CORE MAKING PROCESS

• Core Making Consist of the following Operations:

1. Core Sand Preparation2. Core Moulding3. Core Banking OR Core Drying4. Core Finishing

1. Core Sand Preparation

• Core Sand means The Mixture of Sand and Binder.

• Sand has Mainly Silica, and its Grain Size Is Small.

• In Pure Sand there is no Natural Bond, So for get more strength add Binders.

• Which is used to increase Strength and toughness of the Core.

• The binders are Mainly of two types:1. Organic Binders

Line cid Oil, Starch, Wheat powder, Dextrin, Resin, Pitch, etc.

2. Inorganic Binders Bentonite Silica Flour, Iron Oxide, and Fire Clay.

• The core sand are generally mixed in (1) Roller mills, and(2) Core Mixers.

2. Core Moulding

• Cores are made manually or with machines.• Green sand cores are made by ramming the

sand mixer into boxes, the interior of which have desired shapes and dimensions.

• The method used to ram core are usually done by machines for large production.

• Core making machines are mainly classified as 1. Core blowing machine

2. Core ramming machine

• e.g., Jolting machine, Squeezing machine, Slinging machine, Core Blower, etc.

• For low volume or large cores, the sand mixtures is compacted into the core box by core blowing that fills the core sand into core box by compressed air.

• Fragile and medium size cores are often reinforces with steel wires and rods so that they will have sufficient strength to resist the forces.

• In large core, perforated pipes or arbors are used.

3. Core Banking OR Core Drying

• After the cores are prepared and placed on metal plate or core carriers.

• They are baked to remove moisture and to develop the strength of the binder in core ovens at temp. 150⁰ to 400⁰C.

• Which depends on the types of binder used, the size of the cores, and the length of the baking time.

• The core plates called Driers are usually perforated to permit the circulation of gases and to lessen the sticking of the cores to the support.

• According to the kind of production, the core-drying ovens are classified as:

1. Batch type oven 2. Continuous type oven3. Die-electric baker

Batch type ovens are used for baking variety of cores in batches.

The cores are generally placed either in drawers or in portable racks which are finally placed in the oven.

Fuel used: Gas, oil, coal

Continuous type ovens are preferred for a high rate production of small and medium-size cores.

The core racks moves slowly through these ovens on a continuous chair or rail.

The loading and unloading is continuous, with backing time controlled by the rate of travel of the conveyor.

Core-drying ovens are usually heated by coal, coke, oil, gas, or electricity.

Die electric bakers can bake cores in a small fraction of the time required for baking the same cores in conventional ovens.

Dielectric heating is employed in modern core ovens for high quality cores made from resin binders.

The material to be heated is placed between the parallel cement bonded asbestos plates or electrodes and a high frequency current is passed through it.

Advantage: faster in operation, good temp control.

4. Core Finishing

• Core finishing process is done by the following processes:

1. Cleaning:- All the rough places and unwanted fins or

projection are removed by brush, filing, or abrasive tool.

Core is apply a fine refractory coating or core wash to the surface. This also called ‘core-dressing’ .

2. Sizing:- Filing, scraping, or grinding process are done

for getting proper shape and size. And it is measured with the help of template

or gauge.3. Core assembly:- If there is more than one part in core it is joint

with help of core-pest, talc, dextrin, water, etc. For large part also joint by nut and bolt.