At present, insulating materials made of mineral fibres are the most effective. Glass wood makes up the largest portion of the mineral fibres used. Approximately 100 to
150 m³ of glass wool can be made from 1 m³ of glass. After spinning the hot melt of 1300 °C, binders are added to obtain certain product properties. The portion of binders in the end product glass wool is 0.5 % to 7 % depending on the manufacturing process. After spinning, the mat webs (the so-called glass fibre wrapping material) is passed through a hardening furnace at approx. 250 °C and is hardened there. After leaving the hardening furnace, the fibre mat is so strong that it can be cut and further processed. The phenolformaldehyde Bakelite gives the glass wool its dimensional stability.
The washing water circuit plays an important role in the process for the manufacture of insulating mats of glass wool fibres (Fig. 1). The washing water is circulated. During the process binder portions, fine and very fine portions as well as glass fibres accumulate. Therefore, the plant operator is very interested in an effective washing water treatment and recycling. However, they often come up against boundaries or recycling over a prolonged period is not possible. The very fine glass fibres in the circuit lead to increased wear of pipelines, pumps and bends and, consequently, to increased operating costs.
The filters and dewatering units used in the glass wool industry reach their limitations due to the very short glass fibres and particles. The company Isover belonging to the Saint-Gobain Group was also confronted with this problem. For a long time they had been looking for a suitable separation solution for these very fine portions. In November 2009 a vibrating screen from ITE GmbH was tested for four weeks. With their fine screening technology ITE is able to offer screening solutions even for cases where the conventional screens available in the market come up against their limitations. With up to 325 mesh (45 µm effective separating diameter) ITE offers a screening technology that can compete with the separating ranges of lamellar clarifiers and hydrocyclones.
The screening machine used, a 3PSM (Fig. 2) from ITE with 3 frame screens has a screening surface of 2.4 m². The screens are linearly driven by 2 vibration motors of 2.2 kW each and generate a discharge acceleration of max. 6 G. The high acceleration force makes it possible to dewater even fibrous and very finely dispersed feed. The inclination of the screening machine 3PSM can be adjusted, thus directly enabling a variation of the retention time on the screening surface, which leads to optimized dewatering. The entire circulating flow of binders of approx. 8 to 10 m³/h was passed through the vibratory screening machine. In order to counteract blinding of the fine screen meshes, the operator installed a sprinkling system that made process water spraying possible, thus effectively avoiding the formation of jamming particles.
Due to this optimization, the ITE 3PSM successfully stood the test in the required continuous operation. The discharge result was consistently positively evaluated. Both the residual moisture of the material being screened and the discharge throughput were more constant than those of other machines previously tested. The samples of the screened material evaluated in the Isover laboratories had a solids content varying between 18 and 29 wt.-%. The circulating washing water circuit could be stabilized for various days. Variations of the feed volume flow and of its solids content, which were caused by the process, were overcome by the 3PSM without any problems.
A downstream process stage dewatered the mix of fibres and binders to the extent that it became possible to return the solids to the process without a thermal aftertreatment. The screening technology used in oilfields proved to be absolutely suitable for the industry due to its simple structure and rugged design. Another advantage was the easily exchangeable system of frame screens (Fig. 3). This system made a quick change of screens possible leading to minimum downtimes in the production cycle. Due to the wide range of frame screens available, it is always possible to adjust the screening machine to changing operating conditions. The screen program of ITE offers 16 different screens with mesh widths varying between 3360 µm and 44 µm.
ITE GmbH, Alsdorf (D), Tel.: +49 2404 67258-0,