ECO Rubber Hose and Crimp Fittings

[jnelson33]

Hello All,

I am trying to figure out how much to crimp an Epichlorohydrin (ECO) hose down onto a fitting. I'm not looking for numbers, this is all just conversational technical discussion. Our ECO hose has a Viton liner bonded to it as well. With respect to cross-section thicknesses, the Viton is about 1/3 as thick as the total wall is, so it's not really the primary elastomer here. Therefore, most of what I'm talking about will concern the ECO rubber.

My research on ECO rubber has told me about its horrible compression set. Unfortunately, our supplier can't give me an MDS, so I can;t say any discrete properties about their compound. Since ECO rubber does have this characteristic, my thinking is as follows; due to ECO rubber's bad compression set, it would make sense to fully compress the rubber down to a "solid" to ensure that sealing on the fitting is never an issue, correct? If the rubber has been fully compressed, but not plastically deformed, losing the seal should not be an issue for the life of the hose, and my design successfully accounts for that elastomer's negative characteristics.

Unfortunately most of what I turn-up in a search for compression set is all about O-rings, so that's why I am here. For an O-ring they say to do the opposite, less compression is better, which makes sense based on O-ring sealing principles. It's really only sealing on a line, and you want that line to exist while keeping its shape in a dynamic setting, or last for years in a static setup, so over-squeezing the wrong elastomer can be horrible for O-rings, aside from other failures of course.

 

[TugboatEng]

You can't really compress rubber to a solid. Eventually it will just extrude itself put from whatever you're squeezing it with. I would suggest some type of constant tension clamp that will maintain some squeeze even if the hose shrinks a bit.

Without knowing the size, service pressure, or application.

https://www.mcmaster.com/#7329K11

https://www.mcmaster.com/#8946K51

 

[jnelson33]

Thanks for the feedback. I realized that I forgot to clarify, compress to a solid as an analogy. Even if it's impossible, it was just a way of trying to convey what I'd like to do essentially.

I can't really use constant force clamps like that; these are crimp fittings and have a collar that is swaged down onto the hose.

See example: Link

The hose material is non-negotiable as well. There's no way that we can integrate another hose product line, even if it meant reliable crimp fittings with no compression set for eternity.

We are designing our crimp fittings to be used with our current hose product lines. With respect to engineering variables, life cycle variables, etc., I doubt anything like that was ever sorted out, other than making sure it was a non-leaching hose material. In the automotive world, that's what matters most to people buying aftermarket hose. As far as having sorted out the other things mentioned previously, it's not usually on my boss' radar.

Regardless, a crimp fitting collar is swaged to a predetermined diameter by two collets in a special machine. So with this style of fitting, there is no such thing as a constant force clamping mechanism unfortunately.

This is why I was bringing up a strong vs weak crimp for this ECO rubber. I was just hoping for general advice, like rule of thumb type advice for this type of rubber if being used as stated.

 

[TugboatEng]

Those types of fittings usually cut through the outer jacket of the hose and bite in to the reinforcement. If you have a Viton tube and a compatible reinforcement, the jacket material should have little to no affect on the performance of the fitting.