cleaning, casting defects and die castings. cleaningfettling of castings

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    Cleaning/Fettling of Castings

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    Cleaning

    After the metal has solidified and cool in the mold. These molds go to a shake out station where the sand and casting

    are dumped from the flask. The casting are shaken free from the molding and some dry sand

    cores are knocked out.

    This process of shake out is called the cleaning of castings. Actually shake out is done by two methods, manually or

    mechanically. Generally mechanical shake out are used for large scale work. This unit consists of heavy mesh screen fixed to a vibrating frame. The screen vibrate mechanically and quick separation of sand from

    other parts.

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    Cleaning

    The manually work is done for small castings. In this work the stationary gratings are mounted and molds are break by

    dropping the molds over gratings. After that the sand is return to the storage bin , flasks are sent to the

    molding sections and castings (production) go to the cleaning departmentfor fettling.

    FETTLING. The complete process of cleaning of castings called fettling. It involves the removal of the cores, gates, sprues, runners, risers and

    chipping of any of unnecessary projections on the surface of the castings. The fettling operation may be divided in to different stages. Knocking out of dry sand cores. Dry sand cores may be removed by

    knocking with iron bar. For quick knocking pneumatic or hydraulic devices are empolyed, this

    method is used for small, meduim work. For large castings the hydro blastprocess is mostly employed.

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    FETTLING.

    Removal of gates and r isers. Gates and risers can be removedfrom casting by several methods depending upon size and metalused.

    With chipping hammer. It is particularly suited in case of grey ironcastings and brittle materials.

    The gates and risers can easily be broken by hitting the hammer. With cutting saw. These saws may be hand saw and power saware used for cutting the ferrous like steel, melable iron and for nonferrous materials except aluminum.

    Mostly the hand saws are used for small and medium but whenpower and used for large work.

    With flame cutting.This type of method is specially used forferrous materials of large sized castings where the risers and gatesare very heavy.

    In this the gas cutting flames and arc cutting methods may beemployed .(it is not applicable for small castings.)

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    FETTLING.

    For sprue cutt ing. The shear is specially made tool on punch press base . In this there is heavy matching steel jaws are fitted. It is mostly used for melable iron soft and medium , hard steel brass bronze

    Al, Mg. Shears are limited to small work ,but are very fast and economical. With abrasive cut of machine. These machines can work with all metals

    but are specially designed for hard metals which can not saw or shearedalso where flame cutting and chipping is not feasible.

    It is more expensive than other methods. Removal of fins, rough spots and un wanted projections. The casting

    surface after removal of the gates may still contain some rough surfaces leftat the time of removal of gates.

    Sand that is fused with surface. Some fins and other projections on the surface near the parting line. The need to be cleaned thoroughly before the casting is put to use.

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    FETTLING.

    The fins and other small projections may easily be chipped off with the helpof either hand tools or pneumatic tools.

    But for smoothing the rough cut gate edges either the pedestal or swingframe grinder is used depends upon the size of castings.

    For cleaning the sand particles sticking to the casting surface sand blastingis normally used.

    In this method the casting is kept in a closed chamber and a jet ofcompressed air with a blast of sand grains or steel grit is directed againstthe casting surface which thoroughly cleans the casting surface.

    The shots used are either chilled cast iron grit or steel grit. Chilled iron is less expensive but is likely to be lost quickly by fragmentation. In this process the operator should be properly protected.

    Unlike this method is adopted for small as well as for large and moreefficient and ensure good polish. This work is dangerous due to harm full dust, but today the equipments has

    been improved.

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    FETTLING.

    An other use full method for cleaning the casting surface is thetumbling.

    This is an oldest machine method for cleaning the casting surfaces. In this method the castings are put in large sheet shell or barrel

    along with the castings and small piece of white cast iron called

    stars. The barrel is supported on horizontal turn ions and is related at thespeed varying from 25-30rpm for 15-30 minutes.

    It causing the castings to tumble over to another, rubbing against thecastings and the stars.

    Thus by continuous peeing action not only are the castings cleaned

    but also sharp edges are eliminated. How ever one precaution to be taken for tumbling is that the castingshould all be rigged with no frail or over hung segments which mayget knocked off during the tumbling operation.

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    FETTLING.

    Repairing the castings. Defects such as blow holes ,gas holes ,cracks mayoften occur in castings.

    Some times castings are broken , bent or deformed during shake out orbecause of rough handling.

    The castings are wrapped during heat treatment or while it cools down inthe molds.

    Such defective castings are not be rejected out right for reasons ofeconomy.

    They are there fore repaired by suitable means and put to use unless thedefects are such that they cannot be remedied.

    In this regard the large size cracks blow holes can be rectified by differenttypes of welding methods are employed.

    This method is depends upon the nature of castings mean the ferrous ornon ferrous castings.

    The castings are become bent due to some reasons given above, if thecastings are ductile they can be straightened or bent back with lead mallet.

    Hydraulic jacks or hydraulic presses are also used for same. When is necessary to make special dies they are fitted to hydraulic presses

    or some times drop hammers are used.

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    Casting defects.

    Casting defects are usually not an accident but they occur because steps inthe preparation of molds are not properly controlled.

    Actually several types of defects may occur during casting considerablyreducing the total out put of casting besides increasing the cost of theirproduction.

    It is there fore essential to under stand the causes behind these defects so

    that they may be suitably eliminated. Casting defects may be defined as those characteristics that create a

    deficiency or imperfection contrary to the quality specification imposed bythe design and service requirements.

    defects in casting may be of two basic types. Major defects which cannot be rectified, resulting in rejections, total loss. Minor defects which can be remedied and there by leave a reason able

    margin for profit. Broadly the defects may be attributed to. Unsatisfactory material used in molding, core, mold making. Incorrect advice by supervisor. Unprofessional management, faulty organization, poor work discipline or

    lack of training.

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    Casting defects.

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    SPECIAL CASTING PROCESS

    So far, the details of science of sand casting processes have beendiscussed.

    But sand casting is not suitable nor economical in many applicationswhere the special casting processes would be more appropriate.

    In the following topics the details of some of the commonly usedspecial casting methods would be described.

    GRAVITY DIE CASTING METHODS This is also called as Permanent Mould Casting. Moulds made of sand are destroyed after casting. So the moulds

    can not be reused. So for producing a large number of castings, a permanent mould is

    necessary. A permanent mould is made of heat resisting cast iron, alloy steel,

    graphite or other suitable material. So the same moulds can be used again and again after each

    casting.

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    GRAVITY DE CASTING

    METHODIS Permanent moulds are made of two halves for easy removal of

    castings. Pouring cup, runner and riser are provided in the mould halves

    itself. The two halves are hinged on one side.

    They ar