Matching relationship between injection molding machine tonnage and cooling auxiliary equipment is explained below using a reference calculation method for your reference only.

 

In injection molding process, mold cooling and hydraulic oil cooling are crucial for ensuring product quality, shortening molding cycle, and extending equipment life. Cooling system of an injection molding machine mainly consists of a cooling water tower, a circulating water pump, and supporting piping. Properly matching injection molding machine tonnage with cooling auxiliary equipment directly affects production efficiency and operating costs.
This article aims to explain matching relationship and selection principles between injection molding machine's clamping force (tonnage), cooling water tower tonnage, water pump power, and head. A specific selection calculation is provided using a 1000T hydraulic injection molding machine as an example.

Cooling requirements of injection molding machines mainly come from three aspects:
1. Mold Cooling: After molten plastic is injected into mold, it needs to be cooled by cooling water channels to remove heat and solidify product. Mold cooling accounts for majority of the total cooling load of injection molding machine.
2. Hydraulic Oil Cooling: Hydraulic system of a hydraulic injection molding machine generates a large amount of heat during operation, which needs to be cooled by an oil cooler.
3. Barrel Cooling: Feeding section of barrel needs appropriate cooling to prevent raw material from melting prematurely.
The greater clamping force (tonnage) of injection molding machine, the larger equipment size, the larger injection volume, the higher mold heat load, and the greater required cooling capacity.

3.1 Concept of Cooling Tower Tonnage
"Tonnage" of a cooling tower usually has two meanings:
- Refrigeration Ton (RT): Indicates heat dissipation capacity of cooling tower. 1 refrigeration ton is approximately equal to a cooling capacity of 3024 kcal/h.
- Water tons (t/h): Indicates circulating water flow rate that cooling tower can handle per hour.
In injection molding industry practice, cooling capacity of a cooling tower is measured in RT (cooling tons), while injection molding machine's clamping force is measured in TON (tons).
3.2 Ratio between Injection Molding Machine and Cooling Tower
Based on industry practice, ratio between an injection molding machine and a cooling tower can be summarized as:
> Cooling Tower : Injection Molding Machine = 2 : 1
That is: Injection Molding Machine Tonnage (TON) ÷ 2 = Required Cooling Tower Tonnage (RT)
This ratio is a conservative empirical value derived after comprehensively considering the total heat load of mold cooling, hydraulic oil cooling, and barrel cooling.
3.3 Estimation of Cooling Water Flow Rate
Cooling water requirement of an injection molding machine increases with its tonnage. Based on industry experience, approximate cooling water consumption for injection molding machines of different tonnages is as follows:

For 1000T-class injection molding machines, above data can be used to estimate required cooling water volume proportionally, or technical parameters provided by equipment manufacturer can be consulted. Generally, cooling water requirement for large injection molding machines is in range of 200-300 L/min.

4.1 Determining Pump Flow Rate
Pump flow rate should meet cooling water flow rate required by injection molding machine, while considering pipeline friction losses and safety margins. It is generally recommended to add a 10%-20% margin to calculated value.
Pump flow rate (Q) should meet following requirements:
> Q ≥ Cooling water demand of injection molding machine × Safety factor (1.1~1.2)
4.2 Determination of Pump Head
Selection of pump head requires comprehensive consideration of following factors:
Pipeline friction loss: related to pipe length, pipe diameter, and pipe material; Local resistance: Pressure loss from fittings such as elbows, valves, and filters; Mold water resistance: Resistance of cooling water channel itself; Vertical lifting height: Height difference between cooling tower and injection molding machine; Pressure required for cooling tower spraying
When selecting a pump, following should be ensured: > Pump head ≥ Total resistance × 1.1 (safety factor).
4.3 Determination of Pump Power
Shaft power of pump can be estimated using following formula: > P = (ρ × g × Q × H) / (η × 1000)
Where: P: Shaft power (kW); ρ: Density of water (1000 kg/m³); g: Acceleration due to gravity (9.81 m/s²); Q: Flow rate (m³/s); H: Head (m); η: Pump efficiency (generally taken as 0.6~0.8). In actual selection, a motor power slightly greater than calculated shaft power should be chosen.

5.1 Basic Equipment Information
Equipment Type: 1000T Hydraulic Injection Molding Machine; Clamping Force: 1000 TON; Cooling Components: Mold Cooling + Hydraulic Oil Cooling + Barrel Cooling.
5.2 Cooling Tower Selection
Step 1: Determine Cooling Tower Tonnage
Based on industry experience, ratio of cooling tower to injection molding machine is 2:1.
> Required cooling tower refrigeration tons = 1000 ÷ 2 = 500 RT
Step 2: Convert to Water Tonnage (Optional)
"Refrigeration tons" and "water tons" of a cooling tower are not entirely equivalent. Generally, cooling tower models are labeled in refrigeration tons. For a 1000T injection molding machine, configuring a 500RT cooling tower is standard industry practice.
Step 3: Determine Cooling Water Flow Rate
Based on industry data, cooling water requirement for a 1000T injection molding machine is approximately 250-300 L/min (15-18 m³/h). Considering a safety margin: > Design circulating water volume ≈ 20 m³/h
A 500RT cooling tower typically has a rated processing capacity far exceeding 20 m³/h, sufficient to meet cooling needs of a single 1000T injection molding machine. If multiple injection molding machines share a cooling tower, cooling water requirements of all machines must be added together before selecting a new tower.
5.3 Circulating Water Pump Selection
Step 1: Determine Pump Flow Rate
> Pump Flow Rate = Injection Molding Machine Cooling Water Demand × Safety Factor; > = 18 m³/h × 1.15 ≈ 20.7 m³/h; Recommended Selection: Flow Rate ≥ 20 m³/h
Step 2: Determine Pump Head
Assuming following site conditions:
Difference between cooling tower installation height and injection molding machine height: 5 m; Total pipe length (supply and return water): Approximately 80 m; Equivalent resistance of pipe fittings (elbows, valves, filters, etc.): Approximately 8 m; Mold water resistance: Approximately 5 m; Required pressure for cooling tower spray: Approximately 3 m; > Total resistance ≈ 5 + 8 + 5 + 3 = 21 m; > Design Head = 21 × 1.1 ≈ 23 m. Recommended Selection: Head ≥ 25 m m (Considering a certain selection margin)
Step 3: Determine water pump power
Calculate using formula: > P = (1000 × 9.81 × 20 / 3600 × 25) / (0.7 × 1000); > ≈ (1000 × 9.81 × 0.00556 × 25) / 700; > ≈ 1.95 kW
Considering motor efficiency and starting torque, actual selection: > Recommended water pump motor power: 3 kW or 4 kW.
5.4 Summary of Selection Results

 

6.1 Multiple Injection Molding Machines Sharing a Cooling System
When multiple injection molding machines share a cooling system, cooling water requirements of all equipment should be added together, then cooling tower and water pump should be selected based on the total flow rate. At the same time, attention should be paid to balanced design of pipeline to ensure that each piece of equipment receives sufficient cooling water flow and pressure.
6.2 Cooling Water Temperature Control
Inlet water temperature of a cooling tower is generally 37℃, outlet water temperature is 32℃. For molds with strict requirements on cooling water temperature (e.g., ABS requires 10-25℃, PC requires 10-15℃), a chiller needs to be added after cooling tower for secondary cooling.
6.3 Cooling Tower Type Selection
Circular Counterflow Cooling Tower: Compact structure, good cooling effect, suitable for most injection molding workshops. Counterflow Closed-Circuit Cooling Tower: Good water quality protection, high water saving rate (up to 95% or more), but requires higher pump head and has a larger initial investment.
6.4 Key Points of Piping Design
Cooling water flow velocity is generally controlled at around 2 m/s. Water supply pressure is generally controlled at 0.1-0.2 MPa to meet requirements. Monitoring devices such as filters, pressure gauges, and thermometers should be considered.

Matching relationship between injection molding machine tonnage and cooling auxiliary equipment can be summarized as follows:
Cooling tower tonnage ≈ Injection molding machine tonnage ÷ 2 (in RT). Water pump flow rate is determined by injection molding machine's cooling water demand, requiring a 10%-20% safety margin. Water pump head is calculated comprehensively based on on-site piping conditions, elevation differences, and mold resistance, requiring a 10% safety factor. Water pump power is determined by both flow rate and head; appropriate margins should be allowed during selection.
Taking a 1000T hydraulic injection molding machine as an example, it is recommended to configure it with a 500RT cooling tower, a circulating water pump with a flow rate ≥20 m³/h and a head ≥25 m, and a matching 3-4 kW motor. In actual selection, appropriate adjustments should be made based on specific site conditions, ambient temperature, product requirements, and other factors.