Shearex HM-90SV front-mount mulcher

Chosen for timber, not for width

At 230 cm the HM-90SV is barely wider than the HM-88LV beneath it in the Shearex HM front-mount mulcher range, and it draws the same 178 to 288 L/min. Nobody should buy it for coverage. What separates it is a published optimal target material diameter of 40 cm against 25 cm, a build weight of 1,938 kg, and a minimum carrier power of 170 hp against 140 hp. This is a head bought because of what is standing on the block.

Above it there is only the HM-100SV2, a 250 hp dual-motor machine in a category of its own. On the excavator side, the VM-60SR takes the same 40 cm material and reaches ground this head cannot stand on, which makes those two the real alternatives to weigh.

What 40 cm does to the duty cycle

The difference between 25 cm and 40 cm material is not a matter of degree. A rotor working light regrowth spends most of its time accelerating back to speed between light loads; a rotor working 40 cm stems spends long periods near relief with the carrier pushing. Everything downstream of that changes: heat generation rises, rotor speed recovery becomes the operator’s main skill, holders take shock loads instead of abrasion, and travel speed is set by the timber rather than by the ground.

That is also why the published minimum carrier power is 30 hp higher than the HM-88LV’s on identical flow. Power is flow multiplied by pressure, and heavy timber loads the pressure side continuously rather than in bursts. The worked method is on the VM-50SR page; the hydraulic power calculator will run it with the carrier’s measured figures. As an illustration only, the bottom of the flow window at an assumed 350 bar already accounts for around 104 kW, which leaves a 170 hp carrier a modest margin for travel, cooling and driveline losses and puts the top of the window out of its reach entirely.

Volume per hectare decides the job, not diameter

The published target takes this head out of scrub and into mature stems on right-of-way, mine site and plantation rehabilitation work. What decides whether a block pays, though, is tonnes of fibre per hectare rather than the width of any single trunk. Doubling stem diameter roughly quadruples the fibre the rotor has to reduce, so spacing governs the rate: widely spaced large trees can be steady work while a tight stand of identical stems is slow and costly despite every one sitting inside the published figure. Felling or shearing first and reducing the residue afterwards is frequently the cheaper order of operations on tight stands. Maximum diameter versus production diameter carries that arithmetic, and Australian hardwood explains why local species make it harder again.

Specifying the carrier and the motor together

A purpose-built carrier removes the compatibility question and replaces it with a specification question. The circuit fundamentals are set out on the HM-60 page and apply here at larger numbers, but two items deserve particular attention on this head.

The first is cooling under sustained pressure rather than sustained flow. A carrier that holds temperature through a morning in light material can still climb through a summer afternoon in 40 cm timber, because near-relief operation converts a far larger share of the power into heat. Hydraulic cooling and heat covers the mechanism, and the VM-65SV page carries this family’s fullest treatment of cooler specification.

The second is motor build. Specify it against the carrier’s measured circuit rather than its brochure figure: a head geared for flow the machine cannot supply will simply run at lower rotor speed in exactly the timber it was bought for, and the symptom presents as weak performance rather than as a specification error. See hydraulic matching.

Weight also has to be checked even on a purpose-built machine. A front-mounted 1,938 kg head governs ground pressure and stability on slopes, and the manufacturer’s attachment guidance is the document that matters; the skid steer and track loader class page explains why this head sits well outside conventional loader territory.

Mine sites, easements and plantation residue

The contracts are mining and pipeline corridors, heavy powerline and transmission easements and plantation thinning and re-establishment, all of them jobs where pushed-up rows and leftover trunks have to be broken down on the spot. Windrows are the hardest ground in this business for tooling: they hide stumps, rock and old wire beneath a soft surface that gives the operator no warning at all. Carbide is the defensible choice across most of this work, with blades kept for clean green material where ground contact is rare; blades versus carbide teeth compares them.

Holders, not teeth

On light material tooling wears. On 40 cm timber and in windrows tooling breaks, and it is holder damage rather than tooth wear that stops a head working, because a holder is a welding repair rather than a spanner change. Budget by the hectare, keep holders as well as teeth in the truck, and confirm Australian stock and realistic lead times with Machinery Specialist for the items that cannot be improvised; wear parts to price before buying lists them.

Where it hands over

A front-mount head works only ground the carrier can traverse, and on batters, drains and steep or wet corridors the VM-60SR on a 20 to 25 tonne excavator will produce where this head cannot, as excavator mulcher versus skid steer mulcher sets out. A 230 cm head on a large carrier is also a permit and float question to answer before tendering rather than after. Step down to the HM-88LV where material stays under 25 cm and the job is measured in hectares. Step up to the HM-100SV2 only for genuinely industrial clearing behind a 250 hp carrier.

Rotor speed recovery is the whole operator skill

In 40 cm timber the difference between a productive day and a frustrating one is almost entirely in how the operator manages rotor speed. The rotor stores its cutting energy in its mass; every bite spends some of it, and the carrier’s job is to put it back before the next one.

Push into a large stem faster than the circuit can restore speed and the rotor loses bite, the machine starts pushing instead of cutting, the circuit heads for relief, and the heat that follows makes the next recovery slower still. Work the stem from the top in layers, let the rotor recover between passes, and accept that the machine dictates the pace in heavy material. On a carrier near the published 170 hp minimum this is not a refinement, it is the only way the head reaches its rated material at all.

Mine sites and corridor compliance

Much of this head’s work sits inside someone else’s management system, and the constraints are usually more demanding than the vegetation. Mine sites bring induction requirements, vehicle standards, isolation procedures and traffic management plans that apply to a mulching carrier exactly as they do to haul equipment. Transmission easements bring the asset owner’s approach distances, permits and outage arrangements. Both bring reporting.

Practically, that means mobilisation is a programme of its own, and it is worth pricing as one. It also means the machine and crew should be specified to meet the site standard rather than adapted after arrival, since a carrier turned away at the gate for a missing standard costs a week. Clearing on these projects frequently carries conditions under state and local vegetation rules as well, which is worth reading before the work is priced; native vegetation approvals sets out what to look for, and exclusion zones for thrown material and the machine’s working envelope should be established under applicable WHS procedures and the manufacturer’s instructions.

Fire risk when the head is working hard

A head reducing 40 cm timber makes heat, sparks against rock and a great deal of dry fine material, and it does so in the seasons when that combination matters most. The controls are unglamorous and they work: blow down the belt housing, guarding and the carrier’s engine bay at every break rather than at the end of the shift; check bearing temperatures by hand; inspect for hydraulic weeps, because a fine spray onto a hot surface is the mechanism that starts most machine fires; keep the firefighting equipment on the machine serviceable and accessible; and stop work when total fire ban or site conditions require it. Fire risk in clearing operations covers the routine in full, and on mine and easement projects the client’s own restrictions are usually tighter than the statutory position.

Commissioning, and the review at a hundred hours

Because so much of this head’s performance depends on the motor build matching the carrier’s real circuit, commissioning should produce evidence rather than a signature. Measure flow and pressure at the coupler with the head fitted, run under full load in representative material with oil temperature logged, note the rotor speed reached and the recovery time, check belt tension after the first shift and the first week, and torque the tooling holders after the first few hours.

Then review at about a hundred hours against the rate the work was priced on, with production, oil temperature and holder replacements recorded together. A head that is producing below expectation with normal temperatures is a technique or material problem; one producing below expectation with rising temperatures is a circuit or cooling problem. Distinguishing the two early is worth more than any warranty conversation later.

Confirm before ordering

• Fibre per hectare on the blocks being tendered, and the spacing that produces it
• Whether felling or shearing first would beat mulching in place on the densest blocks
• Carrier meets 170 hp and its circuit holds 178 to 288 L/min continuously at pressure
• Motor build specified against the carrier's measured circuit, and stated on the order
• Cooling capacity assessed for sustained near-relief operation in summer, not for light material
• 1,938 kg against the carrier's capacity, stability and ground pressure on the intended terrain
• Holders as well as teeth in the spares budget, costed per hectare
• Transport width and permits, plus delivered price including mounting plate, hoses and harness

Frequently asked questions