It pays to protect your hot runner

Hot runner maintenance can prolong the life of the mold and improve the quality of the molded components, according to Husky, who offers its customers a hot runner maintenance and refurbishment program.

Hot runner systems have hit their stride as the desire to reduce scrap and improve efficiency and productivity has caused mold buyers to shell out the added dollars for the technology. Husky Injection Molding Systems is one of the largest manufacturers of hot runners and temperature controls in the world, so it has a vested interest in seeing that its customers receive the benefits of these systems over the long term. To help with that, the company offers its hot runner maintenance and refurbishment program.

Kevin Reid, product manager for refurbishment at Husky, says the program is a combination of hot runner maintenance and repair that keeps the system doing its job for the life of the mold, which is typically about 10-12 years. “With proper maintenance you can get even longer life,” comments Reid.

The refurbishment process includes both mold and hot runner maintenance items, and may involve changing out cavities and cores, which “would be crucial to keeping that longevity,” Reid notes, adding that Husky “still has tools in the field after 15-20 years.”

The key advantage to having a hot runner system in a mold is keeping the melt stream hot vs. a cold runner tool that’s generating scrap on every shot, Reid explains. “The runner system stays contained within the hot manifold ready for use during the next cycle.” While these systems are typically used in a high-volume tool, hot runners also have benefits for a single-cavity tool where there are multiple drops or gate locations per part.

Husky offers a three-year leak-proof warranty as an incentive for customers to send their systems back for refurbishment throughout the life of the tool. One interesting note is that while maintaining the tool is key to the program, Husky believes that it also offers a way for the company to maintain the relationship with the customer as well.

Reid says Husky also tries to work with its customers on its competitors’ systems that the customers might have. “In most cases we don’t refurbish the whole system, but maybe the manifold or tip assembly. We can get rid of contamination in the melt stream, or use a scope to make sure there are no restrictions in the melt flow,” he notes.

Another benefit to hot runner maintenance—which Reid says is equally important to overall mold maintenance—is that it saves up to 40% compared to the cost of a new hot runner system. “A lot of customers today have pretty rigorous preventative maintenance [PM] schedules for their molds but neglect the hot runner system,” notes Reid. “We try to highlight the benefits of maintaining the hot runner system as being equally critical to productivity and part quality.”

Inspect, clean, upgrade
Within one to three days of receiving the system, Husky performs an initial inspection, and notifies the customer of the repair and maintenance items recommended, including the costs. “We try to save as much as we can on older systems,” says Reid. “For example, the manifold might be rusted or cracked, or pitted from a corrosive resin, and we would highlight to the customer those key components for replacement. In other instances, we would save the part with rework capabilities such as resurfacing the plates and regrinding the mating surfaces.”

Some of the maintenance Husky performs includes cleaning the residue built up from some resins inside the melt channels, which has a direct impact on color change, and cleaning the water channels to remove mineral buildup. In some cases, customers are running less than full cavitation. With Husky’s hot runner maintenance program, the tooling can be brought back to running full cavitation, with restored gate quality and part quality.

Another advantage to Husky’s program is that it allows customers the opportunity to implement new technology that perhaps wasn’t available when the hot runner was originally put on the mold. “For example, a 10-year-old system might not have the Ultra Seal technology we have today. It might have the older technology, which is sealed by thermal expansion,” says Reid. “The program is an insurance policy implementing that new technology to limit potential failures down the road.”

Money in your pocket: Cycle time reduction
In one case, Husky received the hot runner system from a mold that made PET preforms. It was a 48-cavity mold that runs 99 million parts annually, but was running with one cavity down. “With this being PET, the cycle time reduction was geared more toward the mold side than the hot runner side. It involved cleaning out the waterlines on both the mold and hot runner system to get rid of buildup and contamination, which reduces the amount of turbulent flow, which increases cooling time, thus lengthening the cycle time. You need an open water channel for good cycle time, and our refurbishment process includes cleaning out the waterlines.”

Cleaning out the waterlines was one initiative that took the cycle time from 13.5 seconds before refurbishment to 12.7 seconds after the service. The hot runner maintenance also resulted in an annual increase of 8 million more preforms being produced.
Gate quality is also key. “You don’t want to have to add a sorting process as a secondary finishing operation or perform any other type of secondary inspection,” Reid states. “A poor gate vestige can create problems for the customer, especially in medical parts, where a gate vestige might snag or tear a latex glove.”

There are key components that are wear components in a system, such as nozzle tips (the heating source at the gate), thermal gating (open hole with a heat source), and valve gates, in which a pin blocks off the gate. Both the valve stem and the tip are wear components. “We recommend, depending on the material you’re running, that your maintenance intervals be adjusted accordingly. Different resins have different effects on the tool, as well as how much you run the tool.”

A lot of customers are seeing the benefits of Husky’s hot runner maintenance program, and Reid said he’s seen an increase in the refurbishment business over the last three to four years. “The hot runner system is a value-added portion of the mold, and by having one or more drops down, the loss of output over a month might be OK, but over a year, what’s the loss to the customers? Not just loss in cycle time and parts, but energy loss, increased overhead, and the idea that you have to run a lot longer to make up for the cavities that are blocked off. Do the math!” says Reid. “In the big picture, they have to run another week or two to make up for the down cavities. If a customer realizes the long-term loss in resin, energy, and scrap, it will definitely shed light on the extra benefits that hot runner refurbishment provides.” —Clare Goldsberry