Furnace Manufacturer

By Author: shailesh solanki
Total Articles: 7
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Article about Furnace
IMPORTANT PARAMETERS FOR SELECTION OF AN INDUCTION FURNACE A CUSTOMER'S PERSPECTIVE
An induction melting furnace is the most important equipment in a foundry. Proper functionality of the same attributes to more than 50% of all issues related to the performance of the unit. The decision making process of selecting an Induction Furnaces involves, consideration of 2 major criteria
1. Cost of the furnace 2. Sizing of the furnace
The Cost of the furnace is a very important factor while furnace selection .However the cost of the furnace is not merely the price of the furnace alone but it includes
1. The Initial cost of furnace 2. The Running cost of furnace
Initial cost:
Initial costs are divided into
1. Price of furnace 2. Price of auxiliaries 3. Area required for Total installation 4. Cost of installation
Price of furnace: Factors affecting the furnace price are
1. Technology incorporated 2. Material of construction used 3. Specifications of the furnace
Price of furnace auxiliaries:
The induction furnace cannot operate without ...
... installation of proper auxiliaries like, cooling tower, pipelines, pumps, underground tanks, emergency overhead tank, flow switches, hose pipes etc
It is necessary for the customer, while calculating the cost of the furnace to include the cost of all auxiliaries, irrespective whether supplied by the manufacturer or purchased by the customer from other sources. Factors affecting the furnace auxiliary prices are:
1. Technology 2. Customer related specific requirements 3. Specification /capacity of auxiliaries
Installation cost:
Costs of installation, at times, greatly adds to the price of the furnace and most of the times this is ignored by the customer while selecting the furnace. Here an optimum layout and location becomes very important, considering electrical, structural and efficient material handling requirements.
Erection and commissioning charges are a part of installation costs and these have to be finalized during the furnace selection process.
Running cost of the furnaces:
The Reliability of the furnace and Efficiency are the major parameters which decide the running costs of the furnace.
Reliability is a function of the design and the material of construction used. It is directly related to the up time of the furnace. The natural consequence is lower maintenance costs and breakdowns.
Maintenance costs are a breakdown dependent cost. Higher the breakdowns, higher the maintenance costs. Breakdowns lower the production and increase the foundry production costs.
Factors which effects the maintenance cost are:
1. Availability of spare parts 2. Cost of spare parts 3. Cost of service
One should consider all the above factors when arriving at the variable costs of operating an Induction Furnace.
Efficiency: Energy content of molten metal at any specified tapping temperature in (kwh)
The furnace efficiency =------------------------------------------------------------------------------------------------------------- *100
Electrical energy used to reach the above condition in (kwh)
Thus lowest specific energy consumption means highest efficiency.
It must be remembered that running costs should also include the running costs of the auxiliaries.
The initial cost should be given a weightage of 25% and 75% weightage ought to reserved for the operational costs while selecting an Induction Furnace.
Furnace sizing is one of the most important criteria while selection
Factors affecting the furnace sizing are
1. Power available 2. Melt rate 3. Job size requirement 4. Type of metal
Normally a furnace specified in kw rating and kgs capacity
Furnace rating (Kw), is the power requirement for melting and raising the temperature for a particular batch size in a rated time plus the power losses in the system.
The heat content required to melt and raise the temperature of a specified material can be calculated using the, average specific heat and latent heat of fusion per kg in kwh in the following manner
Weight of material X specific heat (average) KJ/Kg/C X ^T (final temperature’s- ambient temperature0C) + latent heat of fusion X Wt of material
3600
To arrive at the energy content of molten metal in KwhWhen we input electrical energy to the furnace there are various losses like
1. Coil loss 2. Conversion loss 3. Transmission loss 4. Load matching losses etc
These have to be added to the above theoretical heat energy to arrive at the input energy in (kwh). Thus the furnace rating and capacity are a function of all those losses since the theoretical energy required for melting a specified material is constant.
Power density is a very important criteria during furnace selection for small furnaces. It leads to
1. improved equipment utilization, 2. lowers batch melting times, 3. improved efficiency due to lower radiation and conduction losses. Generally a Kw to Kg ratio of 1:1 to 1:4 is ideal for foundry furnaces.
Frequency:
Frequency, an important but ignored parameter which plays a prominent role in induction melting. In order to acquire highest electrical efficiency, furnaces of different capacities must be matched with proper frequencies considering the metal to be cast.
Frequency produces
1. Skin effects ( depth of penetration)
2. Natural churning effect(h/d ratio)
Skin effects (Depth of Penetration ) depend upon the applied frequency and the resistivity of the metal, resistivity keeps on changing with temperature change,
The depth of penetration δ=503 √resistivity of metal in (ohm – cm)
------------------------------------------------------------------
√ (Relative permeability of metal) X √frequency applied in HZ
During melting operations (at a given frequency) the depth of penetration of inductive current increases with increase in temperature. When the depth of penetration is higher than the charge material thickness, distinct current cancellation occurs within the so called electromagnetically “thin” body, and this reduces the joule effect which Is necessary for efficient heating, For efficient melting electromagnetically thick materials must be used. At lest 6 times higher than the depth of penetration.
Natural churning of the melt is another frequency dependant phenomenon, which plays a crucial role when alloying different materials.
Its also helps in proper heat distribution in the molten metal. It is indicated by the h/d ratio
79 X applied power (kwh) X efficiency (Coil)
h/d ratio= -------------------------------------------------------------------------------------------------
wt of metal X √applied frequency in Hz X materials resistivity (ohm- cms)
besides frequency, churning also depends on input power, furnace efficiency, material weight, viscosity of the melt and metal resistivity.
The importance of having a good Power Factor
When the supply and load both are sine waves ,the power used is a product of voltage, current and the phase angle between them.
Therefore PF = cosØ (Ø is the phase angle) Or PF = KW/KVA
Thus the Power Factor is the ratio of the watts used to the volt X amp supplied.
Losses in the system, bus bars, switching, cables, etc. are directly proportional to the square of the current. Losses( P) = I2R where I denotes amperes and R the Resistance. Therefore it is desirable to have as high a Power Factor as possible, to minimize I2R losses.
HIGH PF = low I2R losses ( 99% and above )
=Low losses in the system
LOW PF = high I2R losses ( below 99% )
= high losses in the systems.
A detailed study of the above mentioned furnace parameters will help in selecting a most efficient Induction Furnace for a specific application.
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