Why inspect before shipping
Once a container leaves the plant, every problem becomes more expensive. A wrong marking can be fixed in a day at the plant, but not after the goods are sea-freighted halfway across the world. Pre-shipment inspection compares the finished lot with the approved specification and the retained sample, while correction is still possible. It does not replace process control at the plant; it confirms that the controls worked for this lot.
The depth of inspection depends on the value, the application and the history with the plant. A repeat order from a proven partner may need a lighter check than a first lot of a new designation. In either case the inspection plan should be agreed before production starts, not after the goods are packed.
Sampling: how many pieces to open
Bearings are inspected by sampling, not by checking every piece. A common approach is to draw a random sample from several cartons, using a standard sampling table and an acceptance level agreed in writing, then record results per sample. For small lots, a fixed number of pieces per designation is often used. Three principles apply:
- Draw from different cartons and pallet layers, not from the top of one box.
- Keep the drawn pieces identified, so a failed piece can be traced to a carton and batch.
- Agree in advance what happens if the sample fails: a wider sample, a full sort by the plant, or rejection of the lot.
The inspection plan
The table summarises the usual items. Acceptance limits come from the drawing, the datasheet or the standard that applies, such as ISO 492 for tolerance classes; they are agreed per order and are not stated in general articles.
| Item | How it is checked | Why it matters |
|---|---|---|
| Designation and suffixes | Visual check against the order, on bearing and label | Wrong clearance or seal type is a common error |
| Bore, outside diameter, width | Calibrated gauges or a dial bore gauge | Fit on shaft and in housing |
| Radial internal clearance | Clearance gauge or tester | C3, CN or C2 must match the order |
| Rotation feel | Hand turn, listening for roughness | Detects dirt, damage and tight spots |
| Noise or vibration | Vibration tester against a reference piece | Motor and appliance quality |
| Hardness (HRC) | Hardness tester on sample rings | Fatigue life and wear |
| Surface and rust | Visual check under good light | Transit and storage damage |
| Seals and shields | Seating, appearance, grease leakage | Contamination and grease loss |
| Marking and label | Compare with artwork and sample | Brand, batch code, spelling |
| Packing | Wrapping, carton, pallet, weights | Protection in transit |
Additional items, such as cleanliness, roughness or cage condition, are added when the application calls for them. The tolerance and clearance basics are explained in the tolerance and clearance guide.
Dimensions and clearance in practice
Measure at room temperature and let the pieces rest in the measuring room first, because steel changes size with temperature. Use calibrated instruments and record the instrument number on the report. For bore and outside diameter, take readings at more than one angle and position to catch out-of-round parts. For width, measure at several points. Compare the readings with the nominal ISO value and the tolerance class on the order, and keep numerical results, not just pass or fail; trends across lots reveal tool wear before it becomes a defect.
Radial clearance is checked with a gauge that applies a defined measuring load; the result is compared with the group named in the suffix, such as C3. Remember that clearance after mounting is smaller than clearance before mounting, so the group on the order should reflect the fit and the temperature of the application.
Noise, rotation and hardness checks
Three checks need a little more care because they depend on method rather than on a single reading. Rotation feel is the quickest screening test: an experienced inspector turns the bearing by hand under a light axial load and listens and feels for roughness, tight spots or a gritty sound. It is subjective, so compare against the retained sample rather than against memory. Noise or vibration testing is more objective but depends on the test rig, the speed and the load, so use the same rig and setting for the sample and for the lot, and record the grade agreed on the order, such as a Z or V group.
Hardness is checked on a sample of rings, or on parts cut from a lot where destructive testing is agreed. The result is reported in HRC and compared with the range specified for the steel and heat treatment. A hardness result that drifts between lots is an early warning of a furnace or quench problem, long before field failures appear. Where the application is demanding, ask also for cleanliness and roughness records for the lot.
Marking, cleanliness and packing
Many shipping disputes concern details that are not engineering at all. Check that markings are legible, correctly positioned and spelled the same on the ring, the box and the carton. Check that batch codes appear where agreed. Compare box artwork and label wording with the approved sample. Look at the wrapping: rust protection paper or a VCI sleeve, the oil film, the carton strength and the pallet. Weigh a few cartons and compare with the packing list. The reasons behind these checks are described in bearing packaging.
Recording results and deciding
- Open the report with the order number, designations, lot size, sample size and date.
- List each check with the result, the instrument and the acceptance limit.
- Attach photographs of the sample, markings, carton labels, pallet and loading.
- State a decision: release, release with remarks, hold for rework or reject.
- File the report with the batch records and keep a retained sample from the lot.
The decision should be made against the criteria agreed at the start. If the lot is borderline, discuss it with the plant on the day, while the goods are in front of you. A lot that is released with remarks should name the issue and the agreed remedy, so that it does not reappear unannounced on the next order.
Who inspects
Options are the plant's own quality department, a third-party inspection agency, the buyer's own representative or the sourcing desk. For first orders and demanding applications, an independent party is advisable, because it reduces the temptation to rationalise a borderline result. The desk can organise inspection at the plant and share the report, and the broader approach is described on the quality control page. Include the inspection plan in your enquiry through the quote form, and see the audit checklist for upstream checks.