goldenshinner

hybrid RTV/Silicone mold

36 posts in this topic

oh i almost forgot. the update. my small experiment on bonding strength. the liquid silicone caulk(100%) applied over cured RTV did cure and adheare to the RTV. pulling with some pressure was ok, but allot of pressure would separate the two. i think that for very limited number of cast cycles this would work fine. ...the RTV liquid applied to cured Silicone Caulk is still wet and curing(3days now!).

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I only have a little experience with RTV, but I have quite a bit with epoxy. If some RTV formulations are anything like some epoxy formulations, the two parts MUST be mixed EXACTLY as intended or there will be a cure failure. This could be part of your problem since you said you overdosed on the hardner. Now, you would think that if you OD on hardner (or catalyst) the material will cure faster and maybe harder. Sometimes this is the case, but not always. I would think that those RTV formulations that have to be mixed according to ratio/weight, instead of 1:1 by volume, would be more succeptable to cure failure if not mixed to the appropriate ratio. I'm not sure, but that could be the real culprit to your cure failure. Just a thought.

TJ

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Husky    13
oh i almost forgot. the update. my small experiment on bonding strength. the liquid silicone caulk(100%) applied over cured RTV did cure and adheare to the RTV. pulling with some pressure was ok, but allot of pressure would separate the two. i think that for very limited number of cast cycles this would work fine. ...the RTV liquid applied to cured Silicone Caulk is still wet and curing(3days now!).

Call it a hunch, but if it hasn't cured yet, it won't.

Can you tell me the ingredients, name and brand, please.

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muskydan666    1

Hi!It is very important to follow the mixing ratio for rtv silicon!!!If you dont!It will never cure!and!personely I use all rtv silicon when I make a mold!It cost me a little more but im sure that my mold is perfect!Time is money!and I dont have a lot of time to lose!Cheers and good luck.Dan

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dow corning 3110. ive used this one in the past before and like it. also the manufacturer has several different mix ratios of catalyst. the different ratios will cure faster or slower, and the end result will be different hardness and streach properties. I think you are right though. the last time i had a mold cure this slow it never did after weeks of waiting. i think i will be forced (like last time) to coat the surface with pure catalyst. and wipe it clean after curing compleately. oh for those interested the last time this happened to me, it was because i didnt mix the heavy setled bottom of the silicone jar well enough, the result when i scraped everything out to pour the mold, was areas that had thick unmixed(with catalyst) sections. adding extra catalyst might alter the cured properties to the point that it is a tad hard but atleast it is cured at that point. now due to my experimentations a mold that took me 14hours to set up, has tons of soft spots due (not caused by lack of catalyst) but to interference with the 100% silicone rubber(which i am pretty sure has sulfer in its chemical structure, the sulfer is interfearing with the polymerization reaction) . well this should get interesting. thanks all again

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ok updates on the mold. finaly finished it. not completly happy with results. i would deffinitly do it different next time. firstly i recomend large sized chunks of Silicone caulk if you plan on adding it to uncured rtv. as it slightly affects rtv cure rate. rather i would try next curring caulk over the skim RTV coat, as it will adhear almost as well as the rtv over rtv with time. if it is a valuable casting then one pour rtv is the only way

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also for the record i would like to mention that in spots were the cured caulk chunks were placed close to other chunks or close to the outside wall i had spots that cured slowly or were soft. one spot a caulk chunk was lying against the box wall and all rtv was still soft after over 1 week of curing(well mixed batch of rtv+catalyst).

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ok, finaly not trying to be anoying. i had problems casting this weekend i used up a bottle of alumilite regular(super plastic) trying to get just one model out of my mold. the stuff set up thick in like 3 seconds. hardly enough time even to compleatly mix the stuff. and not enought time to be able to even pour the stuff. i ended up trying to fill each mold side up with the thick paste like substance and glue two sides together with 2-ton. once cured each side was brittle and would break under almost no pressure. what am i doing wrong! oh and this is a large casting. did also try mixing with smaller batches with no results. and i had the work area a cool dry place.. one person recomended i switch plastic types. im currious what others say as far as ideal urathane and proceddure to cast a large musky bait. thanks

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ive studied that tutorial several times. it makes perfect sense. what i didnt probably realize is that alumilite regular is not the same as the Rc3. regular has pot(set up time) of 90 sec. it actualy set to the point of not being able to stir at all within 4-10 sec range! im afraid to shovel another $100 in experimenting on another plastic. im tossing it in my head between a 2gal alumilite RC3 and the smooth on feather lite. this time im going to chill the stuff way down to perhaps say 30deg or so. as i need to mix a fair amount and still pour it in through my pour hole.

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