Case studies

Rotating Equipment-

Installation, alignment, shim and tire change on kilns, dryers, screens, and calciners.

Introduction | Benefits | Requirements and techniques  

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Introduction....

      Materials processing equipment can be very large and subsequently extremely expensive. The internal temperature of some of these huge "dryers" can exceed 1800 degrees Fahrenheit. At these temperatures the steel shell would simply melt away under hundreds of tons of material weight that are suspended often several stories above the ground. To withstand these internal temperatures the shell is lined with refractory material that is made to operate at these temperatures and insulate the shell from the heat. This refractory lining is not strong enough to support the load of the material being processed, so it  must be uniformly supported by the shell or it will crack and disintegrate, subsequently destroy the shell. The refractory is a majority of the cost of the unit so maintaining it is of great concern.
      The shell is in turn supported by shims that rest against the ID of thick solid steel tires that run on smaller rollers called trunions. The trunions are set at a slight axial angle to the tire to offset  the downhill forces of the shell slope angle and weight, loaded with  material. This slight misalignment is necissary to control thrust, but it also causes wear of the trunion and tire surfaces. If the angles of the multiple trunions are uneven or incorrect, the wear will be excessive and expensive in repair and downtime costing. 

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Benefits.....

More accurate alignment of all components will absolutely increase lifespan of the entire machine and sub assemblies.      CAD based reporting and analysis eliminates mistakes in interpreting the problems, and makes any required movements or changes more definate and reliable. Allows for trending and trouble shooting with high speed and detail.      Saves precious downtime by individual component inspection and whole unit geometry checks. Allows for many operations to be done in advance of outages, with confidence of fit up in time of outage need.

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     With the usage of the Laser Tracker, we can map out the profile of the shell in the tire pad region and machine the appropriate shim thickness, radius, and taper to maximize contact between the tire and the shell. This will extend the life of the refractory, shell, shims, and tire, by evening out the support and concentricity of the tire to the shell.
      Another major value-add of using this technology if that the shims can be pre-machined to match the shell profile and tire I, before the outage, therefore shortening the outage sustantially.
      The tire can be inspected onsite at the manufacturer or at the jobsite, to verify that the size and roundness requirements have been met, prior to installation. This tire inspection alone can save many days of outage. If the tire roundness is not as expected (not uncommon with larger tires), attempting the shim installation will take much longer than planned, and may even result in having to have the tire reground to satisfy shell to gear, and pier to pier alignments and run-out requirements.

     The characteristics of the shell and tire that we are most concerned with is the sag  or "squash " due to gravity. The circumferential diameters will be the same, no matter the shape, but unless the tire has the same amount, and shape of ovality as the shell, the distance between the shell o.d. and the tire i.d., will have changed. This distance corresponds exactly to the shim pad thickness. Therefore some steps need to be taken in the installation procedure to accommodate for this.
     The most convenient way to install the shims is by rolling the shell on temporary rollers, allowing the shims to be placed in at the top, where the clearance is greatest. If the shell cannot be turned, there will be considerable force required to insert the shims at the side and bottom locations. This is only because the shell ovality will be changed from removing the old tire and supporting the shell in a different fashion.
     Also the initial shimming should be done using the pre-machined shims, 4 each, located at 90 degrees apart. This will be the fastest way to assure the best concentricity of the shell to the tire. The #20 and 30 shims will have to be driven in, as the shell will be closer to the tire than normal in these areas. The diagrams below help illustrate the concept.

The shim thickness' are based on the deviations of the shell from a perfect cylinder, using the best fitting method of root mean squares. In order for the best concentricity of shell to tire, to be obtained, the first four shims installed must be machined to their respective thickness', which will not likely be the same. Using shims equal thickness will set the shell off center, due to shell non-uniformity.

The shell is always going to squash more than the tire. Because of this, the shell will be oversize at the sides, and undersize at the top and bottom, in relation to the tire. Placing shims in at the side positions will be difficult to say least, as the shell will be closer to the id of the tire at these points. As you shim, you will be moving the shell back to its original shape when it was supported by the old tire.

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