A brief detail in shell molding.

1. MAHARISHI MARKANDESHWAR UNIVERSITY
SADOPUR, AMBALA
A
Seminar Report
on
SHELL MOLDING
Department of Mechanical Engineering
SUBMITTED TO: SUBMITTED BY:
Miss. Preeti Saini Pankaj Kumar
B. Tech. (Mech.)
7th Semester
75144042

2. CONTENTS
SR. NO. PARTICULARS PAGE NO.
01. Introduction 01
02. Process 03
03.
Properties & Considerations of manufacturing by shell
molding casting
05
04. Types of molds 06
05. Sand used for casting 07
06. Pattern materials 08
07. Binders used in sand casting for molding 13
08. Core ovens 14
09. Melting of metals 15
10. Defects in sand casting 16
11. Common defects in casting 17
12. Mechanicalmolding equipment 18
13. Advantages 22
14. Disadvantages 22
15. Application 22
16. Resins 23
17. References 25

3. 1
INTRODUCTION
Shell molding, also known as shell-mold casting, is an expendable mold casting process that uses a resin
covered sand to form the mold. As compared to sand casting, this process has better dimensional
accuracy, a higher productivity rate, and lower labour requirements. It is used for small to medium parts
that require high precision. Shell mold casting is a metal casting process similar to sand casting, in that
molten metal is poured into an expendable mold. However, in shell mold casting, the mold is a thin-
walled shell created from applying a sand-resin mixture around a pattern. The pattern, a metal piece in
the shape of the desired part, is reused to form multiple shell molds. A reusable pattern allows for higher
production rates, while the disposable molds enable complex geometries to be cast. Shell mold casting
requires the use of a metal pattern, oven, sand-resin mixture, dump box, and molten metal.
Shell mold casting allows the use of both ferrous and non-ferrous metals, most commonly using cast
iron, carbon steel, alloy steel, stainless steel, aluminium alloys, and copper alloys. Typical parts are
small-to-medium in size and require high accuracy, such as gear housings, cylinder heads, connecting
rods, and lever arms.
The shell mold casting process consists of the following steps:
Pattern creation - A two-piece metal pattern is created in the shape of the desired part, typically from
iron or steel. Other materials are sometimes used, such as aluminum for low volume production or
graphite for casting reactive materials.
Mold creation - First, each pattern half is heated to 175-370°C (350-700°F) and coated with a lubricant
to facilitate removal. Next, the heated pattern is clamped to a dump box, which contains a mixture of
sand and a resin binder. The dump box is inverted, allowing this sand-resin mixture to coat the pattern.
The heated pattern partially cures the mixture, which now forms a shell around the pattern. Each pattern
half and surrounding shell is cured to completion in an oven and then the shell is ejected from the
pattern.
Mold assembly - The two shell halves are joined together and securely clamped to form the complete
shell mold. If any cores are required, they are inserted prior to closing the mold. The shell mold is then
placed into a flask and supported by a backing material.
Pouring - The mold is securely clamped together while the molten metal is poured from a ladle into the
gating system and fills the mold cavity.

4. 2
Cooling - After the mold has been filled, the molten metal is allowed to cool and solidify into the shape
of the final casting.
Casting removal - After the molten metal has cooled, the mold can be broken and the casting removed.
Trimming and cleaning processes are required to remove any excess metal from the feed system and any
sand from the mold.
Examples of shell molded items include gear housings, cylinder heads and connecting rods. It is also
used to make high-precision molding cores.

5. 3
PROCESS
The first step in the shell mold casting process is to manufacture the shell mold. The sand we use for the
shell molding process is of a much smaller grain size than the typical greensand mold. This fine grained
sand is mixed with a thermosetting resin binder. A special metal pattern is coated with a parting agent;
(typically silicone), which will latter facilitate in the removal of the shell. The metal pattern is then
heated to a temperature of (175 °C-370 °C).
The sand mixture is then poured or blown over the hot casting pattern. Due to the reaction of the
thermosetting resin with the hot metal pattern a thin shell forms on the surface of the pattern. The
desired thickness of the shell is dependent upon the strength requirements of the mold for the particular
metal casting application. A typical industrial manufacturing mold for a shell molding casting process
could be 7.5mm thick. The thickness of the mold can be controlled by the length of time the sand
mixture is in contact with the metal casting pattern.
The excess “loose" sand is then removed leaving the shell and pattern.
The shell and pattern are then placed in an oven for a short period of time, (minutes), which causes the
shell to harden onto the casting pattern.
Once the baking phase of the manufacturing process is complete the hardened shell is separated from the
casting pattern by way of ejector pins built into the pattern. It is of note that this manufacturing
technique used to create the mold in the shell molding process can also be employed to produce highly
accurate fine grained mold cores for other metal casting processes.
Two of these hardened shells, each representing half the mold for the casting are assembled together
either by gluing or clamping.
The manufacture of the shell mold is now complete and ready for the pouring of the metal casting. In
many shell molding processes the shell mold is supported by sand or metal shot during the casting
process.
Sand mixed with
thermosetting resin
binder

6. 4
Shell and Pattern are baked in oven to harden shell mold
Metal Pattern
Sand mixed with
thermosetting resin
binder
Metal Pattern
(with shell)
Left over sand mixed
with thermosetting resin
binder

7. 5
Moulding Shell
PROPERTIES AND CONSIDERATIONS OF MANUFACTURING BY SHELL
MOLD CASTING
 The internal surface of the shell mold is very smooth and rigid. This allows for an easy flow of the liquid metal
through the mold cavity during the pouring of the casting, giving castings very good surface finish. Shell Mold
Casting enables the manufacture of complex parts with thin sections and smaller projections than green sand
molds.
 Manufacturing with the shell mold casting process also imparts high dimensional accuracy. Tolerances of
0.25mm are possible. Further machining is usually unnecessary when casting by this process.
 Shell sand molds are less permeable than green sand molds and binder may produce a large volume of gas as it
contacts the molten metal being poured for the casting. For these reasons shell molds should be well
ventilated.
 The expense of shell mold casting is increased by the cost of the thermosetting resin binder, but decreased by
the fact that only a small percentage of sand is used compared to other sand casting processes.
 Shell mold casting processes are easily automated
 The special metal patterns needed for shell mold casting are expensive, making it a less desirable process for
short runs. However manufacturing by shell casting may be economical for large batch production.

8. 6
TYPES OF MOLDS
Green-Sand Molds:
A green sand mold is very typical in casting manufacture, it is simple and easy to make, a mixture of
sand, clay and water. The term green refers to the fact that the mold will contain moisture during the
pouring of the casting.
 Possess sufficient strength for most casting applications
 Good collapsibility
 Good permeability
 Good reusability
 Least expensive of the molds used in sand casting manufacturing processes
 Moisture in sand can cause defects in some castings, -dependent upon the type of metal used
in the sand casting and the geometry of the part to be cast.
Dry-Sand Molds:
Dry-Sand molds are baked in an oven, (at 300F - 650F for 8-48 hours), prior to the casting operation, in
order to dry the mold. This drying strengthens the mold, and hardens its internal surfaces. Dry-Sand
molds are manufactured using organic binders rather than clay.
 Better dimensional accuracy and surface finish of cast part.
 More expensive manufacturing process.
 Manufacturing production rate of castings are reduced due to drying time.
 Distortion of the mold is greater
 Generally limited to the manufacture of medium and large castings.
Skin Dried Molds:
When sand casting a part by the skin-dried mold process a green-sand mold is employed, and its mold
cavity surface is dried to a depth of 1.25-2.5 mm (0.5 -1 inch). Drying is a part of the manufacturing
process and is accomplished by use of torches, heating lamps or some other means, such as drying it in
air.

9. 7
 Mold surfaces are dried
 Used for large castings
 Have higher strength than green-sand molds
 Better dimensional accuracy and surface finish
 Drawbacks:
 Distortion to the mold is greater
 Castings susceptible to hot tearing
 Slower production rate
SAND USED FOR CASTING
Silica sand (Si02) with additives (or silica mixed with other minerals) is used for sand casting.
Properties of a Sand Casting Mixture:
Moisture Content:
Moisture content affects the other properties of the mixture such as strength and permeability. Too much
moisture can cause steam bubbles to be entrapped in the metal casting.
Grain Size:
This property represents the size of the individual particles of sand.
• Small grain size yields better surface finish on the cast part, can be closely packed, have lower mold
permeability and enhances mold strength
• Large grain size is more permeable, to allow escape of gases during pouring
Shape of Grains:
This property evaluates the shape of the individual grains of sand based on how round they are. Less
round grains are said to be more irregular.
Irregular grain shapes tend to strengthen molds due to interlocking, compared to round grains which
provide a better surface finish).
Disadvantage of interlocking: tends to reduce permeability.

10. 8
Strength:
The strength is the ability of the sand casting mixture to hold its geometric shape under the conditions of
mechanical stress imposed during the casting process (ability to retain mold shape during packing and
pouring).
Permeability:
The ability of the sand mold to permit the escape of air, gases, and steam during the casting process
(gases liberated from the mold and solidifying metal).
Collapsibility:
The ability of the sand mixture to collapse under force (Or ability of the sand to be shake out).
Flowability:
The ability of the sand mixture to flow over and fill the casting pattern during the impression making
phase of the manufacturing process, more flowability is useful for a more detailed casting.
Refractory Strength:
During the pouring of the molten metal in sand casting manufacture, the sand mixture in the mold must
not melt, burn, crack, or sinter. The refractory strength is the ability of the mold sand mixture to
withstand levels of extreme temperature.
Reusability:
The ability of the sand casting mold sand mixture to be reused to produce other castings in subsequent
manufacturing operations
PATTERNS MATERIALS
 Wood - common material because it is easy to work, but it warps
 Metal - more expensive to make, but lasts much longer
 Plastic - compromise between wood and Metal
 A parting (release) agent is applied on the pattern surface in order to provide easy removal of the
pattern from the mold.

11. 9
 Patterns may be made as one-piece or multiple-piece (split, match plate).
 Patterns are commonly made larger than the casting because of the shrinkage effect. Also, due
to machining or finishing allowance. Shrinkage allowances are usually 1-2%.
 The pattern surfaces are never made perpendicular to the mold parting surface. The taper of the
pattern surface, which provides narrowing the mold cavity towards the mold parting surface, is
called draft. Draft allows easy removal of the pattern and the casting from the sand mold. The
draft angle is commonly 1-3%.
 Fillets: All sharp corners must be rounded to facilitate molding and filling.
Shrinkage allowance is the correction factor built into the pattern to compensate for the contraction of
the metal casting as it solidifies and cools to room temperature. The pattern is intentionally made larger
than the final desired casting dimensions to allow for solidification and cooling contraction of the
casting.
Because different shrinkage allowances must be used for the individual types of metals cast, it is not
possible to use the same pattern equipment for different cast metals without expecting dimensional
changes. For internal cavities the allowances should be negative.

12. 10
The machine finish allowance provides for sufficient excess metal on all cast surfaces that require
finish machining. The required machine finish allowance depends on many factors:
o the metal cast,
o the size and shape of the casting,
o casting surface roughness and surface defects that can be expected,
o the distortion and dimensional tolerances of the casting that are expected.
Draft allowance:
All the surfaces parallel to the direction in which the pattern will be removed are tapered slightly inward
to facilitate safe removal of the pattern. This is called ‘draft allowance’.
General usage:
External surfaces, internal surfaces, holes, pockets

13. 11
Core and core print
 Cores are used to make holes, recesses etc. in castings
 So where coring is required, provision should be made to support the core inside the mould
cavity. Core prints are used to serve this purpose. The core print is an added projection on the
pattern and it forms a seat in the mould on which the sand core rests during pouring of the
mould.
 The core print must be of adequate size and shape so that it can support the weight of the core
during the casting operation.
Distortion allowance (camber)
 Vertical edges will be curved or distorted
 This is prevented by shaped pattern converge slightly (inward) so that the casting after distortion
will have its sides vertical
 The distortion in casting may occur due to internal stresses. These internal stresses are caused on
account of unequal cooling of different sections of the casting and hindered contraction.
Prevention:
 providing sufficient machining allowance to cover the distortion affect
 Providing suitable allowance on the pattern, called camber or distortion allowance (inverse
reflection)

14. 12
BINDERS USED IN SAND CASTING FOR MOLDS, CORES
Clays:
Fire clay (kaolinite)
Southern bentonite (calcium montmorillonite)
Western bentonite (sodium montmorillonite)
Secondary mica clays (illite)
Oils:
Vegetables (e.g. linseed oil)
Marine animal (e.g., whale oil)
Mineral (used for diluting oils given above)
Synthetic resins, thermosetting:
Urea formaldehyde
Phenol Formaldehyde
Cereal binders made from corn:
Gelatinized starch (made by wet milling, contains starch and gluten)
Gelatinized corn flour (made by dry-milling hominy)
Dextrin (made from starch, a water-soluble sugar)
Wood –product binders:
Natural resin (e.g., rosin, thermoplastic)

15. 13
Sulfite binders (contain lignin, produced in the paper pulp process)
Water-soluble gums, resins, and organic chemicals
Protein binders (containing nitrogen):
Glue
Casien
Other binders:
Portland cement
Pitch (a coal-tar product)
Molasses (usually applied in water as a spray)
Cements (e.g., rubber cement)
Sodium silicate (water glass, CO2 hardening binders
CORE OVENS
Continuous ovens:
 Are those through which the core moves slowly on the conveyor
 Continuous loading and unloading is followed and hence the baking time is controlled by the
rate of travel of the conveyor.
 Generally same sized cores are used in this.
Batch type ovens:
 No movement of cores occur
 Electricity, gas, oil are used for heating and temperature is maintained uniformly and closely
controlled by suitable instruments.
 Temperature is of the order of 450oF and this depends upon the binder.
 heating elements are properly spaced to have uniform/same temperature distribution throughout
the container.
 replacing new air from outside is done through blowers so that moisture can be controlled.

16. 14
MELTING OF METALS
Gases in metals:
The gases in metal are important in deciding the defect free castings. In metal castings, gases may be
mechanically trapped, generated due to variation in their solubility at different temperatures and phases,
generated because of chemical reaction.
Gases generally present are: hydrogen, nitrogen
Hydrogen: Based on the solubility of hydrogen, metals are divided as
Endothermic (metals like Al, Mg, Cu, Fe, Ni), Exothermic (like Ti, Zr)
The solubility of hydrogen in various metals are shown in figure. Here solubility S is the volume of H2
gas absorbed by 100 g. of metal. The solubility of hydrogen in solid and liquid phases (pressure = 1 atm)
at solidus temperature is given in table.

17. 15
Hydrogen removal:
For non-ferrous metals, chlorine, nitrogen, helium or argon is used. For ferrous metals and Ni based
alloys, nitrogen cannot be used. They form nitrides that affect the grain size. In this case, carbon
monoxide is used.
Nitrogen removal:
Carbon monoxide can be used. A marked decrease in solubility of nitrogen in ferrous metal leads to
porosity in casting. Vacuum melting is used nowadays for preventing the solution of gases in metals.
DEFECTS IN SAND CASTINGS
Sand blow and Pinholes: defect consisting of a balloon-shaped gas cavity or gas cavities caused by
release of mold gases during pouring. It is present just below the casting top surface. Low permeability,
bad gas venting, and high moisture content of the sand mold are the usual causes.

18. 16
Sand wash: surface dip that results from erosion of the sand mold during pouring. This contour is
formed in the surface of the final cast part.
Scab: It is caused by portions of the mold surface flaking off during solidification and gets embedded in
the casting surface.
Penetration: surface defect that occurs when the liquid penetrates into the sand mold as the fluidity of
liquid metal is high, after solidifying, the casting surface consists of a mixture of sand and metal. Harder
ramming of sand mold minimizes this defect.
Mold shift: defect caused by displacement of the mold cope in sideward direction relative to the drag.
This results in a step in the cast product at the parting line.
Core shift: displacement of core vertically. Core shift and mold shift are caused by buoyancy of the
molten metal.
Mold crack: ‘fin’ like defect in cast part that occurs when mold strength is very less, and a crack
develops, through which liquid metal can seep.

19. 17
COMMON DEFECTS IN CASTING
Misruns: castings that solidify before completely filling the mold cavity. This occurs because of
(1) low fluidity of the molten metal,
(2) low pouring temperature,
(3) slow pouring,
(4) thinner cross-section of the mold cavity.
Cold Shuts: This defect occurs when two portions of the metal flow together but no fusion occurs
between them due to premature freezing.
Cold shots: forming of solid globules of metal that are entrapped in the casting. Proper pouring
procedures and gating system designs can prevent this defect.
Shrinkage cavity: cavity in the surface or an internal void in the casting, caused by solidification
shrinkage that restricts the amount of molten metal present in the last region to freeze. It is sometimes
called as ‘pipe’. Proper riser design can solve this problem.
Microporosity: network of small voids distributed throughout the casting caused by localized
solidification shrinkage of the final molten metal.
MECHANICAL MOLDING EQUIPMENT
Mechanization of molding operation is accomplished by using molding machines which are designed to
perform operations of compacting the mold sand and removing the pattern plate.
The common machines are:
 Jolt machine
 Squeezer machine

20. 18
 Jolt - squeeze machine
 Jolt - squeeze rollover machine
 Diaphragm molding machines
 Jolt rollover pattern-draw machine
 Sand slinger
Jolt-squeeze molding machine

21. 19
Contour-diaphragm molding
Incomplete Casting:
Sections of the casting did not form. In a manufacturing process causes for an incomplete casting could
be;
 insufficient amount of material poured,
 loss of metal from mold,
 insufficient fluidity in molten material,
 cross section within casting's mold cavity is too small,
 pouring was done too slowly,
 pouring temperature was too low.
Misrun, A casting that has solidified before completely filling mold cavity.
Incorrect Dimensions or Shape:
The casting is geometrically incorrect, this could due to;
 Unpredicted contractions in the casting during solidification.
 A warped casting.
 Shrinkage of the casting may have been miscalculated.
 There may have been problems with the manufacture of the pattern.
Mold Shift, defect occurs when cope and drag or molding boxes have not been properly aligned.
Diaphragm

22. 20
Inclusions:
Particles of slag, refractory materials sand or deoxidation products are trapped in the casting during
pouring solidification. The provision of choke in the gating system and the pouring basin at the top of
the mold can prevent this defect.
Penetration:
When fluidity of liquid metal is high, it may penetrate into sand mold or sand core, causing casting
surface to consist of a mixture of sand grains and metal. The coarser the sand grains more the metal
penetration.
Cleaning and Finishing:
A range of finishing processes is usually undertaken, these include:
Cleaning and inspection of casting:
 cleaning to remove residual sand, oxides and surface scale, often by shot or tumble blasting;
 Removal of excess metal or surface blemishes, by grinding, sawing or cutting;
 Rectification of defects by welding;
 machining;
 Heat treatment, (if needed);
 Priming, painting or application of a rust preventative coating.
Cleaning process:
 Tumbling barrels
Sand blasting and shot blasting
 Grinding
 Chemical treatment
Inspection Methods:
 Destructive inspection, various specimens are removed from various sections to test for
strength, durability, porosity, and any other defects.
 Non Destructive inspection, all methods which make possible the testing or inspection of a
material without impairing its future usefulness.

23. 21
 Visual inspection to detect obvious defects such as misruns, cold shuts, and severe surface
flaws.
 most widely used
 experienced inspector knows where are defects
 Dimensional inspection (measurements) to insure that tolerances have been met.
 Ultrasonic inspection,
 internal defects can be detected by introducing high -frequency sound waves in to the metal
casting.
 internal flaws and locations can be determined by analysing reflected sound waves
ADVANTAGES:
 Can form complex shapes and fine details,
 Very good surface finish, High production rate,
 Low labor cost,
 Low tooling cost,
 Little scrap generated.
 Can produce very large parts,
 Many material options,
 Scrap can be recycled,
 Short lead time possible.
DISADVANTAGES:
 High equipment cost,
 Poor material strength,
 High porosity possible,
 Poor tolerance,
 Secondary machining often required,

24. 22
APPLICATIONS:
 Cylinder heads,
 connecting rods
 Engine blocks
 manifolds,
 machine bases,
 gears,
 pulleys.
RESIN
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly
coniferous trees. Resins are valued for their chemical properties and associated uses, such as the
production of varnishes, adhesives and food glazing agents. They are also prized as an important source
of raw materials for organic synthesis, and as constituents of incense and perfume. Plant resins have a
very long history that was documented in ancient Greece by Theophrastus, in ancient Rome by Pliny the
Elder, and especially in the resins known as frankincense and myrrh, prized in ancient Egypt. These
were highly prized substances, and required as incense in some religious rites. Amber is a hard
fossilized resin from ancient trees. More broadly, the term "resin" also encompasses a great many
synthetic substances of similar mechanical properties (thick liquids that harden into transparent solids),
as well as shellacs of insects of the superfamily Coccoidea.
Other liquid compounds found inside plants or exuded by plants, such as sap, latex, or mucilage, are
sometimes confused with resin, but are not chemically the same. Saps, in particular, serve a nutritive
function that resins do not. There is no consensus on why plants secrete resins. However, resins consist
primarily of secondary metabolites or compounds that apparently play no role in the primary physiology
of a plant. While some scientists view resins only as waste products, their protective benefits to the plant
are widely documented. The toxic resinous compounds may confound a wide range of herbivores,
insects, and pathogens; while the volatile phenolic compounds may attract benefactors such as
parasitoids or predators of the herbivores that attack the plant. The word "resin" has been applied in the
modern world to nearly any component of a liquid that will set into a hard lacquer or enamel-like finish.
An example is nail polish, a modern product which contains "resins" that are organic compounds, but
not classical plant resins. Certain "casting resins" and synthetic resins (such as epoxy resin) have also

25. 23
been given the name "resin" because they solidify in the same way as some plant resins, but synthetic
resins are liquid monomers of thermosetting plastics, and do not derive from plants.
Resin of a pine
The resin produced by most plants is a viscous liquid, composed mainly of volatile fluid terpenes, with
lesser components of dissolved non-volatile solids which make resin thick and sticky. The most
common terpenes in resin are the bicyclic terpenes alpha-pinene, beta-pinene, delta-3 carene and
sabinene, the monocyclic terpenes limonene and terpinolene, and smaller amounts of the tricyclic
sesquiterpenes, longifolene, caryophyllene and delta-cadinene. Some resins also contain a high
proportion of resin acids. The individual components of resin can be separated by fractional distillation.
A few plants produce resins with different compositions, most notably Jeffrey Pine and Gray Pine, the
volatile components of which are largely pure n-heptane with little or no terpenes. The exceptional
purity of the n-heptane distilled from Jeffrey Pine resin, unmixed with other isomers of heptane, led to
its being used as the defining zero point on the octane rating scale of petrol quality. Because heptane is
highly flammable, distillation of resins containing it is very dangerous. Some resin distilleries in
California exploded because they mistook Jeffrey Pine for the similar but terpene-producing Ponderosa
Pine. At the time the two pines were considered to be the same species of pine; they were only classified
as separate species in 1853. Some resins when soft are known as 'oleoresins', and when containing
benzoic acid or cinnamic acid they are called balsams. Oleoresins are naturally occurring mixtures of an
oil and a resin; they can be extracted from various plants. Other resinous products in their natural
condition are a mix with gum or mucilaginous substances and known as gum resins. Many compound
resins have distinct and characteristic odors, from their admixture with essential oils. Certain resins are
obtained in a fossilized condition, amber being the most notable instance of this class; African copal and
the kauri gum of New Zealand are also procured in a semi-fossil condition. Solidified resin from which
the volatile terpene components have been removed by distillation is known as rosin. Typical rosin is a
transparent or translucent mass, with a vitreous fracture and a faintly yellow or brown colour, non-
odorous or having only a slight turpentine odour and taste. It is insoluble in water, mostly soluble in
alcohol, essential oils, ether and hot fatty oils, and softens and melts under the influence of heat, is not
capable of sublimation, and burns with a bright but smoky flame. This comprises a complex mixture of
different substances including organic acids named the resin acids. These are closely related to the
terpenes, and derive from them through partial oxidation. Resin acids can be dissolved in alkalis to form
resin soaps, from which the purified resin acids are regenerated by treatment with acids. Examples of
resin acids are abietic acid (sylvic acid), C20H30O2, plicatic acid contained in cedar, and pimaric acid,
C20H30O2, a constituent of galipot resin. Abietic acid can also be extracted from rosin by means of hot
alcohol; it crystallizes in leaflets, and on oxidation yields trimellitic acid, isophthalic acid and terebic

26. 24
acid. Pimaric acid closely resembles abietic acid into which it passes when distilled in a vacuum; it has
been supposed to consist of three isomers.
Uses
The hard transparent resins, such as the copals, dammars, mastic and sandarac, are principally used for
varnishes and adhesives, while the softer odoriferous oleo-resins (frankincense, elemi, turpentine,
copaiba) and gum resins containing essential oils (ammoniacum, asafoetida, gamboge, myrrh, and
scammony) are more largely used for therapeutic purposes and incense.
Resin in the form of rosin is applied to the bows of musical string instruments because of its ability to
add friction to the hair to increase sound quality.
Ballet dancers, as well as boxers in the old days, may apply crushed resin to their shoes to increase grip
on a slippery floor.
Resin has also been used as a medium for sculpture by artists such as Eva Hesse, and in other types of
artwork.
In the early 1990s, most ten-pin bowling ball manufacturers started adding resin particles to the covers
of bowling balls. Resin makes a bowling ball tackier than it would otherwise be, increasing its ability to
hook into the pins at an angle and (with correct technique) making strikes easier to achieve.
Resin is also used in stereolithography.

27. 25
REFERENCES
 https://www.google.co.in/
 https://en.wikipedia.org/wiki/Shell_molding
 http://www.custompartnet.com/wu/shell-mold-casting
 http://www.iitg.ernet.in/engfac/ganu/public_html/Metal%20casting%20processes_1.pdf
 http://nptel.ac.in/courses/112107077/module2/lecture10/lecture10.pdf
 http://thelibraryofmanufacturing.com/shell_mold_casting.html