Since the cold runner system wastes the plastic that fills the runner, it may not be the best choice if the job calls for an expensive specialty plastic. If the product won’t be used in food or a medical device, scrap from the runner can often be reground and reused. However, the regrinding process is expensive in itself, as well as noisy and dirty. In most applications, the proportions of new to reground materials are strictly controlled, which can lead to a build-up of unusable material.
With the hot runner system, there is little or no scrap, eliminating this additional cost.
Hot runner systems often have faster cycle times, which reduces processing costs. Hot runner systems also produce less wear and tear on the equipment, helping to increase uptime and reduce maintenance costs. The ability to design mold channels to ensure that the material flows the same distance from each nozzle helps improve quality by moderating pressure and thermal variations This may be extremely important with certain resins that have limited processing margins.
In addition to the speed, product quality and resin characteristics of the job, it makes sense to consider other factors that can affect overall costs. Consider the availability of engineering and design assistance that the supplier may provide to help you get the most from the system you choose. Also consider service costs—cold runner systems may be more reliable because of their simplicity.