Vacuum Casting

With over 15 years experience in polyurethane resin processing, Martello are specialists in Vacuum Casting.

Using primarily their own range of unique “THIN-RIM®” resins Martello can supply vacuum cast polyurethane components up to 500mm x 380mm x 340mm with a component weight of up to 1.2Kg. Typical timescales for vacuum casting are 2 weeks from order to first off parts. You may only need rapid prototyping services for your requirements depending on the volumes requried for your project.

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RIM Machine

Martello also offer polyurethane resin pieceparts produced by Resin Injection Moulding (RIM). Our RIM machines have been modified to work with vacuum chambers to produce detailed mouldings. RIM technology complements the vacuum casting machines in that it enables fast gelling resins to be processed successfully.

SOLVENT RESISTANCE OF POLYURETHANE RESINS

Rigid PUs generally have good resistance to solvents.
Rigid polyurethanes do not dissolve in solvents. The solvent will penetrate the body of the part and the absorbed area will swell and become weak. The longer the contact time the more solvent is allowed to penetrate and a greater volume becomes weaker.

The standard test is to immerse a cured sample of given dimensions in a solvent. This is then sealed and left for a given period, normally weeks. The sample is removed and weighed. This is compared to the sample weight before immersion. In cases of low resistance much solvent is absorbed and the dimensions change. Various test schedules are available for different applications such as fuels, coolants and hydraulic fluids. There are also the added complication of potential temperature variations in use.

Any effect would be influenced by frequency of contact, duration of contact and thickness of the part.

Chemicals in regular contact:
Ethanol and IPA would have no effect on cured rigid PU.
Acetone will affect PU. Repeated cleaning will start removing the surface. Long contact times will mean the acetone will penetrate the PU and soften it.

Chemicals in occasional contact:
Toluene, Heptane and Hexane will not affect cured rigid PU.
Dichloromethane is a particularly aggressive material when used with PUs. The same comments apply as with acetone.

Chemicals with possible but infrequent contact:
As a general rule strong acids and bases do not have much effect on rigid PU. The effects will depend on the chemistry and concentration of the acids or bases. Nitric acid at a high concentration will probably give yellow staining. With these materials you could get colour changes if there are interactions with pigments. We would recommend testing with the types of acid or base likely to be encountered.
Tetrahydrofuran, another very aggresive material in contact with PUs. The comments regarding acetone are still valid, the additional factor here is the very slow evaporation rate. If the PU absorbs this material it will take some time to come out so the PU will be softer for longer.

We would recommend testing to be sure there will be no problems. A quick and easy way would be to take one of your swatches suitably cured and rub part of it with the solvent you want to test on a cloth or rag. Do a known number of rubs (50-60) but make sure there is an untreated area next to where you are testing. Allow the sovent to evaporate and hold the part so the rubbed surface gives a glancing angle with a light source. Look for any differences in surface reflection between the rubbed and untreated surface.
If there are any differences you may need to do some further testing.

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