Fixed vs Mobile Gantry Shear: The Real Trade
The fixed-versus-mobile decision is usually presented as a lifestyle choice — stability against flexibility — when it is actually an engineering trade with measurable terms on both sides. Force against mobility. Continuous duty against deployment speed. Cost per ton against transport cost. This article puts numbers-shaped descriptions on each side of the trade, so the decision can be made against your operation rather than against a preference.
For the mobility case in detail, read the mobility guide; for the fixed-installation specification, the buying guide is the framework.
The Trade, Term by Term
| Dimension | Fixed gantry | Mobile gantry |
|---|---|---|
| Force ceiling | Highest in category — portal frame on foundation | Lower-to-mid range — chassis carries reaction |
| Duty rating | Quoted against declared shift pattern, three shifts possible | Lighter or intermittent duty |
| Installation | Foundation, anchorage, electrical scope | Position, connect, run |
| Deployment time | Weeks to months including civil works | Days |
| Power | Grid supply typical; generator/diesel options | Generator or diesel typical |
| Cost per ton over life | Lower at heavy duty | Lower at light, dispersed duty |
| Relocation | Not designed for it | The point of the design |
Read the table as a set of exchanges rather than a ranking. Every row is something the mobile design gives up to buy the bottom row, and something the fixed design gives up to buy the top rows. The operation decides which exchanges are worth making.
When the Fixed Trade Wins
The fixed installation wins when three conditions hold, and they usually hold together:
Heavy material as a daily diet. Plate at the heavy boundaries, continuous HMS, demolition feed with adhered sections — the material where the portal frame’s force distribution and the anchored foundation’s reaction capacity decide the machine. Our Q91-630 is the continuous-HMS watershed at 60 to 80 tons a day, and the range runs to the 2000-ton flagship.
Continuous duty. Two or three shifts, declared honestly, with a maintenance window inside the production plan. The fixed build is quoted against that duty; the mobile build is typically not.
A stable site. The material comes to the yard and stays coming. The foundation project is a one-time cost amortized over a decade of tonnage, and the installation lead time is absorbed by the site work rather than by a project deadline.
When those three hold, the fixed installation’s lower cost per ton at heavy duty compounds into the machine’s whole economic case — the three-shift economics guide covers the arithmetic at mill scale.
When the Mobile Trade Wins
The mobile trade wins when the operation’s binding constraint is location rather than tonnage:
The material moves. Demolition and infrastructure projects, scattered collection, phased relocations — the machine follows the work, and the transport cost per move is smaller than the material’s travel cost per load.
The site is temporary or cannot be built on. Rented ground, permissions with end dates, ground that will not hold anchorage. The foundation is not a cost in these cases — it is an impossibility.
Deployment speed has value. A project with a deadline prices weeks. The mobile unit’s days-not-months deployment is worth real money when the alternative is a project waiting on civil works.
The duty is light or intermittent. Below the mobile design’s duty rating, its limitations never bind — and the operation gets a machine that matches its actual rhythm rather than one specified for a duty it does not run.
The Test That Decides It
One question settles most cases: does the material come to a fixed point, or does the machine go to the material? If the material comes — a yard, a mill intake, a buyer’s specification — the fixed trade wins. If the machine goes — projects, scattered sites, phased work — the mobile trade wins. Operations that answer “both” usually need two machines rather than one stretched across both answers.
Send the material profile, the site pattern, the shift pattern and the power situation, and the written recommendation comes back within two business days naming the arrangement your numbers support — including, when it is the honest answer, the fixed class you did not ask about.
The Amortization Arithmetic
The fixed-versus-mobile trade is an amortization question wearing an engineering costume. The fixed installation’s foundation, anchorage and electrical scope are a one-time cost amortized over a decade of tonnage — at heavy continuous duty that per-ton figure is small, which is why the fixed trade wins there. The mobile unit skips the foundation but pays a transport cost per move and typically carries a higher cost per ton at any duty it can perform. The two curves cross at a point determined by your duty and your move frequency, and the crossing point is the decision.
Heavy duty with rare moves sits far on the fixed side; light dispersed duty with frequent moves sits far on the mobile side. Operations between the two should compute both per-ton figures rather than compare purchase prices — the purchase price difference is usually smaller than the operating difference over the machine’s life.
The Hybrid Answer
Some operations genuinely need both: a fixed station for the production duty and mobility for the project work. The honest answer there is two machines rather than one stretched across both — and the pairing is specified the same way a shear-and-baler line is, with the handoffs documented and each machine sized against the material it will actually take. The operations that try to serve both duties with one mobile machine discover the force ceiling binds on the production material and the transport cost binds on the project material, and neither duty gets the machine it needed. Two right-sized machines beat one stretched machine in almost every case the trade-off arithmetic produces.
The Site That Changed Its Mind
One failure mode is worth naming because it is expensive: the operation that bought mobile for flexibility, then settled. The machine that moved twice in ten years paid the mobility premium — transport, permits, loading — for a capability the operation never used, and it carried the lower force ceiling and duty rating the whole time. The reverse failure is the operation that bought fixed, then won a project contract that required the machine elsewhere, and discovered the foundation was not a cost but a location. Both failures come from the same source: the site pattern was a preference rather than a document. Write the pattern down, honestly, before the design is chosen.
The Decision, Written
The fixed-versus-mobile decision should end as a written sentence, not a feeling: the material comes to a fixed point or the machine goes to the material. Everything else in this article — the force ceiling, the duty rating, the amortization arithmetic, the site pattern — exists to make that sentence writable against evidence rather than preference. Write it, attach the numbers that support it, and send both with the inquiry. The quotation that comes back within two business days will name the arrangement the evidence supports, and the operation will own the decision rather than remember it.
Buyer FAQ
Is the mobile design just a fixed machine on wheels?
No — the chassis carries reaction force differently than an anchored portal frame, which is why the force ceiling and duty rating differ. It is a different structure, not a mounting option.
Can a mobile unit be upgraded to fixed duty?
Not structurally. The duty rating follows the chassis, and a mobile build quoted beyond its rating is the most expensive way to own one. The honest conversation at quotation is about the duty the mobile build actually carries.
What is the cost per move?
Permits, route planning and loading or crane arrangements, costed per relocation. For monthly movers it is routine; for a one-time move it erases the mobility premium.
Which gantry class suits a mobile application?
Mobile designs concentrate in lower-to-mid force ranges, and the class follows the material rather than the preference. The recommendation comes back in writing against your material profile and site pattern.
What if my operation has both fixed and project work?
Two machines sized to their jobs usually beats one machine stretched across both. The quotation will say so if that is what your numbers support, in writing. Write the sentence, attach the numbers, and send both with the inquiry — the recommendation comes back in writing within two business days. The crossing point of the two per-ton curves is the decision, and it is computable before the order from the duty and the move frequency alone. Two per-ton figures, computed honestly, decide more yards than any purchase-price comparison ever has. The decision ends as a written sentence supported by two computed per-ton figures, and that sentence is what the quotation should be written against. The decision ends as a written sentence supported by two computed per-ton figures, and that sentence is what the quotation should be written against before either machine is specified. Write it, attach the numbers that support it, and send both with the inquiry — the recommendation that comes back names the arrangement the evidence supports.