The Cup That Got Stiff in the Cold
We used a standard NBR (nitrile) suction cup (article 113) to lift parts in a cold storage room (5°C). The cup worked at room temperature. In the cold room (5°C), the cup got stiff (the rubber hardened). It didn’t conform to the part (the seal was bad). The vacuum leaked. The part dropped. The problem: NBR rubber gets stiff (hardens) at low temperatures. The cup needs to be flexible to seal. We switched to a silicone cup (flexible at low temperature). The cup sealed. The mistake was using an NBR cup in a cold environment (NBR stiffens below 0°C). The material must match the temperature.
Vacuum cup material temperature range matches the rubber to the environment. This article covers the choices.
The Cup Materials
NBR (Nitrile)
Standard rubber (article 113). Oil-resistant. Cheap. Temperature range: -20°C to +80°C. But at the low end (below 0°C), it stiffens (gets hard). For a cold room (5°C), it works (but stiffens below 0). For room temperature (20°C), it’s fine. The standard for general use.
Silicone
Flexible at low and high temperatures. Temperature range: -60°C to +200°C. Food-grade (FDA). Used for cold (freezer) or hot (oven) applications. More expensive than NBR. But it’s flexible at 5°C (and -40°C).
FKM (Viton)
Chemical-resistant. High temperature (+200°C). Used for aggressive chemicals (solvents). Expensive. Overkill for general use. Not for cold (it stiffens).
| Material | Temp Range | Best For |
|---|---|---|
| NBR (nitrile) | -20 to +80°C | General, room temp, oil |
| Silicone | -60 to +200°C | Cold (freezer), hot, food |
| FKM (Viton) | -10 to +200°C | Chemicals, high temp |
Step 1: Match the Material to the Temperature
For a cold room (5°C or below), use silicone (flexible at low temp). The NBR cup that stiffened was at 5°C. Silicone stays flexible. For a hot application (an oven, 150°C), use silicone or FKM (NBR melts at 80°C). For room temperature (20°C), NBR (cheap) is fine.
The cup temperature rule: NBR stiffens below 0°C. For a cold environment (5°C or below), use silicone (flexible). The cup that got stiff was NBR in a cold room. For high temperature (over 80°C), use silicone or FKM. The material’s temperature range must cover the application.
Step 2: Food / Pharma (Silicone)
For food or pharma (washdown, article 77), the cup must be food-grade (FDA). Silicone is food-grade. NBR is not (it has additives). For a food line, use silicone (even at room temp). It’s more expensive but compliant.
Step 3: Chemicals (FKM)
For a chemical environment (solvents, oils), use FKM (Viton). NBR swells in some solvents. FKM resists. Check the chemical compatibility (the cup’s manufacturer lists compatible chemicals).
Step 4: Wear (Article 128)
The material also affects wear. NBR wears (in high cycles). Silicone is softer (wears faster in abrasive applications). FKM is harder (wear-resistant). For high cycles (millions of picks), use a wear-resistant material (FKM, or a NBR with a wear coating).
A Cup Material Checklist
- What is the environment temperature? (°C?)
- Is it cold (below 5°C)? Use silicone?
- Is it hot (over 80°C)? Use silicone/FKM?
- Is it food/pharma? Use silicone (FDA)?
- Is there chemicals? Use FKM?
- Is it high cycles? (Wear? Article 128?)
- Does the cup stiffen? (Cold? NBR problem?)
- Does the cup seal? (Flexible?)
- Is the cup material compatible? (Manufacturer list?)
- Are spare cups in stock? (Article 100?)
The Bottom Line
Vacuum cup material temperature range matches the rubber to the environment. The cup that got stiff was NBR in a cold room. Use silicone for cold (or hot, or food). NBR for room temperature general. FKM for chemicals. The cup that sealed in the cold wasn’t the cheapest one — it was silicone.
