METHOD FOR PRODUCING A MEMBRANE FOR A MEMBRANE VALVE

Description

[0001] The invention relates to a method for manufacturing a diaphragm for a diaphragm valve. PTFE is a material that cannot be injection molded. The processing steps for manufacturing a PTFE diaphragm for a diaphragm valve include pressing a powder, sintering the resulting green compact, and hot forming (quenching). On the other hand, thin-walled components cannot be manufactured by injection molding with long flow paths.

[0002] KR 2019 0006281 A discloses a method for manufacturing valve diaphragms.

[0003] JP H06 234141 A discloses an injection molding of fluorinated resin by injecting fluorinated resin of a certain melt viscosity into a mold at a high shear rate, so that the resin is formed with the average particle diameter of a certain value, and subsequently pressing the resin into the desired shape.

[0004] The object of the invention is therefore to simplify the complex process for manufacturing a diaphragm for a diaphragm valve and at the same time to provide a diaphragm for high-purity processes.

[0005] The problem underlying the invention is solved by a method according to claim 1. Advantageous embodiments and examples of the invention are found in the dependent claims, the description, and the drawing. A first aspect of the description relates to a method for producing a diaphragm for a diaphragm valve. The method comprises: conveying a polymer melt through at least one feed channel into a mold cavity, which is bounded by a first mold and a second mold; moving the first and the second mold towards each other; removing the at least one diaphragm from the mold cavity; and separating a sprue from the at least one diaphragm removed from the mold cavity.

[0006] The provided process advantageously simplifies the manufacturing of the diaphragm for the diaphragm valve. In particular, it provides a material-friendly manufacturing process that enables the production of the thin-walled diaphragm.

[0007] An advantageous example is characterized in that an opening of the at least one feed channel is arranged adjacent to an actuating axis of the membrane, or the actuating axis of the membrane passes through the opening of the at least one feed channel.

[0008] Advantageously, the cavity can be filled evenly from this essentially centrally located sprue. The molten plastic thus flows radially and uniformly into the mold cavity in all directions, preventing internal stresses in the resulting membrane. In its liquid state, the molten plastic therefore travels a short flow path to the outside. This is particularly advantageous with shear-sensitive PFA.

[0009] In an advantageous example, an opening of the at least one feed channel is connected section by section to a narrow side of the membrane to be produced.

[0010] This prevents a build-up in the area of ​​the membrane, which is later subject to flexing movements.

[0011] An advantageous example is characterized in that the first form with the at least one feed channel comprises a negative contour of the dry side of the membrane, and wherein the second form comprises a negative contour of the wet side of the membrane.

[0012] Advantageously, the wet side, i.e., the side of the membrane that comes into contact with the process medium, is manufactured without a sprue. Consequently, the surface of the wet side of the membrane is not disturbed by unwanted sprue residue or post-processed areas. Potentially problematic surface tensions created by the sprue are also avoided on the wet side. Unwanted dirt particles adhering to the wet side of the membrane are thus prevented. The cleanability of the wet side of the membrane is improved.

[0013] An advantageous example is characterized in that the method comprises: inserting a connecting section of a connecting pin for attachment to a valve stem into a central recess of the first form, wherein a retaining section of the connecting pin is spaced apart from a surface of the first form surrounding the recess and from a surface of the second form.

[0014] Advantageously, the connecting pin is surrounded by the plastic melt on both sides due to the aforementioned spacing, thus securing it to the membrane in a way that prevents it from being pulled out.

[0015] It is also possible, of course, to manufacture the connecting section from the same material as the membrane. The membrane material can thus be formed directly during the injection molding process. Alternatively, the connecting section can be attached subsequently by welding or similar methods.

[0016] An advantageous example is characterized in that the first form is arranged in a fixed position, and the second form is movable relative to the first form.

[0017] For example, the feed channel is advantageously designed in the first fixed form, which simplifies the entire device for manufacturing the membrane.

[0018] An advantageous example is characterized by the fact that the polymer melt comprises at least one fluoropolymer, in particular a perfluoroalkoxy polymer, PFA.

[0019] The described method makes it possible to produce complex and thin membranes for diaphragm valves using, for example, PFA. Furthermore, it allows for the creation of highly purified process environments without the risk of unwanted material leaching from the membrane into the process medium.

[0020] An advantageous example is characterized by the fact that the polymer melt is free of additives.

[0021] The additive-free design of the membrane expands its range of applications for highly sterile applications, as unwanted material ingress is prevented.

[0022] A second aspect of the description concerns a diaphragm for a diaphragm valve, which is manufactured using the method described in the first aspect.

[0023] The drawing showed: Figure 1 shows a two-part diaphragm for a diaphragm valve; Figures 2, 4, 5, 7 and 9 each show a device for manufacturing the diaphragm in a schematic section; Figures 3 and 6 each show a schematic flow diagram; and Figure 8 shows two diaphragms in a schematic top view with an exemplary feed channel structure of the device.

[0024] Figure 1Figure 1 shows a perspective view of an exemplary two-part diaphragm 100 comprising a first diaphragm 102 facing the valve body of a diaphragm valve and a second diaphragm 104 facing the actuator of the diaphragm valve. The second diaphragm 104 is, for example, made of an elastomer. Through-openings 110-116 serve, for example, to guide fasteners such as studs. Of course, other embodiments are also conceivable, in particular diaphragms with a substantially round outer contour and / or without the through-openings 110-116. Naturally, one-piece diaphragms are also possible, which, for example, only have the first diaphragm 102.

[0025] The two-part diaphragm 100 is clamped in a lateral area between the valve body and the actuator. A functional area 120 of the two-part diaphragm 100 is pressed onto the valve seat of the valve body to close the fluid channel for process fluid formed by the valve body and a wet side 122 of the first diaphragm 102. This movement is caused by an actuator rod moved by the actuator along an actuating axis 180, which, for example, presses against the two-part diaphragm 100 with a pressure piece. A sealing rib 130 of the first diaphragm 102, indicated in the figure, presses against the valve seat. Of course, the sealing rib can be omitted in other embodiments. The fluid channel is opened by moving the two-component diaphragm 100 away from the valve seat. The diaphragm 102 is manufactured according to the process steps described below.

[0026] The adjusting axis 180, for example, runs perpendicular to an imaginary membrane plane in the region of an imaginary center point of the membrane.

[0027] The diaphragm 102 comprises a static, central area S1, which is pressed onto the valve seat on the wet side to close the diaphragm valve. Except for pressure loads, this area S1 is not moved significantly.

[0028] The diaphragm 102 comprises a dynamic area D surrounding the central area S1. The dynamic area D, through its movement, ensures that the central area S1 can be lifted from the valve seat, thus opening a cross-section for the flow of the process fluid. The movement of the dynamic area corresponds to a concentric flexing motion.

[0029] The diaphragm 102 comprises a static area S2 enclosing the dynamic area D. The diaphragm 102 is clamped between two components of the diaphragm valve in this static area S2 and seals the diaphragm valve to the outside.

[0030] Figure 2 A schematic section shows a device for manufacturing the membrane 102. Figure 1 For this purpose, a polymer melt 202 is fed through at least one feed channel 204 into a mold cavity 206. The mold cavity 206 is bounded by a first mold 210 and a second mold 220. The first mold 210 is stationary. The second mold 220 is movable relative to the first mold 210. The positioning axis of the membrane to be produced passes through the opening 212 of the at least one feed channel 204.

[0031] The first shape 210 with at least one feed channel 204 comprises a negative contour 214 of the dry side of the membrane 102. The second shape 220 comprises a negative contour 224 of the wet side 122 of the membrane 102.

[0032] In another example, the feed channel 204 is assigned to the negative contour 224 of the wet side.

[0033] It is in the Figure 2 A state is shown in which the plastic melt 202 exits the feed channel 204 and spreads radially through the central opening 212 in the same proportion within the mold cavity 206. Only after this state is reached are the first and second molds 210, 220 moved towards each other.

[0034] The polymer melt 202 comprises at least one fluoropolymer, in particular a perfluoroalkoxy polymer, PFA. In one example, the polymer melt 202 is additive-free and consists, for example, only of the fluoropolymer, in particular the perfluoroalkoxy polymer, PFA.

[0035] A control unit 230 operates a plasticizing unit 240 and a linear actuator 250 according to the process steps described here. The plasticizing unit 240 is designed to plasticize the plastic, which is present, for example, in powder or pellet form, and to feed the resulting plastic melt to the feed channel 204. The linear actuator 250 is designed to move the second mold 220 along an actuating axis 280, which corresponds to the actuating axis 180 of the diaphragm valve in which the diaphragm is later used.

[0036] Figure 3This shows a schematic flowchart. According to step 302, the first and second forms 210 and 220 are positioned a distance apart from each other. The state after performing step 302 is shown in the Figure 2As shown, in step 304, the molten plastic is conveyed towards the cavity or mold cavity 208. The melt entering the cavity spreads out there. While the molten plastic is being conveyed, in step 306, the second mold 220 is moved from its first position towards the first mold 210. In step 308, the conveyance of the molten plastic is stopped, while maintaining pressure on the filled cavity. In step 310, the second mold 220 is moved away from the first mold, and in step 312, the membrane is removed from the mold cavity along with its sprue. In step 314, the sprue, which is formed at least partially by the molten plastic that has solidified in the feed channel, is removed. The sprue can be removed by sawing or punching along an imaginary parting line.After performing step 314, a trim is visible at the point where the sprue was cut off.

[0037] Figure 4 shows in contrast to Figure 2 The finished membrane 102 is inside the device. It is in the Figure 4 This shows a state in which the first and second forms 210, 220 were moved towards each other and the membrane 102 was compressed between the forms 210, 220. Accordingly, the Figure 4 the state before performing step 310 of the Figure 3 .

[0038] In Figure 4 The distance between the two shapes 210, 220 corresponds to the wall thickness of the membrane 102. Figure 2In contrast, the distance between the two mold halves 210, 220 is approximately twice the wall thickness of the membrane 102 to be produced. Thus, between the start of the conveying of the polymer melt towards the mold cavity and the end of the pressing process, the volume of the mold cavity is reduced by approximately half. In further examples, the distance between the two mold halves can be reduced from a maximum opening or maximum distance at the start of the melt inflow to a minimum stroke, which is between 25% and 75% of the maximum opening, where the minimum stroke corresponds to one wall thickness of the membrane.

[0039] The Figures 5 and 6 This illustrates another example of the manufacturing process for membrane 502. Unlike membrane 102 from the previous example... Figure 1 , 2 and 4The membrane 502 includes a connecting pin 510. Furthermore, the opening 212 of the at least one feed channel 204 is arranged adjacent to an actuating axis 180 of the membrane 102. The feed channel 204 thus leads into the mold cavity at a point which corresponds to the static area S1 of the membrane 102. Figure 1 This is assigned to the mold cavity. Advantages arise, for example, from the fact that the feed channel leads into the mold cavity at a point that corresponds to one of the static areas S1, S2 of the membrane and / or the membrane's actuating axis, so that the molten plastic enters this area first and spreads to other areas by flowing. The membrane is moved less in the static areas S1 and S2. Flow lines and edges therefore do not form in the movable area of ​​the membrane located between the static areas S1 and S2.

[0040] Regarding the procedure according to the Figure 3 Furthermore, the procedure according to the Figure 6a insertion 602 of a connecting section 512 of a connecting pin 510 for connection to a valve rod into a central recess 504 of the first form 210, wherein a retaining section 514 of the connecting pin 510 is spaced apart from a surface of the first form 210 surrounding the recess 504 and from a surface of the second form 220.

[0041] Figure 7 and 8 This illustrates one implementation of the previously explained process using a film sprue. For example, it shows... Figure 7 In a schematic section, the device for producing at least one membrane 702a, 702b is shown. For features not mentioned below, reference is made to the previous description, whereby the indices 'a' and 'b' have been appended to the reference numerals in order to distinguish, for example, the two mold cavities 208a and 208b.

[0042] In contrast to the previous examples, the essentially circular membrane 702a, 702b is produced. Naturally, the procedure outlined below and the previously explained process steps are transferable to round and angular outer contours of the respective membrane.

[0043] In contrast to the previously described examples, the molten plastic 202 is introduced between the two molds 210 and 220 via the common feed channel 204. Exiting feed channel 204, the melt is deflected into at least two further feed channels 704a and 704b, whose perpendicular extension to the plane of the drawing increases in the direction of the respective mold cavities. The solidified molten plastic located in feed channels 704a and 704b can also be referred to as a film gate. At the end of each feed channel 704a or 704b is an opening 712a or 712b, which forms the boundary to the respective mold cavity 208a or 208b. The opening 712a, 712b of the at least one feed channel 704a, 704b adjoins a narrow side 705a, 705b of the membrane 702a-b to be produced in sections. The feed channel 704a, 704b thus leads into the mold cavity at a point which is assigned to the static area S1.The circular arc to which the opening 712a, 712b connects with the membrane 702a, 702b has a central angle between 90° and 20°, in particular between 80° and 40°, and in particular between 70° and 50°. A trim 706a, 706b is located on this circular arc, which is created when the sprue is removed from the membrane 702a, 702b.

[0044] A tab 708a, 708b projecting beyond the outer contour of the membrane 702a, 702b, which is provided, for example, for the arrangement of an electronic data carrier, is located on the side of the membrane 702a, 702b opposite the trim 706a, 706b.

[0045] Figure 9 A schematic section shows the production of at least one membrane 702a-b using film casting. For matching features, refer to the Figure 7 and 8 and their description is referenced. In contrast to the Figure 7Mold half 902 and mold half 210 are fixedly arranged relative to each other. Mold halves 210a and 210b, however, are movable at least along axes 280a and 280b.

[0046] The control unit 230 operates a plasticizing unit 240 and at least one linear actuator 250, or the linear actuators 250a and 250b, according to the process steps described here. The linear actuators 250a and 250b are configured to move the associated second form 220a or 220b along the respective actuating axis 280a, 280b, which corresponds to the actuating axis 180 of the diaphragm valve in which the diaphragm is subsequently used.

[0047] The plasticizing unit 240 is designed to plasticize the plastic, for example in powder or pellet form, and to feed the resulting plastic melt to the feed channel 204.

[0048] In contrast to the previously explained example of the Figure 7 and 8After flowing through the common feed channel 204, the molten plastic 202 encounters the inner wall of mold 904, which is fixed relative to the feed channel 204. The inner wall's position relative to mold 210, and thus to the common feed channel 204, remains unchanged until the membrane is removed. Exiting the feed channel 202, the melt is deflected into at least two further fixed feed channels 704a and 704b, whose perpendicular extension to the plane of the drawing and to axes 280a-b increases in the direction of the respective mold cavities. In this case, the feed channels 704a and 704b are bounded by mold 902 and mold 210, respectively, with both molds 902 and 210 being fixed relative to each other. This means that the feed channels 704a and 704b have a constant internal volume regardless of the movement of the molds 220a and 220b, which has a beneficial effect on the flow properties of the melt.This results in smaller velocity differences and a correspondingly lower shear, which has a beneficial effect on the material structure of the manufactured membrane. The solidified polymer melt located in the feed channel 704a, 704b can also be described as a film gate. At the end of each feed channel 704, 704b is the fixed-size opening 712a, 712b, which forms the boundary to the respective mold cavity 208a, 208b. The opening 712a, 712b of the at least one feed channel 704a, 704b adjoins a narrow side 705a, 705b of the membrane 702a-b to be manufactured in a section. The feed channel 704a, 704b thus leads into the mold cavity at a point that is assigned to the static area S1.

[0049] The feed channels 704a, 704b have a height, i.e., a spread parallel to one of the axes 280a-b, that is less than the thickness of the membrane to be produced. In a form not shown, the feed channels 704a, 704b can also have the same height as the membrane to be produced.

Claims

1. A method for producing at least one diaphragm (102; 502; 702a-b) for a diaphragm valve, the method comprising: conveying (304) a plastics melt (202) through at least one feed channel (204; 704a; 704b) into a mold cavity (206) which is delimited by a first mold (210) and at least one second mold (220; 220a, 220b); moving (306) the first and the second mold (210, 220; 220a, 220b) toward each other while the plastics melt (202) is being conveyed; removing (312) the at least one diaphragm (102; 502; 702a-b) from the mold cavity; and severing (314) a sprue from the at least one diaphragm (102; 502; 702a-b) removed from the mold cavity.

2. The method according to claim 1, wherein the diaphragm (102; 502; 702a-b) comprises a static central region (S1), a dynamic region (D) enclosing the central region (S1), and a static region (S2) enclosing the dynamic region (D), and wherein the feed channel (204; 704a; 704b) leads into the mold cavity at a point which is assigned to one of the static regions (S1, S2).

3. The method according to claim 1 or 2, wherein an opening (212) of the at least one feed channel (204) is arranged adjacent to an adjustment axis (180) of the diaphragm (102) to be produced, or the adjustment axis (180) of the diaphragm (102) to be produced passes through the opening (212) of the at least one feed channel (204).

4. The method according to claim 1 or 2, wherein an opening (712a; 712b) of the at least one feed channel (704a; 704b) adjoins, in portions, a narrow side (705a; 705b) of the diaphragm (102; 502; 702a-b) to be produced.

5. The method according to any of the preceding claims, wherein the first mold (210) with the at least one feed channel (204) has a negative contour (214) of the dry side of the diaphragm (102), and wherein the at least one second mold (220; 220a, 220b) has a negative contour (224) of the wet side (122) of the diaphragm (102).

6. The method according to any of the preceding claims, comprising: introducing (602) a connecting portion (512) of a connecting pin (510) for connection to a valve rod into a central recess (504) of the first mold (210), wherein a holding portion (514) of the connecting pin (510) is spaced apart from a surface of the first mold (210) surrounding the recess (504) and from a surface of the at least one second mold (220; 220a, 220b).

7. The method according to any of the preceding claims, wherein the first mold (210) is arranged so as to be stationary, and wherein the at least one second mold (220; 220a, 220b) is movable with respect to the first mold (210).

8. The method according to any of the preceding claims, wherein an internal volume of the at least one feed channel (204; 704a; 704b) remains constant between the conveying step (304) and a step of removing the at least one second mold (220).

9. The method according to any of the preceding claims, wherein a stationary mold (902) is arranged between at least two second mobile molds (220a, 220b), which stationary mold at least in portions delimits a feed channel (704a; 704b) opening into the mold cavity.

10. The method according to any of claims 1 to 7, wherein an internal volume of the at least one feed channel (204; 704a; 704b) decreases between the conveying step (304) and a step of removing the at least one second mold (220).

11. The method according to any of the preceding claims, wherein the plastics melt (202) comprises at least one fluoropolymer, in particular a perfluoroalkoxy polymer, PFA.

12. The method according to any of the preceding claims, wherein the plastics melt (202) is free of additives.