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TRI’s Bearing Design Philosophy Regarding Bearing Clamping Methods

June 15, 2015

The following write up is from section 1 of the Catalog of TRI Journal Bearings which can be downloaded from www.turboresearch.com

Many rotating equipment manufacturers seat a bearing in an end wall of a bearing standard / pedestal and use the standard cover to hold the bearing in place. This design method is definitely simple and low cost, and it works when the air temperature surrounding the bearing standard / pedestal is “ambient”, i.e., not heated.
However, there are applications for which this clamping design is not very effective and even inappropriate. For applications where the wall of the standard/pedestal is heated by exposure to hot steam escaping from shaft seals of a turbine, or is exposed to the radiant heat from an adjacent hot turbine, the standard / pedestal wall grows due to thermal expansion. While the bearing inside is cooled with lube oil in the neighborhood of 130 to 160 deg F, the external heating may cause the temperature of the standard wall to increase to 250 deg F. For a fit diameter of 32 inches and a temperature differential of 100 deg F, a gap between the two grows by 0.020 inches (0.5 mm) so that the bearing gets quite loose in the fit, even if clamped with a slight interference when installed cold. Looseness of bearings contributes greatly to increased rotor and bearing vibrations, as well as fretting of the bearing seat, which is why TRI considers this design to be inappropriate for hot steam turbine applications.
Consequently, where possible, TRI prefers to use a bearing clamping design wherein the bearing top half has an integral “strongback”, and the ears of the top half are bolted directly to the horizontal joint, as shown on Page 3. In this case, the standard cover can get hot and expand, but the bearing remains tightly fastened to the lower half. In a number of retrofit cases of TRI journal bearings, bolt holes are drilled and tapped into the horizontal joint and the standard cover is milled way to provide space for the ears of the bearing top half to fit.
This design of a top half bearing with ears and hold down bolts into the horizontal joint is definitely more expensive than fitting a round bearing into a hole in a wall, but the long term benefits of vibration control for light weight, high speed, high power density turbine rotors cannot be matched any other way.
It is important to give proper credit for the origination of this design feature. GE Engineers in Schenectady, New York developed this design method in the 1930s for the very reasons cited above. It became a standard GE bearing design feature by approximately 1940.
Through many years of solving severe bearing damage problems and various difficult rotor vibration issues, TRI has developed a large repertoire of bearing designs that were “custom or special designs” at the time, but which over the years have become “TRI standard bearings”. Many are now relatively popular designs.
TRI continues to design and manufacture the journal bearings presented in this catalog, or similar bearings adapted to meet customer’s specific needs, or other designs to suit new applications.

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February 2015 Tech Note

February 10, 2015

TRI release a new Tech Note today. This month, Dr. Mel discusses fluid drive scoop tubes. Our experience has shown that these critical parts sometimes fail. Understanding the reason why they fail gave way to a better design for scoop tubes.

LINK: February 2015 Tech Note

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New Generator Fans

December 23, 2014

We just finished two generator fans on an expedited schedule. The fan below has a twin. These fans were milled from forgings. They spent seven days on two CNC horizontal mills. After the blades were machined, they got a final bore, polishing and were balanced to 40 g-in at 600 RPM. Production time from the receipt of the material was just under two weeks.

TRI Heavy Duty Generator Fan

TRI Heavy Duty Generator Fan

 

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Emergency Lube Oil System

August 25, 2014

TRI just complete an emergency lube oil system that uses an uninterruptable power supply (UPS).  The UPS provides AC power to a lube oil pump. Because AC components are generally easier and cheaper to acquire,  the new system was cheaper, lead times were shortened and the AC technology simplifies any future replacement parts.

  • DC power supplies are quite common in the electric generation industry. There are several drawbacks to DC emergency lube oil systems:
  • Large banks of DC batteries have to be handled with a great deal of caution.
  • DC motors must be specially designed for speed stabilization.
  • Implementing DC switchgear often is problematic.
  • It is difficult today to find electrical suppliers who have any significant understanding of DC power systems.  It is difficult to get DC components that you need, even when you have exact specifications for equipment that was commonly available a few years ago.

TRI emergency lube oil systems are customized to our customers needs.

  • Pumps and AC drives can be incorporated that are already implemented at the customer site. This reduces replacement parts and training.
  • Components are sized for the lube oil requirements. 
  • Piping and hardware can be customized for harsh environments. 

Call TRI at 800-363-8571 if you are looking to upgrade or install a new emergency lube oil system.

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Fluid Drive Upgrades

May 14, 2014

Back in 2007, Dr. Mel created a presentation for fluid drive upgrades. This presentation explains how fluid drives are used specifically with boiler feed pumps. The operational history and the changes to the standard practices led to issues for which TRI has engineered solutions.

 

 

 

 

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Controlling Oil Whirl with a Pressure Dam Bearing

March 28, 2014

In this video, we explain oil whirl and how a 2nd area of high pressure created by a pressure dam can tame the vibration caused by oil whirl.

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Bearing Dovetail Grooves

March 25, 2014

Many bearing in the field use a dovetail bore design. TRI Transmission and Bearing Corp. explains why the dovetail design leads to Babbitt wipes and bearing failures.

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