Section 5

UNDERCUT

During welding of the final or cover pass, the exposed upper edges of the weld preparation tend to melt and to run down into the deposited material to fill the resultant grooves at the edge of the weld bead. The result is a groove that may be intermittent or continuous and parallel to the weld bead. _______may be caused by excessive welding, current, incorrect arc length, high speed, incorrect manipulation etc. This is called?

MACHINE TEARS

What are caused by dull cutters. They will show up as short, irregular lines at right angles to the direction of machining. They are the result of the tool removing metal more through a tearing action than through a cutting action?

STRESS CORROSION

Another serious problem occurs in situations where a component is under stress in a hostile or corrosive environment. Both factors contribute to the rapid growth of cracks?

RUNNER

A channel through which molten metal flows from one receptacle to another. The portion of the gate assembly that connects the down gate, sprue or riser with the casting. Parts of patterns and finished castings corresponding to the described portion of the gate assembly.

LAPS

A fin of surplus metal on the end of a billet may be caught and folded into the surface during subsequent rolling. The bent-over metal, while forced tightly against the main stock, will not bond to it. The resulting ____ is a possible initiation point for a fatigue crack?

CORROSION

A metal may interact chemically with its environment, producing a deterioration of the metal. This deterioration can be either uniform or localized. _____ can reduce the load-bearing area of a part and can cause the creation of pits, which act as stress raisers?

GREEN SAND UNDRIED SAND RISER

A reservoir of molten metal connected to the casting to provide additional metal to the casting, required as a result of shrinkage before and during solidification.

Cold Lap

A similar condition occurs with the failure of a stream of molten metal to unite with solid metal, such as pouring splash, chaplet etc. They can frequently be detected by visual inspection and look like a crack with a smooth and curved contour. If it is only a surface condition, it is frequently called a?

VENT

A small opening in a mold for the escape of gas.

CORE

A specially-formed material inserted in a mold to shape the interior or another part of a casting which cannot be shaped as easily by the pattern. In a ferrous alloy casting, the inner portion that is softer than the outer portion or case.

PIPING

As the casting solidifies, the metal contrasts if there is not an adequate supply of molten metal to the center of the casting. If, for some reason this supply is cut off, a cavity results. This central cavity is called "_____", and usually occurs in pure metals and alloys having narrow ranges of solidification temperatures?

MICROPOROSITY

As the metal cools and solidifies, small crystals, originally initiated at the wall of the mold, grow in the unrestrained direction, or toward the hot metal. The result is a columnar structure pointing toward the center of the casting. Branches may grow perpendicular to these columns and the result is the pine tree known as dendrite. As the branches of the dendrites link up, small pools of molten metal are isolated from the main supply, and, in freezing separately, contract to leave tiny voids or micropores?

INTER-GRANULAR CORROSION

Corrosion occurring preferentially at the grain boundaries. This is called?

CENTRIFUGAL CASTING

Cylindrical shapes may be made by pouring liquid metal into a permanent cylindrical mold while it is rotating rapidly. The liquid metal is forced against the inside of the mold by ______action, where it solidifies to produce a tube or cylindrical-shaped object such as a pipe. The wall thickness of the object will depend upon the amount of metal poured. When the metal has solidified, rotation is stopped and the specimen or "inner lining" removed. The ______ force acting on the metal while it is solidifying increases the density and strength of the part. The process is suited to the manufacture of pipes, tubes, bushings, linings etc., although it can also be used for more complicated shapes, where an entire mold, complete with cores, risers, gates etc. is spun about its axis. This is called the?

INCOMPLETE PENETRATION

Frequently, the root of a weld will not be adequately filled with weld metal and a void will be left, which may show on a radiograph as a continuous or intermittent dark line. This ____ _____may be caused by too small a root opening, too large an electrode, insufficient weld current, excessive welding speed, improper groove preparation etc. This type of defect is generally not acceptable and requires complete removal and re-welding. This is called?

GAS INCLUSIONS

Gas may be formed in molten metal for various reasons and may be trapped if there is insufficient time for it to escape before solidification. The trapped gas is usually in the form of round holes, termed porosity or blowholes, or of an elongated shape called piping or wormholes. Gas formation may be caused by chemical reactions during welding, high sulphur content in plate and/or electrodes, excessive moisture in the electrode or on base plate edges, too short an arc, incorrect welding current, wrong polarity. Piping or gas holes often occur in a straight line near the center of the weld bead and may be called linear porosity. This is called?

Inherent Discontinuity.

If a discontinuity introduced during initial production from the molten state, it is then termed an?

Processing Discontinuity.

If a discontinuity is caused during further processing, fabrication or finishing, it is called a ?

FORGING BURSTS OR CRACKS

If a material is forced at a temperature at which it does not have sufficient strength to withstand the high internal stress, a pattern of short, sharp internal ____may result. These___ or raptures are not normally visible on the surface are called?

HOT TEARS

If a section begins to shrink while still hot and there is not a sufficient supply of liquid metal, the resulting internal stress will tear the metal. This is because, while hot, the metal has relatively low strength. This is call?

Service Discontinuity

If discontinuity caused of the end product, due to the environment or load, or perhaps both- these are called?

PRIMARY INGOT CASTING

If the end use of the molten metal is not to be a part casting, the usual practice is to pour it into an____ mold. The ____ is usually either cylindrical or oblong in shape and is in a convenient size and shape for easy handling. It is destined for further processing. Defects associated with casting conditions are somewhat similar to those described under part castings. This is called?

COLD SHOTS

If the metal is poured too rapidly when casting, turbulent flow may result. One of the several problems this may cause is the splashing of the metal into the mold ahead of the pour. These splashes may solidify and will not bond properly into the casting. This unfused inclusion of metal is called a?

Cheek

In a large or complicated casting may require a three-part mold in which the center portion between the cope and drag is called the?

DEFECTS IN GAS WELDING

In the ____ ____ process, faults or defects can occur that remain in the completed weld. These are blowholes, incomplete fusion, slag inclusions, lack of penetration, porosity and cold shuts. Certain metals have such a high affinity for oxygen that oxides form on the surface almost as rapidly as they are removed. In oxyacetylene operations, these oxides are removed by means of fluxes. The proper control of the torch flame plays an important part in securing the most desirable deposit of weld metal. A neutral flame is commonly used for most welding operations, except for high carbon steel, when a reducing flame is used. When a bronze filler rod is used, a slightly oxidizing flame gives best results. The common metals and welding rods requiring fluxes are bronze, cast iron, brass, silicon bronzes, stainless steel and aluminum?

Silica Sand

In the case of Sand Castings, which is generally used as a mold material because of its refractory properties, low cost and availability?

Green Sand

In the case of Sand Castings, which sand is given plasticity by means of a clay binder that may be present in the sand or be added to it. Sufficient water is added to hold the mixture together?

Dry Sand Mold

In the case of Sand Castings, which sand is given plasticity in a similar fashion as the green sand mold is dried before the metal is poured into it?

Cope/Drag

In the case of making a mold, it is made in two halves, the upper portion being called the ___ and the bottom portion the ___?

COLD SHUTS

In the casting process, it is desirable to fill the void evenly, so that it cools uniformly. One technique is to have the mold filled from two or more channels, all leading into the same cavity. If, when the flows from two such channels come together, one of them is too cold or is covered by a heavy oxide film, fusion does not take place. The resulting separation is called a?

DIRECT CHILL CASTING

In this process, molten metal is poured into a short aluminum mold with a movable base, which is slowly lowered as the metal solidifies. Cooling is achieved by water directed in the mold and on the ingot as it is lowered. This method of casting (which is semi-continuous) permits a high degree of control of discontinuities such as cracks and inclusions, and the ingot so produced tends to be more homogeneous in structure than that produced in permanent molds. The main fabricating operations for converting a primary ingot are casting, forging, rolling and extruding. The products so produced may go directly into industrial or consumer goods, be further fabricated by such processes as wire drawing or tube drawing to alter their cross-section, or undergo further operations such as bending, roll forming or spinning, to alter their shape?

SHELL MOLDING

In this process, the mold material is made of a special type of sand, in which is mixed a powdered thermosetting plastic. The metal pattern used to produce the part is heated to about 200 degrees Celsius and the mold material is shaken evenly upon it to form a thin layer. The plastic hardens quickly to form a ____, which is then heated for a short time at a higher temperature. It is then removed from the pattern. The impressions in the sand mold will form one half of the mold cavity. A similar procedure is used to produce the other half of the mold. The two parts placed together complete the mold. The mold is usually backed up by the other material to provide added strength before casting. ____ _____ provides a part with high dimensional accuracy and good surface finish, which may eliminate subsequent machining or finishing. The production rate is relatively high and the process is suited to production of small parts that require close tolerance. This process is called?

DISCONTINUITIES

Indications which do not affect the performance of the part in its intended service should be referred to as?

OVERSTRESS

It may happen that a part is accidentally exposed to a load which is much greater than its design load. When this occurs, the component should be checked for plastic deformation or fracture, both of which may have occurred to relieve the high stress within the part. This is called?

LAMINATION

Large porosity, pipe and non-metallic inclusions in slabs or billets are flattened and spread out during the rolling and forging processes. These flattened discontinuities are known as?

DIE CASTING

Low melting point metals and alloys may be cast under pressure in a ____ ____machine that uses metal molds or dies to form the metal: liquid metal under gravity or other pressure is forced into the pair of dies, which come together automatically. The metal solidifies quite rapidly and the resultant casting is dropped or pushed down from the dies when they separate. The dies may be water cooled and the process made automatic. They are made with great care and produce parts with close dimensional tolerances and of a strong, fine grain structure. ____ ____ is a production operation used when a large number of similar parts is to be produced. This is called?

SHRINKAGE

Metal contracts or shrinks when changing from the liquid to the solid state, and defects will occur in a casting unless sufficient molten metal is available to feed it. Defects may take the form of cavities, branch-like tears, sponginess or the form of micro-shrinkage characteristics of magnesium or some copper base alloys

CHAPLET

Metal support for holding cores in place within sand molds are called?

CASTING DISCONTINUITIES

Most ______ ____ occur during the critical stages of pouring and solidification. These are called?

SLAG INCLUSIONS

Most weld inclusions contain ____ that has been trapped in the deposited metal during solidification. The ____ may come from the electrode coating or flux employed. The purpose of the flux is to remove impurities from the metal. If the metal fails to remain molten for a period sufficient to allow ____ to rise to the surface, some____ may be trapped within the metal. In multi-pass welding, insufficient cleaning and brushing of the bead between passes may not remove all the ___ coating. This may then be trapped in the metal by subsequent passes. Dirty and irregular surfaces, ripples or undercut will contribute to slag entrapment. ___ ____- are frequently associated with lack of penetration, poor fusion, oversize root faces, too narrow a groove and faulty electrode manipulation. This is called?

STRINGERS

Non-metallic inclusions in slabs or billets, that are thinned and lengthened in the direction of rolling, by the rolling process, are called?

FATIGUE

Repeated or fluctuating stresses, well under the tensile strength of a material, may lead to ____ cracks. Such cracks tend to form as microscopic fissures, then grow progressively. Current maintenance practice is to use nondestructive testing frequently enough to monitor fatigue crack growth, thus enabling the component to be removed from service before failure occurs. The rate of crack propagation is the factor which determines the inspection frequency?

SEAMS

Surface irregularities, such as cracks, on the slab or billet, are stretched out and lengthened during rolling and are called; ___ may also be caused by folding of the metal due to improper rolling._____ are surface discontinuities and on finished bars will appear as either continuous or broken straight lines. On round bar stock, they will appear as straight or slightly spiral lines, either continuous or broken?

Casting Methods

The casting of metals involves the pouring or injecting of molten metal into a cavity of a particular shape, where it is allowed to solidify. The cavity or mold may be an intricate shape, so that when the solidified metal is removed, a part is produced which, with or without further preparation, may be used for its designed purpose. This is known as?

SPRUE

The channel that connects the pouring basin with the runner. Sometimes used to mean all gates, risers, runners and similar scrap.

ROLLING

The ingot must be converted to an intermediate shape, which is more suitable for further processing. Common products of the intermediate ____ mill are the bloom, with a square end section, larger than 150mm, and the slab, which has a rectangular end section with a width always greater than tree times its thickness. Further ____ of these shapes is done to produce such products as rails, I-beam, plates and bar stock. The____ operation consists of passing the hot metal between two rolls, which through the application of pressure, reduce the size of the metal shape. By repeating this procedure through several sets of ___, with the metal always above the re-crystallization temperature, the original ingot is gradually formed into its final shape. In some cases, the material is ____ as cold as a finishing operation. This is called?

GATE

The portion of the runner in a mold through which molten metal enters the mold. Sometimes the generic term is applied to the entire network of connecting channels, which conduct metal into the mold cavity.

COPE

The upper or topmost section of a flash, mold or pattern?

HALIDE ATTACK

There is very little actual data on this subject, but, in principle, corrosion by halogens occurs in essentially the same fashion as in oxygen, sulphur or nitrogen attacks. Upon contact with the surface, the gas will oxidize the metal surface and form a halide layer. The scale produced will offer some measure of protection against further attack. Metal____ compounds, having very high vapor pressures, will become subject to a very rapid reaction if a critical temperature is exceeded. The scale will volatize and leave the metal surface exposed and unprotected.

PLATING OR PICKLING CRACKS

These cracks may occur if, during the _____cleaning process, the surface of the part is disturbed sufficiently to cause the release of internal pressures. The result is a fine pattern of cracks.

HOT TREAT CRACKS

These cracks will be found on a part that has been heat-treated, and are probably due to rapid quenching of parts with a non-uniform cross-section. Large cross-sections will cool more slowly than thin cross-sections. If the two are present in the same piece of material, the different cooling rates will set up internal stresses, which may cause cracking?

INTER-CRYSTALLINE CORROSION

This is a serious type of corrosion, created when the attack is against the grain boundaries from the metal surface. A crack-like discontinuity develops and such cracks can cause failure due to reduced cross-section. This problem arises when a difference in corrosion potential develops between the thin grain boundary zone and the adjacent grains. This potential difference may be caused by the difference in chemical composition between the two zones and can develop, as a result, in the migration of impurities and alloying elements to the grain boundaries. Sulphur and halogens attack titanium and nickel alloys to cause inter-granular corrosion.

INVESTMENT CASTING or PRECISION CASTING

This method can produce castings with close tolerances and smooth surfaces, which require little or no further machining or grinding. Several investment casting processes have been developed from the "lost-wax" process, which is still widely used. They involve the use of a wax or plastic pattern to form the mold cavity. This pattern is then removed by melting or evaporation, leaving the cavity into which the metal is poured. The wax or plastic is made in quantity from metal or plaster-of-paris dies. The patterns are then coated with a thick layer of slurry or "investment", which forms the final mold. The fine dimensional accuracy that can be obtained by the investment method makes this process ideal for complicated parts that are difficult or impossible to forge or machine. It is generally ideal for production of parts weighing less than 1 kg, although larger casting have been fabricated by this method. This is called?

CRACKS

This type of defect is always serious because of its propagating nature. Stresses set up during solidification of the metal will cause the metal to _____ and rapture. Hindrance to contraction of the metal due to mold design or casting design can provide the stresses that cause the rapture. The form of the rapture will depend upon the stage of solidification of the metal at the moment the rapture occurred?

INCLUSIONS

What are non-metallic materials, usually oxides or sulfides, within the sold metal structure. Their effect, which depends upon their number, size and dispersion, is due to their having a lower melting point than the metal, and to their relative brittleness. The low melting point can be harmful during hot working and welding processes; their brittleness can cause them to act as stress raisers, encouraging the formation of cracks under stress. In most cases, these defects occur near the surfaces as a skin effect. In some instances, however, the_____ may occur at the center of the casting, depending upon the flow of metal. They tend to be irregular in shape, rather than spherical or oval?

Forging Laps

What are the discontinuities caused by the folding of metal in a thin plate on the surface of the forging. They are irregular in contour?

BURN THROUGH

What area is that portion of the weld bead where excessive penetration has caused the weld pool to be blown into a pipe or vessel. It is caused by factors that produce excessive heat in one area, such as high current, slow rod speed, incorrect rod manipulation etc?

SEGREGATION

What is a complex phenomenon that results when one or more alloying elements are not properly diffused and concentrated in certain areas. Because alloys solidify over a temperature range, the first material to solidify (at high temperature) will be of a different composition that that which solidifies at the low end of the range. This may result in a non-uniform distribution of the alloying elements, and may have serious consequences through the effect on the mechanical properties of the alloy.

Micro-Shrinkage

What is a discontinuity peculiar to magnesium castings but is not a true shrinkage porosity. The voids are the most definite, compared to those due to shrink porosity in aluminum and tend to join up in a continuous network. The types of micro-shrinkage are often defined as being of the feathery or sponge type. An inter-dentritic type of shrinkage found in tin bronze castings is also called?

ROOT CRACKS

What is caused by high constraint, poor fit-up, poor penetration, shallow and wide beads, low plate temperature and high carbon, high alloy weld metal. Upon cooling, the weld metal and adjacent heated zone begin to contract and shrink in length, width and height. Because of the restraining action provided by the surrounding cold metal, the hot weld metal is put under tension. As the weld metal cools, it loses ductility so that the tendency to crack increases continuously, all the way down to ambient temperature?

Shrinkage Porosity or Sponge

What is caused when there is an insufficient supply of molten metal at a certain area, which results in a lacy or honeycombed dark area on a radiograph. The shrinkage voids are of irregular outline, as distinct from the round or elongated void of gas porosity?

HOT CRACKS

What is fostered by high joint rigidity, a concave weld contour (especially if the bead is wide and shallow), a high carbon content and possibly a high sulphur or silicon content. This type of crack may depend to a large extent upon the geometry of the joint. This is especially true if the contour of the bead is affected by the design of the joint?

DEFECTS

What is it called when a discontinuity indications are judged unacceptable to specifications criteria?

Welding

What is the process of joining two or more pieces of material, often metallic, by a localized coalescence or union, across an interface. The ____ process usually involves complex physical and chemical phenomena, varying with the nature of the weld strength, without deterioration of material properties. Adequate design and control of _____processing are best achieved through careful consideration of the basic physical and metallurgical reactions involved in the formation of ____. This is called?

MACHINING

What is the removal of metal by the action of a sharp cutting tool. There are various types of cutting tools, manners of tool movement, work movement and equipment configurations. This is one of the final processes to which a part is exposed, and the result is a smooth shiny surface. Because _____ is done on the surface of the material, any defects produced would be surface defects.This is called?

FORGING

What is the working of metal into a useful shape by hammering or pressing, and is the oldest of the forming processes. Most ____operations are carried out hot, although some metals are cold-____. The hot working of metals in the _____ process results in an improvement in the mechanical properties. This method of shaping is therefore used in the manufacture of parts requiring good mechanical properties. Improvements in the mechanical properties result from: A general consolidation of the metal and closing of gas and contraction cavities by means of mechanical pressure. A refinement in the crystal structure. An interruption in the continuity of inter-granular concentrations of impurities and inclusions. _____ is done on either a hammer or a press. A horizontal press (_____machine) is used in certain instances for_____ small parts; otherwise _____ machines are of vertical type, the lower die of which is fixed, while the upper die is movable, being carried on a vertical ram. In the case of hammers, the die is raised mechanically, and the blow is struck by the die falling freely. With presses, force is used to raise and lower the die and the metal is worked by slow, steady pressure. ____ is not only employed to produce parts of a shape that canned be rolled, but also for parts of simple uniform shape, round or rectangular, when theses are large or when the quantity required is too small to warrant a roll set up. Tool steels are often____with a view to improving their properties. ______ may be considered under two categories: Where the working surface of the dies is flat or of uniform curved contour, and shaping is done by manipulation, using tools or simple shape. This is called "open-die" _____. Where impression dies are used and the metal is shaped by being forced into the die impressions. This is called "closed-die" _____. In the first category are ____ of simple round or rectangular cross-section, and ____ of more complicated shape, which are so large that the "sinking" of closed dies would be impractical or too costly. Small _____ of complicated final shape may be rough____ on simple dies and then machined to final form if the number required is too small to justify the cost of an impression die. In this category, also, are hollow ____ parts. For these, the center metal of the rough piece of proper size is either machine out cold (trepanned) or it is punched out using suitable dies on a press. The part is then forged on a mandrel, passing through the center hole and supported at both ends so that the mandrel acts as the bottom die. In closed die _____on a hammer or vertical press, the lower die has an impression corresponding to one half of the part to be made, while the upper die has an impression corresponding to the other. But more commonly, they incorporate a series of impressions in which the part is successively shaped to final. Closed die _____ is commonly known as "drop _____." Around the impressions, the dies are shaped to provide space for the excess stock, as it is not practical to have exactly the amount of metal required to fill the impressions. The excess metal that is forced into this space is referred to as "flashing" or "flash." After ______, this is trimmed off in suitable dies. The closed die forging business is so competitive that the losses in trim scrap provide one of the most important areas for economy. The hot _____ process whereby bolts, for example, are headed, is referred to as "hot upset_____" or "hot heading." In this process, a bar of uniform cross-section is gripped between grooved dies and pressure is applied on the end in the direction of the axis of that bar by means of a heading tool. The metal flows under the applied pressure and fills the cavity between the dies. _____ is only one of the processes carried out with the material at a temperature above its re-crystallization temperature. The re-crystallization temperature is defined as the temperature at which the deformed (or heavily stressed) grains within the structure spontaneously reform into uniform stress-free grains. This is called?

Shrinkage Cavities

What occur usually at hot spots in the castings. They may be associated with feeding heads such as risers and, in such instances, are often referred to as "pipes." A type of shrinkage characteristic of the more dense metals or alloys consists of long string-like voids that may run roughly parallel to each other or intertwine in a branch-like network. The network may occur in bands within the metal, often near its center, and may be referred to as "centerline shrinkage." It is often hard to differentiate between severe, branch-like shrinkage and hot tears.

LACK OF FUSION

What occurs at weld interfaces, where adjacent layers of metal, or the base metal and weld metal, fail to fuse properly due to a very thin layer of oxide that forms on the metal surfaces. It is usually caused by failure to raise the temperature of the base metal or previously-deposited weld metal high enough to allow any oxide layers, slag impurities, etc. to rise to the surface?

UNDER BEAD OR HARD CRACKING

When ___ or ___ ___ occurs it invariably does so in the coarse grains of the heat-affected zone of the steel. It is attributed to the effect of dissolved hydrogen released from the electrode or from the solidifying metal. This can often be avoided by preheating or by use of basic electrodes?

CRATER CRACKS

When a welding arc is broken, a shrinkage crater will form if inadequate molten metal is available to fill the arc cavity. Arc craters are often the site of weld defects because the last metal to solidify freezes under a high degree of constraint and may exhibit segregation. These conditions can produce hot cracking and subsequent service failures. This is known as?

GAS CAVITIES-POROSITY

When gas is developed during the pouring of a metal casting and cannot escape through the mold itself or through the risers or other outlets, it may be trapped in the molten metal. It may be formed by release from the molten metal itself, from the green sand mold, from water vapour or merely by turbulence caused when pouring the metal?

GRINDING CRACKS

______ the surface of a part will cause the surface to heat up. If a coolant is not used, excessive heating and cooling of the surface may result in fine sharp cracks, which occur at right angles to the direction of ____?

Gas holes (blow holes)

are caused by air, mold or core gases and water vapor being wrapped in the casting, usually on the cope side, during solidification. They occur singly or in clusters and appear as smooth, round, elongated or oval shapes of varying size. Sometimes an extremely long _______ appears like a shrinkage cavity, although it differs from a shrink in that the ends of the ____ _____ are smooth and round?

Cold cracks

begin at the surface and their presence can often be verified by visual inspection?

Gas porosity

is a discontinuity that is caused by dissolved gases in the molten metal that become trapped in the solid casting. The size and the amount vary with the gas content of the metal and the rate of solidification of the casting. ____ _____in the form of small pockets or voids appears as round, irregular or elongated shapes that occur over large areas, if not over the entire casting?

Plating

what is a part that is done to protect it from its environment, to protect the surface against wear, or to increase its attractiveness. There are many types of _____ that can be applied, just as there are many ways of applying them. An important part of the plating process is the cleaning or pickling, which precedes the surface treatment. This is done in a chemical bath, and it is this phase which gives rise to most_____ discontinuities?