Every machine has two kinds of parts: the ones that should last its lifetime, and the ones designed to wear. Confusing the two is expensive — over-stocking long-life parts ties up cash, while under-stocking wear parts costs production hours. Here is how to separate them.
1. The usual wear parts by category
| Category | Typical items | Replacement trigger |
|---|---|---|
| Sealing | O-rings, oil seals, gaskets, gland packing | Leak, or at every scheduled overhaul |
| Bearing & sliding | Bearings, bushings, liners, wear strips | Noise, clearance, temperature rise |
| Drive | Belts, chains, couplings, sprockets | Elongation, cracking, scheduled interval |
| Process contact | Blades, scrapers, mixing paddles, dies | Dimensional loss, wear measurement |
| Fastening | High-strength bolts, lock nuts, anchors | After disassembly (many are single-use) |
2. How much to stock: the ABC approach
- A items — cheap, frequently used, generic (seals, belts, standard fasteners): stock 3–6 months of consumption. They are cheap insurance.
- B items — moderate cost, predictable wear (bushings, liners): stock one full set, reorder when issued.
- C items — expensive, long life, machine-specific (shafts, housings, custom gears): don't stock. Keep the drawing and the supplier ready, and know the lead time.
3. Material upgrades that pay for themselves
| Symptom | Usual cause | Upgrade |
|---|---|---|
| Shaft breaks at the shoulder | Fatigue / stress concentration | 42CrMo or 40CrNiMoA, larger fillet radius, shot peening |
| Journal wears quickly | Soft surface | Induction hardening to HRC 45–55 |
| Bolts loosen or snap | Grade too low / no preload control | 10.9 with torque spec; consider nylon lock or wedge washer |
| Corrosion in wash-down area | Carbon steel | 316 stainless fasteners, Dacromet coating |
4. Order wear parts together with the machine
Spare parts shipped inside the machine crate cost almost nothing extra in freight, and they are on site before the first service interval. This is the single easiest reduction in total cost of ownership.
5. Keep a parts book, not a memory
For every wear item record: part number, drawing or sample photo, material, supplier, lead time, and last price. Machines outlive purchasing managers; a parts book survives both.
6. How we support maintenance buyers
- Supply wear parts against a sample or drawing, including reverse-engineered non-standard items
- Material upgrade recommendations with the reason stated
- Consolidated annual shipments to reduce freight and customs handling
- Fastener kits and seal kits per machine