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Keywords of this article:  injection molding 
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injection mold 
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injection mold 
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blow molding 
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Injectionstretch blow molding is used for the production of high quality and highclarity containers. As the demand in packaging is on the rise, advancedtechnologies play a crucial role in facilitating efficient injection stretchblow molding process and relevant production lines.

Blowliner Medium with a material throughput of up to 130 kg PET per hour.
Blowliner Medium with a material throughput of up to 130 kg PET per hour.

Injection stretch blow molding process is divided into four stages: injection, stretching, blowing, and discharge.

The plastic is melted and then injected into a mold to form a preform. The preform is then conditioned to the correct temperature and is ready for stretching and blowing to the finished shape.

When the preform is in the mold, a stretch rod is introduced to stretch the preform longitudinally and using two levels of air pressure, the preform is blown circumferentially.

After a set time for cooling, the mold opens and the preform is removed via drop chutes or robotics. Then, the process can be repeated.

New single-stage machine ensures high flexibility and quality

With the development of the single-stage injection stretch blow-molding machine Blowliner, the Kiefel daughter company, Mould & Matic, has opened up a new market. The machine is now in use in the pharmaceutical and food industry.

It is available in three sizes. The bestseller is the Blowliner Medium with a material throughput of up to 130 kg PET per hour. Like its smaller and larger siblings, it also processes PET, PP and HDPE. Thanks to its intelligent concept, it can be upgraded to multi-layer applications at any time.

Above all, the premium sector, which attaches great importance to the high quality and transparency of packaging, values the single-stage system.

The injection molding unit is at the beginning of the linear machine. This is a vertical hydraulic Engel machine with up to 4,000 kN clamping force and a clamping surface of up to 800 x 1000 mm - depending on the size of the system. The plasticizing unit processes PET, PP and HDPE. Here the preforms are created, these range from 8 to 64 cavities depending on the product.

Each machine can be upgraded with a unit for the production of multi-layer preforms. This permits production of preforms made of PP with barrier layers of EVOH or PET with PA. Still warm, they are removed by a linear robot with a gripping mandrel and the preforms are transferred to the stretch-blow unit with a clamping force of up to 400 kN.

The machine works with one to four-rows blow tools that accept preforms with diameters from 10 to 150 mm. Each series of cavities has its own pre- and main blow valve so that the pre- and main blow pressures can be set individually. This makes it possible to run different product variants on one tool.

The entire stretch-blow unit has servo motor drives that provide exact repeatability, precision and energy efficiency. The valve technology makes it possible to set the pilot and main blow pressures in increments of 0.1 bar. A customer-specific blow study determines the optimal material distribution in the blow mold during the proving process.
Blowliner product sample.
Optionally, process monitoring can use pressure sensors to measure the main blow pressure while it is applied. If the pressure drops unexpectedly, the plastics processor immediately receives an alarm message. If a customer wishes, the Blowliner is available as a spray-blower without the stretching component.

At the end of the blowing process, the vacuum gripper of the integrated linear unloading system removes the finished products from the tool and places them precisely on a conveyor belt or directly in boxes.

Many considerations flowed into the tool technology during the conception of the Blowliner. The solution lies in a balanced hot channel tool with a needle lock system.

The capacity for different product sizes and tool configurations, however, was by no means everything.

Quick tool changes should be included, which can even be handled by a single operator if necessary. An air cushion tool carrier for the injection mold and one on rollers for the blow mold make the quick change possible while a hall crane is unnecessary.

The tool changes are easy and the operator uses the equipping carriage to move the tool to the machine and quickly and ergonomically changes the injection mold by means of a cable pull and roller conveyors.

Except for the injection molding machine and the hot channel system, all components of the Blowliners are from Mould & Matic. The entire machine control and software comes from Micheldorf and is programmed in Beckhoff.

To optimize process reliability, camera inspection of the containers and a leak test are optionally available.

The company advises on the choice of materials and the design of preforms and bottles. The preforms determine the cycle times of the stretch-blow process, therefore the material distribution in the final product and thus wall thicknesses. In other words, intelligent preform design realizes material savings and higher cycle times.

The Blowliner M permits cycle times of ten seconds, the little brother Blowliner S can even manage less than eight seconds. This gives the market a spray-stretch-blow technology that plays in premiere league when it comes to top league quality, flexibility and productivity.

Vacuum drying for trial and short runs

LPD vacuum dryers from Maguire Products Inc. were reported to have substantially cut startup and changeover times, reduced energy use, and dry materials more uniformly than desiccant dryers.

The injection stretch blow molding lines of R&D/Leverage.R&D/Leverage, a specialist in tooling for injection stretch blow molding of PET bottles, said that a switch from desiccant dryers to vacuum dryers has solved multiple problems.

After the company replaced desiccant dryers on seven Nissei ASB and Aoki injection stretch blow molding lines with LPD vacuum dryers, the savings in time were dramatic, according to Alan Tolley, managing director.

While the desiccant dryers need four to six hours to dry material, the LPD dryers take only one hour and twenty minutes from a cold startup,” said Mr. Tolley, “and in subsequent drying cycles, this is reduced to forty minutes.”

Besides startups, the desiccant dryers also posed problems with job changeovers. R&D/Leverage builds single-cavity “pilot” tools for making samples, plus multi-cavity tools for commercial-scale operation. The tools undergo trial runs on the seven injection stretch blow lines, which process at rates up to 70 kg/h. The company typically has five or six tool changes per week.

The LPD dryers give us much more flexibility when testing different grades of resin on one tool,” said Mr. Tolley. “Because we are not a production-scale facility with long product runs, the desiccant dryers were always a challenge for us, posing problems with getting the material dried properly. The worst thing was to be held up by drying issues while we had customer visitors who came from as far away as China or South America.”

Five of the seven LPD dryers at R&D/Leverage.
Other advantages of the LPD dryers cited by Mr. Tolley include improved resin filtration, which provides enhanced bottle clarity due to less contamination, and more flexible throughput control for the single-cavity pilot tool versus high-cavitation production tools.

Along with the seven LPD dryers, R&D/Leverage installed a central Maguire Weigh Scale Blender, which is important because the industry now requires incorporating more recycled material.

The blender delivers to the molding process precisely controlled batches of virgin and recycled polymer, colorants, and additives. Most customers ship their own material to R&D/Leverage for use in producing sample bottles. The company uses up to ten different colors at varying percentages.

Because the LPD vacuum dryers dry more quickly and efficiently than desiccant dryers, they impose less stress on the material and less heat history. “The vacuum dryers provide absolutely more stable material,” said Mr. Tolley. “In the past we had to change desiccant every six months because we were doing so much stopping and starting of our molding processes. That meant added cost and added maintenance.”

Even with the considerable advantages for vacuum drying, the number one reason for switching from desiccant systems may well be energy savings, according to Paul Edmondson, managing director of Maguire Europe.

Considering that drying polymer can account for 15% of the total process energy of a molding operation, a compelling reason for using vacuum dryers is that they consume up to 80% less energy than desiccant systems,” said Mr. Edmondson.

While the example of R&D/Leverage demonstrates that the speed and quality of vacuum drying can enable toolmakers and laboratories to make enormous gains in productivity, the advantages over desiccant systems are also available to processors in full-scale production.

Vacuum drying has the potential to be the dominant means of drying polymer, because energy savings and increased productivity will always be in demand,” concluded Mr. Edmondson.

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