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FAQs Products

A slew drive is a worm or pinion driven slewing ring enclosed in a housing. Upon customer  request, gear boxes, electrical/hydraulic motors, brakes and encoders can be included. Seals keep the lubricant inside while keeping dust and dirt outside. Thanks to the integral slewing  bearing, a slew drive can carry axial & radial forces and moment loads at the same time.

  • Slew drives are ready­to­install units: “Bolt, connect, slew – done!”
  • Maximum load­carrying capacity and output torque in a compact, space­saving  design
  • Available in a variety of sizes and ratings
  • Fully enclosed housing – low maintenance, clean appearance
  • Simple to order – easy to mount, no adjustments required
  • Fast customization thanks to modular product structure
  • Proven designs, high reliability and long life

A slewing ring is a large diameter antifriction bearing made from quenched and tempered  steel including one, two, or three raceways of balls or rollers to carry axial & radial forces and moment loads at the same time. Bolt holes in the inner and the outer ring provide for an easy installation. Internal or external gears are an option on the slew ring; the teeth are directly cut  into either the inner or outer bearing ring and the raceways are induction hardened. Seals are attached on both sides to prevent the lubricant from escaping.

Product Selection criteria

Since slew drives include the full drive train, are fully enclosed and are lubricated at the factory, they are very popular in applications which require an easy & quick installation, safe operation in harsh environments and low maintenance. With their high power density (high load capacity and high torque in a small envelope), they are ideal for applications such as man lifts, drill rigs, steering gears and fun rides.

Find here an overview on slew drives.

Slewing rings are preferred for larger diameters where a housing would be too heavy and costly. Typical slewing rings examples include large cranes, tunnel boring machines, multi-MW wind turbines and bottle filling lines.

Find here an overview on slewing rings.

WD (worm gear) slew drives offer a high gear ratio and an unsurpassed torque for a given envelope.  However, they cannot be rotated continuously or at output speeds above 3 rpm in order to avoid excessive heating (ref. Product features – Duty Cycle). For such applications, WD units are available with bronze ring gears (ref. Product features – Bronze wheels). Worm gear units have a lower gear efficiency and are not engineered to swing away in case of back-driving loads. This must be carefully considered in the design of any application. (ref. Product features – Self-locking).

SP (spur gear) slew drives can be rotated continuously and at higher speeds, but have a smaller gear ratio resulting in lower torque. Pinion driven units feature a higher gear efficiency thus allowing for back-driving unless a brake is used.

Worm gears usually have the motor in the plane of the slewing bearing unless an angled gearbox is used, whereas pinion driven solutions have motors rectangular to the slewing bearing unless an angled gearbox is used.

WD-L is a light series slew drive including a ball slewing bearing (one or two rows) and one or two worms acting on one worm wheel. It is the first choice in light applications such as mobile equipment, fork lift rotators, turntable handling equipment and boom rotating devices.

WD-H is a heavy duty series slew drive comprising a two race roller bearing for higher capacity and one or two worms acting upon one slew ring yielding the maximum torque available at smallest size and weight. It is an IMO exclusive, patented product and unique for the industry.  Typical applications are steering gears for heavy transportation, rock drill rigs, tilt rotators attached to excavators and antenna drives.

If space is not a limitation, a WD-L slew drive may be used which would be larger in width (diameter) and would have an increased weight compared with a WD-H worm drive of a comparable output torque and moment load capacity. However, the total height of the WD-L drive would be smaller than a WD-H unit.

Product range

Yes. You can choose from a standard product range of slew drives and slewing rings. In case a standard product does not fit your application, we engineer customized solutions. Please contact your sales engineer and fill in the Application Data Sheet.

Yes. Our application engineers would be pleased to design the perfect slewing ring or slew drive for your application. In general, we have a variety of options available for component materials, coatings, special seals, and greases. Slew drives can also be designed for permanent operation, extreme temperatures and can even be made explosion proof.  Peripheral add-on component such as motors, brakes and encoders can also be customized.

Yes, for instance support rings can be mounted on slewing rings. For large quantity orders valve blocks, hydraulic connections, linking brackets and sensors can be connected to slew drives or even housings can be tailored to your needs.

Slew drives:

WD-L series comes standard in (9) different sizes.
WD-H series comes standard in (5) different sizes.
SP series comes standard in (15) different sizes.
Raceway diameters range from 156 to 1,091 mm.
Output torques are available up to 446 kNm.
Moment loads up to 1.100 kNm.
Axial Loads are available up to 7,777 kN.
Radial Loads are available up to 3,528 kN.

For the right selection, please have a look at our catalog or contact our sales engineers. Generally, slew drives can be customized.


Slewing rings:

Raceway diameters vary from 120mm to 6,000mm.

Yes. Many different sizes for a variety of applications are stocked in our warehouses in Germany and the U.S.A. – for available sizes please contact our sales engineers.

Yes. Replacement parts are available for slew drives and slewing rings, e. g. seals, attachments, etc. Please contact our sales engineers for parts availability and pricing.

Product features

Yes, we supply several attachments suitable for the respective product.

Our sales engineers will assist you in the selection of the matching components. Any of these items can be specified and assembled on your drive by IMO prior to shipment from the factory.

Yes, for the WD-L and SP series, both in gearing as well as the raceway. The WD-H series does not have an option for reduced backlash.

A bronze wheel is the first choice in applications requiring longer duty cycles in terms of power-on/off intervals and slewing rate. It improves the gear efficiency so that there is less heat build-up in the worm gear. If you are unsure whether to use a standard or a bronze type worm gear, please contact our sales engineers and provide a duty cycle of your application.

Yes. We can paint slew drive housings and slewing bearings to most specifications and color codes.

Yes, if required. We offer several options for corrosion protection at a variety of ratings. IMO will specify coatings, seals, grease and other items in order to meet customer requirements for the harshest environments. With over 30 years of designing for tough environments, we will have a solution to meet your needs. Please contact us to discuss options.

The SP (spur gear) slew drive series is capable of true continuous rotation.

This is an IMO exclusive drive and you will not find another fully assembled and sealed slew drive system on the market which is able to rotate continuously.

Like all worm gear systems with a high gear ratio, our WD (worm gear) slew drives series requires short intermittent rest periods to dissipate heat built up during operation. However, for such cases, bronze worm gears are available as a solution which has been proven in many applications engineered by IMO. Contact us to explore the potential use of bronze gearings in your application. Based on your duty cycle IMO will be able to check power-on/off requirements.

Generally, all standard slew drives are enclosed. Upon customer request, we can also supply a set that includes drives (worm or pinion) and mating slewing ring without including a housing. In such a case, the customer would need to assemble the individual components and set contact pattern and backlash for proper function and lifetime of the system. Contact us for assistance.

Typically, grease is used as a lubricant for all slew drives and slewing rings. Few customized slewing ring designs are oil lubricated. Approved lubricants for raceways and gearing can be found in IMO’s Installation & Operating Manual.

Electrical AC motors can be used or hydraulic motors. Encoders, brakes and gear boxes can be added as required.

Slewing rings are often driven by multiple internal or external gears. Usually they are positioned opposite to each other to balance forces. Worm slew drives come with one or two motors, whereas pinion driven units may have one or more motors to spread the load along the circumference of the slew bearing integral teeth.

By default it is not possible to mount the motor on both sides of the same worm shaft. However, for most WD slew drives, it is possible to supply tailor-made slew drives with a mirrored worm shaft orientation upon request. Please contact our sales engineers for more information.

No. Based on customer requirements, we can supply slew drives without a motor/gearbox. That said, more often than not, our customers prefer receiving the fully assembled drive from the factory and ready-to-install without any adjustment work needed.

The selection of a motor (and a gearbox if required) is based on the recommendations from IMO engineering, after studying the customer‘s application. If a certain motor or gearbox brand is preferred by the customer (for example, for reasons of simplified spare parts supply), IMO should be informed. If technically possible, we will consider such preferences.

In case of a horizontal output axis, the driving shaft must always be placed at the bottom to ensure appropriate lubrication of the worm or pinion.
In case of a vertical output axis, the WD-L and SP units should preferably be placed with seals pointing down to minimize the impact due to weather impact unless otherwise sheltered.  That said, seals pointing up are generally also possible.
For WD-H units it makes no difference (same seals on both sides).

All requirements for storage, transportation, installation, operation, safety, maintenance, de-commissioning and disposal can be found in our Installation & Operating Manual for slew drives and slewing rings.

All IMO slew drives rotate more than 360 degrees.

No. There are WD (worm gear) slew drives which are non-self-locking due to their higher worm pitch (ref. Product features – Worm - double threaded). But even single-threaded worm gears may start rotating slowly under presence of back-driving forces and vibrations. In such cases, a brake has to be used, if a 100% safe hold is required. On the other hand, WD slew drives will not swing away in case of a sudden back-driving load. The gear capacity should always be higher than the maximum expected back-driving load thus avoiding gear damages.

SP (spur gear) slew drives are generally non-self-locking.

In WD (worm gear) slew drives a double-threaded worm is used in applications with a horizontal slew drive output axis or when the output axis is inclined more than 5° from the vertical. This negates the so-called ‘Stick-Slip Effect’ and ensures a jerk-free operation even in reverse load situations due to the higher worm pitch and gear efficiency.

General information

Please contact our sales engineers or submit an inquiry.

You can download our slew drive or slewing ring pdf catalog here. For a printed version of the catalogs please send us an e-mail or an inquiry.

We ship worldwide. Contact our sales team and distributors.

These items are available for immediate shipment:

Standard slew drivesand slew bearings are stocked at our manufacturing plants in Germany, Gremsdorf and in our warehouse in Summerville/SC, U.S.A.
Customized wind turbine pitch bearing spare parts are stocked at IMO works in Germany and at IMO’s distributor in the U.S..

For items from Germany manufacturing lead-times can vary from 1-2 weeks for standard drives, and up to 10-18 weeks for tailor-made slew drives and slew bearings depending on the degree of customization, size, weight and other features.

Ocean shipping times are 3-5 weeks depending on destination.

Air shipping time is 1 week at minimum.

If you have already selected a product, please contact our sales engineers.

If we can assist you in selecting the right product, please fill in the application data sheet for slewing rings or slew drives and/or contact our sales engineers.

A 12 month warranty is granted as per IMO Terms & Conditions included in our quotations. An extended 2 or 3-year warranty is available upon request for an additional fee. IMO does not warrant that the products are fit for a purpose intended by customer unless the product application has been approved by IMO engineering. Compliance to IMO’s Installation & Operating Manual is mandatory.

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