Quick answer: for freezing and chilling lines, PE is the toughest of the three common resins when cold, PP stiffens and loses impact strength as temperature drops, and POM stays hard and dimensionally stable but is less forgiving of a knock. The working temperature range is a property of the material grade supplied, not of the belt series, so confirm it on the order. Then design for two things the catalogue will not tell you: the belt gets shorter in the cold, and it has to keep draining while everything on it is trying to freeze.
Cold behaviour, material by material
Plastics do not fail in the cold by melting or corroding. They go brittle. The resin gets stiffer as it cools, the impact energy it can absorb drops, and a belt that shrugged off a dropped frozen block in September cracks on the same impact in a cold room. That is the failure mode to design against.
| Material | Behaviour as it gets colder | Where it fits on a cold line |
|---|---|---|
| PE (polyethylene) | Keeps more of its toughness than the other two, stays the most forgiving of impact | The usual first choice for freezing tunnels and cold rooms, particularly where product drops onto the belt |
| PP (polypropylene) | Stiffens noticeably and loses impact strength; still the workhorse for chilled rather than frozen duty | Chilling, draining and cooling sections above freezing, and freezer lines with gentle loading |
| POM (acetal) | Stays hard and holds its dimensions well, but absorbs impact poorly | Where cold plus high belt pull meet, and impact is controlled |
Ask for the working temperature range in writing, tied to the grade being supplied. Two belts of the same series in the same resin family can have different low-temperature limits if the grade or the additive package differs, and no honest supplier will give you a single number that covers the whole range.
The belt gets shorter, and that changes the order
Every belt in a freezer is installed warm and runs cold. The frame is measured on a workshop floor at ambient, and then the whole assembly is pulled down by tens of degrees. Plastic contracts far more than the steel frame around it, so both the width and the length come in.
Width contraction is usually the easy half. The belt pulls away from the frame, so binding is not the risk; losing edge control is. Length contraction is the half that causes call-outs. A modular belt runs with controlled slack in a catenary rather than under tension, and length change goes straight into that catenary. Sized to look right warm, the belt can come up tight at working temperature, which loads the drive and starts pulling the hinge joints hard against the rods.
Two practical consequences. First, run the contraction number for your actual temperature swing before you fix the belt length; the formula and the coefficients for PP, PE and POM are in the thermal expansion guide and there is no point repeating them here. Second, remember that a modular belt cannot be adjusted in anything smaller than one pitch. You add or remove a whole row, which is 25.4 mm on the 966 series and 50.8 mm on the 400 series. On a long conveyor the contraction easily exceeds one pitch, so the take-up and catenary have to absorb whatever is left over after you have rounded to the nearest row. Leave that room deliberately instead of discovering it on commissioning day.
Ice changes the friction picture
Belt pull calculations assume a friction factor between the belt and the wearstrip. In a freezer that factor is not a constant. A dry cold belt on a dry wearstrip slides more or less as expected. Add meltwater from a defrost cycle, let it refreeze in the return path, and the drag can rise sharply for the first minutes of a run until the ice is worn through. Product juices are worse than water, because they freeze stickier and they get into the hinge joints.
Three things follow from that. Keep the return path clear and supported, because a sagging return that touches the frame is where ice bridges form; return wheels earn their money here. Choose a belt style that lets liquid leave the belt rather than pool on it. And check the hinge joints for free movement during scheduled maintenance, since a belt with stiff joints will not lie flat and will start to wander.
The rod material is worth a conversation on a cold wet line as well. Nylon 4.6 mm and PP 7.8 mm rods are both available, and they behave differently in a wet freezer. Confirm which one is being supplied rather than accepting the default.
Open area is an airflow decision, not just a drainage one
On a washdown line the open area of a belt is about drainage. In a freezing tunnel it is about how much cold air can get through the belt to the underside of the product. A flat top belt in a blast tunnel freezes the top of the product and insulates the bottom, so the tunnel runs longer than it needs to.
| Series and style | Pitch | Thickness | Open area | Materials |
|---|---|---|---|---|
| 916 large radius | 25.4 mm | 13 mm | 60% | PP / POM |
| 926 flush grid | 12.7 mm | 8.9 mm | 37.7% | PP / POM |
| 900 raised rib | 27.2 mm | 13.7 mm | 31.7% | PP / POM / PE |
| 400 raised rib | 50.8 mm | 21.5 mm | 29.4% | PP / PE |
| OPB large open grid | 50.8 mm | 16 mm | 29% | PP / PE |
| 4802 raised rib | 38.1 mm | 13.5 mm | 27.3% | PP / PE |
| 4809 raised rib | 57.15 mm | 23.8 mm | 24.2% | PP |
Open area is not free. A more open module has less plastic in section, and on the 916 that shows up in the belt strength, 14,200 N/m in PP. In a spiral freezer the pull accumulates through every tier, and a spiral tower is not simply a belt turning a corner, so an open belt in a tall spiral is exactly the case where the belt pull calculation has to be done properly rather than assumed. The radius and spiral belt guide covers the turning geometry, and the full range is on the radius and spiral belt page.
When the product sticks instead of drains
Open area helps liquid fall away. It does nothing for a product that freezes onto the belt surface, and raw meat, dough and glazed product all do. The answer there is contact area, not open area. A nub top surface holds the product on small raised points, so there is far less surface for it to bond to, and it releases at the transfer instead of riding round the return.
That is why the 976 nub top appears on frozen food lines despite having no open area at all, and why the 936 nub top, at 38.1 mm pitch and 33,000 N/m in PP, is a common answer for raw meat that has to run cold and heavy at the same time.
Cleaning a belt that ices up
The cleaning cycle is often the real temperature extreme on a freezer line. A belt sitting below zero and then washed with hot water sees a swing far wider than production ever produces, and it sees it fast. Size the frame clearances for the hot end of that swing, not just the cold end. Make sure water can actually leave the belt and the frame before the line goes back down to temperature, because trapped water becomes ice in the return path. And schedule the joint check for right after a wash, when any stiffness is easiest to feel.
What to send with the enquiry
- The lowest running temperature and the cleaning temperature, both of them
- What the product is and whether it arrives wet, glazed or sticky
- Whether product drops onto the belt, and from what height
- Belt width, conveyor length, and for a spiral, the number of tiers
- Existing belt series and pitch if this is a replacement
Send that to the contact form or by WhatsApp and you will get two options back with the trade-off spelled out: material, open area and belt strength, and what each choice gives up. The full straight-running range is on the modular belt page, and if you have not fixed the belt style yet, the selection guide is the place to start.
