![]() There are a number of companies that offer PET robots for machines that don’t have them. This helps, but robotic machines with three servo-driven takeout stations cut cycle times easily by 40%. The latter machines can be adjusted to eject the parts while the mold is opening so that the only waiting time is for the ejectors to move back. Extremely fast robot speeds allow the mold open/close sequence to be as quick as those for free-drop machines. Robotic takeout or free-drop: Machines with three, four, or even six post-mold cooling stations allow removal of preforms from the mold as soon as they are cold enough that they won’t buckle (around 160 C, or 320 F). It should be adjusted to get the desired demolding temperature. Cooling time should be a minimum of 1.5 sec but can be as high as 20 sec for very thick preforms. The following criteria are particularly important for closure and perform mould maker: a high degree of standardisation and modularisation of the tools, which allow a high degree of flexibility in order to quickly change the design or to expand the mould variation. This shrinkage is important to allow the preform to be easily removed when the cores move away from the cavities. The preform now shrinks away from the cavity and onto the core and cooling is less efficient. Very thin preforms do this a lot because with cavity channels as low as 2 mm (0.080 in.), almost half of the preform weight sticks to the cold mold walls and is already at or close to solid density by the time injection is finished.Ĭooling time: As soon as the preform is sufficiently cooled to avoid sink marks, the machine can switch over to cooling time. Cost-Effective: PET preform molds are cost-effective, making them an economical choice for manufacturing PET preforms in large quantities. A slider also makes the removal of the preform easy and fast. Mold frames and pitch layouts for all major platforms and preform applications. However, preforms already cool down as they are being injected. This makes it easy to remove the unfinished preformling from the mandrel. PET Molds ranging from 2 to 144 Cavities. This difference is about 13%, and for many years we taught to move the transition or switchover point to the 13% mark of the total injection stroke. Hold Time: The purpose of hold time is to supply resin that is needed to fill out the voids in preforms as they shrink from a melt density of 1.15 g/cm3 to the solid density of 1.33 g/cm3. For example, a 525 g preform with a wall thickness of 8.5 mm (0.335 in.) can be filled at 27 sec, resulting in a fill speed of 19.4 g/sec/cavity. However, thicker preforms can be filled much quicker, as it is easier for the resin to be pushed through the tool channels. This works well for preforms up to about 4-mm wall thickness. Injection time: Resin suppliers suggest a fill speed of 8 to 12 g/sec/cavity.
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