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TECHNICAL DETAILS PAGE |
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) The slew ring is the component of a crane that allows the upper part of a crane to caring the jib to rotate allowing a wide movement of the carrying hook. |
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The earliest slewing mechanism was simply a series of wheels that ran in a circle allowing a plate on top of the wheels to slide round with a minim of friction. This simple method was the one used in the earliest Coles steam cranes |
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The early steam units had cast iron wheels under the platform, to turn the platform a large gear on top of the platform was engaged with a small cog gear. The large gear was fixed to the base carriage unit so when the small cog gear rotated the upper platform rotated around the large gear. |
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A secondary function of the large gear on the upper platform was to provide motion to the crane carriage. When the rotating platform was locked onto the carriage the small cog gear rotated the large gear transferring rotation to a shaft down into the carriage than then onto the driving wheels. This large central slew gear can be seen on this image of the gears from the 3 ton 1928 mobile. |
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| Although the above system continued to be used Coles in 1884 had patented a slew ring that combined the large gear wheel and rotating wheel platform into one unit. This is the layout that was to develop in the type used today. The problem with all the above was that they still relied on the central shaft to keep the upper crane fixed down to the carriage. |
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With the development of ball bearings the use of the wheeled slewing carriage faded and large sealed bearing were used. | |||||||||
| As bearings developed the advantage of the roller bearing were realised and the thrust bearing was developed. Here as seen in these cross sections the rotating rollers (red) are fixed between bolted flanges (green) so that they are above, below and at the side of the rotating slewing ring (blue). This takes the thrust of the load in all directions, upward, downward and to the side. | ||||||||||
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