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Lathe Operations: Facing

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Facing Operations Facing is the process of removing metal from the end of a workpiece to produce a flat surface. Most often, the workpiece is cylindrical, but using a 4-jaw chuck you can face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

When a lathe cutting tool removes metal it applies considerable tangential (i.e. lateral or sideways) force to the workpiece. To safely perform a facing operation the end of the workpiece must be positioned close to the jaws of the chuck. The workpiece should not extend more than 2-3 times its diameter from the chuck jaws unless a steady rest is used to support the free end. Cutting Speeds

If you read many books on machining you will find a lot of information about the correct cutting speed for the movement of the cutting tool in relation to the workpiece. You must consider the rotational speed of the workpiece and the movement of the tool relative to the workpiece. Basically, the softer the metal the faster the cutting. D…

Heat Treatment of Tools

General purpose tools like chisel, hammer, file, punch, lathe tools etc. are manufactured by forging. These tools are normalized immediately after forging to restore their original structure and to relieve stresses and strains set up while forging. Hardening is carried out to induce hardness at the working end and simultaneously tempering is carried out to make the body tough to absorb shock while working. Hence heat treatment has got unique importance in the field of production industry as it helps to induce desired qualities which enable the tools to serve their purposes. Heat treatment of different tools is described below.

Cold Chisel

A cold chisel is generally forged out of tool steel or H.C.S. It is to be normalized after forging and the cutting edge is to be ground to the correct angle. Hardening and tempering is done by single heating method.

In this method the chisel is heated upto 2” from the cutting edge in clean fire to a temperature of 7600C (cherry red).Then the tool is rem…

Heat Treatment of Non - Ferrous Metal

Generally annealing is carried out on non-ferrous metals. Annealing makes the metal soft. This property enables the worker to work upon the metal easily, and also prevents the metal to crack or fracture while being hammered, forged or rolled.

Copper

Copper tends to become hard and brittle, when hammered or cold worked. It can be softened by annealing. All plates, rods, tubes etc of copper are thoroughly annealed before use. Annealing is done by heating to a dull red colour (650°C), keeping the pieces at this temperature for a few minutes, and then quenching in water or allowing it to cool in the air. During the process of drawing into wire, copper must be annealed to avoid fracture.

Copper should not be heated in a reducing atmosphere, such as coal gas or carbon monoxide produced on the brazing hearth with a slow fire. Prolonged heating at a high temperature will also produce brittleness due to very coarse crystallization.

Brass

Brass is hardened by cold working. It can be annealed by heat…

Iron-Carbon Equilibrium Diagram

Alloys of the Iron carbon system are of the most vital importance to the modern industry due to their extensive, versatile applications. The Iron carbon system provides the most prominent example of heat treatment and property alteration based on the transformation from one form to other on application of heat and eutectoid decomposition. Because of its outstanding importance, the heat treatment of the iron-carbon system has been studied in more details than most alloy system. Types of steels and cast iron depend upon the percentage of carbon present in the steel or cast iron. As per the carbon percentage, two types of steels are there.

Hypo-Eutectoid Steel. Steels that contain less than 0.87% carbon are known as hypo-eutectoid steels.

Hyper-Eutectoid Steel. Steels that contain more than 0.87% to 1.8% of carbon are known as hyper-eutectoid steels.

Iron is allotropic metal. It exits in more than one type of lattice structure depending upon temperature. It may be face Centered Cubic (FCC) …

Purpose and Sequence of Case Hardening

Steel components are used in many applications that require a hard and strong surface to resist wear and abrasion combined with a tough core to withstand shock and fatigue. This condition can be obtained by an alteration in the composition of the surface layer of a steel component followed by the application of a suitable "heat treatment. The surface region in which the properties and composition have been altered is known as the case, and the production of a hard surface is known as case hardening. In this process, the steel is caused to absorb such elements as carbon, nitrogen or a mixture of the two. When carbon alone is absorbed, the process is known as carburizing ; when nitrogen is added, the process is known as Nitriding, and when both are absorbed the operation is known as carbo- nitriding or cyaniding.

Purpose.The purpose of case hardening is as follows:

(a)          To induce high carbon content on the metal surface while leaving the core of the metal soft.

(b)          To…

Methods of Case Hardening

Various types of surface hardening or case hardening processes are.

(a)       Carburising

(b)       Cyaniding

(c)        Nitriding

Carburising

The formation of a high carbon case is carried out by heating the steel in contact with a carbonaceous material. Carbon diffuses on to the surface layers of the metal, and the case is subsequently hardened by a suitable heat treatment. According to the nature of the carbonaceous material, three processes are recognized.

(a)       Pack (solid) carburizing.

(b)       Gas carburizing.

(c)        Liquid carburising.

Pack Carburising. The steel components are packed in a container together with a carbonaceous material which decomposes at high temperatures with the release of carbon. The container is sealed with a lid and heated to above the upper critical temperature (900- 950°C) for 3-6 hours according to the depth of case desired. At this temperature, the austenite absorbs carbon and the penetration is about 0.030-0.060”. Higher carbon contents than this w…

21 Useful Key Terms of Heat Treatment

Heat treatment is a process applied to metals to achieve certain desired properties. It is carried out by heating to a definite temperature, soaking for a specific period and cooling the metal at a prescribed rate as well as in a prescribed media. Terms pertaining to heat treatment are defined below.

Key Terms With Their Definition


Eutectic.The word Eutectic is used to indicate the lowest possible freezing or melting point of any combination of two metals or elements. It corresponds to a definite proportion of two substances and has a fixed freezing point.
Eutectoid.The term Eutectoid is always associated with a particular composition of the involved alloying elements that has the lowest freezing point. The eutectoid of steel contains 0.87% carbon (pearlite)
Hypo-Eutectoid Steel. Steels that contain less than 0.87% carbon are known as hypo-eutectoid steels.
Hyper-Eutectoid Steel.Steels that contain more than 0.87% carbon are known as hyper-eutectoid steels.
Solution.Certain substances will …

Soft Soldering and Its Glossary of Terms

Soft soldering is the process of joining metal parts by heating and running a low-melting point alloy between the two surfaces being joined. As cooling takes place, the alloy solidifies and results in a secure joint.  For most purposes, the low- melting point solder alloy is a composition of lead and tin.  Solder melts at a temperature less than 3000C, which is far below the melting temperature of the metal being joined and produces a low strength joint.

Soft soldering is used extensively in sheet metal work for joining parts which are not exposed to the action of high temperatures and are not subjected to excessive loads and forces. It is used not only to make a mechanical bond between surfaces but also to provide a leak proof seal when liquids have to be contained. It can also be used to provide a permanent electrical connection. To provide a secure joint, it is essential that the joint surfaces are perfectly clean and free from rust, grease or any other substance likely to prevent g…

Composition and Types Soft Solders

The solders generally used in industry are alloys of tin, lead and zinc. Tin-lead solders are used to join most of the metals as they have good corrosion resistance to most of the metals. Sometimes silver, cadmium, antimony and bismuth are also added to solders. It is essential that solders must have a lower melting point than the parent metals. The melting point of a solder should be as near as possible to the parent metal to be joined so that a more tenacious joint is affected.

Composition of Soft Solder

Soft solders are mostly alloys of lead and tin. All the plain tin / lead solders become solid at 1830C. The temperature at which these become completely liquid depends upon the composition. The temperature increases as the lead content increases or tin content decreases.

Some solders pass through a considerable pasty stage before becoming completely liquid to solid. The above figure shows that 20% tin and 80% lead solder becomes completely liquid at 2760C and solid at 1830C. The solder…

Flux Used in Soft Soldering

The operation of brazing, soldering and welding has brought out the use of fluxes in service. Flux is a chemical substance, which is made for cleaning the surface of the job and preventing oxidation in operations, such as welding, soldering and brazing. It is rather difficult to have satisfactorily brazed or soldered joints without the use of fluxes. Therefore it is very essential to use flux in soldering, brazing and welding. Soldering flux may be defined as a substance (solid or liquid) applied to a metal to make solder flow readily and gives a permanent joint. The success of a solder depends to a large extent upon the proper choice of flux.

Purpose

The soldering fluxes are needed due to the following reasons:

(a)          To clean the surface of the base metal during heating.

(b)          To eliminate impurities appearing on metal surface.

(c)          To breakdown the surface tension of molten solder which helps the easy flow.

(d)          To prevent the formation of fresh oxides by for…

Types of Soldering Iron

In most cases of soft soldering process, direct application of heat is avoided as it is difficult to control. It is to avoid damage to electrical connections, melting away of thin sheets and damage to other equipment where application of direct heat can cause distortion. It can also interfere with the heat treatment given to the job for a specific purpose. Hence a hand tool called soldering iron is used for indirect application of heat.

The soldering iron is used to melt the solder in the soldering process. The bit of soldering iron is made of copper which conducts heat into the metal to be soldered. Soldering irons are used for soldering metals having small areas of contact. Soldering iron is generally heated by means of a gas flame, blowlamp, coke fire or electricity. After obtaining the required temperature the soldering iron is used for soldering operation.

Soldering Irons

Types of Soldering Iron

The various types of soldering iron are described below:

(a)        Common Soldering Iron

(…

Successful Soft Soldering Process

Method of Soft Soldering

To carry out successful soft soldering, the following process is to be adopted:

(a)          Clean the parts thoroughly.

(b)          Tin the parts to be joined, if necessary.

(c)          Assemble the job in proper position.

(d)          Apply flux slightly.

(e)          Melt the solder between the joints with a hot, clean and tinned soldering iron.

(f)           Allow the solder to get completely cooled.

(g)          When it is cooled, wash it properly with clean water (normally warm soapy water).

(h)          Remove all the traces of the flux, which will make the metal corrosive if left in contact with metal.

NOTE

(a)       Use the minimum amount of solder, this makes the strongest joint.

(b)       Always keep the iron tinned to facilitate the flow of solder.

(c)        Excessive heating of the tinned iron will cause oxidation and requires ‘re-tinning’.

Causes of Faulty Soldering

Causes of faulty soldering are as follows:

(a)          Surface not cleaned thoroughly.

(b)    …

Hard Soldering Process and Flux

Soldering Process

A large number of joining processes are used in industry to make the finished products like aeroplanes, ships, cars, vehicles, radios, televisions, computers, machine tools and domestic appliances. Different methods used for joining components are riveting, brazing, welding, screw fastening devices, etc. In the engineering industry, for instance, soldering finds applications in making turbine blades and discs, pipelines, radiators, fins, in air-cooled engines, bicycle frames, industrial receptacles, gas equipment, etc.

Soldering is the process of joining two or more similar or dissimilar pieces of metal by the application of low melting alloy (solder) and heat.

Before describing soldering process in detail, in order to produce successful soldered joints following important points need to be adhered:

(a)          Metals to be soldered together must be chemically and mechanically cleaned. All the oxides, grease and dirt must be removed.

(b)          Metals to be soldered to…

Hard Soldering an Alternative to Brazing

Hard soldering (silver soldering) is an alternative to brazing. It specially implies the use of the filler materials containing silver, which have lower melting point than brazing spelter and therefore associated with greater ductility and often greater strength. Hard soldering is general term used to cover brazing and silver soldering. However, hard soldering can be defined as an intermediate stage between low temperature soft soldering and high temperature brazing.

The operation of brazing and hard soldering are almost identical and the two terms are used synonymously. Hard soldering normally means silver soldering, which has a lower melting temperature than brazing. Silver soldering is used principally for fine work and in case where joint is required to be stronger than soft soldering, but where, at the same time it is not desirable to raise the work to the brazing temperature.

Groups of Hard Solders

Hard solders can be divided into following two groups:

(a) Low Temperature Silver Bra…

Advantages, Disadvantages, Precautions in Brazing

Advantages of Brazing

Following are the advantages of brazing:

(a) Brazing is used to join a large variety of dissimilar metals.

(b) Properly brazed joints are pressure tight.

(c) Pieces having great difference in cross-sectional areas can be brazed.

(d) Thin sheets, pipes and gauges that can't be joined by welding can be joined by brazing.

(e) Complex assemblies can be fabricated by this method.

(f) A brazed component has ability to preserve protective metal coating.

(g) Brazing can be done on cast and wrought materials.

(h) Corrosion resistance joints can be produced by this method.

(j) Brazing preserves metallurgical characteristics of a material better than welding.

(k) After brazing a component maintains more precision tolerances than welding.

(l) Brazing processes can be automated for bulk production.

(m) Non-metals can be joined to metals.

Disadvantages of Brazing

Following are the disadvantages of brazing:

(a) It requires tightly mating parts.

(b) It requires proper cleaning.

(c) Size of th…

Brazing and Its Applications

Brazing is defined as a process of joining similar or dissimilar metals in which molten filler metal is drawn by capillary action into the space between closely adjacent surfaces of the parts to be joined.

In general, the melting point of the filler metal lies above 5000C but below the melting point of the parent metals being joined. The brazing alloy is often called spelter and can be plain brass (50% copper and 50% zinc). Increasing of the zinc content decreases the melting point of the spelter. Borax is used as a flux for brazing.

Brazing alloys containing phosphorus are referred as ‘self-fluxing brazing alloys’. These alloys contain silver, phosphorus and copper or copper and phosphorus. These alloys are very much in use for manufacturing refrigerator and electrical assemblies etc.

Applications of Brazing

There are various applications of brazing. Some of these are given below:

(a) Brazing is used for fastening of pipe fittings, tanks, carbide tips on tools, radiators, heat exchangers,…

Methods of Brazing

Torch Brazing. This method requires very little equipment and is more frequently practiced. It involves the use of a type of gas blowpipe fitted with the combination of air and gas regulators by means of which both the size and nature of the flame can be adjusted to suit the work. The gas combinations used and the temperatures obtained from them are given below:

Torch Brazing

(a) Compressed air-coal gas : 10000C to 11510C

(b) Coal gas-oxygen : 21000C to 22000C

(c) Hydrogen-oxygen : 24000C

(d) Oxy-acetylene : 32000C

In general, slightly oxidizing flame should be used. The torch is usually kept in motion to achieve a general heat all over the work, rather than a local heat and the envelope of the flame is used for this purpose. Torch brazing is quicker in action than other brazing methods, and suitable for small repetition work such as assembly of instruments, wireless and electrical components.

Furnace Brazing. Furnace as a heating source for brazing is best suited for brazing large or simila…

Brazing Various Metals

Brazing of Aluminium

Pure Aluminium and certain aluminium alloys can be joined by aluminium brazing. A filler material or a brazing rod, usually, an alloy of Aluminium and Silicon of a lower melting point than that of parts to be brazed is used for aluminium brazing. One of the filler materials contains 10 to 13% silicon and melts at 5750C. This is 850C below the melting point of aluminium. It is clean and smooth flowing in action with a good penetrative and wetting power, which causes it to flow into and around the joint readily as soon as its melting point is reached.

A flux which removes the surface film oxide and melts at lower temperature than that of the filler rod is essential for easy operation. When heated to a liquid state, flux should flow smoothly and cleanly ahead of molten filler metal. ALDA flux is provided for brazing of ground equipment and general engineering works.

Parts to be brazed must be cleaned and free from oil and grease. Sharp edges should be removed by filing …