Core-Making Process and Application
An Image of a Metal Core box
What is a core making or making of core? A core is a moulded shape or object which is used in forming the internal shapes of cylindrical or hollow shapes. Cores have contributed a lot in the production of many metallic objects that have hollow shapes. Think of how bore holes drilling machines will be without the cylinder found inside them. These cylinders came into existence with the help of core. Core is first produced before it is inserted into the core mould which results to the formation of the cylinder.
There are some processes that lead to core making in the foundry workshop. This starts with mixing of core sand with appropriate additives. These additives are added to strengthen the moulding material. Other steps involve in core making includes filling, compacting, hardening and even painting in some cases.
Cores are not made for making sake as they have their own applications. One of the applications of core is discussed in this chapter of this text. These details are conducted step-by-step accompanied with appropriate pictures for easy comprehension.
Tools used in Core Making
In core making, there are specific tools used in the making processes. Tools in this context are devices and things used in carrying out core making processes. These tools are: core sand, additives (sawdust in this practical), rammer, reinforcement, core box, parting powder, clamp and scrapper.
The core sand and the additive, which is saw dust, are used as the moulding material. These two are properly mixed with equivalent addition of water. Rammer is used when it comes to compaction.
It is used to compact moulding materials. Core box is one of the principal if not the most principal tool used in making of core. It is made of two halves. In core making, these two halves are clamped together with clamp or tie with wire. Parting powder is rubbed on the internal surface of core box for easy separation. The reinforcement can be of cast iron. A cast iron is rigid; it can be positioned in the core box and sand can be rammed around it (Core and Core Making by Francis D. Roper, Allen and Unwin). The scrapper is used for removal of the left over sand or remaining moulding material after compacting.
Steps involved in Core Making
Filling and compacting: The first step is filling of the core box with the moulding material after parting powder has been spread on the interior part of the core box. The two halves of the core box are clamped together with the help of clamp. Flexible wire can be used to join them together in the absence of clamp. Tightness is ensured so that the final shape of the core is not altered. After clamping, the box is partially filled with moulding material. The moulding material is the mixture of the core sand and saw dust.
Reinforcement is forced into the middle of the core box and more of the material is added and compacted with rammer. The compaction is carried out from the top and bottom of the moulding box. This is to enhance the rigidity of the core. The core box is removed and the core hardened for use.
Halves of Core Box
- Hardening: It is the process of making the wet core to be stronger for further use in making of hollow shapes. This can be carried out with the use of heating machine or allowing the core to be hardened at room temperature. Leaving the core to harden at its own room temperature is for it to be left were it was made. After some days, it becomes hardened on its own. The number of days to be taken for the hardening is dependent on the size of the core.
- Painting: After hardening of the core, the next step is painting of the core. Though this stage is ignored in some industries and metallurgical institutions, it is considered by some foundries. The painting is made for easy removal whenever it is used to make hollow shapes. For sand core, which is of the main concentration in this write up, it is being broken at the end of construction of the hollow shapes.
Application of Core in Cylinder Casting
A cylinder is the central working part in many machines. It is found in many pumping machines and engine blocks. The cylinder produced on this write-up using core is the one found in borehole machines.
The production of this part involves casting process and the molten metal used is that of aluminium. In cylinder casting that involves the use of core machine, the machine operator places the cores in the masks, insert them in depressions provided for the purpose (Moulding and Core Making by Pennsylvania State University). This application is conducted without machine and the cylinder casting is made with core box.
The production stage starts with pattern making which is the ‘photocopy’ of the cylinder that is yet to be produced. Accurate measurements of the diameters, widths and lengths of the cylinder are taken. The measurements are done with the callipers, steel rule and other necessary devices needed. Wood is used for the construction of the pattern so that there will be no difficulty in shaping. The pattern is properly formed with shaping machine which operates with electrical power.
A mould is made using moulding boxes which contains location pins. These location pins are used for proper positioning of the box. Making of mould starts with placing of the cylindrical shaped pattern into the moulding box. The box is filled with moulding sand or moulding material that is used in preparation of the mould. The mould is rammed well to avoid collapsing of the mould when raised up for the formation of the top path which is called the cope. The ramming process is done with a device called rammer. The moulding sand that is left after ramming is scrapped out with the use of hand scrapper.
A second moulding box is placed on top of the drag. The pipes which are to form the risers and the runners are placed on top of the drag before filling with moulding sand. After filling, ramming and scrapping, the pipes that form the risers and runners are removed. Suitable openings must be provided for introduction of liquid metal (Foundry Core and Mould making by the Carbon dioxide Process by A. D Sarker). Vents are made for easy evolution of gases from the mould. The cope is then removed from the drag for creation of the ingate system. Note that parting powder is sprinkled on top of the cope before the formation of the drag. The function of the parting powder is for easy separation of the two moulds.
The mould is left to dry and after the cope is placed on top of the drag. The core which was produced in the first place is placed on the impression made by the cylindrical pattern before covering with the cope. After the covering, the location pin is used to enhance tightness before pouring of the molten metal.
The molten metal used in this cylinder casting is of Aluminium. The Aluminium when melted at temperature of 660.3 0 C is poured through the runners made on the mould. The liquid metal flows from the runners into the ingate systems and from there into the mould cavity. An indication that the mould is filled is identified through the risers. Once the metal melts began to come out through the risers, the mould is filled. The proper shape of the cylinder is formed and produced on solidification. The core when it is made of sand is broken and the remaining result is the cylinder. This is the simple sequence of operation in making of casted cylinder.
Conclusion of the Topic
Core making is one of the major topics being offered in the department of Metallurgical and Materials Engineering. Justice has been done to this topic as the techniques involved in core making have been discussed in detail. These techniques involve filling and compacting, hardening and painting. Another sub-heading discussed in this write-up is the application of core in cylinder casting.
- Core and Core Making by Francis D. Roper, Allen and Unwin;
- Moulding and Core Making by Pennsylvania State University;
- Foundry Core and Mould making by the Carbon dioxide Process by A. D Sarker.