The melting point of polypropylene is often quoted at around 160 C, which sounds generous. A filter screen under load at a fraction of that temperature is already in trouble, and the gap between the datasheet number and the practical limit catches people out.
Why the useful limit is lower
Load. A screen under pressure differential is under continuous stress. Polymers creep, and creep accelerates sharply as temperature rises. A screen that holds its shape at 20 C can deform slowly at 70 C under the same load.
Time. Datasheet figures are short-term properties. A screen that sees thousands of hours at elevated temperature ages – oxidation embrittles the surface and the wires become fragile.
Chemistry. As covered in our article on chemical compatibility, temperature multiplies chemical attack. The two limits interact.
Thermal cycling. Repeated heating and cooling works the attachment points and the wire crossings.
What the practical range looks like
For continuous loaded service, we would want to know before recommending PP above roughly 80 C, and for anything sustained above that we would be looking at other materials. Intermittent excursions higher than that are often acceptable. Exact figures depend on load, chemistry and required life, which is why we ask rather than quote a single number.
What you see as you approach the limit
- Progressive deformation – the screen dishes in the direction of flow and stays dished
- Loss of tension in the mesh, which changes the aperture and the filtration
- Embrittlement after extended exposure, so wires crack rather than bend
- Joint failure at the frame, usually before the mesh itself fails
What to do about it
Derating. If your temperature is above the comfortable range, a heavier wire gauge and more support spacing points buy usable life.
Cooling upstream is often cheaper than a more exotic material.
A different polymer where the temperature genuinely cannot be reduced. This is a bigger step than it sounds, because the whole frame and sealing arrangement changes with it.
Accepting a shorter life and planning for it. Sometimes the right answer is to treat the screen as a consumable with a defined change interval, and that is a perfectly respectable decision if it is made deliberately.
What to tell your supplier
Continuous temperature, peak temperature including cleaning cycles, pressure differential, and the fluid. Those four determine whether PP is viable. Guessing at any of them is how screens end up failing in weeks.
What to do instead, in order of cost
Before changing material, there are three cheaper moves. The first is to reduce the load on the screen by increasing the face area, which lowers the stress at the same temperature. The second is to add support, which shortens the span and cuts the deflection that drives creep. The third is to cool the stream upstream, which is often simpler than it sounds and solves the problem outright.
If none of those are available, the material has to change, and the frame, seals and cleaning regime change with it. That is a bigger project than most people expect, which is why it is worth exhausting the mechanical options first.
Where a hotter process is a permanent feature, it is usually worth specifying for it from the start rather than retrofitting after a season of short screen life.
Our position
We make PP filter screens and we will tell you when PP is the wrong answer. A screen that fails early costs us more in goodwill than the order was worth, so if your process runs hot we would rather have that conversation first.