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Slim or Wide Filler Bars?

What is the effect of using slim filler bars about 100mm wide as pads for rotary kiln tyres, could they possibly introduce load peaks on the shell such that could cause cracks? What is their general disadvantage over much wider pads of say 400mm wideness in relation to a kiln of 4.6m internal diameter.

As long as the narrow bars (100mm) are sufficient in number (aim for at least 65 to 70% coverage around the circumference) then no shell stress issues will arise. Narrow bars are often used as an economic choice since they will likely be flat bars and not rolled like the wider bars need to be. The bars should fit intimately with the shell. Fit specifications usually require that any space between the bar and the shell be no more than .3mm. This will vary according to bar style particularly if they are a welded style arrangement. This is less critical for floating bars. The narrow bars have two disadvantages. First it is difficult to get a high percentage of circumferential coverage since the space between the bars, needed for the stop blocks, is likely significant compared to the width of the bar; the wider the bar the better the coverage; more coverage produces less wear. When the same space between them exists, the narrow bars will wear faster than the wider ones. Secondly the narrow bars will have a tendency to bend in the middle due to tire drag. This will get to look like the bars are smiling on the upturning side of the kiln and frowning on the down turning side of the kiln. Putting stops in the middle of the bar underneath the tire to prevent this is an added cost that negates the economic advantage of using narrow bars. Wider bars are always recommended for good service life.

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