WO2020257834A1

WO2020257834A1 - Apparatus and method for melting metal chips

Info

Publication number: WO2020257834A1
Application number: PCT/AT2020/060243
Authority: WO
Inventors: Harald SEHRSCHÖN
Original assignee: Sehrschoen Harald
Priority date: 2019-06-24
Filing date: 2020-06-15
Publication date: 2020-12-30
Also published as: AT522726A1

Abstract

The invention relates to a melting furnace (1) for melting and/or controlling the temperature of molten material (15), comprising at least one combustion chamber (11) which is formed by a furnace housing (3) with a furnace feed section (2), and which has a burner (9) connected to it and a flue gas outlet (12); a cover (5) which, with the furnace feed section (2), forms a melting chamber (16); at least one apparatus (7) for feeding metal chips (6) into the melting chamber (16); at least one melt gas line (8) for discharging gases from the melting chamber (16), the melt gas line (8) leading into the combustion chamber (11).

Description

The invention relates to an apparatus and a method for melting metal chips in a melting furnace.

In the production of cast parts, when machining these cast parts, chips are generated that have the same alloy as the cast part and represent a valuable raw material for remelting in series production. However, these chips are contaminated by cooling lubricants and have to be separated from these cooling lubricant residues and other impurities using a complex processing process.

Therefore, when pressed, chips are often traded as scrap with little value. Another problem results from the collection of chips and non-pure ones, which means that chips are also unpopular in the scrap trade, as they entrain substances added to the melt that reduce the quality of the alloy. For example, iron and copper are mentioned in aluminum alloys, although these are added consciously for the strength and other properties of the alloy, but they are disadvantageous in terms of corrosion resistance. An alloy with recycled aluminum that should be free or poor in these substances, the scrap supplied must be free or poor in these substances, since these substances can hardly or no longer be removed from the melt. It is therefore obvious that chips that are difficult to examine for their real composition are unpopular in this recycling process.

In a production line, on the other hand, the chips that can be fed into the melting process by type during processing represent a considerable economic advantage because the costs of chip processing are reduced and the dross created from the chips by oxidation is reduced. This not only saves the user disposal costs but also raw materials. For example, in the aluminum industry, the price of the raw material of an alloy in the form of ingot is twice as high as the buyback value of chips of the same alloy. In particular in the manufacture of components with a high chip volume, there are significant cost advantages when the chips are reused in production. In addition, there is no need to transport chips by truck from production to aluminum manufacturers.

In foundries, gas-fired crucible furnaces are used for the production of cast parts to melt the ingot. The crucible absorbs the ingot and when these are melted the melt. The crucible is in a refractory brick lining and is surrounded by a combustion chamber. The crucible is preferably heated in this combustion chamber with a gas burner. The exhaust gases and the flame heat the crucible and then draw off over a chimney. The crucible is closed by an insulated lid to reduce heat radiation. The disadvantage of these crucible melting furnaces is that they can only be charged with ingots and scrap. If chips are brought into such crucible furnaces and cooling lubricants are still adhering to them, tests have shown that flash flames and high smoke formation occur, and the chips oxidize very strongly due to their large surface area and there is considerable aluminum oxide formation, so-called dross, which makes a significant proportion of the chips is converted into dross instead of into melt.

The object of the present invention was to overcome the disadvantages of the prior art and to provide a device and a method by means of which a user is able to remelt the metal chips from the machining of cast parts in a melting furnace.

This object is achieved by a device and a method according to the claims.

The device according to the invention comprises a melting furnace for melting and / or temperature control of melt - At least one combustion chamber which forms a furnace housing with a furnace insert to which a burner is connected and has a flue gas outlet;

- A cover which forms a melting space with the furnace insert;

- At least one feed device for metal chips into the melting chamber;

- At least one melt gas line for discharging gases from the melting space, characterized in that the melt gas line leads into the combustion chamber.

With the device according to the invention, chips to which cooling lubricants still adhere can be fed into the melting chamber. This melting chamber is closed by a cover. As a result of the heat, the cooling lubricants adhering to the chips evaporate and form a flammable gas, hereinafter referred to as melt gas. This melting gas is a composition of different gases and has an astonishingly high calorific value. However, without a closed melting chamber, there would be immediate combustion with the atmospheric oxygen. It is therefore advantageous to collect these melting gases when the chips are melted by a cover in a closed melting chamber before combustion and to feed them to the combustion chamber as fuel gas.

An advantageous further development is when the cover that is placed on the furnace insert and forms the melting chamber is designed to be movable. The cover, for example a hood made of heat-resistant steel, can be mounted vertically relative to the furnace insert. This enables the furnace to be used, in particular a crucible for charging pigs to be made accessible. It is also advantageous if the cover is pivotably mounted over the furnace insert and can be pivoted away from the furnace insert. As a result, further devices can be brought over and into the furnace insert for the melt treatment. For example, degassing with an impeller or the addition of finishing substances is conceivable. In order to increase economic efficiency, it is advantageous if a cover hood can be moved relative to two furnace inserts which each form a lower furnace part with a furnace housing is. For example, a lower part of the furnace can be operated as a holding furnace with a simple cover when it is completely loaded, whereas the cover hood on the second lower part of the furnace is operated by the method in question. The lower parts of the furnace can be exchanged using an exchange system. The cover can also be relocated. In a further embodiment, for example, a tilt function can be provided in order to empty the melt. The furnace insert can then, for example, have a beak-shaped pouring element or there is another pouring or emptying element on the furnace insert. The melt can also be conveyed out of the furnace insert via another device such as a pump.

It is advantageous if a conveyor system for the chips is provided in the cover or in parts of the cover. The cover can also be made in several parts. For example, as a ring with a lid or a hemispherical element. In the simplest case, an opening is provided in the cover through which the chips are thrown in. The opening does not necessarily have to be closable if the melting gases generate an overpressure in the melting chamber due to the gasification and are drawn off via the melting gas line attached to the cover in such a way that the melting gases do not escape and the introduction of atmospheric oxygen can be controlled in this way, that there is no ignition / deflagration of the melting gases in the melting chamber. To prevent this, a recirculation of exhaust gas from the combustion chamber into the melting chamber can be provided in order to reduce the oxygen content. The oxygen in the air that is available for combustion is burned in the melting chamber with the carbon released from the cooling lubricant to form combustible carbon monoxide (CO) and the hydrogen is combined to form H2O water and gaseous CxHy hydrocarbons, for example C7H16. Tests have shown that this proportion of molten gas results in a very high calorific value when the dirty chips are melted. For example, flue gas analyzes have shown that 100g of chips to which 1g of cooling lubricant adheres already provides the heat to melt the chips. It is advantageous to close the opening for introducing the chips by the conveyor system with the cover. This reduces the atmospheric oxygen brought into the melting chamber. A continuous conveying system is particularly advantageous for continuous operation and constant melt gas generation. For example, a screw conveyor system is applicable. All other conveyor systems are also conceivable, including dosing systems that bring in the chips in the form of briquettes or other compacted forms. Briquette introduction offers the advantage of covering and the entrainment of atmospheric oxygen into the

To reduce the melting space. A type of piston pump can always deliver a defined volume of chips and air into the closed melting chamber.

It is advantageous if a gas supply is provided in the cover which allows the melting gases to be mixed with other gases, for example with exhaust gases with a low residual oxygen content.

A probe for measuring the composition of the melting gases in the melting chamber is advantageous in order to set this process in an advantageous manner not only through experiments. In this way, the gases fed to the combustion chamber via the melt gas line can be determined and set via a control unit.

For example, the melt gases are fed into the combustion chamber via the melt gas line, where a set flame fires into the combustion chamber via the burner and the exhaust gas contains enough residual oxygen so that complete combustion of the melt gas is possible. That's how it wears

Melting gas to fire the furnace insert.

It is also advantageous if the melt gas line is fed to the burner that fires the combustion chamber and the melt gas is also burned with the gas. Furthermore, a method for melting metal chips in a melting furnace comprising the steps

(i) conveying metal chips into the melting chamber,

(ii) feeding the melt gases produced by the melting into the combustion chamber of the melting furnace and

(iii) Burning the melt gases. proposed to operate the device according to the invention particularly economically.

It is particularly advantageous if the chips are conveyed into the melting chamber and stirred into the melt with a stirrer. This minimizes the burning off in the form of scabies.

Another improvement in carrying out the method is that the chips are stirred into a prepared melt. For example, the chips could also be introduced directly into the furnace insert, for example a ceramic crucible, and melted over the crucible wall or floating on the melt.

It has been shown to be more advantageous if a first melt is produced in the crucible from ingot and then the chips are stirred into the melt with a stirrer. Through this process step, the chips are surrounded by the melt, whereby the melt gases are also generated, but the oxidation of the surface to aluminum oxide of the chips is minimized. This results in less dross / aluminum oxide than if the chips are conveyed into the melting chamber and, for example, float on the surface until they are melted. An advantageous further development is when the melting gases are guided from the melting chamber to the combustion chamber by a conveying device in the melting gas line.

For a better understanding of the invention, it is explained in more detail with reference to the following figures.

They each show in a greatly simplified, schematic representation:

Fig. 1 cross section through the melting furnace

At the outset, it should be noted that in the various embodiments described, the same parts are provided with the same reference numerals or the same component designations, whereby the disclosures contained in the entire description can be transferred accordingly to the same parts with the same reference numerals or the same component names. The location details chosen in the description, such as above, below, laterally, etc. refer to the figure immediately described and shown, and if there is a change in position, this information should be transferred to the new position.

FIGURE DESCRIPTION

In FIG. 1, a cross section through the melting furnace (1) of the device according to the invention is shown in a greatly simplified manner. The furnace insert (2) and the furnace housing (3) form the combustion chamber (11) and the lower melting furnace part (4). The combustion chamber (1 1) is heated by means of a burner (9) and the furnace insert (2), for example a crucible, metal is melted in the furnace insert (2).

The flue gas outlet (12), for example a chimney, brings the completely burned exhaust gases into the atmosphere after a certain dwell time in which they still heat the furnace insert (2). In the melting operation, the furnace insert (2) is heated by the burner (9) and its flame (11) as well as the flue gas and melt (15) is produced from ingot. By placing the cover (5) on, chips (6) which may be contaminated with lubricants can be introduced into the melt (15) via a feed device (7) and advantageously be stirred into the melt via a stirrer (14) for faster melting. As a result, the lubricants that adhere to the chips evaporate and partially burn and form flammable gases in the melting chamber (1 6), in particular gaseous hydrocarbons and carbon monoxide and water vapor formed by atmospheric oxygen, this gas mixture, referred to as melt gas in the present description, has a high calorific value. For example, with 100g of chips with 1-2g of cooling lubricant residues, the heat of fusion of the chips can be applied. The expanding gas mixture is fed to the burner (9) via a Schmelzgaslei device (8) and burned with the fuel gas (13) in the flame (10). Only indicated by dashed lines, it is also conceivable to feed the melt gas directly to the combustion chamber (11) via the melt gas line (8). In this case, however, the burner (9) and the flame (1 0) must be set so that sufficient residual oxygen in the combustion chamber (1 1) is guaranteed for the complete combustion of the melting gases. It is particularly advantageous if the melting gases are fed into the combustion chamber (11) or into the burner (9) via a conveyor (17) in the melting gas line (8). This can also prevent deflagration in the melting chamber (16). In the figure also indicated only by dashed lines, an exhaust gas feed line from the Rauchgasab passage (12) into the melting chamber (16) is possible. As a result, the residual oxygen content in the melting chamber (16) and subsequently in the melting gas can be reduced, which in turn reduces the deflagration and the calorific value of the melting gas is increased as there is less carbon monoxide formation in the melting chamber (16) and in the melting gas line (8) . Because of the entrained oxygen from the air, parts of the hydrocarbon burn to form carbon monoxide, which also has a calorific value that can still be used.

The exemplary embodiments show possible design variants, whereby it should be noted at this point that the invention is not limited to the specially shown design variants of the same, but rather various combinations of the individual design variants with one another are possible and this possibility of variation due to the teaching of technical flandeln through representational Invention is within the skill of those skilled in the art. The scope of protection is determined by the claims. However, the description and the drawings should be used to interpret the claims. Individual features or combinations of features from the various exemplary embodiments shown and described can represent independent inventive solutions. The task underlying the independent inventive solutions can be found in the description.

All information on value ranges in the objective description should be understood to include any and all sub-ranges, e.g. The indication 1 to 10 is to be understood in such a way that all sub-areas, starting from the lower limit 1 and the upper limit 10, are included, i.e. all subranges start with a lower limit of 1 or greater and end at an upper limit of 10 or less, e.g. 1 to 1, 7, or 3.2 to 8.1, or 5.5 to 10.

For the sake of clarity, it should finally be pointed out that for a better understanding of the structure, some elements have been shown not to scale and / or enlarged and / or reduced.

List of reference symbols

Melting furnace

Oven insert

Furnace housing

Lower part of the furnace

cover

Shavings

Feeding device

Melt gas line

burner

flame

Combustion chamber

Flue gas outlet

Fuel gas

Stirrer

melt

Melting room

Conveyor

Exhaust pipe

Claims

P a t e n t a n s p r ü c h e

1. Melting furnace (1) for melting and / or temperature control of

Comprising melt (15)

- At least one combustion chamber (11) which forms a furnace housing (3) with a furnace insert (2) to which a burner (9) is connected and has a flue gas outlet (12);

- A cover (5) which forms a melting chamber (16) with the furnace insert (2);

- At least one feed device (7) for metal chips (6) into the melting chamber

(16);

- At least one melt gas line (8) for discharging gases from the

Melting space (16), characterized in that the melting gas line (8) leads into the combustion chamber (11).

2. Device according to claim 1, characterized in that the cover (5) is designed to be movable relative to the furnace insert (2).

3. Apparatus according to claim 1, characterized in that a Rüh rer (14) protrudes into the melting chamber (16).

4. Apparatus according to claim 1, characterized in that a conveying device (17) is arranged in the melt gas line (8).

5. The device according to claim 1, characterized in that from a gas supply line (18) is arranged in the melting chamber (16).

6. A method for melting metal chips in a melting furnace (1) comprising the steps,

(i) Conveying metal chips (6) into the melting chamber (16), (ii) Feeding the melt gases produced by the melting into the combustion chamber (11) of the melting furnace (1) and

(iii) Burning the melt gases.

7. The method according to claim 6, characterized in that the

Melt gases burn ver with the residual oxygen of the burner (9) in the combustion chamber (1 1).

8. The method according to claim 6, characterized in that the

Melt gases are fed to the burner (9) and burn with the fuel gas (13) in the burner flame (10).

9. The method according to claim 6, characterized in that the

Melt gases are drawn from the melting chamber (16) via a conveyor (17) and fed to the combustion chamber (11) or the burner (9).

10. The method according to claim 6, characterized in that the metal chips (6) are stirred into the melt.