Sunday, 6 September 2015

Clear RTV test

So I waited and waited for that clear RTV (rubber) sample to arrive. Frustratingly it arrive late on Thursday to late to get a 5kg order in before the weekend >.<

This rtv is 2x the price of the normal stuff so i really did have to wait to see how the test come out (a rare case of patience for me) and I'm glad I did. What I knew is this was 40shore hardness (compared to the the 20-25shore I normally have) but with not point of reference there was know way of know how hard it would be.

So I made Up 2 mould boxes (abit a little too over sized). As soon as I weigh out the main part in I knew it wasn't right for me. The Silicone was thick, really thick it was hard to degas and I had to take great care in pouring it then degassed the mould again and it still looked like I couldn't pull a high enough vacuum to pull all the bubbles out. The RTV also clung to the bucket which left a frustrating wastage which meant I could only pour 1 test mould.

Surprisingly the cured mould didn't have any bubbles in it so I guess the degassing did work and it was only surface tension bubbles. Here you can see the ghostly Hunchie shin suspended in the silicone (the pen was to help the camera focus).

Now the fun and games started holy fruit of the ball is this stuff hard and it didn't help the mould was a bit too thick either. Even with the help of my wife it was a job to cut this mould. In the end I had to trim 1.5cm off the parting line side just to get it to relax it enough to cut down to the part. At one point i was thinking I would just have to cut the part out but lucky that wasn't the case

The mould its self is actually quite good (as you can see below) it aligns nicely and this was the most tricky part to cast but all the venting and bridging (2vents 6brigdes) help the bubbles out. However it takes considerable strength to pull the part out of the mould which is a fingernail killer.

So in conclusion it made a nice mould but boy is it too hard to use esp if every mould was made like this. Glad I didn't buckle and buy a 5kg tub it would of hurt my wallet and my poor fingers.

I did order another clear rtv sample from another company it was 13shore (so softer) that comes on Monday but I really running out of time to get these moulds done so I've also ordered 5kg of the blue stuff just get her done because I know it produces good moulds only downside is your cutting blind.

1 comment:

  1. You can get 28 shure (spelling?) clear rtv, I use it for smaller parts, it costs more because of the platinum used in its manufacturing, but if used correctly it's light years better on casting and shelf life of the actual mold is longer, not to mention you get way more decent casts before it goes bad on you