A 500 kg raw batch has an overall loss on ignition of 9 per cent. What is the fired mass?
Answer: C
Nine per cent of 500 kilograms is 45 lost, leaving 455. The loss is calculated on the raw mass, so it is subtracted from rather than added to the figure weighed out. Fired yield is what the costing per finished piece is built on.
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A body is 50 per cent clay with 13 per cent loss on ignition and 50 per cent non-clay with no loss. What is the overall loss on ignition?
Answer: D
Half the batch loses thirteen per cent and half loses nothing, so the weighted average is 6.5 per cent. Losses combine by mass fraction, which makes the arithmetic a simple weighted sum. Each material contributes its own loss in proportion to its share.
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Match each calculation with the correction it requires.
List I
A. Weighing out a wet raw material
B. Predicting the fired mass
C. Scaling a recipe to a batch
D. Recovering a recipe from a batch
List II
1. Multiply each percentage by the batch mass
2. Divide by one minus the moisture fraction
3. Divide each mass by the batch total
4. Subtract the loss on ignition
Answer: A
Correct answer: A-2, B-4, C-1, D-3
Four calculations and four operations. A wet material is corrected by dividing by one minus the moisture fraction. A fired mass is obtained by subtracting the loss on ignition. Scaling a recipe to a batch multiplies each percentage by the batch mass. And recovering the recipe from a batch divides each mass by the batch total - the inverse of the third.
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All of the following change the mass actually weighed out EXCEPT
Answer: B
Loss on ignition affects the fired mass but not what goes on the scale, since the material is weighed before it is fired. The other three all alter the quantity that has to be weighed out on the day. Only the kiln loss is invisible at the scale.
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State whether the following is true or false.
Loss on ignition affects the mass weighed out at the batch scale.
Answer: C
It affects only the fired mass, since the loss happens in the kiln long after weighing. Confusing the two is a common source of error in yield and costing calculations. Weighing happens before the kiln and the loss happens inside it.
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Arrange the steps of preparing a body batch in the order they are carried out.
1. Weigh out the corrected quantities
2. Convert the recipe percentages to masses
3. Mix and check the resulting body
4. Correct each mass for the moisture in the delivered material
Answer: D
The moisture correction must be applied before weighing rather than afterwards, since it changes what goes on the scale. Doing the steps out of order produces a batch whose dry proportions are not what the recipe intended.
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Two clays contain 22 and 34 per cent alumina. In what ratio should they be blended to give 26 per cent?
Answer: A
The first is 4 below the target and the second 8 above, so they mix in inverse proportion, two to one. The mixing rule works for any two materials blended to a value lying between them. Distances from the target are used in inverse proportion.
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Assertion (A): Two materials cannot be blended to a value outside the range between them.
Reason (R): Any mixture is a weighted average of the two component values.
Answer: B
Both are true and the reason gives the constraint: no proportion of a 22 per cent and a 34 per cent clay will reach 40 per cent, so a third material is needed whenever the target lies beyond both components. The rule sets a hard limit on what blending can achieve.
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State whether the following is true or false.
Blending two clays can produce an alumina content higher than either of them.
Answer: C
A mixture is always a weighted average and therefore lies between the two values. Reaching beyond either requires a third material with a higher content than the target. Two components bracket the achievable range between them.
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A slip is 65 per cent solids by mass. How much dry material is in 500 kg of slip, and how much water?
Answer: D
Sixty-five per cent of 500 kilograms is 325 of solids, leaving 175 of water. Slip solids content is quoted by mass unless stated otherwise, and the distinction from volume matters a great deal. A volume basis would give a quite different figure for the same slip.
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