GB2302167A

GB2302167A - Feeding of fragmentary scrap

Info

Publication number: GB2302167A
Application number: GB9512000A
Authority: GB
Inventors: Michael Pownall
Original assignee: NOTTINGHAM METAL RECYCLERS LIM
Current assignee: NOTTINGHAM METAL RECYCLERS LIM
Priority date: 1995-06-13
Filing date: 1995-06-13
Publication date: 1997-01-08
Anticipated expiration: 2015-06-13
Also published as: GB2302167B; GB9512000D0

Abstract

Turnings are fed from a hopper 22 along a conveyor 240 (preferably a screw conveyor) to a furnace 10. Gasses from the furnace are fed along the conveyor in a direction 100 opposite to that of the turnings to heat the turnings. A magnetic separator 28 removes ferrous material from the, preferably aluminium, turnings. The flue gasses are circulated by fan 300 and ducting 30. Dampers 248, 302 can be used to control the flow of furnace gasses and can be closed for safe removal and emptying of container 282 of the separator 28. An excess heat detector 250 along with control 252 can shut damper 248 to isolate the conveyor. An air lock 222, 224 is provided on hopper 22 to prevent escape of furnace gasses during hopper filling.

Description

FRAGMENTARY SCRAP FEED METHOD AND APPARATUS The present invention relates to a fragmentary scrap feed method and apparatus for a furnace and more particularly to a feed system for aluminium or other non ferrous turnings etc with the facility to magnetically extract ferrous material prior to insertion of the turnings into the furnace and also with the facility of preheating the aluminium turnings prior to their insertion into the furnace.

In the present invention the term turnings is used to refer to small pieces of non ferrous metal (probably aluminium). Aluminium will be used hereinafter to refer to any non ferrous metal.

In any furnace system scrap material has to be fed into the furnace to be subsequently melted. It is advantageous from an environmental view point to be able to preheat the scrap material prior to its insertion into the furnace and also to be able to extract any ferromagnetic material from the scrap prior to insertion of the scrap into the furnace.

It is environmentally unfriendly to allow the escape of any hazardous gases into the atmosphere whilst performing either of the above stages.

In previous know systems aluminium turnings are firstly subjected to the influence of a magnet to remove ferrous material prior to insertion into a furnace or into any preheating stage. This process is, however, not particularly satisfactory since large quantities of useful aluminium turnings are removed during the extraction of the ferrous material since the ferrous material adheres to or is embedded within the aluminium turnings. In many cases the aluminium turnings are covered in lubricating oil from the drilling/melting operation and this tends to make them stick together with any ferrous material thereby causing removal of substantial quantities of aluminium with the ferrous material. Without further processing the aluminium turnings removed with the ferrous material is lost to the operator thereby substantially reducing the yield of the operation.

It is an object of the present invention to provide a system for feeding turnings to a furnace and for preheating the turnings prior to their entry into the furnace and in a preferred embodiment to provide a system for extracting ferrous material from the turnings during the preheating stage.

It is also a further object to preheat the turnings in a sealed environment using exhaust gases from the furnace and to progressively heat the turnings to a higher temperature as they enter the furnace.

The present invention provides a method for feeding turnings into a furnace comprising feeding the turnings from an input along a conveyor towards the furnace, subjecting the turnings to heating from furnace exhaust gases passing along the conveyor in a direction opposite to the direction of the conveyor and pushing the heated turnings into the furnace at the end of the conveyor.

Preferably a magnetic separation stage is provided at an intermediate conveyor position.

Preferably the conveyor is a screw type.

Preferably the conveyor is fed from a hopper and preferably the hopper is provided with gas sealing means.

Preferably the conveyor is also provided with a gas seal at a predetermined position adjacent the hopper.

Preferably the apparatus further comprises an exhaust gas duct connected to the gas tight passageway for circulation of the exhaust gases back into the furnace.

Preferably for isolation the gas tight passageway is provided with a first damper to seal if from the furnace.

Preferably the exhaust gas duct is provided with a second damper to seal it from the furnace.

Preferably the exhaust gas duct is provided with a blower to assist circulation of exhaust gases within the passageway and the duct.

Preferably a flame detector is provided in the passageway and is operative to close the first damper to isolate the passageway if too high a temperature is reached.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which : Figure 1 shows in schematic form a plan view of the fragmentary scrap feed apparatus and furnace system according to the present invention, and Figure 2 shows schematically in partial cross-section the scrap feed system of Figure 1 in greater detail.

With reference now to the drawings, a furnace 10 (shown only partially in Figure 2) which may be of the closed well type is provided, in known manner, with an input door 12 for loading of scrap material and a door 14 for removal of dross. The closed well furnace 10 and its operation in melting scrap is well known and this will not be described further.

The invention concerns apparatus for feeding scrap comprising fragments, for example, machine turnings, of non ferrous material, normally aluminium. The melting of aluminium, being the most usual non ferrous metal will be described and the fragments will be assumed to be turnings which will normally be contaminated with ferrous material.

The apparatus 20 generally comprises a feed hopper 22, connecting to a conveyor 24 driven by a drive motor 26. A magnetic separator 28 is provided in association with conveyor 24 and a gas duct system 30 is also provided connected between conveyor 24 and furnace 10.

The operation of each of these parts will now be described in greater detail with reference to Figures 1 and 2.

Aluminium fragments (turnings) 220 are dropped into feed hopper 22 by, for example, fork lift truck. Hopper 22 is preferably provided with an air lock system 222,224 which may be of the push/pull flap type.

This provides a secondary seal to prevent escape of hazardous gases, as described hereinafter.

The fragments are conveyed by a screw conveyor 240 in a direction indicated by arrow 242 towards the furnace 10. The conveyor passes through a primary gas seal 244 which further prevents escape of hazardous exhaust fumes from furnace 10 from escaping via hopper 22.

The conveyor 240 continues to convey the fragments towards furnace 10 through a further enclosed portion 246 in which the fragments are exposed to hot flue gas flowing in the direction indicated by arrow 100. The hot flue gas is circulated in ducting 30 by means of a fan 300 and as required the flow can be further controlled by a first damper 302 in ducting 30 and a second damper 248 in conveyor 24. These two dampers when completely shut will serve to isolate the flue gas ducting system 30 and the conveyor 24 from the furnace 10.

In the system as the fragmentary scrap moves in direction 242 towards furnace 10 it is heated by hot flue gas flowing in direction 100.

At position 102 nearest to the furnace the flue gas is at its hottest and as it exits into ducting 30 at position 104 it has been cooled by the scrap.

Thus, the fragmentary scrap is progressively heated as it passes along conveyor 240.

Intermediate between positions 102 and 104 there is provided a magnetic separator 28 which comprises two main parts. The first part 280 adjacent to conveyor 240 is the magnetic separator portion which removes ferrous material from the scrap. The second part is a lower hopper 282 which is joined to the first part by a gas tight seal 284.

When full, or at a convenient time, the dampers 248,302 can be closed and then the lower container 282 can be removed, emptied and replaced. If damper 248 is closed first and fan 300 continues to operate then the conveyor 24 can be substantially cleared of all fumes. Thus, the ferrous material can be removed virtually without escape of any hazardous gases.

The advantage of situating the magnetic separator at the position shown is that the fragmentary scrap has been partially heated by the time that it passes the separator. Thus, any solvents will have been wholly or substantially removed. Also, the fragmentary scrap will have been turned over by the screw conveyor 240 and thus the ferrous material will have been shaken loose from the aluminium.

Also, by positioning the magnetic separator remotely from the furnace along the conveyor 24, the separator will not be directly subjected to very high temperatures existing at position 102.

The temperature at the magnetic separator can be controlled by adjustment of fan speed 300 and by adjustment of dampers 302,248 to ensure that it is not subjected to temperatures which would damage its magnetism.

Since the hot flue gases entering at 102 are substantially hotter than the combustion point of, for example, paint it is possible if all toxic substances have not evaporated by position 102 for flames to be generated at this position and for them to pass down the conveyor.

This will be detrimental to the magnetic separator and also may compromise the effectiveness of seals 244 and 222,224.

Thus, in the even that an explosion or serious fire occurs in conveyor 24 at position 102 or close thereto, a detector 250 is positioned intermediate between position 102 and separator 28 to detect excess heat and is operative via a control 252 to shut off damper 248 to thereby isolate conveyor 24 from furnace 10. Fan 300 may continue to operate to draw off hazardous fumes created by any flames in conveyor 24 and will also protect seals 244 and 224,22 by drawing off hot gases.

The fragmentary scrap feed system thereby firstly heats scrap in a progressive manner as it approaches the furnace. It cleans the scrap progressively removing any moisture cutting oils and paint within a semioxygenated controlled atmosphere within the conveyor 24. It also removes ferrous material in an efficient manner since this is not done until after the scrap has been dried and at least partially heated and also rolled round in the screw conveyor 240.

Thus, the efficiency of the furnace 10 is substantially increased and also the purity of the aluminium is increased by virtue of the efficient removal of ferrous material.

Claims

1. A method for feeding turnings into a furnace comprising feeding the turnings from an input along a conveyor towards the furnace, subjecting the turnings to heating from furnace exhaust gases passing along the conveyor in a direction opposite to the direction of the conveyor and pushing the heated turnings into the furnace at the end of the conveyor.

2. A method for feeding turnings into a furnace as claimed in claim 1 in which a magnetic separation stage is provided at an intermediate conveyor position.

3. A method for feeding turnings into a furnace as claimed in claim 2 in which the conveyor is a screw type.

4. A method for feeding turnings into a furnace as claimed in claim 3 in which the conveyor is fed from a hopper and the hopper is provided with gas sealing means.

5. A method for feeding turnings into a furnace as claimed in claim 4 in which the conveyor is also provided with a gas seal at a predetermined position adjacent the hopper.

6. A method for feeding turnings into a furnace as claimed in claim 5 in which the apparatus further comprises an exhaust gas duct connected to the gas tight passageway for circulation of the exhaust gases back into the furnace.

7. A method for feeding turnings into a furnace as claimed in claim 6 in which for isolation the gas tight passageway is provided with a first damper to seal if from the furnace.

8. A method for feeding turnings into a furnace as claimed in claim 7 in which the exhaust gas duct is provided with a second damper to seal it from the furnace.

9. A method for feeding turnings into a furnace as claimed in claim 8 in which the exhaust gas duct is provided with a blower to assist circulation of exhaust gases within the passageway and the duct.

10. A method for feeding turnings into a furnace as claimed in claim 9 in which a flame detector is provided in the passageway and is operative to close the first damper to isolate the passageway if too high a temperature is reached.

11. A method for feeding turnings into a furnace substantially as described with reference to the accompany drawings.