[Jack Houpe]

Richard I could listen to that for hours, I'm a curious weird guy. 

As of late my son is doing thousands of metal breast plates for military contractors, he's done wash down rooms, cooling towers for commercial buildings, water tanks, restaurant kitchen floors and walls, foundations for basements, roofs that are flat, trucks that fenders are rusted out and many many more things. His main business is truck beds for dealerships but we have made some cool stuff with it.

[Richard]

Jeff,

My sway bar bushing measured 70A on the durometer.

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Jack, you’re good. Both terms work. But if you want to be persnickety about it.

Urethane is the correct term for the monomer, the building block of the system chemically. Polyurethane is the term used when the monomer (urethane) has been stimulated either by heat or a catalyst to link together the individual monomer molecules into longer chains of molecules.

The chemistry of the catalyst is adjusted to control how long the chains become, and how much cross linking they form with other chains. The longer the chain the more elastic the polymer(elasticity), the more cross linking the more stiffness (modulus) the polymer will have.


The two part castable resins range from about 20a to 90a durometer. The catalyst chemistry is the controlling factor in the hardness of the part. These are designed for the chemical reaction to work at room temperature. They can take up to a week to fully cure into their final properties.

The injectable urethanes contain a heat activated catalyst. The reaction goes quickly and the part is ready to go as soon as it cools. These are not for the DYI guy.

Sorry you mentioned it right. Retired Chemical Engineer who spent his work life in polymer based industries couldn’t resist the explanation.

 
Thanks for the info Richard, this stuff is Greek to me, glad for your info. The one video I was watching shows him baking the parts in his wife’s oven after he casts them, guess that is your cross linking? He did it while his wife was away! I have a small toaster oven that I think will be perfect for this.

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Jeff,

My sway bar bushing measured 70A on the durometer.

Excellent, thanks! 70A it is then. I am looking at the products from Smooth On, PMC-770 is their 70A urethane product.

https://www.smooth-on.com/products/pmc-770/


Casting video I was talking about:
https://youtu.be/RDgW5tSr6Ss?si=mWkFPQQivjd1VdB3

Love to know your thoughts on this Richard, just remember I am an electrician/mechanic, not a chemical engineer! Haha!

[Richard]

My thoughts are that I am probably going to do this on my own sway bar bushings. I replaced mine about 3 years ago, but they are showing signs of minor distress. The only ones I could find are split to allow you to slip them over the bar. I don’t like the design. The bushing is starting to squish at the slit for the split.

I think the approach I will use is to learn how to use some simple 3d modeling and dimension the bushing. Then I will send it to a 3d printer and have some molds made. The idea is to make the mold thin enough to simply fracture it away from the part after curing. Coat the mold with a release agent before pouring in the liquid urethane mixture. It is just not on my right now list right now.

The purpose of the oven is to speed up the cure. A chemical reaction rate doubles for every ten degree rise in temperature. If you are willing to wait a week, the reaction will complete at ambient and you won’t risk contaminating the toaster. And yes, you are correct the cross linking between the molecular chains is exactly what is going on in the cure.

[Jack Houpe]

I use 2d CAD program most of the time but when drawing 3d I use this FREE software and its very easy to learn and use. We have an Artillery 3d printer I bought on auction that does an outstanding job for the $100 it cost. Some of the plastic parts on old cars are no longer available and making them has been fun.

https://www.tinkercad.com/

[Richard]

Thanks Jack, I will look into that.

[caryt]

I'm replying to this old post as it may help others. You may be able get Bushings from Energy Suspension, they have X-Treme Duty Commercial polyurethane.
They can also custom make what you need.