Green sand moulding

LABORATORY REPORT ON THE PRINCIPLES OF GREEN SAND MOULDING


ABSTRACT
This report gives the account of the principles involve in the green sand moulding. It entails the step by step procedures to be taken in making moulding. Here in this report, some foundry terms like; the cope and the drag, the runner, ingate, etc. will be discussed.
Moulding however is important in the casting as it dictate the shape or form to which the cast is going to assumed. It necessary that fine green sand should be used for a better output.


















INTRODUCTION
The main objective of this report is to give the account of my familiarity with the principles of the green sand moulding and some foundry terminologies.
There are several moulding methods that could be employed to moulding. But each method is depend on the type of metal or alloy to be cast.
Sand casting is however one of the most popularly available casting technique and it involves moulding with green sands. Green sands are the mixture of sand grains (e.g silica sand), clay, water and other special additives to develop specific mould properties needed for the production of the premium castings.
The following are the materials needed for moulding:
The pattern to be mould
The green sand
The moulding boxes
The rammer
Sand muller
Sprue cutter
Riddle and bottom board
Parting sand and strike-off bar
However the under listed flow is the step by step procedure in making moulding:
Sand preparation→Pattern making→Core making→Moulding→Closing
Finally, in this report details will be given on some specific characteristics a moulding sand most have.







PROCEDURE
The following are the step taken during the experiment:
At first, I made the green sand from the mixture of silica sand, clay (which was
used as a binder), water and additives.
I allow mulling to occur up to 3minutes and the open the bottom of the muller to
allow the sand to dump out.
I took a handful of the sand and squeeze it to affirm that it the strength is sufficient
for the moulding.
I did not use the cope because floor moulding was done
I leveled the floor with the sand about 3cm high and then compact it to give a fine
smooth surface.
I placed the pattern diagonally on the sand and make it sink about 0.5cm down
I dusted the surface with the parting sand and then placed the drag on the top of the
pattern.
Then I put a rod very close to the pattern before I filled the drag up it sand and
thereafter ram the sand around the pattern using the rammer until a rigid and
strength-full state is observed within the moulding flask.
More sand is added to until the drag is filled to overflowing and the ram again, the
excess sands were leveled using the strike-off bar.
Then I remove the rod I had put when filling the drag to create a cavity for the
sprue and the riser.
Now I separate the drag from the floor cope and removed out the pattern.
I realign the drag and floor cope back haven demarcated the pin holes before.
Cut the sprue and the riser to make a very complete moulding
Then I blow off the sands from the mould and I ensured that the sprue holes is
clearn.
I realign the mould back properly and cover the riser up to avoid particle and air
with the mould cavity till the molten metal will be ready for pouring.





















































DEFINITION OF TERMS
DRAG: drag is the top part of a moulding flask. The drag aligns the cope. A typical drag is illustrated in the fig2 above.
RAMMER: it is the tool use to compress the moulding sand. The hand off a rammer is made of tool and resembles like handless mallet with one end flat and the other end blunt edge. A typical rammer is shown in the figure below.







MOULDING FLASK: it is tooling use to contain a mould in metal casting. It has only sides and there is no top or bottom. It is use to form frame around the mould.  But in actual sence moulding flask is the cope and grad pulled together. See the figure bellow:








SPRUE: a sprue is the passage through which the liquid material is introduced into a mold. In many cases it is controls the flow of material into the mould. Sprue is however the passage through which a molten material is introduce into a mld and the term also refers to the excess material which solidifies as in the sprue passage
 RISERS: risers are also known as the feeders. They are reservoirs built into a metal casting mould to prevent cavities due to shrinkage. See figure7 below.
GATING SYSTEM: this particular term is referred to all passageways through which the molten metal passes to enter the mould cavity. The gating system is made up of; pouring basin, sprue, runner, gates and risers.








ADVANTAGES OF SAND CASTING
Nearly any alloy: Sand castings can be readily produced in nearly any ferrous or non-ferrous alloy. Some other casting processes will melt and pour super-alloys in vacuum, but that is not typically done as a sand casting. Some materials cannot be “worked”, and must be produced as a casting.
Low tooling cost: The relatively low cost of tooling makes sand casting a process of choice for lower volume needs. Patterns do wear so the material selected for the pattern (typically wood, plastic, or metal) will depend on the expected usage quantity of the part being produced. Though not necessarily cheaper in the short run, the use of machined (or “patternless”)  moulds may be a cost effective option for components with expected lower usage over a longer period of time.
Versatile – Size, Weight, Shape: Sand castings can be produced in weights from ounces to 200+ tons. Through the use of cores, internal structures can be cast in place. Shaped parts rely mainly on the imagination of the designer. Most sand castings, however, will need at least some machined surfaces, either because of innate tolerance limits of the process, or the need to mate with other components.
Any Quantity : Because the tooling cost can be minimal, sand casting may be appropriate for a single piece run. Alternatively, there are automotive components that are produced using this process, so it may also be used in high volume applications.  Other elements of design and tolerance are often more important than quantity when selecting this as the preferred casting process.
Timing: The casting process itself may be quicker than some others, like investment casting, but it is important to consider the post-casting processes like machining that may be required when computing total lead times.
DISADVANTAGES OF SAND CASTING
Lower Dimensional Accuracy : No-bake molding can deliver better dimensional accuracy and repeatability than green sand molding, but this process will, on average, provide less precision than other common casting processes.
Pattern Maintenance : While of lower cost than tooling for other casting processes, there is still an art to pattern creation. Patterns can be bulky so storage must be managed; this is especially significant if the casting is produced infrequently. Patternless molding can relieve some challenges of pattern storage and maintenance.
Surface Finish : Sand castings tend to deliver a rougher surface finish than other casting processes. That point may be moot if certain surfaces are machined anyway, or if surfaces in the as-cast condition are acceptable.

CASTING DEFECTS ASSOCIATED WITH MOULDING
The following are the casting defects associated with moulding:
Shrinkage defect
Gas porosity defect
Blow holes
Sand burning
Inclusion
Pouring metal defect
Metallurgical defect  and etc
COURSES AND PREVENTION
The following are the possible course of the aforementioned defects ;
Inadequate core venting
Excessive release of gas from core
Excessive moisture absorption by the cores
Low gas permeability of the core sand
Moisture content of sand too high, or water released too quickly
Gas permeability of the sand too low
Sand temperature too high
Bentonite content too high
Too much gas released from lustrous carbon producer

The following are the possible prevention measures;
Improve core venting, provide venting channels, ensure core prints are free of
dressing
Reduce amounts of gas. Use slow-reacting binder. Reduce quantity of binder. Use a
coarser sand if necessary.
apply dressing to cores, thus slowing down the rate of heating and reducing gas
pressure.
Dry out cores and store dry, thus reducing absorption of water and reducing gas
pressure.
Reduce moisture content of sand. Improve conditioning of the sand. Reduce inert dust content.
Improve gas permeability. Endeavour to use coarser sand. Reduce bentonite and carbon carrier content.
Reduce sand temperature. Install a sand cooler if necessary. Increase sand quantity.
Reduce bentonite content. Use bentonite with a high montmorillonite content, high specific binding capacity and good thermal stability.
Use slow-reacting lustrous carbon producers or carbon carriers with higher capacity for producing lustrous carbon. In the last instance, the content of carbon carriers in the moulding sand can be reduced.










CONCLUSION
However at the end of the experiment I was able to understand the techniques involved in sand moulding. Also so many foundry terms are no longer a strange words to me again.