Cooling machines and processes
Grows the importance of refrigeration
The solution proposed in this article represents an important advance in the field of cooling systems applied to the industry of manufacturing and processing of plastics and rubber. Frigel Firenze to created an innovative series of machines for the realization of the cooling system Ecodry System
Even though the different types of transformation of plastics may differ from the other, a common in the cooling system principle can be applied. In fact, injection molding, as other types of extrusion and compression molding possess similar cooling requirements:
I. cooling machine, which includes all the parties that should be cool to ensure the proper functioning of the same if production machine.
II. cooling process, which includes only those parts that must be cool at a controlled temperature for the solidification of plastics once processed.
I. cooling machine
Most of the machines for plastics processing are hydraulic drive. A part of the mechanical work done by the electric pump is transferred to the oil in the form of heat, causing the temperature to increase. Adequate oil operating temperature ranges between 45 ° and 50 ° C, so we need a cooling system. Production machines are usually fitted with a heat exchanger agua-aceite appropriate dimensions and a thermostatic valve that controls the flow of cooling water by the permutador. The importance of this valve is to maintain the temperature of the oil at the levels indicated by the manufacturer of the machine.
Too cold, i.e. highly viscous oil involves a high consumption of energy by the engine's pump, which shortens its useful life. On the other hand a too hot oil, i.e. little viscous, leads to leaks in the boards and hoops tóricos and long-term reduction in your life.
Other points which require cooling on an ongoing basis, as the area of plasticizing, the twin-screw, etc., as well as water or oil temperature controller, are also included in the cooling of the machine.
Figure 1
The total requirement for cooling of machines for plastics processing Department, can vary depending on the type of process; However, we can estimate that it represents between 50 and 90 per cent of the total cooling demand.
To sum up the basic aspects of cooling machine, we can note that:
-Is the most important thermal burden (50 / 90 per cent) of the total required for the cooling system
-Does not have sense to use water cooled for cooling, the required temperature is higher than 35 ° C; It is sufficient to use water at room temperature for cooling.
-There is a strict control of the temperature for cooling
-No need to customize the cooling system for each user, so a central cooling plant is the ideal solution for machine cooling.
Solutions
Traditional solutions:
-Water discarded: this solution belongs to the past, not only for technical reasons (embedding problem) and severe requirements of filtering, but also by legal provisions that limit ever more drinking water from natural sources (springs, rivers, Lakes). In some way, or in some cases, there may be limited availability of water. In addition, growing awareness of the environmental protection discriminates quite rightly, this type of cooling due to thermal pollution that results in the course of the water.
- Cooling tower: this system has been used for a long time. However installation problems, together with the high costs of maintenance of a "circle open", have led to systematic replacement for industrial water closed circuit coolers equipped with refrigeration compressors. In fact, some of the most serious problems associated with cooling tower, as problems of scaling, formation of seaweed, bacterial contamination and acid corrosion, must deal with continuous maintenance and costly.
- Industrial refrigerator: water coolers and cooling plants, have been developed as a typical solutions to the problems of the above cooling systems. However, the use of compressors for refrigeration for the cooling of machines requires a high consumption of energy, which translates into high energy costs. In order to reduce energy costs, "ambient cooling systems" have been proposed recently as an alternative to save energy during the cold seasons. However, for technical reasons, industrial freezers must operate with a temperature of cooling water not exceeding 15 - 18 ° C, even when the necessary oil temperature is 40 to 50 ° C. This limits the possibility of saving energy in a period of extremely short year.
Figure 2
In addition, industrial water chillers and refrigeration plants are complex machines and require highly trained personnel to carry out the work of installation and maintenance.
The new solution
- Dry cooling system: provides the latest technology for air-water heat exchange. It consists of an extensive area of copper and aluminum fitted with fins and axial fans high speed of movement. These heat exchangers offer great reliability and a good function; they are able to maintain the water temperature a few degrees on the ambient temperature. The major technological development carried out in its construction, has allowed a significant reduction in its price. They are the perfect solution for cooling machine; working in a closed circuit, avoiding the consumption of water and the complicated work of maintenance characteristic of cooling towers; In addition, its power consumption represents one-eighth part of consumption of the industrial refrigerator with refrigeration compressors.
Only need a simple, cost-effective distribution facility, because the pipes not is isolate and do not require air due to its outdoor installation ducts. Finally the total absence of maintenance makes the dry cooler represents the most reliable solution in the long term. In table 1 is a schematic comparison of the above solutions.
Comparative exampleLet us look at the power consumption considering the case indicated in table 2. A 350-ton injection molding machine, needs of 15,000 to 17,000 Kcal/h. for his "machine cooling". The net saving of money that can be obtained using a dry cooler would be approximately 325,000 pesetas per year, with a period of depreciation of 4 months, without considering the minimal costs of installation and maintenance
II. cooling process
The cooling process is strictly and exclusively designed for the plastics industry, which is very different from the cooling machine.
In any type of production process (moulds, Calenders), cooling conditions are extremely important to achieve better quality and higher productivity of the process in itself same. In particular, the more acortemos the cooling time, more will increase productivity. Similarly, a correct cooling improves the quality of the product, reduces waste and optimize the overall effectiveness of the production process.
Therefore, it is clear that, depending on the raw material that is processed, the manufactured article and the conditions of production, each process in particular has its own set of parameters optimized for the cooling of water (temperature, pressure, speed of movement), which differ from other processes under way.
The second basic aspect of the cooling of process is the possibility of repeating the optimized number of parameters of cooling when manufactured a same article. It makes no sense find optimized cooling conditions to achieve the best results, if the system is not able to maintain its constant and exact values.
Summarize the key aspects of the cooling of process, we can point out:
Solutions
Traditional solution
The only solution available to date was the water cooler industrial of great capacity with cooling compressors. These plants are composed of a central unit for cooling generally with several compressors, which distributed water cooled down all the machines of production through a unique distribution circuit. Therefore, cold water is supplied to the lowest temperature required between all users. All processes that need less cooling only can be controlled by reducing the flow of chilled water (fluxómetro).
The reduction in the level of flow of chilled water through the process, makes the temperature of the water have a thermal difference between the input and output, implying an uneven temperature distribution in the metal surface that is in contact with the plastic.
It is clear that this type of solution can never satisfy the requirement of cooling of the above mentioned process. A centralized cooling plant presents the following disadvantages:
The new solution
frigel firenzecompany, represented in Spain by Alimatic, has created a series of machines for the realization of a cooling system, which has been baptized with the name ecodry system.
It's a refrigerator of ultra-compact process. As it has been pointed out, the solution for the cooling of process should provide an adaptable cooling system the user to cool this particular process independently of the others. Until now this solution was impossible to practice owing to the dimensions of the industrial coolers, the level of noise and annoying airflow produced by fans of the condenser.
Today, thanks to the technological development in the manufacturing of heat exchangers type plate for cooling and the microprocessor electronic control, is possible to have coolers of reliable Ultracompact process and high precision, with the following technical characteristics:
-Do not produce air flow, because they operate by condensation of water.
-Are of small dimensions, only one-fifth of the traditional large-capacity water cooler, so that they can be installed close to occupy little place.
-Provide a continuous temperature control to keep it accurate and consistent with a margin of maximum error of '' 11C. "
-They may provide the user a rate of flow of water that is twice that of traditional industrial coolers, which enables a perfect uniformity of temperature in the entire piece of work.
-They can be programmed by the same process through serial tickets machine, both to establish the temperature for process refrigerator alarm command, thus by eliminating full waste.
-Allows the automatic emptying of the circuit of the process, facilitating change of molds without the mixture of water and glycol leaks may occur.
-They are equipped with an automatic device for ambient cooling that makes operating the compressor only when the temperature of the water from the central plant is higher than the established. This allows a significant savings of money in the cooling process.
As mentioned earlier these process coolers are by condensation of water; This implies that the cooling - less than 40 ° C water - give the thermal load collected from users
In practice, each process refrigerator will give its own thermal load to the same central plant that cools down the machine, i.e. dry cooling system.
This type of cooling system consists of:
-A refrigerator of ultra-compact process of high precision, whose dimensions are put in place to the estimated production of the machine.
-A centralized plant of dry cooling to dissipate, with low-cost energy, so the heat produced by the machine in the process as the heat produced by the process coolers.
-A supply chain not isolated where circulates cooling water at room temperature.
Francisco Centelles
Alimatic Technical Director
| Table 1 | |||||||
| Solution point | Cooling tower | Industrial cooler | Dry cooler | ||||
| electricity consumption | under | very high | under | ||||
| water consumption | high | absent | absent | ||||
| cost of inverión | under | very high | medium | ||||
| cost of plant | under | very high | minimum | ||||
| maintenance | specialized and permanent | specialized and permanent | absent | Table 2 | |||
| 350 Ton injection molded. | Industrial water cooler | Dry cooler | |||||
| Cooling requirement | 15000-17000 Kcal. / h | 15000/17000 Kcal. / h | |||||
| Maximum required electric power | 8 kW. | 1.1 kW. | |||||
| Average energy absorbed * | 6.1 kW. | 0.8 kW. | |||||
| Price enfriam. per hour | 104, - pts/hour | 14-pts/hour | |||||
| Cost enfriam. per year base 3600 hs. work/year | 374.400,-PTS./Año | 50,400,-pts/year | |||||
| * Calculations based on temperature environment of North Italy Cost of kW./h.:17,- |
Optimization of the production process | ||||||
| Capacity of production |
Quality of the product |
Minimum rejection |
Time dead |
Cost of the exercise | |||
| Cooling efficiency | Precise temperature control | Perfect productive responsiveness | Boot Mould change |
Energy rationalisation | |||
| High pressure High flow rate of flow in mold |
High flexibility adjustable in the control panel |
Record time Independence between the process |
Global warming Automatic emptying |
Energy-saving Minimum loss |
One of the basic aspects of the cooling of process is the possibility of repeating the optimized number of parameters of cooling when manufactured a same article | Dry cooling system works in a closed circuit, avoiding the consumption of water and typical maintenance of cooling towers, and its electricity consumption is very low | |
