New Technologies in Hot Runner Systems

By Liz Stevens, contributing writer, The American Mold Builder

Even as they tout the enduring strengths of hot runner systems, hot runner makers are not sitting still. We asked a handful of hot runner manufacturers to give a glimpse of the improvements and new technologies unfolding in their systems, and to share their insight about the recent waves of change. We spoke with INCOE’s Jim Bott, business development manager – mobility/automotive/heavy truck; Robert Harvey, director of sales North America at HRSFlow; Brenda Clark, engineering manager at HASCO America; Mastip’s marketing manager, Steven McKinlay; and Greg Osborn, industrial sales manager – North America at Synventive Molding Solutions.

Why Hot Runner?

To set the stage for discussing changes stemming from new technologies and the rise of automation in injection molding, we first asked the manufacturers to make the case for using a hot runner system as opposed to a conventional cold runner setup. 

“Making the decision whether or not to incorporate a hot runner in a build,” said HRSFlow’s Robert Harvey, “will depend on a variety of factors.” One factor is the anticipated production volumes because for very low volume runs, a hot runner’s price may be too rich. Other factors, he said, include “the material type to be used and its cost, and the impact of the cycle time difference between cold and hot runners.” The correct types of source material must be chosen for use in hot runners, and Harvey also pointed out that the amount of sprue or scrap material that can be eliminated by removing the cold runner, and the desirability and ability to reprocess scrap material also are important considerations for whether a hot runner is a good fit.

INCOE’s Jim Bott approached the question by describing a given and then the few factors that, in his opinion, would rule out the use of a hot runner system. “Starting with Hot Runner 101: There is the given of reducing or eliminating the cold sprue of a cold runner by instead using a single hot nozzle,” he said. “There only are a few instances where hot runner technology cannot be value add, and what comes quickly to mind is low volume – but that would be an oversimplification.” Regardless of the production volume, many part designs require hot runner technology to properly fill the parts to meet performance requirements. In the end, Bott narrowed down the poor candidates for hot runner systems to “perhaps very low cost, non-technical, low volume parts, and also, parts that need the cold runner for packaging purposes or conveying logistics. And certainly, some plastic materials – such as thermosets and liquid silicone rubber – cannot be processed with hot runner technology.”

Greg Osborn, of Synventive, focused on production volume and part size, while also noting the scrap-reducing nature of hot runners. “Production levels and part size are important factors to consider,” he said, “when deciding between cold runner or hot runner conveying systems. The higher production volumes made possible with hot runner systems allow the added expense of a hot runner to be absorbed over the higher quantity of parts.” Osborn stressed that part size can play an important part in the decision. “Small parts being fed by a cold runner can often lead to increased cycle time because of the longer processing times required by the cold runner system,” he said. At the other end of the size spectrum, he said, “many large parts like automotive bumpers and fascia also lend themselves well to production on hot runner systems, thereby avoiding the complex or unfeasible three-plate design that a cold runner system would require to feed these large parts for filling.” 

Hot Runners for Faster Production, Less Waste, Better Quality

When asked how today’s new hot runner technologies address the demand for faster cycle times, reduced waste and improved part quality in plastics processing, Bott was happy to field the question. “From the inception of hot runner technology,” he said, “all of these ‘pain points’ have been the solution focal points of the technology.” Bott stated that these higher demands and requirements have presented hot runner solution providers with challenges that require ever-advancing technology. “The latest in technology includes advancing heater, sensing and heater controller technology,” Bott said. “It also includes upgrades to machining, cutting, probing and inspection technologies. There have been upgrades in flow simulation hardware and software, and there is continuing development of nozzle tip designs.” 

Osborn echoed Bott’s assertion that hot runner technology offers inherent advantages in terms of increased speed, improved part quality and reduced scrap. “Replacing the cold runner with a hot runner system will allow the processor to avoid waiting for the cold runner to harden before ejection, thereby reducing cycle time along with slashing the need for further operations to dispose of or regrind the cold runner,” said Osborn. He pointed out that the cold runner often is processed through a grinder to reduce it to small chips and then reintroduced into the part as a fractional percentage blended with the virgin material – a practice which may re-use scrap, but which wastes energy and labor. 

Osborn stated that new technologies in hot runners allow processors to utilize hydraulic or electric actuators, precisely controlling the position and profile of the valve pins. “The increased accuracy of the opening of the valve pin,” he said, “allows for a more consistent, repeatable pin opening which provides better balance between parts in molds. These new actuators also allow the processor to control the profile of the valve pin opening, reducing part stress which often is not visible until the finish painting or chrome processes.” By this time, he pointed out, hundreds or thousands of parts may have been molded that must then be scrapped. 

Harvey explained that servo technology is being used to great effect to address the demand for higher quality, faster production and less waste. “HRSflow is leveraging servo technology to affect pressure regulation with more powerful tools than have been available in the past,” Harvey said. “The very accurate repeatability of the servo, together with the ability to process at each gate independently, is increasing the capability to produce a high-quality part repeatably.” This improvement in precise and repeatable production of parts naturally increases yield and reduces the amount of scrap in an operation. 

HASCO’s Brenda Clark pointed to her company’s wide range of standardized hot runner manifolds and nozzles that address the use of most of today’s engineered process materials. “Standardized hot runner parts,” she said, “make it easy to replace spare parts such as heaters, thermocouples and nozzle tips. This allows for manifold and nozzle selection to best match the customer’s application from the start. It also gives  moldmakers the choice to build their own hot half or to have their supplier build a system for them.”

The technology to which Clark refers reduces waste by eliminating cold runners that will need to be reground or thrown away. “These systems ensure high part quality by keeping the melt flow within the manifold naturally balanced,” she said. “Reviewing all application requirements allows the supplier’s engineers to review mold flow analysis and propose the proper standard system components for each project. This balance eliminates any burnt material or dead spots that could degrade the material that is transferred into the molded parts.” 

Steven McKinlay brought up Mastip’s advances for mold cooling, valve gating and cap insulators, and improvements in nozzles. Using flow analysis software, Mastip works with its partners to recommend designs for mold cooling around the hot runner gate, which is critical to cycle times on fast cycling tools. “Improving gate cooling provides better hot runner control,” McKinlay said, “and this is especially true with thermal gates that utilize gate cooling inserts. Conformal cooling also is improving efficiency by positioning cooling in hard-to-reach places and optimizing cooling where it is critical.” 

According to McKinlay, there is an increased demand for valve gated hot runners, which are ideal for faster cycles because they eliminate the time for gate solidification. As McKinlay explained, “Valve gates allow for a larger gate diameter which reduces the shear stress on material and can improve part quality while also creating a clean cosmetic gate.”

The Latest in Hot Runner Technology

When asked about the latest developments in hot runner technology, the manufacturers described a bevy of advances: predictive maintenance, servo gate technology, additive manufacturing, multi-material molding, improved material flow and advances in color change.

Bott sees big changes coming in how plants operate. “With some molders achieving and others approaching ‘lights out’,” he said, “digital transformation is advancing. Accommodating workers who are working remotely is definitely more of a need than in the past. If this trend continues – where workers spend X number of days at the facility and X number of days working remotely – Industry 4.0 will become more of a necessity.”

In terms of hot runner preventive maintenance, Bott said, “It tends to be reactive rather than preventive. Something breaks or wears, causing the molding process to shut down.” Some plant operators have already climbed aboard the predictive maintenance bandwagon; others will surely follow soon. “This can be achieved with the hot runner supplier adding sensors to fluid inlets/outlets and perhaps in other locations. By teaming with producers that supply technologies for electronic count cycles, communicating and inputting data, and tracking the ordering of spare parts, hot runner suppliers can begin to offer predictive maintenance technologies and also offer technology that supports remote work.”

Harvey used this topic as an opportunity to further describe servo technology. “Servo valve gate technology is by far the most substantial recent advancement of hot runner technology,” he said. “This is truly changing injection molding by taking the processing away from the injection piston and placing it at each gate independently.”
This allows for family molds with no limits since each cavity can have its own process. And it allows for the precise, repeatable placement of weld lines – for a stronger, better-looking product. “Servo valve gates provide a tool for affecting the magnitude and location of warp,” Harvey explained. “When only the pressure that is required is applied, there is an overall reduction in tonnage and mold deflection.”

Clark pointed to machine system size limitations. “New requirements for multi-cavity tooling calls for increasing the cavity numbers while keeping both the mold size and the molding machine size down. The need is for more production within the same facility footprint, and for reducing the need to purchase new machinery,” she said. “These expectations are making hot runner system builders think outside of the box.”

Clark explained that with the advent of additive manufactured “steel” inserts being applied to hot runner manifold manufacturing, a new door has been opened. While this manufacturing process is cost prohibitive on larger manifold systems that are already well covered through conventional machined manifolds, Clark said that “additive manufactured hot runner manifolds should be kept in mind for use in a smaller footprint, keeping the cost of tooling economical.” She stressed that melt flow should remain balanced and smooth machined, without dead spots but still easily manipulated within the manifold to address the nozzle pitch required. 

McKinlay described some of the challenges that materials add to hot runner design. “As consumer goods companies look to differentiate their product lines from competitors, designers are combining more than one material into their final product.” This type of molding is referred to as multi-material, bi-material or 2k molding. It is common with consumer goods, such as toothbrush handle grips, that have a combination of rigid, durable plastic combined with a soft layer, like TPE, for comfort. “A common requirement that Mastip is experiencing is providing a hot runner to service a 3-color mold,” he said. “In order to process more than one material, highly specialized hot runners are designed to fit within more complex molding tools like stack, tandem or rotating platen tools.” 

McKinlay explained that molding systems that inject more than one sized part at a time can take advantage of sequential filling, which would be achieved through a hot runner valve gate system with valve pin timing controlled by sequential controllers. Another advance is rheologically balanced manifolds that are developed with the use of high-end flow analysis software.

Osborn wrapped up the new tech topic by pointing out the rapid industry changes that suppliers must respond to. “The need for lighter weight vehicles and to reduce post-processing part finishing has created opportunities for hot runner suppliers,” he said. “And the need to mold in-color large parts has created a demand for new technologies within hot runners to reduce scrap while efficiently changing colors between part runs.”

Osborn explained that features such as smooth flow transitions in the hot runner to avoid stagnation areas in the system, along with nozzle tip features, allow for faster color changes. This reduces scrap and decreases changeover times for different colored resins in the molds. “Hot runner suppliers also have  had to increase their expertise in mold flow engineering,” he said “and to incorporate their systems into the software. They have become consultants in part design and nozzle placement, to allow for faster and more efficient color changes.”

Hot Runners and Automation

The hot runner experts wrapped it up with a few quick thoughts on how automation and hot runners are impacting one another. Harvey stated a simple but powerful effect that hot runners have on automation: “Hot runner technology can facilitate automation in that the cold runner – which needs to be handled and segregated from finished parts – is no longer produced. This paves the way for increased automation of parts removal.”

Clark cited this advantage, too. “With hot runner system use on the molding floor,” she said, “the need for extra robots to remove cold runners can be reduced. This way robots can be targeted to specific molded part removal – a more important function for plant floor automation.” Clark also suggested that temperature controllers are important pieces of hot runner hardware that facilitate automation. A system with temperature controllers can be tailored to meet production needs, from simple single zone controllers all the way to multi-zone touch screen parametric controllers. “The newest controllers,” said Clark, “should allow the user to set parameters like soft start, boosts and classification of heaters, and critical alarms.” 

McKinlay also included temperature controllers in his comments about hot runners and automation. “Temperature controllers are used at the molding level,” he said, “to adjust valve pin timing and to monitor and control the molding process. IoT devices are being used to optimize molding efficiency, focusing on continuous innovation to improve part quality through the use of temperature and pressure sensors within the mold.”

Osborn pointed to a handful of hot runner-automation interconnections. “New technologies in electric-driven valve gates allow a quicker response to valve pin opening,” he said. “And enhanced controller technologies are providing easier communication between the press and the valve pin operating sequence. Also, in-cavity sensor technologies allow for adjustments within the hot runner system, to accommodate for viscosity changes between lots of materials. As the industry moves into bio-resins, these viscosity differences could become broader, increasing the further need for closed loop communication to adjust temperatures within the hot runner system to create a more stable process.”

Hot runners are a hot ticket these days, thanks to continuous innovation and courtesy of technological advances that just keep unfolding.