sand casting steps

7/31/2019 Sand Casting Steps

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SAND CASTING STEPS


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Advantages of sand casting


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Low cost of mold materials and equipment.

Large casting dimensions may be obtained.

Wide variety of metals and alloys (ferrous and non-ferrous) may be cast (including high

melting point metals).

Disadvantages of sand casting

Rough surface.

Poor dimensional accuracy.

High machining tolerances.

CoarseGrain structure.
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This process takes advantage of the lowboiling point of foam to simplify the investment

casting process by removing the need to melt the wax out of the mold
http://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Boiling_point


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LOST FOAM CASTING STEPS


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For liner also the same procedure:


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Centrifugal casting

Centrifugal casting is a method of casting parts having axial symmetry. The method involves

pouring molten metal into a cylindrical mold spinning about its axis of symmetry.

The mold is kept rotating till the metal has solidified.

As the mold material steels, Cast irons, Graphite or sand may be used.

The rotation speed of centrifugal mold is commonly about 1000 RPM (may vary from 250 RPM to

3600 RPM).

A centrifugal casting machine is schematically presented in the picture:

Centrifugal casting process

Mold preparation

Pouring

Cooling

Casting removal


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Finishing

Mold preparation

The walls of a cylindrical mold are first coated with a refractory ceramic coating, which

involves a few steps (application, rotation, drying, and baking).

Once prepared and secured, themold is rotated about its axis at high speeds (300-3000

RPM), typically around 1000 RPM.

Pouring

Molten metal is poured directly into the rotating mold, without the use of runners or a

gating system.

The centrifugal force drives the material towards the mold walls as the mold fills.

Cooling

With all of the molten metal in the mold, the mold remains spinning as the metal cools.

Cooling begins quickly at the mold walls and proceeds inwards.

Casting removal

After the casting has cooled and solidified, the rotation is stopped and the casting can be

removed.

Finishing

While the centrifugal force drives the dense metal to the mold walls, any less dense

impurities or bubbles flow to the inner surface of the casting.

As a result, secondary processes such as machining, grinding, or sand-blasting, are

required to clean and smooth the inner diameter of the part.
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A cylinder liner is a

cylindrical part to be fitted into an engine block to form a cylinder.

Formation of sliding surface

The cylinder liner, serving as the inner wall of a cylinder, forms a sliding surface for

the piston rings while retaining the lubricant within.


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The most important function of cylinder liners is the excellent characteristic as sliding

surface and these four necessary points.

(1)High anti-galling properties

(2)Less wear on the cylinder liner itself

(3)Less wear on the partner piston ring

(4)Less consumption of lubricant

Bearing bushes

Piston bearings


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A piston ring is a split ring that fits into a groove on the outer diameter of apiston in

a reciprocating engine such as an internal combustion engineorsteam engine.

The three main functions of piston rings in reciprocating engines are :

Sealing the combustion/expansion chamber.

Supporting heat transfer from the piston to the cylinderwall.

Regulating engine oil consumption.

Fly wheel


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A flywheel is an inertial energy-storage device.

It absorbs mechanical energy and serves as a reservoir, storing energy during the period

when the supply of energy is more than the requirement and releases it during the period

when the requirement of energy is more than the supply

The Basic Permanent Mold Process

Permanent mold casting (gravity die casting) is a casting process involving pouring a molten

metal by gravity into a steel (orcast iron) mold.

The permanent mold casting is similar to the sand casting process . In distinction from sand molds,which are broken after each casting a permanent mold may be used for pouring of at least one

thousand and up to 120,000 casting cycles with the rate 5-100 castings/hour.

Manufacturing metal mold is much more expensive than manufacturing molds forSand

casting orinvestment casting process mold. Minimum number of castings for profitable use of a

permanent mold is dependent on the complexity of its shape.

Ferrous and no-ferrous metals and alloys are cast by the permanent mold casting

process: Aluminum alloys, Copper alloys, Magnesium alloys, zinc alloys, steels and Cast irons.

Permanent mold casting process

Design aspects of permanent mold casting

Advantages and disadvantages of permanent mold casting
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Permanent mold casting process

The interior surfaces of the two parts (cope and drag) of a permanent mold are coated with

a thin ceramic coating. The mold is preheated before coating to 300-500F (150-260C).

The cores are inserted and installed in the mold assembly.

The mold is closed.

The molten metal is poured into the mold.

After the casting has solidified and cooled down to the desired temperature the mold is

opened and the casting is withdrawn from it.

The gating system is cut away from the casting.

The finish operations are carried out.

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Design aspects of permanent mold casting

Permanent molds are made ofCarbon steels, grey cast irons, Graphite (for

casting steels and Cast irons) orbronze.

Since the metallic mold of a permanent casting expands when it is filled with a molten

metal and then both the casting and the mold shrinks during cooling the shrinkage allowances

taken in the permanent mold design are smaller than those in the Sand casting.

External cooling (by water or air) may be used for creating desired solidification direction

and reducing shrinkage defects and internal stresses.

Parts of 0.4 lb (0.1 kg) to 150 lb (70 kg) may be cast.

The section thickness of permanent mold casting may vary in the range 0.1 - 2 (2.5-50

mm).

The dimensional tolerances are 0.015-0.06 (0.4-1.5 mm) depending on the casting section

thickness.

Allowances of 0.01-0.03 (0.25-0.75 mm) are taken for the dimensions crossing the parting

line of the mold.

The draft angle is commonly 1-3%.

Permanent cores are commonly used for permanent mold castings, however if a casting has

cavitys shape not allowing a withdrawal of the core it is made of chemically bonded sand or

other materials used for preparation of expendable cores. New consumable cores are added
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after each pour. The process combining permanent mold and consumable parts (cores) are

called semi-permanent casting.

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Advantages and disadvantages of permanent mold casting

Advantages of permanent mold casting process are determined by relatively high cooling rate

caused by solidification in metallic mold:

Bettermechanical properties.

Homogeneous grain structure and chemical composition.

Low shrinkage and gas porosity.

Good surface quality: 40-250 inch (1-6 m) Ra.

Low dimensional tolerances: typically about 0.04 (1 mm}.

Little scrap process.

Disadvantages ofpermanent mold casting:

High cost of the molds.

Limitations in casting of high melting point metals into metallic molds.

Intrinsic and complex shapes can not be cast.

Large parts can not be cast.
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Pressure Die Casting

Pressure die casting is a quick, reliable and cost-effective manufacturing process for production of

high volume, metal components that are net-shaped have tight tolerances. Basically, the pressure

die casting process consists of injecting under high pressure a molten metal alloy into a steel mold

(or tool). This gets solidified rapidly (from milliseconds to a few seconds) to form a net shaped

component. It is then automatically extracted.

Advantages of Pressure Die Casting :

Lower costs compared to other processes.

Economical - typically production of any number of components from thousands to

millions before requiring replacement is possible.

Castings with close dimensional control and good surface finish


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Castings with thin walls, and therefore are lighter in weight

High Pressure Die Casting

Here, the liquid metal is injected with high speed and high pressure into the metal mold. The basic

equipment consists of two vertical platens. The bolsters are placed on these platens and this holds

the die halves. Out of the two platens, one is fixed and the other movable.

High Pressure Die Casting Process

This helps the die to open and close. A specific amount of metal is poured into the shot sleeve and

afterwards introduced into the mold cavity. This is done using a hydraulically-driven piston. After

the metal has solidified, the die is opened and the casting eventually removed.

Types of High Pressure Die Casting:
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Both the processes are described below. The only difference between the two processes is the

method being used to inject molten metal into the die.

Hot Chamber Process

The hot-chamber process is applicable only for zinc and other low melting point alloys that does

not affect and erode metal pots cylinders and plungers.

The basic components of a hot-chamber diecasting machine and die are illustrated below:

Types of Pressure Die Casting

Depending upon the pressure used, there are two types of pressure die casting namely High

Pressure Die Casting and Low Pressure Die Casting. While high pressure die casting has

wider application encompassing nearly 50% of all light alloy casting production. Currently

low pressure die casting accounts for about 20% of the total production but its use is

increasing. High pressure castings are must for castings requiring tight tolerance and

detailed geometry. As the extra pressure is able to push the metal into more detailed

features in the mold. Low pressure die casting is commonly used for larger and non-critical

parts.

However, the machine and its dies are very costly, and for this reason pressure die casting

is viable only for high-volume production.

HOT CHAMBER DIE CASTING PROCESS

Hot chamber machines are used primarily for zinc, copper, magnesium, lead and other low

melting point alloys that do not readily attack and erode metal pots, cylinders and plungers.

The injection mechanism of a hot chamber machine is immersed in the molten metal bath

of a metal holding furnace.

The furnace is attached to the machine by a metal feed system called a gooseneck.


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As the injection cylinder plunger rises, a port in the injection cylinder opens, allowing

molten metal to fill the cylinder.

As the plunger moves downward it seals the port and forces molten metal through the

gooseneck and nozzle into the die cavity.

After the metal has solidified in the die cavity, the plunger is withdrawn, the die opens and

the casting is ejected.

COLD CHAMBER DIE CASTING PROCESS

Cold chamber machines are used for alloys such as aluminum and other alloys with high

melting points.

The molten metal is poured into a "cold chamber," or cylindrical sleeve, manually by a

hand ladle or by an automatic ladle.


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A hydraulically operated plunger seals the cold chamber port and forces metal into the

locked die at high pressures.

Low Pressure Die Casting

High quality castings, of aluminium alloys, along with magnesium and other low melting point

alloys are usually produced through this process. Castings of aluminium in the weight range of 2-

150 kg are a common feature.

The process works like this, first a metal die is positioned above a sealed furnace containingmolten metal. A refractory-lined riser extends from the bottom of the die into the molten metal.

Low pressure air (15 - 100 kPa, 2- 15 psi) is then introduced into the furnace. This makes the

molten metal rise up the tube and enter the die cavity with low turbulence. After the metal has

solidified, the air pressure is released . This makes the metal still in the molten state in the riser

tube to fall back into the furnace. After subsequent cooling, the die is opened and the casting


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extracted.

With correct die design it is possible to eliminate the need of the riser also. This is because of the

directional freezing of the casting. After the sequence has been established, the process can be

controlled automatically using temperature and pressure controllers to oversee the operation of

more than one diecasting machine.

Casting yield is exceptionally high as there is usually only one ingate and no feeders.

Low Pressure Die Casting Process

Application of Pressure Die Casting

Automotive parts like wheels, blocks, cylinder heads, manifolds etc.

Aerospace castings.

Electric motor housings.

Kitchen ware such as pressure cooker.


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Cabinets for the electronics industry.

General hardware appliances, pump parts, plumbing parts.

sand casting steps

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