It is an important component of an amusement ride, requires continuous maintenance and periodic replacement. Let's find out how to measure the play and when a slewing ring needs to be replaced.
WHEN REPLACING THE BASIC BEARING (SLEWING RING)
by Enrico Fabbri
Almost all attractions use a basal bearing (also commonly called “SLEWING RING”) to allow the rotation of components such as column-arm. Let's find out in detail how it is built, the necessary maintenance and when replacement is necessary.
There are both toothless slewing ring on the market, used, for example, to connect an arm with a passenger vehicle, and toothed slewing ring, used for example, to transmit movement thanks to the action of the pinions. In both cases, the slewing ring have balls or rollers inside to allow the rotation of the two parts.
They are built with high-strength steel machined with milling machine according to the required precision. Unlike what you think, it is the internal spheres (or rollers) that wear out over time.
The characteristics of wear resistance of the steel and the precision of the workings depend on the design of the manufacturer of the slewing ring and therefore there may be significant differences between the different manufacturers available on the market. The attraction manufacturer selects the slewing ring manufacturer who guarantees the minimum quality level based on the ride project.
Inside the slewing ring there are steel balls necessary to allow the rotation of the two parts. Even when the balls are regularly lubricated, they are still subject to wear over time and therefore, after a certain number of working hours, the slewing ring must be replaced.
On the external part of the slewing ring there are teeth that allow to transmit the movement of the two parts thanks to the rotation of the pinion. The lifespan of the teeth of the slewing ring (as well as of the teeth of the pinion) depends on the forces that are transmitted multiplied by the number of working hours accumulated. Even when the teeth of the slewing ring are regularly lubricated, they are still subject to wear over time and therefore, after a certain number of working hours, the slewing ring must be replaced.
During the design phase of an amusement ride, the type of slewing ring to be used is determined, also identifying the theoretical life span expressed in hours of work beyond which the slewing ring must be replaced. In some cases, the actual wear could be greater or less than when theoretically programmed, due to the real forces acting on the amusement ride and the frequency of the lubrication performed. We recommend that you check this information in the ride use and maintenance manual or by contacting the ride manufacturer.
ATTENTION: The average lifespan of a slewing ring is not unlimited and must be replaced periodically even if it apparently does not show signs of wear on the outside.
Many operators tend to underestimate the action of the wear of a slewing ring, especially as regards the wear of the internal balls which are not directly visible.
The wear of the internal balls is progressive over time based on the number of working hours. Over time, the play between the balls and their seat increases and the slewing ring starts to show a play even in the absence of particular noises. When the play exceeds the designated limit, the wear actions accelerate and the forces of the ride movement can cause the detachment of the component with high chances of causing a major accident.
ATTENTION: An excessively worn slewing ring can cause a serious accident to the ride without warning.
We remind you that the state of wear of the teeth of the slewing ring does not represent an indication of the level of wear of the internal balls, because they are due to two factors disconnected from each other.
Depending on the type of use of the slewing ring on your ride, it may be necessary to replace it periodically, for example every 10/15 years. It is therefore recommended to plan these activities and keep all the documentation relating to the purchase and assembly in the Logbook.
HOW TO CHECK THE WEAR OF THE SLEWING RING
Let us now try to understand when a slewing ring is excessively worn and therefore when it must be replaced. First of all, the information contained in the ride manufacturer's use and maintenance manual must be evaluated. If this information is inaccurate or not available, an experimental measurement of tooth wear and wear of the spheres located inside the slewing ring can be performed. It is a complex operation that must be performed for competent people.
To determine the wear of the teeth of the slewing ring it is necessary to use a feeler gauge and verify that the space between the teeth of the pinion and the teeth of slewing ring does not exceed a value pre-established by the technical standards. Assuming that the teeth of your rotating ring have a module (thickness) of 15mm, the maximum suggested distance measurable should not be greater than 0.5 / 1.0 mm.
To determine the wear of the internal balls of the slewing ring it is necessary to use a precision instrument, move a ring of the slewing ring and read the clearance existing between the two rings of the slewing ring. The slewing ring generally used on the rides are large in size with two turns of internal balls. The maximum allowable clearance is established by the manufacturer of the slewing ring and depends on the diameter of the internal balls. Assuming a ball diameter of 20mm, the maximum clearance is about 2mm, which is reduced to about 1mm for the slewing ring which have internal rollers instead of the balls. We enclose in this article the recommendations of a builder of international importance often used by builders of attractions.
HOW TO REPLACE A SLEWING RING
Let's see what to do when you need to replace a slewing ring. This is a complex activity that must be performed at the ride manufacturer or with the assistance of competent people. Below are the essential points by way of example.
The first phase is that relating to the disassembly of all the components connected to the slewing ring, including any electric sliprings.
The new slewing ring must have at least the same technical characteristics as the original one. During the installation phases, the minimum clearances between the teeth of the pinion and the teeth of the slewing ring must be respected. This procedure could be more complex when two or more pinions are present on the same slewing ring. The lack of minimal play between the teeth of the pinion and the teeth of the slewing ring can cause excessive strain on the teeth and therefore premature breakage of the teeth.
The slewing ring can be fixed with new screws having a strength class equal to the original ones. The screws must be tightened with a special wrench with the load indicated by the manufacturer of the slewing ring.
We remind you to replace the tubes used for the internal lubrication of the slewing ring. It can often happen that these tubes get blocked preventing correct internal lubrication of the slewing ring and therefore significantly reducing the life time of the slewing ring.
Written by Mr. Enrico Fabbri firstname.lastname@example.org
Original date: February 2020
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