SAND TESTING PREPARATION (GREEN SAND)

 

OBJECTIVE:  To measure the following properties of moulding sand, green

                           compression strength and permeability.

 

APPARATUS:                 

1. Materials: Silica sand, Coal Dust, Bentonite, Water

2. Equipment: Permeability Machine, Sand Reamer, Universal Sand

                      Strength Testing Machine

3. Hand Tools: Specimen tube, ruler

 

                         

                                                (a)                                            (b)         

 

                         

                                                (c)                                            (d)

 

 

Figure 1.(a) Permeability machine,1.(b)Strength testing machine,1.(c)Ramming machine & funnel and1.(d) specimen.

 

 

 

 

 

THEORY:

                               

1. Green compression strength

 

Green compression strength refers to the stress required to rapture the sand specimen under compressive loading. The sand specimen requires rupture the sand specimen under compressive loading. The sand specimen is taken out of the specimen tube and is immediately put on the strength testing machine and force requires to cause the compression failure is determined. The green strength of sand is generally in the range of 0.03 to 0.16MPa.

         

2. Permeability

 

The rate in cc/min at which air will pass through the standard compression specimen is used as an index of permeability Standard permeability is determined by measuring the time necessary for 2000cm³ of air pass through the standard specimen while it is confined in the specimen tube and under pressure of 10 gm/cm² .if the time is determined the permeability number can be calculated from the formula. 

 

          Where:              =  volume of air = 2000 cm

                                                = height of the specimen = 2 inches

                                                 P = pressure = 10gm / cm

                                                A  = cross sectional area of sand specimen = 1in

                                                T   = time, sec, for 2000cm³ air to pass through specimen

 

The formula reduces to AFS Permeability:

                        P= 3000.7   for old machine with Hg

                              T(sec)

 

The formula reduces to AFS Permeability For Ridsdale-Dieter

                        P=                    30557_____________ = 30557                      

                              Air pressure in cm x time in (sec)           p x t

 

 

 

 

PROCEDURE:         

 

Standard Test Specimen Preparation

 

1.      Sand to be test is collected at the amount of 175 g.

2.      With the help of a funnel the sand are then filled in a steel tube and stopper are placed at the other end of the tube.

3.      The tube then are bring to the ramming machine to gives three times impact by turning the machine handle three times.

4.      After that the tube is carried out from the ramming machine and placed to the permeability machine. (permeability machine is turned on and the scale are set to zero first)

5.      Permeability number is obtained and recorded in 30 minutes. (Three times).

6.      After got the permeability number, the sand specimen then removed from the tube and the cross sectional area also the height are measured and recorded.

7.      Afterwards the specimen being placed to the adapter of the universal sand strength testing machine.

8.      The initial reading is taken by setting the magnet pieces to the zero reading. 

9.      The specimen is compressed by turning the handle until it fails and the reading is recorded for analysis purposed.

10.  Step 1 to 9 is repeated for the mass of 165g and 145g.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RESULT:                   

 

Raw Material
Silica sand	400 g
Bentonite	20g
Coal Dust	22 g
Water	10%

 

 

Green Compression strength			Permeability
Specimen	Mass (g)	Height (mm)	20 sec	30 sec
1	175	62	53	50
2	165	58	58	57
3	145	51	65	64

           

Sample calculation for specimen 1 at 20 seconds:

 

                                               

 

                                                P =

 

                                               P = 100.65 cc/min

 

            Readings are obtained according to the three samples of weight, 175 g, 165 g and 145 g, however only the first reading managed to get a height of 50.8±0.125 mm. Since the value of 50.8mm falls below the weight of 145 g , the exact theoretical value are calculated as below.

 

The desired height is 50.8 mm and x is the desired weight.

                        Using interpolation, the value of x is determined as below,

 

=

                                                               

                                                                  X = 144.43 g

 

 

For the 142.06 g of mass, the specimen undergoes Permeability Test and after three readings, the average value obtained by interpolation was 65.2 kg/ N

The Green Compression Test, this specimen started to fail/crack at 15 kN/m.

Theoretical value of Permeability for the mass 144.43 g is 100.65 while the experimental value determined from the experiment is 65.2 kg/ N

 

 

Percentage of error,

 

100.65 – 65.2        X 100   =   54.37 %

                                            65.2

 

         

 

DISCUSSION: 

 

There is a different in the actual and the experimental value of permeability, These different are cause by a several factor such as moisture contain in the sand specimen is drying or effected by the surrounding temperature. The experiment was done with three dissimilar value of mass and for each value of mass the time taken are long. As a result the water contain in the specimen sand box are condensed to the atmosphere. Inexperience student who running the test and other factor.

For the green compression strength test, the specimen fails at unproperciate force because the specimen keeps drying. It also because of the cold dust, bentonite and water mixture are not perfectly right.

CONCLUSION:

                       

It is found that a lot of factors present causing errors in readings of the data. It begins from the first step which is, the sand pored into the funnel directly to the test tube. While doing this, some of the sand will stick at the funnel and the accuracy of mass is totally reduced. Next, when it is being rammed in the rammer machine, the same thing happens where a small number of sand will also stick at the head of the rammer. Again, the mass of the specimen will be reduced. Even the loss of sand due to these processes is very little but it still affected the whole process especially in terms of sand volume. Since the volume drops, thus the dimension of the specimen required will not be accurate. So, the desired height of 50.8 ±0.8mm may not be achieved.

For the permeability test, the first value of permeability managed to get in the range of 50.8 ±0.8mm, but the other did not because the volume of air flows through the sand specimen dries it up slowly and causing the sand specimen to be drier and more air can pass through it.

For the green sand compression strength, a machine is being used to test the specimen’s strength. The specimen that undergoes this test was the 144.43 g specimen which states the reading of 50.8mm in height. The specimen is tested until it fails at 15 kN/m.

In order to success in this particular experiment, the sand needs to be mixed with the correct amount of bentonite, coal dust and water. Excessive amount of water would make the sand harder in uniformly condensed even in a short while. So know we can understand that there is a need to control the temperature accurately to avoid the condensation process, since it wills influent the value of permeability.