AU626483B2 - Process and device for compacting powdery materials - Google Patents

Description

l:4ui COMMONWEALTH OF AUSTRALIA Patent Act 1952 6 6483 p n M D T. T SPT~rTTFTOAT T n N

ORIGINAL

(ORIGINAL)

Class Int. Class Application Number Lodged 74384/87 5 June 1987 o et 0 0 0 ."'.Complete Specification Lodged Accepted O0 0 0 00 me+ 64~ 0 8 o ee o0.0, Priority: Related Art 0 0e 0 o 0r «s Published 13 June 1986 0 0i 0 00~ 40101 aName of Applicant GEORG FISCHER AKTIENGESELLSCHAFT .Address of Applicant Muhlentalstrasse 105, CH-8201 Schaffhausen, Switzerland Actual Inventor HANS LEUTWILER Address for Service F.B. RICE CO., Patent Attorneys, 28A Montague Street, BALMAIN. 2041.

Complete Specification for the invention entitled: "Process and Device for Compacting Powdery Materials" The following statement is a full description of this invention including the best method of performing it known to me:fti:

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16- '-3 Title: PROCESS AND DEVICE FOR COMPACTING POWDERY MATERIALS Inventor: Hans Leutwiler a 0 o 1" 0 00 0000 9040 S0 00 0 000 10 o o g o 0 o0 0

SPECIFICATION

This invention relates to a process for compacting powdery materials, in particular casting materials, by app.Lying pressure to the material which is placed into the molding device having a model plate with a model thereon, a filling frame end a mold frame placed on top of the model plate.

Background of the Invention Various processes are known for compacting powdery or granular materials for the purpose of manufacturing casting molds made of sand.

process which uses gas pressure. A gas mixture is ignited to create an exothermic reaction. The resulting gas pressure then compacts the materials, resulting in a sand mold.

German Patent 1,097,622 describes a compacting process in which the compacting of the materials occurs by releasing the pressure of a highly compressed gas.

Compressed gas molding devices which are used for performing these compacting processes operated exclusively on the principle of acceleration compression. A pressure surge is generated, acting very rapidly on the mass of material, and also

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t l 1 Ts::: A'i 0 0 0400 0 0 o •15 a os a 0 0 o9 .o 20 O a accelerating it. Compaction occurs as a result of the compression of the granular or powdery material at the model or pattern. Ideally, each sand particle is affected by the pressure wave and the absorbed acceleration energy is transferred to each successive powder layer until the model device is reached. This would result in a uniformly compacted shape with a Aigh degree of hardness, the resulting mold being usable to manufacture precise, high-quality castings.

Clay-like molding powders, which must be transported from the preparation station to the mold box in the manufacturing plant, are most often used for compacting purposes.

When the material mass arrives at the mo2d box, it is initially not a completely homogenous mass because lumps form during transportation as a result of collisions which cause some compacting. The collisions can be traced to the tendency of the mass to overcome the relative difference in heights which must be overcome during the lengthy transportation to the mold box.

Furthermore, the need for efficient production requires that the model plates be occupied to a considerable degree. This leads to the fact that the clearance between the mold box wall and the model becomes ever smaller. In order to manufacture a usable and high quality mold, however, these interstices which become ever smaller must be homogeneously filled with sand. But this is not always possible for the reasons described above so that there is already a predisposition toward undesired bridge-building across these interstices when the material mass is poured into the mold box.

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i i B i-i a -3- When the pressure surge is applied to compact the material mass, the pressure wave takes effect with equal force on the bridge areas. Because the compression forces have a uniform effect on the support areas of the bridges, they are made firmer in their respective positions.

Summary of the Invention Accordingly, an object of the present invention is to improve the known processes so that unifnrmly compacting shapes can be reproduced with a high degree of hardness. In particular, it is important for narrow edge areas to obtain high durability values which are a prerequisite for industrial production. In addition, it is important for efficient operation to be possible within a given, short processing time.

o 15 In one aspect the invention comprises a process for o compacting powdery casting material in a molding apparatus o including a mold plate, a model on the mold plate and a ao filling and forming frame comprising o°o placing a mass of powdery casting material in the filling and forming frame surrounding the model, applying a first pressure surge G 1 to the exposed surface of the mass of casting material at a time t I to place the mass of material into a flow motion in a direction of the model, and applying a second pressure surge G 2 to at least one surface of the material mass in the direction to influence the material mass area gap such that the pressure surge

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2 occurs before or during the effective interval of the pressure surge G 1 on the surface of material area A.

In another aspect the invention comprises a process for compacting powdery casting material using a gas pressure surge in a molding apparatus including a mold plate, a model on the mold plate and a filling and fo: ming frame comprising placing a mass of powdery casting material in the ~1.

f R4 3a filling and forming frame surrounding the model, applying a first pressure surge D 1 to the exposed surface of the mass of casting material at a time tl, and applying a second pressure surge D 2 at a time t to a material area A having a predetermined separation from the exposed surface of the material in the direction of the model, and wherein the medium introduced by pressure surge D 2 is removed at least in part from the material mass.

In a third aspect the present invention comprises an apparatus for compacting powdery casting material using a gas pressure surge in a molding apparatus including a mold S plate, a model on the mold plate and a filling and forming ,9~o 15 frame surrounding the model and defining a cavity for receiving the casting material comprising the combination of o means for applying a first pressure surge D 1 to the exposed surface of the mass of casting material at a time t'1 means on the forming and/or filling frame for applying a second pressure surge D 2 at a time t 2 to a i 24 2 material area A having a predetermined separation from the .ooo exposed surface of the material mass in the direction of the model, and i %41 means defining apertures in the model plate for removing the pressure medium introduced by pressure surge

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i!1 0 ii 4 mold plate, a model on the mold plate and a fillingand forming frame substantially surrounding the mo 1 and defining a cavity for receiving the casti material comprising the combination of means applying a first pressure surge D 1 to the e osed surface of the mass of casting material at time tl, means for applying a second press:e surge D 2 at a time t 2 to a material area A ha ing a predetermined separation from the exposed s rface of the material mass in the S°°direction f the model, and means defining apertures in the el plate for removing the pressure medium 0 15 Brief Description of the Drawings O In order to impart full understanding of the manner in which these and other objects are attained in accordance with the invention, particularly advantageous embodiments thereof will be described with 20 reference to the accompanying drawing, which forms a 0000 oo. part of this specification, and which shows a schematic 0 side elevation, in partial se-tion, of a mold apparatus in accordance with the invention with which the method of the invention can be practiced.

25 Description of the Preferred Embodiment i: o As will be recognized from the following, the process of the present invention operates with the conversion of large amounts of compressed air per unit of time whereby pressures in the range of from about 1 to about 10 bar are applied.

The mold box configuration is loosely filled with casting material. The surface 8 of the mass of casting V 'kA,/ i 1 a 1^ material is essentially level and is within the filling frame For the purpose of compacting the mass of material, a pressure surge is applied. When the pressure surge is applied, a first pressure surge G 1 occurs at a time tj and is applied to the free material surface and the material mass begins to move back and forth in the direction of the model device, layer-bylayer. A second or further pressure surge G 2 is applied to a material area A at a time t 2 This material area A is a part of the filled-in material 000 0' 0 ,omass and is located a predetermined distance in the S° direction of the model 2 from the free, exposed surface 0o0 8 of the mass of material. Pressure surge G 2 is o 15 usually applied to the material surface in material o I area A prior to pressure surge G 1 taking effect.

However, it is also possible to apply surge G 2 after the pressure surge G 1 has already been applied to material area A.

20 Pressure surges G 1 and G 2 can be derived from one and the same pressure source. Alternatively, they can be applied independentL_' of each other from different 0000 o° pressure sources.

When pressure surge G 1 is applied to the free material surface 8, the upper layer of the material mass is compacted, pressea together. This compaction occurs suddenly so that the compacted area ;i moves, somewhat in the manner of a wave, in the S_ direction of the model as a result of the suddenly applied pressure. Pressure surge G 2 arrives at the material mass in material area A, at a specified distance from the free material surface 8. The material area A is influenced by the pressure surge as to its flow behavior. The sand particles in this I:i~ a oo 00o Do*.- 0 15 0 20 a 0 0 0 0 0 00 0 0 a tt material area A are pressed away from the mold box wall so that the friction between che sand particles and the mold box wall is nearly eliinated.

When pressure surge G 2 is applied, the G 1 pressure surge can then arrive at the surface of the material mass. When G 1 is taking effect, the material mass is displaced in a compacting motion. As a result of this compacting motion, the material area A is also set in motion and shifted in the direction of the surface of the model. This shift endures until surgn GL catches up to the affected area of the G 2 pressure surge.

While pressure surge G 2 is taking effect, the friction between the mold box wall and the material is almost eliminated along the contact area of the material mass which is in motion due to the effect of the G 1 pressure surge. The duration of the G 2 pressure surge represents the time required for the G 1 and G 2 surges to compensate for pressure, until the G] pressure wave arrives at the material area A or the effective area of G 2 In order to adjust the effect of pressure surges

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1 and G 2 optimally with respect to each other, a difference in the effective time of the two pressure surges of a ma.ximum of 195 ms has been shown to be Sri.rnt id :x heiht fr exale.. of 1000 mm. Good results were also achieved in experiments in which the pressure surge G 2 was introduced about 5 seconds before pressure surge G 1 to the material.

As a result of the steps described above, which lead to reduction in the friction between the sand particles and the mold box wall, the flow capacity of the material mass is influenced directly which, in turn, has a direct effect on the compacting capacity on 00 0 0040 o 60 *040

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7 the material mass. The prerequisite for good compacting is good flow capacity which only results if the material mass exists in a more or less homogenous state.

The illustration shows a cross-section of a mold device. The model 2 is placed on a model plate 1.

Model 2 is surrounded by a mold frame 3 and filling frame 4 is positioned on the mold frame to 2orm a mold box. A compression chamber, not fully shown in the figure, is indicated by wall 5. A series of apertures 9 through model plate 1 have openings positioned between the mold box wall 3 and model 2. Prior to the compacting procedure, the region around and above the model is substantially filled with molding sand 6.

0 15 When the compacting procedure is initiated, a 0 O9 pressure surge D, is activated at time t I at the surface 8 of the material. At time t 2 pressure surge

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2 appears on the mold sand in material A. Because at time t 2 the material in area A is not compacted, this 0o00 So,° 20 area is fluidized and moves as a mass in the direction o 00 of the model plate along with the pressure wave front caused by pressure surge D 1 also moving in the 0.0 0 o 0 direction of model plate. i| 'The additional amount of air inserted into j material area A is removed through apertures 9 when it 0 °00 reaches the model plate 1. The removed air can be 00000: removed from the molding system by means of canals 10 i which can be vented to the surrounding atmosphere.

The additional amount of air is extracted from the material mass in the molding area during the effective duration of pressure surge D 1 because air captured in a material mass would be compressed when the material mass is compacted which would prevent the uniform compaction of material at that location which, as r 7, 1

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0 0 0 O e f l o o o e,'0 o 0 0 0 S«0 00'004 o o 0 00 0 0 0(00 already mentioned, would lead to poor quality of the mold shape. The a p5= i :'c'rpcLrated to overcome this problem and serve to extract excess air which has been displaced by the material mass. The pressure existing in conduits 10 can be made lower than that of the surrounding pressure by suction means, causing a suction effect which enhances the removal of additional amounts of air from the material mass from that area between the mold box wall 3 and model 2.

Apertures 9 are advantageously positioned along the mold box wall in the model plate. Depending upon the clearance from the mold box wall 3 to the model 2, and depending upon the degree of complexity of the model, the apertures can be positioned closer to each other and the diameters thereof can be varied. It is, in any event, important that the apertures be positioned in the area of the vertical projection on the model plate of the effective range 11 of pressure surge D 2 Experiments have shown that a desirable result occurs if the sum of the total areas of the apertures 9 is equal to at least 1% of the exposed model plate surface area between mold box 3 and model wall 2A.

The process according to the invention assures that in the critical material areas, that is, between the model and the mold box, the compacting capacity of the material is ic..i e'2 v. .w behavior by reducing the friction between the material mass the mold box wall.

While certain advantageous embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in 4 ii o o a 2 00 0 0 o a o 0 0000 Q 0

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Claims (11)

1. A process for compacting powdery casting material in a molding apparatus including a mold plate, a model on the mold plate and a filling and forming frame comprising placing a mass of powdery casting material in the filling and forming frame subt e n all 1 surrounding the model, applying a first pressure surge G 1 to the exposed surface of the mass of casting material at a time t I to place the mass of material into a flow motion in tfhe-c direction of the model, and applying a second pressure surge G 2 to at least one surface of the material mass in the direction to influence the material mass area gap such that the pressure surge G 2 occurs before or during the effective interval of the pressure surge G 1 on the surface of material area A.

2. A process according to C. iim 1 wherein each pressure surge is initiated by a gaseous medium. 0 4 0 4 0 4 S 4 0444

3. A process according to Claim pressure surges G 1 and G 2 are derived pressure source.

4. A 4 snn cr cla 4 pressure surges G 1 and G 2 are derived pressure sources. 1 wherein the from a single from separate- from separate i i i: 2 10a A process according to claim 1 wherein pressure surge G2 is applied to the material surface no more than 195 milliseconds after pressure G 1 and is maintained until pressure surge G 1 reaches the material area A of pressured surge G 2

6. A process according to claim 5 wherein pressure surge G 2 is applied at a time t 2 and wherein the delay between tl and t 2 is no greater than 80 milliseconds. Sa. oo 9 09*0 SC 009 I~ t I 1 SI -11 I r i L J f T 1 1 1 1; 2 pressure surge G 2 is applied at a time t 2 an erein 3 the delay between tl and t 2 is no great an 4 milliseconds. 1 6. A process acco g to Claim 5 wherein 2 pressure surge G2 pplied to the material surface no 3 more than 19- liseconds after pressure G 1 and is 4 mainta' until pressure surge G 1 reaches the material 0 0 a 1 7. A process according to'Claim 6 wherein the S2 effective duration of pressure surge G 2 is variable. 2 0 a o 1 8. A process according to Claim 6 wherein the °do° 2 pressure of pressure surge G 2 is varied during the 3 interval of application thereof. 1 9. A process according to Claim 8 wherein the 2 pressure surge G 2 is applied in a pulsating fashion. o 4A 06 1 10. A process according to Claim 6 wherein the S' 2 pressure of pressure surge G 2 is maintained for a i 3 predetermined interval of time during the compacting 4 procedure. 0 o 1 11. A process according to Claim 1 wherein 2 pressure surge G 2 is introduced no more than 55 seconds 3 before pressure surge G 1 and is maintained until S4 pressure surge i has reched tril area of a pressure surge G 2 1 12. A process according to Claim 11 wherein N _A n f W 12 2 pressure surge G 2 is introduced 5 seconds before 3 pressure surge G 1 1 13. A process for compacting powdery casting 2 material using a gas pressure surge in a molding 3 apparatus including a mold plate, a model on the mold 4 plate and a filling and forming frame comprising placing a mass of powdery casting material in the 6 filling and forming frame abstati surrounding the o- 7 model, 8 applying a first pressure surge D 1 to the exposed 9 surface of the mass of cascing material at a time tl, and 11 applying a second pressure surge D 2 at a time t 2 to a 12 material area A having a predetermined separation from 13 the exposed surface of the material mass in the 14 direction of the model, and wherein the medium 9D9& 15 introduced by pressure surge D 2 is removed at least in .16 part from the material mass. a 1 14. A process according to Claim 13 and wherein 2 air is removed from the interior of the forming and S> 3 filling frame until the pressure surge D 1 reaches the 4 model plate. 1 15. A process according to Claim 13 wherein the 2 injected gaseous medium is removed from the area of the 3 model. li 13 1 16. A process according to Claim 15 wherein the 2 injected gaseous medium is removed from the area of the 3 model by suction. 1 17. An apparatus for compacting powdery casting 2 material using a gas pressure surge in a molding 3 apparatus including a mold plate, a model on the mold 4 plate and a filling and forming frame SraBf surrounding the model and defining a cavity for 6 receiving the casting material comprising the °ap 7 combination of o; 8 means for applying a first pressure surge D 1 to the oQ 9 exposed surface of the mass of casting material at a 10 time tl, 11 means on the forming and/or filling frame for applying 12 a second pressure surge D 2 at a time t 2 to a material 13 area A having a predetermined separation from the d 14 exposed surface of the material mass in the direction 15 of the model, and °1 16 means defining apertures in the model plate for i 4 4 17 removing the pressure medium introduced by pressure 18 surge D 2 1 18. An apparatus according to Claim 17 wherein 2 said apertures are located between said model and the i 3 surrounding frame. 1 19. An apparatus according to Claim 17 wherein 2 said apertures are located within the vertical 3 projection of the effective area of pressure surge D 2 4 on said model plate. Li I cQ If 1 I

14- An apparatus according to claim 17 wherein the total area of said apertures is equal to at least 1% of the area of the model plate between said model and said frame.

21. An apparatus according to claim 17 wherein said apertures are suction columns.

22. An apparatus according to claim 21 wherein the diameter of each said column is smaller than the particle diameter of said casting material.

23. An apparatus according to claim 22 and further including an impulse generator for producing said pressure surge.

24. An apparatus according to claim 22 and further including rapid combustion means for generating said I. pressure surge. S 15 25. A process for compacting powdery casting material Substantially as hereinbefore described with reference to the accompanying drawings.

26. An apparatus for compacting powdery casting material ub.tantially as hereinbefore described with reference to '0 the accompanying drawings. DATED this 26th day of March 1992 GEORG FISCHER AKTIENGESELLSCHAFT Patent Attorneys for the Applicant: F.B. RICE CO. 'NIO f'I I J