Foundry Lab

FOUNDRY AND FORGING LAB

Syllabus 

 Compression. Tensile and shear Part A ( Sand Testing) tests on universal sand testing Testing of moulding and core sand machine     

Permeability test Hardness tests Sieve analysis Clay content test Moisture content test

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Part B (Foundry Practice) Use of foundry tools and other equipments Preparation of moulds using two moulding boxes

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Part C( Forging operations) Preparing minimum three forged models involving upsetting, drawing and bending operations. Estimation of length of the raw material

MANUFACTURING “The Process of Converting Raw Materials Into Products”

Manufacturing ? 

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Manufacturing in its broadest sense is the process of converting raw materials in to useful products It includes i) Design of the product ii) Selection of raw materials and iii)The sequence of processes through which the product will be manufactured

Manufacturing Processes Manufacturing Processes Casting

Machining

Forming

Joining

( Additive (Net shape ( Subtractive (Net shape secondary proces primary process) secondary process) secondary process)

Casting 

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Casting is the process of pouring molten metal in to a mould cavity of required shape & size and allowing for cooling It involves a series of operations i) Pattern making ii) Core making iii) Mould making iv) Melting v) Pouring vi) Cleaning

Types of casting Casting

onventional Methods Green sand mould Dry sand mould

Unconventional Methods

CO2 Moulding (Strong mould) Permanent (Metal mould)

Shell Moulding (Thinn mould)

Investment casting (Precision Centrifugal ( without core) Continuous Casting (Open)

Advantages & Disadvantages Advantages

Disadvantages

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Design flexibility

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Reduced costs

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Dimensional accuracy

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Versatility in production

Lot of molten metal is wasted in riser & gating Casting may require machining to remove rough surfaces

Machining 

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Machining of metal involves forcing of cutting tool through the excess material of the workpiece. The excess material is progressively separated from the workpiece in the form of chips to get required shape

Types of machining Machining Conventional

Turning by lathe m/c’s Grinding by grinding m /c’s

Unconventional EDM, ECM, EBM, LBM

Forming 

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Shaping of a component by the application of external forces Metal is deformed plastically under the action of externally applied forces

Types of forming Forming

Based on working temp Based on stress applied Based on energy used Cold Hot

Compression Tension Combined Shear

Conventional

Forging, rolling, drawing et

Unconventional Explosive forming, Electro hydraulic

Joining 

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In engineering practice none of the product can be made in a single process the products are assembly of many individual parts Joining is a general term covering many process like welding, brazing, soldering, riveting and other mechanical fastening methods

Types of joining Joining

emporary fastening

Permanent fastenin

Bolts & nuts

Riveted

Screws

Welding Fusion Solid state Soldering Brazing

Casting 

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Casting is one of the oldest manufacturing process and even today is the first step in manufacturing most of the products It is based on the property of a liquid to take up the shape of vessel containing it. Products ranging from a few mm to several m and a few grams to several tons

Foundry is the place where metal is melted and casting are produced

Similar to that of making ice cubes in a refrigerator

Casting Terms  

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Pattern- replica of the part to be cast Molding material- material that is packed around the pattern to provide the mold cavity Flask- rigid frame that holds the molding aggregate Cope- top half of the pattern Drag- bottom half of the pattern Core- sand or metal shape that is inserted into the mold to create internal features

Casting Terms     

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Mold cavity- combination of the mold material and cores Riser-additional void in the mold that provides additional metal to compensate for shrinkage Gating system- network of channels that delivers the molten metal to the mold Pouring cup- portion of the gating system that controls the delivery of the metal Sprue- vertical portion of the gating system Runners- horizontal Parting line- separates the cope and drag

Six Basic Steps of Casting 

Pattern making

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Core making

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Moulding

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Melting

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Pouring

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Cleaning & inspection

The Pattern A full‑sized model of the part, slightly enlarged to account for shrinkage and machining allowances in the casting 

Pattern 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  Plaster of paris  Wax –precision casting

Types of Patterns (a) solid pattern ( single piece) (b) split pattern ( Two piece) (c) match‑plate pattern (d) cope and drag pattern (e) Sweep pattern (f) Skeleton pattern

Core in Mold 

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A core consists of two portions: the body of the core and one or more extensions (called prints) Cores are used to create internal cavities. Core is a separate entity placed in a mould to produce a corresponding cavity – hole or undercut – in the casting Cores for sand casting are manufactured by packing specially prepared sand in core boxes Chaplets

Moulding The cavity in the sand mold is formed by packing sand around a pattern, then separating the mold into two halves and removing the pattern Major part of Moulding material in sand casting are – 85-90% silica sand (SiO2) 3-7% bonding material e.g., clay cereal etc. – 3-6% water Requirements of molding sand are: (e) Refractoriness (f) Cohesiveness (g) Permeability (h) Collapsibility –

Melting • Furnaces most commonly used in foundries:  − Cupolas 

− Direct fuel-fired furnaces

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− Crucible furnaces

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− Electric-arc furnaces

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− Induction furnaces

Pouring the Molten Metal 

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For this step to be successful, metal must flow into all regions of the mold, most importantly the main cavity, before solidifying Factors that determine success:   

Pouring temperature Pouring rate Turbulence

Sections of foundry Sand additives

Metal

Sand

Sand mixing & preparation Melting Handling molten metal

Moulding

Pouring Melting Section

Moulding Section Shaking out Finishing Heat treatment

Inspection & Testing

General layout of foundry Foundry store

Melting Furnaces Grinding

Sand Moulds ready for pouring Muller Inspection Bench

Core making

Preparation of sand mould SAND CASTING

Before any casting can take place a wooden pattern is made precisely. This is called pattern making and in industry this is a very skilful job. Any inaccuracy at this stage will result in the final cast being wrong or even failing.

Drag is placed inverted on the mould floor and pattern is placed at the center of the box

Preparation of sand mould

Special casting sand will soon be packed around the pattern for easy removal of pattern from parting powder is sprinkled over and around it. It stops the casting sand sticking to the pattern and pulling away with it when the pattern is finally removed from the Castingsand. sand is then shaken through a sieve (called riddled sand) so that only fine particles fall around the pattern. This is called facing sand and it must be fine so that detail on the pattern shows up on the final casting.

Preparation of sand mould

The drag is then packed with more casting sand and then ram it down firmly using a ramming tool. The tool has two ends, one is cylindrical and is used for general packing down of the sand. The other end is quite pointed and this can be used for packing sand close up to the pattern.

When the drag is packed fully it is levelled off (called ‘strickled off’) using a straight steel bar.

Preparation of sand mould

The entire drag and its contents are then turned over so that the base of the pattern can be seen

A top box called a ‘cope’ is then placed on top of the drag and locating pins are put in position so that the casting boxes cannot move sideways.

Preparation of sand mould

Sprue pins are positioned. One usually on the back of the pattern and the other to the side. These will eventually provide an entrance and exit for the molten aluminium when it is poured into the sand. The sand is packed/rammed into the cope in the same way as the drag.

Preparation of sand mould

The top box (the cope) is then removed and if all is well the cope with the sand inside should lift off the drag (bottom box) without the sand falling out. A small ‘gate’ is cut below the position of one of the sprue pins. This will help the molten metal to flow into the cavity left by the mould. Small tools are available or can easily be made to dig a variety of shapes in the casting sand. They are similar to small trowels

Preparation of sand mould

The pattern is removed using a ‘spike’. Before removing the pattern it is a good idea to gently tap the spike so that it loosens the pattern from the sand. It can then be lifted away from the casting box The cope (top casting (drag). box) is placed back on top of the drag and the locating pins put in position. Before this is done vents can be created using a thin piece of welding rod, pushing it through the sand . This allows gases to escape once the molten metal is poured.

Preparation of sand mould

The molten metal is poured with great care. The molten metal is poured down the hole left by the first sprue pin (now called the ‘runner’). As it runs down the runner it flows through the ‘gate’ cut by the trowel, into the cavity left by the pattern and up the riser (the hole left by the second sprue pin). The casting should be left for at leastWhen an hour before removed removal from the sand from the sand, the runner and riser are cut away and the casting is ready for machining

Sand Testing

Sand testing 

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Each foundry should draw out a minimum test programme which should be strictly followed for control of the sand system Controlling quality of sand in a foundry is very important as the quality of the casting depends on the quality of the mould sand The quality of the mould and core depends on the sand, binder, additives used & also on the percentage of each of the constituents Sand testing provides clues for improving casting quality Since molding sands and core sands are important in foundry operations, their control and testing is

Testing of mould & core sand        

1)Preparation of standard test specimen 2)Mould hardness test 3)Core hardness test 4)Moisture content test on foundry sand 5)Sieve analysis 6)Clay content test 7)Permeability test 8)Compression, shear test

1)Preparation of standard test specimen 

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The standard specimen is prepared using a standard sand rammer and specimen tube accessories.The specimen is rammed with three blows. The weight of the ram may be 63-72 N by weight. The ram is dropped from a height of 50mm . The specimen is rammed with three blows- This is the standard procedure. This operation that is ramming sand three times compacts the sand to a standard hardness

2)Mould hardness test

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Mold surface hardness is the resistance offered by the surface of a green sand mold

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An instrument for determining the mold surface hardness shall measure the depth of penetration in to the mold surface of a plunger having a load applied at a 90º angle

3)Core hardness to the mold surface test Core hardness is the resistance offered by the surface of a dry sand core

4)Moisture content test on foundry sand 

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In clay bonded sand some moisture is essential to develop working strength. The influence of moisture may be harmful if the proportion is not controlled within the definite limits. The strength of a sand is also influenced by its moisture content. It is therefore important to make certain that the sand contains the correct percentage of water Two methods i) simply by measuring the weight difference between the green sand and the dry sand, then calculating percentage of moisture = (W1-W2)/W1X100 ii) chemical method: by speedy moisture teller

5)Sieve analysis

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The grain size is expressed by number known as grain fineness number. For determination of grain fineness number of a given sand sample, a standard sieve set is used. The apparatus consists of eleven sieves mounted one above the other. The shaker vibrates the sieve by motor arrangement. So the sand placed at the top sieve gets screened and get collected on different sieves of different sizes depending up on the size of the grain. The sieve system is vibrated for some

6)Clay content test

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The necessary bonding strength for mouliding sand is clay, so that after ramming the mould doesn’t loose its shape. However as the quantity of the clay is increased, the permeability of the sand decreases. Clay is responsible for bonding the sand particles together. It influences strength permeability and other moulding sand properties. Known quantity moulding sand is taken and washed with water and NaOH. Then dried and reweighed The weight of clay is given by the difference

7)Permeability test Gases and water vapour are released in the mould cavity by the molten metal and sand.  If they do not find opportunity to escape completely through the mould, they will get entrapped and form gas holes or pores in the casting  The sand must therefore be sufficiently porous to allow the gases and water vapour to escape out.  This property of sand is referred to as permeability.  The apparatus has an arrangement which allows controlled amount of air to pass through a sand sample and the time taken for all the air to pass through the same is measured Permeability no = VH/PAT V= volume of air, H=height, P=pre 

8)Compression, shear test 

Strength tests have been devised to test the holding power of various bonding materials in green and dry sand

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The strength is governed by the amount of bonding materials The universal sand strength testing machine is used to test the strength of sand Compressive strength, shear strength, tensile stregth of the moulding sand is done on this G universal sandGstrength machine by replacing the different grippers Test machine gives direct reading

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Hand tools used in moulding In hand moulding processes, all the moulding operations, such as ramming the sand, placing and drawing the pattern, turning over the moulding boxes, etc, are performed by hand  A number of hand tools which are used by the molder to perform above mentioned operations are shown below 1)Bellow : A bellow is used to blow loose sand particles from the pattern and the mold cavity 

Hand tools used in moulding 2) Lifter or cleaner: It lifts dirt or loose sand from the mold. It is used for repairing and finishing the sand mold cavity

3)Heart & square: It is employed for finishing the mould cavity

4)Hand rammer:It is used for ramming the sand in molds

Hand tools used in moulding 5)Floor rammer: It is larger in size as compared to hand rammer. It is used for floor molding 6)Hand riddle:It consists of wire mesh fitted into a circular wooden frame. It is used for cleaning, removing foreign matter from sand

7)Sprue pin: It is tapered wooden rod which is placed in the cope to make sprue cavity.

Hand tools used in moulding 8) Trowels: used to finish flat surfaces of the mould, cut ingates, make joints or repair moulds

9)Smoothers and corner slics:They are employed to repair and finish corners, edges, round and flat surfaces

Hand tools used in moulding 9)Gate cutter: it is a shaped piece of sheet metal . It is used to cut the gate

10)Shovel : used to transfer moulding sand from store to place of use. Also used to mix and temper the moulding sand

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