• PT Youtube
  • PT Facebook
  • PT Linkedin
  • PT Twitter
11/1/2008 | 2 MINUTE READ

Vacuum Venting Keeps Molds Running Longer

Facebook Share Icon LinkedIn Share Icon Twitter Share Icon Share by EMail icon Print Icon

In tough economic times, facing hungry competition here and abroad, molders cannot afford to ignore preventable problems that slow cycles, cost machine downtime and mold maintenance, and waste material on reject parts.

Related Suppliers

In tough economic times, facing hungry competition here and abroad, molders cannot afford to ignore preventable problems that slow cycles, cost machine downtime and mold maintenance, and waste material on reject parts. One unnecessary drag on productivity is gas and air entrapment in the mold, which is not always cured by conventional venting approaches. That lesson was learned by Infinity Molding & Assembly Inc. in Mt. Vernon, Ind., a $15-million custom injection molder of parts for transportation, electronic, and medical markets. Infinity molds resins such as PPS, acetal, rigid PVC, PPA, LCP, PC, and PBT on 40 presses from 35 to 610 tons. Many of the parts are small and complex.

Poor venting can take a toll on the product and the process, says Joseph Crowdus, v.p. of technical services. “It can result in flashing, voids, bubbles, burn marks, and flow lines on the part. But more devastating is the potential for frequent production downtime for mold maintenance from contamination or tool erosion.”

In one case, Infinity was molding a thinwall battery component of clear, rigid PVC. “The parts were tiny, the shot size was 20 g, and we ran it in a multi-cavity tool,” says Crowdus. “The tool was vented in a traditional manner, but we had fits running the part. The vents weren’t able to fully evacuate air from the mold. Trapped air caused burn marks on the parts and short shots.” Infinity considered the option of slowing injection to make sure the mold vented adequately, but that caused short shots.

In addition, polymer residue remaining from the interaction with the trapped gas would build up and clog the vent channels after just a few days of operation, prompting a shutdown for mold maintenance. “Once the vent is clogged there is nothing you can do but clean the mold,” Crowdus says. Infinity breaks the mold down completely for cleaning and maintenance. The mold could be out of production from one work shift to an entire day, not to mention the off-spec parts made before production was halted.



To eliminate gas entrapment, Infinity purchased a Mold-Vac air/gas evacuation system from CAE Services Corp. The self-contained, stand-alone system pulls a vacuum on the vents during injection, and its patented air blowback function assists in ejection and helps clean and purge the vents and ejector pins after every cycle. “The blowback feature helps the tool to stay cleaner longer, and is a real benefit in extending time between cleanings. We run it on every cycle,” says Crowdus.

The microprocessor controlling both the vacuum and blowback functions receives a signal from the injection press then applies a vacuum that can be adjusted from 0 to 24 mm Hg. The system purges air at a rate of 0.02 cu in./sec, said to be the fastest in the industry. Vacuum and blowback operate on a timer setting programmed by the molder. Users mount the portable unit beside the press, position two limit switches, and connect vacuum tubing from the unit to the mold. The mold requires an air-tight seal. Infinity seals off a particular geometry in the part, or the entire mold, depending on the application.

With Mold-Vac, Infinity extended the time between maintenance shutdowns for the mold running the PVC battery part by a factor of at least two or three, which Infinity says is typical when it employs the device. Lower rejects are another benefit. Infinity has six Mold-Vac units and uses them with 10% to 15% of its active molds. “We use it with tough to vent applications” says Crowdus.


  • Creating a Mold-Repair Plan-Part I: The Mold Layout Sheet

    Regardless of mold type, the goal of the maintenance shop always is the same: Get a mold production-ready after it has been removed from service.

  • Solving Issues with Gloss

    Your problem may be related to tooling, material, processing, or combinations thereof. Here’s how to find the root cause.

  • How to Determine Maximum Mold Cycle Counts

    At my first production meeting with my new employer, I was told, “We want you to establish a preventive maintenance program that is based on maximum cycle counts for all our molds.” Then, before I could launch into an explanation of how best to determine maximum cycle counts, I was hit with the follow-up: “So, how many cycles do you think our molds can safely run before we need to clean them?”Leaving my crystal ball at home and unable to get my x-ray vision working, there was no way to answer this question with any real accuracy.


Thanks for considering a subscription to Plastics Technology. We’re sorry to see you go, but if you change your mind, we’d still love to have you as a reader. Just click here.