How To Start A Mold That Has No Tip Insulators


Dark to light color changes on hot runner systems can sometimes be time consuming and costly. Excessive downtime and scrap during color changes cut into a company’s profit margin making them less competitive. Thermal gate (hot tip) designed hot runner systems are common and can be unusually difficult to clean depending on the hot runner tip design. This paper will discuss ways in which to assist with dark to light color changes on hot runner systems that are hot tipped.


An injection molders top priority is to have the highest possible productivity by utilizing the least amount of capital. Dark to light color changes are a common area that cut into a company’s productivity because of the dark color contaminating in the lighter color part (see figure 1). In many situations the streaking’s origin is in the hot runner system. The hot runner system is a complicated piece of tooling that on occasion allows for dead spots in which color hangs up. The goal for injection molders is to be able to clean these dead spots fast and efficiently.


Thermal Gate System

Thermal gating or hot tip gating generally represents a more economic mold investment compared to valve gating. The thermal gate forms a small, solidified, cold plastic slug (bubble) inside the gate bore during the cooling time of the plastic part (see figure to right). This slug remains in the gate during the mold open phase, part ejection and mold close motion. With the next injection, the pressurized melt flushes the cold slug into the melt stream that fills the empty cavity. While all molding parameters (pressure, temperature and time) are still focused on producing a quality plastic part, they are also responsible for the formation of the thermal gate at every cycle to avoid drooling and stringing of the gate.

The issue with purging a thermal gate system is removing the color from the bubble at the gate of the hot runner system. The larger in size the bubble the more difficult it is to clean. The color in a smaller bubble may be removed by increasing the hot runner tips 100°F and using Ultra Purge to clean the machine. However, if the bubble is large in size, it will not be possible to remove the color without taking further actions.

Insulator Tips

One way to counter large bubbles in the gate is to install thermoset inserts in the gate area. The inserts will reduce the size of the bubble making it easier for the Ultra Purge to remove the dark color. Increasing the temperature of the hot runner tip will also assist with the removal of the color. Most hot runner manufactures offer thermoset inserts as an option to their customers.

Thermal Gate With No Insulator Tip

Companies that have thermal gate hot runner systems but no tip insulators installed will have to use a different approach for cleaning and maintaining the hot runner system. The best solution for this scenario is to purge the machine with the Ultra Purge and to then remove the cavity plate. After the cavity plate is removed, and time has been given for the tips to cool, each plastic bubble will have to be manually removed (see figure 2). After all the bubbles are removed the cavity plate may be put back and natural resin will be run through the machine. As a result, the bubble will become natural resin and in turn make color changes easier because no dark color will be present in the gate. Using the Ultra Purge for dark to light color changes after this task has been complete will be sufficient for color changes.

Figure 2


Using the Ultra Purge for dark to light color changes will reduce downtime and scrap resulting in a savings for injection molders. Companies that have thermal gate hot runner systems will benefit from pulling the bubbles and establishing natural resin in the gate area. After this task has been accomplished color changes will be fast and easy when using the Ultra Purge.