Stalam offers an advanced alternative: radio frequency (RF) thawing, a technology designed to overcome these challenges and optimize industrial processes.

Traditional thawing methods

Cold room thawing

Cold water thawing

Tumbling thawing

Open air thawing

Radio frequency thawing: the Stalam advantage

RF thawing works by generating electromagnetic waves that penetrate deep inside the product and interact directly with the water molecules contained in the food matrix. Because water molecules are dipoles, they continuously try to align with the alternating electric field produced by the radio frequency generator. As the field changes direction millions of times per second, the molecules oscillate rapidly, creating internal friction. This friction is what produces heat uniformly throughout the product.

Key benefits:

• Speed: large blocks of frozen food can be thawed in minutes, rather than hours or days.
• Uniformity: electromagnetic energy ensures even temperature distribution throughout the product.
• Quality preservation: minimal drip loss, maintaining texture, color, and nutritional properties.
• Safety: rapid thawing reduces the time food spends in the bacterial growth temperature range.
• Flexibility: RF systems are suitable for a wide range of products—from meat and seafood to vegetables and prepared meals.

With Stalam’s RF thawing solutions, including the COLDWAVE+ series, industrial processors can increase throughput, reduce energy consumption, and maintain the highest product quality, all while complying with strict food safety standards.

FOOD

Tempering and defrosting

Defrost in minutes, avoid drip loss, improve yield.

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FOOD

Defrosting Catalogue

Learn more about our radio frequency (RF) equipment.

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L'articolo Industrial food thawing: why choose radio frequency technology proviene da Stalam.

Aflatoxins are one of the most potent and dangerous groups of mycotoxins, produced by certain moulds such as Aspergillus Flavus and Aspergillus Parasiticus. These moulds grow in agricultural commodities such as tree nuts, peanuts, rice, corn, sorghum, wheat, millet, sesame seeds, sunflower seeds, cotton seeds, chili peppers etc. and in a variety of spices. Aflatoxins are produced by fungal action during production, harvest, storage and processing.

When moulds start contaminating the commodity, powdery, grey-green spores may develop on the surface of the product and aflatoxins may be produced by the fungi when the kernel moisture is around or above 15 percent. High ambient temperatures, drought stress and insect injury may contribute to increased aflatoxin contamination.

Aflatoxins have been associated with increased liver cancer in interaction with chronic hepatitis B virus (HBV) infection. They may interact also with other viral infections such as those caused by Epstein-Barr virus. In addition, aflatoxins cause Aflatoxicosis and may result in growth faltering and immune suppression in children. 

The solutions in the market

The best approach to mitigate the problem of aflatoxins is prevention since, once the commodity is heavily infested by toxic fungi, there is no feasible solution to remove them. Before storage, crops should be properly dried and sanitized to prevent the development of moulds.

Chemical control has been reported to be a successful alternative to prevent fungal infestation. On the other hand, the treatment is very expensive and usually affects the sensorial properties of the product. Besides, this kind of treatment is not acceptable in organic farming, whose processes must be chemicals-free and therefore more susceptible to aflatoxin contamination.

If no treatment has been carried out during the pre-storage phase, optical screening can be used to remove the contaminated grains, yet with the consequent high product and financial losses.

The Radio Frequency (RF) technology has proven to be very effective when used for pre-storage sanitisation of agricultural commodities. It can be used simply as a moisture reduction (drying) method but also to disinfest (pest elimination) and sanitise (microbe load reduction) a large range of substrates (cereals, grains, pulses, nuts, herbs, spices, etc.). The process is 3 to 10 times faster compared to conventional treatments and, other than reducing and stabilising the moisture content of the commodity as required, is capable of ensuring 100% mortality of even the most heat resistant pest species in all their development stages or to achieve 2 to 3 log reduction of the t.b.c. within the commodity, including particularly moulds and yeasts.

Radio Frequency has proven to be far superior compared to the conventional sanitization methods for the specific purpose of preventing the formation of aflatoxins in several agricultural substrates, proving excellent results in terms of both efficiency and product quality.

More information on aflatoxins

https://www.efsa.europa.eu/en/topics/topic/aflatoxins-food

FOOD

Disinfestation and Sanitisation equipment “SANICROP+”

Patented RF equipment for the disinfestation and sanitisation of agricultural commodities

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SUCCESS STORIES

Mulino Marello

Mulino Marello chooses Stalam for the drying and disinfestation of cereals

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L'articolo How to avoid aflatoxin contamination in crops? proviene da Stalam.

In agriculture moulds are a persistent and significant problem, as they are the cause of dangerous mycotoxins, as aflatoxins; they usually grow in commodities such as tree nuts, peanuts, rice, corn, sorghum, wheat, millet, sesame seeds, sunflower seeds, cotton seeds, chili peppers and in a many varieties of spices.

When molds start contaminating the commodity, powdery spores may develop on the surface of the product. The contamination finds its ideal environment in high ambient temperatures, drought stress and insect injury.

So, the best approach to mitigate the problem of moulds is prevention since, once the commodity is heavily infested by them, there is no feasible solution to remove them.

Before storage, crops should be properly dried and sanitised to prevent the development of moulds.

The Radio Frequency technology has proven to be very effective when used for pre-storage sanitisation of agricultural commodities. It can be used simply as a moisture reduction (drying) method but also to disinfest (pest elimination) and sanitise (microbe load reduction) a large range of substrates (cereals, grains, pulses, nuts, herbs, spices, etc.).

Benefits of Radio Frequency process:

• 3 to 10 times faster compared to conventional treatments
• Completely chemicals-free 
• Ensures 100% mortality of even the most heat resistant pest species
• Achieves 2 to 3 log reduction of the t.b.c. within the commodity
• No deterioration of chemical and physical characteristics
• Energy saving technology

L'articolo Sanitisation of agricultural commodities with RF technology proviene da Stalam.

The reader is certainly conversant with the technological problems related to the drying of textile fibres after dyeing (or any other wet treatment) – i.e. the problems related to the transition of the material from the wet state to the dry state – and is well aware of all the difficulties that interfere with the attainment of a well stabilized product, within which the equilibrium moisture is evenly distributed in the whole of the mass.

The reader is also fully conversant with the difficulties encountered in trying to maintain a satisfactory “hand” of the dried product and to reduce the tensions which are generated during heat treatment, mainly in wound yarns.

The above being stated, we wish to make it clear what we mean by “conditioned weight”. We mean that the material, once it has dried after being dyed, is of the same weight as before dyeing, that is, the dyed product is brought back to its former weight, without having been impoverished of the nourishing liquors, all such liquors being evenly distributed within the product mass in the correct ratio.

In other words, once it has dried, the material is expected to present the same weight and equilibrium conditions it had before it was dyed. A certain amount of soaking liquor at the end of the dyeing process – though at different rates consistently with the different nature of the fibres – can be removed at a modest cost by means of mechanical hydroextraction operations, such as for instance suction, squeezing or centrifugation. In all such instances, a greater moisture content would be noticed in the fibres that are closer to the surface wherefrom water is being expelled. Obviously not all water can be removed mechanically – the remainder could only be removed by changing the state of water, i.e. by turning water into steam.

For turning water into steam, the water contained in the wet product mass should be given the energy required for the change of state.

Since water, as stated previously, resides in the mass unevenly, owing to the mechanical stresses brought about by the initial hydroextraction processes, it would as well be necessary that such energy be given in amounts proportional to the specific water content in each individual part of the mass.

It would also be desirable that the evaporation phenomenon would occur without causing tensions on the fibre, but on the contrary that there would occur a steaming action within the product which would cause the fibres to swell, thus emphasizing the “colour” effect and generally improving the handle.

The heating through RF replies to these necessities

As it is already known, the use of electromagnetic RF fields allows the endogenous heating of lots of products thanks to the phenomena of electromagnetic energy dissipation.

It is also known that, once the features of the oscillating field are fixed, the entity of the endogenous heating mainly depends on a quantity, characteristic of the materials, called “loss factor”.

Especially even when there are small amounts of electrolytes dissolved in the water, it has a high loss factor so that when a moist product is subjected to the action of an electromagnetic RF field a quick heating of the same is obtained and so its removal from the product in the form of steam.

Compared with the classic solutions, the drying of textile fibres by means of RF has a series of specific advantages which together with those noted and already emphasised related to RF treatments generally, contribute an absolute superiority to this kind of process both in qualitative and economic terms.

We will shortly explain which these advantages are.

The dissipation of the energy of the RF electromagnetic field occurs almost exclusively in the soaking liquor; the textile product is not involved in the phenomena.

As a matter of fact, the soaking liquor has a very high loss factor related to the substances of which all kinds of fibres are made, even if they are of natural, artificial or synthetic origin. So the fibres are only marginally concerned by the heating of the endogenous type, with obvious advantages both in terms of the product’s quality and in terms of the processes’ energetic efficiency: the fibres are not subjected to harmful and useless overheating and the energy of the RF field is Xively used for the evaporation of the soaking water.

The high energetic yield is translated into immediate economic advantages resulting still more clearly in situations in which the conventional drying techniques appear to be scarcely efficient and that is to say when the water must be removed from materials with a very low moisture content. The most important feature of RF is its ability of acting Xively on the moisture content without useless losses in the surrounding environment.

The energy dissipation of the electromagnetic field by unit of volume of the treated material is higher where there is more soaking liquor.

As a matter of fact in the parts of the product containing more water, the local loss factor is correspondently higher and so also the capacity of dissipating electromagnetic energy in the form of heat.

This means that when a certain amount of product with uneven moisture content (between piece and piece, or inside the pieces themselves) is subjected to a RF treatment (for instance yarns in packages, hanks or other), the areas with a higher moisture content become the centre of a higher endogenous heat generation and so of liquor evaporation, so that the treatment produces a levelling effect of the moisture content.

At the end of the operation, having given in a Xive way the correct amount of energy to the different parts of the material, the excess of liquor will be eliminated leaving the material itself in a perfectly conditioned state.

L'articolo How to dry textile fibres correctly? proviene da Stalam.

Yeasts and molds are a major problem in the storage, processing and marketing of mushrooms, even if grown and stored inside a carefully controlled environment and conditions. These pathogens can easily spread bacterial diseases through the crop and generate high product loss. STALAM has combined its expertise in the pasteurisation of packaged fresh food products and in the disinfestation of dry agricultural commodities to develop the first Radio Frequency (RF) unit specifically designed for the pasteurisation of dried mushrooms in bulk.

In the STALAM RF pasteurisation system the microbial and enzymatic inactivation is achieved by means of a gentle dielectric heating treatment which combines synergistically thermal and cell membrane electroporation effects. This dual action of the RF field is lethal for the biological entities contaminating the food substrate, thus providing a valuable sanitation and shelf-life extension technique. Significant microbe load reductions can thus be achieved without using chemical preservatives or applying drastic thermal treatments which would have detrimental effects on the physical and sensorial characteristics (especially the flavour) of the product. The treatment consists in a rapid exposure of the mushrooms to an electromagnetic field generated between a couple of electrodes inverting their polarity at 27.12 MHz frequency, inside a temperature-controlled process tunnel. The tunnel temperature, the RF voltage between electrodes and the speed of the belt carrying the mushrooms between the electrodes are the process parameters to be set according to the microbial inactivation level required.

The treatment ensures that the product is brought quickly and uniformly to temperatures necessary for the required level of microbial inactivation, but not so high to alter the mushrooms taste and flavour. The entire pasteurisation process takes just a few minutes. 

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L'articolo Pathogens in dried mushrooms: RF technology is the solution. proviene da Stalam.

Stalam has developed a Radio Frequency dryer that allows to optimize the continuous washing-drying cycle of natural latex or polyurethane mattresses after washing and mechanical hydroextraction. The equipment is mostly dedicated to industrial laundries serving hospitals, barracks, rest homes, hotels etc… for their washing and sanitisation requirements. The process is quick and uniform (up to 10 mattresses per hour), speeding up delivery times to customers and ensuring a rapid pay-back period.

Discover more…

L'articolo Stalam introduces a new RF dryer for industrial laundries proviene da Stalam.

The Dunlop process: how to improve efficiency and quality in the production of latex foam?

Natural latex is a liquid compound harvested from the rubber tree (Hevea Brasiliensis) whose major cultivations are located in Southeast Asia. Once collected from the tree, the liquid is mixed with ammonia and TMTD/ZnO to better preserve its properties. This standardized LA-latex (low-ammonia latex) is used as raw material to produce balloons, gloves, sanitary articles etc. but also latex foam goods such as mattress cores and pillows. 

DUNLOP process: the origins

In 1887, John Boyd Dunlop (1840–1921), born in Scotland, invented the first inflatable tire for his son’s tricycle based on the thermal vulcanization of natural rubber and then patented it on December 7, 1888. Two years later, however, his patent was officially invalidated because another Scottish inventor, Robert William Thomson (1822-1873), had already patented the same technology in Great Britain, France (1846) and in the USA (1847). Nevertheless, the process was named after Dunlop and became the main system for vulcanizing rubber and latex foam products.

Technologies become industrial standards: DUNLOP and TALALAY methods

There are currently two standard methods for the production of latex foam items: the DUNLOP and the TALALAY processes. Invented in the late 1940, the TALALAY process takes longer time and is more complex than the DUNLOP process. This system is used just by few producers worldwide and has just a small market share. The basic raw materials in both systems are natural latex (NL) or SBR-latex (styrene-butadiene-rubber) or blends of both.

The DUNLOP method

If pure natural latex is used, the latex “milk” is mixed with the required chemicals. Once matured, the compound is foamed up with a mechanical mixer (SBR-latex can be foamed up without maturing) and filled into metal molds. A gelling agent is added to the mixture, to generate a fast reaction that stabilizes the foam structure. The molds are then placed in a steam oven or tunnel to vulcanize the cores.  Since foamed products are good thermal insulators, the molds are fitted with a large number of pins to transfer the heat into the foam itself. Once vulcanized, the pillow or mattress core is stripped, washed, dried and is finally ready for sale.

The TALALAY method

In the TALALAY process three more phases are necessary before the vulcanization step:

– the mold is only filled by 40-60%. Then it is closed and air is pumped out to expand the foam to fill the entire volume of the mold;

– the foam is frozen to -20°C to stabilize the structure;

– CO2 is injected though a valve into the mold to gel the foam.

The rest of the process follows the same steps of the DUNLOP process, i.e. vulcanizing, stripping, washing and drying.

The traditional Dunlop vulcanisation process uses steam as the heating mean to activate the cross-linking reactions of polymer chains. Foam, having plenty of tiny air bubbles within, is by nature a poor thermal conductor and therefore letting heat soak into thick mattress core or pillow molds is a slow and inefficient process. Costly and heavy metal molds fitted with many metal pins are actually used in the attempt to speed up the process, but it still remains time- and energy-consuming.

During the decades some chemicals have been replaced to improve the overall process, but the basic process, ie. the cross-linking of rubber molecules with sulphur, hasn’t changed up to date, along with the typical drawbacks of conventional heat transfer methods.

Slow process, high energy losses. Is there a solution? Yes, there is!

The “new Dunlop process”

The Radio Frequency technology overcomes the main inconveniences of the traditional Dunlop process because it does not rely on heat transfer, so even thick, shaped and dense latex foam items (mattress cores, anatomic pillows, etc.) can be heated up and vulcanized quickly: actually, Radio Frequency is instantly absorbed in a controlled amount (adjusted as required by the machine itself) by the water contained in the foam, uniformly throughout its volume. Thus, heating of the foam and its full vulcanization just take a few minutes, in the center as on the surface.

The RF vulcanization machines are therefore much smaller (shorter) compared to the conventional carousels or tunnels working with steam having the same hourly throughput, and the energy consumption can be cut as much as 50%.

Molds can be made of light and inexpensive composite materials that allow weight reduction of over 60% compared to traditional metal molds: the reduced mold mass contributes significantly to the lower energy consumption. Moreover, appropriate mold materials allow for an easy and quick stripping of the vulcanized items. Last but not least, mold design is more flexible, not being bound to the presence of pins.

It should also be mentioned that the Radio Frequency technology can be successfully used even for the production of continuous latex foam sheets (LPC , topper or even a true mattress) up to 12 cm thickness and more, in a much shorter time and reducing significantly the energy consumption, considering also that the traditional steam vulcanization of sheets thicker than about 5 cm is an almost impossible task due to the lack of heat penetration in the absence of metal pins.

What about latex foam drying after vulcanization, washing and squeezing?

The same technical reasons that make Radio Frequency more efficient and cost-effective compared to the traditional steam-based vulcanization methods, can be applied to the final drying phase of latex foam products after washing and squeezing.

The benefits of using Radio Frequency dryers rather than steam-heated dryers can be summarized as follows:

• fast and uniform drying: about 20 minutes are sufficient to dry even thick and dense mattress cores below 1% residual moisture content, without any wet spots; also shaped products like pillows and anatomic seats dry perfectly uniformly in thicker parts as in thinner portions;
• no yellowing of the product surface, due to low temperature in the drying tunnel (RF heats the product core, not its external surface);
• short conditioning time, so the product can be packaged for shipment quickly after drying without any risk of moulding on the way to customers;
• significant reduction of drying equipment footprint, thanks to the short process time;
• energy-efficient in-line process, reduced drying and product handling costs;
• reduced carbon foot-print, being an electro-thermal technology.

It can therefore be said that the Radio Frequency technology is a real revolution in the latex foam industry, both in the vulcanization and the drying phases, providing latex foam producers with huge benefits in terms of production efficiency, cost saving and product quality.

(the picture is a courtesy of Latexfoam Technology B.V.)

L'articolo The Dunlop process: how to improve efficiency and quality in the production of latex foam? proviene da Stalam.

Insect pest infestation (moths, beetles, weevils etc.)  is a major problem in the storage, processing and marketing of cereals such as rice, corn, buckwheat, sorghum, etc.

Typically, chemical fumigants X methyl bromide) are – or were – used for postharvest pest control but regulatory issues, environmental concerns, potential health hazards, reduced acceptance by consumers and the increase of the organic market have pressed the industry to develop non-chemical treatment alternatives. Such alternative methods include: ionising radiation (effective but requiring substantial investment to establish irradiation facilities and protection systems; additionally there is great public concern over the use of ionising radiation in the food chain), controlled atmosphere treatments (not applicable to all commodities and requiring long treatment times), cold treatments (applicable in some cases but lengthy and very expensive) and heat treatments.

Various heat treatment techniques, alone or in combination with cold or controlled storage conditions, have been investigated.

Conventional heating methods use forced hot air (sometimes in combination with steam) or hot water to bring pests temperature to a lethal level. Conventional heating is simple and easy to control, however it is an intrinsically slow process and it is well known that prolonged heating can be detrimental to quality of food products. Actually, in many cases it has been found that an effective pest control process by conventional heating is incompatible with the commodity’s final quality in terms of physical, chemical and nutritional characteristics.

Direct heating methods by electromagnetic waves, instead, allow for rapid and uniform sanitisation of many agricultural commodities. Unlike conventional thermal techniques, where heat is transferred to the product through its surface from an external heat source by conduction, convection or irradiation, a Radio Frequency field generates heat directly inside the entire product mass. In this way, pests are heated rapidly (generally to 55-70° C in 3-5 min), ensuring the complete mortality of adult insects and larvae, along with a TCB reduction, in just a few minutes.

RF sanitisation is organic (chemicals-free) and the process cost is low, thanks to the short residence time and the low power consumption.

Stalam has introduced SANICROP+, a RF equipment especially designed for the large-scale disinfestation of dry agricultural commodities. Read more…

L'articolo Pests in cereals, what kind of remediation? proviene da Stalam.

When a purchasing decision has to be taken among different equipment which can perform the same operation, the most important comparison criteria to be taken into consideration are:

• the quality (ie. the added value) of the products obtained from each equipment;
• the overall costs deriving from the use of each equipment.

These criteria have to be evaluated when comparing equipment performing the same operation by means of similar technologies, but they are even more important when comparing equipment which apply totally different technologies.

For instance, when we consider the drying of fibres and yarns after dyeing or any other wet treatment, different technologies are available for this purpose: there are “conventional” methods, where the textile product is heated / dried by means of hot air blown onto or through it, or alternatively, the “radio frequency” technique, where the textile product is heated / dried in an endogenous (volumetric) way by means of a suitably generated electromagnetic field.

Let us analyse in more details the main features and the practical implications of various conventional drying methods.

Drying rooms – drying cabinets

These are the simplest and oldest drying systems, which play nowadays a marginal role in textile mills worldwide, due to some major drawbacks, namely:

• extremely long and inconsistent drying times;
• poor control of the residual moisture content within the product;
• too much space / volume required to obtain a reasonable product output;
• very low energetic efficiency.

As a logical consequence, drying rooms / cabinets are used very rarely, mainly for the drying of very small dye-batches or of extremely delicate products that cannot stand the thermal and/or mechanical stresses to which they would be submitted in other drying equipment.

For the above reason, we will not consider anymore this drying method in the rest of these notes.

Chamber dryers – semi-rapid dryers

These dryers became – and still are – rather popular, thanks to the reasonably low capital investment required and to the overall acceptable level of performance in terms of drying times, running costs and quality of the dried products.

On the other hand, the majority of the end-users report several drawbacks which make chamber and semi-rapid dryers far from being an ideal solution within the modern yarn dye-houses.

The most common inconveniences reported include:

• long drying times and correspondingly high energy consumption are found with dense (tightly wound or highly compressed) packages, with fine count yarns and with packages having large diameter;
• longer time is also required in order to dry bleached white and light shades without yellowing problems (due to the need to keep low the air temperature);
• accurate loading of the packages on the carriers / trolleys is necessary to avoid preferential air paths which cause severe loss of efficiency and very long drying times;
• the external ambient conditions (air temperature, humidity) strongly affect the drying efficiency, thus causing noticeable inconsistency of the drying times from batch to batch;
• as the drying time is affected by too many variables which cannot be kept under proper control, it is difficult to predict and set accordingly the end of drying cycle of each batch, therefore under- or severe over-drying occur rather frequently;
• the surface of packages becomes dirty (this phenomenon is very evident with white and light shades) due to the large volume of external air passing through the yarn – in spite of air filtering systems, which require frequent and accurate cleaning operations;
• uneven residual moisture distribution within the same batch, from package to package, is found depending on their position in the carrier;
• packages having different diameters or winding densities are dried unevenly;
• the residual moisture content within each package is not evenly distributed;
• overdrying of the whole batch is necessary to ensure the absence of wet packages or wet spots within the packages;
• rather long conditioning time of the yarn is required after drying;
• some displacement and evaporation of finishing chemicals and softeners occur;
• there is no possibility to exploit the nominal drying capacity of the machine when smaller, variable size dye-lots have to be processed. The main problem is that very often small dye-lots cannot be loaded together (due to colour contamination problems and/or to the difference in the drying time needed for each lot); furthermore, partial loads solution lead to a correspondingly higher drying cost per kg of product;
• loading and unloading operations of the carriers / trolleys are quite labour intensive, unless full automation is available (but it is very expensive and little flexible);
• there is no possibility to use the dryer for different products other than yarn packages (this is a major inconvenience for all dye-houses where textile products in various forms such as loose fibres, hanks, tops etc. are processed).

Due to the above reasons, we can say that only in the case of rather soft, small and regularly shaped yarn packages, especially made of synthetic or blended yarns in coarse counts, dyed in medium size lots, the chamber and semi-rapid dryers are a viable and economically convenient solution within a package dyehouse, ensuring an acceptable compromise between quality and cost.

On the other hand, in case of tightly wound or compressed yarn packages, or having large diameter, or not having consistent weight or winding, of fine count or highly hydrophilic yarns, in various different batch sizes and colours, especially white and pastel shades, delicate yarns etc. this drying method is not the recommended solution.

Rapid dryers – pressurised dryers

Many yarn dyeing machinery manufacturers have included in their production range the so called rapid dryers or pressurised dryers, such that the dye-carriers bearing the soaking-wet yarn packages coming out from the dyeing vessels can be placed directly inside drying vessels – having the same shape and size – where the water extraction and drying processes are carried out as a single operation.

Actually, the main advantage of these dryers is the low labour cost deriving from the extraction of the unbound moisture followed by drying being carried out in the same equipment, this requiring only a single, fast and very simple loading operation.

Another advantage, especially if compared to chamber and semi-rapid type dryers, is the much shorter drying time required for various products, which normally does not exceed a couple of hours  – at least with the most recent and efficient rapid / pressure dryers – provided the cooling water temperature fed to the moisture condensation unit of the equipment is low enough (which is not always the case, especially in countries having a hot climate).

On the other hand, rapid / pressure dryers have several technical and economical drawbacks: we can say these equipment are subjected to, and actually exasperate – due to the very strong air flow and to the high temperature gradients within the packages – all problems generally related to drying methods by hot air convection, as previously described for chamber and semi-rapid dryers (with the only exception that in this case the air circulation is carried out in a closed circuit, so that the external air humidity and dirtiness do not affect the process).

Moreover, in addition to the problems already mentioned, further serious inconveniences are specific to rapid / pressure dryers, namely:

• due to the high air temperature and pressure, the yarn is thermally and mechanically stressed, so that its physical properties such as strength, elasticity, softness and hand are negatively affected;
• due to the same reasons, yellowing, discoloration, colour migration are quite common phenomena;
• again, the strong air flow generates a lot of hairiness in the yarn, which causes various inconveniences when the yarn is woven or knitted;
• some yarn hairs accumulate in the equipment during the drying process, and this makes it necessary to carry out frequent cleaning / washing operations of the vessel, especially when light shades have to be dried after dark shades (to avoid cleaning after every drying cycle, batch scheduling / colour sequencing during the day – starting from the lighter shades – is recommended, but this is not always feasible);
• the functioning of the equipment is very noisy and a lot of heat is released to the ambient.

Notwithstanding the above drawbacks, the main disadvantage of rapid / pressure dryers is the very high overall utilities’ cost.

In more details, the electricity, steam and cooling water consumption of rapid / pressure dryers is very high for two main reasons: the mechanical hydroextraction operation, which is the cheapest way to eliminate the large amount of unbound water retained by the product when coming out from the dyeing vessel, prior to the drying process, is not efficiently performed by the vacuum / pressure treatment which the product undergoes and consequently a very large amount of water has yet to be eliminated by evaporation; furthermore, when the drying process is approaching to the end (ie. when the final moisture which is strongly bound to the core of the fibres, has to be eliminated), the heat transfer efficiency from the air to the residual moisture, as well as the efficiency of the moisture condensation system, become very low, therefore large amounts of mechanical and thermal energy and of cooling water have to be wasted to eliminate just a little remaining amount of moisture.

The Radio Frequency drying technology

As an obvious consequence of what we described above, in the last three decades most textile fibres and yarns dyers adopted the radio frequency drying technology within their operations, as this method brilliantly solves all the problems related, directly or indirectly, to heat transmission phenomena, ie. to all conventional drying equipment.

We mention herebelow the main advantages of the RF technology in the drying of yarn packages and, more generally, of all textile substrates:

• very short and consistent drying times (generally from 15 to 50 minutes, depending on the moisture content to be evaporated) with all products, irrespective of product size, density, yarn count, shade, etc.;
• perfectly controlled and uniform drying process, leaving very even residual (regain) moisture distribution within the packages, from package to package, from batch to batch, thus eliminating the need of long yarn conditioning time after drying;
• full flexibility irrespective of the product type (yarn packages, hanks, tops, loose fibres, etc.);
• any product or batch size can be dried with the same high efficiency, maintaining the same unit drying cost;
• high energetic efficiency (about 65-70% of the total energy consumption of the equipment is exploited for the drying process itself) with no heat dispersions to the ambient;
• no influence of external ambient conditions (humidity, temperature) on the drying performance / time;
• just-in-time and instantaneous operation, no pre-heating required;
• no yellowing, no discoloration, no contamination between different colours;
• no need for batch scheduling / colour sequencing / frequent dryer cleaning;
• no hairiness generated in the yarn;
• no dirtiness on the surface of the yarn due to air pollution;
• negligible displacement and evaporation of finishing chemicals;
• better physical and mechanical properties of the yarn, thanks to short drying time, low drying temperature and no mechanical stresses;
• in many cases the rewinding operation after drying can be avoided.

From the economical and operational points of view, one may argue that in comparison with the single and very simple handling operation required by the rapid / pressurised dryer to process an entire dye-lot, RF drying implies two separate, labour intensive operations: the first one for loading and unloading the centrifugal hydroextractor, the second one to feed the packages to the RF dryer.

However, it should be noted that in spite of the costs due to additional handling and to the hydroextraction operation, the practical experience of several end-users shows that even where the hourly labour wages are quite high X in western Europe or in the USA) total costs of RF drying are still significantly lower than those of rapid / pressure drying.

Conclusions

The main advantage of using rapid / pressure dryers is the ease of operation and, consequently, the very low labour cost. However, total utility costs are the highest among various drying methods – even if heat recovery systems are duly installed and utilised – and, even considering the high hourly wages paid in western European countries and USA, such high utility costs are not compensated by the reduced manpower requirements. Therefore, this drying method remains, eventually, the most expensive one and also the one which gives, in general, the poorest quality level in the dried products.

From the technological point of view, the main difference between rapid / pressure dryers and chamber / semi-rapid dryers is that in the latter the hot air is pushed through the product at a much lower pressure / speed, so that the drying times are longer but a lot of (expensive) mechanical / electrical energy can be saved.

On the other hand, the weak air flow through the product cannot perform the required mechanical hydroextraction operation, which has therefore to be accomplished separately in advance, exactly in the same way as when using RF dryers. It means that, even though utility costs are quite lower (not far from the ones achieved with RF dryers), the main advantage of using rapid / pressure dryers is totally lost when using chamber / semi-rapid dryers. Moreover, most of the problems related to the poor quality of the dried products and to the intrinsic lack of flexibility of all conventional drying methods by heat convection are still there, even if not as dramatically as with the rapid / pressure dryers.

On the contrary, RF drying, while ensuring the lowest possible overall running costs compared to all conventional drying methods (even including the most economical, new generation chamber / semi-rapid dryers) is the only technology which allows the attainment of the highest quality standards and the highest degree of operational flexibility, which, in their turn, result in an increase of the overall profitability within the dyeing – drying operations of all textile mills.

L'articolo Textile dryers, what’s the best choice? proviene da Stalam.

The choice, implementation and monitoring of freezing and defrosting methods are of paramount importance in the quality control of raw food materials and processed products.

Nevertheless, the defrosting process of irregular product shapes, bone-in meat, fatty pieces etc. is a challenging task for most technologies, including the ones that use electromagnetic fields.

Based on 40 years’ experience in RF technology, Stalam designed a defrosting equipment that addresses the specific problems related to this kind of products, in order to achieve a tempering process as uniform as possible.

How can RF solve the energy transfer related to irregular-shaped products?

The energy of radio frequency and microwave fields is absorbed by the different substrates as a consequence of the “dielectric losses” occurring inside them. Each material has its own “dielectric loss factor” which depends upon its chemical, physical and morphological characteristics and has different values in relation to said characteristics and to the frequency the material is submitted to.

At higher frequencies (such as microwaves), the differences among the loss factors of the various products (or of the various phases / materials forming the product) are usually much smaller than the ones at lower frequencies, typical of RF waves. It means that radio frequencies are much more Xive in heating products with different chemical, physical, morphological properties, thus making easier to control the thermal treatment of different materials. This characteristic is extremely useful in drying and defrosting applications: as the dielectric loss factor of water (especially if it contains ionic species, even in very small quantity) is much higher than the one of all the possible substrates in which it can be found (textile fibres, food products, wood, etc.), the radio frequency can be absorbed by a material containing water in a very Xive way, thus allowing a process which will be extremely quick, effective and will deliver outstanding quality results, considering that the substrate itself will be involved in the treatment (energy transfer) in an indirect, and thus marginal, way.

This Xivity cannot be obtained at higher frequencies (such as MW) and therefore, most of the meat and fish processors nowadays prefer the radiofrequency technology to defrost their frozen raw materials.

Stalam RF defrosters are widely used by customers for the defrosting of: baby pig halves, bacon, pork ribs, pork legs and many other irregular of fatty and bone-in products.

L'articolo How to achieve a uniform defrosting of irregular-shaped meat and fish products with fat and bones? proviene da Stalam.

In baking ovens, after the “development” and the actual “baking” phases, at least one third of the oven length (the final section) is dedicated to “colouring and drying” the product.
As the product loses moisture, its thermal conductivity falls and evaporation slows. The evaporation is further compromised by the crust formation that acts both as a heat and mass transfer barrier.
The removal of the final excess moisture from the product is therefore a difficult task: the conventional oven finds it hard to transfer heat to the centre without the risk of over-colouring, which will result in a dark and out of specification product. Over-baking (browning) has also been recognised as one of the causes of Acrylamide formation, a suspected carcinogenic substance formed during cooking, baking and frying of carbohydrate-rich food products.
In July 2017, European Member State representatives voted in favour of a European Commission proposal to make it mandatory for food business operators to reduce the presence of acrylamide.
The new European acrylamide legislation 2017/2158 came into effect on April 11, 2018.
This is the stage where RF post-baking is of greatest value.
The RF electromagnetic field, due to its ability to transfer energy to the product volumetrically and Xively according to the moisture location, will overcome the low thermal conductivity and the crust heat barrier and directly dry the (wetter) centre of the product without affecting the desired colour.
Practically, combining a traditional oven with a post-baking RF equipment, it is possible to manage the baking process as follows: development, baking and colouring of the product will take place in the traditional oven, while the last phase of drying will take place in the RF equipment, with noticeable advantages in terms of energy saving, process time and final product quality. 

L'articolo How to prevent the acrylamide formation during the baking process? proviene da Stalam.