I wonder if high temp rtv gasket maker might work?
DIY Tesla Impulse Turbine
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,... high temp rtv gasket maker is what I meant when I said, high temp silicone. Either the Red or the Copper should work, but both will likely require a filler material as they both dry very flexible. Unless a solid powder is blended in, the final spider may be too squishy soft.I've found that all off-the-shelf quick-set epoxies remain slightly flexible after they fully set, a bit like hard rubber, which is close to the original spider material. Even though I don't know their temperature limits, due to their similar flex properties as the original spider, this is my first choice.
Having worked a bit with Silicon RTV makers.... 3Bond (JAPAN) make a gasketing material that "cured" all the oil leaks on Sumps and timing chests on ALL Japanese engines by all makers. Loctite (Europe) were going to make some for Nissan in the UK under licence from 3 Bond, but then 3 Bond opened a Belgian mixing plant to mix the stuff in Europe so that never happened. I tested some Loctite development stuff versus the 3-Bond material. It had a huge % of filler, compared to most other RTVs available. Gave it tremendous durability and resistance to "squeezing-out" from joints with vibration, thermal movement etc. between joint faces, however, often the aluminium or thin steel was nearly destroyed when dismantling. BUT when applied to engines lasting 150,000 miles, the OEM business preferred the longevity and durability of the joint compared to replacement costs if it was ever serviced... The filler made the finished material as hard as boot-heel rubber... So it you can buy some 3 Bond gasket stuff and make inserts you may have a relatively hard and durable elastomer insert.
BUT Silicon rubber is not normally a material for the application you have. Heavy cycling compressive loads. I strongly recommend you get some Polyurethane rubber and cut to size, shape for the inserts. This is among the most fatigue resistant material for this sort of application, and should withstand 100C, I think?
Search on-line for specs of material before you spend $s. Your project is costing a lot, so you don't want to waste $s, but apply sensible money where required. You may also find that tyre tread rubber is very fatigue resistant and can handle the temperature. To cut rubber with a razor-edged knife lubricate the blade with water, or soapy water. NOT petrol, etc. or grease! Big blocks of rubber may be cut from old tyres? (scrap Industrial tyres can be worn in the middle but have thread blocks on the edge that are big?). You can also cut hard rubber with a hacksaw - with water to lubricate the blade.
Glue rubber with "Rubber glue" as using superglue or similar works well initially, but has very poor durability against fatigue failure in this sort of cycling application.
K2
BUT Silicon rubber is not normally a material for the application you have. Heavy cycling compressive loads. I strongly recommend you get some Polyurethane rubber and cut to size, shape for the inserts. This is among the most fatigue resistant material for this sort of application, and should withstand 100C, I think?
Search on-line for specs of material before you spend $s. Your project is costing a lot, so you don't want to waste $s, but apply sensible money where required. You may also find that tyre tread rubber is very fatigue resistant and can handle the temperature. To cut rubber with a razor-edged knife lubricate the blade with water, or soapy water. NOT petrol, etc. or grease! Big blocks of rubber may be cut from old tyres? (scrap Industrial tyres can be worn in the middle but have thread blocks on the edge that are big?). You can also cut hard rubber with a hacksaw - with water to lubricate the blade.
Glue rubber with "Rubber glue" as using superglue or similar works well initially, but has very poor durability against fatigue failure in this sort of cycling application.
K2
Thanks for all the detailed information Steamchick.
Besides the Red and Copper RTV I mentioned, I'm not sure what other gasket maker materials are available here in Thailand. 3Bond sells quite a few epoxies, RTV, Contact glues, etc here in Thailand,....I'll need to look for their gasket maker.
Whatever I do, I wont spend a large sum of money on a repair as a new plum coupler is only $4.00 including shipping.
Is "the right stuff" by permatex available to you? I've seen that stuff hold up exceptionally well in uses like head gaskets for air compressors.
Possibly mixed with a fiber like fiber glass or carbon fiber, it would hold up?
An alternative would be to have one 3d printed from nylon, if you know someone with a printer.
Carving one out of uhdpe could be another root.
I think Polyurethane might creep a bit at those temperatures?
NapierDeltic
Well-Known Member
I agree with Steamchick; gasket silicone might not cope with cyclic loads; though special silicone varieties can do the job.
On the other hand, fabric reinforced rubber like that for conveyor belts can do it; and is many times used as such, cut or machined to shape. I remember it was even used on cheap car couplings as flexible torque transfer link.
https://www.autodoc24.ro/piese-de-schimb/cuplaj-elastic-cardan-10807/trabant
Rubber can be cut / shaped with an (angle) grinder or other abrasive discs used for hand-tools (Dremel).
On the other hand, fabric reinforced rubber like that for conveyor belts can do it; and is many times used as such, cut or machined to shape. I remember it was even used on cheap car couplings as flexible torque transfer link.
https://www.autodoc24.ro/piese-de-schimb/cuplaj-elastic-cardan-10807/trabant
Rubber can be cut / shaped with an (angle) grinder or other abrasive discs used for hand-tools (Dremel).
I Googled "The Right Stuff",.... seems the only way I can buy it here is through e-Bay in 300ml tubes, at $45.00 each plus $95.35 shipping.
As I said, I can buy a new coupler from China for $4.00 including shipping.
IF my epoxy spider fails, I will make another spider using Red RTV, which I already have, mixed with a little Cab-o-sil, to thicken and stiffen the RTV. I already have some Cab-o-sil, which is made of shaved silica having a melting point of 1700 deg C.
For what it's worth, NapierDeltic's idea of tire rubber was a really good one!
I agree,...skillfully cutting a plum coupler spider from an old tire would likely work,....it's my ability to cut each of the spider legs within a tolerance that wont throw all the pressure to one side of the coupler, that's in doubt
Freeze it and cnc?I agree,...skillfully cutting a plum coupler spider from an old tire would likely work,....it's my ability to cut each of the spider legs within a tolerance that wont throw all the pressure to one side of the coupler, that's in doubt
At what temperature do auto tires "freeze"?? Must be well below the -40 C winters I've driven my car. Although freezing the rubber while CNC milling it would likely work, it doesn't seem very practical. Remember, I can buy the entire coupler for $4.
Hmmm, but I thought the $4 coupler had polymer buffers that melted with the heat? Maybe I have missed other mods you have made to keep the coupler cooler than previously?
My GUESS was that a high-speed milling cutter (very sharp) should be able to shape tyre rubber tread blocks? But I'm not about to try... (leaving the tyres on the car).
K2
My GUESS was that a high-speed milling cutter (very sharp) should be able to shape tyre rubber tread blocks? But I'm not about to try... (leaving the tyres on the car).
K2
Ha good question. I used to have unlimited access to liquid nitrogen so I forget things can be hard to cool. Google has no easy answer for me as to the glass transition point.
Back in post #300 I wrote: "I THINK the coupler melted from heat created by friction as the stainless steel TT drive shaft spun inside the aluminum coupler, after the steam heat loosened the connection. I don't believe the steam heat alone melted the coupler's plastic spider. I'll tighten the coupler onto the shaft a bit tighter for the next test,...hopefully, that will be enough.
I still believed this analysis to be true, but I needed to be certain in order to avoid another spider melt-down.
So I removed a spider from a new coupler purchased from the same company, dropped spider into a glass of water and popped glass & spider into the microwave set on high, until the water was boiling nicely. Using a hemostat clamp, I squeezed several of the spider's legs and observed no deformation, and in fact, I could not feel any difference in flexural rigidity between hot and cold spider. When re-assembling the coupler, I observed that the spider had not changed shape or size as it fit tightly between the two halves of the coupler.
Conclusion: these couplers can be used in temperatures up to at least 100 deg C.
Brilliant!
I have a domestic pressure cooker (for cooking vegetables and meat) which would go to about 115deg.C. (15psi). But I think that sending my pressure cooker to you would cost more than $4...
Or some salt in the water could raise the boiling point if you need to go higher than 100C?
I wish I was just down the road, so I could come and learn more from your work.
K2
I have a domestic pressure cooker (for cooking vegetables and meat) which would go to about 115deg.C. (15psi). But I think that sending my pressure cooker to you would cost more than $4...
Or some salt in the water could raise the boiling point if you need to go higher than 100C?
I wish I was just down the road, so I could come and learn more from your work.
K2
Me too! This is a wicked project!
Of all the high temperature rotating equipment I have been around they all used metal for couplers. I think with your machining skills you could easily make one they are designed for expansion and will accept slight misalignment of the shafts. The only polymer ones used were on lower temperature equipment. There are several designs in the industrial market you could copy. Shaft mounting and alignment procedures did take time.
