Capping torque is the rotational force applied to a cap when it is screwed onto a bottle. It is the single most common cause of capping problems — and the most overlooked specification in purchase orders. Too low, and the cap leaks or falls off. Too high, and the cap cracks the bottle or consumers cannot open it.
What Torque Actually Does
When a cap is threaded onto a bottle, torque creates axial (downward) force that compresses the cap liner against the bottle finish (the sealing surface). This compression creates the seal. The relationship is:
- Too little torque → insufficient liner compression → leaks, contamination, cap loosening in transit
- Correct torque → full liner compression, hermetic seal, consumer can still open it
- Too much torque → stress on bottle threads and finish → cracks, stripped threads, stress cracking over time
Target Torque Ranges
Torque is measured in inch-pounds (in-lb) or Newton-meters (N·m). Typical ranges by cap diameter:
| Cap diameter | Application torque (in-lb) | Removal torque (in-lb) |
|---|---|---|
| 18–20mm (pharma, nail polish) | 6–10 | 4–8 |
| 24mm (small bottles, juice) | 8–14 | 5–10 |
| 28mm (PCO beverage bottles) | 10–18 | 6–12 |
| 33–38mm (food jars, chemicals) | 12–20 | 8–14 |
| 45–53mm (wide-mouth jars) | 14–25 | 10–18 |
| 63–89mm (industrial drums) | 20–40 | 15–30 |
Removal torque (the force needed to open the cap) is typically 60–80% of application torque because the liner material relaxes slightly after sealing.
Why Torque Control Matters on Chinese Machines
Not all Chinese capping machines control torque the same way:
Spindle cappers rely on spring pressure and disc geometry to limit torque. They are fast and simple but less precise — actual torque varies ±15–25% depending on cap quality, bottle variation, and disc wear. Fine for consumer goods where exact torque is not critical.
Chuck cappers use programmable torque motors with digital control. Torque accuracy is ±2–5%. Essential for pharmaceuticals, cosmetics, and any application where consistency matters. More expensive but worth it when torque specification matters.
Hand-held capping guns use a clutch that slips at a preset torque. Accuracy is ±10–15%. Adequate for low-volume or repair work.
How to Verify Torque on a New Machine
Before accepting delivery:
- Ask the factory to specify the torque range they will set for your cap and bottle combination — in writing, with units
- Request a video of the machine capping your actual bottles at that torque setting
- Bring or ship a torque meter (e.g. Cap torque tester) to measure actual removal torque on capped bottles
- Check consistency: cap 10 bottles and measure removal torque on each — variance should be within ±10% of the setpoint
If the factory cannot demonstrate torque control or refuses a video test, that is a red flag. Move to a supplier who can.
Common Torque Problems and Fixes
| Problem | Cause | Fix |
|---|---|---|
| Caps leak after sealing | Torque too low, liner not compressed | Increase torque setting; check liner material |
| Bottles crack at the finish | Torque too high for bottle material | Reduce torque; check bottle thread quality |
| Caps loosen in transit | Torque correct initially but liner relaxes | Use higher-torque liner material; add induction seal |
| Inconsistent torque across bottles | Worn discs (spindle) or clutch drift (chuck) | Replace worn parts; recalibrate |
| Consumer complaints: “too hard to open” | Removal torque too high | Reduce application torque; use easier-grip cap design |
Specifying Torque in Your Purchase Order
Include these lines in your RFQ or purchase order:
- Cap type and diameter (e.g. 28mm PCO 1810 screw cap)
- Bottle material and neck finish standard (e.g. PET, 28mm 3-start)
- Required application torque: ___ in-lb (± tolerance)
- Required removal torque range: ___ in-lb
- Torque control method: spindle / programmable chuck / clutch-type hand-held
- Acceptance criteria: 10-bottle removal torque test within ±10% of setpoint
This turns a vague “capping machine” order into a measurable specification — and gives you grounds for a warranty claim if torque is wrong.
For verified capping machine suppliers, browse our capping machine directory — 253 factories covering screw, ROPP, snap, and trigger cappers.