Clay and moisture content

LABORATORY REPORT ON THE DETERMINATION OF THE MOISURE AND CLAY CONTENT OF GREEN SAND


ABSTRACT
The quality of castings in a green sand mould is influenced significantly by its properties, such as green compression strength, permeability, mould hardness, and others, which depend on input parameters. The relationships of these properties with the input parameters, like sand grain size and shape, binder, water, clay, etc. are complex in nature.
The goal of this paper is to determine the green sand mould compressive strength in case of input parameters.
A good moulding sand however, must possess the following properties. The properties are determined by the amount of clay, moisture content and by the shape and size of the silica grain in the sand;
PERMEABILITY
COHESIVENESS OR STRENGTH
ADHESIVENESS
PLASTICITY
REFRACTORINESS
BINDING
CHEMICAL RESISTIVITY
FLOWBILITY

However, all this properties at the end of the experiment were achieved as a result of taken important consideration to controlling the amount of clay and moisture content of the sand during sand preparation.








INTRODUCTION
Sand moulding processes are the oldest moulding methods and still remain the most popular world-wide. Sand mould, into which molten metal is poured to produce a casting of desired shape can be made from either dry or green sand. In each case, the moulding sand consist essentially of base material such as silica, zircon, olivine, chromite or any other which imparts refractoriness to the moulding sand; the clay and or other binders which bind the  refractory- based particles together and the additives which are often organic whose primary function is to impart special properties to the moulding sand.
However this report will give the account of detail steps involves in maintaining the strength, plasticity, flowability  and other properties of a good moulding sand. An important parameter here in that will be discussed are the clay and moisture contents.
At present, there are many methods for measuring the moisture content of green sand, and they can be divided into two categories of direct method and indirect method. In the direct method, the absolute moisture content can be measured by heat or chemical reaction. For the indirect method, the moisture content is obtained by measuring the physical parameters or performance indexes related to the moisture. In general, the direct method has high precision but long measurement period, so it is only suitable for laboratory while unsuitable for the production line. Although the precision of the indirect method is not as high as the direct method, it can be used for online measuring the moisture content of green sand due to the fast speed.










OBJECTIVES:
To stress the importance of water in moulding sand
MATERIALS ROVIDED:
A sample of the green sand
Crucible
An oven
A weighing balance
Distil water
1 litre capacity jar
Dry moulding sand
Rotating machine
Weighing machine
1% aqueous solution of NaOH











PROCEDURE I
The following are the step taken for the determination of moisture content:
I weighed he green sand sample of about 100g into the crucible of known mass M0.
I then placed the crucible and its content inside the oven, in which the temperature
was then maintained between 105 – 110oC.
The crucible was brought out and weighed at an intervals of ten minutes.
I repeated the experiment for the same sample until a constant mass was obtained
(i.e. for about five(5) times continually.
After the fifth time the sample was brought out.














DATA AND RESULTS
If:
The mass of the crucible = M0
The mass of given Sand + crucible = M1
And the mass of the sand + crucible = M2
Then:
 The mass of the green sand = M1 – M0
The final mass of sand = M2 – M0
And the mass of sand the moisture in the sand is = (M1 – M0) – (M2 – M0) = M1 - M2

TABLE OF RESULTS
S/N
WEIGHT OF GREEN SAND

1.0
104.66g

2.0
96.73g

3.0
96.40g

4.0
96.38g

5.0
96.40g

Table 1
Initial Weight of sand = 100.51g
Mass of crucible = 7.51g


Calculations
M0  =  7.51g
M1 = (100.51 + 7.51) g = 108.02g
Final mass of the sand = 96.40g
M2 = (96.40 + 7.51) g = 103.91g
And the mass of sand the moisture in the sand is
(M1 – M0) – (M2 – M0) = M1 - M2
108.02g – 103.91g = 4.11g
Moisture content  =
       =  x 100
      =
      = 4.089g









PROCEDURES II
The following are the step taken for the determination of clay content:
 I weight of 50g out of the dry moulding sand out of the previously processed sand.
This is poured into a jar of 1litre capacity with diameter 90mm,
A 450mL of distilled water is poured into the jar with the content
Then I added 25mL of 1% aqueous solution of NaOH to the jar.
Having securely closed jar, I keep on shaking the jar gently for sufficient time to allow the content to settle
Then additional water is added to a level of 150mm.
After 10mins the excess water is siphoned away and the operation is repeated all over
After the end of the 3rd time the system is allowed to stand for about 5mins and this continuous for as long as the water remaining under the stand.
However the left over could not be filtered, dried nor weighed because the clay could not be emptied from the used jar (see the figures below). Hence the clay content cannot be calculated.










            Before settling      after settling


DISCUSSION OF RESULTS
A noticeable decrease in the moisture content is observed as shown in the table 1 above. This decrease is as a result of the repeated addition of water to the sand sample and particularly because of the sample duration in the oven.
Hence it can be realised that the heat or dryness play an important role to the estimation of the moisture content.
Haven poke nosed into other group values, differences were observed in the various moisture contents. The various are as a result of; (i) systematic error that might have occur during weighing (ii) random errors that are caused by the air during measurement.













QUESTIONS AND ANSWERS

(1)  Observation precaution taken to ensure successful result
I avoided systematic error during my measurement.
I ensure the temperature range is not exceeded.
I avoided extra time limit.
(2) The determined moisture content of the green sand from the experiment is 4.089g
(3) Importance of moisture in the moulding and core sand are;
Moisture increases the compartment of the moulding and core sand.
Moisture also helps to keep the nutrient content in the sands from being loosed away easily.
Moisture increases moulding sand flowability
Moisture improves the strength of the moulding and core sand
(4) Some differences:
i. Differences between the dry sand and green sand
 a.  Dry sand is basically the sands that has loses some certain percentage of their moisture content. They are mostly sands that have being used one or more times for moulding while green sands are sands that still retain most of their moisture content. And they contain more good moulding sand properties compare to dry sands.
b.  Green sand is a mixture of sand with 20-30% clay having total amount of water from 6-10%.green sand mould is used for small size casting of ferrous and non ferrous metals. Dry sand is a green sand moulds when baked or dried before pouring the molten metals.


ii.  Difference between the moisture and water of crystallization of the sand
Moisture content is the quantity of water contained in a material measured through weight loss on drying while water of crystallization of sand is a measure of free water in a sample and ranged between 0 and 1.
(5)  Determine the clay content of the sample you are given:
Clay content could not be determined. The experiment was inconclusive.
(6)  In what way does clay content affect the moulding and core sands:
Clay reduces permeability of sand and increases the strength of the sand. An adequate percentage of clay content will increase the flowability of the moulding and core sand. Adding it into sand can increase its ability to stick together but reduces the ability of the metal to outgas.












CONCLUSION
It can be concluded that, water is very crucial in the moulding sand as it helps to keep the sand weigh constant and also to improve many moulding sand properties.
Hence one must be accurate in take appropriate volume of water to be used during moulding and core sand preparation.