In the middle of last year, Engel company took over the development and sales of PET preform injection molding machines from its long-term partner SIGCorpoplast, which has expanded Engel's machine types to cover a wide range of applications. These machines appear on the market under the name Engel MacPET and produce PET preforms for stretch blow molding of PET bottles.
At the heart of every MacPET preform high-performance injection molding system is a toggle closure machine for quick turnaround production. The injection side is equipped with a special pressure-retaining device (Fig. 1). The pressure-retaining device specially developed for PET injection is Engel's PET plasticization device that is different from other manufacturers. During the pressure holding and cooling phases, it allows the melt to be metered for the next injection. Before the next injection, the remaining melt in the pressure-retaining device is completely discharged into the space in front of the screw and follows the first-in, first-out injection principle, which shortens the time for the thermal stress to act on the melt. The MacPET series machines consist of five types of machine with clamping force up to 5000kN, which are particularly suitable for applications in 12, 16, 24, 32, 48, 64, 72 or 96 cavity moulds.
At the same time, through the long-term cooperation between Engel and SIG Corpoplast, more than 100 such machines are operating reliably in 20 countries on all continents of the world. The 5 point double toggle lock cooperation together with the accumulator not only ensures the quick opening and closing of the mold, but also ensures the extreme rigidity of the clamping system and the gentle operation of the mold. When the mold is 96-cavity, the mold opening and closing time including the removal of all plastic parts is 2.8 seconds maximum. The energy-saving oil pressure system includes a servo-controlled progressive transmission pump for all screw movements, which makes economical operation of the machine possible. Energy consumption is reduced to a very small extent.
Gentle plasticization creates consistently high quality
MacPET's injection device has a short, space-saving design, and is equipped with a stacking screw (diameter ratio between 22 and 24, depending on the diameter of the screw) as a general machine, ensuring a gentle treatment of the melt, although it The plasticizing ability is very high. If the melt is to be colored, the screw will have an integrated mixing device for optimal uniformity. If a constant concentration of acetaldehyde is present in all cavities is a special quality requirement, electrostatic mixing elements are installed in the forward space of the screw (standard concentration is max. 3 ppm, measured in preforms or blown bottles) Acetaldehyde is produced by the inevitable mechanical and thermal stresses in the melt during plasticization .
The economic benefits of the PET preform production line have a very important relationship with the demoulding system. In order to shorten the cycle time as much as possible, the preform is cooled partially inside the mold and partly outside the mold. Engel's linear robots for MacPET machines are equipped with special demoulding devices with integrated cooling systems. A four-fold rotating device ensures that the preforms are subsequently cooled for the duration of the four injection cycles before they are stacked (Figure 2). A peeling device with a beam monitoring system ensures that the preform is removed from the mold and caught by the robot.
Simple operation
Injection molding machines, ejection robots, and peripherals share the same control panel. Like the general machine, the robot controller is integrated into the machine control system, not only to facilitate the operation, but also to minimize the time required for data exchange. For the same reason, the cycle time is extremely short. The machine control system is generally compatible with other component models, such as cooling systems for molds and robots, upstream drying and conveying systems for PET pellets, and dry gas separators for ring molds, all of which are integrated into the system.
Satisfactory partners
In designing these entire production units, Engel collaborates with suppliers that are strong in their respective fields of expertise. Each partner is also responsible for the after-sales service of their equipment.
New standard for high performance preforms
Although Engel's MacPET machines are already working at the maximum possible efficiency, Engel has set even more ambitious goals: The next step in development will focus on increasing the ratio of the number of cavity cavities to the machine specifications. At the K2004 exhibition in Düsseldorf, Germany, the top of this high-performance preform production will be a brilliant debut.