Dryers for glass fibres

Within its range of industrial radio frequency dryers, STALAM has developed specific engineering solutions to address the needs of drying glass fibres in various forms, mainly direct rovings, assembled rovings, yarns and chopped strands.

Precision-wound direct rovings weighing up to 40 kg each, placed vertically or horizontally on the RF dryer’s conveyor belt with suitable wooden or composite material holders - designed for the automated handling and transport systems used within the factory - can be dried down to a residual moisture content below 0.1% in a time range of approx. 2 to 4 hours (depending on the winding density and the fibre count) instead of the 20 - 30 hours usually required by conventional hot air circulation ovens. The longitudinal (transverse) expansion of the rovings during the process does not exceed 2-3 mm and there is neither migration towards the roving’s outer layers of the finishing chemicals (resins, starch, lubricants, etc.) nor the surface yellowing effect which is a typical drawback of conventional drying.

A number of leading glass fibre producers worldwide are enjoying the benefits of the RF drying technology, having several STALAM equipment in operation in their factories since the mid-nineties.

• Some of the special features of STALAM RF dryers designed for glass fibre rovings are:
• full stainless steel construction of inlet and outlet tables, ceiling and floor of the drying cabinets, electrodes, moist air exhausters;
• special strong, modular type conveyor belt, made of fire-proof composite material wide conveyor belt and electrode system, to ensure low power density, gentle drying and better moisture removal using low electrode voltages (ie. no arcing occurs in the drying cabinets);
• automatic electrode voltage control system at the optimal values, separately in each drying cabinet (this ensures perfect drying in all working conditions with reference to partial or full loading and to the actual inlet moisture content);
• power adjustment circuit through variable motorised coupling capacitor, with no need to adjust the upper electrode position for power regulation;
• additional anti-condensation units for the drying cabinets to avoid water droplets falling onto the product;
• air or water cooling system of the triodes, at the customer’s choice;
• RS3060C triodes (output power up to 85 kW) for longer life and better reliability;
• several optional devices and accessories are available.

As a preliminary guide-line, according to the specific features of the product (direct rovings or assembled rovings, size of the roving, fibre count, type of winding, type of support, moisture content, finishing chemicals, etc…) the following table may be taken into consideration when evaluating an investment for RF drying facilities:

PRODUCTION CAPACITY DATA FOR GLASS FIBRE DRYING


* Each RF module: 40 kW or 60 kW output power

STALAM can provide customised solutions to satisfy any production requirement: we have successfully installed the world’s biggest RF dryers for glass fibre rovings (weighing up to 40 kg each), comprising of 6 drying modules in line, having an overall length of 31 m and a production capacity up to 40 tons/day.

Benefits of the RF technology for the drying of glass fibre rovings

- PRODUCTION CAPACITY FROM 2 tons/day TO 40 tons/day EACH DRYER
- SHORT DYING TIME (80-90% lower than conventional hot air systems)
- REDUCED ENERGY CONSUMPTION
- CONSISTENT DRYING WITH NO WET SPOTS
- NO OVERHEATING, NO YELLOWING, NO MIGRATION OF FINISHING CHEMICALS
- CONTINUOUS AND JUST-IN-TIME OPERATION
- EASY AUTOMATION