ZR24 Slewing Drive Planetary Gearbox — Right-Angle Bevel-Planetary, 2-5 Stage

Ten/Ta/To EP-ZR24 occupies the upper-heavy segment of Korea Ever-Power ZR slewing drive series and introduces a capability absent from the smaller frames: a true 5-stage planetary reduction that reaches ratios up to 4,347:1 within a single gearbox housing. This extreme reduction range makes the ZR24 uniquely suited to ultra-low-speed, ultra-high-torque slewing tasks such as offshore pedestal crane rotation, ship-unloader boom positioning, and heavy piling rig mast indexing where output speeds below 0.5 rpm are routine.

At the 3-stage and above configurations, continuous output torque rises to 25,000 Nm — exceeding the headline 21,000 Nm specification by 19% — because the additional planetary stages distribute the transmitted load across more gear contacts, reducing the stress per tooth. Peak torque reaches 51,000 Nm across all multi-stage variants, providing ample headroom for wind gust overloads and emergency braking events on large crane structures.

Pre-Installation

Verify the mounting surface flatness is within 0.1 mm across the bolt circle diameter. Clean all mating surfaces of paint, rust, and debris. Confirm the slewing ring pinion module and tooth count match the specified output pinion. Check the oil level through the inspection port and top up with ISO VG 220 PAO synthetic if transport has caused settling below the minimum mark.

Pinion Engagement Setup

Set the pinion-to-slewing-ring backlash to the value specified for the slewing ring module (typically 0.05-0.15 mm at the pitch circle). Use a dial indicator on the output pinion tooth flank during ring gear rotation to verify consistent backlash around the full 360 degrees. Inconsistent backlash indicates slewing ring runout or mounting surface non-flatness that must be corrected before commissioning.

Motor and Brake Connection

For hydraulic motor installations: verify the motor drain line is plumbed to tank before applying system pressure. For electric motor installations: verify the motor rotation direction matches the required slewing direction before coupling. For units with fail-safe brakes: verify the brake releases fully when hydraulic or electric release pressure is applied before attempting any loaded rotation.

First-Run Protocol

Run the gearbox unloaded for 15 minutes in both rotation directions at 50% rated speed. Monitor the housing surface temperature — it should stabilise below 70 deg C ambient + 30 deg C rise = 100 deg C absolute. Listen for any abnormal metallic sounds indicating gear or bearing issues. After the unloaded run, apply 25%, 50%, 75%, and 100% load in 15-minute increments. Record the housing temperature at each step.

The ZR24 input flange accepts both high-speed axial piston motors (BF01/02 interface) and low-speed high-torque orbit motors (IS02/IS10 SAE interface). The choice between motor types depends on the system pressure, required output speed, and whether the hydraulic circuit is open-loop or closed-loop. The table below provides starting-point motor displacement values for the most common ZR24 application scenarios.

Values are starting-point estimates at 250-350 bar system pressure. Final motor sizing must account for actual duty cycle, ambient temperature, and hydraulic system losses. Contact our engineering team for verified motor-gearbox matching.

Standard: -40 to +80 deg C ambient. At sustained operation above 60 deg C, reduce the oil change interval to 2,000 hours. Below -20 deg C, use ISO VG 150 PAO or consult for arctic-grade VG 100 lubricant to ensure adequate cold-start oil flow to bearings.

Dust-tight (6) and protected against temporary immersion in water to 1 metre depth for 30 minutes (7). Multi-lip FKM seals resist hydraulic oil, seawater, diesel fuel, and common cleaning chemicals. Suitable for high-pressure washdown environments without additional covers.

Housing exterior coated with zinc phosphate primer and marine-grade polyurethane topcoat. Suitable for ISO 12944 C4 (high salinity) environments without additional galvanic protection. For C5-M (offshore platform splash zone), specify the optional stainless steel breather valve and external epoxy coal-tar topcoat.

Thermal power ratings (Pt) are valid to 1,000 metres above sea level. Above 1,000 m, reduce the Pt value by 1% per 100 m of additional altitude due to reduced air density for convection cooling. Above 3,000 m, forced air or liquid cooling is recommended regardless of duty cycle.

Why does the ZR24 3-stage deliver more continuous torque than the 2-stage?

This counter-intuitive result occurs because the 3-stage and above configurations use a different bevel input sub-variant (R10 and R06) that distributes the input torque across a larger bevel gear pair than the R16 variant used in the 2-stage. The larger bevel pair provides greater tooth contact area, higher load capacity, and consequently higher continuous torque rating at the output. The 2-stage R16 variant prioritises compactness and higher thermal power capacity rather than maximum torque.

What is the practical lower speed limit of the ZR24 5-stage at ratio 4,347?

At a motor input speed of 1,450 rpm (standard 4-pole IEC motor), the output speed is 0.33 rpm — one full revolution every 3 minutes. There is no mechanical lower speed limit; the gearbox operates equally well at 0.01 rpm as at 0.33 rpm. However, at extremely low output speeds, the lubricant film thickness at the output bearing decreases, so operation below 0.05 rpm for extended continuous periods should be discussed with our engineering team to evaluate boundary lubrication conditions.

Is the ZR24 suitable for offshore platform crane applications with DNV or Lloyd certification requirements?

The standard ZR24 is manufactured under ISO 9001:2015 with full material traceability. For applications requiring classification society approval (DNV, Lloyd, BV, ABS), we can supply units with witnessed material testing, witnessed factory load testing, and the documentation package required for type approval submission. Lead time for classification-witnessed units is typically 8-12 weeks. Contact our engineering team with the specific classification society and notation required.

Can the ZR24 replace a worm-gear slewing drive on existing equipment?

In most cases yes, with an adapter plate to match the existing mounting bolt pattern. The ZR24 right-angle output geometry is identical in concept to a worm-gear drive, so the system layout remains unchanged. The primary benefit of replacement is a step-change in efficiency (89-93% versus 40-75%), which directly reduces the hydraulic pump displacement required and lowers oil temperature in the system. Provide the existing drive mounting dimensions and we will confirm compatibility within 24 hours.

We retrofitted two harbour mobile cranes from worm-gear slewing drives to ZR24**3 units. The hydraulic system oil temperature decreased by 18 deg C under the same duty cycle because the gearbox is no longer converting half the input power into heat. That temperature reduction alone extended the life of every hydraulic component in the circuit. We are now specifying ZR24 on all new builds.

Ordered 4 units for a piling rig project, ZR24**5 configuration at ratio 882. The 5-stage gives us the ultra-low speed we need for precise segment positioning. Product works as specified. Minor issue: one unit had a small paint defect on the housing flange surface which we had to clean before mounting to ensure proper metal-to-metal contact. Not a performance issue, just a cosmetic QC point that should be caught at the factory.

Replacement slewing drive for an offshore pedestal crane. The original European unit had a 16-week lead time for replacement. Ever-Power delivered a dimensionally compatible ZR24 in 6 weeks with full material certificates for our class survey. Been running for 9 months in North Sea conditions with no issues. The zinc phosphate coating is holding up well against the salt environment.