Solving Heat Problems: Quenching a Hot Knife Blade

In summary, the problem is asking for the minimum amount of water needed to quench a 400 degree C steel knife blade with a mass of 80g without raising the water temperature above its boiling point. The answers provided were 22, 33, 44, or 55g. To solve this problem, we use the equation Q=mc∆T to find the amount of heat lost by the steel and gained by the water. We know the initial temperature and specific heat of the steel, so we can calculate the total heat in the blade. Then, we use the specific heat of water to find the amount of heat required to raise the temperature from 20 to 100 degrees. Finally, we can determine the
  • #1
Dx
I missed the test question can anyone explain what they did to solve for this.

In grinding a steel knife blade(SH=.11 cal/g*C) the metal can get as hot as 400C. If the blade has a mass of 80g, what is the minimum amount of water needed at 20C if the water is not to rise above the boiling point when the hot blade is quenched in it?

answers were: 22, 33, 44 or 55g

I tried using Q=mc[del]T then the difference of the two but didnt work that way, can anyone please help me?
TY
Dx :wink:
 
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  • #2
Originally posted by Dx
I tried using Q=mc[del]T then the difference of the two but didnt work that way, can anyone please help me?

I don't know what you mean by "the difference of the two", but to do this problem at the most basic level you have to assume that all the heat lost by the steel is gained by the water.

Heat lost by steel: qS=mScSΔTS
Heat gained by water: qW=mWcwΔTW

You have the initial temps of both the steel and the water. Assume that the steel and water come to thermal equilibrium. The only unknown is mW.
 
  • #3
You know the temperature of the blade is 400 degrees C, the mass is 80 grams and the specific heat is .11 cal/g*C so the total heat in the blade is 400*80*.11= 3520. How many calories does it take to raise 1 gram of water 1 degree? (That's what Tom meant by sw, the specific heat of water. Good job, Tom.) That's physical constant that should be given in your book just as the specific heat of steel was.

Once you know that, how many calories are required to raise the temperature from 20 to 100 degrees?

Finally, once you know that, how many grams of water do you need to account for all those calories?
 

1. How does quenching help in solving heat problems for a hot knife blade?

Quenching is a process where a hot metal object, in this case a knife blade, is rapidly cooled by immersing it in a liquid. This helps in solving heat problems for a hot knife blade by quickly reducing its temperature and preventing it from becoming too soft or losing its sharpness due to overheating.

2. What liquids can be used for quenching a hot knife blade?

There are various liquids that can be used for quenching a hot knife blade, such as water, oil, brine, and even air. Each liquid has its own specific properties and can produce different results, so it is important to choose the right one based on the type of metal and desired outcome.

3. How do I know when the hot knife blade needs to be quenched?

One way to determine when a hot knife blade needs to be quenched is by monitoring its color. When the blade reaches a bright orange or yellow color, it is an indication that it is ready for quenching. Additionally, if the blade starts to lose its sharpness or becomes too soft, it also needs to be quenched to prevent further damage.

4. Are there any risks involved in quenching a hot knife blade?

Yes, there are some risks involved in quenching a hot knife blade, such as the potential for the blade to crack or warp due to the rapid change in temperature. It is important to follow proper safety precautions and techniques, such as controlling the quenching process and using protective gear, to minimize these risks.

5. Can quenching be used for any type of metal?

Quenching can be used for a wide range of metals, including carbon steel, tool steel, and stainless steel. However, the type of liquid used and the quenching process may vary depending on the specific properties of the metal. It is important to research and understand the properties of the metal before attempting to quench it to ensure successful results.

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