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Hot Runner Systems in Injection Molding

The use of hot runner systems in the injection molding is rising due to the fact that they provide a more perfect technique of molding plastic parts. The cost saving can be substantial, and part standard is very often much excellent than cold runner.

With the rising sophistication of today’s plastic injection molds, the use of warm runners is becoming an industry standard. Many application just are not possible with old standard sprue and chill runner system, and warm runners provide a best way to maintain uniform wall thickness and get rid of knit lines and flow lines.

What are the benefits of warm runner systems?

  • Capability to decrease gate vestige
  • Uniform wall thickness
  • Lower cycle times
  • Elimination or reduction of knit lines
  • Less waste
  • Best for high cavitation molding
  • Generally the only technique for micro-molding. The center to center distance of the warm runner tips is as little as 17mm.
  • Many big molds rely exclusively on warm runners. Cold runners cannot meet the demands.

What about the maintenance of warm runners?

Warm runners systems need a new level of skill on the part of the mold maker. Anyway, this does not mean that it is overly hard or highly specialized. A well designed system is relatively free from maintenance, once it is rightly installed.

mold maker
mold maker

It can, and does happen, that mold makers become upset with these systems and swear that they are too much issue. This is generally due to the fact that the system is not rightly installed or badly operated in the molding process.

The leading system producers have a well-trained team of experts on hand to help in the right installation and operation of the system. The time spent listening to these experts is time well spent!

Long term advantages

Even though there is a primary investment with hot runner systems. It is simple to justify the long-term advantages. Without rising the complexity of the design of the mold, a hot runner equipped mold can significantly decrease costs. Because the hot runner is designed and produced independently, yet concurrently, the lead times are not affected.

Mold maker should forever advise techniques for his customers to decrease molding costs and rise the output of the mold. Being knowledgeable with different runner system is a best way to demonstrate an active role in supporting the molders bottom line. This in turn makes the likelihood of increased business even bigger for the mold maker.

Plastics Technology

Structural Foam Goes All-Electric

What may be the first all-electric structural- foam molding machine was recently built by Milacron’s Elektron Technologies unit in Batavia, Ohio, in cooperation with structural-foam specialist Uniloy Milacron in Manchester, Mich. This development occurred because a major foam molder wanted a large all-electric machine for the sake of energy savings, oil-free operation, and noise reduction. Uniloy’s Springfield Div. always uses two-stage injection for its structural-foam machines, so Milacron adapted its Sidewinder two-stage electric injection unit to this process. This being the first foam application of a two-stage electric machine, Milacron says, Uniloy developed a new screw design, a barrel-cooling system, and gas- injection metering hardware for the Sidewinder. 

The result was a 550-ton Powerline machine that reportedly provides highly consistent foam melt with both gas injection and chemical blowing agents, as well as a wide range of shot sizes. The separate shooting pot allows use of any shot size from 100% down to 3% of machine capacity. The machine molded an electrical housing (see photo) of GE’s Noryl PPO/PS alloy with nitrogen gas. The part weighs 83 oz and has a 15% weight reduction with a typical foam/skin structure. The Sidewinder unit can be converted to standard high- pressure injection molding with a simple screw change. 

Cooling Screw Cranks Up Foam Output

A new screw design for foam extrusion is believed to be the first to use cross-flight melt channels to increase cooling and foam output. The channels perforating the curved flights scoop hot polymer off the screw root and brings it into contact with the cooled barrel. In the single-screw cooling extruder of a tandem foam line, it reportedly increases output by 25-40%. Developed and patented by Plastic Engineering Associates Inc., Boca Raton, Fla., The Turbo-Cool screw was publicly discussed for the first time at the SPE ANTEC meeting in Dallas in May, though it is already used commercially by several large producers of PS-foam sheet for clamshells and board for construction. 

Integrated Stretch-Blow Machine Is All-Electric

The upcoming K 2001 show in Dusseldorf, Germany, will see the debut of the first all-electric integrated PET injection stretch-blow molder from Automa of Italy (represented here by Automa Machine & Tool Inc., Maple Grove, Minn.). The servo-driven NSB100 system is designed to run at three times the production rate of conventional ISBM machines. For example, it reportedly can mold 16-oz bottles at 5000/hr. NSB100 will have a 5:1 ratio of injection to blowing cavities (up to 20 and four, respectively). 

Automotive TPO Goes Antistatic

Two versions of Sequel 1514, a new mar-resistant TPO from Solvay Engineered Polymers, Auburn Hills, Mich., are being used in the tailgate liner and protective moldings atop the tailgate and side rails surrounding the cargo box on the Ford Explorer Sport Trac vehicle. The liner compound is the first static-dissipative TPO to be used in an automotive role. The parts are molded by Ventra Plastics in Russellville, Ky. 

Although Ford initially specified ionomer for the moldings, Ventra foresaw processing advantages in TPOs that could cut costs. Tests by Ford and Ventra confirmed that durability of Sequel 1514 matched that of ionomer, but the TPO’s improved flow permitted downgauging from 3.5 to 3 mm, and the ionomer required longer cycles to prevent sticking in the plastic mold.

Colorants for Packaging Offer Light Protection

A new line of color concentrates for packaging of light-sensitive retort products has been developed by Ferro Corp.’s Plastics Colorants Div., Stryker, Ohio. The new Light Blocker Concentrates are said to be heat stable and to meet FDA standards for direct food contact at retort temperatures. Five light pastel shades are said to provide both uv and visible-light protection for nutrients in milk-based products. 

These concentrates are intended for use in LDPE, LLDPE, HDPE, PP injection molding, and PS bottles, injection molded containers, and thermoformed sheet. Letdown ratios are 10:1 to 50:1, depending on layer thickness and shelf life. These customizeable concentrates reportedly offer cost- saving opportunities. For example, they can permit downgauging an outer white layer over the light barrier, using a monolayer structure, or eliminating foil.