Persico SpA of Nembro, Italy, has sold its first full-electric version of its fully automatic Leonardo rotational machine to a customer in Finland.
“We got rid of the diathermic oil mold heating and cooling systems. This means that there will be no need for an oil change every two years—by itself a great contribution towards reducing the environmental footprint of the production process,” said Sergio Zilioli, Persico sales manager. “The innovative heating system on the new machine consists of a series of resistors applied directly on the mold surface.”
Persico officials did not name the customer, but said the company will use the Leonardo to make organic waste composters and dry toilets that do not need connected to a sewer system. Running at full capacity, the company will make 30,000 units a year, according to Persico.
Also at Rotoplas'11, Persico outlined its research into using vacuum inside the mold to reduce the problem of bubbles on the outside surface of a rotational molded part. Persico carried out tests comparing the results of different grades of polyethylene molded under the same processing conditions but with different internal mold pressures.
Persico claims that Leonardo is the only rotomolding machine that can pressurize and depressurize the cavity of a rotating mold. During the tests, pressure was reduced inside the mold during melting. Once melting was completed, the pressure was brought back up
During tests, a molding cycle using the vacuum method led to the complete removal of air bubbles in the wall and outside surface of the part.
Why does it work? According to Persico, when carrying out the sintering stage under vacuum, the bubbles trapped among the powder contain only about one-fourth the amount of air compared to normal molding, even through the volume of material is the same. Also, the bubbles created when the polymer melts are much smaller and reach the collapse threshold more quickly for materials with the same surface tension.
Second, at the end of the melting process, when internal mold pressure is brought back up to atmospheric pressure, the external pressure on the bubbles becomes much greater, causing the volume of the bubbles to decrease to a fraction of their original size. The bubbles then begin to collapse rapidly, leaving the part free of surface blisters and internal voids.
Ferry Industries Inc. of Stow, Ohio, is selling the Leonardo machines in North America.
Tel. 330-920-9200, fax 330-920-4200, email [email protected].
