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…

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 passes through a pasty stage in the transformation from liquid to solid. This feature is useful in some plumbing applications or where work is coated by dipping in a bath of molten solder.



A solder which contains 60% tin and 40% lead has a lower melting point. It is in solid state at 1830C and becomes completely liquid at 1880C. So it is especially used in electrical work where a longer cooling period could damage insulation or the component.



Sometimes a little percentage (maximum up to 3%) of antimony is also added to make harder and stronger joint because it expands on cooling. A solder containing antimony is not recommended for zinc and galvanised work. Bismuth is also added to soft solder to lower down the melting point.



Solder Compositions as per Indian Standard (IS): 193-1982



IS:193-1982 covers the requirements of non antimonial and antimonial soft solders for general use, solders for use at high temperature and solders for special applications.



(a) Tin-Lead Solders for General Use. These can be non-antimonial solders and antimony solders.



(i) Non-antimonial Solders. These solders contain a very small percentage of antimony. Some examples are as follows:



Non-antimonial Solders


























Tin %Antimony % (max)Lead %
65 ± 0.50.65Remainder
50 ± 0.50.50Remainder
20 ± 0.50.20Remainder


(ii) Antimonial Solders. These solders contain good percentage of antimony. Some examples are as follows:



Antimonial Solders































Tin %Antimony % (max)Lead %

 
50 ± 0.52.5 - 3.0Remainder
32 ± 0.51.6 - 1.9Remainder
18 ± 0.50.9 - 1.2Remainder
02 ± 0.50.2 - 0.5Remainder


(b) Solders for Services at High Temperature. These solders are more difficult to use. Some examples are as follows:



Solders for Services at High Temperature






























Tin%Antimony%Lead%Silver%
95 ± 0.54.75 - 5.250.07 Max0.02 Max
4.75 - 5.250.10 MaxRemainder1.4 – 1.6
0.75 - 1.250.10 MaxRemainder1.4 – 1.6


Forms of Soft Solder. Soft solders are supplied or manufactured in various forms such as bars, strips, tapes, solid wires, cored wires, ingots, washers, pastes, paints, etc.



Special Type of Solders



Resin Core Solder.  Normally the solder and flux are two separate things but in resin core, solder is prepared in such a way that it is made in the form of thin tube and flux is filled inside the tube (i.e. core). In this, the solder and flux both are available at the same time. Soldering with resin core solder is easy, less time taking, clean and has more strength. It is usually used in soldering of electrical, radio, computer and TV components.



Standard Grades of Soft Solder



Standard grades of solder including those provided in service are given below. All these standard grades start to melt at about 1850 C. But special solders whose melting point is up to 3100 C are also available. The paint solders are applied with brush. Some standard grades of solder are given in table as follows:



Grades of Soft Solder








































































































NameGradePb.

%
Sn.

%
Sb.

%
Bi.

%
Melting point (0C)Uses
Tinman’sA34651180General use
B47.5502.5225Aircraft general use
C58-5939-402.24227Pipes, radiators, coolers and general work
PlumberD69-7029-301.17248High grade plumbing and lead cables
G58-5941-420.4230Zinc galvanized iron, electrical and general works
ElectricalM53-5444-452.7215Electrician, tinsmiths and instrumental works
PlumberM55-5644-45223Instrument works
PewterE25255093Commercial use
N80.5-8118-18.50.021275Dip soldering


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