RF DRYING TECHNOLOGY

A wet product submitted to a radio frequency (RF) field absorbs the electromagnetic energy, so that its internal temperature increases. If a sufficient amount of energy is supplied, the water is converted into steam, which leaves the product; that is to say, the wet product gets dried.
The heating/evaporation process carried out by means of radio frequency is:

endogenous: the thermal energy is not supplied to the wet product by an external heat source, but rather it is generated directly throughout its mass;

selective: the electromagnetic energy is absorbed mainly by the moisture and not by the product itself;

controlled: the heating/evaporation rate is directly proportional to the amount of electromagnetic energy supplied, and this energy can be controlled precisely.

Thanks to these features, the radio frequency drying of textiles, after dyeing or any other wet treatment, has the following advantages:

high energetic efficiency: the electromagnetic energy is transferred directly to the whole of the wet product, without losses to the surroundings, instantaneously, and is entirely exploited for the drying process; furthermore, the energy transfer is not negatively affected by variable parameters such as the dimensions or the density of the product;

outstanding quality of the dried product: all problems normally caused by the heat transmission phenomena are totally eliminated, so that the product dries quickly and uniformly down to the desired residual moisture level, with a beneficial steaming and bulking effect of the fibres which greatly improves the physical properties like elasticity, softness, hand and colour effect.

STALAM RADIO FREQUENCY DRYERS

STALAM radio frequency dryers have some specific design and construction features which allow their users to obtain the maximum benefits from the RF technology in terms of quality of the dried products, reduced operating costs, operational flexibility and equipment reliability.

The RF generators are entirely designed and manufactured by STALAM; they are of the "lumped components" type, having high efficiency (Q factor) and outstanding reliability; all components and circuits are easily and quickly accessible.

The cooling system of the triodes is made up of a double water circuit; it is designed to allow the longest possible life of the triodes and does not require periodic maintenance operations. Upon request, and as standard in some specific applications, STALAM also supplies generators fitted with a forced-air cooling system.

The RF power adjustment is accomplished by means of a semi-automatic circuit which controls the power supplied to the product being dried through a variable capacitor, located in the generator. No continuous raising or lowering of the upper electrode for RF power adjustment is required in STALAM dryers: the electrode is fixed or automatically positioned at pre-set heights.

The power density is as low as 5 to 15 kW(RF)/m2 of electrode surface. Therefore the heating/evaporation process is extremely gentle and the quality of the dried product is greatly enhanced.

The construction is modular, in the sense that high capacity dryers are made up of two or more drying modules, connected in series; this construction principle allows STALAM dryers to work with reduced RF power densities in all circumstances. Further modules can be added to the first at any time, so that considerable investment and floor space savings are possible.

The construction materials are mainly stainless steel and aluminium, to ensure a long life of the dryers even in difficult working environments, and all electrical and electronic components used are of the best international makes, other than amply oversized, to guarantee the highest level of reliability.
STALAM dryers are also equipped with electromagnetic field leakage preventing and RF interference suppressing systems, in order to comply with all safety and electromagnetic compatibility regulations in force in the different countries.