METHOD OF HEATING THE BOTTOM PLATE OF A STRING MOULDING APPARATUS AND STRING MOULDING APPARATUS

Abstract: The present invention relates to a method of heating one or more elements of a string moulding apparatus that come in contact with moulding sand and to a string moulding apparatus in which one or more of the elements that come in contact with moulding sand are heated. The string moulding apparatus comprises a moulding chamber (1) between a squeeze plate (2) and a pivoted squeeze plate (3). The squeeze plates (2, 3) are driven by a hydraulic system (12, 13, 14, 15, 16, 17). The elements are heated with the hydraulic fluid of the hydraulic system (12, 13, 14, 15, 16, 17).

Description: METHOD OF HEATING THE BOTTOM PLATE OF A STRING MOULDING APPARATUS AND STRING MOULDING APPARATUS TECHNICAL FIELD 5 The present invention relates to a method of heating one or more elements that come in contact with moulding sand of a string moulding apparatus of the kind set forth in the preamble of claim 1 and to a string moulding apparatus with one or more heated elements that come in contact with moulding sand of the kind set forth in the 10 preamble of claim 12. BACKGROUND ART String moulding apparatus relate to foundry machinery in which the moulding sand 15 is introduced into the moulding chamber of the string moulding apparatus in order to produce string of vertically parted moulds, of e.g. green-sand. In the high-speed green sand moulding technique the sand is bonded by a clay binder capable of forming an instant bond on the application of pressure, thus allowing low cycle times. 20 Green sand is a mixture of sand and a clay binder i.e. betonite. The normal moisture level in the required for an effective bonding is in the range of 3 to 4 weight % but the range can be higher or lower in extreme situations. A too low moisture level leads to insufficient bonding, whereas a too high moisture level can cause damp- explosions of the moulds when the molten metal is poured in. 25 From a sand mixer station, in which the moulding sand is mixed continuously to maintain its uniform properties, the moulding sand is transported to a sand supply unit that supplies the moulding sand to a sand shot system. The sand shot system introduces the moulding sand into the moulding chamber by means of compressed air. The sand shot system comprises a sand valve and a sand storage container. 30 The sand supplied to the sand shot system by the sand supply unit has a temperature above that of the surrounding environment, typically the temperature of the sand is intended to be about 30 to 40 °C but can under certain circumstances be higher. Before opening the sand valve for refilling the sand storage container the space in the sand storage container is vented. The expansion of the pressurised air 35 in the sand shot system cools the sand shot valve and the sand storage container that therefore have a temperature typically below that of the surrounding environment. The moulding chamber has normally a temperature close to that of the surrounding environment, i.e. typically about 20°C. The difference in temperature between the moulding sand and the above mentioned elements of the string moulding apparatus that come in contact with the moist moulding sand leads to condensation. At the side plates, the top plate and in particular at the bottom plate of the moulding chamber the condensed water leads to corrosion of the hardened steel. The area of the bottom plate in front of the moulding chamber, i.e. there where the last of the previously produced mould parts remains, until a new mould part comes out of the moulding chamber and pushes the mould string over the distance of the width of a mould part away from the moulding chamber, is the most critical in this respect. The last of the previously produced mould parts, and thus a warm one, rests on this part of the bottom plate for the length of a complete cycle. Consequently this area of the bottom plate is suffering most from the influence of the condensed water. Due to the chemicals in the green sand the condensed water tends to form chemical compounds which accelerate the corrosion effect on the bottom plate. The top surface of the bottom plate usually made of hardened steel, in order for it to have a high wear resistance. The wear resistance of the hardened steel is however strongly reduced if the steel is exposed to corrosion since the crystal- and boundary structure is damaged and the hardened steel looses its high wear resisting properties. Thus, the wear-plate will wear faster than is expected. In order to avoid or at least reduce the condensation it is known from DISAMATIC ® 2013 MK5 Sand Moulding Machine, Spare Parts, Edition 11/95 to provide the bottom plate with an electric heating element. These electric heating elements have however a limited life span and their replacement is cumbersome and leads to considerable loss of production time. Further the electric heating elements consume a lot of energy. At the inside of the walls of the sand storage container and the sand valve the condensed water increases the moisture contend of the moulding sand so that it becomes sticky and adheres to the walls. The sand shot procedure is problematic or even impossible when the moulding sand adheres to the inside of the walls of the sand shot system. DISCLOSURE OF THE INVENTION It is the object of the invention to provide a method of heating one or more elements that come in contact with moulding sand of a string moulding apparatus of the kind referred to above, which is more reliable and energy efficient. This object is achieved by the characterising features of claim 1. By heating one or more elements that come in contact with moulding sand with hydraulic fluid of the hydraulic system of the string moulding apparatus the waste-heat of the hydraulic fluid can be used positively, sand adherence can be avoided or at least reduced and corrosion can be avoided or at least reduced. It is another object of the invention to provide a string moulding apparatus of the kind referred to above, which is more reliable and energy efficient. This object is achieved by the characterising features of claim 12. By providing means for heating the elements that come in contact with moulding sand with the hydraulic fluid of the hydraulic system of the string moulding apparatus the waste-heat of the hydraulic fluid can be used positively, sand adherence can be avoided or at least reduced and corrosion can be avoided or at least reduced. According an embodiment of the invention the hydraulic fluid is flowed through a conduit formed in the bottom plate. According an embodiment of the invention the conduit is arranged such that the whole bottom plate is heated. According an embodiment of the invention the conduit is arranged such that an overproportional part of the of the conduit is formed in the part of the bottom plate most remote from the moulding chamber where the last of the previously mould parts remains for the time of one production cycle of the apparatus. According an embodiment of the invention the bottom plate comprises a support plate supporting a wear plate. According an embodiment of the invention the conduit is formed in the support plate. According an embodiment of the invention the top surface of the bottom plate is heated to such an extend that the top surface of the bottom plate that is intended to support the mould parts is heated up to a temperature equal to or higher than the temperature of said mould parts supported by the bottom plate. According an embodiment of the invention the side surfaces and/or the top surface of the moulding chamber are heated with hydraulic fluid. According an embodiment of the invention the sand storage container and/or the sand valve are heated with hydraulic fluid. BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed part of the description of the present invention, the invention will be explained in more detail with reference to the exemplary embodiments of the string moulding apparatus and the method of heating the bottom plate of string moulding apparatus shown in the drawings, in which Figures 1a, 1b and 1c are diagrammatic views, partially in cross-section, showing the apparatus in various stages, Figure 2a is a view on the side of a bottom plate, and Figure 2b is a view on the top of a support plate of the bottom plate. DETAILLED DESCRIPTION OF THE INVENTION Referring now to the drawings, the apparatus illustrated in Figures 1a, 1b and 1c comprises a combined mould-making and casting apparatus, e.g. of the DISAMATIC® type. This apparatus as such and its mode of operation are well known in the art, and for this reason it is only dealt with broadly in this specification. In the apparatus shown in Figure 1a-c, a sand storage chamber 11, adapted to receive sand from a sand supply system (not shown) is used for temporarily storing the moulding sand 10. A sand valve 22 comprising a closure member 23 is arranged on top of the sand storage container 11. For filling the sand storage container 11 with sand from the sand supply unit, the sand valve is temporarily opened by moving the closure member 23 from a closing position to an open position. During the actual moulding operation air under pressure is supplied to the space above the sand 10 by means not shown here through the air inlet/outlet 24 in order to introduce moulding sand 10 into the moulding chamber 1. Before opening the sand valve 22 for refilling the sand storage container the space above the sand is vented. The expansion of the pressurised air cools the sand storage container and the sand valve. The moulding chamber 1 , situated as shown below the supply chamber 11 , is limited in the lateral direction by pattern plates which are supported by a squeeze plate 2 and a pivoted squeeze plate 3, respectively. Box-less mould parts 8 are made from loose green-sand, i.e. sand with moist ciay as binder, in the moulding chamber 1 defined between a pattern located on a squeeze plate 2 and a pattern located on movable and upwardly pivoted -squeeze plate 3 in a downwardly pivoted position of the squeeze plate 3. In the moulding chamber 1 the sand is compacted between the squeeze plate 2 and the pivoted squeeze plate 3 to form a mould part 8 as shown in Figure 1b. In the next step of the production cycle the pivoted squeeze plate 3 is conveyed forward and pivoted upwards to the position as shown in Figure 1c, after which the mould part 8 is conveyed by the squeeze plate 2 to abut against the mould string formed by previously produced mould parts 8. The newly produced mould part 8 is then further pushed out until the mould string is conveyed over a distance corresponding to the thickness of T of a mould part 8 in the direction indicated by an arrow A. When the mould part 8 is conveyed out of the moulding chamber 1 by the squeeze plate 3 it slides over the bottom plate 5. In the mould string, the front side of a mould part 8 together with the rear side of the previously produced mould part 1 defines a mould cavity 9. Further down the string, at a casting station (not shown), the mould cavity 9 is cast with a molten metal through an inlet 21 , which may be on a side or bottom wall of the mould below the level of the mould cavity 9, by means of a casting device, e.g. a ladle 20. It will be appreciated that the casting of the mould cavity 9 must take place while the mould string is stationary, i.e. within the intervals between each time the squeeze plate 2 advances the mould string through a distance corresponding to the thickness of a mould part 8 in the direction A. In the time that the mould string is stationary the last of the produced mould parts 8 rests on the bottom plate 5, while the rest of the mould string rests on a mould string conveyor 19. The last part of the bottom plate 5 is exposed mostly to the condensation problem, since the last produced mould part 8 is warmer than the bottom plate and rests for a relatively long time at this part of the bottom plate 5. Thus, there is enough time for damp of the mould part 8 to condense on the bottom plate 5 if the latter was not heated. Together with the chemicals in the moulding sand the condensed water can form chemical compounds that speed up the corrosion of the bottom plate 5. A linear hydraulic actuator arrangement comprising a linear hydraulic actuator 12 for driving the squeeze plate and a linear hydraulic actuator 13 for driving the pivoted squeeze plate 3, is adapted to move the squeeze plate and the pivoted squeeze plate 3 towards each other under high pressure for the mould part forming operation and move the squeeze plates 2,3 back and forth in the other steps of the production cylce. The hydraulic linear actuator 12 is directly connected to the squeeze plate 2 at one end and connected on the other end to a stationary block 6 which is integral with the base frame of the string moulding apparatus. The linear hydraulic actuator 13 is connected at one end to the pivoted squeeze plate 3 through push-pull rods 18 and at the other end connected to the stationary block 6. The linear hydraulic actuators 12, 13 are supplied with hydraulic fluid under pressure, preferably hydraulic oil, by a hydraulic system comprising a valve system 14, a pump 15, and a reservoir or tank 16. The hydraulic fluid is returned from the hydraulic actuators 12 and 13 and/or the valve system 17 through a return conduit 17. The return conduit 17 is connected to a conduit 7 in the bottom plate 5. By flowing the warm hydraulic fluid through the bottom plate 5, the heat in the hydraulic fluid is transferred to the bottom plate 5. When the hydraulic fluid leaves the conduit 7 it is returned to the hydraulic fluid to the tank 16. The return conduit also hydraulic fluid to a conduit (not shown) in side plates and the top plate 4 of the moulding chamber. The return conduit 17 further conveys hydraulic fluid to a conduit in the walls of the sand storage container 11 and/or the sand valve 22. According to an embodiment of the invention the return conduit 17 also conveys hydraulic fluid to a conduit (not shown) in the squeeze plate 2 and to a conduit (not shown) in the pivoted squeeze plate 3. With reference to Figures 2a and 2b, the bottom plate 5 is shown in detail. The bottom plate is built up of a support plate 5a and a hardened steel wear plate 5b. This construction is used since the mould parts 8 are conveyed slidingly over the bottom plate 5. The sand of the mould parts 8 has a high abrasive effect which causes the conveying surface of the bottom plate to wear out. Therefore the wear- plate 5b is made of hardened steel. The wear resistance of the hardened steel is however strongly reduced if the steel is exposed to corrosion. When such a steel corrodes the boundary structure and the crystal structure are is damaged and the hardened steel looses its high wear resisting properties. Thus, the wear-plate 5b will wear faster than is expected when the bottom plate is not heated. Further the corrosion takes also place between the wear-plate and the bottom thereby forming rust. When the wear plate 5b is worn out it is exchanged with a new wear-plate 5b. The conduit 7 is arranged in the bottom plate 5a, in a groove in the top surface of the support plate 5a. The groove is sealed by the wear plate 5b that is fixed on top of the support plate 5a. The hydraulic fluid can either be conveyed in the groove itself or in a tube arranged in the groove. The path that the conduit 7 follows is chosen such that the whole bottom plate 5 is warmed up, whereby the path is chosen such that the part of the bottom plate 5 most remote from the moulding chamber 1 , i.e. there where the last of the previously produced mould parts 8 rests, receives overproportional part of the heat from the hydraulic fluid. Hereto the path of the conduit 7 in that part of the bottom plate forms a serpentine pattern. The bottom plate 5 is heated up to such an extent that the top surface of the bottom plate 5, normally formed by the top surface of the wear plate 5a, is heated up to such an extent that it has a temperature equal to or higher than the temperature of the sand mould parts supported by the bottom plate. According to an embodiment of the invention, the warm hydraulic fluid is conveyed in a tube arranged in the groove in the support plate 5a. LIST OF REFERENCE NUMERALS 1 Moulding chamber 2 Squeeze plate 3 Pivoted squeeze plate 4 Top plate 5 Bottom plate 5a Support plate 5b Wear-plate 6 Stationary block 7 Conduit 8 Mould part 9 Mould cavity 10 Moulding sand 11 Supply chamber 12 Hydraulic actuator 13 Hydraulic actuator 14 Valve 15 Pump 16 Tank 17 Return conduit 18 Push-pull rod 19 Mould string conveyer 20 Ladle 21 Inlet 22 Sand valve 23 Closure member 24 Air inlet/outlet

Claims: CLAIMS: 1. Method of heating elements (2,3,4,5,11,22) of a string moulding apparatus for producing a mould string having vertical parting lines between the mould parts (8) comprising a moulding chamber (1) between a) a squeeze plate (2), b) a pivoted squeeze plate (3), c) a top plate (4), (d) two side plates, and e) a bottom plate (5), he string moulding apparatus further comprising f) a sand storage container (11) arranged above the moulding chamber (1), g) a sand valve (22) arranged on top of the sand storage container (11), and a hydraulic system (12,13,14,15,16,17) for driving the squeeze plate (2) and the pivoted squeeze plate (3), characterised by the step of heating one or more of said elements (a) to (g) with hydraulic fluid of the hydraulic system (12,13,14,15,16,17). 2. Method according to claim 1, c h a ra ct e r i s e d by the step of flowing hydraulic fluid of the hydraulic system (12,13,14,15,16,17) through a conduit (7) formed in the bottom plate (5). 3. Method according to claim 1 or 2, characteri sed in that the bottom plate (5) extends out of the moulding chamber (1) for providing a transport surface that supports a mould (8) part when is pushed out of the moulding chamber (1) towards the mould string of previously produced mould parts (8). 4. Method according to claim 2 or 3, c h a r a c t e r i s e d by the step of arranging the conduit such that the whole bottom plate (5) is heated. 5. Method according to any of claims 2 to 4, c h a r a c t e r i s e d by the step of arranging the conduit (7) such that an overproportional part of the of the conduit (7) is formed in the part of the bottom plate (5) most remote from the moulding chamber (1) where the last of the previously produced mould parts (8) remains for the time of one production cycle of the apparatus. 6. Method according to any of claims 1 to 5, ch aracte ri sed in that bottom plate (5) comprises a support plate (5a) and a wear plate (5b) fixed on top of the support plate (5a). 7. Method according to claim 6, c h a ra cte ri s ed in that the conduit (7) is formed in the support plate (5a). 8. Method according to any of claims 1 to 7, ch a racte ri sed in that the top surface of the bottom plate (5) that is intended to support the mould parts (8) is heated up to a temperature equal to or higher than the temperature of said mould parts (8) supported by the bottom plate (5). 9. Method according to any of claims 1 to 8, c h a r a c t e r i s e d by the step of flowing hydraulic fluid of the hydraulic system (12,13,14,15,16,17) through or along the side plates and/or the top plate (4) of the moulding chamber (1). 10. Method according to any of claims 1 to 9, c h a r a c t e r i s e d by the step of flowing the hydraulic fluid of the hydraulic system (12,13,14,15,16,17) through or along the sand storage container (11) and/or the sand valve (22). 11. Method according to any of claims 1 to 10, ch a racte ri sed in that the waste-heat of the hydraulic fluid is used to heat up the elements (a) to (g). 12. String moulding apparatus for producing a mould string having vertical parting lines between the mould parts comprising: a moulding chamber (1) between (a) a squeeze plate (2), (b) a pivoted squeeze plate (3), (c) a top plate (4), (d) two side plates, and (e) a bottom plate (5), the string moulding apparatus further comprising (f) a sand storage container (11) arranged above the moulding chamber (1), (g) a sand valve (22) arranged on top of the sand storage container (11), and a hydraulic system (12,13,14,15,16,17) for driving the squeeze plate (2) and the pivoted squeeze plate (3), characterised by means (7) for heating one ore more of the elements (a) to (g) with hydraulic fluid of the hydraulic system (12,13,14,15,16,17). 13. String moulding apparatus according to claim 12, cha racterised in that the means (7) for heating the bottom plate (5) comprise a conduit (7) formed in the bottom plate conveying hydraulic fluid of the hydraulic system (12,13,14,15,16,17). 14. String moulding apparatus according to claim 12 or 13, c h a r a c t e r i s e d in that the bottom plate (5) extends out of the moulding chamber (1) for providing a transport surface that supports a mould part (8) when it is pushed out of the moulding chamber (1) towards the mould string of previously produced mould parts (8). 15. String moulding apparatus according to claim 13 or 14, c h a r a c t e r i s e d in that the conduit (7) is arranged such that the whole bottom plate (5) is heated. 16. String moulding apparatus according to claim 14 or 15, c h a r a c t e r i s e d in that the conduit (7) is arranged such that an overproportional part of the of the conduit (7) is formed in the part of the bottom plate (5) most remote from the moulding chamber (1) where the last of the previously produced mould parts (8) remains for the time of one production cycle of the apparatus. 17. String moulding apparatus according to any of claims 12 to 16, c h a r a c t e r i s e d in that bottom plate (5) comprises a support plate (5a) and a wear plate (5b) fixed on to of the support plate (5a). 18. String moulding apparatus according to claim 17, cha racterised in that the conduit (7) is formed in the support plate (5a). 19. String moulding apparatus according to any of claims 12 to 18, characteris e d in that top surface of the bottom plate (5) that is intended to support the mould parts (8) is heated up to a temperature equal to or higher than the temperature of said mould parts (8). 20. String moulding apparatus according to any of claims 12 to 19, characteris e d in that the means (7) for heating the side plates and/or the top plate (4) are formed by a conduit in or aside the side plates and/or top plate (4) conveying hydraulic fluid of the hydraulic system (12,13,14,15,16,17). 21. String moulding apparatus according to any of claims 12 to 20, characteris e d in that the means (7) for heating the sand storage container (11) and/or the sand valve (22) are formed by a conduit in or aside the sand storage container (11) and/or the sand valve (22) conveying hydraulic fluid of the hydraulic system (12,13,14,15,16,17). 22. String moulding apparatus according to any of claims 12 to 21, characteris e d in that the waste-heat of the hydraulic fluid is used to heat up the elements (a) to (g)- 23. String moulding apparatus according to any of claims 17 to 22, characteris e d in that the conduit in the bottom plate (5) is formed by a groove in the top surface of the support plate (5a), whereby the groove is sealed by the wear plate (5b) fixed on the support plate (5a). 24. String moulding apparatus according to any of claims 17 to 22, c h a r a c t e r i s e d in that the conduit in the bottom plate is formed by a tube in a groove in the top surface of the support plate (5a).

Inventors: JOHANSEN JAN BECHMANN, JOHANSEN, JAN, BECHMANN
Applicants: GEORG FISCHER DISA AS, JOHANSEN JAN BECHMANN, GEORG FISCHER DISA A/S, JOHANSEN, JAN, BECHMANN
Application year: 1999
Main classification: B22C11
IPC codes: B22C9, B22C11