spring 2010 Clay, Metal, and Casting, Projects Class (S.J Choi ) page 1 of 7Mold making & Casting Handout(For chemical based materials)* MOLD MAKING PAST & NOW People have been making molds for thousands of years, dating back to ancient Egypt andChina. Through the years, a variety of materials have been used to make molds including sand,wax, glue, animal fat, gypsum, alginate, metal, plastic, re-usable vinyl, gelatin and others. Still use a variety of materials, but a majority uses one of four different flexible rubber productsfor the following reasons: 1) these rubbers reproduce exact detail 2) flexibility allows for easyremoval (demold) from the original model and the cast piece, 3) they generally give long life,allowing for multiple reproductions, 4) because they generally yield many reproductions, whichalso makes them cost effective. These rubber products are latex, poly-sulfides, poly-urethanes,and silicones.* MATERIAL ADVANTAGE AND DISADVANTAGE The next few paragraphs review these common mold rubbers along with advantages/disadvantages of each.I. Latex : To make this rubber usable as a mold material, the raw rubber is usually processedwith ammonia and water. Latex is almost always brushed onto an original model (not poured). - ADVANTAGE: Natural, One-component system, Inexpensive, Thin-walled, Strong and exhibitgood abrasion resistance.. Latex molds are also good for casting wax and gypsum.- DISADVANTAGE: Shrinkage (10 to 20%), Ammonia odor, Making molds with latex rubber isslow and time consuming. Brush-on molds made with latex require as many as 20 brush coats,with 4 hours of drying time between each coat. (* new latex products on the market with lowershrinkage and no odor). Latex molds are generally not suitable for casting resins.II. Poly-sulfide rubbers : Two-component systems (base plus curative; A+B), Available formaking molds that are poured or brushed on. - ADVANTAGE : Soft, "stretchy" and long lasting (over 40 years), Good for making molds withsevere undercuts,fine detail. Not inhibited by sulfur or water based modeling clays, Minimalmodel preparation. Good for casting wax (lost wax process) and gypsum plasters.- DISADVANTAGE: Mostly offensive odor. Newly made poly-sulfide molds may stain plaster.Poor abrasion resistance (not good for casting concrete, production casting of resins. Accuratemix(A,B part system) by weight (scale required), Moderate cost; higher than latex and urethanesbut lower than silicones.III. Silicone rubbers : Two-component systems (base plus curative; A+B), Available in ahardness range of very soft to medium. Cured with either a platinum catalyst or a tin catalyst.Available for pouring, brushing or spraying types.
page 2 of 7- ADVANTAGE : Best release properties of all the mold rubbers. Good for production casting ofresins (poly-urethanes, polyesters and epoxy). No release agent is required. No post-productioncleanup. Good chemical resistance and high temperature resistance (400°F / 205°C andhigher). Only suitable for casting low melt metal alloys (i.e. tin, pewter, lead).- DISADVANTAGE: High cost . Sensitive to substances (sulfur clay for example). Thick (highviscosity), Lot bubble.(* Using brush-on rubber mold, the time factor between coats is long(longer than urethanes or poly-sulfides, shorter than latex). Accurate mix(A,B part system) byweight (scale required). Shrinkage. No long library life.IV. Polyurethane rubbers : Two-component systems (base plus curative; A+B), Low cost.Available for pouring, brushing or spraying types.- ADVANTAGE : Easy to use, Simple mix ratio by volume (i.e. 1A: 1B) - No scale required. Widehardness range. Low viscosity. No vacuum for bubble. Good abrasion resistance. Less expen-sive than silicones and poly-sulfides.- DISADVANTAGE: Worst release properties, Very adhere to anything. Need good model prepa-ration ,Moisture sensitive, May bubble if exposed to moisture (working on humid day, for exam-ple). Limited shelf life (effect from ambient moisture in the air.)* PROCESSWhether you choose a silicone, polyurethane or poly-sulfide, read the technical bulletin for thatproduct. Every technical bulletin has important information about that specific products use(most common applications), technical information (mix ratio, Shore hardness, viscosity, curedstrength, etc.), and much more. There is also information about safety, general mold makingtechniques and how to get the most out of your cured mold.These materials are safe if used properly and as directed. Follow these general safetytips:* Mold making and casting is not for children. Keep all materials out of the reach of children.* Good ventilation is essential.* Wearing rubber gloves and long-sleeve garments will help minimize skin contact. Uncuredrubber can be removed from working surfaces with WD-40,acetone,etc.* Be aware of your temperature. The workshop and all materials (including your mold) should bemaintained at, or near, room temperature (77° F / 25°C). The colder the environment, the longermold rubber will take to cure and if the temperature is too cold, (50°F / 10°C), the rubber will notcure at all. Warmer environments will reduce the amount of time you will have to mix and pouror brush on rubber.* Humidity should also be kept at a minimum. High humidity will react with polyurethane moldrubbers .
page 3 of 7* Working surfaces should be accessible from at least two sides and should be level in all direc-tions. To protect the surface from spills and stains, cover the tabletop with news paper or brownwrapping paper. Also, wear "disposable" clothing. These materials will permanently stain cloth-ing.* Dont risk a valuable model. . . Test the material in question on a similar surface before apply-ing to the model(especially, between the mold rubber (sealer, release agent, etc.) and the modelsurface* Materials Needed For Making Mold and Casting• Disposable clear containers• News paper or Brown paper• Modeling clay• Mixing containers/Measuring Containers• Mixing Sticks/ knifes• Sealing agent• Release agent• Coddles• Clamps(vinyl and latex)• Cheap brushes• Rubber band• Glue gun* Making A Flat-Back One-Piece Block MoldStep 1: Start With a Model - Models can be made of virtually any material: wax, clay, plaster,stone, concrete, paper, metal, bone, fabric, etc.Step 2: Build a Containment Field - The purpose of a containment field is to prevent the liquidrubber from leaking out the sides or bottom and contain it until the liquid turns to a solid, flexiblecures. The containment field can be something as simple as a paint can, cigar box, cake pan,coffee can, etc. Or construct a " mold box."For molding irregularly-shaped molds, the baseboard can be cut to the desired con-tour. Uselight gauge sheet metal, linoleum or cardboard for the side wall. Overlap and tape pieces to-gether. Hold in position with cord and wedges.Step 3: Secure the Model - Using silicone caulk, a glue gun, Instant epoxy, or clay, you mustsecure the model to the baseboard. We have rolled modeling clay into thin beads and pressedthe clay around the back perimeter of the model. We then center the model in the mold box andpress firmly on the piece in all directions. This flattens the clay and creates a tight seal under themodel to prevent rubber from leaking underneath. You can also nail or screw the model to thebaseboard, but this damages the model. If the model is highly porous, it should be vented fromunderneath to prevent trapped air from forcing bubbles in the rubber.
page 4 of 7Step 4: Seal the Seams - To prevent the liquid rubber from leaking out the sides or bottom ofthe mold box, all seams are sealed. You can use silicone caulk, a glue gun, Instant epoxy™ ormodeling clay. (Remember, if using silicone rubber for your mold, do not use silicone caulk.)Step 5: Apply Sealing Agent - Models made of porous materials (plaster, stone, concrete, wood,etc.) require a sealing agent to seal surface porosity. Clays that are water-based or sulfur-basedmust also be sealed. Suitable sealers include shellac, paste wax, and petroleum jelly thinnedwith mineral spirits.Step 6: Apply Release Agent - After sealing the models surface, applying a release agent willallow a model to be easily released from the cured rubber. Use a release agent specificallymade for mold-making and casting. Using the wrong release agent will result in the mold rubbersticking or bonding to your model or the mold rubber will not cure.* Wrong Release AgentsSpray Vegetable Oil (Pam)Mineral OilPetroleum JellyMotor OilSpray Lubricants (WD40)* Right Release Agents Universal Mold Release / Any kind of Release Products (Mann Ease Release Series) Mold release agents come packaged in both convenient aerosol sprays or economical liquidsthat can be brushed on or sprayed on using a non-aerosol sprayer.Note: If using a silicone rubber, do not use a silicone-based release agent to release the moldrubber from the model. It is not necessary. If releasing silicone rubber from silicone rubber (mak-ing a two-piece block mold, for example), use special one (Manns Ease Release™ 800 non-silicone-based release).* Proper Application Of The Release Agent Warning! Failure to properly apply a release agent will result in the rubber completely stickingto the model, or sticking in some places but not in others (spot sticking).* The proper way to apply a release agent is to:1) Apply a light mist coating over the entire surface of the model and surrounding forms(any surface that will come in contact with the rubber). Do not over-apply!
page 5 of 72) Use a clean paintbrush to brush the release agent over the surface of the model andsurrounding forms. Make sure that intricate detail, undercuts and hard-to-reach areasare coated as thoroughly as possible.3) Apply another light mist coating and let dry for 10 minutes. Do not soak your model with release agent. Over-applying release agent will result intiny bubbles on the working surface of your finished mold (pin-holing) and will be re-flected in castings taken from the mold. Once "sealed" and "released," our model is nowprepared. The next step is to measure, mix and pour the mold rubber over our model.* Release Agents ChartOriginal ! ! Molding Compound ! ! Release Type Suggestions(#products from T.C.S)Clay, Metal, Plastic ! Urethane Rubber! ! ! Silicone! ! UMR, 2251, 2300, 2601, 2910Clay, Metal, Plastic RTV Silicone! ! ! Wax/Teﬂon! ! 500, 2310, 2831Clay, Metal, Plastic! Urethane/Epoxy Plastic! ! Mixture! ! ! ! 200Plaster! ! ! Urethane Rubber! ! ! Wax/Soap! ! 2310, 2831Plaster! ! ! RTV Silicone! ! ! Wax! ! ! Sonite Seal, 2831RTV Silicone! ! RTV Silicone! ! ! Non-Silicone! ! ! 800Plastilina, Plaster! ! Polysulﬁde Rubber! ! Wax! ! ! Sonite Seal, 2831, PVAConcrete! ! Urethane Rubber! ! ! Oil/Soap!! ! Castor Oil, In & OutAqua-resin! ! Silicone Rubber! ! ! None! ! ! (just use Kiril-B)Aqua-resin! ! Alginate!! ! ! SEPR-8! ! ! ! SEPR-8Aqua-resin! ! Latex Rubber! ! ! Parﬁlm, PVA! ! Polyester Parﬁlm, PVA
page 6 of 7* Measuring Mold Rubber As stated earlier, some mold rubbers require accurate weighing of components (A +B). These include most silicones (Smooth-Sil series), poly-sulfides (FMC series) andsome poly-urethanes PMC series). If you are using a mold rubber that requires a scale,use an accurate scale such as a gram scale or a triple beam balance.* Mixing Mold Rubber One of the most common reasons for mold rubber not properly curing is improper mixing. It isimperative that you develop and practice a good mixing technique.Mix Parts A + B for at least three minutes.• Be Thorough, Not Fast! Most mold rubbers give you plenty of time to mix and apply.• Do not whip the material or create a vortex -- this will introduce air into the mix that may resultin air bubbles on the working surface of the finished mold.• Stir slowly and deliberately, making sure that you scrape the sides and bottom of your mixingcontainer several times.When you think you have mixed the rubber enough, mix it again just to make sure.* Pouring Mold Rubber With the mold rubber thoroughly mixed, it is now time to pour it over our original model. Do notpour rubber directly onto the model as this may entrap air. Instead, find the lowest point in themold box and pour the rubber there -- in a single spot and at a slow, constant rate. Let the rub-ber rise up and over the model. This will displace air from the lowest point and help minimize airentrapment. You will notice tiny air bubbles rising and dissipating on the surface. You can further dissipatethese bubbles by lightly passing a heat source (hair dryer or heat gun) over the surface.* Let the Rubber Cure...The next step is easy . . . let the rubber turn from a liquid to a flexible solid (cure) overnight (16hours) at room temperature (77°F /25°C).* Accelerating the Cure If you want to reduce the cure time of the rubber, you have two options:1) Cure accelerator can be added and will reduce the cure time. Mostly added to Part B andmixed thoroughly before adding Part A. Consult their Technical Bulletin for more information.2) Apply Heat. Warmer temperatures will cause the rubber to cure faster.
page 7 of 7* Demold After the rubber has cured, it is time to remove our original model from the finished mold, or"demold." If all went well . . . The rubber flexes easily and the original model should releasefrom the cured rubber. The mold should reflect every last bit of detail (down to a fingerprint) ofthe original model.* Casting Into A Finished Mold There are a variety of materials that can be cast into a finished mold.Wax - For candle-making, reproducing jewelry, and sculpture (the lost wax process).Gypsum Plaster - For architectural restoration, reproducing sculpture.Modified Gypsum - For making exterior or interior architectural elements, sculpture, metal cold-casting.Concrete - Statuary (ornamental) and architectural elements.Modified Concrete - Exterior architectural castings, ornamental concrete, sculpture reproduc-tions.Urethane Resins - Reproducing sculpture, jewelry, special effects, tooling & prototyping, gen-eral purpose interior/exterior applications, industrial parts.Polyester Resins - Plastic castings, architectural elements, sculpture, laminations, reinforce-ment.Epoxy Resins - Vacuum form molds, production tooling, foundry patterns, forming dies, hardrollers, industrial parts.Urethane Foams - Arts & crafts, industrial uses and special effects. Straight casting, backfill-ing, encapsulation, cushioning.* Material Supply- The Complete Sculpture ; On/Off line : 90 Vandam St, between Hudson St and Greenwich St/www.sculpt.com/ 1-800-9-SCULPT- www.smooth-on.com- www.tekcast.com- www.rubbermoldcompounds.com- www.polytek.com
spring 2010 Clay and Casting, Projects Class (S.J Choi ) page 1 of 3Making a Brush On Rubber MoldThe advantage of making a mold by brushing rubber onto the model is that it minimizesthe amount of rubber used, saving you material costs. Making a brush-on mold,however, requires more time and labor vs. pouring rubber.Brush-on rubbers come in different forms and may be mixed one-to-one by volume (ure-thanes such as Brush-On 40t), or may require an accurate scale for weighing compo-nentsMaking A Brush-On Mold Step-By-StepThe process for making a brush-on mold is almost like making a pour-on mold.Step 1: Build a dam(like coddles) around the model- Because of brushing on 3 Dimen-sional model and flowing Rubber material, it needs a dam (like coddles) not to run downduring applying rubber. And it lays news paper or brown paper under the model. Themodel should be accessible from all sides. A platform that rotates 360 degrees makesbrushing rubber onto the model very easy.Step 2: Seal The Model - Some model out of clay that contains sulfur, it must be sealedusing spray shellac. Remember: Failure to seal the model may result in the mold rubbernot curing.- Reminder: If you are using silicone rubber (such as Mold Max 30) to make your mold,do not use shellac as a sealer. Instead use either Super Seal or acrylic spray.Step 3: Apply A Release Agent - Universal Mold Release will make it releasing easilyand is absolutely necessary if shellac was used as the sealer.* Proper way to apply release agent:• Apply a light mist coating to all surface, forms and mounting platform.• To ensure thorough coverage, use a soft brush to brush the release over the model’ssurface, into undercuts and over areas of fine detail.• Apply a second light mist coating and let dry for 10 minutes prior to applying the moldrubber.
page 2 of 3Step 4: Measuring Mold RubberThe mold rubber we will feature for this demonstration is “Brush-On” 40. Part A is aliquid and Part B is a paste. When combined in equal amounts (by volume--no scalerequired), Brush-On 40 self-thickens and can be applied to a vertical surface withoutsagging.Dispense the paste (Part B) into the measuring container. Using a spatula or stirringstick, be sure to eliminate any air voids. Use a spatula to level off at the top and thor-oughly empty contents into a mixing container.Fill the same measuring cup to the top with the Part A liquid and empty into the the mix-ing container. With Parts A and B now properly measured and dispensed into the mix-ing container, proper mixing technique is used to blend the components.Mix thoroughly for three minutes, making sure that the sides and bottom of the con-tainer are scraped several times. Parts A + B should blend thoroughly to a uniform colorwithout any signs of streaking in the mix.Step 5: Applying the RubberAt least four layers of Brush-On 40 are necessary to build a suitable mold thickness.Generally, 3/8”-1/2” (.95 cm - 1.3 cm) is adequate.The first layer is generally known as the “detail coat,” and is applied thinly to themodel surface with short, dabbing strokes. Subsequent coats can be applied with morefluid strokes and will give the mold strength and durability.In applying the first coat, you should strive to cover every last bit of detail on the modelsurface, and coat hard-to-reach areas and undercuts. In this case, care is taken to en-sure coverage of all features, particularly the eyes, nostrils and in and around the ears.The base is also covered.Once the model is covered, it is allowed to dry for 30-40 minutes (at room tempera-ture) until “tacky.” Tacky means that the rubber has started to cure and is no longer“wet.”
page 3 of 3 It is sticky to the touch, but will not come off on your finger (use only a gloved hand or aspatula to touch the rubber). Note: Colder temperatures will prolong the cure time, while warmer temperatures willaccelerate it. Do not apply the second coat if the first coat is still wet!Step 6 : Applying The Second CoatWhen the first coat has become tacky, apply the second coat. The second coat is ap-plied with longer, more fluid strokes and completely covers the first coat. Be care-ful not to disturb the first coat.After the model is covered (if you use small amount of pigment, this coat makes it easyto determine when it is covered), the rubber is again allowed to become “tacky” priorto applying the third coat.Apply the third coat, unpigmented this time. Allow this coat to “tack up.”Apply the final coat--with pigment.Between third and final coat, attach the keys for holding the support shell on tackycondition. It prevents for detaching rubber mold from support shell. The keys should beused same material and can be prepared left over from first or second coat process.After the final coat is applied, all coats are allowed to cure overnight (16 hours atroom temperature).Step 7 : Applying The Support ShellWith the rubber fully cured and still on the model (do not demold yet!), a reinforce-ment shell (mother mold) must be applied to the model.Again, the purpose of the support shell is to maintain the shape of the rubber moldwhen casting into it.The support shell should be out of plaster, fiberglass, plastic, resin and some productsdesigned for the support shell.
Introduction of Fiberglass(2010 Spring Class Demonstration)BackgroundFiberglass refers to a group of products made from individual glass fibers combined into a va-riety of forms.Glass fibers can be divided into two major groups according to their geometry :1)continuous fibers used in yarns and textiles (reinforcement material for molded and laminated plastics)2)discontinuous (short) fibers used as batts, blankets, or boards for insulation and filtration. (Fiberglass wool, a thick, fluffy material for thermal insulation and sound absorption)Example : in ship and submarine bulkheads and hulls; automobile engine compartments andbody panel liners; in furnaces and air conditioning units; acoustical wall and ceiling panels;and architectural partitions.History : Artisans created glass strands for decorating goblets and vases during the Renais-sance. A French physicist, Rene-Antoine Ferchault de Reaumur, produced textiles decoratedwith fine glass strands in 1713, and British inventors duplicated the feat in 1822. A British silkweaver made a glass fabric in 1842, and another inventor, Edward Libbey, exhibited a dresswoven of glass at the 1893 Columbian Exposition in Chicago.Glass wool, a fluffy mass of discontinuous fiber in random lengths, was first produced inEurope at the turn of the century, using a process that involved drawing fibers from rods hori-zontally to a revolving drum. Several decades later, a spinning process was developed andpatented. Glass fiber insulating material was manufactured in Germany during World War I.Research and development aimed at the industrial production of glass fibers progressed in theUnited States in the 1930s, under the direction of two major companies, the Owens-IllinoisGlass Company and Corning Glass Works. These companies developed a fine, pliable, low-costglass fiber by drawing molten glass through very fine orifices. In 1938, these two companiesmerged to form Owens-Corning Fiberglas Corp. Now simply known as Owens-Corning, it hasbecome a $3-billion-a-year company, and is a leader in the fiberglass market.Raw Materials : The basic raw materials for ﬁberglass products are a variety of naturalminerals and manufactured chemicals. The major ingredients are silica sand, limestone,and soda ash. Other ingredients may include calcined alumina, borax, feldspar, nephe-line syenite, magnesite, and kaolin clay, among others. Silica sand is used as the glassformer, and soda ash and limestone help primarily to lower the melting temperature.Other ingredients are used to improve certain properties, such as borax for chemicalresistance. page 1
Fiber glass FormsFiberglass Mesh - Alkali Resistant Mesh for reinforcing casts or mother molds, reinforcing Winterstonesculpture and setting mosaic tile. Cuts easily (Mesh is white, the teal color in this picture is only the background for the picture.)Fiberglass Veil. A super thin veil for reinforcing casts or mother molds. Ideal for applying to highly de-tailed areas.Fiberglass Mat. chopped-strand mat for reinforcing casts or mother molds. page 2
A/R Fiberglass (Loose Strand)- Flexible for use in concretes, Winterstone and any alkaline base me-diumFiberglass Cloth. Plain weave, 14mils thick. Use this fiberglass cloth to create high strength parts. It ispopular for lamination and high strenth casting. It is also, often used in fiberglass mold making.AquaGlass (AQG) Chopped Strand - This ﬁberglass is specially design to work with Aquaresin as botha reinforcement material and thixotropic additive. The ﬂexibility of the ﬁberglass facilitates easy mixingwithout and preliminary soaking. " Aquaglass is also ideal for any type of water-based application like:plaster, hydrocal, ultracal, fgr-95, forton mg and matrix g. Not for Cement. page 3
MAKING A FIBERGLASS MOLD- The first step is to apply a gelcoat of Resin which will be the mold surface.- The gelcoat should be in contrasting color to the surface of the part you will make. Since mostparts are light colored, black gelcoat is commonly used. - If the gelcoat is to be brushed on, two coats must be applied, and the first coat must cure sev-eral hours before the second coat is applied. - When the gelcoat has cured so that it cannot be scratched off with the fingernail at the edge ofthe mold, which takes from 2 to 4 hours to overnight in cool or humid weather, you are ready forthe “skin coat.”- Between first and second coat, you can apply fiberglass mat.- The resin should be applied with brush or a mohair roller until no white fibers remain.- Be careful not to over-catalyze when laying up the glass. Above 75°F one 10-15 cc of hardenerto the quart will generally suffice. Below 70°F, 20 cc per quart. Do not work below 65°F. - For a large mold, it is good to apply just one layer per day. After the “skin coat,” you can use1! oz. mat for a faster build-up. Generally, woven roving is not used in molds because the pattern transfers through the mold tothe gelcoat. If it is necessary to use woven roving for strength in a large mold, it is applied aftera thickness of 3 or 4 layers of mat has cured hard. The thickness required in a mold dependsupon size and shape and the number of parts to be taken off. For a dinghy mold to be used onlya few times, four layers of mat might be adequate. page 4
The regulations of ﬁberglass operationsA number of regulations can apply to ﬁberglass operations. These regulations stem from thetypes of products used and types of wastes generated by the industry. Table A lists typical ﬁber-glass processes, products and wastes. The regulations, referenced in the table, protect workerhealth and safety, community rights and the environment. (Table A -- Typical Fiberglass Processes,Products Used and Wastes) "- Worker Health & SafetyThe states Department of Labor and Industries implements worker health and safety regulations.If you employ one or more people in your shop, you must ensure that: •! Workers have access to appropriate safety and protective gear, like gloves and respirators. •! Workers understand any hazards associated with their job. Hazardous products must be identiﬁed and labeled, and information about the product must be kept on-site.! •! Workers are not exposed to excessive levels of air-borne pollutants, like styrene.- Resin -- Often Hazardous because it is ﬂammable and contains styrene monomer."- Initiators & Catalyst - Often Hazardous because theyre ﬂammable and explosive due to per-oxide content.Worker Safety -- Fire Risk : Local ﬁre codes regulate ﬂammable products, like acetone andresins. Especially, peroxide catalysts must be stored in an explosion-proof cabinet.Air Emissions : Fiberglass can create smog, damage the Earths ozone layer, impact humanhealth and affect the environment.Hazardous Wastes : Some ﬁberglassing wastes are regulated because they are hazardous. Forexample, spent acetone is regulated because it is ignitable, and spent emulsiﬁer is sometimesregulated because it is toxic to ﬁsh. page 5