Rotating platform for carousels: slewing-ring turntable base

01

Size the slewing ring for combined load and tipping moment

Machine Design's introduction to slewing rings, prepared with information from Rotek, explains that one ring carries axial, radial and tilting moment loads together, and that some rings are used on turntables whose diameters are well beyond the bearing diameter, the moment capacity giving the stability. Catalogue capacities are non-simultaneous: the thrust capacity accounts for no moment or radial load, so combined loads must be turned into an equivalent load, for static raceway checks the load on the highest loaded rolling element. [3]

The same article advises selecting a ring on static capacity with an application service factor where slewing is intermittent with a broad spread of loads, and notes that dynamic capacity may govern in high-cycle use. For running torque under ideal conditions it uses a friction coefficient from 0.003 to 0.008 as a representative range and load distribution factors of 4.37 for balls and 4.1 for rollers, with starting torque about one-third above running torque. [3]

Speed is limited by ring type. SKF states that its four-point contact ball slewing bearings accept tangential speeds up to 4 m/s, while crossed cylindrical roller types are limited to approximately 1.5 m/s in continuous slewing and 2 m/s for brief periods. [1] Editorial calculation: on a 1,000 mm raceway, 4 m/s corresponds to about 76 rpm and 1.5 m/s to about 29 rpm.

Editorial note: for a carousel, list the deck mass, the heaviest load at the largest radius, the number of stations loaded at once and the start-stop cycle, so the supplier can calculate the resulting axial load and tilting moment against its static load curve.

Send the deck diameter and mass, payload per station and its radius, worst-case off-centre loading, rotation speed and angle, start-stop cycles per hour, drive type (pinion and motor), base frame drawing with flatness achievable, bolt size, indoor or outdoor use, and temperature range.

02

Make the base frame flat and stiff before bolting

SKF states that slewing bearings have limited rigidity because of their small cross-section relative to diameter, so the support structure should be designed for maximum axial and radial rigidity. It limits overall flatness of the support surface to tc = (dm + 1,000)/10,000 mm, where dm is the mean raceway diameter, limits flatness variation between consecutive measuring points to 0.0002 × n, and limits radial conicity to B/1,000 across the support width B. [1]

TGB's installation manual sets the maximum flatness deviation from the raceway diameter as δp = (Dr + 500)/10,000, reached only once in each 180° as a sine-like wave. [2] Editorial calculation: for a 1,000 mm raceway, SKF's formula allows 0.20 mm and TGB's 0.15 mm; follow the figure of the maker whose ring is fitted.

SKF requires machined support surfaces free from rust, paint or burrs and gives a roughness range printed as Ra = 3.2 to 6.3 mm, which reads as a unit misprint for micrometres; confirm with the maker. It names hexagon head bolts to DIN EN ISO 4014 in strength grade 10.9 for securing slewing bearings. [1]

TGB gives tightening torques for 10.9 metric bolts on non-lubricated threads from 15 ± 1 Nm (M6) and 126 ± 10 Nm (M12) to 609 ± 50 Nm (M20), and requires bolts to be preloaded crosswise in three steps of 30%, 80% and 100%, with thread locker on the last three to five threads. Bolts are retightened after no more than 100 hours of first operation, and its manual also says to retighten every 3 months; split rings and split washers are not permitted and bolts, nuts and washers are not reused. [2]

03

Plan regreasing for the platform's duty

TGB ties regreasing to speed and environment, for operating temperatures between −20 °C and 65 °C, linear speeds below 4 m/s and low to medium loads, and names insufficient lubrication as the cause of slewing ring failure it finds more than any other. [2]

SKF states that the permissible operating temperature of the slewing bearings in its catalogue is “determined primarily by the spacer and seal material and the grease used for lubrication” and “typically ranges from –25 to +70 °C.” [1] Gear teeth on the ring are greased separately; TGB describes brushing grease onto the teeth or using a lubricating pinion. [2]

04

Carousel platform data the slewing-ring maker will ask for

These are the order fields for a carousel platform, read against the slewing-ring sources above.

05

Send the deck, load and base data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Deck: [diameter; mass]
Loads: [payload per station; radius; worst off-centre case]
Motion: [speed; angle; cycles per hour]
Drive: [pinion; motor; brake]
Base: [frame drawing; flatness achievable]
Bolting: [size; grade]
Environment: [indoor or outdoor; temperature; dirt]

See manufacturer records Send an enquiry through CNFX