G1/4 plug leaks on aluminum hydraulic blocks

[73lafuite]

Hello,

For some years we have been using high strength 7075T651 aluminum to make drilled blocks. The yield strength of this aluminum is 500Mpa (73,000 psi). Previously they were steel.

After about 2000 pressure cycles 0 to 150bar, we found some plugs G1/4-ED Voss that were not tightened one of which had unscrewed several tenths of a mm until the ED seal extrudes .
On another power plant, it is an electro-distributor cartridge with 2-way valve with 3/4-16 UNF layout that has unscrewed. And the seal in the inlet cone was extruded.

These power-units operate approximately 8 hours a day. There is a 0.75kW-2l / min electro pump unit that runs less than 5% of the time to charge a battery. At night the temperature of the block falls between 0 and 25 ° C. In operation the block heats a bit because the coils of the electro-distributors are powered.

It's been over 30 years that we do the same kind of equipment. Since we changed the material of the blocks we have this phenomenon.

Questions: Does anyone know this phenomenon? And what solution did he bring?

 

[hydtools]

Perhaps plug and valve were not installed tight enough.

Ted

 

[MikeHalloran]

Both pressure cycling and thermal cycling need to be evaluated against material parameters other than the yield strength. Aluminum is not a direct replacement for steel, especially in cyclic applications.

You might also consider retention means other than threads, like the cylinders that use two half grooves and a tangential entry, coupled with a malleable ring pressed in as a straight bar through the tangential groove entry. I forget what it's called, but it's been in commercial use for a couple decades in compact cylinders. I've never seen one unscrew.

Or go back to steel, and consider a more machinable grade like 12L14, better drills and fixturing etc, to speed up the cycle time, and perhaps consider reducing the thickness to control weight, if that is an issue.



Mike Halloran
Pembroke Pines, FL, USA

 

[73lafuite]

Hello,
hydtools and MikeHalloran:; thanks for your advices. We will study what changes we need to make.
cordially

 

[hydtools]

I have sucessfully used 6061-T6 for many manifolds on mobile applications which experience wide temperature and cyclic pressure variations to 2500psi. All plugs, fittings, and cartridge valves remained tight.

Ted

 

[TimSchrader2]

Hello

We also do alot of what hydrools mentioned on boats that go to the North Atlantic. 3000 psi Alum 6016 T6 blocks are common. But they would not be cycled as much as your saying. They do often go to 3000psi+

 

[73lafuite]

Hello,
Thank you for your feedback that reassures us.
Decisions taken following other responses in Europe are:
1. Change supplier. Voss plug tests (with the "Voss coat" treatment) proved to be bad compared to the competition.
2. Increase the tightening torque.