Ball Clay & China Clay Testing Procedure for Properties & Quality
Step 1 :
Let us start the test procedure by doing sampling first. For doing sampling, the material i.e Ball clay or china clay has to be collected from the material storage bin. Collect the material for testing from five different areas like bags randomly and mix the material after collecting equally. The material is called as Sampled Material.
Step 2 :
Next is Moisture test, Now measure and weigh 100 gm of sample material using weighing balance in a plate made of steel, for reference note the weight as S1. The weighted sampled material has to be kept in a drier at 100° - 105°C for 2 hours. Remove the material from drier now note the material weight again as S2.
Moisture % = ((W1 – W2)/W1)*100.
Using the formula given above calculate the moisture %. For the weighed S1 material (7 Kg) add 4 liters of water and cover the bucket. If the material is not completely dry, then as per moisture content percentage add extra material to compensate moisture content in weight of the material. Let the material soak for around 12 to 19 hours.
Step 3 :
Next the Alkali Demand test, We have to prepare Sodium Silicate solution by using 100gm of sodium silicate in a mug, for weighing it weighing balance can be used. Now add 100 gm of water to the mug containg sodium silicate and stir with stirrer to prepare [1:1] Sodium Silicate Solution.
Keep a bucket containing S1 material soaked with water and place it under the stirrer. Now switch on the stirrer and the material starts bunging. Using a weighing balance weigh the Sodium Silicate solution and add little by little (1 gm once) till the material turns fluid from sticky stage and transform into slip. Once it becomes fluid, then check for Fluidity & Thixotropy using torsion Viscometer. Weigh & Add Sodium silicate solution till the Thixotropy becomes less than 20.
Step 4 :
When the slip attains the Thixotropy of less than 20, record the amount of Silicate Solution added in slip. Using the formula given below the Alkali Demand can be calculated,
Alkali Demand (%) = ((x/2)/W1)*100
Where x – Amount of sodium Silicate solution added(gm)
S1 – Weight of the Material used (7 Kg).
Step 5 :
The Density measurement has to be done, measure the weight of Pycnometer with lid and record the weight as S1.
The slip has to be poured in Pycnometer and closed with the lid, then measure the weight of Pycnometer with lid and record the weight as S2.
Calculate the Density of the Slip by using the formulae,
Specific Gravity = (W2 - W1) gm/cc
If the density of slip is,
< 1.550 gm/cc – Add Extra material to adjust it 1.550gm/cc as per calculation
>1.550 gm/cc - Add Extra water to adjust to 1.550gm/cc as per calculation.
Step 6 :
To measure the Fluidity and Thixo, take the prepared slip in a plastic bucket and mix well in a stirrer for 1 min with 400 rpm. Using a stopwatch record the time of the process. Pour the slip into the cup and place into the tray of Torsion viscometer and immediately take the reading i.e. flow ability at 0 minute FO (Fluidity of the Slip). Restart the stop watch.
Take the viscometer reading at 6 minute and record it as flow ability at 6 minute (F6).
Now calculate the Thixotropy using Thixotropy at 6 minute = F0-F6 If Thixotropy is not equal to < 20 degrees, then adjust with addition of [1:1] silicate solution and bring it down to < 20 degrees.
Step 7 :
To do Residue test, using weighing balance take 100g of slip in a steel plate. Sieve it through 200#, collect the retained residue on the sieve in a steel plate. Then keep the steel plate into dryer at 105°-110°C for 2 hours.
Measure the weight of Residue & note it as S1. Repeat the same process with 325# to get the % Residue in 325#. Calculate the % of residue using the formula given below.
Residue % = W1
S1à Weight of residue.
Step 8 :
To do the Shrinkage Test, measure the length of the shrinkage bar mould as L1. Cast the shrinkage bar mould with the slip of required Quantity. Then demould it after 12 hours and dry it in normal air for 5 hours. Keep it into a dryer at 50° C – 55 °C for 5 hours. Put it into dryer at 100°-105°C for 24 hours. Measure the length of dry sample bar with Vernier caliper and record it as L2. Fire the bar in the tunnel kiln and get the bar after firing. Measure the length of fired bar with Vernier caliper and record it as L3.
Calculate the Shrinkage using the formula given,
Dried shrinkage (%) = (L1-L2)/L1*100
Fired shrinkage (%) = (L2-L3)/L2*100
Total shrinkage (%) = Dried shrinkage (%) + Fired shrinkage (%)
Step 9 :
The LOI test is done by measuring the weight of the Shrinkage Bar using weighing Balance and note it down as S1. Send the Shrinkage bar to Kiln and get the bar after fired from the Kiln. Weigh the Shrinkage bar after Fired. Note the Weight as S2.
Calculate the LOI % using the formula given below,
LOI % =( W1 – W2)/W1 * 100
S1 – Initial Weight of bar
S2 – Final Weight of the bar after Fired
Step 10 :
Now the Water Absorbtion test has to be done. Cut a small portion of fired Shrinkage bar. Refer to Water absorption test to complete the Water Absorption Test.
Step 11 :
Next the MOR test, cast the MOR bar mould with required quantity of slip. Demould it after 12 hours. Dry it in normal air for 05 hours. Put it into dryer at 50°C - 55°C for 5 Hours & then 100°-105°C for 24 hours. After taking it from dryer to cool them to room temperature, put the samples into desiccators for 30 min.
Perform MOR test for 5 No’s of dry MOR bar and the record the load value for each bar. Calculate the MOR for 5 bar using the formula given,
8*P*L MOR = П* D3
P= load applied (kg)
L= length (cm)
D= Diameter of the bars (cm)
Step 12 :
To find the cast rate, take 2 litres of slip in a small bucket. Clean and condition the cast rate mould. Pour and completely fill the mould with required slip for 1 hour (for ball clay) & 1/2 (for China Clay). After 1 hour (for ball clay) & 1/2 (for China Clay) then tilt the mould and remove the excess slip and then dry for half an hour. After drying Cut the pieces at bottom portion (three pieces) using punch (cutting Ring). Using Vernier Scale measures the thickness of the three pieces, finally calculate the average.
Step 13 :
Now do CaCO3 Test, Take 10% HCl Solution of 50 ml using Pipette and pour it in small glass beaker. Put 10 gm amount of Clay sample into 10% HCl solution. Observe the effervescence occurred and record it in a result sheet whether it is OK or NOT OK.
Venkat Mani is a Ceramic Engineering Graduate from India, working in Sanitaryware production line for 10 years. He shares Meaningful content related to sanitaryware professionals that others find useful.