Due to cost considerations, many customers used cooling water towers to cool molds in the past. In principle, a mold is a heat exchanger. Heat is transferred from the molten plastic to the mold, and then the mold is continuously circulated. Only a small part of the cooling medium in ice water enters the air and the die plate of the injection molding machine, so there is not much pressure on the injection machine and the film plate. However, it is worth mentioning that a considerable part of the plastic molding cycle is used for cooling methods and methods, and sometimes it can even account for more than 75% of the plastic molding cycle, so it is absolutely necessary to control the cooling time to a minimum. Improve the efficiency of plastic molding. For example, a mold with a 15-second molding cycle, such as changing the original cooling tower water to ice water generated by a chiller, can be shortened to 12 seconds or even faster. Although the initial cost of choosing a chiller is relatively high, it can increase output by 25%, and in the long run, it can achieve great benefits.
So, how to choose ice water energy? From the above we can know that it is related to the specific heat capacity of the molding material, the temperature during the melt, the weight, and the temperature when the product is demolded. In the actual selection of chiller, it is difficult to obtain relatively complete data. According to our past years of planning and supporting sales experience,? T = 200 ° C, which is an average value of many commonly used products after years of statistics. If the hot glue lane is attached to the mold, the energy of the hot glue lane should also be added to the calculation of cold capacity. Generally, the hot glue lane is based on kw. When calculating, the unit should be converted into kcal / h, 1kw = 860kcal / h. If the amount of water supplied to the factory is sufficient, the temperature is low, and the cost is low, it is not necessary to use a chiller at this time. This is generally not realistic unless the factory can be near a large lake with a relatively low water temperature; the other is to use Urban deep wells supply water to meet the needs of temperature and flow, but often the cost is too high. This method can be used for experimental installations, but it is impractical for factories.
two. Ice water temperature difference The temperature of the mold cooling fluid (ice water) generally changes due to the shape of the processing materials and products, such as polystyrene thin-walled beakers, the mold requires ice water temperature below 0 ° C; and most other cases Below, the temperature of the ice water required by the mold is above 5 ° C, the microcomputer full-function chiller can provide ice water above 5 ° C, and the low temperature intelligent temperature control chiller can meet the requirements below 5 ° C and below 0 ° C.
The temperature difference between the ice and water at the entrance and exit of the mold is often set according to the requirements of the product. In many cases, the temperature difference is 3-5 ° C, but it is sometimes required to be 1-2 ° C. The smaller the temperature difference means that the same amount of heat is taken out, the larger the ice water flow is required, and vice versa. For example: when the temperature difference is 5 ℃, the flow rate is 60l, and when the temperature difference is 2 ℃, the flow rate is 150l.
Third, the ice water flow The ice water flow required by a mold is directly related to the heat to be taken away by the mold and the temperature difference between the ice water entering and leaving the mold. Example: To
The heat of 6480kcal / h is taken away from the mold. If the temperature difference is 3 ° C, what is the minimum flow rate required? Ice water flow q = 6480 ÷ 3 ÷ 60 = 36 (l / min).
Fourth, the softening of the water of the water quality of the ice water is also a problem that cannot be ignored in the process of using the chiller. The pH value of the water also needs to be constantly monitored. The optimal pH value should be equal to 7 and greater than 7. There will be a terrible corrosion phenomenon. If no measures are taken, it will scale in the evaporator and mold, and it will act as heat insulation. In severe cases, it will reduce the energy conversion effect by 30%. Obviously this requires consideration of softening of hard water. The most effective method is to configure an electronic hard water softener in the system. Such a softener is designed and manufactured based on the principle of exchange. Softeners of different specifications can be configured according to different flows, which are directly connected to the circulating water pipeline. Generally, the cost of a water treatment softener is not too high, and a certain proportion of descaling agents can be added to the circulation system in a fixed period .
The formula for calculating the ice water energy required by a pair of molds is:
q = w × c ×? t × s
Where: q is the required ice water energy kcal / h;
w is the weight of plastic raw material kg / h;
c is the specific heat of plastic raw material kcal / kg ℃;
? t is the temperature difference ℃ between the temperature of the melt glue and the product demolding (see the attached table);
s is the safety factor (usually 1.35-2.0). When a single machine is matched, a small value is generally selected, and when a chiller is matched with multiple molds, a large value is used. When an air-cooled chiller is selected, s should also be Choose a larger one appropriately.
For example: a pair of molds to produce pp products, the production capacity is about 50kg per hour, how much cooling is required? How big should be equipped with chiller? Q = 50 × 0.48 × 200 × 1.35 = 6480 (kcal / h); requires 6480kcal / h cooling capacity per hour, ls203s chiller can be used.
The content of the industry involved is still more and more professional, and in the face of the above calculation formula, friends who are engaged in the chiller industry must still fully grasp it! And the same looking for high-quality, cost-effective cold water machinery products are welcome to contact us!
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