Furnace Capacity / Rating Selection
Step 1
The furnace capacity / Rating selection is the most common question bothering for the buyer/prospects. Sometimes it creates confusion, because different manufacturers suggest different combinations.
How should one select the furnace (KW/KG/Hz) which fitted to one’s requirement technically and commercially as well?
Which metal or alloy do one’s want to melt and at what pouring temperature?
Melt rates or melting speed is different for different metal & alloys at particular applied kw, this is due to difference in specific heat of different metal.
At the same time due to different latent heat of each metal, superheating of each molten metal will be different, so different melt rate at particular applied KW.
So we suggest every one to follow the furnace selection process step by step.
For Example
For Different Metal
At particular 600 KW Furnace Compare Brass & Steel Melting
For Steel Melting
1100 KGS / Hr @ 1600°C
For Brass Melting
1900 Kgs/hr @ 1100°C
Summary
So At Same KW, Different Metals, Different Metals Rate
For Super Heating Case.
At Particular KW For Steel Melting.
At 1500°C The Melt Rate Be 1250 KGS / Hr.
At 1600°C The Melt Rate Be 1100 KGS / Hr.
For Same Metal, KW, At Particular Applied KW, Different Pouring Temperature, Different Metals Rate
Once You Configure Your requirement for a Particular Metal Melt Rate @ Temperature Degree Centigrade °C, According To Step One.
No Switch To Step 2.
Step 2
You Must Specify The Liquid Metal Requirement In Tons Or In KGS, Per Month With Working Hours In A Day.
(A) For Steel Ingot
Suppose You Required 1200 TONS / Month Of M.S. Steel Ingot @ 1600°C What The Furnace Size Should Be?
- Consider Working Days – 25 Days
- 1200 TONS ÷ 25 Days Gives 48 TONS Of Liquid Metal @ 24 Hrs Working.
- 48 TONS ÷ 24 Hrs So, Melt Rate Will Be (48/24 = 2) 2 TONS Per Hour
- Now Consider The Unproductive Time Of Cycle, i.e. Time For Deslagging, Charging, Sintering, Lining Etc. So The Furnace Utilization Will Be 80% Thus
–2 TONS / 1 Hr Divided By 0.8. Is 2.0 ÷ 0.8 = 2.5 TONS / Hour Should Be The Required Furnace Melt Rate At 1600°C.
5. Now Refer The Furnace Specification Table. You Will Find The Nearest Melt Rate Can Be Achieved By 1500 KW / 3 TONS Furnace @ 2.6 TONS 1 Hour Melt Rate.
We Have Considered Here 1500 KW Means 1500 KVA (exclusive Power At The Furnace Input.)
So The Answer Is By 1500 KW / 3 TONS Furnace, You Can Produce 1200 TONS Of M.S. Steel Ingots @ 1600°C Per Month.
(B) For Castings (step-2)
Suppose You Want To Make 300 TONS / Month Of Finished Steel Casting, With An Average Yield Of 65% And Utilizing Of Furnace Is About To 75%.
Then What Should Be The Furnace Capacity? Pls Suggest.
At Particular KW For Steel Melting.
- So now 300 TONS +Yield (0.65)
- The total Monthly Molten Metal Requirement For Casting Is 465 TONS/Month.
- Now 465 TONS Divided By 25 Working Days Gives 18.6 TONS Of Molten Metal Per Day Of 24 Hours Working.
- 18.6 TONS Again Divided By 24 Hours Gives Required Melt Rate Of Molten Metal Is 775 KGS / Hr. Now
Considering that the utilisation of The Furnace is 75 %, it Is Due To Sintering, Lining, Deslagging, and Recharging.
Composition Setting Etc. - Thus Actual Molten Metal Requirement Will Be 775 +0.75 l.e. 1033 KGS/Hr.
- Next Step Now, You Refer To The Table & From The Table The Nearest Suitable Furnace, Which Can Give 1033
KGS/Hour Melt Rate Is Fer 1. - So, You Should Select a 600 KW & 1 TON Induction Furnace, Which Will Give You The Suitable Melt Rate.
- Another Main Factor that foundry Men have to decide is what the batch size should be.
The Batch Size Will depend upon The Molten Metal Weight You Required.
For Example
If You Required 600 KGS, 750 KGS, 1000 KGS, Metal At A Time Then You Can Select 600 KW Solid State M.F.
Power Source With 1000 KGS Crucible Or Otherwise, If Your Molten Metal Requirement Is Around 500 KGS Or
Less, Then You Can Select 300 KW X 2 Nos Solid State M.F. Power Source With 500 KGS Crucible.
Step 3
Now What Should Be The Right Frequency?
Normally Frequency Selection Is Not Available, And Is An Important Constraint Too. There Are Many Combinations Of KW And KGS Available At Different Frequencies.
Basically Frequency Is One Parameter Which Affects Stirring.
In A Coreless Induction Furnace Stirring Is Produced By Magnetic Forces Acting On A Molten Metal Because Of Interaction Between The Coil Current And The Current Flowing In The Molten Metal Bath. The Force Is The Strongest At Middle Part Of The Coil So Metal Is Forced At The Central Side Of The Bath From Where It Is Resolved To Upward And Downward. Metal Moves Up Because Of Upward Resolved Force. The Upward Movement Of The Metal In The Center Creates Meniscus A Unique Characteristic Known As A Stirring Effect Is Measured By h/d Ratio (h By d Ratio).
Stirring Effect Is Depending Upon The Power Frequency Applied, The Induction Coil Efficiency, Molten Bath Capacity & Density And Viscosity Of Molten Metal as Well.The Three Major Variable Which Effect Stirring Are,
1) Power
2) Frequency
3) Furnace Size
Stirring Can Be Change With Changing Anyone Of The Major Variable.