Here I have discussed the Sand core making process. I have mentioned 6 steps for making a sand core.
But before that, you should know the materials from which the sand cores are made.
What are Sand Core made of?
Sand cores are made up of core sand mixtures which contain foundry sand and some binders for providing green strength to the sand core.
It is necessary for the sand core to have the green strength so that it can be moulded to the desired shapes.
The core sand mixture generally contains the core sand, 1% core oil, 1% cereal and 2.5% to 6% water.
Besides these ingredients, there are other ingredients which are added to the sand core mixture, like inorganic binders, kerosene oil, parting liquid, etc.
These ingredients are added to the core sand mixture depending upon the type of metal being casted, temperature of the molten metal, size of casting, shape of casting, etc.
Sand Core Making Process
There are 6 steps involved in the Foundry Core Making process.
- Mixing of core sand
- Ramming of core sand
- Venting of core
- Reinforcing of core
- Baking of core
- Cleaning of core
#1) Mixing of core sand
- The first and very important step for core manufacturing is to mix the sand properly, so that the best cores can be manufactured.
- The core binders which provide adhesiveness to the sand particles should also be mixed properly with the sand before adding any moisture to it.
- The moisture content in the sand core mixture should be homogeneous, so that there will be uniform strength throughout the core.
- For mixing the sand, devices like paddle mixers or mullers are used.
#2) Ramming of core sand
- The cores are generally made in the boxes known as core boxes.
- The core sand is filled in the core boxes and it is rammed properly.
- The ramming process can be done by hand or it can also be done with the help of a machine.
#3) Venting of core
- You already know that molten metal has a very high temperature. These high temperatures result in formation of gases.
- So the sand cores that come in contact with the molten metal should have good permeability that can help in removal of hot gases from the core as well as mould.
- For this purpose, the vent holes are made in the core. These vent holes are made with the help of vent wire.
#4) Reinforcing of core
- Some sand cores (which usually have more length) require more strength to resist the pressure of molten metal.
- This need is fulfilled by providing reinforcement to the sand core.
- Wires or arbors in the sand cores are used for reinforcement.
#5) Baking of core
- The core with a flat surface is baked on a core plate such that the flat surface of core rests on the core plate.
- The core is baked at around 260 °C temperature and it is held at 100 °C, so that its moisture content is driven off.
- The core oil has a property due to which it changes from liquid to solid at the temperature of 200 °C to 260 °C and this increases the strength of the sand core.
- For baking the sand core, the dielectric bakers or oven are used.
#6) Cleaning of core
- Cleaning of cores includes three major things. Trimming, Coating, and Muddling.
- Clean cores with good surface finish will ultimately lead to good quality of castings.
- Hence, cleaning of sand cores is essential.