The mold temperature is the variable that most decides the part and the one that is most often adjusted by eye. The surface finish, crystallinity, shrinkage, internal stresses and cycle time depend on it. And yet, in many plants the criterion is still "the number left on the previous shift."
This table compiles typical mold temperature ranges by polymer family. But the correct temperature is of no use if the equipment cannot sustain it: that is why the second half of the article is the one that really matters, and it is the one that is almost never published.
Mold temperature table by polymer
Guidance ranges. The specific grade and fiber load always govern this table: consult the material supplier's file.
| Polymer | temp. mould | Fluid | What happens if you fall short? |
|---|---|---|---|
| Amorphous | |||
| PS | 20–60 °C | Water | Matte parts, internal tensions |
| ABS | 40–80 °C | Water | Uneven gloss, marked weld lines |
| SAN | 50–80 °C | Water | Fragility, poor finish |
| PMMA | 40–90 °C | Water | Loss of transparency, tensions |
| Rigid PVC | 20–60 °C | Water | Poor filling; Be careful with degradation due to excess |
| PC | 80–120 °C | Pressurized water | Severe internal stresses, cracking parts |
| PPO / PPE mod. | 80–110 °C | Pressurized water | Incomplete filling, poor finish |
| SEMI-CRYSTALLINE | |||
| PE-HD | 20–60 °C | Water | Uncontrolled contraction, warping |
| PP | 20–60 °C | Water | Warping, irregular shrinkage, matte finish |
| PA6 | 60–90 °C | Water / pressurized | Low crystallinity: less rigid and unstable piece |
| PA66 | 70–110 °C | Pressurized water | Low crystallinity, subsequent shrinkage in service |
| POM | 80–120 °C | Pressurized water | Post contraction, levels that move with time |
| PBT | 40–80 °C | Water / pressurized | Insufficient crystallinity, poor finish |
| PET (crystalline) | 120–140 °C | Pressurized water | Does not crystallize: transparent and soft piece |
| PPS | 130–160 °C | Pressurized / oil | Low crystallinity, thermal performance that does not reach |
| LCP | 90–150 °C | Pressurized / oil | Poor orientation and welds |
| PEEK | 170–200 °C | Oil | Amorphous piece: you lose almost everything you paid for the material |
Rule of thumb: Fiber-reinforced grades typically ask for the high end of the range, and sometimes above. In semicrystalline mold temperature is not a finishing adjustment: it is what decides the crystallinity, and with it the rigidity, dimensional stability and long-term behavior of the piece.
Do not confuse it with the temperature of the plastic
It is worth stopping here, because it is the most expensive confusion in the sector: in an injector several temperatures coexist and only one controls the temperature control unit.
- molten mass (200–300 °C depending on polymer): the plastic coming out of the screw. The injector puts it on. The temperature control unit does not control it.
- Mold surface (the table above): the steel against which the part solidifies. This one yes.
- equipment fluid: a means to achieve the previous one, never an objective.
If your ABS melts at 240°C, you don't need a 240°C temperature control unit: you need one that keeps the mold between 40 and 80°C. The difference between understanding this and not understanding it is two radically different teams and a budget that is nothing alike.
The part that almost no one tells you: maintaining it
Choosing the number is the easy part. The real problem appears later, and it has three faces.
The temperature jump, not the temperature
A mold is not at a temperature: it is at a temperature map. What determines the quality of the part is not so much the setpoint as the ΔT between input and return and the homogeneity between circuits. A mold with the correct setting and 8 °C difference between zones produces equal warping.
Flow rate matters more than power
If the flow in the channels is not turbulent, the heat is not extracted no matter how much cooling power you have behind it. It is the most expensive and most common mistake: power is bought when the problem was flow rate.
Above 90 °C the physics changes
Water at atmospheric pressure boils at 100 °C, so in practice an open circuit stays around 90 °C. From there there are two ways: pressurize the water or switch to oil. And that decision conditions the entire installation.
What equipment each range calls for
Our range covers from 25 to 180°C in water and up to 300°C in oil. This is the criterion with which we select family:
| Temperature | Family | Fluid | Typical polymers |
|---|---|---|---|
| Up to 90°C | Water with tank Water Open Tank |
Water | PS, ABS, PP, PE, PMMA, PA6, PBT |
| 90–180 °C | Pressurized water direct (WDC) or indirect (WIC) |
Pressurized water | PC, PA66, POM, PPO, PET cristalino, LCP |
| Up to 150°C | Oil with tank Oil Open Tank |
Thermal oil | Installations that already work with oil |
| 150–300 °C | Oil in closed circuit Oil Closed Circuit |
Thermal oil | PEEK, PPS high demand |
| Below ambient | It is not a temperature control unit | — | It is the work of a fridge |
The border between water and oil is not where people think: we select oil above 160 °C. Below, and if you can choose, pressurized water is usually a better decision. We develop it in water or oil: how to choose the temperature control unit.
Frequently asked questions
What mold temperature does ABS need?
Between 40 and 80 °C in most degrees. Below 40 °C the gloss becomes irregular and the weld lines become marked; Above 80 °C you lengthen the cycle without gaining anything. A water temperature control unit with a tank covers the entire range.
And polypropylene (PP)?
From 20 to 60 °C. It's a semi-crystalline, so the mold temperature decides the shrinkage: if you're looking for dimensional stability, go up within the range and keep the ΔT low between circuits.
My plastic melts at 240 °C, do I need a 240 °C temperature control unit?
No. Those 240 °C are the temperature of the melt and are set by the injector. The temperature control controls the surface of the mold, which in ABS works between 40 and 80 °C. A water system with a tank more than covers that range. It is the most common mistake we see and it multiplies the budget for no reason.
At what temperature do I need pressurized water?
From 90 °C. Water at atmospheric pressure boils at 100°C and an open circuit doesn't get there with any margin. Pressurizing works with water up to 180 °C, preserving the thermal advantage of water over oil.
Why does my piece come out warped if the instructions are correct?
Because the reference is not the temperature of the mold. Almost always the problem is the ΔT between input and return, or the difference between circuits, not the number on the display. Before touching the setpoint, measure the difference between zones and check that the flow is turbulent.
Why does PEEK need 170–200°C?
Because underneath it doesn't crystallize. An amorphous piece comes out that loses a good part of the mechanical and thermal performance for which the material is paid. In that range there is only one realistic option: oil.
A manufacturer since 1978
This table summarizes what we see every day in the plant: most of the problems attributed to the material are actually thermal control problems. If you have a reference that resists you, tell us the material, thickness and geometry of the circuit and we will tell you what we would do.
Check out our range of industrial temperature control units o talk to a technician.