ELECTRICAL HEATING – PART – 13
AJAX WYATT OR VERTICAL CORE FURNACE & CORELESS FURNACE
AJAX WYATT VERTICAL CORE FURNACE
Ajax Wyatt vertical core furnace [This is an improved version of direct and indirect core type furnace]
1. This furnace makes use of vertical crucible instead of a horizontal one for the charge.
2. The shell of this furnace is made up of heavy steel.
3. The top of the furnace is covered with an insulated cover which can be removed for charging.
4. The inside of the furnace is clay lined for yellow brass and alumina for red brass and bronze.
5. Apart from V-Shaped channel, U-shaped and rectangular channels are also employed.
6. The circulation of molten metal is kept up round the V-shaped portion by convection currents in the two halves of the V-shaped.
7. Since it is a vertical core type furnace the tendency of the currents to interrupt the secondary circuit is due to pinch effect is avoided due to weight of the charge in the main body of the crucible.
8. For continuous operation V-Shaped portion must be kept of charge in order to maintain continuity of the secondary circuit.
9. This furnace can be operated at power frequency.
10. Its operating power factor is about 0.8 to o.85 and with normal supply frequency its efficiency is about 75%.
1. Suitable for continuous operation.
2. It is widely used for melting and refining brass and of other non-ferrous metals and alloys.
HIGH FREQUENCY-CORELESS FURNACE
This furnace consists of three main parts (i) Primary winding (ii) the refractory contained and (iii) frame which includes supports and a tilting mechanism.
1.The main feature of this furnace is that it contains no heavy iron core with results there is no continuous path for the magnetic flux.
2. Its construction is simple and its weight is less compared to other furnaces.
3. Due to less weight it is conveniently tilted for pouring.
4. This furnace is mainly operated at high frequency
5. Skin effect exists in this furnace
6. The primary winding coils are made of hollow tubes and are cooled by circulation of water through them.
7. Convenient shape of crucible may be used.
8. Generally frequency in the range of 500 to 1000Hz is employed for large furnaces of upto 5 tons,
9. Frequency of 105 are employed for smaller laboratory furnaces for melting a small quantity of finely divided metals.
10. For efficient operation, the ratio between the diametre (d) of the charge and the current penetration (t) should be nearly 8 i.e. d/t = 8.
1. The charge is put into the crucible and primary is connected to the ac source.
2. The magnetic flux produced by the primary winding setup eddy currents in the charge
which, tend to flow concentrically, and are sufficient to heat the charge to melting point and also setup electromagnetic forces which produces stirring action.
3. The magnetic coupling between the primary and secondary winding is low, hence the furnace power factor is lies between 0.1 and 0.3.
4. Static capacitors are used to improve the power factor.
5. By increase the charge diametre d, efficient operation can be achieved even at low frequencies. This is the reason lower frequencies are used for larger furnaces and vice versa.
1. Low erection cost.
2. Low operating and maintenance cost.
3. Charging and pouring is simple.
4. Suitable for intermittent operation.
5. Simple power control devices can be employed.
6. Suitable for precious metal melting.
7. Less melting time.
8. Free from dirt, smoke and noises.
9. Fast in operation.
10. Possible for accurate temperature control.
1. Its initial cost is very high 3 to 4 times that of any other type.
2. It is only economical in sizes up to 4-5 tons.
It is highly suitable for the production of highest grade alloy steel and there is no contamination of the product by impurities.
Post time: Jan-08-2018