Vertical Mount Bevel Helical Bucket Elevator Head Shaft Gearbox

A vertical bucket elevator handling petroleum coke or ore fines is one of the least forgiving positions in a bulk-handling plant. The gearbox sits 50 metres above grade on a steel head platform, runs continuously, and carries the full suspended weight of a loaded boot-to-head chain strand every second it operates.

The MTB3SV12-56-C is a three-stage right angle gearbox built for exactly the described position. Frame size 12, nominal ratio 56:1, solid output shaft, vertical mounting attitude, shaft arrangement form C.

The Engineering Challenge at an Elevator Head

Consider a typical duty in a coke calcining plant: 500 t/h of calcined petroleum coke lifted 55 metres on a central-chain elevator. Pure lifting power is 74.9 kW; digging resistance at the boot, chain friction and sprocket losses push the installed requirement to roughly 112 kW.

A 132 kW four-pole motor at 1,470 rpm is selected. Through a 56:1 reduction the head shaft turns at 26.25 rpm, giving 1.37 m/s chain speed on a 1,000 mm head sprocket — inside the 1.2–1.5 m/s band where discharge remains centrifugal and clean.

The steady-state torque demand at the output shaft is 48,020 Nm. The MTB3SV12 frame carries a nominal mechanical rating of 90,000 Nm, so the installation runs at a service factor of 1.87.

A figure of 1.87 is not padding. Bucket elevators generate breakaway torque of 200–250% of running torque when restarted into a flooded boot, and AGMA 6013 guidance for 24-hour mining duty with heavy shock places the minimum service factor at 1.75.

Three Gear Stages, One Bevel Set

The gearbox uses a single spiral bevel stage followed by two helical stages. The bevel set turns power through 90 degrees, allowing the motor to stand in the vertical plane while the solid output shaft couples directly to the horizontal head shaft.

The arrangement removes the long, cantilevered motor bedplate demanded by an inline unit. On a congested head platform, footprint recovered is inspection access gained.

All gearing is carburised from 20CrMnTi and 17CrNiMo6 alloy steel, hardened to 58–62 HRC at the case, then profile ground to ISO 1328 accuracy grade 6. Ground flanks hold the contact pattern under the bending moment a loaded elevator imposes, and they cut mesh noise by 6–8 dB(A) against a lapped equivalent.

Tapered roller bearings in heavy series carry the output shaft, with calculated L10h life above 50,000 hours per ISO 281 at the rated overhung load of 180 kN measured at mid-shaft extension.

Pain Point One: Abrasive Ingress

Coke dust and ore fines are the primary killers of elevator head gearboxes. Particles migrate along the output shaft, chew through a single radial lip seal in weeks, and contaminate the oil sump with silica harder than the bearing raceways.

The MTB3SV12-56-C uses a taconite sealing cartridge at the output shaft — a non-contact labyrinth with laminar rings, backed by two grease-purgeable chambers. Fresh grease pushed through the outer chamber at each 500-hour service interval carries contaminant outward, never inward.

Oil breathing is handled by a filtered steel breather with a 10 µm element and desiccant cartridge. A plastic vent plug on an outdoor elevator head is an open invitation for airborne fines and condensate.

Exterior protection is a two-pack epoxy system at 240 µm dry film thickness, rated to ISO 12944 category C5-M for coastal and chemically aggressive atmospheres.

Pain Point Two: Shock Load and Load Runback

A loaded elevator strand will run backwards the instant power is lost. Reverse rotation dumps 55 metres of material into the boot, buries the tail sprocket, and frequently tears buckets off the chain.

A sprag-type backstop is fitted to the high-speed shaft of the MTB3SV12-56-C, sized to a holding capacity of 130% of the 90 kNm nominal output torque referred through the 56:1 ratio. Mounting on the high-speed shaft keeps the sprag element small and its inspection cover accessible from the platform walkway.

For controlled restarts into a partially flooded boot, a 5.5 kW auxiliary drive can be flanged to the rear input shaft extension. Creep speed at 1:60 of main speed allows an operator to rotate the strand through a full circuit and empty the boot before the main motor is energised.

Where starting torque must be limited further, a hydrodynamic fluid coupling between motor and input shaft caps breakaway torque at approximately 160% of rated motor torque and brings the loaded strand up over 6–10 seconds.

The QT500-7 ductile iron housing is ribbed and stress relieved, sized around the combined thrust and bending moment of the bevel stage rather than around torque alone. Two large inspection covers give direct sight of the bevel mesh and the intermediate helical mesh without breaking any coupling.

Pain Point Three: Thermal Rating Below Mechanical Rating

Frame size 12 carries 90 kNm mechanically, but heat rejection — not tooth strength — is what limits many continuous-duty installations. At 40 °C ambient with still air, the ribbed housing dissipates 118 kW.

Add a shaft-mounted axial fan with a directing cowl and the figure rises to 175 kW. An oil-to-air cooler with motorised pump lifts continuous capacity to 260 kW and holds sump temperature below 85 °C even at 50 °C ambient inside a covered head house.

For plants with process water available, an internal stainless cooling coil in the sump is the lower-cost route, handling roughly 200 kW at 6 m³/h of 30 °C water.

Fill is 95 litres of PAO synthetic ISO VG 320. Synthetic lubricant extends the change interval to 16,000 operating hours against 4,000 hours for a mineral oil at equivalent sump temperature — four oil changes avoided over a typical four-year campaign between major shutdowns.

Configuration Notes: Form C and Vertical Mounting

Shaft arrangement form C fixes the output shaft direction relative to the input shaft and the housing feet. Specifying the arrangement code at enquiry stage prevents the most common field problem on right angle units — a gearbox delivered with the output extension facing away from the head shaft.

A solid output shaft was chosen over a hollow shaft design because the elevator head shaft is a through-shaft carrying the sprocket between two pedestal bearings. Torque transfer is by a gear coupling with 1.5° angular capacity, absorbing the thermal growth and pedestal settlement typical of a steel head structure.

Vertical mounting brings its own lubrication requirement. Upper bearings on a vertically arranged unit sit above the static oil level, so the MTB3SV12-56-C uses an internal pressure feed from a shaft-driven pump, with a differential pressure switch wired to the plant control system.

Selection Data and Ordering

TANHON manufactures the MTB heavy duty bevel helical range across frame sizes 5 through 24, covering 1.5 kW to 1,500 kW and output torques from 4 kNm to 900 kNm, with nominal ratios from 8:1 to 450:1 in two-, three- and four-stage builds.

ATEX Group II 2G/2D versions are available for coke handling and petrochemical zones with combustible dust, including surface temperature monitoring and conductive paint systems. All units are built under ISO 9001 and ISO 14001 with CE and EAC marking.

To specify an elevator head gearbox, supply lift height, rated capacity in t/h, head sprocket or pulley diameter, material bulk density and abrasiveness, ambient temperature range, starts per hour, and the head shaft diameter and bearing centres. TANHON engineering returns a rated selection with thermal check, backstop sizing and a dimensioned general arrangement drawing within two working days.