EP2676748A2

EP2676748A2 - A mechanical rotary casting sand reclaimer and a method for manufacturing castings from reclaimed casting sand

Info

Publication number: EP2676748A2
Application number: EP12181760.5A
Authority: EP
Inventors: Jozef Danko; Rafal Danko
Original assignee: Fabryka Osi Napedowych - Skb Spz Oo Spkomandytowa
Current assignee: SKB DRIVE TECH SPOLKA AKCYJNA
Priority date: 2012-06-19
Filing date: 2012-08-24
Publication date: 2013-12-25
Also published as: PL223318B1; EP2676748A3; PL399560A1

Abstract

The object of the invention is a mechanical rotary casting sand reclaimer, having a base with a grain hole and a lock, wherein the base contains a rotor supported by a vertical bearing, coupled with a driving motor by means of a belt transmission, and an abrasive ring installed on the base and enclosed within a cylindrical casing oriented concentrically to the rotor. The reclamation unit comprises an abrasive ring (5) with a profiled internal surface and a cylindrical external surface with lugs on its perimeter and on the bottom of the ring located within the cylindrical casing (4). It further comprises a rotor supported by a vertical bearing, the rotor having abrasive blades or rods (6) and located in the base concentrically to the abrasive ring (5). The rotor is connected with a driving motor (7) by means of the belt transmission. It further comprises a ring air blade (9) installed on the top surface of the abrasive ring (5), the ring air blade having a dedusting chamber casing (10) attached to it. The casing (10) is equipped with a casting sand batch hole (11) and a side revision window (12). On the top surface of the abrasive ring (5) there is further installed, coaxially with the axis of the chamber, a telescopic dedusting duct (14) ending (13), the dedusting duct (14) being connected with a dedusting cyclone (17) and a suction fan (18). The dedusting duct (14) has sensors (15) for measuring air velocity and a triboelectric dust counter; the sensors (15) being connected with a triboelectric sensor signal converter (16) and a controller of the rotational speed of the driving motor (7).

Description

This invention relates to a mechanical rotary casting sand reclaimer and a method for manufacturing castings from reclaimed casting sand.
Casting technology encompasses filling of prepared moulds with liquid metal, which, during solidifying, forms a casting in the shape determined by the shape of the form. This invention concerns the technology of casting, which uses disposable sand moulds, that is moulds made of moulding sand, whose main component is quartz sand. Such a mould may contain a core made of core sand, with higher resistance than moulding sand.
For economical and environmental purposes, waste casting sand, that is moulding sand and core sand, is submitted to reclamation for its reuse in the production of moulds for further castings. The parameters of reclaimed sand are of high importance for the quality of castings, as unequal sand parameters may lead to deficiencies in produced castings as well as dimensional inaccuracies.
Under standard processes, in order to recover the grains, waste casting sand is submitted to preliminary reclamation involving separating mechanical pollution, fragmentation of lumps, sieving the casting sand and determining the scale for the size grade of reclaimed material and re-separating of mechanical pollution. Afterwards, the casting sand undergoes secondary reclamation, under which the sand grains are released from the residue of waste binding material, after which the sand grains are cleaned of undesirable reclamation products by dedusting and finally, sand grains of specified size and uniformity of grain are produced.
In casting industry the most widely used method in the process of secondary reclamation is mechanical dry reclamation, especially for sodium silicate hardened with esters, self-hardened sand with synthetic resin as well as casting sand wit bentonite, providing that the obtained reclaim is used for casting sand of the same type. Mechanical dry reclamation is also applied in combination with pneumatic method for waste casting sand with high level of the utilisation of sand grains which is usually hard to reclaim, including burned casting sand with bentonite, with sodium silicate, hardened with CO₂, casting sand with cement and casting sand with phosphate binder.
Rotary reclaimers for mechanical reclamation of casting sand are used as auxiliary equipment for sand reclamation plants in advanced dry reclamation systems, or as self-dependent reclamation slot units for small casting plants. In both cases their application is most efficient for the secondary reclamation of uniform casting sand.
In mechanical rotary reclaimers the course of casting sand processing is a result of joint basic reclamation operations, which successively decrease the thickness of the shell of waste (inactive) binding material on the grain surface (wiping and abrading under friction force), or crumbling and grinding the shell under collision and dynamic forces. The above impact is induced in the work space of reclaimer through intensive rotary movement of the rotor equipped with external lugs and elements setting the particles of reclaimed sand into dynamic circulation. Collision of grains or sudden change of stream direction and momentum, resulting from a stroke into disc, bring the effect of waste material shell crumbling, which favours the purifying of sand grains.
A German patent DE4212097 features a rotary system of mechanical reclamation produced by Vogel-Schemmann. This device provides variable rotational speed of the rotor and is used for the reclamation of casting sand with bentonite as well as reclamation of bentonite. The reclaimer operates casting sand dedusting and abrading the shells of waste binding material in a tank with cylinder walls, using a rotor with abrasive discs with vertical rotation axis, driven by a motor fixed on the bottom off the tank connected by a coupling with the rotor axle and operating in fluidised layer of casting sand. The lower part of the tank is connected with circumferential air supply, which develops air overpressure under the casting sand layer and brings it into a state of fluidisation. The upper part of the reclaimer has a dedusting duct on which a photo optic system for measuring the dusting of drained air is installed. On the basis of the amplitude of photo optic signal measuring the dust content in the air, the control system changes the rotational speed and separates reclamation cycles into several phases of various intensity of their impact on the casting sand. During the first phase of reclamation, which involves combining the blowing of air through the casting sand at relatively low rotational speed of the rotor with abrasive discs, both dust additives to moulding sand (bentonite, coal dust) are recovered. The intensive reclamation phase may include two different levels of intensity, which are achieved based on relevant signal value settings, controlling the rotational speed of the rotor. The final phase of reclamation involves abrading the residues of binding material shells and dedusting the reclaim at low abrading intensity (slower rotation of the rotor). In general, the control system concerns the duration of control, yet it is not known what forces the change of rotor's rotational speed between phases. It may be the other way round, that arbitrary speed selection forces the amplitude of dust signals.
An American patent US5439044 presents a rotor device for mechanical reclamation operating periodically, with variable rotational speed of the rotor, which is used for the reclamation of casting sand with bentonite as well as for bentonite reclamation. With this reclaimer, casting sand dedusting and waste binding material shell abrading is realised in a cylindrical casting sand tank with walls smooth on the inside and external coat with three separated ring air chambers, of which the lower chamber is closed with the drain hole bottom, whilst the upper chamber is closed with a ring shaped lid adjacent to the wall of the tank where casting sand undergoes reclamation. The chambers supply air to the cylindrical tank by first providing air from the lower chamber, through a gap on the perimeter of the cylinder, to the casting sand in the bottom area of the tank; the middle chamber provides air through nozzles made of porous material into the central area of the cylinder filled with casting sand; whilst the upper chamber provides compressed air through nozzles located on the perimeter of the cylinder above the casting sand level. The reclamation is operated by setting casting sand into circulation using a rotor with abrasive blades and vertical rotation axis, driven by a motor attached to the lid of cylindrical tank, supporting the circulation with air provided from the lower and middle chamber, inducing the effect of aerial fluidisation. The motor on the tank lid has a spindle installed on the extension of the propeller shaft; the spindle has a rotor mounted on its top, which moves in the fluidised layer of casting sand. The upper part of the reclaimer has a casting sand batch hole and a dedusting duct on the lid in which a photo optic system for measuring the dusting of drained air is installed. On the basis of the amplitude of photo optic signal measuring the dust content in the air, the control system changes the rotational speed and separates reclamation cycles into several phases of various intensity of their impact on the casting sand.
The aim of the invention is improving the method of casting production, whereby the casting sand grains are recovered during the phase of waste casting mass (casting sand) reclamation; the properties of the sand grains give better quality of the castings formed in casting moulds made from reclaimed sand, particularly from cores.
The object of the invention is a mechanical rotary casting sand reclaimer, having a base with a grain hole and a lock, wherein the base contains a rotor supported by a vertical bearing, coupled with a driving motor by means of a belt transmission, and an abrasive ring installed on the base and enclosed within a cylindrical casing oriented concentrically to the rotor. The reclamation unit comprises an abrasive ring with a profiled internal surface and a cylindrical external surface with lugs on its perimeter and on the bottom of the ring located within the cylindrical casing. It further comprises a rotor supported by a vertical bearing, the rotor having abrasive blades or rods and located in the base concentrically to the abrasive ring. The rotor is connected with a driving motor by means of the belt transmission. It further comprises a ring air blade installed on the top surface of the abrasive ring, the ring air blade having a dedusting chamber casing attached to it. The casing is equipped with a casting sand batch hole and a side revision window. On the top surface of the abrasive ring there is further installed, coaxially with the axis of the chamber, a telescopic dedusting duct ending, the dedusting duct being connected with a dedusting cyclone and a suction fan. The dedusting duct has sensors for measuring air velocity and a triboelectric dust counter; the sensors being connected with a triboelectric sensor signal converter and a controller of the rotational speed of the driving motor.
Preferably, the abrasive elements of the rotor have a shape of rods or blades and are located horizontally on each of the vertical walls of the head with a square cross-section, in at least 2 rows with spaces between the rows equal to the double height of the rods or blades.
Preferably, the height of the abrasive ring is 2 to 3 times higher than the vertical distance between the upper row of the abrasive rods or blades of the rotor and the bottom of the bowl, and the cross-section of the inner ring has a shape of a logarithmic spiral recoiling down from the ring top to its base.
Preferably, the telescopic ending of the dedusting duct, situated coaxially with the axis of the dedusting chamber has a telescopically adjustable extension length.
Preferably, the walls of the dedusting duct have sensors measuring air velocity and a triboelectric dust counter, wherein outside the dedusting duct there is positioned a triboelectric sensor signal converter and a controller of the rotational speed of the driving motor.
Another object of the invention is a method for manufacturing castings from reclaimed casting sand, in which the casting sand moulds and cores are submitted to a two-phase reclamation, including a preliminary and a secondary reclamation, after which the reclaimed casting mass is used for manufacturing further sand moulds. The reclaimed casting mass is additionally submitted to a third phase, which makes use of a mechanical rotary casting sand reclaimer. The reclaimer comprises an abrasive ring with a profiled internal surface and a cylindrical external surface with lugs on its perimeter and on the bottom of the ring located within the cylindrical casing and a rotor supported by a vertical bearing, the rotor having abrasive blades or rods and located in the base concentrically to the abrasive ring. The rotor is connected with a driving motor by means of the belt transmission. The reclaimer further comprises a ring air blade installed on the top surface of the abrasive ring, the ring air blade having a dedusting chamber casing attached to it. The casing is equipped with a casting sand batch hole and a side revision window. On the top surface of the abrasive ring there is further installed, coaxially with the axis of the chamber, a telescopic dedusting duct ending, the dedusting duct being connected with a dedusting cyclone and a suction fan. The dedusting duct has sensors for measuring air velocity and a triboelectric dust counter; the sensors being connected with a triboelectric sensor signal converter and a controller of the rotational speed of the driving motor. During the third phase of reclamation the rotary speed of the driving motor is controlled depending on the readings of the air velocity sensor and the triboelectric sensor readings. The sand moulds and cores are manufactured from the casting mass obtained after the third phase of reclamation.
The invention subject is presented by means of an exemplary embodiment on a drawing, in which:

Fig. 1 presents a diagram of the technology line for carrying out the method according to the invention;
Fig. 2 presents a partial vertical half-section of the mechanical rotary casting sand reclaimer equipped with a system for measuring generated dust and gas flow velocity in the dedusting unit;
Fig 3 presents internal vertical cross-section of the abrasive ring unit and abrasive rotor;
Fig 4 presents a top view of the cross-section of the reclamation unit at the level of the lower (first) row of abrasive rotor blades;
Fig. 5 presents a change of TrueRMS value during a sample monitoring of dust concentration in the reclaimer dedusting unit, using triboelectric dust counter.
Fig. 6A presents test casting of a wedge in a mould made of moulding sand from a second level reclaim, and Fig. 6B presents test casting of a wedge produced according to the invention method.

Fig. 1 presents the diagram of the casting technological line for operating the subject invention processing. The melting plant 101 includes an induction furnace for melting rough casting and a system transporting liquid metal to the moulding station 102. The moulding station 102 may serve as manual moulding station, equipped with moulding sand mixer-sprinklers and tipping grates. The moulding station 102 can also serve as an automatic moulding station, equipped with a rotary caster, automated mixer-sprinkler, mould production line and table vibrator. The moulding sand used to produce moulds at the moulding station 102 is a mixture of new sand, second level reclaim from the station 105 and third level reclaim from the station 106, serving as facing sand for castings where particular precision in retaining the external shapes of castings is required. Cores and casting moulds requiring higher precision are prepared in the core department 103. They are formed from third level reclaim supplied from the station 106, i.e. sand of the highest purity and no thermal expansion. As the sand is purified from resin and does not change its shape when in contact with liquid metal, the cores obtained from this sand are dimensionally stable and no resin content minimises the potential of its gassiness, which prevents many casting flaws. Castings moulded at the station 102 are taken to the casting storage 107, whilst flat moulds and cores go to the first level reclamation station 104, where standard preliminary reclamation process is performed, that is separating mechanical pollution, fragmentation of lumps, sieving the casting sand and determining the scale for the size grade of reclaimed material and another separation of mechanical pollution. Part of the reclaimed sand is reused as a component of moulding sand, and part goes to the second level reclamation station 105, where standard secondary reclamation process is performed, whereby the sand grains are released from the residue of waste binding material, after which they are cleaned of undesirable reclamation products by dedusting and finally, sand grains of specified size and uniformity of grain are produced. Part of the reclaimed sand is added as raw material to moulding sand at the moulding station 102, and part goes to the third level reclamation station 106, which is the mechanical rotary casting sand reclaimer described in detail in Fig. 2-4, in which sand purified from resin residues and resistant to thermal expansion is obtained. After the third level reclamation, sand is given as raw material for the production of cores at the station 103 and moulds for castings requiring higher precision workmanship.
Fig. 2-4 present the third level reclaimer operated at the station 106, with round base 1, grain hole 2 and grain hole lock 3, connected with cylindrical casing 4 of the abrasive ring 5 with profiled internal surface and cylindrical external surface and a rotor with abrasive elements 6 located concentrically to the abrasive ring in the base, and connected with a driving motor 7 by means of belt transmission 8 installed in the base of the device 1.
On the top surface of the abrasive ring 5 in cylindrical casing 4 a ring air blade 9 is installed, connected with dedusting chamber casing 10 equipped with a waste casting sand batch hole 11, side revision window 12 and the ending 13 of telescopic dedusting duct 14, located in the chamber axis. The dedusting duct 14 has sensors measuring air velocity, and a triboelectric dust counter 15. Beyond the duct 14, a triboelectric sensor (15) signal converter 16 is installed. Apart from the above, the dedusting unit contains also: dedusting cyclone 17 and suction fan 18.
Casting sand for the reclamation is supplied through the waste casting sand batch hole 11 into the dedusting chamber 10, then it falls into the abrasive ring 5, where it undergoes reclamation processing using the rotor with abrasive elements 6 located on the side walls of a two-piece head with square cross-section, driven by driving motor 7 through belt transmission 8, at a rotational speed controlled by the motor rotational speed controller 19 according to processed signals in electronic system 16 with sensors 15 located in the duct 14.
The waste casting sand is subject to dynamic impact of abrasive elements 6 of the rotor unit, installed horizontally in vertical walls of the two-piece square head in at least 2 rows. At least two rotor arms are installed (with screws) in each row on the opposite, external walls of the head, one above the other. At the end of each arm, at the side of the abrasive ring, one vertical abrasive disc is installed; the external profile edge of the disc is located 5-10 mm from the shaped surface of the abrasive ring (at this altitude) and tilted reversely to the direction of its movement by approx. 15-20 degrees in relation to the plane crossing both arms of a given rotor row. The rotor arms in the upper part of the square head are situated analogically to the above, with arm units and the head turned by 90 degrees in relation to those in the bottom row. Spaces between arms in a given pair and between the arm rows are the same and their length and similar to the height of elements comprising a given pair of rotor arms (blades, round or square rods). In particular, the spaces between the rows may be of double length of the rods or blades. Waste casting sand poured into the device is set in motion using rotary arms of the rotor unit and the portion which has not been pushed through the spaces between the arms and rows of the rotor is radially forced to the external surface of the abrasive ring, where it is dropped at high perimeter speed to the internal surface of the abrasive ring 5 with a profile of logarithmic spiral recoiling from the top. Intensive movement of casting sand facilitates purifying the sand grains by wiping and abrading of the shells of waste binding material. The stream of processed sand is wound by a curvature on the top surface of the abrasive ring 5 in the direction of the rotor axis and pours down to the bottom where it is again processed by the rotor with abrasive elements. 6.
The preferable height of the abrasive ring with profiled recess equals 0.3 - 0.4 of the diameter designated by the outer cover of the ring, 2-3 times bigger than the distance between the upper arms of the rotor unit's uppermost abrasive elements and the bottom of the bowl. During the reclamation cycle, casting sand is dedusted in two stages: first, by the air sucked from the environment to the sand grain through vertical gaps between the cylindrical casing and lugs A on the external surface of the abrasive ring, and then through vertical ducts, connected with the gaps between lugs B located radially on the perimeter of the bottom surface of the abrasive ring. The second dedusting stage id operated in the area of the air blade, situated on the top surface of the abrasive ring, using vortexed air sucked from the environment.
After the reclamation processing time (set arbitrarily or controlled by electronic system) has passed, the purified sand grains is removed from the reclaimer through the grain hole to one of the receivers.
Dusty air is sucked out through the dedusting duct 14 with sensors measuring air velocity and a triboelectric dust counter to the dedusting cyclone 17 with dust reception system and then to the suction fan 18.
The electronic system measuring dust generated in the reclamation process and gas flow velocity in the dedusting unit has two, independent measuring tracks.

· Triboelectric dust counter to monitor dust concentration in the reclaimer dedusting system,
· monitoring system to measure the velocity of air flow in the reclaimer dedusting system. Both of the above values allow to determine the expenditure of moulding sand, and then, the weight of dust collected during the process.

Measuring principle

Measure converters use the method of measuring the volume and speed of dust by converting electric current generated from colliding and rubbing of measuring probes on the particles of dust transported in the dedusting duct.
The probes are installed parallel to one another and perpendicularly to the flow direction. Fig. 5 presents a change of TrueRMS value during a sample monitoring of dust concentration in the reclaimer dedusting unit, using triboelectric dust counter. Signal value decrease is a result of dust volume decrease in the dedusting chamber, from which it was collected. It is clearly visible that at the beginning of the measuring process a large volume of dust substance is transported, its value is decreased at the final stage of the process, when the volume of binding material is reduced due to its abrading off of the grain surface. The measurement is performed at single air speed for the dust flowing in the dedusting duct. Monitoring of speed also helps to determine useful data, such as dust concentration in the gas during transport, which constitute the basis of automatically initiated change of the driving motor rotational speed when a reduction of the growing volume of dust, generated in a given sand grain processing cycle, contained within the air stream is indicated by the measuring system of the triboelectric dust counter. Tracking the dynamics of changes in the volume of liquids in the air stream and comparing them with the set course of the process by the measuring system facilitates the differentiation of the intensity of impact on the reclaimed sand grains in a given cycle, through automatic change of the driving motor's rotary speed.
The device and method according to this invention allow to generate castings with improved functionality.
The application of casting sand from third level reclamation for the production of sand moulds and their cores significantly increases the precision of the retention of the internal and external surfaces of the castings, thus reducing excessive processing costs. This is demonstrated in Fig. 6A presenting test casting of a wedge according to norm ASTM A 536-84 in a mould made of moulding sand from a second level reclaim, and in Fig. 6B presenting test casting of a wedge produced according to the invention method. The application of the invention method allows to obtain castings of CT 7 tolerance grade, according to norm PN -58M-04251 (for which the tolerance equals 0,78mm). Products obtained using the invention method have low surface coarseness, with Ra parameter measured according to norm PN-EN ISO 1302:2002 at a level below 25. The ignition loss of the moulding sand after third level reclamation is below 0.6%, which allows to obtain moulds with high durability, low friability, high level of sand grains uniformity and low gas excretion. The gas excretion of the moulding sand after third level reclamation is above 20cm³/g, which allows for significant reduction of faulty castings, to approx. 1% of their total number.

Claims

A mechanical rotary casting sand reclaimer, having a base with a grain hole and a lock, wherein the base contains a rotor supported by a vertical bearing, coupled with a driving motor by means of a belt transmission, and an abrasive ring installed on the base and enclosed within a cylindrical casing oriented concentrically to the rotor, characterized in that the reclamation unit comprises:
- an abrasive ring (5) with a profiled internal surface and a cylindrical external surface with lugs on its perimeter and on the bottom of the ring located within the cylindrical casing (4),

- a rotor supported by a vertical bearing, the rotor having abrasive blades or rods (6) and located in the base concentrically to the abrasive ring (5),

- wherein the rotor is connected with a driving motor (7) by means of the belt transmission

- and further comprising a ring air blade (9) installed on the top surface of the abrasive ring (5), the ring air blade having a dedusting chamber casing (10) attached to it

- wherein the casing (10) is equipped with a casting sand batch hole (11) and a side revision window (12)

- and wherein on the top surface of the abrasive ring (5) there is further installed, coaxially with the axis of the chamber, a telescopic dedusting duct (14) ending (13), the dedusting duct (14) being connected with a dedusting cyclone (17) and a suction fan (18)

- wherein the dedusting duct (14) has sensors (15) for measuring air velocity and a triboelectric dust counter; the sensors (15) being connected with a triboelectric sensor signal converter (16) and a controller of the rotational speed of the driving motor (7).
The mechanical rotary reclaimer according to claim 1, characterized in that the abrasive elements (6) of the rotor have a shape of rods or blades and are located horizontally on each of the vertical walls of the head with a square cross-section, in at least 2 rows with spaces between the rows equal to the double height of the rods or blades.
The mechanical rotary reclaimer according to claim 1, characterized in that the height of the abrasive ring (5) is 2 to 3 times higher than the vertical distance between the upper row of the abrasive rods or blades (6) of the rotor and the bottom of the bowl, and the cross-section of the inner ring has a shape of a logarithmic spiral recoiling down from the ring top to its base.
The mechanical rotary reclaimer according to claim 1, characterized in that the telescopic ending (13) of the dedusting duct (14), situated coaxially with the axis of the dedusting chamber (10) has a telescopically adjustable extension length.
The mechanical rotary reclaimer according to claim 1, characterized in that the walls of the dedusting duct (14) have sensors (15) measuring air velocity and a triboelectric dust counter, wherein outside the dedusting duct (14) there is positioned a triboelectric sensor (15) signal converter (16) and a controller of the rotational speed of the driving motor.
A method for manufacturing castings from reclaimed casting sand, in which the casting sand moulds and cores are submitted to a two-phase reclamation, including a preliminary and a secondary reclamation, after which the reclaimed casting mass is used for manufacturing further sand moulds, characterized in that:
- the reclaimed casting mass is additionally submitted to a third phase, which makes use of a mechanical rotary casting sand reclaimer, comprising:
- an abrasive ring (5) with a profiled internal surface and a cylindrical external surface with lugs on its perimeter and on the bottom of the ring located within the cylindrical casing (4),

- a rotor supported by a vertical bearing, the rotor having abrasive blades or rods (6) and located in the base concentrically to the abrasive ring (5),

- wherein the rotor is connected with a driving motor (7) by means of the belt transmission

- and further comprising a ring air blade (9) installed on the top surface of the abrasive ring (5), the ring air blade having a dedusting chamber casing (10) attached to it

- wherein the casing (10) is equipped with a casting sand batch hole (11) and a side revision window (12)

- and wherein on the top surface of the abrasive ring (5) there is further installed, coaxially with the axis of the chamber, a telescopic dedusting duct (14) ending (13), the dedusting duct (14) being connected with a dedusting cyclone (17) and a suction fan (18)

- wherein the dedusting duct (14) has sensors (15) for measuring air velocity and a triboelectric dust counter; the sensors (15) being connected with a triboelectric sensor signal converter (16) and a controller of the rotational speed of the driving motor (7),

- and wherein during the third phase of reclamation the rotary speed of the driving motor is controlled depending on the readings of the air velocity sensor and the triboelectric sensor readings,

- and wherein the sand moulds and cores are manufactured from the casting mass obtained after the third phase of reclamation.