WO2025098925A1

WO2025098925A1 - Electroforming process

Info

Publication number: WO2025098925A1
Application number: PCT/EP2024/081051
Authority: WO
Inventors: Johannes Hendrikus Maria BERENSCHOT; Pouwel Evert LUNING; Nicolaas Maria Josef OUDE LUTTIKHUIS
Original assignee: Veco BV
Current assignee: Veco BV
Priority date: 2023-11-10
Filing date: 2024-11-04
Publication date: 2025-05-15
Anticipated expiration: 2026-05-10
Also published as: NL2036237B1

Abstract

Process of electroforming a sheet (1) comprising at least one product (2, 3) and surroundings (4, 5) by applying a metal in an electrodeposition step on electro-conductive sections (15) of a substrate (9). The product is interconnected to the surroundings and/or to adjacent products forming part of said sheet, by one or more tearing lines (6). Before the electrodeposition step one or more non-conductive strips (13) are provided on the surface area of the substrate at a position where the one or more tearing lines (6) are to be formed. During the electrodeposition step the non-conductive strips (16) are partly overgrown by the metal to form a series of overgrowth bridges (21) bridging the non-conductive strip (13).

Description

ELECTROFORMING PROCESS

The invention relates to a process of electroforming a sheet comprising a plurality of products by electrodeposition of a metal on a substrate .

In an electroforming process , a metal , usually nickel , is electrodeposited in an electrolytic bath onto pattern of electrically conductive spots on the surface of a mandrel or similar substrate . Once the deposited material has been built up to the desired thickness , the electroformed product can be separated from the substrate .

A plurality of products can be made by electroforming on a single substrate , as is for example done with segments for sugar screens . In such cases , the products are produced as a single sheet , which is then cut into pieces in a final production step to separate the individual products . This keeps the products tight and flat on the substrate during the electroforming process and during any further process steps , such as chrome plating . An example of electroformed sugar screen segments is disclosed in WO 98 / 30309 .

The products can be cut from the sheet by manual cutting . However, this work is labour-intensive and physically demanding . More advanced techniques , such as laser cutting or hydro- j et cutting, can also be used, but require complex and expensive tooling and machinery, particularly in view of the si zes of the products to be cut .

US 4 , 243 , 495 discloses a process of continuous electroforming of metal sheets using lines of weakness for bending or separating portions . These lines of weakness are formed by rows of rectangular perforations . Tearing along such lines results in rough edges with sharp points .

It is an obj ect of the invention to provide a low cost process allowing fast and easy but accurate separation of individual electroformed products with accurately defined outer dimensions . The obj ect of the invention is achieved with a process of electroforming a sheet on a substrate , in particular a mandrel , the sheet comprising at least one product and surroundings by applying a metal in an electrodeposition step on electro-conductive sections of the substrate . The electroformed product is interconnected by a tearing line to the surroundings and/or to adj acent products forming part of the sheet . Before the electrodeposition step one or more non-conductive strips are provided on the surface area of the substrate at a position where the one or more tearing lines are to be formed . During the electrodeposition step the non-conductive strips are partly overgrown by the metal to form a series of overgrowth bridges . Where they fully bridge the strip, the overgrowth spots are formed by two opposite fronts of overgrowing metal to form the one or more tearing lines . The fronts do not fully merge but show a limited adhesion, so they have only limited tearing resistance and can be torn apart by a force below the tearing strength of the electrodeposited metal . Hence , tearing resistance is low compared to tearing lines made of electroformed perforations and tearing results in less sharp points or burrs . Yet , the overgrowth spots are strong enough to stabili ze the electroformed sheet on the substrate surface , also during successive coating or plating process steps .

The non-conductive strip can for example have a main width and a series of constrictions of reduced width . Electrodeposition is continued until the constrictions are overgrown, and finished before positions of the non- conductive strip at a distance from the constrictions , i . e . , positions where the width of the non-conductive strip is the main width, are overgrown . The overgrowth spots bridging the strip will develop at the position of the constrictions . This allows to position the overgrowth spots accurately, e.g., at regular distances to form a tearing line with a predictable and uniform tearing resistance.

In a specific embodiment, the constrictions are defined by one meandering side of the non-conductive strip being bent or bulged inward, while the opposite side of the non-conductive strip is straighter than the meandering side, e.g., substantially straight. In this respect, meandering means that goes from left to right and back relative to its longitudinal direction in a wavy or zigzag manner, preferably with a substantially regular amplitude and frequency .

The constrictions can for example be V-shaped, e.g., with the tip of the V-shape being nearest to the opposite straight side of the non-conductive strip. This creates a bulging overgrowth front at the meandering side merging with a straight linear overgrowth front at the opposite straight side. This way, tearing the tearing line will give relatively smooth edges at the product edge formed by the straight linear overgrowth front.

Tear resistance of the tearing lines can be adjusted by adjusting the contact surface area of the bridging overgrowth fronts, e.g., by adjusting the thickness of the electrodeposited layer and/or the width of the overgrowth fronts. The thickness can be increased by increasing process time and/or electric charge used for electrodeposition .

Another way to adjust tear resistance, is by adjusting the brittleness of the electrodeposited metal.

Also the width of the non-conductive strip is an important control parameter for adjusting the tearing resistance. If V-shaped constrictions are used, the shape of the V-shape can also be adjusted to influence the tearing resistance , in particular the width of the V-shape at the top or the width at the opposite side of the V-shape .

In a speci fic embodiment , the tearing lines include a first tearing line and a second tearing line running parallel to the first tearing line . The first and second tearing lines enclose a tearing strip, which can be torn in a fast and easy manner .

In a more speci fic embodiment , the first and second tearing lines are formed on a pair of parallel ones of the non-conductive strips , both having a straight side and an opposite side meandering to define the constrictions . The meandering sides of the parallel non-conductive strips may for example face each other . This leaves relatively sharp burrs on the edges of the torn tear strip but produces much smoother contour edges on the separated product with the fracture surfaces being slightly recessed .

To make it easier to grip the tearing strip, one or both ends of the tearing strip can be provided with a widened pull tab .

To improve corrosion resistance and wear resistance , the sheet can be coated or plated, for example chrome plated after separation of the sheet from the substrate and before separating the at least one product from the sheet by means of the tearing line .

The at least one product can for example be a screen or screen segment , comprising apertures , such as sugar screen segments . Sugar screens are used for separating sugar crystals from massecuite . Various patterns of the slot-shaped passage openings can be used . A set of such sugar screens segments can be arranged to form a sugar screen to be placed on a support screen . The assembly of support screen with sugar screen is positioned on a conical carrier, which is part of a centri fuge for separating sugar crystals from massecuite .

The apertures of such screen segments are typically slot-shaped and formed on non-conductive aperture forming strips having a larger width than the constrictions of the non-conductive strip for forming the tearing line , e . g . , having a width larger than the main width of the non- conductive strip for forming the tearing line . Where the metal layer overgrows the non-conductive aperture forming spots rounded edges are formed, improving performance of the screen . Since the non-conductive aperture forming strips are wider than the constrictions of the non-conductive strips forming the tearing lines , overgrowing of the metal does not result in overgrowth spots bridging the respective aperture .

The invention is not limited to sugar screen segments but can also be used for other electroformed sheets with products to be separated, such as screens for oil filtration, paint filtration, solid ceramic particle sieving, inj ection molding sieving, etc . .

The invention is further explained with reference to the accompanying drawings showing exemplary embodiments .

Figure 1 : shows a sheet produced by a process according to the invention in top view;

Figure 2 : shows a detail of the sheet of Figure 1 with a torn tearing strip ;

Figure 3 : shows six consecutive steps of the process ;

Figure 4 : shows part of a substrate prepared with non-conductive spots ;

Figure 5 : shows the part of the substrate of Figure 4 after electroforming of the sheet ; Figure 6 : shows the sheet of Figure 5 after separation;

Figure 7 : shows a cross section along line VI I -

VI I of Figure 5 ;

Figure 8 : shows a cross section along line VI I I -

VI I I of Figure 5 .

Figure 1 shows a metal sheet 1 comprising a piano of eight products : four sugar screen segments 2 and four strips 3 of a sieve assembly .

The products 2 , 3 are surrounded by intermediate material 4 and a border 5 of the sheet 1 . The border 5 and the intermediate material 4 are waste products that can for example be recycled .

Each one of the products 2 , 3 has a contour bordered by double tearing lines 6 enclosing a tearing strip 7 . The individual products 2 , 3 can easily be separated from the sheet 1 by tearing the respective tearing strip 7 .

The sugar screen segments 2 are provided with slot-shaped apertures 8 ( see Figure 2 ) . After separating the sugar screen segments 2 and strips 3 , they can be arranged in a support screen, so as to use them for separating sugar crystals from massecuite .

Figure 2 shows the tearing lines 6 and the tearing strip 7 in more detail , at a moment when the tearing strip 7 is torn of f . The tearing lines 6 are formed during electroforming of the sheet 1 .

Six consecutive steps of the electroforming process are shown schematically in Figures 3A-3F with the respective layers in cross section . It starts with preparing a substrate , in particular a mandrel 9 , with electroconductive areas 10 where metal should be deposited and non-conductive areas 11 where apertures should be formed, as shown in Figures 3A and 4 . This can be done by applying a pattern of non-conductive spots on a conductive mandrel , or by applying a inverted pattern of conductive spots on a non-conductive mandrel . Conductive mandrels are treated to create a mechanical parting layer, or are chemically passivated to limit electroform adhesion to the mandrel so the electroformed product can easily be separated . Mandrels of non-conductive materials , such as glass , silicon, or plastic materials , require deposition of a conductive layer prior to electrodeposition . Such layers can for example be deposited by using vacuum deposition or sputtering techniques .

The mandrel 9 is placed as a cathode in an electrolyte bath containing a salt of the metal to be electroformed, usually nickel . An anode is also placed in the electrolyte bath . The anode can for example be made of the metal to be electroformed, or of di f ferent metal , such as platinum . A direct current is applied form the anode to the mandrel 9 via the electrolyte , which causes metal ions in the electrolyte to deposit onto the conductive surface parts of the mandrel 9 as a metal layer forming the sheet 1 .

Figure 4 shows in detail a surface of the mandrel 9 prepared for electroforming the sheet of Figure 1 . The non-conductive surface areas 11 include non-conductive aperture forming spots 12 where the slot-shaped apertures 8 of the screen segments 2 should be formed, and pairs of parallel non-conductive strips 13 defining the position where the two tearing lines 6 should be formed . Between these non-conductive strips 13 is a conductive surface 14 defining where the tearing strip 7 should be electroformed . The non-conductive aperture forming spots 12 are surrounded by conductive areas 15 where screen material is to be deposited . Both non-conductive strips 13 have a straight side 16 bordering the conductive areas 15 where screen material is to be deposited, and a meandering side 17 with regularly spaced constrictions 18 bordering the conductive area 14 . At the position of the constrictions 18 , the meandering side 17 bends towards the straight side 16 and back to form the constrictions , e . g . , with a flattened V-shape . At the position of the constrictions 18 , the gap between the meandering side 17 and the straight side 16 is substantially less than the width of the non-conductive aperture forming spots 12 .

Figures 3B-3F show deposition of a metal layer at a position of a constriction 18 . Metal 19 is deposited on the conductive areas . Figure 3B shows the moment when the layer of metal 19 is j ust as high as the non-conductive strip 11 . The metal electrodeposition is continued, so as to allow the metal 19 to overgrow the non-conductive strip 11 with rounded overgrowth fronts 20 growing towards each other . At the non-conductive aperture forming spots , this results in slot-shaped apertures 8 with rounded edges , which helps to prevent clogging . Overgrowing is continued until the overgrowing fronts 20 at either side of the non- conductive spot 11 meet each other and grow together to form an overgrowth bridge 21 bridging the full width of the non- conductive spot 11 ( Figure 3D) . It has been found that these overgrowth fronts 20 do not merge but show limited cohesion . At this stage , tearing resistance may still be too low, so overgrowing is continued until the thickness of the contact area 22 between the two overgrowing fronts 20 is suf ficient to provide a desired tearing resistance ( Figures 3E and 5 ) . The sheet 1 is then separated from the mandrel 9 ( Figure 3F) and can for example be chrome plated or subj ected to any other post processing step . In a final step, the individual products 2 , 3 can be separated from the sheet 1 and used .

Figure 5 shows the sheet 1 on the mandrel 9 in top view after the constrictions 18 of the non-conductive strips 13 forming the tearing lines 6 have been bridged by the overgrowth bridges 21 . The borders of the non-conductive spots 11 are overgrown . Since the non-conductive aperture forming spots 12 are wider than the constrictions 18 of the non-conductive strips 13 forming the tearing lines 6 , the overgrowing layer 19 cannot fully bridge the slot shaped apertures 8 , but only the constrictions 18 . The overgrowing layer 19 can also not bridge the wider parts of the non- conductive strips 13 , so slits 23 remain open between the constrictions 18 . The two rows of slits 23 alternating with overgrowth bridges 21 form the tearing lines 6 of the tearing strip 7 . This way, tearing lines 6 are obtained with equidistantly spaced overgrowth bridges 21 providing a substantially constant tearing resistance .

The meandering border lines of the two parallel non-conductive strips 13 ( see Figure 4 ) face each other in a symmetrical arrangement . As a result , the overgrowth bridges 21 form outwardly pointing protrusions of the tearing strip 7 . When the tearing strip 7 is torn and removed, the fracture surfaces 25 left by the torn overgrowth bridges 21 are slightly recessed in the side edges 27 of the separated product , as shown in Figure 6 .

Figure 7 shows a cross section along line VI I-VI I in Figure 5 , through a slit 23 .

Figure 8 shows a cross section along line VI I I- VI I I in Figure 5 through an overgrowth bridge 21 . The tearing resistance can be adj usted by adj usting the si ze of the contact area 22 between two overgrowth fronts 20 . This can be done by adj usting the thickness of the contact area ( thickness being the dimension in a direction under right angles with the tearing line 6 ) and/or by adj usting the width of the contact area (width being the dimension in a direction in line with the tearing line 6 ) . The thickness can be adj usted by adj usting the electrodeposition process time or by adj usting the electric power applied during electroforming . The width of the contact area 22 can be adj usted by adj usting the width N of the narrowest part of the V-shaped constriction of the non-conductive strip ( see Figure 4 ) . The tearing resistance can also be adj usted by adj usting the pitch between the constrictions 18 of the same non-conductive strip 13 , the width W of the widest part of the V-shaped constriction 18 or the width S of the non- conductive strip 13 at a distance from the constrictions 18 .

The tearing strip 7 between the tearing lines 6 can be torn by successively breaking the overgrowth bridges 21 of the adj acent tearing lines 6 . As shown in Figure 1 , widened pull tabs 24 are provided at the ends of the tearing strips 7 , so the ends of the tearing strips 7 can easily be gripped to start tearing the tearing strip 7 .

Claims

1. Process of electroforming a sheet (1) comprising at least one product (2, 3) and surroundings (4, 5) by applying a metal in an electrodeposition step on electro- conductive sections (15) of a substrate (9) , wherein the at least one product is interconnected by one or more tearing lines (6) to the surroundings and/or to adjacent products forming part of said sheet, wherein before the electrodeposition step one or more non-conductive strips (13) are provided on the surface area of the substrate at a position where the one or more tearing lines (6) are to be formed, and wherein during the electrodeposition step the non- conductive strips (16) are partly overgrown by the metal to form a series of overgrowth bridges (21) bridging the non- conductive strip (13) .

2. Process according to claim 1, wherein the non- conductive strip (13) has a main width and a series of constrictions (18) of reduced width, wherein electrodeposition is continued until the constrictions (18) are overgrown by the overgrowth bridges (21) , and wherein electrodeposition is finished before positions of the non-conductive strip (13) at a distance from the constrictions (18) are overgrown.

3. Process according to claim 2, wherein the constrictions (18) are defined by one meandering side (17) of the non-conductive strip (13) being bent or bulged inward at the positions of the constrictions, while the opposite side (16) of the non-conductive strip is straighter than the meandering side, e.g., substantially straight.

4. Process according to claim 3, wherein the constrictions (18) are V-shaped.

5. Process according to any one of the preceding claims, wherein the tearing lines (6) include a first tearing line and a second tearing line running parallel to the first tearing line, the first and second tearing lines enclosing a tearing strip (7) .

6. Process according to claim 5, wherein the first and second tearing lines (6) are formed on a pair of parallel ones of the non-conductive strips (13) , both having a straight side (16) and an opposite side (17) meandering to define the constrictions (18) , wherein the meandering sides of the parallel non-conductive strips face each other.

7. Process according to claim 5 or 6, wherein a pull tab (24) is formed at one or both ends of the tearing strip (7) .

8. Process according to any one of the preceding claims, wherein the sheet (1) is coated or plated, for example chrome plated, after separation of the sheet from the substrate (9) and before separating the at least one product from the sheet by means of the tearing line.

9. Process according to any one of the preceding claims, wherein the at least one product is a screen or screen segment (2) , comprising apertures (8) .

10. Process according to claims 2 and 9, wherein the apertures (8) are slot-shaped and formed on non-conductive aperture forming spots (12) having a larger width than the constrictions (18) of the one or more non-conductive strips (13) for forming the one or more tearing lines (6) , e.g., having a width larger than the main width of the one or more non-conductive strips for forming the one or more tearing lines.