All hot runner systems need a heat source to operate as designed, however not all hot runner systems are heated by the same methods. The type of heater technology your hot runner system uses can significantly affect molding performance, molded part quality and system cost. No heating method exists that is ideal for every scenario and each one has their own pros and cons but illustrating their differences may help you in understanding how your hot runner system is constructed and provide you with some additional insight on your next purchase. Some hot runner systems may use a mix of heating methods depending on the components of the system and application but for the purposes of this discussion we will focus on manifold heater elements.
The main types of manifold heating methods include Embedded Heat Sources (Brazing, Pasted, Pushed-in) or External Heat Sources (Heater Pads/Plates). Selecting the right heater element is always a careful balance of performance, reliability and cost (both initial investment and operating). Many factors are also weighed including type of industry, part geometry, mold design, part variables and production requirements.
EMBEDDED HEAT SOURCES
- Compared to External Heat Sources, Embedded Heaters offer a range of advantages
- Heater element channels optimized through CAE analysis for enhanced thermal profile
- Enhanced energy efficiency
- Helps protect heater elements from physical damage
- Extended life
- Generally ideal for small to large symmetrical manifold designs with tight or standard pitch dimensions
Brazed-in Heaters generally offer the best performance and reliability making them ideal for achieving the highest molded part quality and long term production. Using advanced CAE analysis, heater channels can be optimized for each manifold to achieve unbeatable thermal balance. Thermal balance of the manifold is a critical variable in achieving excellent balance of fill results and therefore superior part quality.
As the element is set into a recessed heater channel, the greater contact area is much more efficient at transferring and maintaining heat than traditional heater methods and helps protect the element from physical damage. The Brazing process also completely eliminates any air gaps that can lead to heater failure through electrical arcing. Brazed heaters are often made to higher quality standards than other heaters and therefore have a very low failure rate. With a lifespan able to exceed 10 years, they have the ability to outlast well beyond the life of the mold. While brazed heaters require a higher initial investment, this is typically offset by higher quality part production reducing scrap rate, eliminating heater replacement costs and minimized downtime. Part quality aside, the higher the cavitation and longer the production run the more it makes sense to invest in Brazed heaters.
Paste-In heaters are considered to be mid-range heaters. They are more economical than the brazed version however there is a trade-off in performance and reliability. Although the paste-in technique attempts to eliminate air gaps, the method is not 100% so there is a relatively higher risk of heater failure which does occur at a higher rate (vs. Brazed). This production challenge is offset by the potential ability to replace the element in the field, although it’s not always possible. Regardless of the potential for increased downtime, Paste-In Heaters are still a great option for molders looking for performance with a more economical initial system price.
Push Heaters, like Paste-In heaters, are considered to be mid-range heaters but their design favours faster in-field replacement. Since there is no “pasting” step required it helps minimize any servicing downtime. However, with the elimination of the paste, there is less contact area which can increase energy consumption. The element itself also has a more limited bending radius which can restrict its applications. Available in a wide range of standard lengths, diameters and wattages, Push Heaters are an off the shelf item so sourcing spares globally is also quick and easy.
EXTERNAL HEAT SOURCES
Compared to Embedded Heat Sources, External Heaters offer a range of advantages
- Lowest cost for more economical up front system pricing,
- Ability to use multiple heaters to increase number of temperature control zones (ideal for manifolds with long pitch/asymmetrical designs-automotive),
- Easiest to replace,
- High standardization allowing for easy global access to spare parts from multiple sources
By now, you may be wondering what sense it makes to use Heater Plates when there are several “better” options available. Truth is, although Heater Plates would be considered lower performance under the same circumstances as the other options, Heater Plates are a good choice for a completely different type of mold design. Their ideal applications are on molds that benefit from having additional zones of control. Typically this would be large/high pitch/nonsymmetrical manifolds (automotive, and large parts for white goods for example).
Evaluated on a larger scale and utilizing CAE optimization analysis it is possible to achieve a good overall thermal profile, better than if a single continuous element had been used for the same application. Also, Heater Plates are the most economical, the easiest and fastest to replace and are a common standard off the shelf component offered by a wide range of global suppliers. While high reliability is always beneficial, automotive molds have a lifespan limited to 3 to 5 years so the lower system price is better positioned to offset some failure related downtime.
Mold-Masters has been manufacturing the industry’s leading hot runner and temperature control systems since 1963. Mold-Masters designs, manufactures, and supports a full range of hot runner products, including hot runner systems, temperature controllers, hot halves, and gating technologies. To learn more about Mold-Masters hot runners visit milacron.com
*The content in this article is to be used as a general guideline only. Hot runner manufacturers may have significant differences in how they implement each type of heating element. Speak to your hot runner supplier for more details.