If you want the Flex 80 to bond to steel just make sure the steel surface is clean (I'd use plain old soap and water if possible) and dry then get the Flex 80 on there before it hits full cure (full cure is usually after a couple days). I've bonded Flex 30 to a wooden block by demolding it from a silicone mold after two hours and put it immediately on the block and it has yet to let go of the block. I left it alone for a full day and it bonded like I wanted it to.
Now here's the big warning - it may bond or it may not bond with steel, I personally haven't tried it with steel so I can't vouch for the hold. From how I've seen the Flex 30 hold to wood and the Flex 50 & 70 to RC-3, the Flex 80 SHOULD hold to the steel but I personally haven't tested it so I can't guarantee it.
Can you show us a picture of where the Flex 80 is going? I'd like to be sure it will have something around it just in case it doesn't bond well.
I'm making some carburetor to manifold boots for an old Honda. I've had the bases for them laser cut. I added a ring of countersunk holes for the rubber to pass through and grab onto so it's actually moulded through the plate. I nickel plated a test one to stop it rusting (may or may not be a good idea) so the flex 80 would actually be bonding to nickel not steel.
The mould is an open pour with a lid with a ring of vent holes that then gets pushed onto it. Once filled I insert the steel plate then put the lid on and into the pressure pot.
The first test one I made came out of the mould well and looked good but after several days it's still quite soft (durometer says it's about 40 instead of 80), tears easily and peeled off the plate without much effort. I believe my Flex 80 is off. I bought it a few months ago and it sat unopened since. I opened it a week or so ago and the A side was crystalised, even though the bottle was still sealed. For this test one I filtered the chunky bits out with a paint filter but I think it's still dead. I ordered a new bottle from the local supplier a couple of days ago and hopefully it'll be good when it arrives.
Did you shake both sides well before pouring? I know it sounds odd but sometimes it does make a difference. The nickel plating might not be that big of a problem but again, this is the Flex series so it may react differently than the RC-3 and I haven't personally tested what it might have a problem with. You did right by filtering the chunks, you can still use it for something else but as you've already tested durometer and it says it's not up high enough, then definitely go with a fresh bottle.
Give Alumilite a call and let them know about the unopened bottle being bad, they may have suggestions on what else it could be used for or help you figure out why it did that - sometimes you have to be a little "picky" with how you store some things. And sometimes some products have no problems with how you store them - Brian holds our record of the oldest container of RC-3.
Thanks for keeping us updated and pictures are great helpers. And definitely let Alumilite know what the first batch did, they count on us who use their products to let them know if there are problems so they can fix them.
Yep, shook both bottles before pouring. I've done a little more research about bonding to metal and I've got some things to try so I'll start giving them a go. This includes: - Sanding or etching the surface, presumably to roughen it up a bit to give something more for the rubber to grab onto. - Applying some shellac as a primer - Applying a special urethane bonding primer (from another company) if the shellac doesn't do a good job.
Steel plate scuffed up with some medium sandpaper and then given a light spray of shellac.
I decided to try with the original crusty flex 80 again. As per the datasheet I warmed up the B side in a water bath for a bit then shook the buggery out of it. It may have improved a little but still very chunky and I only got about 50% through a filter. Maybe I stuffed up the mixing ratio the first time or maybe it was my extended curing but it came out of the mould significantly stiffer than the first one (my durometer says it's about 70). I left it in a heated pressure pot for at least 6 hours, possibly longer, then unplugged the heat and left it in the pressure pot over night. So far the bonding to the plate is looking good but I'm going to leave it for a few days to cure fully before doing any testing with it.
Well 70 is closer to what it should be and a lot better than 40 so I'd call that a win. You might have some of Side A due to having to filter Side B but by filtering it at least you can use it for something and have it closer to what it *should* be which is good. Keep us updated on how the testing goes.