MANUFACTURING

PROCESSES

ASSIGNMENT #2CASTING DEFECTS

&

REMEDIES

SUBMITTED BY:

Yashvinder Singh (111501)

Sahil (111502)

Section - H1

INTRODUCTION

Metal casting is one of the direct methods of manufacturing the desired geometry of component. The method is also called as near net shape process. It is one of the primary processes for several years and one of important process even today in the 21st century.

Out of the several steps involved in the casting process, moulding and melting processes are the most important stages. Improper control at these stages results in defective castings, which reduces the productivity of a foundry industry. Generally, foundry industry suffers from poor quality and productivity due to the large number of process

parameters, combined with lower penetration of manufacturing automation and shortage of skilled workers compared to other industries. Also, Global buyers demand defect-free castings and strict delivery schedule, which foundries are finding it very difficult to meet.

Casting process is also known as process of uncertainty. Even in a completely controlled process, defects in casting are found out which challenges explanation about the cause of casting defects. The complexity of the process is due to the involvement of the various disciplines of science and engineering with casting. The cause of defects is often a combination of several factors rather than a single one. When these various factors are combined, the root cause of a casting defect can actually become a mystery. It is important to correctly identify the defect symptoms prior to assigning the cause to the problem. False remedies not only fail to solve the problem, they can confuse the issues and make it more difficult to cure the defect. The defects need to be diagnosed correctly for appropriate remedial measures, otherwise new defects may be introduced. Unfortunately, this is not an easy task, since casting process involves complex interactions among various parameters and operations related to metal composition, methods

design, molding, melting, pouring, shake-out, fettling and machining. The proper classification and identification of a particular defect is the basic need to correct and control the quality of casting.

LIST OF DEFECTS

01. Shrinkage

02. Cold Shut

03. Mismatch

04. Blow holes

05. Pin Holes

06. Fin

07. Drop

08. Swell

09. Metal Penetration

10. Hot Tears

11. Porosity

12. Scabs

13. Hard Spots

14. Buckles\Rat Tails

15. Misrun

SHRINKAGE

Shrinkage cavity is a void on the surface of the casting caused mainly by uncontrolled and haphazard solidification of the metal.

4

Causes:

-inadequate and improper gating

-poor design of casting involving abrupt changes in thickness

-too high pouring temperature

Remedies:

-Use the suitable composition that is adjusted silicon and (1.80 to 2.10) or carbon equivalent (3.9 to 4.1) .Carry out proper ramming and maintain optimum pouring temperature and time.

Cold Shut

When two streams of molten metal approach each other in the mould cavity from opposite directions but fail to fuse properly, with the result of discontinuity between them, it is called a cold shut.

Causes:

-low temperature of molten metal

-improper gating system

-too thin casting sections

-slow and intermitted pouring

-improper alloy composition

-use of damaged pattern

Remedies:

- Smooth pouring with the help of monorail.

- Properly transport mould during pouring.

- Arrange proper clamping arrangement.

-providing appropriate pouring temperature.

Mismatch

It is a shift /misalignment between two mating surfaces or the top and bottom parts of the casting at the mould joint.

Causes:

-worn dowel in patterns made in halves.

-improper alignment of mould boxes due to worn out/ill fitting mould boxes.

Remedies:

- Properly arrange box warpage.

- Properly move boxes with pins.

- Properly clamp the boxes.

Blow Holes

Balloon-shaped gas cavities caused by release of mould gases during pouring are known as blow holes.

Causes:

-ramming is too hard.

-permeability is insufficient.

-venting is insufficient.

Remedies:

-moisture content of moulding sand should be controlled

-sand of appropriate grain size should be used.

-ramming should not be too hard.

-moulds should be adequately vented.

Pin Holes

Pin holes are tiny blow holes appearing just

below the casting surface.

Causes:

-sand with high moisture content.

-absorption of hydrogen/carbon monoxide gas in the metal.

-alloy not being properly degassed.

-steel is poured from wet ladles.

-sand containing gas producing ingredients.

Remedies:

-reducing the moisture content of moulding sand.

-increasing its permeability.

-employing good melting and fluxing practices.

-improving a rapid rate of solidification.

Fin

Fins are excessive amounts of metal created by solidification into the parting line of the mold

Causes:

-inadequately weighted sand as well as incorrectly assembled moulds and cores.

-over flexible bottom boards.

-loose plates and improper clamping of flasks.

Remedies:

-correct assembly of the mouldand cores used for casting.

Drop

Drop is an irregularly-shaped projection on the cope surface caused by dropping of sand.

Causes:

-low green strength of the moulding sand.

-low mould hardness.

-insufficient reinforcement of sand projections in the cope.

Remedies:

-moulding sand should have sufficient green strength.

-ramming should not be too soft.

Swell

Swells are excessive amounts of metal in the vicinity of gates or beneath the sprue

Causes:

-insufficient or soft ramming.

-low mould strength.

-mould not being adequately supported.

Remedies:

-sand should be rammed evenly and properly.

Metal Penetration

Penetration occurs when the molten metal flows between the sand particles in the mould. These defects are due to inadequate strength of the mold and high temperature of the molten metal adds on it.

Causes:

-low strength of moulding sand.

-large size of moulding sand.

-high permeability of sand.

-soft ramming.

Remedies:

-use of fine grain with low permeability.

-appropriate ramming.

Hot Tears

A hot tear is a fracture formed during solidification because of hindered contraction.

Causes:

-faulty casting design leading to excessive stresses at certain portions in the casting.

-very hard ramming.

-too much shrinkage of molten metal.

-incorrect pouring temperature.

-improper gates and risers.

-low flowability of molten metal.

-high sulphur content in molten metal.

Remedies:

-ramming should not be too hard.

-modification in pattern to take care of residual stresses.

Porosity

Porosity is pockets of gas inside the metal caused by micro-shrinkage during solidification.

Causes:

-dissolved hydrogen and sulphur dioxide in molten metal.

-excessive poring temperature.

-slow rate of solidification.

-high moisture content of the mould.

Remedies:

-maintenance of proper melting temperature.

-casting should be made to solidify quickly by using proper gating and risering.

-permeability of the mould should be increased.

-moisture content of mould should be kept low.

Scabs

Scabs are surface slivers caused by splashing and rapid solidification of the metal when it is first poured and strikes the mold wall

Causes:

-insufficient strength of mould and core.

-uneven mould ramming.

-lack of binding material in facing as well as core sand.

-Faulty gating.

-intense local heating due to slow running of molten metal over sand surface.

Remedies:

-appropriate ramming.

-improved gating system.

-addition of sufficient binders in facing and core sands.

Hard Spots

These spots are formed due to the local chilling by moulding sand which leads to the formation of white cast iron at those places, rendering them hard.

Causes:

--faulty metal composition.

-faulty casting design resulting in relatively more rapid cooling of certain spots.

Remedies:

-modification of casting design.

-modification of casting composition.

Buckles/Rat Tails

Rat tail or a buckle is a long, shallow, angular depression caused by expansion of the sand.

Causes:

-excessive mould hardness.

-lack of combustible additives in the moulding sand.

-continuous large surfaces on the casting.

Remedies:

-suitable addition of combustible additives to moulding sand.

-reduction in mould hardness.

-modifications in casting design.

Misrun

When the molten metal fails to fill the entire mould cavity before the metal starts solidifying , resulting in an incomplete casting, the defect is known as misrun.

Causes:

-low temperature of molten metal

-improper gating system

-too thin casting sections

-slow and intermitted pouring

-improper alloy composition

-use of damaged pattern

Remedies:

_ Smooth pouring with the help of monorail.

_ Properly transport mould during pouring.

_ Arrange proper clamping arrangement.

-providing appropriate pouring temperature.