The family of GUM rubber molding presses by IMG (Industrie Meccaniche Generali) was developed in synergy with Duplomatic Motion Solutions, a long-standing partner company. Duplomatic’s hydraulic components offer valuable help for particularly performing motion controls.
di Silvia Crespi
Based in Capriano del Colle, near Brescia, IMG has a strong specialization in the segment of presses for the injection moulding of rubber and plastic materials. Among its functional solutions there is the family of GUM presses for the moulding of rubber, with a horizontal Hydroblock seal and horizontal reciprocating screw injection. This family also includes GUM 300 ton press with a closing force of 3000 kN and injection capacity of 500/700/900 cm3 (various options). Just like the best part of machines manufactured by the Brescia-based company, this machine too was developed in synergy with Duplomatic, partner of IMG ever since the beginning in 2006.
All the movements of the press may be managed by hydraulic components
The main phases of the workflow of this press are the loading of material, the opening/closing of the mould and the injection of the material itself into the mould. Fabrizio Bonfadini, IMG, followed the development of the application personally: “The management of the press – he explained – is mainly entrusted to hydraulics. A pump servo system, consisting of a brushless motor which drives a gear pump and a drive which carries out a PQ(pressure/flow) control make up the “heart” of the machine. The most important contribution, however, is linked to the movements which may not be controlled directly using the servo pump. “It is essential for the opening and closing phases of the mould to occur gently and, in terms of dynamics – Massimo Ripamonti, Technical Director Hydraulic Systems di Duplomatic, stated – the servo pump does not allow to control in the best way the particularly sensitive movements which are carried out at a certain distance from the pump itself. A horizontal press is considerably long and the P/Q servo pump used in its management is found some metres away from the cylinder which opens and closes the mould. Using servo proportional valves with special cursors allows to manage acceleration and deceleration smartly. The task is entrusted to DDPEJ servo proportional valves, dedicated to this type of control. A position sensor placed on the opening/closing cylinder detects exactly the position of the mould; movement is managed optimally by means of a sophisticated closed positioning loop. These performances would be impossible using just the servo pump; they require valves designed specifically for this application, capable of monitoring and improving motion performances locally”. Even loading rubber has its critical issues. The quality of the item is not only determined by the material, but also by the way it is plastified. Rubber undergoes a first pre-heating which brings it to a temperature of 70-90°C; it is then transferred to a mould where it is vulcanized at temperatures which vary from 180 to 240°C. In order to keep the material compact, without air bubbles, the drawing phase is monitored by a back-pressure valve (PDE3G-025), again by Duplomatic, allowing to obtain a constant weight and volume of the material and therefore a constant volume and weight of the finished product.
A long-standing partnership destined to last
“The partnership between Duplomatic and IMG – Bonfadini concluded – is long-standing and dates back to IMG’s foundation. Duplomatic, to all intents and purposes, acts as an external technical department. On various types of machines, the hydraulic poising elements which distribute oil have been designed by Duplomatic; the company does not just supply components, but it is also involved in the study phase for the definition of the piping’s size, so as to prevent load losses. Today almost all of our presses, with different production technologies, are built in synergy with Duplomatic; a valuable partnership, especially where we need particularly performing motion control”.