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  • Thermal Set Rubber Hose?

    Hi Folks. I'm restoring an old Datsun Roadster and one of the rubber formed cowl drain hoses has deteriorated quite badly and are no longer available. My idea was to make some sort of "mandrel" that I could slip a thermal set rubber hose over. Heat it to whatever it was supposed to be heated to and somehow remove the mandrel. I've gone to Thomas register but the problem is I'm not sure of what exactly I need. Thought I'd see if any of you have come across a product like this or if it even exists. Thanks in Advance.
    Chris

  • #2
    I was involved with the manufacture of a RIGID FIBERGLAS part similar to what I believe you are describing. Of course, fiberglas is not appropriate for your application, but the method may be of some help. The parts were made like this:

    Make a strong aluminum female mold of the outside of the hose. Then wrap a cloth refrigerated and impregnated with cold fiberglas resin (in my case) around a bicycle innertube. Then place your polymer-impregnated cloth/innertube (you are on your own here as to what polymer to use in your application - fiberglas resin needed refrigeration in my application or it would set too fast!) inside the female mold. Inflate the innertube with air to force the polymer/cloth against the inside of the mold. The cloth had to slip over itself while this expansion process was being done. Then remove the part and extract the innertube from it. Parts were for military helicopters.

    The mold was carefully machined from aluminum in two pieces so it could be parted and the finished part (rigid fiberglas) removed. It was also very strong to take the pressure.

    In your case, someone else here may know something about SBR (styrene-butadiene rubber) and the appropriate cord (like tire cord in mfg of tires) and the appropriate surfactant system to ensure wetting of the cord by the SBR. Also need a release agent for the mold. In your case, you could leave the innertube inside the assembly unless it would degrade too soon. If so, you might consider carefully wrapping the innertube with heavy aluminum foil to geep the SBR off of it, allowing it to be extracted.

    Simple, huh?? Good Luck!! A.T.

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    • #3
      ttok- That wasn't for the Explorer was it? What you're describing sound like a wet layup is that correct? Sounds unusual not to be using pre-preg for parts. I've made molds using aluminum outside molds and an inside mold of RTV-J rubber for the inside molds. The parts were made of pre-preg aramid (kevlar) and glass. Since this is a heat curing process we used the different CTIs (rate of thermal expansion) to cause the rubber mandrel to press against the aluminum mold.

      This was an unusual part in that it needed to be molded on the inside and out. Most of the tooling I've made has only had one molded surface. For the application Chriss is asking about only the inside surface needs to be controled. For this application a plaster mandrell would be my recomendation. A plaster mandrell is a hollow plaster tube with sufficient wall thickness made in the shape of the inside mold line (IML) and allowed to dry. Any appropriate release is then applied and the material is layed up or formed over the mandrel and allowed to cure. The plaster is then broken out. Since this sounds like a one off job you probably don't want to go through the process of building a slosh mold to build up the plaster to form a mandrel. You might try looking around for some type of flexible tubing you can form plaster over or inside of and cut away after the plaster drys.

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      • #4
        Yep, I knew yo guy's would have some good ideas. I forgot to mention dimensions. OD is 1.5" and wall thickness is 1/8". Clamps holdthe tube in place so dimensional control is not REALLY critical. Mostly overall shape.
        Yes, it is technically a "one off" but as the part is no longer available I may be willing to invest time in something a little more permanent so others could get these pieces.
        I had considered the outer mold idea and using something like FLEX-AN but couldn't figure out the mandrel portion. Liked the both ideas as far as mandrels go - thanks again.
        Chris

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        • #5
          Chriss: I owned an old Mercedes 190 sl with bad rubber. I made some parts with liquid neoprene. Hose was made with a oiled or saran wrapped core (such as plaster of paris) and repeately dipped. made first dip, wrapped some fiberglass aand dippedagain and again. I sure would not trust my "ffix" in any importnt place, But for gaskets, drain hoose, home made grommets it worked ok and looked fine.
          Steve

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          • #6
            Interesting idea Doc. Was the hose still flexible when the Neoprene solidified?
            Chris

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            • #7
              Dave - I consulted on the mfg of the part - I believe it was for the Blackhawk. Yes. we used pre-preg, but it cured too fast. The external portion of the part was about 2 ft long, sort of like a square duct with several bends and open ends. The exterior was finished, but not the interior. The specification required several thicknesses of woven fiber and it was a trick to get the cloth to slide over itself - took several hundred pounds pressure and refrigeration to move that cloth into place before it set up.

              When I first read the question, I was thinking that Chriss wanted to make a molded heater hose, not just an atmospheric drain. I agree that your method is best for his application.

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              • #8
                ttok - don't understand how pre-preg could set up too fast. Oh well. Steve's post reminded me of something else. The part that I mentioned was the spar for the MD Explorer. It needed to be molded inside and out to recieve the control surface skin and a plug fitted to the inside of the spar. All parts were epoxied together at one time in a jig with an air blader to evenly distribute clamping pressure. The jig was made in so-cal and came to me when MD got taken over by the Lazy-B (Boeing) and we got the new contract for the parts. The air bladder was IMNSHO poorley made with silicon rubber sheet, caulk, and a pipe nipple. After it blew out I replaced the air bladders with new ones by wetting out glass cloth with RTV silicon rubber caulk thined with xylen and wrapped around a plaster core. Got rave reviews from the assemblers that had to use it.

                Chris- if your thinking it might be worth the effort to make tooling I would suggest making a model of the IML (Inside Mold Line) out of wood, PVC pipe, or copper tubing bent to form. Next, out of fiberglass make a mold with flanges and ribs formed around the model. With the mold finished, pour in a plaster slurry to coat the mold. Repeat the plaster slurry untill you've built up a wall thickness to about 3/16". After the plaster has hardened and been pulled from the mold bake it at LOW heat to drive off residual water. Fill any pits and treat with any appropriate release agent. Plaster mandrel is now ready for use.

                BTW Datsun roadsters are very cool, wish I could have one sitting next to my '70 Land Cruiser. Do you have a 1600 or 2000?

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                • #9
                  Thanks Dave,
                  Its a 2000. I have a 1989 240 SX that I am waiting to swap the driveline into. Love the look of the older stuff but want reliability and parts availability as well. The real bitch with these cars is getting sheet metal. I've had to build an English wheel just to make some of the stuff for this car. Many of the visible parts are being repro'd but the problem with the sheet metal and some other rubber pieces is there simply aren't enough cars left to make the tooling $$$ work. Anyone can buy MGB & Triumph stuff but the old Japanese stuff is TOUGH. I work for a FORD store that aso owns a Toyota one so I can appreciate your love of the 'Cruiser.
                  Chris

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                  • #10
                    Landcruiser-Don't leave the pavement without one!

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                    • #11
                      Yep, matter of fact the stuff was down right floppy. No stretch, just limp. nuff coats and re-inforcing inside and it was stiff enough to hold its shape- but don't try to make critical items or pressure hose of any soort- just my opinion- never tested it for strength.

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