Article deriverd from "Automazione Oggi" nr. 223, March 2000, page 179

Automation for wood recycling

Valerio Alessandroni

The Mauro Saviola Group is among the first in Europe for chipboard panel production: Super-Flash from Automa has been adopted as the supervision system for the new Sit 2000 factory.

The first production nucleus of the Mauro Saviola Group was born at Viadana in the Province of Mantua in 1963, a system of production activities now comprising nine companies: Sadepan Chimica, Sia, Sit, Silla, Sadepan Legno, Sacic Legno, Sitapan, Nuova Rivart and Sitech. Nine companies which interact according to a criterion of geographical and sectorial diversification to satisfy the needs of a dynamic, continually developing market: that of wood.
The principal Saviola Group products are formaldehyde, liquid and powdered urea resins, liquid melamine resins, decorative melamine paper, raw chipboard panels, special waterproof and fireproof panels, fibre and MDF panels, enhanced panels, twin and post-formed laminated panels, continuous plastic laminates and edging.
Over the years the Group has caused a veritable revolution in chipboard panel production, moving from the use of poplar brushwood to the exploitation of recycled wood. Recovering and reusing 'clean' natural wood coming from the most diverse industrial processes contributes to protecting and safeguarding the environment, limiting the felling of trees and forests. Moreover, waste of wood is avoided, helping to solve the problem of industrial waste disposal.

The Group's chemical and technological know-how has also permitted the production of panels with increasingly less emission of formaldehyde into the environment, of special fireproof panels for fire prevention and of waterproof panels intended for environments with a high humidity level. This policy also includes the installation of new electrical precipitators in the Group's companies. These allow atmospheric emissions to be kept considerably below the parameters defined by the regulations.

The new Sit 2000 factory of Mortara (PV), inaugurated by the Saviola Group in 1999, represents a model of integration between technology and nature, with a 50 m continuous press that develops a daily production capacity of 2000 m3 of chipboard panel.
The system, co-ordinated with structures, services and plant for chipboard panel production, takes substance through an integrated, complex cycle of processes involving different technologies: from the panel manufacturing process to melamine paper impregnation to actual enhancing. At the end of a tortuous route the raw panels, through the application of decorative papers, leave the anonymous raw state to be 'clothed' in imitation of the most valued woods. A panel is thus obtained having a better specific weight and properties than those produced using new wood. The Sit 2000 factory was set up with a precise objective: to use only recycled material.
This is unlike the other Saviola Group factories, where a gradual technological conversion has taken place. The plant (the largest of its kind in Italy and among the first in Europe) has thus been fully automated in view of this production process.

Material collection is carried out in various European countries, which ensure approximately 70% of daily requirements. This material is transported to the Mortara factory by rail after an initial treatment to eliminate impurities.

The remaining part of the daily requirement, on the other hand, is acquired through a differentiated collection system. After having accumulated in a large outdoor reception area, the material undergoes an initial treatment to remove the coarser polluting parts: metal, plastic and glass elements, etc. This separation is done by making use of the different specific weight of the materials and the foreign substances thus recovered are subsequently classified and resold.

The wood then starts the processing stage, first going through an iron removal phase using magnetic drums. It is then crumbled in a large chipping machine. Conveyed via a metering screw, the chipped material undergoes a cleaning process to remove the smaller foreign bodies (nails, screws, pebbles, splinters of glass, etc.). The cleaners operate using a vibration system combined with traps arranged is such a way as to capture and eliminate the heavier materials. After cleaning the chipped material is put through a series of mills which refine its fibres, reducing their size even further. The refined material still has a very high humidity level, which must be suitably reduced to an average of 5-6%. This is done by conveying it to a large rotary dryer where it is hit by a current of hot air that reduces the humidity percentage to the optimal value.
The dried material is sieved in the next phase, for division into four size classes for the purpose of removing the pollutants having a specific weight close to that of wood (aluminium, sand, plastic, etc.).
The vibrating sieves perform the required division using calibrated mesh nets and the various types of homogenous material thus obtained are sent to the same number of pneumatic dry cleaners. In these a ventilation action combined with special mechanical systems allows material cleaning to be regulated, keeping it in suspension.
The final separation of pollutants then takes place, again making use of the specific weight differences, while the residual dust is used for thermal cogeneration.
After division into four size classes, for the sole purpose of facilitating removal of the pollutants, the material is then recomposed into two types only, fine and coarse, and sent to the respective warehouses.

From the 'mattress' of wooden flakes to the finished panel
The fine material is conveyed from its warehouse to a resinating machine which kneads it with a mixture composed of resins and accelerating agents. The resulting mixture is then conveyed to the forming machines which prepare the 'mattress' from which the panels will be made.
There are four types of forming machine, two for the thin external layers and two for the coarser layers of material at the centre of the panel. There is a precise reason for this sandwich composition of the mattress: while the coarser fibre in the centre ensures resistance and flexibility, the fine external material provides the panel with an excellent sanding surface.
Since different quantities of fine and coarse material could be produced, the plant is provided with refining mills that are regulated in feedback to obtain balancing material on the basis of the requirements of the final line. This always ensures the correct availability of coarse and fine material.
At this point the mattress undergoes a cold pressing phase, which favours chemical reaction in the gluing mixture and partial degassing of the material. The next step is hot pressing, done by means of a continuous line 50 m long.
The panel is then cut cross-wise to the required length and conveyed to stacking using cooling rollers. Finally the external layers are sanded to guarantee the thickness. This is an indispensable condition for homogenous application of the glue and the paper or melamine facing.

The considerable production volumes and the limited use of personnel have necessitated the adoption of advanced automation technologies to guarantee close control of every phase of the cycle and, in particular, of the chemical-physical properties of the materials on entry to the press.
The choice of supervision system was conditioned by the considerable area of the plant. The supervision system was organised in three parts, dedicated to managing the 'green' material (from the reception area to the dryer), the 'dry' material (downstream of the dryer) and the press. In its turn the green material system is divided into the chipping machine supervision system and the refined material storage system (including the cleaners and mills).
Each of these parts is provided with a video-graphic terminal that allows all the connected services, operating parameters and relative alarms to be kept under control. The dry material system (including the sieves and cleaners) uses three video-graphic monitors in order to display several areas of the plant simultaneously. The whole architecture is based on the Super-Flash supervision system from Automa. This has been programmed in such a way as to initially display an overall page of the controlled area.
Subsequently a specific page can be called for each 'strategic' machine within the area because it is not possible to display all the services in detail in the general page. For example, a page is provided for the chipping machine in the green material section, with all the services connected to it. This organisation of the supervision system is of considerable help in finding and resolving faults because, by selecting one of the services with the mouse, all the operating parameters can be displayed immediately. Moreover, the services are coded with the same symbols used in the electric panel, allowing them to be identified immediately. Super-Flash is run on PCs with the Windows NT 4.0 SP4 operating system. They can be enabled so that, in the case of an alarm, the video-graphic automatically positions on the page involved, where the service causing the alarm turns red (services operating correctly are coloured green while brown shows services that are stopped).
A total for 10 detail pages are provided in the "green section". These can be activated selectively on the three PCs thanks to a program developed using MicroC. Others in the "dry section" are added to these, giving over 1000 services managed in the two sections. All the operating parameters and various types of alarm can be displayed for each service: thermal trip, clogging, rotation control, etc. This allows the reason for a possible plant stoppage to be identified and the subsequent maintenance or repair intervention to be optimised.
The possibility offered by Super-Flash of storing all the plant history data is also very important for the regular operation of the factory, as is the possibility of a daily printout of the absorptions, yields and operating times of the various services.
The data from the various distributed services are collected by means of a PLC network with remote I/Os, which communicate with the PCs used by the supervisor via the TCP/IP protocol. On the other hand the PLCs communicate with each other via the Data Highway Plus protocol. Super-Flash is also used for monitoring the electric panels.
The integration of Super-Flash with the other supervision systems present in the Sit 2000 factory is done by exchange of backed information on the PLCs. Currently only two people are needed to control the whole plant from a raised control room located in the centre of the factory. A series of video-graphic monitors and approximately 10 TV cameras allow the critical points of the line to be managed visually.

Future expansion
The Sit plant will be enhanced in the future by the addition of further mills and cleaners in the 'green' section which, in their turn, will be managed by the Super-Flash system. The addition of this new machinery does not present a problem since Super-Flash has been designed to accept every new plant expansion. In particular, a data collection application using Super-Flash is already in the development stage.