1 Informe de Lab

8/11/2019 1 Informe de Lab

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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



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



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.



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.



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



Image 1. Molds with plaster number III.

Image 2.Silicone rubber mold

Image 3.Fiberglass mold.



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



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



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.



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.



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

http://www.slideshare.net/raecabrera/capitulo-4-materiales-compuestos-9247513

http://www.el-nacional.com/espacios/Resina-termoplastica-polimero-hogar_0_82193940.html

http://www.monografias.com/trabajos/plastitermoe/plastitermoe.shtml#ixzz2xOhhkUNy

http://cerezo.pntic.mec.es/rlopez33/tecno/tercero/plastico/contents/trmoest.html

ANNEXES.



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