Plastic Injection & Resin Casting

[Phil Traxson]

I notice I am getting the blame for starting some of you on the downhill path of resin casting. And I thought nobody really took any notice of the grey-bearded, mad professor type mixing potions in the corner! Thanks very much chaps.

 

I hope some of you take it up seriously, preferably younger than me, as at sometime in the future when I decide to retire, my trade customers will want some one to do the casting for them and I will need some one to point them to.

 

Phil T.

[Phil Traxson]

Don't know what the rest of you on this thread think but is there any mileage in getting the mod's to move this to the specialist interest section as a topic in it's own right? Being more visible there it might flush out one or two more of us casters.

 

Phil T.

[gr.king]

It's just as well that somebody started this bad habit, otherwise we'd all be in the dark.

 

Has anybody conducted any tests to discover whether the application of high frequency vibrations from something such as a small ultrasonic jewellery cleaning tank or an ultrasonic toothbrush makes any substantial contribution to the liberation of trapped bubbles from the little nooks and crannies when resin is poured into the mould?

[gr.king]

Don't know what the rest of you on this thread think but is there any mileage in getting the mod's to move this to the specialist interest section as a topic in it's own right? Being more visible there it might flush out one or two more of us casters.

 

Phil T.

 

Sounds an idea. It would be nice to have input from Jon Hall to this discussion too.

[c2c]

It's just as well that somebody started this bad habit, otherwise we'd all be in the dark.

 

Has anybody conducted any tests to discover whether the application of high frequency vibrations from something such as a small ultrasonic jewellery cleaning tank or an ultrasonic toothbrush makes any substantial contribution to the liberation of trapped bubbles from the little nooks and crannies when resin is poured into the mould?

 

Well I guess someone had to come of the closet sooner or later!  

 

Good point as that works with concrete, constructors use vibrators!  Have used a spin caster yet?

[c2c]

Has anyone bought any RTV lately, If so what sort of prices are you paying? The cheapest I could find was £50 for 5kg fast cure. 

[peter220950]

Hi,

 

Last time I bought any it was around £24.00 for a kilogram as I recall, that was from John Burn about 6 months ago. - £50.00 seems pretty good for 5kg, where was that from?

 

I would agree with the idea of moving the thread to a specialist area to spread the word. - As a matter of interest I haven't had any great problems with air bubbles in the resin pours but seem unable to get a decent separation with the two part moulds. What are you guys using? - I have tried the silicone mould release spray but usually end up cutting the mould apart.

 

 

 

peterL

 

p.s. in case anyone wondered why you would need to be buying resin in 5kg containers!

 

 

Told you it was addictive.

[gr.king]

I've found vaseline smeared out in a thin but complete layer works perfectly as a barrier when producing two mould halves. Spray-on wax polish performed very poorly by comparison. Obviously you need to make sure that you don't leave "clots" of vaseline in the details on the master. A paint brush is handy for brushing out (or brushing away) any excess thickness of vaseline.

[burgundy]

I've found vaseline smeared out in a thin but complete layer works perfectly as a barrier when producing two mould halves. Spray-on wax polish performed very poorly by comparison. Obviously you need to make sure that you don't leave "clots" of vaseline in the details on the master. A paint brush is handy for brushing out (or brushing away) any excess thickness of vaseline.

From my time making whitemetal castings using a Tiranti centrifuge, I seem to remember that it helped to dissolve the Vaseline in white spirit. That way, you avoided clots and, as a liquid, you could brush it freely into the nooks and crannies.

Hope this helps

Eric

[jonhall]

Sounds an idea. It would be nice to have input from Jon Hall to this discussion too.

 

Sorry, I've been gricing in Germany for a week, so not paying attention.

 

I've used (and regularly demonstrate with) a resin called Easyflo 60 (an American product so don't start on the flo....   ) which is only 60 centipoise thick, so goes into details nicely and does not tend to incorporate air bubbles too much. One tip I was given was to lightly dust the moulds with talc - not as a release agent, but to help break the surface tension so that the resin can wet the sides of the mould. Another advantage is that it is clear, so I can see into my moulds, and prod the bubbles out with a wooden spatula if need be. Pot life is about 2 minutes, and demould after about half an hour.

 

I have seen problems with one of the two parts growing crystals, when new part A should be clear and almost colourless, as it ages then it goes yellow and ultimately orange, this will almost certainly have crystals in the bottle, which if they get into a part will 'weep' monomer forever - there will be nothing you can do about it. I've seen examples from ebay that appear to have been re-packaged in a smaller size (the smallest pack I can get is 3.8lbs ) these seem to be yellowed, I don't know if its a function of an incompatible pack, material that has already been stored too long, or that air has got into the pack during re-packing. Squeezing the bottle to remove the headspace seems to work quite well, I don't know if its moisture or air that is the problem, but you can get 'Polypurge' which is nitrogen in an aerosol to spray in over the top, this extends the life, but in my opinion it also makes the first casts after opening a bit bubbly due to the absorbed gas coming back out of solution - I suspect you need to let the bottles breathe for a few hours befor using them. The other alternative would be to refrigerate - not sure if the domestic authorities would approve, but you could always buy one of those cheap 'beer' fridges and use that. 

 

The rubber I'm using is Silastic 3481. I do have a vacuum pump and chamber in the shed, so I can degas the mould rubber really well, but it isn't strictly necessary, using a Black&Decker voibrating sander without the sandpaper seemed quite effective.

 

All of the products I've mentioned above come from a company called Notcutts http://www.notcutt.co.uk/

 

http://www.rmweb.co.uk/community/index.php?/topic/49713-railtrack-pna-scratchbuilds-and-resin-moulds/

 

http://www.rmweb.co.uk/community/index.php?/topic/30067-sd-sentinel/

 

I think I'm due to demo at Scalefourum in September if anyone wants to have a look.

 

Jon

[c2c]

Hi,

 

Last time I bought any it was around £24.00 for a kilogram as I recall, that was from John Burn about 6 months ago. - £50.00 seems pretty good for 5kg, where was that from?

 

I would agree with the idea of moving the thread to a specialist area to spread the word. - As a matter of interest I haven't had any great problems with air bubbles in the resin pours but seem unable to get a decent separation with the two part moulds. What are you guys using? - I have tried the silicone mould release spray but usually end up cutting the mould apart.

 

 

 

peterL

 

p.s. in case anyone wondered why you would need to be buying resin in 5kg containers!

 

JPEG Image (1493352).jpg

 

Told you it was addictive.

 

Hi Peter it was RTV that was £50 for 5kg! There is a guy on ebay selling it for what would seem to be the best price I have seen so far. When I'm making a mould for spincasting the 10" plates will need around just over a kilo of RTV. If I use the 7" discs they need around 1/2 kg

[Pugsley]

From my time making whitemetal castings using a Tiranti centrifuge, I seem to remember that it helped to dissolve the Vaseline in white spirit. That way, you avoided clots and, as a liquid, you could brush it freely into the nooks and crannies.

Hope this helps

Eric

I've done the same thing. but using lighter fuel rather than white spirit - it 'dries' quicker.

[c2c]

The silicone spray I bought from Tiranti's was ok, but as they advised it had to dry which took a while! But patience pays off as the RTV  separates ok.

 

I think I will try out vaseline & lighter fuel though. 

[lyneux]

I have no problem with the silicone spray bought from Tiranti's. I'd give it a couple of coats though otherwise the mould halves require a bit of oomph to separate them.

[gr.king]

Use of a highly volatile solvent with the vaseline sounds more attractive than use of white spirit on account of the faster drying time, as by the time I get round to the job I often want to get on with the second pour straight away. You'd have to take more care about possible damage to plastic parts of a master with certain flash-off solvents of course.......

[c2c]

I've done the same thing. but using lighter fuel rather than white spirit - it 'dries' quicker.

 

Lighter fuel is also good for smoothing down chavant too!

[c2c]

Out of interest what choice of glue do people here prefer to use for joining resin parts? 

[Phil Traxson]

 

Out of interest what choice of glue do people here prefer to use for joining resin parts?

 

I use one of the "Evo-Stik" type impact adhesives as you get a second chance if you get it wrong. Some of my display models have been together for 15 years now and despite having a fairly rough life are showing no signs of falling apart.

 

Superglues work well too but you have to be right first time, the resin and superglue are both isocyanates and have a great affinity for one another, once together any attempt to part them usually results in everything except the joint breaking.

 

Two part epoxies are ok but take a while to set.

 

I must admit that on the more recent builds I have tended to tack with Impact adhesive and when I'm sure it's all lined up correctly run Superglue down the join and this has resulted in very solid joins.

 

Some of my kits put together by the pattern maker as a trial were built with UHU, they were fine at first but after 5 or 6 years bits started to come apart.

 

Phil T.

[c2c]

 

 

I use one of the "Evo-Stik" type impact adhesives as you get a second chance if you get it wrong. Some of my display models have been together for 15 years now and despite having a fairly rough life are showing no signs of falling apart.

 

Superglues work well too but you have to be right first time, the resin and superglue are both isocyanates and have a great affinity for one another, once together any attempt to part them usually results in everything except the joint breaking.

 

Two part epoxies are ok but take a while to set.

 

I must admit that on the more recent builds I have tended to tack with Impact adhesive and when I'm sure it's all lined up correctly run Superglue down the join and this has resulted in very solid joins.

 

Some of my kits put together by the pattern maker as a trial were built with UHU, they were fine at first but after 5 or 6 years bits started to come apart.

 

Phil T.

 

Like yourself I am a bit wary of using Superglue and usually always look to using an alternative. I've been told that "Gorilla Glue" is supposed to be good but as yet not tried it.

 

Handy to know what people are using though for assembling resin parts, especially patterns as its essential to keep things as neat as possible.  

[Bruciethefish]

As far as glues are concerned, I've generally used Cyano for small bits, & epoxy for large parts, or those likely to be subject to stresses. For separating 2-part moulds, I've always used soap;- I keep a bar of the stuff handy, with a depression in it which I drop water into, then mix with an old brush until suds appear. This solution is then brushed onto all the exposed rubber surfaces before pouring the second half. I don't worry whether this film has dried or not, as it doesn't seem to affect the outcome at all & I've rarely had trouble getting moulds to separate.

[c2c]

As far as glues are concerned, I've generally used Cyano for small bits, & epoxy for large parts, or those likely to be subject to stresses. For separating 2-part moulds, I've always used soap;- I keep a bar of the stuff handy, with a depression in it which I drop water into, then mix with an old brush until suds appear. This solution is then brushed onto all the exposed rubber surfaces before pouring the second half. I don't worry whether this film has dried or not, as it doesn't seem to affect the outcome at all & I've rarely had trouble getting moulds to separate.

 

Cyano isn't that "Rocket Glue" Chris? I haven't tried that yet.

 

Regarding the soap that sounds like a very good idea, I guess it works a bit like a releasing agent. That idea I will try, especially lately as most of my smallest moulds have been 7" in diameter, it can be a bit tough pulling them apart!

[Bruciethefish]

Any good quality 'superglue' will do the job, & I rarely take much notice of which brand I buy. Many builder's suppliers carry various industrial grades at stupidly cheap prices..

[finelines]

When I was at art school rtv rubber was too expensive to let students loose on so we had to make waste moulds in plaster of Paris and used shellac to seal the plaster followed by soap solution.

 

When I started doing whitemetal castings the technique I was taught was to use to use a slightly diluted detergent on the patterns. Paint on and wipe off as much as you can. Use talc to separate the rubbers. I also have graphite powder. If you are using rtv rubber silicon release agents are a no no because they interfere with the chemical reaction.

 

In my periodic wander round a craft shop I found a bottle of liquid Vaseline.

 

Roger

[gr.king]

Regarding the poisoning of the RTV curing process, it may be helpful to rememeber that some suppliers offer both "addition cure" silicones and "condensation cure" silicones. I can't remember which is which at present, but I think the type that we usually use, which requires an accurate addition of a small percentage of catalyst is more tolerant of pollutants than is the other variety which utilises an ostensibly "easier to measure" 50:50 mix of components.

[c2c]

When I was at art school rtv rubber was too expensive to let students loose on so we had to make waste moulds in plaster of Paris and used shellac to seal the plaster followed by soap solution.

 

When I started doing whitemetal castings the technique I was taught was to use to use a slightly diluted detergent on the patterns. Paint on and wipe off as much as you can. Use talc to separate the rubbers. I also have graphite powder. If you are using rtv rubber silicon release agents are a no no because they interfere with the chemical reaction.

 

In my periodic wander round a craft shop I found a bottle of liquid Vaseline.

 

Roger

 

To be honest I have to say I haven't had any real problems with silicone release agent. The one I bought from Tiranti's has been ok apart from maybe a little bit of elbow to separate the halves, but I never encountered any damage or tears when the halves part.

 

My next project will involve using a fair bit of of RTV to produce aluminium mould blocks and I'm quite happy to carry on using silicone release agent.