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…

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 forming a protective layer on the solder.



Qualities of a Good Soldering Flux



The requirements of a good flux are:



(a)          It must remain liquid at the soldering temperature.



(b)          In its liquid state it must act as a cover over the joint and exclude the air.



(c)          It must dissolve any oxide film present on the surface being joined.



(d)          It should be readily displaced from the joint surfaces by the molten solder.



Action of Flux



A  -  Flux solution lying above oxidized metal surface



B  -  Boiling flux solution removing the film of oxide (as Chloride)



C  -  Bare metal in contact with fused flux



D  -  Liquid solder displacing fused flux



E  -  Tin reacting with the base metal to form compound



F  -  Solder solidifying



Types of Fluxes



Soft soldering fluxes can be divided into two categories:



(a)          Active or Chloride Fluxes



(b)          Safety or Protective Fluxes



Active or Chloride Fluxes



Chloride fluxes are used in most of the soldering works. These fluxes quickly dissolve the oxide, rust and grease from the base metal and at the same time act as a barrier to prevent the further oxidation. Unfortunately, all active fluxes have a corrosive residue, so the joint must be carefully washed with hot water after completion of soldering. Otherwise residue of such flux may cause corrosion. The complex type of soldered joint should be immersed in a solution of 1 to 2% (by volume) of hydrochloric acid (HCl) in water then washed carefully in water.



Because of difficulty of avoiding residual corrosion, the use of active fluxes is banned in electrical and other works which cannot be washed effectively. These fluxes are made in various forms as paste, salt or fluid.



Safety or Protective Fluxes



These fluxes are less corrosive in action as compared to the chloride fluxes and less active in removing surface oxides. These prevent oxidation during soldering but will not remove oxide which is already present on the joint surfaces. So surface must be cleaned properly before soldering. These types of flux are especially used on electrical, radio and computer assemblies or other works where complete freedom from acid or corrosion is necessary. These are supplied in four forms as follows:



(a)          Paste / powder flux



(b)          Soldering fluid



(c)          A soldering cream



(d)          Cored solder wire



Specific Fluxes for Different Metals
































MetalsFluxes
SteelAmmonium chloride
LeadTallow
Zinc and galvanised workDilute hydrochloric acid
BrassZinc chloride (Killed spirits) or resin
TinZinc chloride


Different Types of Fluxes and Uses









































































Nomenclature of FluxTypeUses
Compound tinningActiveTinning big-end bearings
Flux, soldering

“Jaydalene”
SafetySoldering of stainless steel conductors of ignition cables
Paste, solderingSafetyAll metals, except stainless steel: where a non-corrosive joint is required
Solution, solderingActiveFor general purpose
Hydrochloric acid(HCl)ActiveFor general purpose, zinc and galvanised iron
ResinSafetyElectrical work
TallowSafetySoldering of lead and zinc metals
Olive oilSafetyPewter (Brittania metal)
Flux, non-corrosiveSafetyFor use in affixing identification labels to steel tubing
Ammonium chloride or Sal-ammoniacActiveFor tinning large surfaces, cooking tins, tinning soldering iron
Phosphoric acidActiveStainless steel pipes
Zinc chloride or D.T.D. 81 or Killed SpiritActiveGeneral engineering work (i.e. sheet metal work)


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