Silver in the aerospace industry
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Silver in the aerospace industry
I was sent this link by my boss and wondered if any of it was true.
http://www.silverinstitute.org/uses.php
I'm prepared to believe it but I have never heard of silver bearings in an aero engine. Please excuse me if I'm making a fool of myself. I've certainly never heard of it with respect to the R3350.
"Bearings
Steel bearings electroplated with high purity silver have greater fatigue strength and load carrying capacity than any other type and are hence used in various hi-tech and heavy-duty applications.
It was a layer of silver on main shaft bearings of the 9,000 horsepower reciprocating engines of the World War II Superfortress that resolved the unacceptable failure rate of its giant engines. Silver, with its superior fatigue resistance, lubricity, corrosion resistance, and thermal conductivity came to the rescue.
Today's commercial and military jet engines deliver 35,000 to 100,000 pound thrusts under high-temperature conditions. Despite the far higher power and a far more rigorous internal environment, silver coated bearings continue to provide the superior performance and critical margin of safety for today's jet engines.
The fan/compressor/turbine rotating components that push the air through the jet engine are all attached to the main shaft. This main shaft rotates on steel ball bearings that roll within steel retaining rings, called cages. Similar bearings are required for the connecting gear boxes that drive accessories such as hydraulic pumps and fuel pumps; all rotate at much higher speeds than ground-based machinery. Steel has a poor coefficient of friction, but placing a layer of silver between the steel ball and the steel cage reduces the friction between the two to a minimum, increasing the performance of the engine and its accessories.
But silver also plays another critical role.
Safety in jet engines is a paramount consideration. Failure of any one of the jet engine bearings would be catastrophic. Rolling contact bearings are lubricated and cooled with synthetic engine oil. In the event of an oil interruption, such as a pump failure, the silver plated bearings provide adequate lubricity to allow a safe engine shut-down before more serious damage can occur. To prepare for such a possibility, the U.S. Federal Aviation Authority (FAA) and airplane manufacturers require fail-safe engine testing for the bearings. The test requires stopping the lubricating oil system for 15 seconds with the engine running at full power and then turning on the lubricating system, then turning off lubrication again for 15 seconds, and repeat for four successive cycles. The dry lubricity of silver always allows jet engines to pass the tests."
http://www.silverinstitute.org/uses.php
I'm prepared to believe it but I have never heard of silver bearings in an aero engine. Please excuse me if I'm making a fool of myself. I've certainly never heard of it with respect to the R3350.
"Bearings
Steel bearings electroplated with high purity silver have greater fatigue strength and load carrying capacity than any other type and are hence used in various hi-tech and heavy-duty applications.
It was a layer of silver on main shaft bearings of the 9,000 horsepower reciprocating engines of the World War II Superfortress that resolved the unacceptable failure rate of its giant engines. Silver, with its superior fatigue resistance, lubricity, corrosion resistance, and thermal conductivity came to the rescue.
Today's commercial and military jet engines deliver 35,000 to 100,000 pound thrusts under high-temperature conditions. Despite the far higher power and a far more rigorous internal environment, silver coated bearings continue to provide the superior performance and critical margin of safety for today's jet engines.
The fan/compressor/turbine rotating components that push the air through the jet engine are all attached to the main shaft. This main shaft rotates on steel ball bearings that roll within steel retaining rings, called cages. Similar bearings are required for the connecting gear boxes that drive accessories such as hydraulic pumps and fuel pumps; all rotate at much higher speeds than ground-based machinery. Steel has a poor coefficient of friction, but placing a layer of silver between the steel ball and the steel cage reduces the friction between the two to a minimum, increasing the performance of the engine and its accessories.
But silver also plays another critical role.
Safety in jet engines is a paramount consideration. Failure of any one of the jet engine bearings would be catastrophic. Rolling contact bearings are lubricated and cooled with synthetic engine oil. In the event of an oil interruption, such as a pump failure, the silver plated bearings provide adequate lubricity to allow a safe engine shut-down before more serious damage can occur. To prepare for such a possibility, the U.S. Federal Aviation Authority (FAA) and airplane manufacturers require fail-safe engine testing for the bearings. The test requires stopping the lubricating oil system for 15 seconds with the engine running at full power and then turning on the lubricating system, then turning off lubrication again for 15 seconds, and repeat for four successive cycles. The dry lubricity of silver always allows jet engines to pass the tests."
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There's a fine writeup of R-2800 development history here.
For this engine, the silver-lead bearing was an interim step, although it was standard on the lower-powered P&W's.
I have also seen silver plate used as an anti-sieze layer on tight rabbetted fits of high-speed shafts. Not sure if this is still current practice.
For this engine, the silver-lead bearing was an interim step, although it was standard on the lower-powered P&W's.
I have also seen silver plate used as an anti-sieze layer on tight rabbetted fits of high-speed shafts. Not sure if this is still current practice.
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Bearing cages are plated as are some of the races within the engines. Specific areas along the length of the shafts are coated in some cases. Always handy to know where the plating shop is for when your mum wants the family silver freshening up 
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Read in the paper the other day that some chaps have come up with a stainless silver alloy, looking at it to a.) increase the attractiveness of silver for jewelry, and b.) as a replacement for Gold plating on electrical connections in cars aircraft etc., at about 1/10 th the price of gold should be attractive.
