Author: Lily Wang Publish Time: 2026-10-13 Origin: Yile Machinery
A replacement girth gear may be accurately manufactured and still cause trouble when it reaches the plant. A mounting hole may not match the existing interface. Segments may not assemble as expected. The supplied inspection report may omit a critical tooth measurement. Or the gear may be damaged during a long sea shipment because its machined surfaces were not adequately protected.
For a ball mill, SAG mill, rotary kiln, or industrial dryer, these are not minor inconveniences. A problem discovered during a scheduled shutdown can delay installation and extend downtime.
Before shipment, buyers should confirm three things: the girth gear meets the agreed manufacturing specification, the supporting records are complete, and the gear is protected for the journey to site. Final operating backlash, contact pattern, and installed runout must then be checked during site assembly and commissioning.
This guide gives procurement managers, maintenance engineers, and OEM buyers a practical inspection checklist for custom and replacement girth gears. It also explains which requirements should be agreed upon before production, rather than added when the gear is ready to ship.
Yile Machinery manufactures custom heavy-duty gears and pinions for rotary kilns, ball mills, crushers, and other industrial equipment. For a meaningful quotation and inspection plan, we recommend sharing the drawing, application details, and required acceptance criteria at the RFQ stage.
A pre-shipment review should normally cover:
Approved drawings and revision status
Material identity and traceability
Heat-treatment records and specified hardness results
Agreed non-destructive testing (NDT)
Tooth geometry and applicable gear-accuracy measurements
Critical mounting and segment-joint dimensions
Factory trial assembly, if specified
Final inspection reports and release documents
Match marks, preservation, packing, and shipping identification
The exact checks and acceptance limits must come from the approved drawing, purchase order, inspection and test plan (ITP), and agreed standard. No single generic checklist can replace those project-specific documents.
The most effective time to define inspection requirements is before the manufacturer begins production.
An ITP should identify:
What will be inspected or tested
Which document defines the acceptance criterion
When each check occurs
Who performs it
Which steps require buyer review or witness
What records will be included in the final document package
For example, a buyer may request an NDT report. That request is incomplete unless the parties also agree on the method, areas to be examined, inspection timing, procedure, acceptance criteria, and reporting requirements.
The same applies to gear accuracy. “Manufacture to DIN,” “meet AGMA,” or “ISO quality required” is not sufficiently precise by itself. The order should identify the applicable standard or specification, required grade or limits, and measured characteristics relevant to the gear.
Buyer tip: Ask the supplier to identify any drawing requirement it cannot measure or verify with its proposed inspection method before approving production.
Start by confirming that the gear being inspected is the gear you ordered.
Review:
Approved manufacturing drawing number and revision
Gear designation and purchase-order reference
Segment quantity and segment identification
Material grade
Mating pinion reference, where applicable
Approved deviations or engineering changes
Identification carried from material or casting stage through final machining
Revision control matters especially in replacement projects. The original equipment drawing may have been modified after field measurements, or mounting details may have been changed to match repairs made to the existing machine.
If a supplier has proposed a material substitution, changed a joint detail, or adjusted a mounting dimension, that change should be documented and approved—not discovered in the final inspection package.
A material test certificate (MTC) helps establish what material was supplied. Depending on the specified material and contract requirements, it may include chemical composition, mechanical properties, heat or batch identification, and the applicable specification.
Check that the certificate:
Identifies the agreed material grade
Can be traced to the supplied gear or segments
Reports the properties required by the purchase specification
Clearly identifies any approved equivalent material
Heat treatment should also be supported by records appropriate to the agreed process. If hardness is specified, the report should show where measurements were taken and whether the results meet the approved range.
Do not assess hardness as an isolated “higher is better” figure. The required condition must suit the girth gear's material, tooth design, duty, and mating pinion. If the order specifies different test locations or requirements for the tooth area and body, the report should make that distinction clear.
Non-destructive testing can identify discontinuities that a visual or dimensional inspection may not reveal. The method must fit the material, part geometry, and defects of concern.
Common methods include:
Method | Typical purpose | Buyer should confirm |
UT — Ultrasonic Testing | Examination for specified internal discontinuities | Examination zones, procedure, coverage, acceptance criteria, report |
MT — Magnetic Particle Testing | Detection of surface and near-surface indications in suitable ferromagnetic material | Areas examined, surface condition, procedure, indication disposition |
PT — Penetrant Testing | Detection of surface-breaking indications on suitable surfaces | Areas examined, preparation, procedure, acceptance criteria |
The appropriate extent of NDT depends on the approved specification. A report stating “UT passed” is less useful than one that identifies the component, method, examination scope, procedure, results, and disposition of any relevant indications.
For segmented gears, buyers may give particular attention to specified high-stress or critical areas, such as tooth roots, rim transitions, joints, mounting features, and approved repair areas. The exact examination zones should be agreed in advance.
Important: NDT does not prove that a gear will never fail in service. It demonstrates that the examined areas met the agreed inspection requirements at the time of testing.
Tooth quality is central to how a girth gear meshes with its pinion. The required measurements depend on the design and the manufacturing standard specified in the order.
Confirm the basic tooth data first:
Module or diametral pitch
Number of teeth
Pressure angle
Helix angle and hand, if applicable
Face width
Tooth thickness and specified measurement method
Depending on the order, the final gear inspection may also address:
Tooth profile deviation
Tooth trace or lead deviation
Pitch variation
Tooth spacing
Relevant tooth-surface condition
Other characteristics required by the approved drawing or gear standard
Ask for a report that identifies what was measured, how it was measured, the applicable limit, and the actual result. A blanket statement that the gear is “precision machined” is not a substitute for agreed measurement data.
For a replacement project, confirm whether the new girth gear will run with an existing pinion or with a newly supplied one. If the old pinion is being reused, its tooth geometry and wear condition should be assessed separately; a factory report for the new girth gear cannot establish the condition of the pinion already at site.
Explore Yile Machinery's gears and pinions range for the types of custom transmission components that may be reviewed together in a replacement project.
A gear can have correctly cut teeth but still be impossible to install within the planned shutdown window.
The final dimensional report should address the critical-to-fit features identified on the approved drawing, which may include:
Mounting diameter or interface geometry
Bolt-hole quantity, diameter, and position
Bolt-circle dimensions
Flange or mounting-face dimensions
Key interfaces or locating features, if applicable
Segment-joint faces
Dowel locations or other locating provisions
Relevant rim, web, and body dimensions
For an older mill or kiln, do not assume the machine's current mounting interface still matches its original drawing. Previous repairs or modifications may have changed the actual dimensions. Field verification before manufacture is often more valuable than discovering a mismatch during installation.
Large girth gears are frequently supplied in segments. In such projects, inspection of individual segments is important—but it may not answer every assembly question.
Where required by the contract, a factory trial assembly can help verify:
Segment identity and sequence
Joint-face fit
Locating features
Bolt-hole alignment
Match marks
Specified assembled dimensions on the factory setup
Buyers should ask the manufacturer what its proposed trial-assembly method can actually demonstrate and request records for the agreed checks.
A factory trial assembly is not the same as final site acceptance. The gear's installed radial runout, face runout, backlash, and tooth contact pattern also depend on the mill or kiln mounting surface, shell condition, pinion position, and installation workmanship. Those values must be measured again after site assembly.
This distinction is particularly important when specifying runout. Avoid putting an unqualified “installed runout” requirement into a factory-only inspection checklist without defining the measurement setup and which party is responsible for the site result.
If a manufacturing defect or nonconformity was identified and corrected, buyers should know what happened.
Request documentation for any agreed:
Repair or rework
Weld repair, if permitted by the purchase specification
Engineering concession
Material substitution
Dimensional deviation
Reinspection after corrective work
The key question is not simply whether a repair occurred. It is whether the repair was permitted, approved where required, performed to an agreed procedure, and reinspected against the applicable acceptance criteria.
An unexplained gap between an initial inspection result and a final “accepted” status should be clarified before shipment release.
Before authorizing shipment, ask for a document index and confirm that all agreed deliverables are present.
A project-specific package may include:
Approved final drawing and revision record
Material test certificate
Heat-treatment record
Hardness test report
UT, MT, or PT reports as specified
Final dimensional report
Gear measurement report
Trial-assembly record, if required
Nonconformance and repair records, if applicable
Final photographs and identification records
Packing list and shipping marks
Not every project requires every document on this list. What matters is that the purchase order and ITP state what the buyer will receive, and that the final package matches those commitments.
If third-party inspection is needed, agree on the inspection body's role and witness or hold points before production. Arranging a witness inspection only after machining is complete may leave important earlier stages impossible to observe.
A successful factory inspection can be undermined by poor preservation or shipping preparation.
Before release, confirm that the packing plan addresses:
Protection of machined faces and gear teeth
Corrosion prevention appropriate to shipping and storage duration
Moisture protection
Secure support of each segment
Prevention of tooth-to-tooth or metal-to-metal transport contact
Clear lifting-point and centre-of-gravity markings where needed
Segment match marks that remain legible after shipment
Packing identification that matches the documents
If the gear will be stored at the plant before installation, tell the manufacturer. A gear moving directly into assembly may need a different preservation plan from one expected to remain in storage for months.
Yile Machinery's broader product range includes other heavy-duty replacement components that may be coordinated within a mill or kiln shutdown project.
Check | Before shipment at the factory | After installation at site |
Material and heat-treatment records | Yes | Review supplied records |
Specified NDT and dimensional inspection | Yes | Additional checks if required |
Gear tooth measurement | Yes | Condition checks as needed |
Segment identification and factory trial fit | If specified | Final assembly required |
Installed radial and face runout | Factory setup only, if defined | Yes—measure on the actual machine |
Operating backlash | Not as a final site value | Yes |
Loaded tooth contact pattern | Not as a final site value | Yes |
Lubrication coverage during operation | No | Yes |
A clear division of responsibility prevents a common purchasing mistake: treating a factory inspection certificate as proof that the entire drive system has been correctly installed and aligned.
Use this short list before issuing shipment approval:
The supplied gear matches the approved drawing revision.
All segments and major components are traceably identified.
Material records match the specified grade.
Heat-treatment and hardness results meet the agreed requirements.
Required NDT reports identify examination scope and results.
Gear measurements include actual values against agreed limits.
Critical mounting and joint dimensions have been checked.
Required trial assembly has been completed and documented.
All deviations and repairs have been disclosed and accepted.
The final document package is complete.
Match marks, preservation, and export packing are confirmed.
A separate site plan exists for installation, runout, backlash, and contact-pattern checks.
No. A manufacturer may measure relevant gear or trial-assembly characteristics in a defined factory setup, but final installed runout depends on the machine's mounting surface, shell condition, segment assembly, and installation. It must be checked at site against agreed limits.
That depends on the areas and defects of concern and on the agreed material and inspection specification. UT may be used for specified internal examination, while MT can be used for specified surface and near-surface examination of suitable ferromagnetic material. Define the method, coverage, timing, and acceptance criteria with the manufacturer rather than requesting “NDT” without further detail.
No. Material records are important, but they do not replace tooth measurements, critical dimensional inspection, required NDT, mounting checks, or site commissioning measurements.
A trial assembly is worth considering when joint fit, segment sequence, and mounting alignment create significant installation risk. Whether it is required—and exactly what will be measured—should be stated in the purchase order and ITP.
Yes. If the existing pinion has substantial wear, pitting, damaged teeth, or an unsuitable contact pattern, it may reduce the life of the new girth gear. Pinion inspection should be part of replacement planning.
Send the gear drawing or measured sketch, equipment application, module, tooth count, face width, segment and mounting details, material requirements, pinion information, requested inspection scope, quantity, delivery schedule, and destination. If drawings are unavailable, provide photographs and field measurements for an initial engineering review.
A good girth gear quotation should explain more than price and lead time. It should make the proposed manufacturing scope, inspection scope, and buyer approval points clear.
If you are sourcing a custom or replacement girth gear for a ball mill, SAG mill, rotary kiln, or dryer, send Yile Machinery:
Your latest drawing and revision
Equipment type and operating application
Gear and pinion data
Material and heat-treatment requirements
Required NDT and gear-accuracy criteria
Segment assembly and mounting details
Required reports or third-party inspection points
Quantity, delivery date, and destination
We can review your requirements for custom girth gears, pinions, and related heavy-duty gears. For other mill, kiln, and industrial replacement components, browse our products, or visit the Yile Machinery Blog for more sourcing and maintenance guides.
Send your drawing and inspection requirements to request a technical review and quotation.
