The responsibility of a contract testing laboratory in meeting these requirements is equivalent to that of a manufacturing firm. Products purchased outside but tested in house. Contract firms performing testing on such products.
The result is not necessarily OOS but does not look like a typical data point. The investigation should be thorough, timely, unbiased, well-documented, and scientifically sound. When evidence of laboratory error remains unclear, a full-scale OOS investigation should be conducted by the manufacturing firm to determine what caused the unexpected results.
Quality Control Unit QA conducts the investigation. It is the simplest form of the pattern. Typical single piece pattern is shown in Fig. Two-piece or split pattern: When solid pattern is difficult for withdrawal from the mold cavity, then solid pattern is split in two parts. Split pattern is made in two pieces which are joined at the parting line by means of dowel pins. The splitting at the parting line is done to facilitate the withdrawal of the pattern.
A typical example is shown in Fig. Single Piece Pattern Fig. Molding sands may be of two types namely natural or synthetic. Natural molding sands contain sufficient binder. Binder In general, the binders can be either inorganic or organic substance. The inorganic group includes clay sodium silicate and port land cement etc. Binders included in the organic group are dextrin, molasses, cereal binders, linseed oil and resins like phenol formaldehyde, urea formaldehyde etc. Organic binders are mostly used for core making.
Among all the above binders, the bentonite variety of clay is the most common. However, this clay alone cannot develop bonds among sand grins without the presence of moisture in molding sand and core sand. Some common used additives for enhancing the properties of molding and core sands are discussed as under. Coal dust: Coal dust is added mainly for producing a reducing atmosphere during casting.
Corn flour: It belongs to the starch family of carbohydrates and is used to increase the collapsibility of the molding and core sand 3.
Dextrin: Dextrin belongs to starch family of carbohydrates that behaves also in a manner similar to that of the corn flour. It increases dry strength of the molds. Sea coal: Sea coal is the fine powdered bituminous coal which positions its place among the pores of the silica sand grains in molding sand and core sand 5. Wood flour: This is a fibrous material mixed with a granular material like sand; its relatively long thin fibers prevent the sand grains from making contact with one another.
The clay and water furnish the bond for green sand. It is fine, soft, light, and porous. Dry sand: Green sand that has been dried or baked in suitable oven after the making mold and cores, is called dry sand. It possesses more strength, rigidity and thermal stability. Loam sand: Loam is mixture of sand and clay with water to a thin plastic paste. Facing sand: Facing sand is just prepared and forms the face of the mould.
It is directly next to the surface of the pattern and it comes into contact molten metal when the mould is poured. Initial coating around the pattern and hence for mold surface is given by this sand. This sand is subjected severest conditions and must possess, therefore, high strength refractoriness. Backing sand: Backing sand or floor sand is used to back up the facing sand and is used to fill the whole volume of the molding flask.
Parting sand: Parting sand without binder and moisture is used to keep the green sand not to stick to the pattern and also to allow the sand on the parting surface the cope and drag to separate without clinging 7. Core sand: Core sand is used for making cores and it is sometimes also known as oil sand.
This is highly rich silica sand mixed with oil binders such as core oil which composed of linseed oil, resin, light mineral oil and other bind materials. Refractoriness: Refractoriness is defined as the ability of molding sand to withstand high temperatures without breaking down or fusing thus facilitating to get sound casting.
It is a highly important characteristic of molding sands. Refractoriness can only be increased to a limited extent 2. Permeability: It is also termed as porosity of the molding sand in order to allow the escape of any air, gases or moisture present or generated in the mould when the molten metal is poured into it.
All these gaseous generated during pouring and solidification process must escape otherwise the casting becomes defective 3. Green strength: The green sand after water has been mixed into it, must have sufficient strength and toughness to permit the making and handling of the mould.
For this, the sand grains must be adhesive, i. Dry strength: As soon as the molten metal is poured into the mould, the moisture in the sand layer adjacent to the hot metal gets evaporated and this dry sand layer must have sufficient strength to its shape in order to avoid erosion of mould wall during the flow of molten metal 6.
Flowability or plasticity: It is the ability of the sand to get compacted and behave like a fluid. It will flow uniformly to all portions of pattern when rammed and distribute the ramming pressure evenly all around in all directions 7. Adhesiveness: It is property of molding sand to get stick or adhere with foreign material such sticking of molding sand with inner wall of molding box 8.
Collapsibility: After the molten metal in the mould gets solidified, the sand mould must be collapsible so that free contraction of the metal occurs and this would naturally avoid the tearing or cracking of the contracting metal.
It is generally used for cleaning the sand for removing foreign material such as nails, shot metal, splinters of wood etc. Even power operated riddles are available for riddling large volume of sand.
Shovel: It consists of a steel pan fitted with a long wooden handle. It is used in mixing, tempering and conditioning the foundry sand by Fig. Showel hand. It is also used for moving and transforming the molding sand to the container and molding box or flask. Sprue Pin Fig.
Rammers Rammers: Rammers are shown in Fig. These are required for striking the molding sand mass in the molding box to pack or compact it uniformly all around the pattern.
Sprue pin: It is a tapered rod of wood or iron which is placed or pushed in cope to join mold cavity while the molding sand in the cope is being rammed. Trowels: These are used for finishing flat surfaces and comers inside a mould.
Common shapes of trowels are shown as under. They are made of iron with a wooden handle. Lifter: A lifter is a finishing tool used for repairing the mould and finishing the mould sand. Lifter is also used for removing loose sand from mould. Lifter Strike off bar: It is a flat bar, made of wood or iron to strike off the excess sand from the top of a box after ramming. Vent wire: It is a thin steel rod or wire carrying a pointed edge at one end and a wooden handle or a bent loop at the other.
After ramming and striking off the excess sand it is used to make small Fig. Slicks: They are also recognized as small double ended mold finishing tool which are generally used for repairing and finishing the mold surfaces and their edges after withdrawal of the pattern Fig. Slicks Swab: Swab is shown in Fig. It is a small hemp fiber brush used for moistening the edges of sand mould, which are in contact with the pattern surface before withdrawing the pattern.
It is used for sweeping away the molding sand from the mold surface and pattern. Swab Gate cutter: Gate cutter Fig. Gate Cutter Bellows: Bellows gun is shown in Fig. It is hand operated leather made device equipped with compressed air jet to blow or pump air when operated. It is used to blow away the loose or unwanted sand from the surfaces of mold cavities. Draw spike: Draw spike is shown Fig. It is a tapered steel rod having a loop or ring at its one end and a sharp point at the other.
It may have screw threads on the end to engage metal pattern for it withdrawal from the mold. Sprue Pin: It is a tapered wooden pin, used to make a hole in the cope through which the molten metal is poured into the mould. It is frame or box of wood or metal. It is made of two parts cope and drag as shown in figure. Raw material required: Moulding sand, Parting sand, facing sand, baking sand, single piece solid pattern, bottom board, moulding boxes etc. Tools Required: 1. Molding board 2.
Drag and cope boxes 3. Molding sand 4. Parting sand 5. Rammer 6. Strike-off bar 7. Bellows 8. Riser and sprue pins 9. Gate cutter Vent rod Draw spike Wire Brush Sequence of operations: 1. Sand preparation 2. Placing the pattern at the centre of the moulding flask 4. Ramming the drag 5. Placing runner and riser 6. Ramming the cope 7. Removal of the pattern, runner, riser 8. Gate cutting Procedure: Mould Making 1.
First a bottom board is placed either on the molding platform or on the floor, making the surface even. The drag molding flask is kept upside down on the bottom board along with the drag part of the pattern at the centre of the flask on the board. Dry facing sand is sprinkled over the board and pattern to provide a non-sticky layer. Freshly prepared molding sand of requisite quality is now poured into the drag and on the pattern to a thickness of 30 to 50 mm.
Rest of the drag flask is completely filled with the backup sand and uniformly rammed to compact the sand. After the ramming is over, the excess sand in the flask is completely scraped using a flat bar to the level of the flask edges. Now with a vent wire which is a wire of 1 to 2 mm diameter with a pointed end, vent holes are in the drag to the full depth of the flask as well as to the pattern to facilitate the removal of gases during casting solidification.
This completes the preparation of the drag. Now finished drag flask is rolled over to the bottom board exposing the pattern. Using a slick, the edges of sand around the pattern is repaired The cope flask on the top of the drag is located aligning again with the help of the pins of the drag box. Sprue of the gating system for making the sprue passage is located at a small distance of about 50 mm from the pattern. The sprue base, runners and in-gates are also located as shown risers are also placed.
Freshly prepared facing sand is poured around the pattern. The moulding sand is then poured in the cope box. The sand is adequately rammed, excess sand is scraped and vent holes are made all over in the cope as in the drag. The sprue and the riser are carefully withdrawn from the flask Later the pouring basin is cut near the top of the sprue.
The cope is separated from the drag any loose sand on the cope and drag interface is blown off with the help of the bellows.
Now the cope and the drag pattern halves are withdrawn by using the draw spikes and rapping the pattern all around to slightly enlarge the mould cavity so that the walls are not spoiled by the withdrawing pattern. The runners and gates are to be removed or to be cut in the mould carefully without spoiling the mould.
Any excess or loose sand is applied in the runners and mould cavity is blown away using the bellows. Now the facing paste is applied all over the mould cavity and the runners which would give the finished casting a good surface finish. A dry sand core is prepared using a core box. After suitable baking, it is placed in the mould cavity. The cope is placed back on the drag taking care of the alignment of the two by means of the pins.
The mould is ready for pouring molten metal. The liquid metal is allowed to cool and become solid which is the casting desired. Aim: To prepare a sand mold, using the given Split-piece pattern. Raw Material required: Moulding sand, Parting sand, facing sand, baking sand, pattern, bottom board, moulding boxes. Placing the split pattern at the centre of the moulding flask 4.
Placing the pattern at the centre of the moulding flask Cope box 6. Placing runner and riser 7. Ramming the cope 8. Removal of the pattern, runner, riser 9. Freshly prepared molding sand of requisite quality is now poured into the drag and on the split-pattern to a thickness of 30 to 50 mm.
Using a slick, the edges of sand around the pattern is repaired and cope half of the pattern is placed over the drag pattern, aligning it with the help of dowel pins Dry parting sand is sprinkled all over the drag surface and on the pattern The sprue base, runners and ingates are also located as shown risers are also placed. Result: The required mould cavity is prepared using the given Split Pattern.
Step :1 Place Drag part of the pattern on mould board and filled with mould sand Step Turn drag box upside down and Place cope box over drag box Step place cope part of the pattern ,riser, Sprue, runner in position and filled with mould sand. Many products, which fulfill the household needs, decoration work and various engineering articles, are produced fromsheet metals.
Common examples of sheet metal work are hoopers, canisters, guards, covers, pipes, hoods, funnels, bends, boxes etc. Such articles are found less expensive, lighter in weight and in some cases sheet metal products replace the use of castings or forgings. The size of the sheet is specified by its length, width and thickness in mm. The commonly used gauge numbers and the equivalent thickness in mm are given below SWG 16 17 18 19 20 22 24 27 30 No.
Thickness 1. Black Iron Sheet It is the cheapest among ail. It has a bluish-black appearance and is uncoated sheet. Being uncoated, it corrodes rapidly. It is prepared by rolling to the desired thickness, then annealed by pleasing in a furnace and then set aside to cool gradually.
The use of this metal is limited to articles that are to be painted or enameled such as stovepipes, tanks, pans etc. Galvanized Iron It is soft steel coated with molten zinc. This coating resist rust, improves appearances, improves solderability, and improves water resistance. It is popularly known as G. Articles such as pans, buckets, furnaces, cabinet etc.
Stainless Steel It is an alloy of steel with nickel, chromium and traces of other metals. It has good corrosive resistance. The cost of stainless steel is very high but tougher than Gl sheets. It is used in kitchenware, food handling equipment, chemical plants etc. Copper It is a reddish colored metal and is extremely malleable and ductile. Copper sheets have good corrosion resistance as well as good appearances but costs are high as compared to Gl and stainless steel.
Because of high thermal conductivity, it is used for the radiator of automobiles, domestic heating appliances etc. Aluminium Aluminium cannot be used in its pure form, but is used in alloy form.
Common additions are copper, silicon, manganese and iron. It has many qualities like high ratio of strength to weight, corrosion resistant qualities, and ease in fabrication and whitish in color.
It is used in manufacturing of a number of products such as refrigerator trays, household appliances, lighting fixtures, window work, construction of airplanes and in many electrical and transportation industries.
Tin Plates It is an iron sheet coated with the tin to protect it against rust. This metal has a very bright silvery appearance and is used principally in making food containers, cans and pans. Lead It is a very soft, malleable, low melting point and possesses high resistance to acid corrosion.
It is having low mechanical strength so it is used to provide lining to the highly corrosive acid tanks. It is also used in radiation shielding.
A list of them is given below: I. Measuring tools II. Marking tools III. Cutting tools IV. Forming tools V. Joining tools I. Vernier caliper 3. Micrometer 4. Sheet Metal gauge The above tools are already explained in the fitting section. The slots are of various widths Fig. Standard wire gauge and each corresponds to a certain standard wire gauge SWG number. The gauge is placed over the edge of the sheet to be measured and a slot is found that will slip over the metal with a light fit pressure.
Standard tables are referred to for Fig. Scriber conversion of SWG numbers to mm sizes. Scriber:It is used to scribe or mark line on a metal surface for a variety of purposes.
It is a metalworker's pencil 2. Trammel: These are used for drawing large circles and arcs that are beyond the limit of dividers. It has two straight, removable legs tapered to a needle point mounted on separate Fig. Trammel Points holders which slide on steel or wooden bar and held in position by thumb screws. Punches: It is used in sheet metal work for marking on sheet, locating centers. There are two types of punches. These are already explained in fitting section in detail.
A snip is a hand shear used to cut thin sheets of gauge size number 20 or above. It works like ordinary scissors. There are several types and sizes of snips available to cut along straight lines or curved lines. Figure a shows a straight snip having straight blades to cut along straight lines.
These snips are used for cutting thin sheets. The heavier types are known as bench shear and block shear. Mechanical Shearing press IV. Stakes: Stakes are the sheet metal anvils used for bending, seaming and forming by using ahammer or mallet.
They work as the supporting tool as well as the forming tools. They are madein different sizes and shapes depending upon the job requirement. Commonly used stakes are Stake Holder The stake holder used in sheet metal shop is a rectangular bench plate as shown in Figure. Stake Holder 2.
The hammers used for sheet metal work are a Setting hammer, for setting down the edge while making double seam, b Raising hammer for forming curved or hollow shape from flat piece, and c Riveting hammer for riveting purpose.
Mallets are soft hammers used to give soft blows which will not damage the sheet at the same time will shape them. The commonly used types of hammers and mallets are shown in Figure. The tool has a groove of required width and depth like a die. This groover is placed over the joint double hem or lock seam and hammered from the top of it, to shape the joint that of the groove as shown figure.
At the bottom of the rivet set there is a deep hole and a cup-shaped hole. The deep hole is used to draw a rivet Fig. Rivet set through sheet metal and cup shaped hole is used to form the finished head of the rivet- Another hole on the aide of the set is to release the burrs that are punched.
Dollies are used to backup rivets, when it is not possible to support the job on a bench. Rivet setItand dolly in is made various shapes and sizes to suit the use as shown in figure. The soldering iron copper is heated using furnace, blower or by electrical resistance. The most common types of seams are as follows: 1. Lap seam: This is the simplest seam used in sheet metal work Figure a. This consists of one edge lapping over the other and joint is made by soldering or riveting.
Grooved seam: A grooved seam is made by hooking two-folded edges together and then off setting them as shown in Figure 5. This joint is self-locking and stronger to some extent than lap seam. Single seam: This seam is used to join a bottom portion to a vertical body as shown in Figure c. The bottom edge is hooked over the bent edge of the vertical body.
This method of joint can be used for square, rectangular or round containers. Double seam: This seam is similar lo single scam with the difference that the formed edge is bent upwards against the body as shown in Figure d. Dove-tail seam: This seam is used to connect a cylindrical piece to a flat as shown in Figure e. The edge of the cylindrical part to be joined is slit at short distance and is bent so that alternate pieces come inside and outside of the joint.
Permanent joint is obtained by soldering or riveting. Flanged burred bottom seam: This seam is used to fasten the bottom of a container to its body. The flange of a cylindrical job is often called a burr. The joint consists of a narrow flange which may be joined to inside or outside of the vessel as shown in figure f. Edge Forming For sheet metal objects strength is given to the edge and the sharpness is eliminated by folding the edge.
The common types of folding used in sheet metal work are as follows: 1. Single hem 2. Double hem 3. Wired edge Figure shows the three types of edge folding. A wired edge consists of an edge wrapped around a steel wire for better strength.
Flat file 3. Scriber 4. Try square 5. Snips 6. Dot punch 7. Stakes 8. Cutting 4. Bending 5. Seaming 6. The size of the given sheet is checked with steel rule. Mark the measurement and make the development surface sketch diagram. The layout of the tray is marked on given sheet. The layout of the tray is cut by using the straight snips. The sheet is bent to the required shape using stakes and mallet.
Now the bent edges are made to overlap each other and stuck with a mallet to get the required joint. The joint is soldered. Care should be taken while cutting with snip. Care should be taken while bending and jumping. The layout of the cylindrical shape pipe is marked on the given sheet.
Now the edges are slightly bent to one is one side and the other is opposite side, using stakes and mallet.
Join both the ends with in a cylindrical shape. Care must be taken while cutting snips. Care must be taken while bending and joining. The fusion of metal takes place by means of heat. The heat may be generated either from combustion of gases, electric arc, electric resistance or by chemical reaction.
Welding provides a permanent joint but it normally affects the metallurgy of the components. It is therefore usually accompanied by post weld heat treatment for most of the critical components. The welding is widely used as a fabrication and repairing process in industries. Some of the typical applications of welding include the fabrication of ships, pressure vessels, automobile bodies, off-shore platform, bridges, welded pipes, sealing of nuclear fuel and explosives, etc.
Most of the metals and alloys can be welded by one type of welding process or the other. However, some are easier to weld than others.
The weldability may be defined as property of a metal which indicates the ease with which it can be welded with other similar or dissimilar metals. Elements of welding process used with common Terminology of welding process welding joints such as base metal, fusion zone, weld face, root face, root opening toe and root are depicted in Figure. Edge preparations For welding the edges of joining surfaces of metals are prepared first.
Different edge preparations may be used for welding butt joints, which are given in Figure. Welding joints Some common welding joints are shown in Figure. Welding joints are of generally of two major kinds namely lap joint and butt joint. The main types are described as under. Lap weld joint Single-Lap Joint This joint, made by overlapping the edges of the plate, is not recommended for most work.
The single lap has very little resistance to bending. It can be used satisfactorily for joining two cylinders that fit inside one another. Double-Lap Joint This is stronger than the single-lap joint but has the disadvantage that it requires twice as much welding. Tee Fillet Weld This type of joint, although widely used, should not be employed if an alternative design is possible. Butt weld joint a. Single-Vee Butt Weld It is used for plates up to The angle of the vee depends upon the technique being used, the plates being spaced approximately 3.
Double-Vee Butt Weld It is used for plates over 13 mm thick when the welding can be performed on both sides of the plate. Welding Positions As shown in Fig. Flat or down hand position b. Horizontal position c. Vertical position d. Overhead position Flat or Down-hand Welding Position The flat position or down hand position is one in which the welding is performed from the upper side of the joint and the face of the weld is approximately horizontal.
Horizontal Welding Position In horizontal position, the plane of the workpiece is vertical and the deposited weld head is horizontal.
This position of welding is most commonly used in welding vessels and reservoirs. Vertical Welding Position In vertical position, the plane of the work-piece is vertical and the weld is deposited upon a vertical surface. It is difficult to produce satisfactory welds in this position due to the effect of the force of gravity on the molten metal.
Here the pull of gravity against the molten metal is much greater. The basic principle of arc welding is shown in Figure1. However the basic elements involved in arc welding process are shown in Figure2. Most of these processes use some shielding gas while others employ coatings or fluxes to prevent the weld pool from the surrounding atmosphere. The basic principle of arc welding 11 Channel for cable 1 Switch box. The basic elements of arc welding Arc Welding Equipment Arc welding equipment, setup and related tools and accessories are shown in Figure.
However some common tools of arc welding are shown separately through Figure. Few of the important components of arc welding setup are described as under. Arc welding power source Both direct current DC and alternating current AC are used for electric arc welding, each having its particular applications. DC welding supply is usually obtained from generators driven by electric motor or if no electricity is available by internal combustion engines.
For AC welding supply, transformers are predominantly used for almost all Arc-welding where mains electricity supply is available. They have to step down the usual supply voltage volts to the normal open circuit welding voltage volts.
The following factors influence the selection of a power source: a. Type of electrodes to be used and metals to be welded b. Available power source AC or DC c.
Required output d. Duty cycle e. Efficiency f. Initial costs and running costs g. Available floor space h. Versatility of equipment 2. These are insulated copper or aluminum cables. Electrode holder Electrode holder is used for holding the electrode manually and conducting current to it. These are usually matched to the size of the lead, which in turn matched to the amperage output of the arc welder.
Electrode holders are available in sizes that range from to Fig. Electrode Holder Amps. Welding Electrodes An electrode is a piece of wire or a rod of a metal or alloy, with or without coatings. An arc is set up between electrode and workpiece. Welding electrodes are classified into following types- i Consumable Electrodes a Bare Electrodes Fig.
Parts of a electrode b Coated Electrodes ii Non-consumable Electrodes a Carbon or Graphite Electrodes b Tungsten Electrodes Consumable electrode is made of different metals and their alloys. The end of this electrode starts melting when arc is struck between the electrode and workpiece.
Thus consumable electrode itself acts as a filler metal. Bare electrodes consist of a metal or alloy wire without any flux coating on them. Coated electrodes have flux coating which starts melting as soon as an electric arc is struck. This coating on melting performs many functions like prevention of joint from atmospheric contamination, arc stabilizers etc. Non-consumable electrodes are made up of high melting point materials like carbon, pure tungsten or alloy tungsten etc. These electrodes do not melt away during welding.
But practically, the electrode length goes on decreasing with the passage of time, because of oxidation and vaporization of the electrode material during welding. The materials of non-consumable electrodes are usually copper coated carbon or graphite, pure tungsten, thoriated or zirconiated tungsten. See our Privacy Policy and User Agreement for details. Create your free account to read unlimited documents.
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