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Several questions about the chiller selection

  • Author:AMC
  • Source:AMC
  • Release on :2015-12-12
First, how the optional chiller
In fact, a pair of mold is a heat exchanger, the heat generated by the incoming molten plastic mold, and then passed by the mold constantly circulating cooling medium - ice water, and only a small part of the air and into the platen injection molding machine. As we all know, plastic molding cycle, a large portion for cooling, sometimes accounted for more than 80% of the plastic molding cycle, so the cooling time to a minimum is absolutely necessary. For example, a pair of molding cycles is generally 20 seconds, as the original cooling tower water instead of ice water cooled chiller produced, it can be shortened to 16 seconds. Although initially selected with the chiller cost is higher, but it can yield a 20% increase in long-term production, we can achieve great benefits. So, how to choose ice energy? From the above we can know that it is the ratio of the thermal molding material, when the melt temperature, weight, and temperature related product release time. The formula for calculating the energy required for ice mold pair is: Q = W × C × △ T × S
Wherein: Q is the energy required to ice kcal / h;
W is the weight of the plastic raw material kg / h;
C is the specific heat of plastic raw materials kcal / kg ℃;
△ T is temperature melt temperature and product release time difference ℃ (see table);
When S is the safety factor (generally the 1.35-2.0), when single match, generally choose a small value, whichever is greater When a chiller and multiple die match, such as choosing air-cooled chiller, S should be appropriately selected larger.
For example: a mold PP products, the hourly production of about 50kg, asked the cooling requirement for how much? How much should be equipped with a suitable chiller?
Q = 50 × 0.48 × 200 × 1.35 = 6480 (kcal / h);
Need 6480kcal / h cooling capacity per hour, can be used PR chiller process, it is difficult to obtain more complete data. Based on our past years of planning, supporting sales experience, △ T = 200 ℃, it is one of many commonly used products, after years of a statistical average.
If the mold with hot glue Road, also will track energy hot glue adding cold calculation of the amount, generally hot glue channel is KW units should be calculated to convert the units into kcal / h, 1KW = 860kcal / h. If adequate water supply factories, lower temperatures, lower cost, then you do not need to use the chiller, which is generally not realistic, unless the plant can lower the temperature of the big lake; the other is to use Deep water supply to meet the needs of urban temperature and flow, but often cost too much. Experimental device can use this method, but for the factory, this is unrealistic.
Second, the ice temperature difference
Mold cooling fluid (ice-water) temperature is generally subject to the processing of materials and products changed greatly shape, such as polyethylene thin-walled beaker, requires ice mold temperature below 0 ℃; while the vast majority of other cases, the mold ice water temperature requirements in more than 5 ℃, fully functional chiller microcomputer can provide more than 5 ℃ ice water, low temperature chiller intelligent to meet the following requirements until 5 ℃ below 0 ℃.
Ice mold temperature difference between inlet and outlet are often set based on product requirements, in many cases, when the temperature difference is 3-5 ℃ is the best, but sometimes need to have a temperature difference of 1-2 ℃. The smaller temperature difference, meaning the same amount of heat taken out, the greater the need of ice flow, whereas the smaller flow needs. For example: the temperature difference is 5 ℃, flow needs 60L, and the temperature difference is 2 ℃, the flow rate is required 150L.
Third, the ice flow
Heat and ice out of the mold of the desired temperature difference between a pair of ice mold and die to take away traffic directly related. For example; to 6480kcal / h of heat away from the mold, if the temperature difference is 3 ℃, flow then at least for how much? Ice-water flow rate Q = 6480 ÷ 3 ÷ 60 = 36 (L / min).

Fourth, the ice water quality treatment
Softened water, in the process of using the chiller is also a problem can not be ignored, the PH value of water also need to constantly observing optimum PH value should be equal to 7, more than 7 PH value will produce terrible corrosion phenomena, such measures are not taken in the evaporator, fouling the mold, it will play the role of insulation, serious, making the energy transition effects reduced by 30%. Obviously this requires consideration of the softening of hard water. The most effective way to configure an electronic water softener in the system, such as an ion exchange softener is designed and manufactured principles. The flow of different sizes can be configured with different softening, directly connected to the water circulation path, the general configuration requirements for water softeners there will not be too high, but also regularly to the circulatory system by adding a certain proportion of detergents .
Fifth, the ice machine flow, pressure
General injection molding mold cooling, ice water pressure selection 0.1 ~ 0.2Mpa, to meet the requirements, and full-featured microcomputer chiller to meet this requirement, when the pressure for higher than 0.2Mpa, to be subject to planning in order to facilitate the use of the appropriate pressure Pump water supply system to meet the needs of.
The relationship between flow rate and pipe diameter table:
Diameter of 3/8 "1/2" 3/4 "1" 1 '/ 4' 1 '/ 2 "2" 3 "
Traffic 1,220,356,090,130,230,560
Sixth, cooling hydraulic oil and feed section of the barrel
Usually hydraulic oil and barrel feed section with cooling towers of water to cool, because it is not only the best way to see production costs alone, but also extremely economical, unless there are specific requirements, is available on the temperature of ice water on Its cooling.
Seven ice pipe insulation
Ice-water pipes must be insulation, pipe insulation because not only can prevent serious loss of cooling capacity, but also to prevent dew condensation formed on the outer wall of the tube. For example: ice temperature 10 ℃, the ambient temperature is 30 ℃, a 25 m long, a surface area of ​​25m & amp; sup2; thermal radiation metal pipes up to 750kcal / h, which is almost 10% 3HP compressor cooling capacity generated around, 5HP compressor cooling capacity generated 6%.
Chiller connection with the mold, usually reinforced hose connection, because it had its own hose insulation function, but longer than 5m, also consider the appropriate thermal insulation.
Schedule: Different materials require injection molding and mold temperature and specific volume heat.
Material injection mold temperature ℃ temperature ℃ hematocrit heat Kcal / kg ℃
Polyethylene 160 ~ 3100 ~ 70 0.55
Polystyrene 185 ~ 2500 ~ 60 0.35
Nylon NYLON 230 ~ 300 25 ~ 70 0.58
Polycarbonate PC 280 ~ 320 70 ~ 130 0.03
Polypropylene PP 200 ~ 280 0 ~ 80 0.48
ABS 180 ~ 260 40 ~ 80 0.40