INTRODUCTION; Moulding is the system of reproducing articles in quantities of identical copies. The original sample is called the “model” or “master”. The die in which it is reproduced is called the “mould” and the reproduction is called the “casting”.
Models are sometimes pre-existing shapes which have been found, or they are made from plastic materials such as clay, “Plasticine” etc. or they are carved from soft materials. These original shapes are the same shape as the castings and are referred to as “positive” shapes. Carvable and machinable materials are Insulag, Mastercarve, Plasticast, and Synwood
Moulds are made by pouring a mould material over the model. Marmould and Multimould can be used for this, they are melted by heating in a microwave oven and turn back to rubber when they are cool. Marmould and Multimould are very elastic and can be used with extensive undercuts. They are generally used for block moulds. You place the model on a hard surface, place a pie, tin, box or container around it and then pour the molten rubber over the model. For large items this can be expensive, so skin moulds are used. Wrap the model with clay, blanket, or some type of textile, then cover with stretch wrap, then cover this enlarged model shape with Keraforce, Plaster of Paris, fiberglass, Insulag or anything that sets hard. Remove the hard shell, remove the wrapping and place the model back inside the shell. Now there is a cavity surrounding the model, which can be filled with Marmould, Multimould or silicone. You may need to split the mould. Use “fences” to create flanges to join the two halves. Models for Multimould need to be impervious, although Keraforce makes a wonderful model.
Simple shapes can be moulded in rigid moulds. See “making a Keraforce mould”. Sometimes you may need to adjust the model a bit to make it mouldable. Plasticast does this well. Sandable wall filler is also useful. If you need to smooth the texture of the model, paint it with Alusmear, let it dry, then sand it.
Castings are made from a host of different materials with a range of properties, for example; Electricast which is very heavy and used in electrical ceramics and glass slumping moulds, Kerapump 10 which is light and easily machined, Keraset which is exceptionally hard, Plasticast which is hard but not brittle, Ettringite cement which is fine, strong and cheap, Synwood which is light and cheap, Trophy mix which resembles stone, Biomould which is like paper mache but sets chemically, light and resilient, Bio White which is like Plaster of Paris on steroids.
Sometimes a parting agent is needed to prevent the casting from sticking to the mould. See “mould releases”.
When the casting is removed from the mould, it usually has lines visible where the mould parts joined. These marks must be removed, the process is called “fettling” and we make ceramic fettling files for this purpose.
Metal castings are also made in moulds, usually consumable, such as Harmonite for gold, Keralite Alcast, Herculite or shell moulding sand for aluminium, Greensand for brass, CO2 sand for iron and steel. (We sell the CO2 binder as "Keragas").
Thermould is an oil bonded sand also known as Petrobond sand. It is a cohesive plastic fine sand giving great detail and a shiny finish to the castings. Used for all non-ferrous metals. All these metal casting materials are soft enough to be crushed by the shrinkage of the metal. Where shirnkage of the metal can contract with crushing anything, re-usable Kerasic dies can be used.
Investment casting is where a wax model is made, coated with ceramic, melted out and metal poured in its place. See “Investment materials”.
The data sheets are difficult to compare, so we have a “Moulding table” for comparison of properties. Last but not least is the pricelist.
A moulding material for casting molten metal. It requires no baking or pre-treatment of any kind. It is a very fine, plasticised, oil bonded sand. The oil prevents oxidation and gives the casting a shiny finish. It takes up very fine detail and the casting requires no surface finishing.
Application; Get two steel boxes, open both ends, accurately located one above the other. Fill one with Thermould. Press the model into the joint face. Powder the surface with talc. Place the other box over it, fill it with Thermould and press it tight. Make a runner and filling funnel. Remove the model, replace the box and cast the metal. When it has frozen, open the box and remove the casting. Discard the burnt Thermould adhering to it and cut off the runner. The whole job can be done in about 10 minutes.
The unburned Thermould can be reused. Ideally it should be remixed in a muller mixer, which has a heavy wheel pressing on the material. Long mixing in a planetary (bakery type) mixer also works. Thermould belongs to a generic group of oil bonded sands called “Petrobond” sand. If the Thermould starts to loose its cohesion, add a bit of Enerflex oil or smokeless two stroke oil. Apart from plasticity, Thermould also exhibits some compressibility. This property makes it quite forgiving towards imperfect compaction.
Use it to cast aluminium, tin, brass, bronze, copper, zinc, magnesium, silver and gold.
Synwood is a new material with properties somewhere between ceramic and resin. It has a silicate bonding system. Its mixing and setting characteristics are more like resins than cementitious materials, though easier and cleaner to work with. It is difficult to characterise the physical properties of the material, because it tends to take on the properties of the filler.
The most important property is cost, which is way below resin costs, and thereby opens a vast field from which composites have previously been excluded because of costs.
The material is supplied as powder and resin, to which you add filler. Typically you use 60 weight parts resin to 40 weight parts powder and add an equal volume of filler to volume of resin-powder mix.
Lightweight fillers are favoured because you can get excellent strength to density ratios. Synwood is normally sold with a perlite filler. You can order Synwood base and add your own filler. Wood chips and sawdust are ideal because they are almost zero cost, and the resultant product is similar to wood, which is becoming unaffordably expensive for many traditional applications. Wood expands powerfully when it absorbs water, and shriks as it dries. Your sawdust should therefore not be added completely wet or dry. What you get is a product that resembles wood, at low cost, cast directly into its final shape with no wastage and no machining and no joining. There are few limitations on design. Because it is moulded, ornate designs are no extra cost. examples of applications are; Binder for chipboard which has good water resistance, better fire resistance, lower cost.
Kitchen cupboard doors and drawers
Perlite is a good lightweight filler. Materials made from it are totally inorganic, fireproof, can float on water for 3 months.
Silica or ceramic grog as filler gives properties similar to fired ceramic. Clay may be added as a filler, but will not make it plastic.
Polystyrene regrinds are a cheap ultralight bulking filler.
Surface treated polypropylene fibres can be added,0,2% to lightweight formulations to reinforce them. They can be cracked, but are difficult to break. Open weave fibreglass "scrim" can be added as reinforcement.
Pigments work well since the opacity is low.
Surface texture is easily produced. Silicone or Multimould makes ideal moulds.
The resin is strongly alkaline and will make your hands rough, the same as working with portland cement. Use hand cream after working it by hand. The material is not toxic or hazardous. Shelf life is unlimited.
Water may be added to all mixes, but the resulting strength and hardness will decrease.
The surface of castings develops higher strength and hardness than the centre.
All consistencies can be made, from pourable to stiff pressing materials. A pourable variant is called "Kerafire" and a sculpting variant is called "Mastercarve". A low strength, low cost variant is caller "Rapolite".
All variants are very easily cut, carved, machined or sanded. The finished surface can be hardened with "Fireproof Paint."
Sorel cement is a very hard cement composed of magnesium oxychloride. There are thousands of variations on the formulation.
Our sorel cement development no. 127076 is a plain sorel cement with no fillers added. Abrasive
grits are commonly added to sorel cements to make polishing wheels or polishing ‘blocks’ for
polishing of granite. Sawdust or cork grindings are added to make high quality flooring,
eg. Corkalium. Vermiculite can be added to make high strength thermal insulation materials.
Sorel may be impregnated into textiles to make them totally rigid. All reinforcing materials are
suitable for sorel cements.
Mixing ratios may be varied through a wide range. It is supplied in 20kg bags of powder and 5,8kg plastic bottles of liquid binder. 53 weight parts powder to 47 weight parts ‘resin’ gives a pourable material with a 1 hour ‘pot life’. Putty consistency sets faster and harder. In watery mixes with no
filler, the powder settles and the bottom of the casting may expand appreciably. The setting
reaction is highly exothermic and large castings get very hot. Setting time ranges from 3 hours to
12 hours, depending a lot on sample size, (larger is faster) ambient temperature and the thermal conductivity of the mould material.
The cement is easy to work with and clean. Wash with water. Castings can be fettled or trimmed
easily up to 12 hours after demoulding. Between 1 and 2 days old they are good for sanding. After 2 weeks full strength is reached and no machining is practical.
Sorel cements have good adhesion to most surfaces and can be used to give a hard finish to plaster, cement, concrete, particle board, polystyrene, polyurethane foam, particle board, even cardboard.
It can be painted on easily.
Filler ratios are impossible to specify, but any mix with roughly equal bulk VOLUME parts of powder, resin and filler will work. The water content of fillers should be watched, the results can disastrous
if bone dry sawdust is used, since it swells with enormous force. Wet sawdust will shrink as it dries
and contribute nothing to the structure.
Sorel cement is an excellent substitute for polyester resin in fiberglass. Sorel is more rigid, fireproof,
UV immune, more forgiving in gel time, and an absolute pleasure to work with compared to
Plasticast is a moulding compound with very useful properties. It has properties somewhere between ceramic and plastic, but its strength development is gradual, allowing easy alterations while working.
Plasticast is made from a resin and a ceramic powder, which can be mixed in different proportions to give putty, paste or pourable consistency.
Typically it is mixed in the ratio 2 parts powder to 1 part resin, poured into a rubber mould and stripped after half an hour. (As soon as it gets warm)
Around 5 minutes after mixing it can be smeared, after 10 minutes it can be cut with even a credit card, after 15 to 20 minutes it can be cut with a knife, after an hour it gets warm from setting, and can be stripped after 35 minutes. It can be sanded easily after 45 minutes, but after 24 hours you need power tools to machine it. It is homogeneous and smooth and very amenable to all kinds of mechanical working.
Times mentioned are influenced by temperature and mixing ratio:
The density is low; 1,3 grams per millilitre at 2 parts powder to 1 part resin.
The colour is a pale beige, with low opacity, so it responds well to pigments. It is compatible with all mineral fillers in our experience. Hollofill (cenospheres) or coarser Pratliperl perlite can be added to make it lighter, or zircon flour or barium sulphate may be added to make it heavier. Other mineral fillers may restrict the machinability. Water dispersible fibres may be added for reinforcing.
Plasticast will adhere well to most surfaces, and it bonds particularly well to previously cast Plasticast. (Sanding it wet may cause the additions to come unstuck). Thus additions may be made to your workpiece as easily as subtractions. Waxes make good release agents. Plasticast is good at cleaning moulds.
Plasticast may be laminated like fibreglass, using open-weave fibreglass matting.
Plasticast expands slightly, around 0,3 % on setting, which can make it unsuitable for some rigid moulds, and extremely useful in other cases.
Plasticast is not flammable, and stable up to 200°C.
Packed in 3kg kits of 2kg powder and 1kg resin, or larger quantities.
Description; A high quality Plaster of Paris made from pure natural gypsum, for use in medical, ceramic and moulding applications.
Chemical composition; 95% minimum CaSO4·H?O
Mineral composition; Approximately 35% Alpha Hemihydrate and 65% Beta Hemihydrate.
Particle size distribution; Typically 100% passing 200 micron
98% passing 86 micron
92% passing 63 micron
Water addition; 1,4 to 1,7 parts powder to 100 parts water.
Ideal water factor 0,64 parts water to 100 parts powder.
Test results below are at 1,57 parts powder to 100 parts water.
Start of setting; 9-12 minutes.
Final set; 29-33 minutes
Linear expansion; 0,20% (2mm / metre.)
Brinell hardness; 360kg/cm²
Claimer; The above data had better be correct, as Dave Onderstall stakes his reputation on it.
Multimould is a soft, highly elastic moulding compound. It has similar properties to silicone moulding compounds except that it is RE-USEABLE, hence the name "Multimould".
Multimould is a copolymer which melts at 160°C. It is non-toxic, but gives off fumes while molten which have a strong odour. It has excellent release properties and takes up very fine detail. No release agents are needed with Multimould. It has a high density (2,75) which helps penetration and levelling.
Multimould is ideal for making direct copies off metal, mineral or resin products. Its high elasticity allows moulding of large undercuts.
Castings may be made in Multimould with cement, plaster of paris, resins, ceramic, refractories, Hardcast, Versimould and polyurethane foam.
Preparation: Make a box to contain the model and the molten Multimould. Use solid materials as far as possible. Thermoplastics will fuse to molten Multimould. If wood is used dry it thoroughly. (Microwave drying is convenient) Melt the Multimould in a microwave oven until pourable. If bubbling and odour are noticeable, reduce heating rate. Multimould has a very low thermal conductivity and melting by any means other than microwave is extremely difficult. Pour the molten Multimould over the model in the box, covering the model but not filling the box. After cooling, fill the top of the box with plaster of paris. This prevents deformation in subsequent mouldings. Strip the mould and cast your product. When you have made all the pieces you require, the Multimould may be re-melted and used for the next mould.
Multimould is sold in slabs of about 850 grams at R216/Kg. This is about half the price of castable silicone compounds, which are not re-usable.
The standard colour is blue.
HINTS FOR WORKING MULTIMOULD
All materials in contact with Multimould must have a melting point higher than 140°C. Materials should preferably be solid, with no porosity. The problem with porous materials like wood, is that the air inside heats up when you pour Multimould over it, the air expands and comes out as bubbles. This can often be overcome by wrapping aluminium foil over the wood. Plaster of Paris dehydrates at high temperatures, and continues to give off water until the Multimould has set. It is best to preheat the Plaster of Paris for 24 hours before using it, to a temperature of 70°C. Low quality Plaster of Paris may crack when heated. Preheating the mould may be desirable if there are narrow cavities.
If your model is porous, preheat it to around 140°C before pouring. Thermoplastics like PVC and Polyethylene will fuse to molten Multimould. Good materials for moulding are metals, glass, and a polished granite slab or smooth glazed floor tile for the base. Remember that highly conductive materials like metal will chill and set the Multimould much faster than insulating materials.
Multimould has very low thermal conductivity, and is therefore difficult to heat up evenly.The answer is a microwave oven. Use a glass bowl and heat it for about 20 minutes. You will probably find that there is a solid skin against the glass and some bubbles in the centre. Stir it with a stick to get the temperature distribution even. Keep re-heating and stirring until it is a thick homogeneous fluid with no bubbles. Lift the bowl out with oven gloves and pour it, being careful not to get any on your fingers! If you overheat it, it will start decomposing and continue to react by itself. This is a disaster! Get it outside as fast as possible. It stinks and needle-like crystals will grow on anything in contact with the fumes. After you have finished with Multimould, heat the oven at maximum temperature on convection, to get rid of any residual smell.
If your mould is too large to heat a single batch in the microwave, you must either store some in a conventional oven while you melt the next batch, or you must cast in layers. If you cast in layers, you must re-melt the surface of the first layer before pouring the second layer. This is best done with a small blowlamp working off disposable camping gas bottles.
PREPARING THE MOULD:
Can you make it in one piece, or must you split it? Multimould will handle large under-cuts. To make the decision, feel the elasticity of the Multimould slab and use your own judgement. You can pour Mutimould onto set Multimould without fusing the two parts. To do so, make sure the set Multimould is cold. Sprinkle some talc onto the surface. A pouch made of a mealie meel bag distributes it well. If you have no talc, flour or other powder will usually do. When pouring, don't let all the Multimould impact on the same area of the set material. Make a box around your model. Usually the model is placed on the floor of the box, with the contact area forming the filling hole. Note that Multimould is very dense, and if your model is less dense, it will float in the molten Multimould. Multimould is very flexible, and normally the mould box is kept in place when using it as a mould.
To prevent distortion, make the mould box a little taller than required, and pour some Plaster of Paris over the set Multimould. The upper surface of the set Multimould is always slightly dished due to shrinkage, so if you place it on a flat surface it will distort.
Multimould gives perfect release from smooth solid surfaces. NO RELEASE AGENT should be used. Stripping can be improved from porous surfaces by application of a bit of soap. When casting into your mould, again, use no release agent, unless you are casting with epoxy or polyester (fibreglass). In some cases a release agent may be required. Use D.O.P., D.I.D.P. (Di-iso-decyl Pthalate) D.I.O.P.etc.
All casting materials are suitable. For good precision and finish at a fraction of the price of epoxy, Keramicalia can supply a dense white marble-like material called Keratab, high strength Sorel cements, called Keraset, quick-setting Versimould, low density Kerapump 3 and a variety of technical materials.
If at first you don't succeed, melt it down and cast again. That is the beauty of Multimould; your mistakes cost you only time.
|Electricast||Heavy ceramic||Powder +10% water||1 hr||3,3||R106/kg|
|Fibre Plaster||Glass slumping||Readymix||air dry||0,6||R161/kg|
|Green sand||Metal casting||Readymix||air dry||1,8||R18kg|
|Harmonite||Gold casting||Powder +60% water||5 mins||1,4||R82/kg|
|Hotmaster||Mastermoulds||Powder + 30% liquid||2 hours||2,6||R109/kg|
|Innerforce||Fibreglass substitute||Powder, resin and textile||½ hour||2,5||R32/kg|
|Insulag||Carving||Powder +60% water||1 hr||0,6||R45/kg|
|Keraforce||Fibreglass substitute||Powder, resin and textile||4 hours||1,7||R38/kg|
|Keralite Alcast||Casting aluminium||Powder +60% water||4 hr||0,8||R26/kg|
|Kerapump 10||Moulding||Powder +30% water||1 hr||1,1||R52/kg|
|Keraset||Hard mouldings||1p powder 1p liquid 1p filler||3 hr*||1-2,5||R30/kg|
|Kerasic||Die casting||powder + 14 % water||1 hr||2,6||R122/kg|
|Keratuff 1||Thin structures||Powder +40% water||1hr||1,1||R53/kg|
|Marmould||Organic moulds||Microwave melting||Temp.||1,0||R189/kg|
|Mastercarve||Sculpting||Powder and liquid||20 mins||0,8||R26/kg|
|Mould plug||Mould plugging||Readymix||no set||0,8||R189/kg|
|Multimould||Re-meltable moulds||Microwave melting||Temp.||1,4||R285/kg|
|Plaster of Paris||White castings||Powder +64% water||10 mins||R43/kg|
|Plasticast||Ornaments||Powder + resin||1 hr||1,3||R67/kg|
|Plastisand||Fake sandstone||Powder + resin||1 hr||1,9||R44/kg|
|Reforce||Multimould masters||Powder + resin||4 hours||R36/kg|
|Safex||Tiles||Intense mixing, water||R10/kg|
|Sandable wall filler||Repair of castings||Readymix, mastic tubes||air dry||0,8||R33/tube|
|Synwood||Casting||Powder and liquid||2hr||0,8||R23/kg|
|Trophy Mix||Fake stone||Vibration cast with water||2 hr||2,7||R18/kg|
|NOTE Powder +60% water means 100 weight parts powder to 60 weight parts water.|
|* Depends on size of casting.|
|NOTE PRICES EXCL VAT|
We stock many fillers useful in moulding. Some common ones are listed below.
|High density||Zircon Flour|
|Fused chrome alumina|
|cheap||Fine, round grain sand|
|Metallic Gold, copper, aluminium|
|Water dispersible fibres|
|Granulated ceramic fibres|
|Rheology modifiers||Silica fume, black and white|
||Synthetic silica fume|
There are many mould releases on the market for different purposes. Here are our recommendations;
Multimould; Needs no release agent.
Silicone; Needs no release agent.
Die casting; Use Aluminium non-wetting Paint for most applications.
Sand casting; Use Zircon coating, sprayed on.
Brass and copper; Use a graphite based coating.
Fibreglass; Use poly vinyl alcohol.
Ceramic into wood; Use oil.
Refractory into steel; Use grease.
Ceramic into plastic; Use Cobra wax floor polish.
Firing ceramic on ceramic; Use high temperature batt wash.
Thermould; Use talc.
A liquid solution of binders. The solution is designed for very rapid drying and is flammable.
Hardening of moulds, especially foundry sand moulds in areas where there is high turbulence. It also allows sodium silicate bonded moulds to be stored for up to a year before use.
Mould hardener can be brushed on or sprayed on. Use between half a litre and two litres per square metre. This will give a penetration of between 1mm and 4mm.
Hardening will occur as soon as the solvents have evaporated. To speed up the drying, ignite the surface with a match.
Clean the spraying equipment or paint brushes thoroughly with solvent after use. Application by a "swab" or rag is convenient, if the equipment can be burned after use. This stuff is seriously sticky, and it usually pays to wear gloves when working with it. If you struggle to get it all off your hands, just dry your hands well ,as with a hot air blower, and once dry the stickyness almost disappears.
Read the safety data sheet.
Example 1; Ceramic strip element hangers.
These are normally pressed in very expensive and complex steel dies from a refractory clay based ceramic. The die costs about R25 000. This method necessitates sharp corners and edges, which are undesirable from an engineering design point of view. Two alternative routes were tried, and both worked well.
The first route was slip casting. In this process, a "slip" of aluminium oxide in water suspension was poured into Plaster of Paris moulds. The moulds suck the water out of the slip, and the casting is removed, dried and fired. The slip must have an extremely low shrinkage for this particular complex shape. Here the Multimould was used to make the master or "case" moulds, from which the plaster production moulds were cast.
The second route was to produce casting moulds from Multimould and the hangers were made directly in these with Keratab.
PREPARATION OF MODEL for both routes.
The sample of a pressed ceramic hanger was first covered in parts with automotive body putty to eliminate certain sharp corners. (This step is usually performed to eliminate chips and scratches on the sample.) The outer corners and sharp edges were then removed with a ceramic nail file. (manufactured by Keramicalia) It was then sanded smooth. A pencil line was drawn around the exact middle of the model, and the model was buried in Plasticine up to the centre line. Clay can be used instead of Plasticine. Natches were then cut into the plasticine, using a teaspoon for one and a knife for the other. These serve to locate the two halves of the mould in the correct position. Sides or "cottles" were added. A filling funnel was built up in Plasticine.
SLIP CASTING: The surface was painted with dissolved bath soap. The first coat was absorbed by the ceramic, but after a few coats the pores were blocked with soap. Plaster of Paris was mixed in the ratio 1,6 weight parts to 1 weight part water and "Blended" for 5 minutes. It was then poured over the model, covering the highest by 10mm. After half an hour it was tripped and turned over. The cottles were placed back and 3 coats of dissolved soap painted onto the surface. Plaster of Paris was poured onto the first side. Stripped, dried and the 2 sides assembled with an elastic band and slip poured in, dried, stripped.
A sculpture Medium.
Mix powder and resin to clay consistency and model to desired shape. Push wires into the wet clay for adding appendages like ears etc. Leave for about half an hour to set before adding appendages. Carve the details. Fresh material can be added to build up detail. Surface may be smoothed with Alusmear or Sandable wall filler. Sand it smooth and paint it, or add texture as desired.
Make a rough frame for the hollow interior out of wood, re-bar, wire or polystyrene. Cover it with birdmesh, chicken mesh, expanded metal or whatever appropriate for the size. Cover the surface with geotextile and tie it to the mesh frame with wire. Paint it with Mastercarve Resin and allow to harden.
Cover with Mastercarve and resin in a smearable consistency (about 60 parts resin to 40 parts powder). Leave for half an hour to set and then add detail in clay consistency, or add another stiffer layer if sculpture is large. Carve it roughly and see if you need to add more material any where. Add and remove material until perfect. Leave the natural texture or sand it smooth once dry. Decorate further.
Artists who wish to use renaissance type skills to chisel from a block, can take a mix of 55 parts resin to 45 parts powder and pour it into a box. It sets in 20 minutes. You cannot “cheat” by pushing wires in.
A moulding compound for reproduction of perfect detail. It is gelatin based and melts at low temperature in a microwave oven. On melting it will be full of very fine bubbles. You may want to give them time to rise to form a foam on the surface which you can skim off. Block mould it over an intricate model and reproduce the item. The model must be dry. Silicone makes an impeccable positive in Marmould. Production moulds can be taken off the silicone with Multimould. Water based casting materials damage Marmould, and after three castings the moulds are no longer perfect. After the first melting, Marmould has a limited lifespan. Use it within three months.
See photos of a puff adder mould. The fifth generation ceramic snakes are still extremely detailed.Marmould is edible. You can add flavours and colouring to make treats, much like wine gums, but softer.
Example; concrete hand.
1. Find the join line from which two halves can be separated with no undercuts. Keraforce is rigid, and no undercuts are possible.
2. Fill in any undercuts with Plasticast.
3. Stretchwrap the model.
4. Mix some Insulag, quite soft and place it on a sheet of plastic.
5. Push the model firmly into the Insulag and bring the Insulag up to just below the join line.
6. Take out the model, unwrap it and place it back in the Insulag cradle.
7. Trim any Insulag which is above the join line.
8. Smear Plasticine, modelling clay, sculptors wax, clay or similar material over the Insulag to bring the surface exactly up to the join line.
9. Use a credit card cut square to check that there are no undercuts.
10. Extend the plasticine about 40mm around the model.
11. Make it smooth and flat.
12. Make locating mounds on the flange.
13. Lubricate all the surface of the plasticine.
14. Push drinking straws into the plasticine to make bolt holes.
15. Fit a base plate parallel to the casting open surface. Use plastic or something slightly flexible.
16. Fit another plank on the open cast surface, also parallel. The plates will form flanges to support the mould level while the second half of the mould is made. They must therefore extend
beyond the highest point of the mould, to equal heights.
17. Make wedges of plasticine at intervals on the outside of the flange, for levering later with a screwdriver.
18. Build up shallow walls on the perimeter of the flange, also using plasticine.
19. Cut strips of Biotextile, SBP membrane or cloth to laminate with. Make narrow ones for around the bolt holes, and some broad ones for the base plank.
20. Make two bowls of slurry; For gel coat; 680g Reforce powder and 420g Reinite binder.
21. For laminating; 550g Reforce powder and 450g Reinite binder.
22. Smear the whole surface with gelcoat, being careful not to trap any bubbles.
23. Pull strips of textile through the laminating slurry, wipe the excess off, and place onto the surface.
24. Two strips thick is enough over the model, one in each direction.
25. Make the flanges about 4 strips thick.
26. Add the final 2 layers using stitch bonded fibreglass mat dipped in the laminating solution. Air bubbles at this point are not a problem. The fibreglass is less flexible than the geotextile,but stiffer.
27. Make struts of folded double textile to support the end plates. The end plates must protrude enough for the half mould to stand on them while doing the next half.
28. Leave for 4 hours to set. It should be hard but still trimable with a sharp knife.
29. Separate from the Insulag support, which can be discarded.
30. Remove the model.
31. Clean the plasticine from the Keraforce.
32. Replace the model.
33. Repeat steps 13 to 29 for the other half.
34. Grind the bolt hole ends flat if necessary.
35. Lubricate the mould.
36. Fit bolts and nuts.
37. Stand the mould upright.
38. Mix the casting compound and pour it into the mould.
39. After it has set, strip the casting, clean the mould, making sure the flanges are also clean.
40. Lubricate, assemble and cast again. Castings should be removed when set, and it is preferable to leave the moulds empty overnight.
MAKING A COPY OF A REAL HAND
- Dip hand in molten investment casting wax.
- Dip hand in ice water bucket.
- Dry hand.
- Repeat dip, dip, dry until a decent layer is built up.
- Wriggle your hand free. The fingernails are difficult to free.
- Place the wax shell in a bucket of sand.
- Mix equal weight parts of Reforce 90 and Reinite binder.
- Pour this into the wax shell*
- Leave overnight to set.
- Remove wax shell, either by chipping it, cold, or by melting the wax. Use a blowtorch or hair dryer to get the last skin of wax off.
- Cool and dry the model hand.
- Melt some Multimould Green in a microwave oven in a Pyrex or ceramic bowl.
- Pour it into a deeper container.
- Dip the model hand into it, then into ice water, dry it, dip it etc until a skin of 4mm is obtained.
- Allow the Multimould to cool to ambient temperature.
- Paint a thin coat of Multimould oil onto the skin.
- Strip it by turning it inside out.
- Turn it the right way round.
- Place the Multimould skin in a bucket of Hollofill. *It helps to suspend a stick in it for later handling
- Mix Reforce 90 and Reinite Binder in 60:40 or 50:50 weight parts. Add pigment?
- Pour into the Multimould skin.
- Stand overnight, paint with Multimould oil and invert it.
Several other materials can be substituted for step 20. Some of these are:
Keratab Ultrafine: Brilliant white.
Kerapump 10: Brown with black streaks.
Zambezi Black: Pitch Black.
Plasticast: Easily colored, less brittle than above.
Marmould: Soft elastic fleshy feel, translucent.
Elasticast: Heavy and grey.
Keraset: Very hard, grey.
Keraset is a range of very hard castable materials based on magnesium oxychloride cements.
They come in two components; powder and liquid. They mix easily and pour freely. After an hour or two they set, generating intense heat. This exothermic reaction is volume sensitive. The larger the casting, the more the heat builds up. For very large castings, special grades are required to prevent the temperature exceeding boiling point, which can cause either foaming or steam explosion.
Keraset is easily coloured. Normally the colours range from pink through red to grey. Black is very attractive. The surface is very opaque, and takes up the exact texture of the mould. A glossy mould gives a glossy casting. Buffing will enhance the gloss.
Keraset 22727 is used for abrasive wheels such as glass bevelling wheels, steel polishing wheels and polishing blocks used by stonemasons. It contains 80 grit fused alumina.
Keraset 22728 is similar but finer, containing 180 grit silicon carbide.
Multimould is a useful moulding material for Keraset, especially for cloning.
Keraset is very hard and abrasion resistant.It will decompose if left standing in water for long periods.
Cold crushing strength after 3 days is 30 MPa, after 6 months 45 MPa.
Mix 68% powder with 32% liquid Keraset Binder.
DESCRIPTION: A pourable or pumpable insulation refractory. It is extremely fine and can be used for precision cast and detailed components. It can also be machined.
MAXIMUM SERVICES TEMPERATURE: 1150°C
CCS: 110°C: 7-12Mpa
THERMAL CONDUCTIVITY: About 0,4W/mK at 600°C
Chemistry: Aluminosilicate cellular insulation.
WATER ADDITION: + 40% by weight.
Coke ovens pumping behind flashplates.
Blocking gas tracking.
Synthetic coals for gas fireplaces.
PACKAGING: 10kg plastic bags
Description; A fine lightweight filler for plastics, resins, silicones, polyurethanes etc.
The particles are hollow bubbles.
Density; O,025 - O,029g/cm3 (25 to 29kg/m3)
Composition; Copolymer plastic.
Particle size; 5 to 100 micron, mostly around 60 micron.
Particle shape; Spherical.
pH: 3 to 4 in water.
Solubility; Can be dissolved in dimethylacetamide or dimethylformamide.
Hazards; The extreme low density and fine particle size allow it to float readily in air, causing irritation when inhaled and an explosion hazard.
Mixing; Use a covered mixer with a horizontal blade, e.g. a ribbon blender or Z-blade mixer, or pre-wet the Kerafluff in the bag. Kerafluff is most unpleasant to work with dry.
Claimer: This information had better be right, because Dave Onderstall stakes his reputation on it.
Investment casting is a tricky business with many variables. No two manufacturers use the same set of materials. If you change any variable, it is likely to cause a problem somewhere down the line.
Start with your mould. It can be metal, silicone or Multimould. How accurate do you need to be? How many wax patterns do you intend to make? For prototyping use Multimould wherever possible, because it is re-usable. (R273/kg + VAT) If you get into massive production, use metal for its chill ability and accuracy.
Next select your wax. Excellent hard waxes are available but expensive. Cheap waxes tend to expand and break the ceramic before melting. For artworks, particularly for origination, plastic waxes are used, and each artist has his own formulation to suit his style and methods.
Now for the casting materials: Large statues mostly use a Plaster of Paris stucco mixed with ash , grass or sand. Medium sized technical castings use a dipping technique. Small jewellery castings are attached to a runner called a “tree” and placed in a “flask” and a plaster/cristobalite slurry is poured over them. For medium sized castings, the wax model is first dipped in a fine slurry of mineral powder bonded with colloidal silica or ethyl silicate. Ethyl silicate can be rapidly hardened by exposing to an amine gas or ammonia. All the smaller, less automated processes use colloidal silica. Keramicalia’s trade name is “Super Binder L”, packed 6kg in 5 litre bottles @ R58/kg. Adhesion to the wax pattern is sometimes a problem, an addition of Plasticast acrylic resin solves it.
The minerals used in dip casting vary. Generally the best is considered to be zircon flour, but chamotte or “Molochite” is also common, and some manufacturers use fused silica for its low thermal expansion. Keramicalia makes a “Zircon coating” which contains some chamotte and suspension agents. After dipping, the first coat is dried. It is then dipped again and then immediately dipped into a fluidized bed with a suspension of grit. We sell chamotte 0-1mm for this, @ R18/kg + VAT. The dipping into slurry and grit is repeated between drying until a 5mm coat is built up.
The wax is then melted out and collected for re-use. The moulds are heated to about 700 ̊C and the molten metal poured into them.
Insulag is a range of very light insulation materials. They are all asbestos free.
Insulag 2 is a white powder, which is mixed with water and trowelled or plastered.
It can be used up to 600°C continuous temperature, or as fire protection. Its thermal decomposition is highly endothermic, giving it very superior fire resistance.
Density is around 0.6g/cm³, depending on water addition.
Thermal conductivity is very low, about 0.2W/mK.
Setting time is around 20 minutes.
Insulag 2 has no shrinkage below 600°C
After setting the material is easily cut, machined or sanded.
It will deteriorate if exposed to rain for long periods.
When used as pipe lagging or boiler plaster, no cladding is required.
Mix by hand in small quantities to desired consistency. It will stiffen as the plasticizer dissolves. Add water as you work, but finish working it within 10 minutes of mixing.
Insulag 1 is the pourable version, for precasting.
Insulag 3 is an ultralight material used in composites.
Insulag 4 is a hard wearing insulation for flooring.
Insulag 5 is very easily removed can be re-mixed with water and re-used. Used where insulation has to be regularly removed for inspection.
Insulag 6 is for cold/ cryogenic insulation. It contains expanded polystyrene in a non-flammable composition.
Insulag 7 is rapid setting insulation.
Insualag 8 is injectable insulation.
Insulag 9 is weather resistant insulation.
Insulag 10 is acid resistant insulation.
Alumina: (alumina oxide) aggregates, bubble, sintered, reactive, calcined splinter chrome alumina, white fused, brown fused, tabular, catalyst, Polishing. Aluminium Hydroxide
Aluminium Hydroxide Gel
Aluminum: powder and granular
Barites (Barium sulphate)
Cab o sil
Clays, Ball clay, Kaolinite, Fireclay, bentonite, pyrophyllite
Fused chrome alumina
Plaster of Paris
A permeable gold casting material with extremely fine detail. It is pourable and sets in 5 minutes.
Use wax based release agents as these tend to push all bubbles off the surface.
Mix with plus 60%water, adding the powder into the water, i.e. 100 weight parts powder to 60 weight parts water. By volumes this is 100cc powder to 88cc water.
Mix by hand until all lumps are dispersed. (About 2 minutes) Pour from a height to form a thin stream into the mould. This stretches and destroys the larger bubbles.
Harmonite sets in 5 minutes and expands slightly. The expansion results in it releasing easily from the model but sticking tightly in the box.
Dry the Harmonite at 170C for 2 hours before pouring metal into it.
Density; Powder, loose fill; 0,68g/cc.
Wet mix; 1,68g/cc
Air dry mould;
170C dried mould;
Grams of powder required per cc of mould;
Development no. 17854
A simple furnace can be made cheaply with parts from Keramicalia for slumping glass;
Element panel; R1732 + VAT
6 x insulating firebricks @ R140 ea R840.00 + VAT
Keratuff 2 base R 31/Kg + VAT
4 x test cubes for legs
Calcium silicate bench protector R555.00 + VAT
7 kg Electricast @ R84/kg R588.00
Ceramic fibre blanket R308.00 + VAT
Note: If you do not use the legs and bench protector you will burn a large hole through your workbench.
Make a heavy, high thermal mass slumping mould from Electricast.
Assemble the furnace.
Place the mould in the furnace and switch it on.
Leave for about 4 hours.
Check for steam with a piece of cold glass.
Once dry, switch off the element panel and allow assembly to cool.
Place glass on top of mould.
Close "door" and switch on.
After an hour, slide door open just a crack and watch glass bending.
Just before slumping is complete, switch off element panel.
Close door and allow to cool slowly.
Note: If normal lightweight moulds are used, the cooling will be too rapid, and the glass will become stressed and crack.
Description; A fine, creamy, self levelling hydraulic bonded, rapid setting castable. It is largely composed of zircon, a zirconium silicate mineral with exceptionally high electrical resistivity. Its main application is the manufacture of electrical components and "potting" applications. After casting it is quite soft and very readily machinable. Nornally it is prefired to 1200ºC, to give very high strength, but it can be used after firing to 400ºC. Strengths of up to 140 MPa have been recorded, using it in putty form with +6% water. Shrinkage on firing to 1200ºC is approximately 1% (With +9% water) Fired colour is buff to beige, unfired it is grey.
Maximum service temperature; 1300ºC.
Mixing; Add plus 9% water for pouring.
Applications; Element supports, leadouts, cuplocks, candle components, bobbins, nozzles, cloning of electrical components.
Packaging; 25kg plastic bags.
Both are remeltable copolymers for highly elastic moulds. Both are substitutes for silicones, their main advantage being that they are cheaper, quicker,and re-usable. Mistakes cost only time. Vinamold was imported from the U.K. Multimould is made in Randfontein by Keramicalia.
Heating; Vinamold manufacturers recomend a heated oil jacket, Keramicalia uses microwaves. Both yield a disaster if burned.
Density; Multimould is high density, 2,75. it has zirconium silicate added to give it better flow under gravity, higher heat capacity to reduce pouring lines especially on metal models.
Opacity; Multimould has opacifier added so that the surface finish is clearly visible on the mould. With Vinamould which is more transparent, surface defects are sometimes only apparent on the casting.
Shelf life; Vinamold surfaces deteriorate and moulds cannot be stored for more than a year. Multimould shows no deterioration after 10 years.
Toxicity; Vinamould is slightly toxic, Multimould is not.
Odour; Multimould now has less odour than Vinamould and can be used as moulds for sweets, chocolate and soaps.
Biomould is a bit like paper maché, but very strong. It sets chemically in 1 to 2 hours. It is easy to work with and can be used with a lot of filler. The formulation can be varied greatly depending on the product desired. The cardboard dust fibres make it quite tough and it can be dropped on the floor without damage.
A typical formulation would be: 62% powder to 38% hardcast binder by weight.
This gives a dough consistency.
If a Biomould formulation is oversaturated with liquid, some will leak out and cause a white discolouration.
Pot life is about 20 minutes. Setting takes between 1 and 2 hours.
On setting Biomould releases a film of liquid against the mould. This releases it from all surfaces. Wash it off.
Pourable formulations form an air dried skin on top, which contracts and may distort the surface. A plastic sheet to stop evaporation will prevent this.
Fresh casting can deform under their own weight until dry. Keep them supported until dry.
Development no. 138009
Bio White is a refractory coating: it is hard, strong, totally UV resistant and weatherproof. Bio White is a powder which reacts exothermically to form a hard calcium aluminate hydrate crystalline compound. It is normally used impregnated into biotextile, a non-woven textile carrier and reinforcing medium. Bio White has a matt white appearance similar to marble.
Bio White can withstand temperatures in excess of 1400°C.
It sets hard in about an hour. High ambient temperatures accelerate set, so does enclosing to eliminate evaporative cooling. Thermal insulation also accelerates setting. A large casting will set in a few minutes and get so hot as to generate steam explosions.
Bio White will replicate the exact texture of a mould. A perfectly smooth mould generates a glossy finish.
Mixing: add 35 weight parts water to 100 weight parts Bio white powder and mix by hand. Use small quantities of mix at a time, not more than 2kg. It is very fluid, too fluid for a gel coat. It can be made into a gel coat by adding 0,1% methocel J75MS into the powder before mixing water.
Packing: 20kg bags +3m² Biotextile
Shelf life: 2 years
Development no. 132209
A paste for coating metal parts which come into contact with molten aluminium. It has various other applications where a hard ceramic coating is needed. It is a very sticky white paste which smears easily onto metal surfaces. It is normally used with Keratex fiberglass open weave. This netting helps with the application, keeps an even thickness and helps to overcome stresses of differential thermal expansion.
It contains a lot of colloidal silica and a small percentage of organic thickener. It goes stiff after long storage, and can be re-mixed to paste without adding any liquid. Re-mixing may leave some lumps, but the fiberglass sorts them out.
Smear a layer onto the surface to be protected. Press a layer of open-weave fiberglass into it and coat with a further layer until the desired thickness is reached. Use gloves to apply it, because the colloidal silica roughens the skin, and the Alusmear takes a while to wash off. Wash it off all skin and clothing before it dries because it STICKS! Dry the coating before immersing it in molten metal. 120C is adequate.
You can dilute it and paint it onto crumbling brickwork to restore the surface.
Several years under cool storage conditions.
8 kg plastic buckets.