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Here again, the results which can be achieved with normal injection in a more or less economical fashion are flimsy, and the tops require extensive ribbing for rigidity.
| Just a few months ago, going against the current of the decline in resin furniture, a leading German company invested heavily in rotary co-injection buying this "giant" press capable of a 55lb. shot. In this case, in the manufacture of tabletops, there is no ribbing, and the surface is clean and rigid. |
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Also, with the five stations, five different sizes of top can be molded in a single cycle, obtaining one tabletop every 120 seconds.
The tops range in size up to 70" x 39". Conventional tops often break because of shrinkage as they are vulnerable at the ribbing due to the behavior of PP over significant lengths. With rotary co-injection, on the other hand, even if there is shrinkage, the part is unlikely to break because it can withstand the internal stress due to its thickness.
Single Station Co-injection - Continuous change of molds plus limited production due to cycle times of 7-8 minutes, or 7-8 pieces per hour. There is also the additional complication of the relative difficulty of the mold changes because of the auto insert and automatic pickup of the large tabletops.
Rotary Co-injection - 660 ton, 5 station machine with an approximately equivalent cost of a single station machine produces up to 30 tops per hour with few mold changes. There is less possibility of damage to the top surface as ejection of the finished article can be done from the injection side as the mold station rotates to the discharge position.
This dramatically decreases the cost of the molds. Only one robot handles the insert of the decorative top as well as the pick up of thedifferent molded parts. Just-in-time inventory management is possible with the variety of sizes which can be produced in one complete cycle.
As is amply evident from these examples of articles currently in production, rotary co-injection is an ideal solution for many applications.
Co-injection is attractive because of the material savings possible and the physical properties of the finished products.
Additionally, the rotary press provides a versatile, space-saving and economical solution for high output production of thick parts with long cooling times.
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