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Converting Deg F To Deg C For Ramp Rates


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#1 Chilly

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Posted 28 December 2013 - 06:00 AM

Following on from the discussion on re-firing and cracks...........

 

I've tried to convert the below ramp from deg F to deg C, and calculate how long the firing will take. (Theory of course, I know the kiln may not be able to keep up/down with the ramp rate, but it will give me a guide as to firing time.

 

 

Cone 6 Glaze Firing

 

100 degrees F per hour to 220 degrees F, no hold

350 degrees F per hour to 2000 degrees F, no hold

150 degrees F per hour to 2185 degrees F, hold 15 minutes

On the way down:

500 degrees F per hour to 1900 degrees F, no hold

125 to 175 degrees F per hour to 1450 degrees F, no hold

Cool naturally from 1450 degrees F

 

 

 

[Deleted text that didn't format - see post after this for ]

 

 

The maths on both sides looks OK.  I converted the deg F to deg C using the Excel Convert formula, and double-checked the results using online conversion sites, so they are correct.  But the results to work out time taken don't make sense.  I used (EndTemp-StartTemp)/Ramp, looking at degF and degC separately, the results look sensible, but I would expect them to be the same as each other.

 

So, why does firing in Deg C takes longer than firing in Deg F.  I don't believe in Santa Claus, and I don't believe these figures either.

 

Can anyone throw any light on this?


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#2 Mart

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Posted 28 December 2013 - 06:11 AM

Your post is unreadable and I can only guess what went wrong.
please use preview next time. :)

Next to "Post" is "More Reply Options" > "Preview Post"

#3 Chilly

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Posted 28 December 2013 - 06:25 AM

Ummm, typed lots of spaces, and previewed it, looks, better, hope it stays.....

 

Deg F                                                                            Deg C                                   

Start temp          Ramp         To           hours           Start temp          Ramp              To           hours

                F                    F           F                                                C                  C                 C            

               32               100      220            1.88                            0              37.8        104.4             2.76

             220               350    2000            5.09                        104              177        1,093             5.60

          2,000               150    2185            1.23                     1,093               66         1,196             1.57

 

 

The maths on both sides looks OK. I converted the deg F to deg C using the Excel Convert formula, and double-checked the results using online conversion sites, so they are correct. But the results to work out time taken don't make sense. I used (EndTemp-StartTemp)/Ramp, looking at degF and degC separately, the results look sensible, but I would expect them to be the same as each other.

 

So, why does firing in Deg C takes longer than firing in Deg F. I don't believe in Santa Claus, and I don't believe these figures either.

 

Can anyone throw any light on this?


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Ann

http://www.readypeda...uk/pottery.html


#4 Mart

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Posted 28 December 2013 - 06:35 AM

You used wrong math.
Converting F to C or C to F is one calculation.

Converting "rate of change" is something else.
 

The formula for converting an F rate to a C rate is C = F / 1.8
The formula for converting a C rate to an F rate is F = C x 1.8

 



#5 Mart

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Posted 28 December 2013 - 06:41 AM

What this means is that 100 F per h = 55.56C per h

 

Now, do not forget to subtract the ambient (usually 20-22C) from correct sides of the calculation

 

You do not start form 0 but from ambient temperature.

 

20C is 68F



#6 Mart

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Posted 28 December 2013 - 07:56 AM

 

Now, do not forget to subtract the ambient (usually 20-22C) from correct sides of the calculation

 

You do not start form 0 but from ambient temperature.

 

Essex, this time of year?? Ambient temp is likely to be closer to 0°C than 20°C !!

 

 

Sure, if you keep your kiln outside or in a room, whit no insulation. Most kiln controllers do not like that 0 C temp at all and think something is broken.

 

Actually, on second thought, forget the subtraction. It's not needed.



#7 Chilly

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Posted 28 December 2013 - 08:50 AM

 

You used wrong math.
Converting F to C or C to F is one calculation.

Converting "rate of change" is something else.
 

The formula for converting an F rate to a C rate is C = F / 1.8
The formula for converting a C rate to an F rate is F = C x 1.8

 

 

32/1.8= 17.7778.   So you're saying that 32F does not = 0C?  Everyhere I look says 32F=0C

 

What this means is that 100 F per h = 55.56C per h

 

Now, do not forget to subtract the ambient (usually 20-22C) from correct sides of the calculation

 

You do not start form 0 but from ambient temperature.

 

20C is 68F

""What this means is that 100 F per h = 55.56C per h""   WHY?

 

 

 

Now, do not forget to subtract the ambient (usually 20-22C) from correct sides of the calculation

 

You do not start form 0 but from ambient temperature.

 

Essex, this time of year?? Ambient temp is likely to be closer to 0°C than 20°C !!

 

It was 7 deg C when I switched the kiln on last night, with a forecast low of 3C, perhaps I should have started my example at one of those two, but 0C is the lowest "operating" temp for my controller, and anything colder than 0C I'm not interested in - tooooo cold!


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#8 Chilly

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Posted 28 December 2013 - 09:46 AM

What this means is that 100 F per h = 55.56C per h

 

 

 

 

While eating my lunch I decided it must need a % calculation to convert the ramp rate.

 

I found a chart in one of my books that gives heating rates for Orton cones, and surprise surprise, the difference between the F ramps and the C ramps is 55.56%.  So I need to multiply the F ramp rate by .5556.

 

Yippeee.  The time taken is now the same for both C and F. 

 

So, Ramp Rates of 100, 350, 100 F become 56, 195, 83 C

 

OK, so what was I doing before I needed to drain the swamp?  Oh yes, I remember............................... 


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#9 Mart

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Posted 28 December 2013 - 09:51 AM

You used wrong math.
Converting F to C or C to F is one calculation.

Converting "rate of change" is something else.
 

The formula for converting an F rate to a C rate is C = F / 1.8
The formula for converting a C rate to an F rate is F = C x 1.8

32/1.8= 17.7778.   So you're saying that 32F does not = 0C?  Everyhere I look says 32F=0C


No, I did not say that  "32F != 0C".
I wrote: "Converting "rate of change" is something else" and you need to use different math.

 

What this means is that 100 F per h = 55.56C per h
 
Now, do not forget to subtract the ambient (usually 20-22C) from correct sides of the calculation
 
You do not start form 0 but from ambient temperature.
 
20C is 68F

""What this means is that 100 F per h = 55.56C per h""   WHY?


Because you do not need to subtract 32 like you have in C to F equation and 9/5 = 1,8.

Here is very good picture, that illustrates this: temperature-conversion

You are wondering, where that "9/5" comes from? It's from (°C × 9/5) + 32 = °F

Notice the 1.8x difference between 100 and 180

#10 Chilly

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Posted 28 December 2013 - 11:43 AM

Mart:  Your first explanation did not make sense to me, your second explanation would have left me more confused.  I'm pleased I was able to work out the answer for myself, as I understand it.

 

I was not wondering where "9/5" comes from.  I am well aware of the calculations required to convert from F to C and vice versa, but converting the ramp rate clearly needed a different theory.


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#11 bny

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Posted 28 December 2013 - 01:37 PM

The methods that Norm Stuart gives below are correct. Rates are converted with multiplication and division only.

Typical trick warm up problem in week 1 of college physics.

You've got it. 
 
Degrees per hour ramp rate is C  =  F / 1.8     or     F  =  C * 1.8
 
But for actual temperature you have to also add or subtract 32,  C  =  (F - 32) / 1.8     or     F  =  (C * 1.8) + 32
 
 
Multiplying/Dividing Adding/Subtracting has never been easy for me without a computer spreadsheet program.
 
Sometimes I'll forget and use a temperature converter for ramp rate, resulting in the wrong answer.
 

I am well aware of the calculations required to convert from F to C and vice versa, but converting the ramp rate clearly needed a different theory.






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