GB2128307A

GB2128307A - Apparatus for the drying and de-oiling of metal swarf

Info

Publication number: GB2128307A
Application number: GB08323621A
Authority: GB
Inventors: Konrad Herrmann; Dr Gunter Schlott; Andreas Witt
Original assignee: Mansfeld Kombinat Wilhelm Pieck VEB
Current assignee: Mansfeld Kombinat Wilhelm Pieck VEB
Priority date: 1982-10-01
Filing date: 1983-09-02
Publication date: 1984-04-26
Also published as: FR2537160B1; DE3319216A1; DD206421A1; GB8323621D0; FR2537160A1; GB2128307B

Abstract

The invention relates to apparatus for drying and de-oiling of metal swarf by combined direct and indirect heating characterised in that in addition to an indirectly acting main burner and a safety burner extending into the combustion zone of a rotary drum an additional burner, directly heating the combustion zone and supplied by fuel of the main burner, is provided at an inclination of 20-25 DEG to the axis of the drum, in the direction of the swarf delivery flow directly over the safety burner, the ratio of indirect to direct heating amounting to 1-4:1. A photo-electric cell is provided above the additional burner to bring the main and additional burners into action on breaking off of the combustion process. <IMAGE>

Description

SPECIFICATION Apparatus for the drying and de-oiling of metal swarf The apparatus is applicable to the processing of metallic secondary raw materials in the form of swarf, especially swarf of aluminium and aluminium alloys, which are dried and de-oiled in rotating drums, turning tubes, etc.

Swarfs regarded as included among metallic secondary raw materials, which occur especially in the swarf-removing shaping of semi-finished goods in many concerns which produce component groups and finished products, require processing before their return into the metal cycle.

Apart from their different external qualities in the form of short and long chips, the latter mostly in cluster form, the causes for this requirement reside primarily in their soiling with the lubricants used in the swarf-removing deformation and with organic substances such as cleaning rags, wood and the like, chips and pieces of other metals and finally, in the case of incorrect storage, with earth, dirt, etc.

In the case of long storage in the open air it is also possible for adhesions sometimes of large quantities of rain water and the commencement of oxidation phenomena to be the reason why processing must be carried out.

In the case of aluminium, in order to render possible at all the production of casting materials which are up to standard, a thorough drying and de-oiling are indispensable, for only thus can iron and aluminium swarf and small pieces be most extensively separated from one another, with subsequent magnetic separation, into practically pure iron and aluminium fractions.

A uniform and nearly complete drying and deoiling is very problematical on account of the frequently varying nature of the swarf to be processed. In Fed. Ger. Pub. Sp. 1,758,475 a process and an installation for the processing of soiled scrap was already provided. The process is characterised in that the soiled scrap is additionally sprinkled with light oil or water in the forward zone of an externally heated rotating drum, whereby subsequently an at least partial combustion of the combustible substances is effected, and in that the sprinkling is regulated automatically in dependence upon the temperature in a region in which the combustion takes place. The installation for carrying out the process comprises a rotating drum which is connected with one open end to a smoke chamber. An elongated chamber with a burner pertains to the drum device.The drum itself is enclosed by a steel housing or jacket which is attached to a small furnace enclosing the forward part of the drum, for the heating, and to a cooling air blower for the cooling of the drum. For the charging of the drum with metal waste a chute is provided. In the vicinity of the chute one or more pilot burners is or are arranged. In operation of the installation the drum is charged with scrap. The evaporation of the water, oil and other volatile and/or combustible substances is effected, apart from the heating of the drum from the exterior, by the fact that a part of the oiL soiling the scrap is burned. The combustion is' aileged to be supported by the pilot burner. According to its content of oil and other organic residues.and of water, the scrap is sprinkled with oil from an oil spray or with water from a water spray.The pilot burner functions as safety burner and is constantly in operation. It has only the task of immediately igniting any possibly forming explosive gas/oil-air mixtures, and in the further sense does not support the combustion.

Apart from the fuel consumption of the burner in the elongated chamber, which serves as afterburner chamber for the smoke gases, about 95% of the fuel consumption for the reading and maintaining of the working temperature in the drum entry region by exclusively indirect heat supply through the jacket are required for the heating of the small furnace, for which a main burner (not listed) serves. This nearly exclusively indirect heating causes a relatively high specific fuel consumption for the main burner and effects under temperature regulation a relatively frequent commencement of the light oil injection in order to cause the greatly fluctuating oil adhesions to the swarf to burn away steadily, which is necessary for safety reasons and must also be constantly observed through an inspection glass.Moreover in the starting up of the installation it is frequently necessary to add light oil, especially diesel oil, separately by hand in order to start the ignition.

When the constant burning process stops, and this can be the case if the water and/or oil contents of the swarf change abruptly, detonations occur and the combustion zone travels into the rear part of the drum which in the normal progress already serves as cooling section. On the other hand the combustion process can be favoured by the sprinkling with diesel oil so that the permissible working temperatures are exceeded, so that the water injection already commences prematurely for cooling. The most essential disadvantages of this already known prior art thus consist in that a high specific energy consumption is necessary for the indirect heating of the drum and for the frequent additional injection with light oil. The injection requires the use of a fuel of low viscosity and relatively high quantity.Since the ignition energy often does not suffice as a result of the greatly fluctuating oil adhesions to the swarf, light oil must also be added separately especially in starting. Furthermore disadvantages exist in the inexpediently high addition of water through the injection and the compulsion of supervision on account of the danger of detonations due to unstable burning away of the oil in the combustion zone.

The indication in the known prior art (Ger. Pub.

Sp. 1,758,475) that the small furnace and the heating jacket can also be omitted in the case of direct heating of the drum is eliminated because in the charging of swarf with high adhesions of water the requisitely high addition of heat leads to the powerful and large flame of directly arranged burners, whereby especially in the case of aluminium oxidation and fusion phenomena occur.

The disadvantages of the direct heating consist further in that the heating and the maintenance of a most constant possible temperature over the entire drum circumference is irregular in the combustion zone region and not clearly limitable from the cooling zone, because a uniform contact of hot combustion gases over almost the entire drum circumference, limited in zone by the small furnace, is lacking.

The danger of exceeding of working temperatures exists intermittently - on the other hand also in the case of swarf with high oil content -- and likewise involves the undesired commencement of fusion processes. Coarse pieces of sinter type thus occurring in some cases remain adhering to the entraining pieces in the drum, but especially disturb ail subsequent separation and delivery processes.

The use of the water spray is in fact capable of reducing this danger but cannot exclude it and would also cause unnecessarily high energy consumption for the evaporation of precisely this water.

Finally the conducting of the combustion and waste gases is so greatly influenced that the waste gas conduction and after-burning system, oriented to indirect heating, would have to be subjected to a modification.

An object of the invention consists in carrying out the drying and de-oiling of metal swarf with reduced specific consumption of energy carriers in the form of liquid or gaseous fuels, especially of the specific addition of high grade light oils, for the intermittent sprinkling of swarf, in rendering possible the use of inferior oils and reducing the overall expenditure of manual labour with simultaneous increase of the working safety and guarantee of a manner of operation compatible with the environment.

By means of the invention a uniform, nearly complete drying and de-oiling of soiled metal swarf is guaranteed with greater energy economy with simultaneous most extensive dust extraction, especially with substantially reduced additions of light oil and water.

In accordance with the invention this problem is solved by a combined direct-indirect heating system which is characterised in that in supplement to an indirectly acting main burner and a safety burner serving as ignition burner, an additional burner supplied by the fuel of the main burner and directly heating the combustion zone is arranged directly beside the safety burner at an axial inclination to the drum of 20... 250 in the direction of the flow of delivered swarf. The supply of fuel to the additional burner is branched off in a proportion at the level of 20 ... 50% from that of the main burner, so that no increase of the fuel supply as a whole takes place for the now combined direct-indirect heating of the combustion zone in the drum.The ratio of the indirect to the direct heating lies in the range 1 ...4:1. In contrast to the main burner, the additional burner is not regulated automatically by a basic and main load, but in the case of the temperature controlled burning of the main burner is constantly in operation with constant gas consumption, that is to say with unchanged flame formation.

The incorporation into the existing temperature regulation regime takes place only in as much as the main and additional burners are set into and out of operation in common. The additional burner is further characterised in that it has no combustion air supply of its own, but the air necessary for the combustion of the fuel is taken from the atmosphere within the drum, to which in turn fresh air is supplied through a regulable valve for the purpose of cooling the swarf in the rear part at the drum exit.

In combination with the mentioned axial inclination of the additional burner, by the omission of the separate combustion air for this burner a soft flame in reducing atmosphere is achieved which sweeps uniformly over the swarf discharged in parabolic form from the vibrator, into the part of the combustion zone where the swarf is lifted and dropped again by entraining pieces of blade form which are arranged in spiral form on the drum circumference.

The reducing atmosphere also prevents an oxidation of the swarf and burning away of part of the swarf if for example there is an admixture of swarf of magnesium materials. The fuel supply can if necessary be throttled as desired by hand, which proves advantageous for example in the case of a lengthy processing of swarf with high oil adhesions.

If on reaching of an upper temperature limit the main burner and additional burner are taken out of operation automatically at the same time, the oil proportions adhering and/or added continue to burn away without flame support. This condition according to experience lasts longer in the case of the combined direct-indirect heating according to the invention than in the case of indirect heating alone. Nonetheless the danger exists that the burning away may cease earlier than the renewed automatic setting in action of the burners on reaching of a lower temperature limit. In order to avoid the then occurring incompiete de-oiling of the swarf, the combustion zone is monitored by means of a photoelectric cell arranged at the end over safety and additional burners, which in the case of lack of brightness in this zone effects a switching on of the burners before the lower temperature limit is reached.

The invention is to be explained in greater detail by an example of embodiment. The accompanying drawing shows the section of a known drum with the proposed combustion apparatus according to the invention for the processing of swarf of aluminium and aluminium alloys.

As may be seen from Figure 1, the apparatus in accordance with the invention consists of a rotatable drum 4 which is connected with one open end to a smoke chamber 7. The drum 4 is enclosed by a steel housing or jacket 8 and is heated by a combustion chamber 5 with main burner 6, attached beneath the drum 4. For the charging of the drum 4 with metal waste a vibrator 3 is provided directly above which a safety burner 1 is arranged. An additional burner 2 is mounted with an axial inclination of 20--250 in relation to the drum 4, and its fuel supply takes place at the level of 2050% of that of the main burner 6 of the combustion chamber 5, so that an increase of the fuel supply is unnecessary. The apparatus is firstly heated up with the main burner 6 and the additional burner 2 for the purpose of reaching the working temperature.The safety burner 1 is in operation constantly, that is even during the heating-up. After the working temperature is reached the supply of swarf by way of the vibrator 3 to the combustion zone is instigated. Since at this moment the additional burner 2 is always in full operation, a separate addition of light oil on to the vibrator 3 beyond the sprinkling becomes superfluous, which was hitherto necessary to initiate the combustion process. On temperature-dependent shutting off of the main burner 6 of the combustion chamber 5 and of the additional burner 2, the burning away of the oils alone continues to take place.If however the combustion process breaks off before the burners are set in action again under temperature regulation, a photo-electric cell 9 arranged above the additional burner 2 can signal this condition and instigate the setting in action of these burners without dolay.

In the processing of oil-rich swarfs which occur for example in the machining of vehicle pistons and are mostly kept separate inter alia on account of their nickel content only the fuel supply to the additional burner 2 is manually constricted to such extent that the sprinkling of the swarf with water, which is unfavourable as regards energy, is eliminated as far as possible.

In comparison with the known prior art the invention is characterised by various advantages.

Thus the productive time proportion of the entire apparatus is increased, since the operation of heating up to reach the requisite working temperature is concluded in about 60% of the time which was necessary with the former indirect heating alone. Since the additional burner 2 is always in operation in the supply of the swarf, an additional addition of light oil beyond the sprinkling, which was necessary for the initiation of the combustion process, is eliminated. Due to the favouring of the combustion process by the soft, directed flame of the additional burner 2 the performance is 10-1 5% greater than without the proposed additional burner 2.Often the existing oil sprinkling, adapted to the use of inferior oils, can even be shut off in general, while nevertheless an output is achieved which corresponds to that with the oil sprinkling in action without the additional burner 2. A further advantage consists in that the previously necessary use of light oils can for example be replaced by use of a mixture of old oils, if the devices for the sprinkling and oil supply are suitably designed, since due to the additional burner 2 even these oils are ignited and burn away, but otherwise they would remain unburned and adhering to the swarf.

It is further of considerabie importance that, compared with apparatuses and processes known hitherto, only about 7080% of the thermal energy are required, since the partially direct heating of the combustion zone in the drum has, as is known, a higher thermal efficiency than the indirect heating, and since the oils adhering to the swarf are burned away completely by the additional burner 2, while without this additional burner 2 they partly vaporise and burn completely only in the after-burning chamber. Finally the ignition temperature is reached more quickly due to the direct energy supply to the swarf.

Claims

1. Apparatus for the drying and de-oiling of metal swarf, consisting of a combustion apparatus of rotary drum form preceded by a charging apparatus which leads past two sprays, actuated by a regulator, for the sprinkling of the scrap material with oil and water, the combustion apparatus being equipped with a steel housing with attached indirect heating equipment in the form of a combustion chamber with main burner and with a safety burner extending by way of the smoke chamber into the rotatable drum, characterised by a combined direct-indirect heating in that supplementarily to the indirectly acting main burner (6) in the combustion chamber (5) and the safety burner (1) arranged in the rotatable drum (4) an additional burner (2) directly heating the combustion zone without separate combustion air and supplied by fuel of the main burner (6) is arranged directly beside the safety burner (1) serving as ignition burner, at an inclination of 20--250 to the axis of the drum (4), the ratio of the indirect to the direct heating amounting to 1-4:1.

2. Apparatus according to Claim 1, characterised in that for monitoring the combustion zone in the drum (4) a photo-electric cell (9) which effects the setting in action of the main and additional burners (6, 2) on breaking off of the combustion process in precisely this zone is arranged on the end on the smoke gas outlet above the additional burner (2).

3. Apparatus for the drying and de-oiling of metal swarf, substantially as herein described with reference to the accompanying drawing.