Extension Springs - Solving Problems

Probably one of the most difficult extension spring problems we had was for barrier springs. These are big extension springs that are used to lift the barriers up when they put barriers around an application.

We have a series of big springs around the World Trade Center that will pop up a barrier to prevent anybody trying to drive towards the building or even towards the Memorial. It takes big heavy extension springs to assist lifting these big plates that will keep any type of truck from penetrating the area around the WTC.

They are used all over the world, even out in the desert around oil fields. They put them in different spots and they pop up automatically by the spring and prevent anybody from getting into the oil field application.

The problem we had to solve was the springs would probably work three or four times and then break. The customer came to us and we looked at the application. It has big plug screws screwed into the end of it so we can use real heavy wire springs.

What we did was come up with an inner and outer arrangement that would enable us to optimize the forces for the application, but we made the springs open wound so we could shot peen them and get a much better fatigue life and also get the coating between the coils.

We ended up with a spring that was about 4’ long, about 6” in diameter, and weighs so much you can’t lift it up yourself. When we put it all together, you get an inner and outer spring acting as one screwed in with plugs. And then we put a big bolt in the end of it that attaches to the two parts that lift up the barrier.

We were able to do that for this customer and we’ve had zero failures because of the reduced stress in the spring, the shot peening and getting the paint in there altogether. And we give them enough force to actually lift up these huge plates and a very quick, quick response.

We had another application where we’re using a spring for a valve that’s called the “steam reclaimer valve” and they are used in steam and all different types of wet applications.

The customer was having a hard time with springs that kept breaking. We looked at the application and eliminated the hook design. We went to a plug design where we screw the plugs in. The tricky part with this extension spring is it had to have initial tension because not only was it stretching but it was also bending in the middle and that bending is what actually made the valve close up and open.

We tried stainless steel and that wasn’t good enough, so we came up with a pretty unique design out of Inconel 718 with screw-in plugs that also provided initial tension. Since we designed the new solution, the customer has had zero problems with breakage. What he has is a very reliable product because these steam reclaimers are sometimes out in the middle of nowhere and if the spring breaks, they’ve got to send a crew all the way out to replace it.

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