Definition:    startup: starting something, a setting into motion. Hot runner: insulated -runner mold, where runners remain molten.

The hot runner is a simple yet complex system that conveys the plastic material to the cavities. The one thing all hot runners have in common is that they use some sort of heat source to heat and maintain the materials temperature properly. The one thing that is not understood universally is the startup of the heaters for a hot runner.

Though heater technology has come a long way and the new hot runner controllers are great, even taking the thought process out of the hands of the operator, one must understand the basics of the heaters and what is going on to prevent issues, and damage to the hot runners and the molds. Smart controllers have soft start built in as well as some older units.

The first stage in the following heat up schedule is to dry the heaters as they can adsorb moisture when sitting around, thus moisture or water as they say is a conductor, and if full voltage is applied can cause shorting of the heater which than leads to replacement of the heater in question. To prevent this issue, what is referred to as a slow start is employed. What this means is a low voltage is applied not so much as to generate the heat we desire but to apply low heat which than drives off any residual moisture that has found its way into our heaters. In a word we are drying the insulation in the heaters. On some systems this is; slow start, preheat or other such name. On newer controllers this is done automatically, and on very old systems it may mean to start at low % setting to start, and then gradually increasing to maximum setting.

The first step in startup is to heat up the manifold and sprue bushing. The manifold heats are turned on and it is allowed to come up to temperature and soak for a period of time. This soaking insures that the thermal expansion is occurring to the block of steel. It is able to expand length and width, unrestricted. Again this also includes the sprue bushing.

The second step now is to turn up the drops so that they can thermally expand, and then seat against the manifold. Since these components have been in some contact with the manifold they have adsorbed some heat and being smaller in mass do not take long to heat up. They also should be allowed to soak so as to come up to temperature.

In all cases use of preheat, slow start must be a standard procedure.

Why are these steps important? They are important because of the design of the system. Since as explained previously a manifold shall thermally expand it must be allowed to do so thus increasing in size so as to position the exit hole over the drops. When we turn on the drops they than thermally expand to seal the hole in the drop to that of the manifold and pushing the manifold also against the mold frame and its pressure button. Yes in some systems the drops and manifolds are screwed together, but we also want them to be in the proper position so as to prevent torqueing of the drops to the manifold.

Though it seems basic in many cases all heats are turned on at the same time and at full heat and this then results in heater short out and or leakage occurs which now take the mold out of production. Using a set procedure for startup of hot runners can prevent many issues.

It is always important to check with the manufacture of the hot runner systems to obtain a startup sequence and the electrical resistance of heaters, and how to check. A tip past on is to dry cycle all hot runners 3 times on the bench previous to placing into production, as heater that are new if they are faulty tend to show up within this time frame.