Take lumps of rock the size of your fist, heat them at approx. 1500°C until they are molten, add bonding agent and spray the glowing soup into a cooled spinning chamber: this is how silicate wool is made, the raw material for Flumroc insulation boards. The large quantities of waste cooling and processing air mixed with fibers and bonding agents are filtered and then released into the air via a stack. A complex control unit manages operation, maintenance, automatic cleaning and safety of the extensive filter system, and the sensor/actuator bus, INTERBUS, transports the necessary status messages, measured data and control commands.

Flumroc AG in Flums, manufacturers of heat insulation products made of silicate wool, employs a staff of about 240, making it one of the biggest employers in the region of Sargans, Switzerland. Flumroc AG evolved from a calcium carbide factory, founded around the turn of the century.

Insulating wool made from lumps of rock
Products for heat and sound insulation and also for fire protection, have been being manufactured from silicate wool in Flums since 1950. The manufacture of the silicate wool boards sounds relatively simple: lumps of basalt=""and dolomite are mixed with silicate wool that has been compressed into briquets, and are fed into a cupola. The rock is melted at  about 500°C, spun into fibers, impregnated to render it water-resistant, wetted with a bonding agent and then hardened again in a special continuous furnace. The infinite quantities of silicate wool mat are cut into boards on a saw line, stacked into parcels and packed. The annual production of silicate wool is in the range of 38 000 tonnes. Every hour, approximately six tonnes of silicate wool per production line are produced from seven tonnes of raw stone. The finished silicate wool products contain at least 95% artificially manufactured non-crystalline mineral fibers. In addition, approximately 0.5 to 3.2 percent of the weight is made up of modified phenol resin as bonding agent and about 0.2% mineral oil to increase the water-resistant property of the silicate wool and to reduce the proportion of dust. In addition to the original lumps of broken rock, a considerable proportion of ready-made silicate wool from manufacturing waste and recycled building rubble is reused – a closed cycle, in which almost no environmentally harmful waste is produced. silicate wool does not burn, does not rot, is easy to manufacture and absorbs neither moisture nor smells – all the requirements placed on an insulating material are fulfilled.

The problem as the solution
In the manufacture of silicate wool insulation boards, 30 000 m³ of process air contaminated with fibers and bonding agent are produced and have to be filtered. And it is precisely these silicate wool insulating boards that also take on the task of filtering this waste air at Flumroc AG. They are normal standardized boards (DUO/50 mm), which otherwise provide outstanding insulation, sound and fire-protection values in rear-ventilated façades and double walls. Tests have shown that the compact two-layer boards are just as suitable as solid matter fine filters. With regard to environmental protection, the fact that the contaminated insulation or filter boards do not have to be disposed of, but can be returned to the production cycle in their entirety as raw material is the particularly interesting thing about this method.

Automation with INTERBUS
The spinning chamber filter is divided into nine sub-chambers and equipped with 283 m² of filter boards. Automation has less to do with the filtering process than monitoring, cleaning and servicing the filter chambers.

The filter chambers are cleaned or used filter boards removed (after approx. 240 operating hours) using water with a pressure of 400 bar. The cleansing nozzle is fixed to a washing crane that can be moved along three axes and can approach 96 predetermined wash points, either manually, semi or fully automatically. The washed out boards and any residual matter drop onto a scratch belt running below the filter chambers and from there are taken to be reused in the furnace. To install the new filter boards, the filter chambers are accessible from two sides. Vertically inwardly closing doors, which are operated and locked hydraulically, form a gangway for the service staff when open. Each of the 16 doors is operated with two hydraulic cylinders and locked mechanically with a further two cylinders. The washing cycle can only be initiated when the doors are closed. Particularly the many  pneumatic valves grouped together on twelve distributed valve islands for the power supply of the cylinders are scanned for status via INTERBUS and supplied with control commands. A Modcon PLC processing approx. 250 inputs and 250 outputs serves as controller.

The reason here for using INTERBUS instead of conventional parallel wiring was not only the reduction in cabling and the simpler options for diagnostics. The space saving in the fully air-conditioned and thus expensive switch rooms played an important role. The entire filter system was developed and implemented by Pamag Engineering in cooperation with Flumroc. Besides a lot of ideas, pneumatics, hydraulics, electric and electronic components, the new spinning chamber   filter comprises no less than 70 tonnes of steel and represents an investment (including engineering) of over 2 mill. Francs.