Efficient dehumidification of tool moulds allows for condensation water free production throughout the whole year
Moulded products - whether injected, blown or vacuum-formed - must be cooled in the cavity of the tool mould using chilled water. However, lowering the chilled water temperature below the dew point of the ambient air causes condensation on the mould surface and involves additional requirements concerning the process.
Moulded products – whether injected, blown or vacuum-formed – must be cooled in the cavity of the tool mould using chilled water. However, lowering the chilled water temperature below the dew point of the ambient air causes condensation on the mould surface and involves additional requirements concerning the process. So moisture can lead to errors on the moulded product and sustainably damage the mould itself or drastically reduce its service life. On the other hand, an increase of the chilled water temperature prolongs the cooling time, slows down the manufacturing process and lowers the productivity. Moreover, the crystallisation rate in the moulded plastic increases in many cases so that, in turn, the product quality suffers. Air conditioning of plants may help, but do not solve the problem. That is why FarragTech GmbH has developed the Mould Area Protection (MAP) systems in order to dehumidify tool moulds and to ensure condensation water free production throughout the whole year, even under tropical conditions.
The moulding process and the cooling time, which usually accounts for the biggest part of the entire cycle time, are expensive and important sections of production. The chilled water used for this purpose should not be cooler than 6° C, because in case of lower temperatures, antifreeze agents must be added in order to prevent freezing of the evaporator in the cold water cooler, which, however, would clearly deteriorate heat withdraw. Up to this neuralgic point, however, a decrease of the chilled water temperature by 1K causes a production increase of one percent and makes thus sense. An unwanted side effect of the cooling using water, the temperature of which is below the dew point of the ambient air, however, is the formation of condensed water in the mould. Simple air conditioning of the plant alone is often not sufficient to prevent that effect, the more so as profit is diminished due to high operating costs.
In order to keep the mould surface free from condensed water, there are dehumidification systems which generate the drying air using an desiccant dryer. By means of this, a very low dew point can be achieved, which is not necessary, however, and is connected with higher effort, because the desiccant must then be regularly exchanged. Due to the more complicated installation, higher costs occur in case of a defect, and an additional energy requirement is necessary for the regeneration of the desiccant. That is why FarragTech for its MAP systems uses simple (ambient) air dryers, which – combined with air conditioning of the plant – is able to diminish heat emitted by the production machines very efficiently and with clearly less expenditure of energy.
Cooling ambient air in two steps
To do so, the moulding area of the machine is isolated from the ambient air and supplied with filtered, dry air from the MAP. This enables a continuous use of chilled water up to a temperature of 6° C without condensation on the mould surface happening. Via a filter, ambient air is sucked and cooled in two steps: at first via a water-cooled heat exchanger, after that in the heat exchanger of the integrated refrigeration circuit, where the air is lowered to a temperature of approx. 3° C by means of the refrigerant R407C. The chilled water, which also serves to mould cooling, is used for pre-cooling of the sucked ambient air during the process. The moisture, which is eliminated as a result of condensation, is collected in a trough and conveyed out of the device using a pump.
The heat out of the evaporator is led with high temperature via the compressor into the condenser. When the pre-cooled ambient air passes the condenser, it heats up to 25° C again and is then blown via a piping system into an isolated cabin surrounding the shape of the production machine. Here the dry, filtered air spreads and finally escapes through gaps and openings which are designed for removing the product out of the machine area. Depending on which course of action is taken, enshroudings or holes in the isolation can become necessary. This must be taken into consideration during the design.
Payback period of MAP devices is usually below one year
Depending on how large the enshrouding of the mould cabins is and how many machines shall be operated using an MAP device, the MAP must also be dimensioned accordingly. Therefore, depending on the relevant machine size and quantity, there are four dryers different in size, via which a stand-alone production machine or those integrated in a central system can be provided. In order to not impede the change of mould, an inspection, or a repair of the machine, the enshrouding has to be adjusted in such a way that it allows for easy access. A pressure switch monitors the pressure drop after the filter mat and alarms the operator should the filter be saturated and cleaning be required. This takes about 15 minutes, because the washable filter mat can be removed from the device with just two motions.
Sometimes a combination with the Internal Air Cooling System (IACS) from FarragTech makes sense, because only cooling via the mould through cold water as possible and good internal cooling can provide optimal, efficient results with the blowing process. Particularly with injection moulding, but also with other processes, cooling is possible only through the mould, anyway, which is why it should take place as sufficiently as possible to not give away any potential. The payback period varies depending on the cost of products to be manufactured and on rejects due to moisture. In some regions with high air humidity, such as the tropics, production without MAP is not possible at all. In other countries, production can be carried out well in the winter, but there are problems in the summer so that the temperature of the chilled water must be increased in order to ensure trouble-free production. That slows down the process and costs money accordingly. As a general rule, a payback period of less than one year can be assumed.
FarragTech was originally founded in 1991 as FASTI by Rainer Farrag, the inventor of the first compressed air dryer, and by Bernhard Stipsits. After both managing directors decided to go separate ways in 2002, Rainer Farrag founded the FarragTech GmbH effective from 1st June 2005. The company specialises in peripheral devices for further processing of plastic resin, increasing the quality of products as well as the productivity of the processing machines. The portfolio of the manufacturer includes resin dryers which are a further development of the compressed air dryer invented by Rainer Farrag, as well as systems for internal mould cooling, various loader and atmospheric air drying devices for mould area protection, of which were also developed by FarragTech. The company currently employs eight staff in its Wolfurt headquarters in Austria. Production takes place in Slovenia, with marketing carried out worldwide.