The beverage industry has been using polyethylene terephthalate (PET) 2-liter plastic bottles primarily for packaging carbonated soft drinks since the 1970s. As that market has grown to encompass bottled drinking water, stretch blow-molding machines continue to produce those plastic bottles. The concept is simple: A pre-form plug is inserted into the blow molding machine heated, and compressed air is injected, “blowing” into the pre-form to create the bottle.
Since the 1970s, blow molding systems have reached a higher level of efficiency, using capabilities such as electromagnetically controlled stretch systems and compressed air recycling components. Intelligent systems that regulate the blowing process, reduce scrap and automatically eliminate bottle process deviations have been added as well.
Manufacturers of stretch blow-molding equipment strive to provide machinery that is faster and more efficient to drive down the total lifecycle costs of their equipment. This, in combination with advances in container material technologies, is changing the requirements of the compressed air needed to support the process. These changes include lower pressure for forming the containers and reduced volume due to recovery capabilities.
Sidel Matrix blow-molders can blow PET bottles in a broad size range (from 0.1 liter to 3.5 liters) with many distinctive bottle shapes.
Air Recovery Systems Capture Portions of High-Pressure Air
Mike Bakalyar, manager, high pressure and niche products, Belliss & Morcom, Gardner Denver Inc., Quincy, IL, an air compressor manufacturer that provides compressed air to PET bottle blowing applications, says that blow molders are being designed with increased efficiency in regards to the way that heating and compressed air are used in the process.
One of the biggest advances is the air recovery feature that captures a portion of the high-pressure air after the blow process and utilizes this to support low-pressure air requirements within the machine. “This feature has reduced overall volume requirements of high-pressure supply,” he explains. “In many cases, the recovered air is in excess of the mold process requirement and is available to augment low-pressure plant air needs or return air to the high-pressure compressor, eliminating a stage of compression.”
Joe Mashburn, area sales manager, AF Compressors USA, Carrollton, GA, another air compressor manufacturer that provides compressed air to PET bottle blowing applications, says the latest advances include the lowering of blow pressures due mainly to the light-weighting of bottles. Improvements in air recovery systems by blow mold machine manufacturers have also reduced the energy consumption related to compressed air.
An AF Compressor PET package equipped with the R-Back-5 Air Recycling System
“In the past, normal blow-mold air pressures to produce PET bottles were typically 35 to 40 bar (510 to 590 psi),” he explains. “The light-weighting of the containers, particularly for water bottles, has reduced the final blow pressure to the 20 to 25 bar (290 to 365 psi) range. This lower pressure significantly lowers the volume of air needed to blow the bottle.”
Air recovery systems also reduce overall compressed air requirements by recycling some of the high-pressure, blow-mold air for low-pressure service air on the blow molding machine, including air for pre-blowing the bottle before high-pressure air is used for the final blow, he adds. In addition, machine suppliers have decreased the dead space between the blow valve and the mold, which also decreases compressed air requirements.
“Early on, when air recycling systems were introduced, we found that the systems were not saving as much air as advertised. Since then, improvements made by blow-mold machine manufacturers have given end users and their compressor suppliers more accurate data to properly size the appropriate compressor for the application,” Mashburn explains.
Sidel’s air recovery system generates savings in capital expenditures and operating costs.
Krones Contiform 3 Innovates Stretching System and Reduces Dead Space Volume
Krones Inc., Franklin, WI, and Sidel, Norcross, GA, are the two major producers of blow molding systems in the U.S. The Krones technology was developed in Germany, and the Sidel technology was developed in France.
Krones’ latest is the Contiform 3 Stretch Blow Molder, which features an electromagnetic linear-drive control system that controls stretching of the bottle and saves energy by recycling compressed air. The machine is designed for all types of bottle manufacturers that utilize the hot fill or the standard process. The platform also features a new blowing V carrier module, which achieves output speeds of 2,250 containers per hour per blowing station.
The Contiform 3 Stretch Blow Molder from Krones Inc. features an electromagnetic linear-drive control system.
Krones’ new stretching system has a major impact on overall air consumption. This is because it is electromagnetic as opposed to pneumatic and requires no compressed air, according to David E. Raabe, who oversees the technical sales of plastic technology at Krones.
Minimized dead space volume is another feature of the Contiform 3 that reduces operational costs. “In the blowing station, the so-called dead space volume has been reduced to a minimum by utilizing every design possibility to the maximum,” Raabe explains. Other features, such as the Air Wizard Plus air recycling system, ensure maximum compressed air savings for every process. A new valve circuit makes it possible to re-use up to 40 percent of exhaust air from the blowing process.
Further reductions have been made in the radiant heat compartment in the heating tunnel. The infrared oven requires 15 percent less energy than its predecessor, due to the Krones closed-tunnel oven design.
“The new stretch system also is maintenance-free and easy to program on a central HMI (human-machine interface) touchscreen. It calibrates the correct air saves automatically and has no stretch-rod shock absorber stops. This reduces mechanical problems that can occur during changeovers,” Raabe says.
Sidel Matrix Reduces Heating and Compressed Air Energy Consumption
Sidel recently introduced the Matrix blow molder, a modular blow molding system available in 200 configurations that reduce energy and material consumption as well as downtime. The system produces lightweight PET containers at a speed of 2,250 bottles per mold per hour.
Electrical consumption is reduced by 45 percent versus that of a conventional oven because it requires fewer heating modules and lamps, according to David Bonhomme, Sidel’s customer service director for North America. The system uses installed power more efficiently, resulting in reduced preform heating time. In addition, air consumption is reduced, resulting in compressed air savings of up to 30 percent.
The system is designed to reduce air consumption during the blow molding process. Instead of releasing compressed air into the atmosphere, the system uses it to feed the pre-blow circuit and the pneumatic system. The extra air is released in the low-pressure circuit of the plant. As a result, the blow molder produces low-pressure compressed air that can be used for downstream operations. The system also recovers the high-pressure air needed for the next blowing cycle.
Available as an option is the Intelliblower, a system that automatically detects and eliminates bottle process deviations and reduces scrap. “The Intelliblower has a strong impact on production uniformity and packaging quality because it ensures control of the pre-blow phase parameters instead of focusing on heating regulation,” Bonhomme says.
Sidel Helps Midwest Coca-Cola Bottling Co. Reduce Blowing Air Pressure by 50%
Sidel works with a variety of customers, including converters that produce empty PET containers on behalf of their clients and brand owners who produce, fill, label and palletize PET bottles for the consumer market.
Sidel recently helped Midwest Coca-Cola Bottling Co., Eagan, MN, reduce blowing air pressure by more than 50 percent in its blow molding operation. The company manufactures bottles and distributes Coca-Cola products throughout the Midwest, and it used Sidel’s Eco Booster service to reduce blowing air pressure and oven electricity across four of its lines, according to Jim Tierney, maintenance manager at Midwest Coca-Cola Bottling.
Sidel’s Eco Booster service analyses a line to identify potential opportunities for savings. Efficiency measurement tools are installed that record the consumption of all utilities (air, water, electricity and carbon dioxide) by individual machines, lines, and production zones. They can even record the activity of an entire plant. Along with measuring consumption and calculating energy costs per bottle produced, the service helps determine the correlation between consumption levels and production procedures (startup, shutdown, changeover and cleaning). This information is used by beverage producers to support initiatives for reducing waste.
“Having the Sidel experts work with our guys to adapt our equipment brought peace of mind that the intervention would be quick and easy, and ultimately led to a short return to production and faster ROI,” Tierney notes.
New Plastic Materials and Thinner Wall Thicknesses Likely to Continue Pressure Reduction Trend
What future advances do experts see in the area of blow molding, especially as it applies to compressed air? Mashburn of AF Compressors USA says there is a possibility that blow pressures will continue to decrease for applications where the weight of the bottle is reduced. “We’ve heard that some testing has been performed at pressures as low as 17 bar,” he says.
New materials and thinner wall thickness will likely reduce the pressure required to form bottles, says Bakalyar of Belliss & Morcom. “It also is likely that the technology will be applied more locally to the product being contained. This trend will increase the population of smaller blow mold stations requiring smaller supporting compressors. Belliss & Morcom compressor products are ready to accommodate these anticipated changes,” he says.
A Belliss & Morcom Oil-Free PET Air Compressor
Bonhomme of Sidel sees the following technological advances in blow molding applications:
- Blow molding pressure will decrease, consequently lowering energy use and costs.
- Enhanced air recovery systems will increase savings in operational costs.
- Implementing new packaging and light-weighting capabilities to create containers will help lower blowing pressures.
- Researching environmentally friendly materials (other than PET) will enable customers to blow mold containers at very low pressures.
- Increasing the use of machine intelligence will help to detect and troubleshoot air leaks and optimize equipment efficiency.
If these experts are correct, the blow molding process will continue to evolve and become even more efficient, which is good news for industries producing large quantities of plastic bottles.
For more information about the companies mentioned in this article, visit AF Compressors USA (www.afcompressors.com), Belliss & Morcom, Gardner Denver Inc. (https://www.gardnerdenver.com/en-us), Krones Inc. (www.krones.com), and Sidel (www.sidel.com).
Neal Lorenzi is a freelance writer based in Mundelein, IL. He has covered a wide range of industries during his 25 years as a writer and editor.
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