Advance Machine Processes ( MECHANICAL PROCESSES )

                                                                               MECHANICAL  PROCESSES 

         Processec Engineering is the science of material transformation. Mechanical processes engineering involves the changes in material properties and composition  due to mechanical effects.

* Separation Methods ;- Classifying and sorting 

            Classification is a mechanical separation method for solid compounds. It utilises either, the geometric features size or the setting velocity of the individual practical for the separation processes. 

Sorting is a mechanical separation processes in which  solid compound containing different materials characteristics is divided into fraction with the same material characteristics. 

* Separation method ;- Separation in a gravity field

            Mechanicals processes engineering in many cases utilises gravity to separate different phase. Gravity can be used to separate a solid phases off from a fluid. 

As well as gravity, centrifugal force can also be use

* Separation method ;- Separation in a centrifugal force field 

          As well as gravity, centrifugal force can also be used as the driving force for phase separation processes. The centrifugal force can be generated either by rotating vessels.

* Separation method ;- Filtration 

          During filtration, solid particles are separated off by a filter medium from a flowing suspension. Suspensions contain insoluble solids finely distributed in a liquid. Usable filter media are sieves, cloths, papers or bulk solids.

* Comminution ;- 

           Comminution alters the particle size and shape and the surfaces of solids. Virtually all solids must be comminuted when being mined or processed.

Abrasive jet machine 

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CONTINUOUS CASTING PROCESS (Asarco Process)

Continuous casting process:-

In Continuous casting process the forming die is an integral part of the furnace and thus there is no problem of controlling the flow of metal . The metal is fed by gravity into the mould from the furnace as it is continuously solidified and withdrawn by the rolls below . The die is water cooled and self lubricating and thus has excellent resistance to thermal shocks . The upper end of the die is in molten metal and thus serves the function of riser and acts as path for dissipation of evolved gases .
      At the time of starting , a similar rod is put into the die till its upper end melts and forms Holding continuity with molten metal , and it is then Furnace withdrawn by rolls and the process becomes continuous . By this process , rounds , tubes , squares and special shapes can be conveniently produced and it is particularly suited to alloys like phosphorised copper and standard bronzes .

      The physical properties of castings Casting - produced are superior to other processes . In continuous casting , solidifying zone being relatively small , practically all problems encountered with feeding and shrinkage are overcome . Problems due to fast cooling in mould zone are faced segregation and cracking ) . A greater degree of control is required in comparison batch casting . Asarco process is shown n fig.

 Uses - Continuous casting process is specially suited to rounds , tubes , squares and special shapes , particularly made from alloys like phosphorized popper and standard bronzes .

Merits - ( i ) Physical properties of castings produced are superior to other processes , because metal is protected from contamination , while melting and being poured .

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Types of SAND in civil Engineering

Types of sand according to size:-

GREEN SAND

DRY SAND

LOAM SAND

FACING SAND

BACKING SAND

SYSTEM SAND

PARTING SAND

CORE SAND


Define all types SAND:_-

          GREEN SAND- It is a mixture of silica sand with 18 to 30 percent clay, having a total water content 6 to 8 percent. The clay and water furnish the bond for green sand. It is fine, soft, light, and porous. Being damp when squeezed in the hand, it retains the shape, the impression given to it under pressure. Moulds prepared in this sand are known as green sand moulds.


           DRY SAND- Green sand that has been dried or baked after the mould is made is called dry sand. They are suitable for larger castings. Moulds prepared in this sand are known as dry sand.


            LOAM SAND- Loam Sand is high in clay, as much as 50 percent  or so, and dries hard. This is particularly employed for laom moulding usually for large castings.


            FACING SAND- Facing sand forms the face of the mould. It is used directly next to the surface of the pattern and it comes into contact with the molten metal when the mould is poured. Consequently, it is subjected to the the severest conditions and therefore, must possess, high strength and ls with refractoriness. It is made of silica sand and clay, without the addition of used sand. Different forms of carbon are uscd to prevent the metal from burning into the sand. They are sometimes mixed with 6 to 15 times as much fine moulding sand to make facings.


          BACKING SAND- Backing sand or floor sand or floor sand is used to back up the facing sand and to fill the whole volume of the flask. Old, repeatedly used moulding sand is mainly employed for this purpose.
     The backing sand is sometimes called black sand because of the fact that old, repeatedly used moulding sand is black in colour due to the addition of coal dust and burning on coming in contact with molten metal.


           SYSTEM SAND-In mechanical preparation and handling unit, no facing sand is used. The used sand is cleaned and reactivated by the addition binder in of water binders and special additives. This is known as system sand, In etimes mechanical foundries, where machine moulding is employed so called system sand is used to fill the whole flask. Since the whole mould is made of this system sand therefore, strength, permeability and refractoriness of this sand must be higher than those of backing sand.


              PARTING SAND-Parting sand is used to prevent the green sand from sticking to the pattern and also to allow the sand on the parting surface of the cope and drag to separate without clinging. This is clean clay-free silica sand which serves the same purpose as parting dust


              CORE SAND- Sand used for making cores is called core sand sometimes called oil sand. This is silica oil sand. This is silica sand mixed with core oil which is composed of linseed oil, resin, light mineral oil and other binding materials. Pitch or flours and water may be used in larger cores for the sake of economy.

Types of SAND in civil Engineering

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Casting process steps

CASTING PROCESS


Define ;-(casting)

          [ In casting, the molten metal is poured into a refractory mould with a cavity of the shape to be made, and allowed to solidify.After solidification, the desired metal object is taken out from the mould. The solidified object is known as casting. Sand moulds are generally used for casting, however, they cannot maintain better tolerances and smooth surface finish. Thus, now-a- 104days metallic moulds are more common.]

[कास्टिंग में, पिघली हुई धातु को एक आग रोक साँचे में डाला जाता है, जिसे आकार की एक गुहा के साथ बनाया जाता है, और जमने दिया जाता है। जमने के बाद, वांछित धातु की वस्तु को साँचे से बाहर निकाल लिया जाता है। जमना वस्तु कास्टिंग के रूप में जाना जाता है। आम तौर पर कास्टिंग के लिए सैंड मोल्ड का उपयोग किया जाता है, हालांकि, वे बेहतर सहनशीलता और चिकनी सतह खत्म नहीं कर सकते हैं। इस प्रकार, अब- a- 104days धातु के सांचे अधिक आम हैं।]

            Various casting processes are as follows- 

(i)        Sand casting 
(ii)       Plaster mould casting
(iii)      Vacuum casting
(iv)      Investment casting
(v)       Slush casting
(vi)      Pressure casting
(vii)     Centrifugal casting
(viii)    Continuous casting
(ix)      Squeeze casting
(x)       Shell mould casting
(xi)      Die casting


Applications of Casting-

(i) Automobile parts such as engine blocks, cylinder blocks, pistons, piston rings, etc
(ii) Machine tool structures, e.g. planar beds.
(iii) Wheels and housings of steam and hydraulic turbines, turbine vanes and aircraft jet engine blades.
(iv) Railway crossings (Mn-steel cast section)
(v) Supercharger casing
(vi) Water supply and sewer pipes
(vii) Sanitary fittings
(ix) Agriculture part
(x) Communication,

Define;-(Moulding)

      Moulding can be defined as a process of making sound mould of sand by using pattern and cores, so that the metal can be poured into the moulds to produce casting.


MOULDING & CASTING PROCESS_

         (I) Expendables mould casting -
                       In this type of casting processes, the mould cavity is obtained by consolidating a moulding material around a pattern. The commonly used moulding material for these processes is sand or some other refractory material. Because of the sand moulding the dimensions accuracy and surface finish of the casting are not up to the requirements of modern  Industries.

NATURAL SEE

(II) Permanent Mould Casting;- 
                    In type of casting processes, the mould is not destroyed after the solidification of the casting and can be used repeatedly. These moulds are adaptable to the production of tens and thousands of castings. The products of this process have smooth surface and better dimensional accuracy. Due to the high cost of permanent moulds their use is limited to mass production of small and medium sized parts of light non- ferrous alloys

(iii) Semi-permanent Mould Casting;-
                 In this type of casting processes, moulds are prepared from high refractory materials like graphite These moulds are less durable as compared to permanent moulds and can only be used for few tens of castings.

Properties of sand in construction

(1) Porosity
(2) Flowability
(3) Collapsibility
(4) Adhesiveness
(5) Cohesiveness or Strength
(6) Refractoriness
(7) Chemical Resistivity

casting process download pdf

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