Starting out in resin casting?

[MGR Hooper!]

I've been told to read up on this thread. Planning on doing some resin casting myself!

[justin1985]

Reviving a very old thread here - but its actually been that long since I last did any casting - and I noticed that I'd mentioned a pre-grouping sand wagon would be my next project to cast "once I've finished the masters" - which was this weekend! Thankfully both the moulding materials and the resin were still good after more than a year in storage. (but I did find out that the hardener stains marble after some dribbled through the newspaper I'd put down onto the marble tile I use as a flat surface for building etches etc!).

 

It took me a few pours to get back the knack of putting a little in the mould, poking the air bubbles out of the undercut corners etc with a cocktail stick, and then topping up the resin. Once I'd got the hang of that again I managed to get several pretty much perfect castings out of both new and old moulds. 

 

One little think I've noticed - and I'm not sure if its related to where I have been poking with the cocktail stick - little extra balls of resin seem to appear in the corners OUTSIDE the mould and only loosely attached to the casting. It doesn't seem to be damage to the mould from the poking, because if I do a second casting from the same mould (and poke out the bubbles again) the little balls of resin will appear in slightly different (but similar) locations. Most are perfect spheres, and appear to be hollow.

 

 

 

You can see them here just under the overhang of the coach roof 

 

And here is one just under one of the sand wagon roof hinges, which I missed when flicking the rest off with a scalpel, before giving it a coat of primer. 

 

 

Anyone have any idea whats happening?

 

Thanks

 

Justin

[peter220950]

As a possible cause it's always worth checking how old your resin is, the hardener in particular seems to absorb moisture over time. I seem to get this sort of explosion from within the casting more when I use resins over about 6 months old. If you put a small amount of hardener in an open cup and leave it out for a day or two, and then use it, the resulting castings resemble Aero. Not sure if the problem is because the resin deteriorates with age, or that as you use it up there's more air in the container. Although yours still sets well even though it's a year old I would try a new batch and use the old up on stuff that's less critical.

 

It only became really apparent when I had occasion to buy it in 5 litre containers which seemed like a good idea at the time.

 

 

 

 

You can see from the above that some of the blobs I cut off were quite large, I put it down to the heat generated by large castings at first, but now I'm pretty sure it's moisture in the resins.

 

Peter

Edited June 6, 2017 by peter220950

[gr.king]

 

Anyone have any idea whats happening?

 

Thanks

 

Justin

 

The rubber forming the mould is inevitably peppered with air bubbles unless you go to the extra trouble of de-gassing it before pouring the original mould. These try to rise through the thick rubber mixture but they don't all escape and are particularly prone to being trapped under any overhanging feature of the master, such as the ends of those roofs. The first few castings may come out perfect if the bubbles in the mould are still sealed by a full skin of rubber, but as the chemical action of the resin resin and mechanical wear and tear slowly eat away at the integrity of the rubber, tiny splits or pinholes will start to make those air bubbles in the rubber accessible to the resin.

 

Stretch the mould in the areas where those resin balls form - then you'll see the ruptured bubbles in the rubber.

[peter220950]

 

 

The rubber forming the mould is inevitably peppered with air bubbles unless you go to the extra trouble of de-gassing it before pouring the original mould. These try to rise through the thick rubber mixture but they don't all escape and are particularly prone to being trapped under any overhanging feature of the master, such as the ends of those roofs. The first few castings may come out perfect if the bubbles in the mould are still sealed by a full skin of rubber, but as the chemical action of the resin resin and mechanical wear and tear slowly eat away at the integrity of the rubber, tiny splits or pinholes will start to make those air bubbles in the rubber accessible to the resin.

 

Stretch the mould in the areas where those resin balls form - then you'll see the ruptured bubbles in the rubber.

While a couple of mine are undoubtedly due to this, particularly as you say on the undercuts, the little ones erupt after the casting has been removed from the mould, and can appear a day or so later, and appear in different places on different castings, so I still suspect that the resin is hygroscopic and it's moisture that's at the root of this particular problem.

 

Peter

[clowe999]

Hi Guys,

thinking of starting making moulds and casting resin components myself. Anyone any idea if Sylmasta are still in business? Apparently, so I was told, they sold a good starter kit. If they are now defunct has anyone a recommendation of a company selling a similar 'all in one' starter kit?

Chris

[Horsetan]

....any idea if Sylmasta are still in business? ....

 

Looks like it

 

Starter kit here

Edited September 22, 2017 by Horsetan

[clowe999]

Many thanks. All the old links I used to use to them, along with their YouTube demos seem to have disappeared from the Internet when I tried yesterday. C.

[Smiffy2]

I bought one of their starter kits about a year ago, their website has changed but it looks like it's all still available. If not, there's always Tiranti.

 

https://sylmasta.com/product-category/casting-mould-making/

 

https://tiranti.co.uk/product-category/mouldmaking/

[gr.king]

An update on resin supplies if any others are having a go:

For the last couple of years I've been buying 1kg quantities from Abacus Technologies, of Rowley Regis, W.Mids. I am told that Abacus has gone out of business.

The resin I have been using was Rampf "Raku Tool", PF3700-1 and PH3970-1. It is evidently some time since I last needed to buy, in anticipation of starting a load of P2 castings last year, as my almost used up current bottles have November 2016 expiry dates! Regardless of that, the bottles have been open for some time, have not lived in the fridge or an inert atmosphere, yet are currently still producing good castings of some wagon loads required by a co-conspirator.

Thanks to a suggestion that came my way as a result of an unbelievable coincidence about ten days ago, I've managed to find a new willing supplier of 1kg quantities of Rampf Resin. Their lists for the right sort of product referred only to PF3700-2 and PH3977, but examination of the data sheets suggests to me that the main user-relevant technical characteristics of these are the same as previous resins. These have come from John Burn & Co of Birmingham. I'll try to remember to let you know how well I get on with these. I wonder if they are simply the updated versions of the resins I was using? I'm not entirely sure whether J. Burn will supply to private individuals, as for simplicity when completing their on-line enquiry form I used a valid company name in one of compulsory fields. Should anybody else encounter a problem perhaps they will let us know?

[peter220950]

If John Burn will supply to me they will supply to anybody!

 

I've been using them for some years now for Sika Biresin, and recently, because of the nightmare the M5 has become, got them to deliver, goods arrived the next working day, very helpful and efficent.

 

Just ring them up and they will take the order and payment by card, if you want to collect just ring beforehand to save delay when you get there.

Peter

[gr.king]

Doubt nicely removed. Thanks Peter.

[Daddyman]

I bought one of their starter kits about a year ago, their website has changed but it looks like it's all still available. If not, there's always Tiranti.

 

https://sylmasta.com/product-category/casting-mould-making/

 

https://tiranti.co.uk/product-category/mouldmaking/

Got something from Sylmasta a week or so ago. I was under the impression that they were what Graeme used. I was also under the impression that they were in Northern Ireland, but they're in Hayward's Heath. 

 

Anyway, the starter kit is still there for £40-ish (inc. postage). There's not enough moulding compound to go with the amount of resin in the kit, so my recent order was for more of the former (Grade 380 rubber), which came next day. 

[gr.king]

I have used a pre-coloured Sylmasta resin in the past and it was certainly okay, albeit at a premium price with the colourant. My impression is that the Rampf Raku-Tool is a little tougher when used in thin walled castings, but I could be imagining the difference.

 

My mould rubber comes form Scarva Pottery Supplies, which is where the Northern Ireland element in my dealings comes in......

[Daddyman]

Further to our conversation at Warley, Graeme, I can now confirm that putting resin casts in the fridge while they set is very effective. If I remember correctly, you were having the same problem as me - that casts were sometimes soft for a few days. Well, I cast the roof shown below the other day and put it in the fridge for an hour. Due to my aversion to 2-part moulds, I cast it in one go in a vertical mould. As you may be able to imagine, I really had to pull to get it out of the mould due to the length of the latter, and it was set hard enough for any amount of wresting, prising, levering and wrenching within an hour. My unrefrigerated casts, by contrast, are still stretchy days later - I'd never have got the roof out and maintained its shape. 

 

 

Edited November 29, 2017 by Daddyman

[gr.king]

Very interesting and intriguing Dave. Have you examined the castings over subsequent hours and days to see whether the refrigeration hastens the full curing process, creating a permanently hard casting in shorter time (which would puzzle me) or does the casting return to a more flexible state if it is allowed to come up to room temperature before its specified hours or days of final curing have elapsed?

 

It was good to see you at NEC by the way. The same goes for all of those who came along to my demo desk to exchange ideas.

[Daddyman]

No, it's absolutely fine, Graeme - no hint of any return to a less stable state. That was my first thought, too - that it might go soggy once it warmed up, but no, the castings are four or five days old, and I think it's safe to expect them to remain robust now. 

 

This is Sylmasta I'm using, of course. Whether other makes are the same, I don't know. 

[jonhall]

Further to our conversation at Warley, Graeme, I can now confirm that putting resin casts in the fridge while they set is very effective. If I remember correctly, you were having the same problem as me - that casts were sometimes soft for a few days. 

 

That's interesting, I would have expected the complete opposite - What I saw with clear resin was that the usual application (paperweight type encapsulation) is a big thick lump, and the exothermic reaction actually helped it to cure, whereas in the thin sections I was trying, it never got quite hot enough so took weeks to go off - it was suggested to me that building a hot box, i.e. a wooden box and lid with a lamp inside and dimmer switch, which could be used to raise the temperature by 15-20°C might be an idea. Resin curing is at its heart a chemical reaction, and most of those tend to work better/faster with more heat not less.

 

I had a couple of batches of Easyflo 95 resin that were always a bit soft - I liked it because the pot life was longer, so you had more time to work big moulds, but the failure rate due to lack of complete curing was too high, and I don't recall if that was some good and others bad from the same bottles, or if it was a case of the entire pack being bad - I think the latter. I don't know if was more susceptible to poor A:B ratio's, one of Easyflo 60's many useful qualities is that it can stand being mixed in a not-quite-right ratio.

 

Jon

[gr.king]

I had the same trouble with Easyflo 95, which I tried for the same reasons, then found a data sheet referring to heated moulds.

 

I also expected, based on similar findings with thick or thin layers, and instructions relating to post-cure heat treatment for some resins, that heating rather than chilling would be the quick way to harden the castings. Once fully cured of course, they will be stiffer when cold - a quality you may or may not want when trying to extract them from a mould. Thick areas will keep their shape even better when stiff, thin areas may break due to brittleness....

 

I can't argue with Dave's experience though. Proof of the pudding!

Edited November 30, 2017 by gr.king

[MGR Hooper!]

Sorry for hijacking... but can anyone guide me to a source where I can get something cast in clear/transparent resin (I need it for a detailing kit I am working one and it's lenses for headlights)

[Andy Hayter]

I too am intrigued.  Chemical reactions usually roughly double in speed for every 10 degree C increase in temperature

[Daddyman]

Interesting what you say about the norm for chemical reactions, which is of course right. I just became convinced that putting things in the airing cupboard was prolonging the softness - for days in fact. So I tried the fridge with the roof. Thing is, I can't remember if I put it in the fridge immediately, or after some time at room temp - maybe 20-60 mins to allow the reaction to happen. I've put stuff in the fridge immediately since then, precisely because I couldn't remember what I did with the roof. And the results have been less immediate: I've had to wait until the morning for hard castings. However, that could be down to a number of things: imperfect A:B mixing (which Sylmasta also tolerates well), and the fact that my A and B are getting a bit "dregsy" at the bottom of the bottle. 

 

Either way, it doesn't matter, as I have hard castings overnight, rather than 3 days later. But I think, given your comments about the heat generated in the reaction, it's probably best to allow that process to finish before putting things in the fridge. 

Edited November 30, 2017 by Daddyman

[Andy Hayter]

Perhaps there is now a logical explanation, if you did put the mouldings in the fridge after the 1 hour notional reaction time.

 

The slightly unusual mould design that you have could mean that the heat generated in the chemical polymerisation reaction finds it difficult to escape.  This could leave the moulding sufficiently warm that it deforms when disturbed in the mould.  Putting it in the fridge overnight allows the heat to dissipate.  

[Daddyman]

The slightly unusual mould design that you have could mean that the heat generated in the chemical polymerisation reaction finds it difficult to escape.  This could leave the moulding sufficiently warm that it deforms when disturbed in the mould.  Putting it in the fridge overnight allows the heat to dissipate.  

This makes sense. However, in open-topped moulds I have the same problem of sloppy castings, as do others, judging by the comments. 

 

The recipe I'll follow in future is: (1) pour the resin into the mould, (2) wait until the leftover resin in the mixing pot cools, then (3) put the castings in the fridge - leaving overnight if necessary. 

[Neil]

From experience castings not setting properly is probably down to either the mix not being right or less than ideal resin. I've always used Sylmasta resins, I mix visually using identical transparent disposable cups to get equal amounts of resin and have never had problems with setting though I leave for an hour rather than the recommended twenty minutes. I wouldn't be happy putting food and curing resin in close proximity. Though Sylmasta resins aren't the cheapest around, the cost savings to be had aren't huge and would in my opinion be a small price to pay for not mixing curing resin castings with food and drink.