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September 27, 2002

6 Min Read
Mini hot runner systems explore new applications

A smaller footprint, cost savings, and greater control over material delivery are reigning in more toolmakers to the mini hot runner stable.   System users and makers share their ideas.

Tool_HotRun_Gunther_duese.jpg

This double nozzle was developed by Günther for a switch application using insert technology. A 64-cavity hot runner system was specified, so Günther provided 32 of these nozzles for the .8g, glass-filled PPS part.

The advantages of hot runner systems are generally well known. The last few years, however, have seen the introduction of several lines of mini or micro hot runner systems, developed to conserve space in the mold and to meet micromolding application requirements.

Mini hot runner systems do have some quirks of design and application that designers and moldmakers should be aware of. IMM spoke with some experts to get their thoughts on how best to use mini and multitip systems.

Gates and Runners
Parts that require unusual gating, either for cosmetic reasons or for unique insert molding applications, are good candidates for mini hot runner systems. Ron Pleasant, president of Pleasant Precision Inc. (Kenton, OH), notes that the very small probes offer an optimal method to gate down into a deep-draw part, such as a lipstick tube cover. In this instance, the gate is placed on the inside of the part due to cosmetic requirements.

“Spacing is not a big deal in these situations, but you have a confined area to get down in there with a small part, so the probe has to be small,” Pleasant explains. “Also, it can’t conduct heat into that core, which is one of the challenges—to get the probe in there with enough clearance that it avoids contact with side walls of the cores; and it must do this without compromising the integrity of the core walls. Sometimes you have to circulate water around the probe, which contacts the probe and the inside of the core. It takes a special probe to allow water to run around the outside of it.”

Tool_HotRun_DME.jpg

A Stellar micro hot runner system from D-M-E enabled moldmaker Electroform to put 16 cavities in a 10x12 mold base and charge its customer half the cost of competing mold shops offering a standard 16-drop hot runner.

Robert C. (Chuck) Massie of Cavaform, based in St. Petersburg, FL,  builds molds primarily for medical applications using commodity resins such as polypropylene and polystyrene. “We build very high-cavitation molds, 64 to 120 cavities, so to cut costs we design a multitip application,” says Massie. “It serves us well, particularly in the commodity resins. Engineering resins usually require a separate zone for each probe.”

Massie says that Cavaform uses a multitip, multiprobe system to gate very small parts such as needle hubs and catheter tips—parts that are fractions of an inch long. He can typically direct-gate four parts off a single probe. “It’s not a mini system per se, but you get a fairly small mold footprint,” he adds. 

Cavaform also uses a proprietary angle-tip nozzle based on a Mold-Masters system. The probe itself comes in at a 45° angle, explains Massie, to allow a gate on the side of a very short part. In a needle hub mold, for example, he can land the gate on a rib and direct-gate a cluster of four to six parts from one drop while keeping a close center line.

Another consideration in small-part applications is the amount of material consumed by a runner system. Dirk Vander Noot, VP of Günther Hot Runner Systems Inc. (Buffalo Grove, IL), explains that in applications where small parts don’t require a large mold, but a large mold is needed to accommodate the runner, a mini hot runner system “allows you to reduce the size of the mold by eliminating the runner, which is especially cost effective in applications where regrind can’t be used.”

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Designing for mini-micro hot runner systems requires consideration of the mold base, waterlines, and machine type.

Insert Possibilities
Pleasant says that another good application for mini hot runner systems is insert molds in which the part has plastic details molded on various locations of the insert. In some cases, Pleasant points out, the mold has slides or other mechanical devices in the same area. “You have to build a manifold that’s balanced to deliver material in a specific spot,” he explains, “and small probes let you tuck these in next to these mechanisms. This is a good place for minis. Some of these have 90° gates, and those are very handy for these various tight places.”

However, Pleasant adds, “those are a real trick to get installed in the mold itself—trying to tuck this probe into a blind hole. You have to do some special mold design techniques to get it in there.”

Another advantage of the mini systems is cost competitiveness. Wade Clark, president of moldmaking firm Electroform Co. Inc. (Rockford, IL), recently won a job to build a 16-cavity washer mold. Clark credits his success with the decision to design the mold using a Stellar micro hot runner system from D-M-E. This allowed him to put 16 cavities in a 10x12 mold base and reduce the cost of the mold by about half of what his competitors quoted using a standard 16-drop hot runner.

Clark noted that most of the challenge of designing for the system was negated by a readily available design from D-M-E. The pre-engineered system design guidelines were accessible online, plus the appropriate CAD files were e-mailed to the designer to plug into the mold design, making it easy to incorporate the Stellar system.

With competitive issues at the forefront of the moldmaking industry, mini or micro systems are proving to be an advantage, as in Electroform’s case. “If I can save my customer half on a hot runner system, I’ll do that wherever I can,” says Clark.

  • Melt channel design. Thermal degradation of the melt as a result of excessive residence time can cause changes in the molded part’s physical properties or lead to burning and black streaks. 

  • Mold base integrity. Mold design for small parts inherently includes tight cavity spacing and large pockets cut into the mold base relative to its size. Mold base integrity to resist clamp and plastic pressures must be considered. 

  • Mold cooling. Cavity spacing of small parts can limit waterline access to the cavity and gate area. Consideration for the proximity and size of waterlines is critical for molding parts with minimal gate vestige and optimum cycle time. 

  • Gate access for direct gating. Direct gating of small parts is generally accomplished with the use of small-diameter thermal gates or edge gating systems. Valve gate nozzles that require a valve stem in addition to the melt channel at the molding surface require more space for access. 

  • Manifold thermal profile. Small-part molding relies on heat input from the manifold heaters for melt uniformity. Heater layout and thermal losses must be considered in manifold design to achieve minimal temperature variation across the manifold. 

  • Machine selection. The molding machine used for small-part molding must be carefully selected. Barrel size and screw type can have a large impact on shot-to-shot repeatability.

Contact information
Husky Injection Molding
  Systems Inc., Milton, VT
(800) 516-9590; www.husky.ca

Pleasant Precision Inc., Kenton, OH
Ron Pleasant; (419) 675-3334
www.roundmate.com
aIMM Infolink 314

Mold-Masters Ltd., Georgetown, ON
Neil Dewat; (905) 877-0185
www.moldmasters.com
aIMM Infolink 315

Günther Hot Runner Systems Inc.
Buffalo Grove, IL
Dirk Vander Noot; (847) 215-7874
www.guenther-hotrunner.com
aIMM Infolink 316

D-M-E Co., Madison Heights, MI
Ken Kurtz; (248) 398-6000
www.dme.net

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