My experiences with using phenolic urethane resin sand for casting.

Discussion in 'Sand Casting' started by Mark's castings, Mar 18, 2023.

  1. This is just a loose collection of my experiences with using phenolic urethane resin sand binder for mould making in a small non ferrous foundry environment. The guy I'm learning from has used it since the 1980's and at the time it had such clear cut advantages that he stopped using green sand completely. There were a few special conditions at the time that made it practical: there was enough domestic foundry demand from manufacturing for the resin to be imported in decent quantities to be fresh and for the supplier to be willing to sell small quantities. These days there's no real importer and any company importing the stuff wants to sell a minimum of two x 1000 litre IBC containers of a product that degrades within six months on exposure to moisture in air and probably UV light too. So the local demand is not there for an expensive product with a short shelf life. The other local advantage was access to high quality super pure silica sand from a mine that supplied Mitsubishi with it's sand for glass making and foundry purposes. Originally the sand was loaded by barge onto the ships and it was possible to get a cheap barge load when barges came South for maintenance at the local shipyard. A barge load would fill a vacant lot and require a dozen or so 10 tonne tip trucks making multiple trips to unload, taking care not to fill the truck's bin more than a quarter of it's volume as the weight would blow the tyres if completely full due to the 1.5 specific gravity of the dry fine sand (it was often wet).

    The advantages are that it's fast: cycle times can be as low as two minutes from mixing to tipping the cured mould out of the pattern. There's no need for flasks, even those snap flasks when pouring the metal. You can make as many moulds as you have resin and sand for and they will store for quite a long time, years in fact if undisturbed.

    The resin has three components all of which are subject to age, temperature, humidity and in some cases retarded by sunlight, so a small test batch is made and cured every session to get the exact ratios correct. For a given session, two components are mixed into a one reservoir and the third component into a second reservoir. The only special equipment are the two metal can reservoirs that gravity feed two glass bottles with a simple hand made lever valve on each bottle: one lever position taps the reservoir to fill the bottle to a predetermined amount, the other lever position dumps the resin into the sand mixer bowl below. A scoop batches the sand and the patterns have the number of scoops required marked on it in felt pen. There is a simple paper table on the wall showing the amount of resin vs scoops of sand to get the correct mix.

    The resin looks like motor oil in colour and viscosity, one component gets dumped into the sand via the bottle lever valve and is thoroughly mixed in, then the second component is dumped in using it's lever valve and a digital egg timer is triggered. The two components blend with the sand for about two minutes and once the egg timer goes off the batch is dumped into a small sheetmetal box under the mixer bowl via a central hole in the mixer. The sand is dumped into the pattern and a second timer triggered: if you are running a fast resin blend and don't get it into the pattern and tamped down with a brickie's trowel and screeded off in time, the sand grains will no longer stick and the sand is dumped off the table under the floor, this is rare and the excess is used to make pouring cups.

    There is no ramming of the sand whatsoever, just tamp it down lightly and tap the sides of the pattern and wait for it to cure. That's probably the most frustrating part of going back to green sand after using resin sand and easily takes the most time compared to resin sand: no need for vibrators, ramming or jolt and squeeze machines, just tamp it down, screed off and wait a bit for the cure.

    The pattern gets a few light raps on the side before cured to ease the extraction of the partially cured mould. Ideally you want the get the mould out of the pattern while it's slightly flexible so any pattern imperfections don't catch and so the mould can be assembled on a flat table to allow the two mould halves to conform to each other and prevent molten metal leaks.

    So that's the PUNB process in a nutshell, the used sand moulds are not recycled as that would involve cooking in an oven and crushing. It's my understanding after reading some product sheets that the resin is designed to break down over time into CO2 and water vapour and the suggested disposal is to use to cap off land fills with it. It goes into a bin and is sent to a specialized land fill and any metal spills must be removed before going into the skip bin. I'll try and find some relevant photos and add them later.

    Resin sand mixer, originally used to mull green sand, the resin batching system is out of sight:

    Last edited: Mar 19, 2023
    Melterskelter and Tops like this.
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  3. Melterskelter

    Melterskelter Gold Banner Member

    Mark, Too bad that material is not more accessible to us peons. It looks like very very nice binder and the molds produced have so many advantages. It sounds like it may be pretty similar to using AIr-Set and similar Furan binders. It would be so delightful to be able to practically use Air-Set or PUNB. I do appreciate your taking the time to write it up.

  4. Rocketman

    Rocketman Silver

    The sand disposal sounds like a rough thing for a small shop, everything else sounds great about it.

    I have seen PEPset and a few others used. The fumes/smoke from the no-bake binders can be pretty noxious. The capability is unmatched, however.
  5. It does have a few downsides, as Rocketman mentioned there's a lot of nasty burning resin fumes to contend with when poured. I suspect molten iron would be so hot the smoke would be greater and could lead to complaints nearby, we pour on a weekend in an industrial area to minimize the smell effects. As far as I can tell, a quality sodium silicate has all the upsides and few of the downsides, especially if you build a gas manifold into the pattern with small holes everywhere to ensure an even, consistent gas reaction.

    You can see a 20 litre can used as a rubbish bin beside the sand mixer in the photo: it's the original 1980's Pepset from a company called Ashland Croder and it could be tuned to cure speeds faster than you could get the mix into a pattern. I can't find much mention of the company now, it probably got merged or bought out over the years and all you can get are similar products from places like Germany.
  6. Melterskelter

    Melterskelter Gold Banner Member

    I only use gas when I am in a big hurry for a core these days. I use NaSilicate catalyzed with propylene carbonate 95% of the time and wait three hours for it to set up. It probably would be ok to strip in less time, but there is enough detail in my cores that require pretty solid binder to draw perfectly. I do reuse the core sand by mulling it in my general casting sand and adding proportional clay and coal. I’ve not tried casting silicate molds without flasks. I suspect it would work ok but might require increasing silicate to 7.5% rather than my standard 5%.

    It is interesting to hear about the practical aspects of PUNB.


    Clay Planet sells (well, maybe used to sell as I don't see it listed at their store now!) Chem Bond 210 (propylene carbonate)
    Last edited: Mar 19, 2023
  7. I took a few more photos today: here's a punb mould for 4" tabletop gemstone diamond saw housing: the casting will get the runner cut off, a hit with the 2" belt linisher and then sand blasted. There are pre-cast dimples where holes need to be drilled and tapped and after a coat of paint it's ready to use. These are going back into production after a long hiatus as secondhand samples are selling for $800 or so.

    diamond saw.jpg
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  8. Rocketman

    Rocketman Silver

    With iron, at least if the volume of metal in it is chunky enough, the gasses escaping from the vents can be lit to burn off, which is much cleaner. Aluminum doesn't have the same temps/btu's in it.
    At the now-defunct iron foundry I worked at, when I made my way out onto the floor on pouring days my first job was a skimmer. Use a steel bar with a crook at the end to make a dam in the ladle spout until the pouring cup was full.
    The gas would erupt out of the core vents on certain molds, it was my job then to wave the hot end of the steel through the gas to touch it off. Wild stuff.

    I had posted a thread on the old BYMC forums with pictures of that foundry, I have them buried somewhere on an old drive, if I run across them I'll toss them up here
    Mark's castings likes this.
  9. That would be good to see.

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