MOUNTING DESIGN, FITTING PRACTICE AND SETTING

ENGINEERING 40 TIMKEN

THRUST BEARING CATALOG

3. Flat-bottom race : If the bottom race is flat (TTHDFLSX/SV), as in figs. 40-41, then apply close fit as per fitting practice guidelines. The flat race permits radial self-aligning of the rollers and conical raceways. 4. Sealing: An oil seal is mounted in the upper plate that is bolted to the cartridge to keep contaminants from entering the bearing assembly. 5. Lubrication: Adequate lubrication is maintained by filling the bearing with high-quality EP grease having a viscosity of approximately 450 cSt at 40 C (104 F).

Fig. 39. Typical screwdown support configuration using a TTHDSX thrust bearing. Fig. 40. TTHDFLSX convex upper race design. Fig. 41. TTHDFLSV concave upper race design.

THRUST TAPERED ROLLER BEARINGS - SCREWDOWN SYSTEMS - TYPES TTHDSX/SV AND TTHDFLSX/SV

Screwdown bearings of these types are used predominantly in metal mills. The bearings used in screwdown systems include single-row tapered thrust designs that are available in a variety of configurations (see pages 117-126 for further details). The heavy-duty thrust bearing makes the connection between the screwdown and the top roll chock, as shown in fig. 39. The operating speed of screwdown systems is very low during gap adjustment. Modern mills will either use the electromechanical screwdown system in conjunction with a hydraulic roll force cylinder, or will solely use the hydraulic roll force cylinder. The primary benefit of hydraulic roll force cylinders is their fast response time compared to the electro-mechanical screwdown systems, but the mechanical system gives more precise location with small displacements. When the mechanical system is used, the screwdown thrust bearing is applied between the main mill screw and top chock. The loads transmitted through these screwdown bearings are extremely high, typically equivalent to half of the mill's separating force, which can be several thousand tons. The operating speed is basically zero as the screw's rotational speed is very slow during adjustment. For this reason, the bearing selection is based on its static capacity (C

0).

Below are a few important considerations to keep in mind when mounting screwdown bearings: 1. Bearing cartridge: The bearing is mounted in a cartridge primarily to contain the lubricant needed for the assembly, but also to unitize the entire bearing assembly. 2. Tapered-bottom race: If the bottom race is tapered (TTHDSX/ SV), then a 3 mm (0.120 in.) radial clearance is suggested relative to the O.D. of the race to ensure that the bottom race will self-align with respect to the upper tapered race. Otherwise, the roller ends will not be properly seated against both the upper and lower large ribs simultaneously. A piloting bushing is pressed into the cartridge and is used for centering the upper race and rollers. The bottom race will be centered by the upper race and roller set.