The mold temperature controller (also called a mold heater/chiller or TCU — temperature control unit) circulates temperature-controlled fluid through the mold's cooling channels. It is arguably the most important auxiliary equipment in injection molding because it directly controls part quality, cycle time, and dimensional consistency.
This guide covers TCU types, sizing formulas, temperature uniformity concerns, and what buyers should verify in their supplier's process capability.
| Characteristic | Water TCU | Oil TCU |
|---|---|---|
| Temperature range | 10°C – 95°C (atmospheric) | 30°C – 300°C (closed system) |
| Higher temp (pressurized) | Up to 160°C (6-8 bar) | N/A |
| Heat transfer efficiency | Excellent (water has 4x the specific heat of oil) | Good but slower response |
| Operating cost | Low | Higher (oil replacement, disposal) |
| Safety | Non-flammable | Fire risk at high temp if leaks occur |
| Maintenance | Scale buildup, corrosion risk | Oil degradation, sludge accumulation |
| Best for | Standard molding (mold temp 40-90°C) | High-temp engineering plastics (mold temp 120-180°C) |
The TCU must be sized to remove the heat entering the mold from the molten plastic. The required cooling capacity (in kW) is calculated as:
Q = m × Cp × ΔT / t
Where Q = cooling power (kW), m = shot weight (kg), Cp = specific heat of plastic (kJ/kg·K), ΔT = temperature drop from melt to ejection, and t = cooling time (seconds).
For most applications, the rule of thumb is 0.5-1.5 kW of cooling capacity per kg/hour of throughput. An undersized TCU cannot maintain the set temperature during high-speed production.
A TCU can deliver fluid at exactly 60°C, but if the mold's cooling channel layout is poor, the mold surface temperature may vary 15-20°C across the cavity. This causes:
Standard practice: measure the mold surface temperature at 5-10 points across the cavity using a contact pyrometer. The acceptable variation depends on tolerance requirements but is typically ±5°C for commercial parts and ±2°C for precision parts.
| Material | Recommended Mold Temp (°C) | TCU Type |
|---|---|---|
| PP | 30 – 60 | Water |
| PE | 30 – 60 | Water |
| ABS | 50 – 80 | Water |
| PS | 40 – 60 | Water |
| PC | 80 – 120 | Pressurized water or oil |
| PA6 / PA66 | 70 – 100 | Pressurized water |
| POM (Acetal) | 80 – 100 | Pressurized water or oil |
| PBT | 60 – 100 | Pressurized water |
| PMMA (Acrylic) | 50 – 80 | Water |
| PEEK | 160 – 200 | Oil |
| LCP | 100 – 150 | Oil |
| Liquid Silicone | 150 – 200 | Oil |
When qualifying a new mold, the molder should: