12" Gauge Cast Iron Turntables
Turntables provide a number of useful functions in overall track system design. Although most of the industry is familiar with a four-way 90º exit, few are aware that 45º exits are also available, to allow custom designs.
The turntable top and bottom should be a precision-machined casting that must be designed as an integral part of a unitized product. Its purpose is to save space when forming 90º turns, and allows easy indexing of paper roll rotation.
The turntable top should also have raised transitions to protect the track impact points; similar to crossovers and switches.
However, the turntable transition should also serve as a self-centering device for the dolly. When a dolly is loaded with a paper roll, the operator is unable to see the dolly. The two "bumps" telegraph to the operator that the dolly is in a centered position and able to be rotated. This prevents the wheels from dragging on the imbedded base, causing damage to the wheels and base.
A machined, spring loaded, stop pin should also be a design feature. The stop pin should be accurately indexed so that upon engagement it precisely aligns the turntable with the entry/exit track.
Turntable bearing designs have varied over the years. The most economical method of rotation is to machine a bearing race into the top and bottom of the casting, and install ball bearings.
Recent technology has developed a means to almost quadruple the hardness of the casting race, theoretically quadrupling its life expectancy (see enclosed excerpt from March 1998 Industrial Heating magazine).
* Inspect raised transition and impact points. Field modify raised transition to original 9/16""depth when transition wears to below 11/16""or damage to impact points will occur. See Drawing Note "A".
* Remove turntable top monthly, remove bearings, clean pit and bearings, examine stop pin for wear and replace if necessary (See Drawing Note "C"). Reinstall bearings, coat with generous amount of 10 W 30 oil and reinstall top.
* Examine vertical edge of base for damage. This is caused by dragging the wheels of the dolly against the base during rotation.
A) Field observation indicates that in some installations the raised transitions, which selfcentered the dolly, are in need of repair or are not used by the operators. Also observed was the rotation of the turntable being commenced (using the paper roll momentum) either before the dolly was centered or after the dolly had passed center. In both situations, the dolly wheels and imbedded turntable base are unnecessarily damaged. In some situations, the damage was so severe that complete turntable replacement was required. Most important to note was the damaged wheels, which then create accelerated wear on the entire track system. See Drawing Note "B".
B) There should be a method to ensure paper rolls are loaded in the center of the dolly. The custom design of each system dictates that the rotational axis of the paper roll is critical, in some areas due to columns, motors, slight pitch of the laydown area, etc. Once the roll has been improperly loaded on the dolly, off-center, it may be necessary, in some turntable locations, to push/pull the loaded dolly away from the turntable center, creating wheel and base damage, as described in Note A above.
D) Splice plates should be pre-installed and hardware included to reduce field labor (field welding and grinding; is an antiquated, labor intensive, track connecting method).
E) Casting ends should be machined for a precise flush joint.
F) Pre-drilled and countersunk bolt holes are necessary to reduce installation time.
© 2001 Capital Track Co.