making urethane tires

[mattb]

Guys, I always have plenty of mold making supplies on hand. The only item I don't have is urethane rubber. I have been thinking of making some urethane tires, but I need some info. I can make a mold with silicone, right? I can then pour urethane in and it will cure and de-mold with no problems? does it need mold release or 2 part mold release painted on the tire molds?

Is it just as simple as making the silicone mold and then pouring urethane in that mold with no other steps needed?

What urethane works best? I buy alumilite at HL now, but used Smoothon exclusively until then. I see their Vytaflex seems to be suitable for tires. What is the cure time of urethane?


any info appreciated

[BARC 1]

Use mold release. You can demold urethane in about 12 hours, but sometimes it is best to wait. They come out pretty sticky. I have wooden dowel of the correct diameter and as soon as I demold them I put them on the dowel and let them fully cure for a few days before actually using them.

[munter]

I have done a few tires...I use an Australian silicone for the moulds and have been using Smoothon Reoflex 40 shore for the tires.
I havent used a mould release agent and have had no ill effects yet.
The urethane instructions say 16 hours cure time but if the temperature is warm then 12 hours is OK.
You also need a dye to give the black colour.

[Dangermouse]

Vytaflex or Reoflex is good - shore 40 for most purposes is good - I have heard of some folks blending different shore ratings as well.

I can't get Vytaflex in small enough quantities so use the reoflex - not sure of the exact chemical differences but if I could get a small pot of it that is what I would try for my next batch.

[nhdungeonracer]

[mattb]

I have some black dye left from when I made silicone tires, Think it will work in urethane? I wasn't sure how you would get mold release inside a tire mold. I use spray maneze. I figured to make tire molds with silicone and only have a small slip for the rubber to go in and the tire to come out. I do have some OOMOO left over and I figured I would use it for the mold. I could use the alumilite high strength. The alumilite really stretches. i can get vytaflex in the sample size from smoothon.

I will get the urethane and when I get time with nothing to do, I'll experiment some.

[chappy]

Hi Matt , if you use the smooth on products, omoo silicone and either vytaflex or reoflex in a bout a 40 shore with black tint, you wont need a release agent. Silicone and urethane dont stickmto each other, you can speed the cure time by making a small box into an oven with tinfoil liner and a 40 watt builb. It will reduce the cure time from 24 to about 12 hrs. You will find the first few tires will be gooey as the mold hasnt cured properly and takes a bout 3 uses or a week of air curing to get rid of the chemical in thenmolf. Like an alcohol it needs to evaporate. If you can, make the tires a bit smaller than what they are to fit onnthe inside diameter as you will get a snap fit. If you go the regular size you will get a fit that needs to be glued.. thenother thing you can do is put the hub imside the mold and thenurethane will stick to,thenhub. This ,akes it easy to cure and true later on. Pour the urethane slowly to avoid air pockets and a bit of vibration helps get any airpockets to
the surface. About 30 seconds with a drill and sanding drum should create enough vibration.
There is a spray you can buy to assist in the evacuation of air bubbles but have never needed it.
Have fun
Bob

[BARC 1]

I use a veterinarian syringe and inject the urethane into the bottom of each mold and the air gets displaced.I usually get perfect tires every time

Shelf life on urethane is not good I have found. Plan on using it up as quickly as you can once opened.