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La Salle University
Materials and design fundamentals
José Luis Rubiano
Laboratory practice#1
Manufacture of molds and parts
JEIMY ALEJANDRA RIVERA CAMARGO Cód. 47122028
MARIA ALEJANDRA SUPELANO TRIANA Cód. 47122042
RODRIGO WBERNEY MARTINEZ SKINNER Cód. 47122016
BRANDON STIK ZAPATA MENDOZA Cód. 47121002
Bogotá D.C
2014
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INTRODUCTION
A mold is a part, or Assembly attached, inside hollow parts but with details and foreign imprints of
the solid future to be obtained. Fluid or plastic material that solidifies becomes the shape of the
mold that contains it is poured inside. There are molds rigid and flexible; molds depends on the
shape of the work piece to seriar, determined by the degree of complexity of the details and thesymmetry of this, being important to facilitate the unmolding it should be as precise as possible;
There are molds of one-piece, two-piece or up to five or more if necessary.
This report will present the development of practice materials and basics of design, in which were
a few molds with plaster stone III and IV and made a few copies of a figure using these molds in
different materials which were resin polyester, paraffin and silicone rubber. The fiberglass was
also used to make other molds.
The objective of this practice is to make molds and copies of parts and the specifics are compare
the different properties of each material used in practice, learn how to make mixes with catalysts
and water needed to bring material to the exact consistency required for work, differentiate each
material in their groups, such as the ceramic polymers and hydrocarbons.
The theoretical framework highlighting the characteristics of each material, methodology and
materials used comparison of the differences, the results obtained along with the answers to a
few questions, conclusions and references will be displayed throughout the report.
THEORETICAL FRAMEWORK
Gypsum is a mineral that comes from different parts of the world. The process begins when
hydrated calcium sulfate is calcined so it loses moisture and is then ground, thus becomes semi
hydrated calcium sulfate, and between more heat is applied, higher humidity will lose (this
moisture is known as water of crystallization).
Gypsum plaster dental stone (type III). This is more resistant and is used for the
construction of models in manufacturing total dentures that are adapted to soft tissue.
Gypsum plaster dental stone of high strength (type IV). The requirements for this are:
resistance, hardening and a minimum of setting expansion. A-hemidrato "Densità" is used
to get these properties. Form particles cuboidal and reduced surface produces these
properties without thicken the mixture too much. This must be resistanttoabrasion.
Silicone rubbers are elastomeric silicone of two liquid components (rubber and catalyst) thatvulcanize at room temperature. After the curing is a material elastic and resistant to some of its
physical properties (by means of auxiliary products or temperature variations) can be varied to suit
different uses. Additives that can be used are silicone fluid, which is used to lower the viscosity
and decreasing the hardness of rubber, and catalyst thixotropic thickening the material so that it
can be applied with a brush or spatula in successive layers. The mechanical property to undergo
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much more elastic deformation under stress than most materials and still return to its previous
size without permanent deformation.
Resin polyester, in its origin, is similar to a piece of glass. Why is added for better handling a
"Styrene" ratio, a solvent which converts it into this fluid we all know. Polyester resins are a pale.
This color can be pale gray or a diluted and off white. Polyester resins are resistant to water andUV rays. This is another reason why are employed by the marine industry. Due to the
thermosetting nature of polyester resins, they can be slightly fragile by its resistance to be folded
or changed. When enough pressure is applied, they may crack or destroy.
Paraffin is common of alkane hydrocarbon group name, the simplest paraffin molecule is
methane, a gas at room temperature; Instead, the heavier members of the series, as the octane
arises as liquids. Solid forms of paraffin, called paraffin wax, come from the heavier molecules.
Paraffin wax is usually as a solid waxy, white, odorless, devoid of flavor, with a typical melting
point between 47 ° and 64 ° C. It is insoluble in water, but it is soluble in ether, benzene, and
certain esters. Paraffin is unaffected by most common chemical reagents, but Burns easily. Pure
paraffin wax is a very good electrical insulator and is good for storing heat. Usually gets the oil, oil
Shale’s or coal.
COMPARE DIFFERENCES IN PROPERTIES BETWEEN DIFFERENT MATERIALS
The two types of gypsum are part of the ceramic, contains 79,07 sulfate anhydrous calcium and
20.93% water % and it is considered a white rock in its purest form, however, usually has
impurities in terms of its color. These types of casts require little water to be very well used. The
number IV compared to the III added resin to improve characteristics of porosity, percentage of
water absorption and most importantly to give better consistency and toughness. This type of
plaster number IV is also used in the copy of surfaces.
Resin polyester is a thermosetting resin obtained by polymerization of styrene and other
chemicals. Hardens at the ordinary temperature and is highly resistant to moisture, chemicals and
mechanical forces. Used in the manufacture of fibers, coatings of blades. Catalyst features very
interesting since it allows the polymerization of the resin, gives characteristics of hardness and
adheres better to the mold. Add approximately 1.0% to 1.8% per 100 Kg of resin.
Polyester resin is used in relation to the fiberglass 2-1; 2 kg of resin is used i.e. for a kg of glass
fiber. Use this material must be very careful that fiberglass much sticks to the garment and may
cause disease in the skin. Also when working with this resin, you must be very fast, efficient and
prepare the appropriate percentage of the mixture in compacted time is less than 2 minutes.
The silicone is polymers that include Silicon together with carbon, hydrogen, oxygen and other
chemical elements. Some common forms include oil silicone, silicone grease, silicone rubber and
silicone resin. Some of themostusefulproperties of Silicones are:
LowChemicalreactivity.
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Lowtoxicity.
Thermal stability (property in a wide range of temperatures from - 100 ° c to 250° C).
MATERIALS
1.
Lego cards
2.
Vaseline
3.
Plasticine
4.
PlasterStone III and IV
5.
Spatula and bowl of dentistry
6.
Polyester resin
7.
Siliconemold
8.
Fiberglass
METHODOLOGY
For this new experience about the ceramics and glass derivatives, delving as first step is armed a
box with tabs of lego so large that it entered our Mickey that was the tab to copy. This box was
placed in on the top of the table and made him a clay base.
First worked with the cast number III, for each gram applied need certain amount of water, which
weighed to obtain the exact mix. Before this gets the tab inside the lego box making that stays
within the dough half, enough Vaseline applied to it and clean the excess. It is necessary that the
bed of clay is well smooth so there are no imperfections in the mold.
After having this ready mix is made it must be poured quickly, but this does not dry so easy. While
you are pouring it is necessary to move the table vertically so that the mixture is uniform and withthe least amount of bubbles. It is left to dry for a few minutes, the mold is removed is perfected at
the sides. The procedure for the other half of the glaze is repeated in order to achieve two molds
to form enamel to join them to copy. An important fact I know must be feeds with clay inside the
box to make it easier to remove the mold and glaze. Also in order to apply the materials which are
going to make the copies pour you for these feeds to certify that the mold is completely filled with
the material. These same steps are performed with the cast number IV obtaining other two molds.
For these two plasters used the same tab to copy to a glaze.
Already with our dry molds were to make the final piece, silicone mold was used for the first part.
This time the silicone was not mixed with water but will add a catalyst, this should be mixed
quickly and then be poured into the mold since it tends to solidify very fast but before applies a
little petroleum jelly to molds so that the silicone non-stick and can be removed easily after. The
first part of the mixture is poured into each mold, then these two come together and the rest of
the mixture is poured by the feeding of the molds. This mixture is allowed to dry for 24 hours and
then the molds are opened and the piece is removed and shuts excess created by feeding.
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Now what was used to make our new piece was resin polyester, which was also necessary to add a
catalyst, is mixed and poured into mold this time all the mixture for feeding but also had to take
into account as in the previous mold that was pouring rapidly since it dries fast. It is left to dry for
a few minutes and you can now open the molds and remove the piece.
For our final mold, we use again one of plaster casts and placed the enamel in the mold. Is thatshort small pictures in fiberglass, then proceeded to prepare the resin, mixed and later with the
help of a brush was poured resin on top of boxes of glass fiber and is was giving evenly to mold
fiberglass according to the enamel. Allowed to dry also minutes, cut leftover edges and turns to
applying fiberglass and resin on the other side in order to meet with two molds. It should not be
forgotten that you apply petroleum jelly mold and work piece.
RESULTS
The different advances in the report of “Engineering materials” laboratory were two different
molds, the first of them is a Nail Polish, and the second is a file of size lego medium. These moulds
are used different materials to investigate and interpret their physical, chemical characteristics
and soto compare them to publicizing findings of their behavior. The materials were:
1.
Gypsum stone III
2.
Plaster stone IV
3.
Resin and resin with fiberglass
4.
Silicone mold and a catalyst
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Image 1. Molds with plaster number III.
Image 2.Silicone rubber mold
Image 3.Fiberglass mold.
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Below is given to know the behaviors that had the materials.
1.
Plaster stone III: used 250 (g) plaster, mixed with 45 (ml) of water, the initial setting time
was 15 to 20 seconds, i.e. was a mixture of manual by means of a spatula for 15 to 20
seconds to make it with a good texture for pouring on top of the piece to shape. For the
final setting time was 90 to 100 seconds approximately, i.e., the time in which plaster wasdelayed getting totally hard and consistent. Immediately I am gypsum consistent structure
was hot and after a short time I am at room temperature. The color is white - grey.
2.
Plaster stone IV: used 250 (g) plaster, mixed with 36 (ml) water, the initial setting time
was 15 to 20 seconds for the setting time end was approximately 120 to 130 seconds. The
time that it took to stay consistent was something greater in relation to the gypsum stone
III, this is explained when we analyze their chemical properties.
3.
Resin and fiberglass resin: resin polyester is light pink in color, is used at room
temperature, in our case, we used 40 grams of resin and a few drops of catalyst and was
poured into molds. To withdraw the piece was that the piece was hot. The same grams of
resin and catalyst is used for resin with glass fiber, mixed with a time of 20 secondsapproximately, and in this case was two copies of part, since it was first necessary to copy
half of the piece, and then the other half. The fiberglass was grey, was difficult to use,
because it adhered to any type of material, was used when half of the resin is poured, and
later the other half of the resin is poured. In less than two minutes this material is already
fully hard with its characteristics of hardness.
4.
Silicone for molds and catalyst: we used a type of silicone which is used for plaster casts.
It was a catalyst that its main function is to give necessary hardness to the part to copy.
After obtaining the part with silicone molds had a high temperature in the thickest part of
the material. This material was the most efficient for excellence to copy the piece. It was
noted that gypsum number III powder is white and after solidifying is has a Beige color.Gypsum number IV powder and solid is the same color tone pink only that solid is a darker
color. At the time of be poured into our plaster container number III and the water is that
it tends to absorb water quickly, has fairly quick thermal reactions, i.e., warming just
begins to solidify. Instead gypsum number IV, but in this case it was observed as gypsum
absorbed much more slowly the water and at the time of be poured into the container
that also warmed up but was a time after having poured and not as in the previous case
where heated much faster could be observed. The mixture of resin polyester had
something very particular should be mixed quickly and then be poured into the mold since
it tends to solidify very fast. The gel is in color and between coffee and purple, where
more resin color has to be more purple, this material can be broken easily by that must be
treated with care. The silicone has no problem pouring fast since it takes approximately 24
hours to solidify, but similarly if you want to more uniformity in the part should mix very
well and spread fast in the mold. Pink pastel-colored, it is very flexible and will not break if
it falls or is it sharply but this material if it can be cut. With the fiberglass should be a little
care can remain on clothing and this pica and it is very difficult to remove the clothes
after. The smell of resin mixed with fiberglass has a very strong smell that can cause
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dizziness or headaches that are must manage from afar and try not smell directly. Glass
fiber are little threads of white glass but mixed with the resin that solidifies take a brown.
QUESTIONS
¿Why solidifies the plaster with water?
"The gypsum or plaster stone is a mineral consisting of dehydrated calcium sulfate. In its crystal
structure there are two molecules of water by one of calcium sulfate. Submitted to roasting,
released part of the water of crystallization, resulting in plaster construction, which to be kneaded
with water, solidifies again and forge, reconstituting the original rock in its natural state on the
facing. Given its porous structure, setting plaster brings exceptional energy efficient properties.
"Their excellent qualities of insulation and hygrometric control make it an indispensable material
in modern construction techniques, using directly on trim and plaster, prefabricated partitions".
¿why solidifies the resin with catalyst?
To forge (is the process of hardening and loss of plasticity of concrete or cement mortar) require
the addition of an accelerator and a catalyst. The accelerator is the component that regulates the
setting reaction times is the catalyst which initiates the reaction, the combination creates a series
of radical free causing the chemical elements of the resin be linked, forming a network ever more
dense making, in a first phase, that it is gelling, and finallyto harden. To be applied on glass fiber, it
gives structure, hardness, body and strength. It is important to note that until the catalyst is not
incorporated, does not produce no reaction by what this component must always be the last in be
incorporated; you can leave prepared resin with Accelerator, pigments, loads and then catalyze it
at the time of use.
¿What is fiberglass?
The strict meaning of the phrase fiberglass refers to a kind of scrim made from tiny glass threads
interlaced between if generating a mesh or plot. Glass threads are obtained through the step,
industrial, liquid glass through a tough piece with small. Then allowed to solidify, making the final
product to remain with sufficient flexibility as to knit together it and form a mesh or fabric or cool.
Reinforced plastic is the result of mix mesh of glass with a resin, which initially liquid then solidify
and maintain the final form or that acquired molds. Characteristics of glass fiber are: excellent
thermal insulation, is inert to many substances including acids and is malleable, highly resistant.
¿Are kind of resins: thermoplastic or thermosetting?
Thermoset resins are resins, phenolic, urea resin, melamine resin, polyester resins, and episodic
resins. That is: they are malleable until heated, then left permanently hardened and do not change
their State even if submits them to the same heat a second time. Compact and hard, material
temperature affects them very little. Insoluble to most solvents. The most commonly used
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thermoplastic resins are polyethylene, polypropylene, polyvinyl chloride, polyester, polystyrene
and polycarbonate. With this material are manufactured toys, mechanical parts, and even helmets
for motorized. It is not soluble in water, but in alcohol and essential oils. Its main and best-known
property is that it melts when exposed to heat and becomes liquid. To cooling down solidifies, is
resistant to solvents, acids and alkalis. It also allows thermal and electrical insulation.
¿Problems with setting?
In general we did not have problems with the solidification of materials making it very fast. If it
was necessary to tie the molds with the gloves to be able to transport it while it solidified of
silicone. If we had a problem with the fiberglass since us it took much to dry the first cast and that
it was because in the resin mixture will add more or less of the necessary catalyst mek peroxide.
With resin polyester had a problem because we delay us in pouring it into the mold and dried,
therefore we had to expect that you dry well to be able to remove it from the container and
return to make the mixture to fill the mold.
¿What is the difference between plaster type III and type IV?
The difference that exists between plaster type III to type IV is that plaster type III, also known as
stone or coecal is used to obtain the master or positive models that do not require too harshly, at
the end of the setting have a compressive strength approximately 350 Kg/cm2; and instead type IV
also known as high strength plaster is used for master or positive models that require greater
hardness and resistance as well as a minimum setting expansion.
¿Why is the plaster heated?
It occurs because the manufacturing process it has lost molecules since it has been heated above
120-150 degrees Celsius. Then add water to make the mixture produces a chemical reaction of
molecules recovery lost.
¿Why heats resin?
The catalyst is an element in which the number of molecules of oxygen is in large proportion
mixed with metilcetiacetona, which is a non-flammable solvent. Resin, on the other hand has
added cobalt, which is an element of metal origin and the sole purpose is to react the molecules of
oxygen catalyst and mixed with the resin molecules and start to harden it. Without cobalt, these
molecules of oxygen is take too long to get rid of the metiletilacetona and make that is between
the molecules of resin which is what makes them hard to cross. Much catalyst means cobalt will
release too much oxygen, very hot, flammable gases mixed with smoke, which will not only
produce a resin with altered physical properties but that they will also possibly generate resin gets
hot in excess.
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CONCLUSIONS
It can be concluded that it must be mixed very well with the catalysts and the water materials and
these should be spread as soon as possible into the molds to prevent drying out and touch make
another mix.
The amount of water and catalyst in each mix must be exact since if it is not, mixing may take
much longer to solidify and its final characteristics may change making molds and the final pieces
are wrong.
So molds plaster number III, number IV and fiberglass don't stick to the original piece and so the
silicone, resin don't stick to the molds must be enough Vaseline but touch remove excess so well is
the copy of the piece.
The use of the clothes and old shoes is very good and necessary since it prevents staining clothes
or skin burn if any drops of these materials such as fiberglass that attaches easily to clothing.
It is better to prevent problems. He learned how to identify the main characteristics of some
elements such as the ceramic, hydrocarbons and polymers, with this quality you can choose the
suitable material for the piece to copy and learn the process of reaction when the element is
poured.
Resin polyester and catalyst have characteristics of hardening with good grip against a plaster cast,
is therefore that all skilled workers materials are these which have characteristics unique to a
moulds, excellent copy piece.
Despite all the restrictions that has the fiberglass and the damaging it can be to health it has very
important properties as good heat insulation, inert to acids, supports high temperatures and othercharacteristics which has given popularity in many industrial applications, for example, in the
construction and maintenance of buildings and in the automotive area.
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CIBERGRAFÍA/CIBERGRAFY
http://usuaris.tinet.cat/jaranda/Poliester_archivos/Page396.htm
http://www.ehowenespanol.com/propiedades-resina-poliester-hechos_107679/
http://www.slideshare.net/KATHARobles/parafina-10214542
http://es.wikipedia.org/wiki/Parafina
http://www.noviplast.com.ar/caucho%20de%20siliconas.htm
http://protesistadental.blogspot.com/2006/11/clasificacin-de-yesos_116395478531374938.html http://www.slideshare.net/GrupoIsep/clases-de-yesos-en-odontologa
http://www.algiss.es/QUIENESSOMOS/Paginas/yeso.aspx
http://www.mpcsa.mx/productosindex.php?Categoria=Resinas+y+Fibra+de+vidrio&Tipo=local
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http://www.monografias.com/trabajos/plastitermoe/plastitermoe.shtml#ixzz2xOhhkUNy
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ANNEXES.