Blow Molding: Putting on the ritz

There’s been a shift in mentality toward blow molding for industrial parts. As the process achieves more, more is demanded of it. In addition, a bit of the injection molding mentality, with respect to expecting higher throughput and using automation, has rubbed off. The net effect is that blow molding is now suitable for a broader range of applications.

“Blow molding lagged a bit in terms of automation. It used to be a labor-intensive process,” says Tim Noggle, product line manager for industrial blow molding with Graham Machinery Group (GMG). “Now we see customers taking a new look at automation. The thought process of injection molding is migrating to blow molding.”

GMG has sold several rotary blow molding systems for industrial applications in recent months. One produces six-quart flower pots at a rate of 42 pots/minute with automated trimming. Another produces gasoline containers using automated downstream operations. Robots assemble the components (nozzles, caps, etc.), apply labels and place the containers in one of two different shipping container configurations.

High productivity can also be achieved by optimizing cycle time. In the Far East, an extremely fast blow molder developed by SIG Kautex is being used to produce a large automotive part that measures 2.3 m in length. The accumulator head on the KBS 2-120/100 achieves an ejection time of just 1.5 seconds for a 3.0 m parison. Due to special process technology, wall thickness varies little from one end of the part to the other. The complex part is made of an extremely low viscosity ABS, and weighs 6.6 kg when finished. Similar parts had previously been produced as two separate components.

Quick change features

The concept of quick product changeover has also migrated to blow molding. Garrtech, a manufacturer of blow molds located in Stoney Creek, ON, has manufactured a series of molds for Vogue Pools that are all designed for quick mold change. Connections for knock out systems, cooling, etc. were all self-contained within the mold.

Italian machinery manufacturer Automa demonstrated at K 2001 another quick changeover option. Automa’s AE 20 accumulator head model can be optimized with automated deflashing for the production of jerry cans. By changing the centre section of the container mold and adjusting the deflashing system, four different sizes of containers can be produced. The cans all start from the same basic mold unit, but have varying heights to produce volumes of 5, 10, 15 and 22 L. Automa reports that this approach reduces the mold cost and speeds up mold changes.

Accumulator head design also plays a role in product changeover. “What helps us when selling to a customer accustomed to injection molding is the fact that our accumulator head achieves fairly quick color changes,” reports Joe Altimari, business director, industrial/ technical blow molding for GMG.

Davis-Standard has redesigned its accumulator head, and cites “ultra-fast” color changeover as one of the benefits. The core tube is chrome-plated for enhanced abrasion resistance and materials flow, which enables faster material and color changes, the company states. Existing Davis-Standard heads can be retrofitted with the new core tube and new plunger technology.

Industrial blow molding machines have also stepped up to the sophistication of injection molding in the area of process control. “At GMG, we’re seeing a requirement for more sophisticated control systems,” says Altimari. “So we’ve switched to a true PC-based control system, which allows a customer to monitor both upstream and downstream operations. It can have a modem to permit remote access. In addition, it has an integrated SPC package.”

Uniloy Milacron also equips its blow molding machines with a PC-based control, Milacron’s patented Xtreem system.

Flat panels command attention

In a departure from the more traditional tank and ducting applications, machinery manufacturers are designing some machines to accommodate the “flat panel” type of applications that have become popular for table tops, shed panels, automobile load floors and institutional furniture.

Last year, Uniloy Milacron delivered a massive tandem blow molding system to Luxembourg to produce wall and roof panels for outdoor storage sheds. “With the dual clamp arrangement, the molder can run two different molds on one machine and produce both roof and wall panels for one shed set at a time,” says Rich Morgan, manager, business development, industrial blow molding.

Uniloy Milacron’s large Tracker series (T1600, T2300 & T2900) can handle parts up to 200 kg and 1.8 m in length, with resin plasticizing rates up to 1000 kg/hr.

SIG Kautex’s new CP-480 offers high-throughput side-by-side molding of large flat panels weighing up to 50 lb. each. One BlowTec CP-480 is used by a U.S. molder of institutional and outdoor furniture. It uses dual 150-mm extruders with an extrusion rate of 1650 lb./hr. each. The accumulator heads have 18 in. maximum tooling capability.

Clamp platen dimensions were customized for this tabletop application — they measure 104 in. by 90 in. wide. Considering the large clamp platen (total clamp weight is 72,000 lb.) and heavy molds, the clamp traverse function features computerized dynamic motion control for high mold opening and closing speeds.

It seems there’s also demand for medium-sized industrial blow molding machines. Reacting to the positive response received for a 78-ton machine introduced last year, SIG Kautex has added another model to its medium-sized KT Series. The new KT-140 has 138 tons of clamp force and accumulator head capacity of 42 lb. or two heads of 20 lb. each. Platen size can be either 54 in. x 72 in. or 60 in. square.

What’s next for blow molding?

Machinery manufacturers report that they are frequently being challenged by new requests from customers. At Uniloy Milacron, customers have asked about blow molding large tanks, in the range of 3000 L capacity. That would mean pushing out 250 lb. of resin in one shot, says Morgan.

Tim Noggle of GMG says some Asian producers are questioning whether portable lavatories can be produced by blow molding.

A more likely near-term development, says Joe Altimari of GMG, will be larger head tooling. Currently, higher volume heads and the capability to do wider parts go hand in hand. For example, says Altimari, if a customer wants to produce a part that is 60 in. wide, it is likely that only a 200 lb. accumulator head has tooling wide enough for the part, even though the part may only require 20 lb. of resin.

Blow molding steps up to meet fuel tank emission standards

Two new technologies for producing blow molded plastic fuel tanks have the dual benefits of meeting strict upcoming emissions standards and using current, proven multi-layer blow molding materials and processes.

Fuel systems supplier TI Automotive has completed testing and validation on the two new methods, and expects to see the technologies put to use in 2005 model-year cars.

One technique is aptly called “Ship-in-a-Bottle” (SIB). “The SIB system encloses fuel pumps, level sensors and other components in a six-layer plastic tank while at the same time improving the robustness of all external connections,” says Chris Quick, director, research and development for TI Automotive.

All the internal components are mounted on a carrier and pre-tested prior to entering the blow molding process. As the parison is extruded, the carrier is inserted, positioned and welded via an automated process. From there, blow molding continues as usual.

The SIB technology requires only one or two openings in the fuel tank shell, whereas past tanks often had up to six or seven. Thus, according to TI engineers, SIB dramatically reduces the level of emissions from the fuel tank system.

“SIB is really a breakthrough,” says Quick. “It allows us to compete with steel tanks and vacuum formed tanks, because we can locate components inside and we have minimized the seam length.”

The second technology developed by TI Automotive for fuel tanks is called Complete Vapor Recove
ry (CVR). Quick explains that the CVR system consists of a standard multi-layer tank and attached components, which are covered by a blow-molded or vacuum-formed cap. The cover is welded to the tank, enclosing all components and tank body seams, with the exception of one line. Vapors are trapped in the area between the cover and tank, and then recycled into the vehicle engine and burned off.