Hot Runner System: Advantages and Disadvantages
Why use hot runner molds?
What is Hot Runner System?
What are hot runner advantages and disadvantages? Firstly, we should know what is hot runner system?
A hot runner system is a feed system that is an assembly of heated components for plastic injection molds, conveys melted plastic from the machine nozzles into the cavities of the molds.
In hot runner molds, a manifold system to heat a mold is made up of two plates. Generally, the manifold regulates the temperature, which it achieves by ensuring the molten thermoplastic in the mold’s runners, maintains the same temperature as the heating cylinder.
Hot Runner Advantages
Cycle Time Reduction
The cycle times for hot runner systems are significantly faster than those for their cold runner counterparts. Doing away with the cold runner will reduce the cycle time since cooling time is controlled by the thickest section. For instance, in some thin-wall injection molding processes, circle time is less than 5 seconds.
Elimination of the Runner
With materials becoming more sophisticated and expensive. Cold runner becomes expensive scrap. Even if the runner can be reused, but in many medical and food injection molding they can’t. Which gets costly, noisy, and dusty during regrinding and storing. When using hot runners, you don’t have these regrind problems and associated costs. In fact, the major hot runner manufacturers get rapid development in the world of oil & plastic have been expensive era. Hot runner is of great significance to the value engineering for enterprises.
Optimal Part Quality
Hot Runners ensure better filling and packing conditions. When plastic is flowing through the cold runner, it transfers heat to the mold plates – causing a pressure drop that results in sink marks and underfilling parts. The hot runner system, on the other hand, maintain a balanced melt flow at a constant temperature from the machine nozzle all the way to the gate to fully fill and pack the cavities. Therefore, hot runner molded parts have good sprue quality, low residual stress after demoulding and small deformation of parts. So many high-quality products are produced by hot runners. For instance, plastics parts in Apple mobile phones, HP printers and Dell computers are made of hot runner molds.
The items are finished products after being molded by hot runners. And the working procedures of trimming a sprue, recycling and processing runners are not needed. An ever-increasing number of companies are automating their plastics molding and assembly. Which has no runners present to get tangled in the mold mechanisms, robots, conveyors, assembly machinery, etc.
Balanced Melt Flow
The flow advantage of the hot runner is that the melt channel is located in separate external heating plate, which is insulated from the surrounding mold plates. Different to a cold runner plate, the hot runner manifold can be designed to have flow channels on multiple levels, to ensure that the resin flows at the same length from the nozzle to each cavity. With the same channel profiles and diameters, a number of turns, heat soak and pressure loss. In other words, the plastic reaches each cavity at the same pressure and thermal history.
A major hot runner advantage is the ability to locate the gate at a wide variety of points on the part. By using of the hot tip gate, valve gate or edge fate, the gate location is allowed to be placed in the most favorable position for part aesthetics and optimum filling in hot runner system.
Hot Runner Disadvantages
While hot runners offers many significant advantages over cold runners, mold users also need to be aware of the disadvantages of hot runner system to choose the right one.
Higher cost to produce molds and maintain equipment. Generally, the price of hot runner components is relatively expensive, and the cost of the hot runner mold maybe be greatly increased. If the finished part is small, the cost of mold tools is high, which is not cost-effective.
High requirement for equipment
High requirements for the use of hot runners. Hot runner mold requires the cooperation and integration of precision processing machinery. Otherwise, components maybe have serious problems in the production process. For example, whenever the plastic seal fails, the plastic melt can spill out and damage the hot runner assembly.
Hot Runner System- Components Overview
In general, hot runner systems consist of manifolds, nozzles, temperature controllers and accessories (see below).