Ceramic filter for metal casting and manufacturing process

Abstract

A method of manufacturing a ceramic foam filter includes sintering a filter body to a temperature above a molten metal to be filtered by the body, forming a plurality of tortuous passages extending through the filter body, each having a repeating and controllable passage geometry, forming a flow path through the plurality of tortuous passages with a continuously varying diameter and area, causing a local increase and decrease in flow rate of the molten metal through the plurality of tortuous passages, and applying a mixture of at least one ceramic powder and at least one binder to form the filter body including the plurality of tortuous passages by additive manufacturing.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to ceramic filters used in metal casting operations to remove inclusions and oxides in liquid metal during metal pouring. BACKGROUND

[0002] Components such as automotive engine cylinder heads and engine blocks are often cast using semi-permanent molds that are filled with molten metal, such as aluminum, which is gravity fed into the mold. Semi-permanent molds (SPM) involve a casting process that can produce aluminum alloy castings with internal passages formed within the resulting castings using reusable metal molds and sand cores. Liquid metal casting operations are used, for example, to pour liquid aluminum into a mold to produce automotive engine blocks and other engine components, such as cylinder heads.

[0003] In known casting methods, ceramic filters are located in the liquid metal pouring path upstream of the mold for filtering inclusions and oxides in the liquid metal, thereby improving casting purity. Known ceramic filters for liquid aluminum material pouring are made from ceramic foam suitable for the temperature of the aluminum melt. In the conventional ceramic foam filter production method, a polyurethane sponge or expanded polystyrene of similar size to the ceramic filter is first immersed in a ceramic slurry. After immersion, the ceramic slurry fills the voids in the polymer sponge. The polymer sponge filled with ceramic slurry is then baked / sintered in an oven. After the polymer sponge is sintered, the remaining material is the ceramic foam filter. However, such materials are susceptible to non-uniform and inconsistent pore sizes, which can result in low filtration efficiency. Non-uniform and inconsistent pore sizes can cause significant variations in the flow rate of the metal through the filter and thus through the system, which can negatively impact mold filling and solidification times. The reticulated ceramic foam filter can also cause significant variations in the flow rate of the metal due to the variation in pore size.

[0004] Accordingly, while the ceramic filters currently used in liquid metal pouring operations achieve their intended purpose, there is a need for a new and improved system and method for filtering inclusions and oxides in liquid metal during mold pouring operations. SUMMARY

[0005] According to several aspects, a method of manufacturing a ceramic foam filter includes sintering a filter body to a temperature above that of a molten metal to be filtered by the body, forming a plurality of tortuous channels extending through the filter body, individually having a repeating and controllable channel geometry, forming a flow path through the plurality of tortuous channels with a continuously varying diameter and area, causing a local increase and decrease in flow rate of the molten metal through the plurality of tortuous channels, and applying a mixture of at least one ceramic powder and at least one binder to shape the filter body including the plurality of tortuous channels by additive manufacturing.

[0006] In another aspect of the disclosure, the method further includes individually shaping the plurality of labyrinthine channels to be sinusoidal in shape.

[0007] In another aspect of the disclosure, the method further includes configuring the plurality of labyrinthine channels to have a first diameter at a maximum cross-section of the elliptical pocket, the first diameter being greater than a second diameter at a neck region where the diameter is reduced.

[0008] In another aspect of the disclosure, the method further includes configuring the filter body to be multi-layered, each layer of the multi-layered having a plurality of labyrinthine channels of different sizes.

[0009] In another aspect of the disclosure, the method further includes removing each layer of the multi-layered to change a total flow rate through the filter body.

[0010] In another aspect of the disclosure, the method further includes providing each layer of the multi-layered with a different wettability.

[0011] In another aspect of the disclosure, the method further includes forming a circular-shaped pocket with a circulation, the pocket including a neck region of reduced area for each channel of the plurality of labyrinthine channels.

[0012] In another aspect of the disclosure, the method further includes forming a flow channel for each channel of the plurality of labyrinthine channels by adding an impact wall oriented at an angle to a flow direction of the molten metal within the flow channel between opposing first and second path channel walls; forming an inner wall of a low-lying cavity in the second path channel wall for trapping objects entrained within the molten metal.

[0013] In another aspect of the disclosure, the method further includes positioning a V-shaped impact wall within a flow channel defined between opposing first and second path channel walls, the channel disposed at an angle to a flow direction of the molten metal within the flow channel; forming an inverted V-shaped wall upstream of the V-shaped impact wall.

[0014] In another aspect of the disclosure, the method further includes sintering at a temperature higher than a temperature of the molten aluminum defining the molten metal.

[0015] According to aspects, a method of manufacturing a ceramic foam filter includes applying a mixture of at least one ceramic powder and at least one binder to form a filter body by additive manufacturing; a plurality of labyrinthine channels extending through the filter body, the plurality of labyrinthine channels including at least a first cross-section having a first area and a second cross-section having a second area less than the first area; a circle-equivalent diameter of the plurality of labyrinthine channels ranging from 0.1 millimeters to 5 millimeters; and sintering the filter body to a temperature higher than a temperature of a molten metal to be filtered by the body.

[0016] In another aspect of the disclosure, the method further includes forming the filter body to be multi-layered.

[0017] In another aspect of the disclosure, the method further includes selecting different flow paths through the plurality of tortuous channels by varying the plurality of tortuous channels in different layers of the plurality of layers.

[0018] In another aspect of the disclosure, the method further includes forming flow paths that vary in diameter and area continuously through the plurality of tortuous channels.

[0019] In another aspect of the disclosure, the method further includes shaping the plurality of tortuous channels as helical channels.

[0020] In another aspect of the disclosure, the method further includes forming the filter body in a plurality of layers, wherein the plurality of tortuous channels of each layer of the plurality of layers have different flow path sizes.

[0021] In another aspect of the disclosure, the method further includes forming a flow path with an impingement wall in each of the plurality of tortuous channels, the impingement wall positioned between opposing first and second path channel walls and disposed at an angle to a flow direction of the molten metal within the flow path; forming an inner wall of a low point cavity in the second path channel wall to trap objects entrained in the molten metal.

[0022] According to aspects, a method of manufacturing a ceramic foam filter includes selecting a ceramic foam filter body having an element geometry of a filter body, the filter body including one of a plurality of tortuous channels extending through the filter body, wherein the plurality of tortuous channels have a repeating and controllable channel geometry; combining a ceramic powder and at least one binder in a combining operation; printing the filter body using the ceramic powder and the binder through an additive manufacturing operation; and sintering the filter body at a sintering temperature above an expected temperature of a molten metal to be filtered by the filter body.

[0023] In another aspect of the disclosure, the method further includes selecting flow paths that vary in diameter and area continuously through each of the plurality of tortuous channels.

[0024] In another aspect of the disclosure, the method further includes selecting the plurality of tortuous channels having a cross-sectional circle-equivalent diameter between 0.1 millimeters and 5.0 millimeters.

[0025] Other suitable fields of application will be apparent from the description herein. It will be appreciated that the description and specific examples are for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0026] The drawings described herein are for purposes of illustration only and are not intended to limit the scope of the present disclosure in any way.

[0027] Figure 1 is a front elevation cross-sectional view of a ceramic foam filter and cartridge according to exemplary aspects;

[0028] Figure 2 is a front perspective view of a ceramic foam filter body according to another aspect;

[0029] Figure 3 is a front perspective view of a ceramic foam filter body according to another aspect;

[0030] Figure 4 is Figure 2 is a side perspective partial cross-sectional view of the ceramic foam filter body shown in

[0031] Figure 5 is Figure 4 is a side cross-sectional view of cross-section 5 in

[0032] Figure 6 is Figure 3 is a side perspective partial cross-sectional view of the ceramic foam filter body shown in

[0033] Figure 7 is Figure 6 is a side elevation cross-sectional view of cross-section 7 in

[0034] Figure 8 is an isometric side elevation cross-sectional view similar to Figure 7

[0035] Figure 9 is a front perspective view of a three-layer ceramic foam filter body according to another aspect;

[0036] Figure 10 is a side elevation cross-sectional view of an impact wall in a flow channel similar to Figure 5

[0037] is a side elevation cross-sectional view of a V-shaped impact wall in a flow channel similar to Figure 11 Figure 10

[0038] Figure 12 is a flow channel diagram of exemplary method steps for forming a ceramic foam filter shown in Figure 1 DETAILED DESCRIPTION

[0039] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[0040] Reference is made to Figure 1 ​​​​, a ceramic filter system 10 is shown that includes a ceramic foam filter 12 having a filter body 14 that provides a plurality of tortuous passages 16 through the filter body 14 for filtering a molten metal such as aluminum. The melt enters the filter body 14 at an upstream end 18, passes through the plurality of tortuous passages 16 through the filter body 14 and exits the filter body 14 at a downstream end 20. The filter body 14 is disposed within a filter cartridge 22 that has an enlarged portion 24 adapted to receive and retain the filter body 14. The filter cartridge 22 includes an inlet section 26 upstream of the filter body 14 and an outlet section 28 downstream of the filter body 14. An inlet end of the filter cartridge 22 receives an input stream such as a heated liquid aluminum melt 30. The melt 30 typically contains inclusions 34 and oxides 36 that are unwanted in the melt 30 and are therefore intended to be removed using the filter body 14.

[0041] When the melt 30 reaches the filter body 14, a substantial portion of the inclusions 34 that are too large to enter the plurality of tortuous passages 16 are trapped at the upstream end 18 of the filter body 14. The plurality of tortuous passages 16 are also sized to trap a substantial portion of the oxides 36, which are shown as trapped oxides 38 within the filter body 14. The melt 40, which has been filtered to remove the inclusions 34 and oxides 36 contained therein, is directed as an exit stream to an outlet end 44 of the filter cartridge 22 to exit the outlet section 28.

[0042] Referring to Figure 2 and referring again to Figure 1 , according to aspects, the first ceramic foam filter 12A includes a plurality of tortuous passages 16A. Referring to Figure 4 and Figure 5 the geometry of the plurality of tortuous passages 16A is shown and depicted in more detail.

[0043] Referring to Figure 3 and referring again to Figure 1 and Figure 2 , according to aspects, the second ceramic foam filter 12B includes a plurality of tortuous passages 16B. Referring to Figure 6 and Figure 7 the geometry of the plurality of tortuous passages 16B is shown and depicted in more detail.

[0044] Referring to Figure 4 and referring again to Figure 2, the example of the plurality of tortuous passages 16A of the first ceramic foam filter 12A are tubular with rectangular looping pockets defining side-by-side passages 16A1, 16A2, and 16A3. According to aspects, the matching upper, middle, and lower columns of the plurality of tortuous passages 16B are generally aligned relative to one another, such as tortuous passage 16A3A, 16A3B, and tortuous passage 16A3C. As previously described, as the molten metal, such as molten aluminum, passes through the plurality of tortuous passages 16A of the first ceramic foam filter 12A, the inclusions and oxides are trapped and removed, and the stream of melt becomes filtered molten metal 40.

[0045] Referring now to Figure 5 and again to Figure 4 , the individual passages of the plurality of tortuous passages 16A include rectangular looping pockets 46 separated by a neck region 48 of reduced area. The neck region 48 of reduced area increases the flow resistance of the molten metal, thus creating an area for trapping oxides 38 as trapped oxides 38 within the filter body 14. The neck region 48 of reduced area also traps any inclusions 34 small enough to enter one of the plurality of tortuous passages 16A.

[0046] Referring now to Figure 6 and again to Figure 4 , the example of the plurality of tortuous passages 16B of the second ceramic foam filter 12B are tubular and sinusoidal, such as tortuous passages 16B1, 16B2, and 16B3 arranged side-by-side. According to aspects, the matching upper and lower columns of the plurality of tortuous passages 16B are generally aligned relative to one another, such as tortuous passage 16B3A and tortuous passage 16B3B. As previously described, as the molten metal, such as molten aluminum, passes through the plurality of tortuous passages 16B of the second ceramic foam filter 12B, the inclusions 34 and oxides 36 are trapped and removed, and the stream of melt becomes filtered molten metal 40.

[0047] Referring now to Figure 7 and again to Figure 6 , the individual passages of the plurality of tortuous passages 16B include elliptical looping pockets 50 separated by a neck region 52 of reduced diameter. The neck region 52 of reduced diameter increases the flow resistance of the molten metal, thus creating an area for trapping oxides 36 as trapped oxides 38 within the filter body 14. The neck region 52 of reduced diameter also traps any inclusions 34 small enough to enter one of the plurality of tortuous passages 16B.

[0048] Referring now to Figure 8 and again to Figure 6 and 7Exemplary tortuous passage 16B3B includes a first diameter 54 defining a first area at a maximum cross-section of the elliptical pocket 50 that is larger than a second diameter 56 defining a second area at the necked-down region 52. The continuously varying diameter and area of the flow passage 58 through the tortuous passage 16B3B results in localized increases and decreases in the flow rate of molten metal through the tortuous passage, which causes increased entrapment of inclusions 34 and oxides 36 within the slower velocity region defined by the elliptical pocket 50.

[0049] Referring now to Figure 9 and referring again to Figures 1 to 8 Filter body 60 is modified from filter body 14 to include multiple layers of filter material having different pore sizes and geometries. First filter layer 62 provides a plurality of first tortuous passages 64. Second filter layer 66 provides a plurality of second tortuous passages 68. Third filter layer 70 provides a plurality of third tortuous passages 72. The plurality of first tortuous passages 64 is different from the plurality of second tortuous passages 68, and the plurality of third tortuous passages 72 is different from the plurality of first tortuous passages 64 and the plurality of second tortuous passages 68. The different tortuous passage geometries provided in the various layers of filter body 60 allow filter body 60 to be "tuned" to filter out different sizes of objects in different respective layers. For example, first filter layer 62 can be used to selectively filter inclusions 34 of a first size range, second filter layer 66 can be used to selectively filter inclusions 34 of a second size range, and third filter layer 70 can be used to selectively filter oxides 36.

[0050] Referring now to Figure 10 and referring again to Figures 1 to 9 Filter body 74 is modified from filter body 14 to include first and second passage walls 76 and 78 of opposing tortuous passages. Flow passage 80 includes an impact wall 82 positioned between the first and second passage walls 76 and 78 of opposing tortuous passages and disposed at an angle to a flow direction 84 of molten metal within flow passage 80. Upstream wall 86 is impacted by components of the molten metal, such as inclusions 88. Inclusions 90 impacting upstream wall 86 travel down upstream wall 86 due to gravity 94 and are trapped with a plurality of other inclusions 92 on an inner wall 96 of a low-lying cavity 98 formed in second passage wall 78. A plurality of tortuous passages 100 are provided within impact wall 82 to allow molten metal to flow through impact wall 82 in flow direction 84.

[0051] Referring now to Figure 11 and referring again to Figures 1 to Figure 10The filter body 102 is improved from filter body 14 and filter body 74 and includes opposing first and second labyrinth channel walls 104 and 106. The flow channel 108 includes a V-shaped impact wall 110 positioned between the opposing first and second labyrinth channel walls 104 and 106, the V-shaped impact wall 110 is positioned at an angle to the flow direction 112 of the molten metal within the flow channel 108. The inverted V-shaped upstream wall 114 is impacted by components of the molten metal, such as inclusions 116. Inclusions 118 that impact the inverted V-shaped upstream wall 114 travel along the inverted V-shaped upstream wall 114 due to the forces of the fluid flow and become trapped with a plurality of other inclusions 120 in an internal cavity 122 of the inverted V-shaped upstream wall 114 at the internal angle junction of the inverted V-shaped upstream wall 114. A plurality of labyrinth channels 124 are positioned within the V-shaped impact wall 110 to allow the molten metal to flow through the V-shaped impact wall 110 in the flow direction 112.

[0052] Referring to Figure 12 and again to Figures 1 to Figure 10 A method of designing and optimizing the porous channel geometry and dimensions of a ceramic foam filter 126 includes, in an initial optimization stage 128, employing computational fluid dynamics based on filtration efficiency and casting quality grade requirements to optimize the ceramic filter design. In an extraction stage 130, information for the optimization stage 128 is extracted from a file of filtration efficiency and casting quality requirements. The design of the ceramic foam filter is then selected in a selection stage 132. In a printing stage 134, the selected ceramic foam filter is printed using an additive manufacturing machine. The exit stage extracts ceramic powder and binder additives from a supply of materials using an additive manufacturing process. In a sintering stage 138, the sintering temperature of the ceramic filter is higher than the temperature required to filter molten metal, such as molten aluminum, after the ceramic filter is printed. In an assembly stage 140, the ceramic filter is assembled with a plurality of materials and layers, such as assembled into the depicted cylinder 22. Figure 1

[0053] The ceramic foam filter of the present disclosure can include controllable porous channel geometry and dimensions in the filter. The porous channels can be selected with variable cross-sectional dimensions. The circular equivalent diameter (ECD) of the cross-section of the porous channels can vary from 0.1 millimeters to 5 millimeters. The ceramic filter of the present disclosure can be formed from an array of channels with channel walls forming a sinusoidal wave pattern translated along the center of the channel. A flow channel or internal channel is conformally arranged along the interior of the channel walls such that a uniform gap is formed between the channel and the internal channel. The channel and the internal channel can be in the same sinusoidal configuration with the gap positioned between four other channels but translated along the long axis of the internal channel at a 90 degree sinusoidal phase.

[0054] ​Channels can also be formed in a pattern that forces the debris to collide with the walls during flow, removing the momentum of the flow particles from the high inertia debris, but allowing the less dense material with lower inertia to pass through the channels with less energy loss. The channels can be supported by vanes between the channels and the walls to maintain their positioning. Multiple layers of structures can be provided with different void geometries and sizes at each layer. Multiple materials with different wetting characteristics can also be printed in the same filter for specific melt treatment. The filter layers can also be printed and assembled separately to adjust the process to achieve optimal performance.

[0055] Printed and non-printed materials can be stacked together to take advantage of the performance characteristics of each base material type. Filters can be printed into unique geometries to extend the life of the filter, for example, for use in a furnace. Large debris can be directed to one area of the filter to keep the rest of the filter clean. This can take advantage of micro or macro characteristics.

[0056] The ceramic foam filter of the present disclosure has several advantages. It includes a ceramic filter with element / channel geometry that includes a variable pore cross-sectional size with a spiral shape or a sinusoidal wave pattern. The ceramic filter can have unique features to shed large debris from the upstream filter face when used in a furnace. The ceramic filter can include variable porous channel cross-section, spiral porous channels, and / or sinusoidal wave channels. The ceramic filter provides a multi-layer structure with different pore sizes per layer, and multiple materials with different wettabilities.

[0057] The description of the present disclosure is merely exemplary in nature and variations that do not depart from the spirit and scope of the present disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.

Claims

1. A method of manufacturing a ceramic foam filter, comprising: sintering a filter body to a temperature above a molten metal to be filtered by the filter body; forming a plurality of filter body meander passages extending through the filter body, the plurality of filter body meander passages each having a repeating and controllable passage geometry forming a continuously varying flow path through the plurality of filter body meander passages to locally increase and decrease a flow rate of the molten metal through the plurality of filter body meander passages; forming the flow path for each of the plurality of filter body meander passages by adding an impingement wall oriented at an angle to a flow direction of the molten metal within the flow path between opposing first and second path passage walls, wherein the impingement wall includes a plurality of impingement wall meander passages configured to allow the flow of the molten metal through the impingement wall; configuring the filter body as a plurality of layers, each layer of the plurality of layers having a different size of the plurality of filter body meander passages; providing a different wettability for each layer of the plurality of layers; and applying a mixture of at least one ceramic powder and at least one binder to form the filter body including the plurality of filter body meander passages by additive manufacturing.

2. The method of claim 1, further comprising individually shaping the plurality of filter body meander passages as sinusoidal shapes.

3. The method of claim 2, further comprising configuring the plurality of filter body meander passages to have a first diameter at a maximum cross section of an elliptical pocket that is larger than a second diameter at a neck region where the diameter is reduced.

4. The method of claim 1, further comprising removing each layer of the plurality of layers to change a total flow rate through the filter body.

5. The method of claim 1, further comprising forming a repeating rectangular pocket including a neck region of reduced area for each of the plurality of filter body meander passages.

6. The method of claim 1, further comprising: forming an inner wall of a low level cavity in the second path passage wall for trapping objects entrained within the molten metal.

7. The method of claim 1, further comprising: positioning a V-shaped impingement wall within the flow path defined between the opposing first and second path passage walls, the passage being disposed at an angle to a flow direction of the molten metal within the flow path; forming an inverted V-shaped wall upstream of the V-shaped impingement wall.

8. The method of claim 1, further comprising sintering to a temperature above a temperature of molten aluminum defining the molten metal.

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