The twin-shaft mixer (pugmill) is where aggregate, filler and binder become asphalt — and where the plant sees the most abrasion. Looking after it keeps cycle times short, batches uniform and unplanned stops rare.
Lock out the mixer drive and air supply before opening covers or reaching inside.
The parts and how they wear
| Part | Wear pattern | Check |
|---|---|---|
| Paddle tips | Worn edges, rounding | Measure against the new profile |
| Mixing arms | Wear where tips are fixed; loosening | Bolt tightness, cracks |
| Liners (floor and side plates) | Thinning, grooves | Thickness measurement; loose bolts |
| Shafts | Wear at seal area | Visual at seal changes |
| Shaft seals | Hot fines and binder leaking out | Leakage at shaft ends |
| Bearings | Heat, noise | Temperature; lubrication |
| Discharge gates | Hardened mix, worn seats | Full closing; leakage |
| Gearbox and synchronization | Oil, noise | Oil level and condition |
Paddle-to-liner clearance
As paddles and liners wear, the gap between them grows. Material left in the gap is not mixed properly, builds up and can harden. Keep the clearance within the manual’s range by adjusting or replacing paddles. A growing gap often shows up first as longer mixing time to reach uniform coating or build-up after shutdown.
Daily and weekly care
| When | Task |
|---|---|
| End of every shift | Run empty; clean gates and visible build-up |
| Daily | Check gates close fully; listen for knocks |
| Weekly | Inspect paddle tips and liners; check bolts; grease bearings as specified |
| Monthly | Measure wear; check seals; gearbox oil |
Replacing wear parts
- Replace paddle tips and liners in sets to keep clearances even
- Use the original material and profile — harder is not always better if it cracks
- Torque bolts to the manual’s values and recheck after the first days
- Check arms and shaft surfaces whenever liners and paddles are off
Why the mixer matters for output
Batch output depends on batch size and cycle time — see batch cycle time. A worn mixer needs longer wet mixing for the same coating, which cuts batches per hour. Good maintenance keeps the rated cycle.
Spare parts to keep
At least one set of paddle tips and liners, some arms, seal kits and gate parts — see the spare parts list. For how the mixer works, see the twin-shaft mixer explained. Back to the maintenance checklist.
