How to Select and Match a Chiller for your Injection Molding Machine?

In fact, a mold is essentially a heat exchanger. Heat is transferred from the molten plastic into the mold and then into a continuously circulating cooling medium, typically ice water. Only a small portion of the heat is released into the air or the mold plate of the injection molding machine. Indeed, the cooling phase plays a crucial role in the plastic molding process due to the inherent characteristics of plastics and the requirement for a high-quality end product. This phase can often account for up to 80% of the entire cycle time. Therefore, minimizing the cooling time is absolutely necessary.

For example, the typical molding cycle of a mold is around 20 seconds. By using ice water generated by a chiller instead of the water from a cooling tower, the cooling time can be reduced to 16 seconds. Although the initial cost of equipping a chiller is higher, it can increase production by 20%. In the long term, significant profits can be achieved through improved productivity.

Now, how do we choose the energy of the ice water? As mentioned above, it depends on the specific heat capacity of the molding material, the temperature during the melting of the plastic, the weight of the material, and the temperature during mold release.

For general injection molding mold cooling, the pressure of the ice water is usually chosen to be between 0.1 and 0.2 M Pa, which is sufficient to meet the requirements. A fully functional microcomputer chiller can meet this requirement. Certainly, if the pressure of the ice water surpasses 0.2 (MPa), it becomes necessary to incorporate a water pump that is capable of satisfying the system’s water supply requirements. Relationship between flow rate and pipe diameter table:

The calculation formula for the required energy of ice water for a mold is q = w × c × t × s.

In the formula:

• q represents the required energy of ice water in kcal/h.
• w denotes the weight of the plastic material in kg/h.
• c represents the specific heat of the plastic material in kcal/kg℃.
• t denotes the temperature difference between the melting temperature of the plastic and the temperature during mold release in Celsius.
• s represents the safety factor, typically taken as 1.35 to 2.0. When matching a single machine, the smaller value is generally chosen. However, when matching one chiller with multiple molds, the larger value is selected. For example, if an air-cooled chiller is chosen, s should also be chosen to be relatively large.

For example, A mold is used to produce PP products with a production rate of approximately 50 kg per hour. What is the required cooling capacity, and what size of chiller would be suitable?

Using the formula: q = 50 × 0.48 × 200 × 1.35 = 6480 (kcal/h). Therefore, the cooling capacity required is 6480 kcal/h. An SIC-3W or SIC-3A chiller would be suitable for providing this cooling capacity.

During the actual selection process of a chiller, it is often challenging to obtain complete data. Based on experience, t = 200°C, which is an average value derived from years of statistics for many commonly used products.

If the mold has a hot runner system, the energy from the hot runner system should also be included in the cooling capacity calculation. Generally, the energy of the hot runner system is measured in kW, so it should be converted to kcal/h. 1 kW = 860 kcal/h.

If the factory has a sufficient water supply with low temperature and low cost, it may not need to use a chiller. However, this is generally not realistic unless the factory is located near a large lake with a relatively low water temperature. Another option is to use water supply from deep wells in the city to meet the temperature and flow rate requirements, but this often comes with high costs. While this approach may be feasible for experimental setups, it is not practical for most factories.

The Temperature Difference of Ice Water

The temperature of the cooling fluid (ice water) in plastic molds generally varies significantly depending on the processed material and the shape of the product. For example, for polystyrene thin-walled beakers, the mold requires ice water temperature below 0°C. In most other cases, the mold requires ice water temperature above 5°C. A fully functional microcomputer chiller can provide ice water above 5°C, while a low-temperature intelligent temperature-controlled chiller can meet requirements below 5°C and even below 0°C.

The temperature difference between the ice water at the inlet and the outlet of the plastic mold is often set based on the product requirements. In many cases, a temperature difference of 3-5°C is considered ideal, but sometimes a temperature difference of 1-2°C is required. A smaller temperature difference means that the same amount of heat is removed, requiring a larger flow rate of ice water, while a larger temperature difference requires a smaller flow rate. For example, with a temperature difference of 5°C, a flow rate of 60 liters is required, whereas with a temperature difference of 2°C, a flow rate of 150 liters is required.

Ice Water Flow Rate

The required ice water flow rate for a plastic mold is directly related to the amount of heat that needs.

The Oretical Considerations for Ice Water Quality

Water softening is an important aspect to consider in the process of using a chiller. The pH value of the water also needs to be continuously monitored, with the optimal pH value being 7. pH values higher than 7 can lead to severe corrosion. If not addressed, scaling can occur in the evaporator and mold, acting as insulation. In severe cases, it can reduce energy conversion efficiency by 30%. It is essential to address the issue of hard water.

The most effective method is to install an electronic water softener in the system. Such softeners are designed based on ion exchange principles. Depending on the flow rate, different specifications of softeners can be installed directly in the circulating water pipeline. The cost of installing a water treatment softener is generally reasonable, and periodic addition of scale inhibitors to the circulating system can also be considered.

Ice Water Machine Flow Rate and Pressure

For cooling in general injection molding mold applications, ice water pressure in the range of 0.1 to 0.2 MPa is sufficient to meet the requirements. A fully functional microcomputer chiller can meet this pressure requirement. If the pressure requirement exceeds 0.2 MPa, additional planning is needed to ensure the use of a water pump with the corresponding pressure to meet the system’s water supply needs.

Cooling of Hydraulic Oil and Feed Section of the Barrel

Typically, cooling water from a cooling tower is used to cool the hydraulic oil and the feed section of the barrel. This method is not only the most optimal but also cost-effective. Unless there are specific temperature requirements, ice water can be used for cooling purposes.

Insulation is necessary for ice water pipelines because insulation not only prevents significant loss of cooling capacity but also prevents the formation of condensation on the outer surface of the pipes. For example, if the ice water temperature is 10°C and the ambient temperature is 30°C, a 25-meter-long metal pipe with a surface area of 25m² can radiate heat up to 750 kcal/h. This is approximately 10% of the cooling capacity generated by a 3hp compressor and around 6% of the cooling capacity generated by a 5hp compressor.

• How to select and pair a chiller with an injection molding machine? You should find a chiller that can efficiently and effectively provide the cooling capacity needed by the injection molding machine while operating under normal ambient temperatures.For your case, you stated that the cooling water condensation temperature should be below 35°C for a water-cooled chiller or below 43°C for an air-cooled chiller
• 1 hp water-cooled chiller can be paired with an injection molding machine that exerts a clamping force of 80 tons to maintain the temperature in the range of 5-10 degrees Celsius.
• The 1HPwater-cooled chiller can be effectively paired with a 100-ton clamping force injection molding machine to regulate the temperature within a range of 10-15 degrees 1hp water-cooled chiller can be matched with an injection molding machine with a clamping force of 120 tons to control the temperature within 15-20 degrees Celsius. (Note: For air-cooled chillers, the matching capacity is 0.8 times that of water-cooled chillers. Therefore, a 1hp air-cooled chiller can be matched with an injection molding machine with a clamping force of 64 tons to control the temperature within 5-10 degrees Celsius.)

1. The second method:

• 1hp water-cooled chiller can be matched with an injection molding machine with a single shot weight of 10 QZ to control the temperature within 5-10 degrees Celsius. Note: 1 QZ corresponds to 28.5g of material. The above formula is for reference, and you should consider the actual situation and choose a suitable chiller accordingly.

1. The pairing of chillers and cooling towers:

According to experience, a 1HP chiller typically necessitates a cooling tower of 1.2 cooling tons to efficiently eliminate the heat produced by the chiller.