 billion annually from the sale of plastics alone.

There are over 15,000 plastic injection molding and plastic manufacturing facilities spread across 50 states in the US. To stay ahead of the competition and capitalize on the growing demand for plastic, manufacturing companies must ensure that their hot runner systems and molding machines are in tip-top shape. Otherwise, they risk losing hundreds of thousands of dollars due to an inefficient process.

Molding machine nozzles could easily cause significant losses if they are not given the appropriate attention. This is because the molten plastic flows from the barrel and passes through the molding machine nozzles before reaching the sprue bushing of the mold. If it doesn’t efficiently make it into the mold, the whole process could be amiss.

If the conditions in the hot runner nozzle are not conducive, the quality of the plastic produced will be poor. To help mitigate this risk, here are some factors molders should always look out for:

Check for Drops In Pressure

The pressure within injection units usually ranges between 10,000 and 40,000 psi. Any significant reductions affect the quality and strength of the plastic products being molded.

Therefore, it is essential that pressure levels are closely monitored and that drops within the body of the molding machine nozzles kept at a minimum. For starters, the body of the nozzle should be as short as possible. The shape of the flow path also contributes to reductions in pressure. Instead of having a straight flow path, it should be conical or tapered. Such shapes are effective in controlling pressure levels which in turn leads to quicker purging.

Keeping tabs on pressure levels also enable molders to quickly identify faulty filters before they cause too much damage.

Monitor Temperature and Control Setpoint

Temperature is a crucial aspect of molding plastics, especially in the first and second stage injection. The molten polymer from the barrel should remain at melt temperature even within the hot runner nozzle. If there are any large variations, the molded plastics will default, and you may notice a blush or halo on the final product.

Though the goal is to ensure that temperature remains consistent throughout the flow, it does not necessarily mean the temperature of the nozzle body should be exactly as that of the barrel. PID auto-tuning controllers can be used to regulate the temperature throughout the process.

Tip Mating With Sprue Bushing

The tip of the machine nozzle is connected to the sprue bushing. This often takes the form of a 25-mm adapter that is screwed into the nozzle body. This section is cold and small compared to the nozzle, thus it cannot have a heating band. As a result, heat ends up being lost in that area which leads to unmelted polymer either drooling, stringing, or clogging the tip.

Though cardboard can be used to insulate, it will only work for a few rounds. Better measures include

  • – Ditching general-purpose nozzle tips. This is because they are too long, thus increasing the area of cooling within the nozzle.
  • – Only using free-flow nozzles or reverse-taper designs when necessary.
  • – Using insulators designed for the section where the nozzle and sprue bushing connect.


You should also make sure that the space between the sprue bushing and the tip of the nozzle is as small as possible. This will help reduce the area where heat can be lost between the nozzle and the final product. However, the contact space should also be sufficient to withstand the pressure of the molten polymer.


Plastic is an integral component of our daily lives. It’s up to the molders to ensure that molding machine nozzles are always in prime condition. This will guarantee quality products and reduce waste.