As a gyratory crusher's mantle wears, tightening the closed side setting can mask the loss—until your product runs finer than your contract allows. Here is how to read the relationship before you buy or sell.
A used gyratory crusher is easy to price on what you can see: frame condition, drive arrangement, motor size. What is harder to read is the state of the crushing chamber itself, specifically the relationship between mantle wear and the closed side setting (CSS). Get that relationship wrong and you can inherit a machine that meets your tonnage target on day one but drifts out of product specification within weeks, long before you have budgeted for new wear parts.
For a manufacturer managing refurbished stock or trade-in units, this is equally a disclosure problem. A buyer who discovers the CSS baseline was not documented will hold you accountable for any off-spec output they produce during the transition. Clear records protect both sides.
In a gyratory crusher, the main shaft carries a conical mantle that gyrates inside a fixed concave (also called the bowl liner). The CSS is the smallest gap between the mantle surface and the concave at the bottom of the crushing stroke. Rock that cannot pass through that gap keeps being worked until it can. The CSS therefore sets the top size of the product leaving the machine.
Reduce the CSS and the product gets finer and the machine works harder to pass each tonne. Increase it and the product gets coarser and throughput rises. The CSS is not fixed; it is adjusted by raising or lowering the main shaft through a hydraulic or mechanical adjustment system, depending on the crusher design.
CSS vs. OSS
The open side setting (OSS) is the maximum gap, reached on the opposite side of the gyrating stroke. The OSS determines the absolute largest particle that can exit the chamber. Both measurements matter when you are verifying product gradation against a contract specification.
The mantle and concave are consumable wear parts, made from manganese steel or similar alloys. As they wear, metal is lost from both surfaces. The effective gap between them grows. If an operator does nothing, the product gets coarser and can exceed the top-size limit in a sales or processing contract.
In practice, operators compensate by tightening the CSS—raising the main shaft to close the gap back to the target. This keeps the product size within specification, but it has two consequences that are not immediately visible in the daily output data.
The result is a machine that appears to be performing—it is making the tonnage, the product looks right to the eye—but the CSS has been tightened so far that any further wear forces a choice: shut down for a reline, or accept off-spec product. When you buy that machine, you inherit that choice.
You cannot determine mantle condition from the outside of a crusher. The measurements you need are inside the crushing chamber, and they require the machine to be stopped, locked out, and physically entered or measured with appropriate tooling. Plan for this during your inspection window.
Ask the seller for the historical CSS settings with dates. A crusher that has been progressively tightened over its last months of operation is telling you that the mantle has been wearing and operators have been compensating. Compare the current CSS against the original commissioning CSS for this machine on this application. If the current setting is significantly tighter than the design or commissioning value, the wear parts are well into their service life.
Reputable sellers will have periodic mantle thickness measurements taken with ultrasonic thickness gauges or direct measurement at defined reference points. Ask for these records with dates and location on the mantle. If no measurements exist, treat the wear-part condition as unknown and price accordingly—or commission a measurement as a condition of purchase. The mantle manufacturer's documentation will state the new thickness at each reference point; compare the current reading against that to get remaining wear life.
The hydraulic or mechanical adjustment system has a finite travel. If the shaft is already near the top of its adjustment range to maintain the current CSS, there is very little room to compensate for further wear before a reline is mandatory. Ask the seller for the current shaft position relative to the maximum adjustment limit.
If the machine has been operating recently, ask for a sieve analysis of product taken from the stockpile under the current CSS. Compare the gradation against your contract specification. A product that is passing the top-size test but showing elevated fines is a signal that the CSS has been tightened beyond the design optimum. This does not require a full pilot run; a single representative sample taken from multiple points across the stockpile face is enough to flag a fines problem.
If no sieve data is available
Do not accept a visual assessment of the product as a substitute for a sieve analysis. Fines variation that breaches a contract specification is not visible to the eye. If the seller cannot provide recent sieve data, factor an independent sample into your due diligence before you commit to a price.
For manufacturers offering trade-in or refurbished gyratory crushers, disclosure of the CSS baseline and mantle condition is not only fair practice—it removes ambiguity that can become a commercial dispute. A buyer who starts operating a machine without an agreed baseline has no way to tell whether off-spec output during the first weeks is a function of the inherited wear condition or their own setup.
Document and provide: the CSS at time of sale, the mantle and concave thickness measurements at defined reference points, the shaft position reading, any recent sieve analysis of product, and the date and tonnage since the last reline. If a reline is pending, state it and reflect it in the price rather than leaving the buyer to discover it after commissioning.
Buyers who receive this documentation can verify the machine against their own contract specifications before they commit. That reduces negotiation friction and positions the manufacturer as a credible, well-organised supplier—which matters when managing repeat business through a dealer network.
Once you have the mantle thickness measurements and the CSS record, you can build a rough remaining wear-life estimate. Compare the current mantle thickness against the new thickness at the same reference points, and against the minimum thickness specified by the mantle manufacturer before mandatory replacement. The fraction of service life consumed gives you a basis for pricing the remaining life into your offer.
Add the cost of a reline—new mantle and concave, installation labour, and downtime—to your total cost of ownership calculation. A crusher offered at an attractive price with a mantle at the end of its service life is not a cheap machine; it is a machine with a reline cost that arrives shortly after commissioning.
The EasiMachines cost-of-ownership calculator lets you enter your own wear-part cost estimates, downtime assumptions and expected throughput to see the multi-year picture. It is an estimate based on the figures you supply, not a quote, but it makes the reline cost visible before you commit.
| Measurement | What it tells you | Red flag |
|---|---|---|
| Current CSS (mm) | The gap the machine is producing product at today | CSS significantly tighter than commissioning value suggests advanced mantle wear |
| CSS history log | Whether and how much the gap has been tightened over time | Steadily tightening CSS with no reline record indicates wear compensation is ongoing |
| Mantle thickness at reference points | Remaining wear metal versus new thickness | Less than 25–30% of original thickness remaining at any reference point warrants immediate reline budget |
| Shaft adjustment position | How much CSS adjustment range is left | Near maximum travel means little margin before reline is forced |
| Sieve analysis of recent product | Actual product gradation under current CSS | Elevated fines proportion signals CSS has been tightened beyond design optimum |
| Tonnes since last reline | Total throughput on current wear parts |
Use the inspection checklist
The EasiMachines printable pre-purchase screening checklist at /resources/inspection-checklist includes wear-part and setting checks for crushing equipment. Use it as a structured prompt during your site visit; it supports, and does not replace, inspection by a qualified person.
Before you enter price negotiations on a used gyratory crusher, ask the seller for the mantle thickness measurements, the CSS gap record, and a recent sieve analysis of product. Lay that data against your contract product specification. If the current CSS is already producing fines at the edge of your allowable range, further wear will push you over the limit before the mantle reaches end of life—and you will face an unplanned reline or a contract penalty, whichever comes first.
If the documentation is incomplete, use the inspection checklist to structure a site visit with a qualified crushing-plant engineer. For machines not yet listed, a Wanted request lets relevant sellers with documented stock find you, rather than you settling for the nearest available machine without records.
Yes. Fitting new mantle and concave wear parts restores the chamber geometry, and the shaft adjustment system can be returned to its original position range. After a reline you should re-establish the CSS at the commissioning value for your application and take a fresh sieve analysis before resuming full production. Keep this record as the new baseline.
Practice varies by operation, but most experienced plant teams measure and log the CSS each time they adjust the shaft and at regular maintenance intervals. The key is consistency: a log that records CSS alongside cumulative throughput tonnage is far more useful than occasional spot measurements, because it lets you project when the next adjustment or reline will be needed.
Yes, the same principle applies. Cone crushers use the same CSS terminology and the same compensation mechanism—tightening the CSS as the mantle and bowl liner wear. The geometry of the crushing chamber differs between a gyratory and a cone crusher, so the specific tolerance thresholds and reference points differ, but the diagnostic approach is the same: request the CSS log, wear-part thickness measurements, and recent sieve data.
A reline is the replacement of the mantle and the concave (bowl liner) wear parts inside the crushing chamber. It requires the machine to be shut down and locked out, the worn parts lifted out using overhead crane or specialised tooling, and new parts seated and backed with an epoxy or metallic backing compound. The work is typically done by the OEM's service team or a specialist contractor, and the downtime can range from a shift to several days depending on crusher size and site conditions.
Disclaimer: The buying and selling guidance in this article is based on EasiMachines' own experience and research. It is general information, not professional, legal or financial advice. Use your own judgement and carry out your own due diligence before you buy or sell; EasiMachines is not responsible for any loss or damage arising from decisions made without that due diligence.
About the author
The EasiMachines Editorial Desk
EasiMachines Editorial Desk
The EasiMachines Editorial Desk publishes practical guidance for industrial machinery buyers, sellers, dealers, manufacturers and auction houses on sourcing, inspection, pricing and selling. It is general guidance, not a certified inspection, appraisal or legal advice: verify specifications and condition with the manufacturer or a qualified inspector. Corrections and practitioner input are welcome via the contact page.
| No reline record means wear-life baseline is unknown |
