Dogbone (BELT TYPE) Expansion Joints

For over 50 years La Favorite Industries and it predecessors have been supplying the steam power electrical industry with the most reliable Dogbone Expansion joints, utilizing the highest quality materials available. We currently offer multiple sizes of Dogbones to support all of our customer's needs. Our extensive production knowledge combined with our hands on field experience allows us to offer a comprehensive package of product, service and support to our customers. We can guarantee consistency and quality of both material and process in production since we are the manufacturer. Because of this, 20 year service lives for our Dogbones are not an unusual occurrence.

Dogbone Expansion Joints operate in a nearly full vacuum environment which generates a force load of approximately 1400 lbs per square foot of surface area. High quality fabric, cover and bulb reinforcement materials play crucial roles in maintaining structural integrity, insuring reliability and reducing chances of catastrophic failure.

DOGBONES IN DEPTH

The Dogbone Expansion joint consists of three major components. The inner fabric reinforcement, outer cover and bulb core. Below is a brief explanation of each part.

Cover Material

Although cover materials can be adaptable for very specific applications, Neoprene remains the best overall cover material. Inherently heat and flame resistant, this versatile material possesses excellent chemical resistance. A very common problem among aged units is bearing oil leaking from turbine bearing units which has no adverse effect at all on the Neoprene cover

Fabric Reinforcement

La Favorite Industries utilizes a high tensile strength nylon fabric to reinforce its Dogbone Expansion Joints. The nylon is impregnated with a synthetic rubber compound and constructed in a 6 or 8 ply matrix (depending on the dimensions of the Expansion Joint) which promotes superior adhesion and strength. Nylon has shown it's self to be superior in its ability to resist breakdown from pinching of poorly designed clamps, water incursion, and direct steam impingement due to failed or missing steam shields. 

Bulb Core

This portion of the Dogbone Expansion Joint is one of the most critical in regards to design and construction. Its inclusion provides greater resistance to the clamping forces and helps prevent extrusion or migration of the rubber and ensures that the bulb as a whole remains seated in the seal groove under the operational loads.

The Evolution of Construction Materials

In the 60+ years that Dogbone Expansion Joints have been in service in the power generation industry, numerous rubber compounds, bulb core and fabric reinforcement materials have been utilized in the construction. In the last 30 years La Favorite has worked hard to ensure that the best possible product is offered to our customers. Staying in touch with the power generation industry has allowed us to learn the challenges they face and how we could utilize industrial material improvements to increase quality and reliability. 

The original Dogbone Expansion Joints of the 1950's were constructed with cotton duck fabric reinforcement. Since this time synthetic materials have been incorporated to offer greater reliability and strength. Rayon and Polyester were the earliest choices due to their improved strength and light weight. After years of case studies throughout the industry that involved polyester use, La Favorite began investigating an upgrade in fabric materials to offer greater reliability in service. Nylon offers increased strength, greater flexibility, better work-ability in regards to construction and splicing and resistance to wicking of liquids that it may come into contact with should the rubber cover become compromised. 

Cover materials have varied greatly over the years. Natural rubber, Chlorobutyl, Neoprene and more recently EPDM have all been tried. EPDM has higher heat resistance, but unless combined with an equally heat resistant fabric, provides no additional protection. EPDM has also shown inherent problems in regards to its lack of oil resistance. Specifically, turbine bearing oil has been found to cause such degradation of EPDM covers as to have caused failures. Therefore, EPDM as far as we are concerned, has very limited application in Dogbones and should only be used in very specific or unusual circumstances. With many bearing oil caused failures, La Favorite reached the conclusion many years ago that Neoprene's inherent  oil resistance as well as good heat resistance and superior bonding is the best overall material for this product. 

What we offer

Over the years there have been numerous design specifications created by a multitude of Condenser manufacturers. Along the way La Favorite Dogbones have been right there to fit the bill. We have taken a more tailor made solution to this wide variation as opposed to a "one size fits all" approach. Many condensers, through years of operation, are out of manufacturer's alignment specifications and require unique solutions to compensate. As such we offer 14 different sizes of Dogbones to suit any number of operating conditions and offer ease of installation. Additionally we offer the unique ability to transition between different size expansion joints utilizing our exclusive splicing technique. All this combined means our customers need not reduce the quality and construction quality of their Dogbone Expansion joints when out of specification conditions arise.

For more information on our comprehensive service please visit our Turnkey page and our Splicing Services page.