Casting mold for casting a support tube for a magnetic resonance imaging scanner with multi-part casing and mandrel

Abstract

Casting mold for casting a support tube (17) for a magnetic resonance imaging scanner (1), wherein the casting mold (60) comprises: a mandrel (70) for defining an inner contour of the support tube (70), wherein the mandrel (70) is manufactured in multiple parts from a plurality of segments (71, 72); a sheath (80) for defining an outer contour of the support tube (17), wherein the sheath has a plurality of segments that can be detachably connected to one another, characterized by the fact that the casting mold (60) has a loose part (90) that can be detachably connected to the mandrel (70) and / or the sleeve (80), wherein the loose part (90) is designed to be arranged during a casting process in a cavity (61) between the shell (80) and the mandrel (70), which is to be filled with a casting material, wherein the detachable loose part is designed to create undercuts already during a casting and to separate the casting from the casting mold non-destructively with the loose part.

Description

[0001] The invention relates to a casting mold for casting a support tube for a magnetic resonance imaging (MRI) scanner. The casting mold has a mandrel for defining an inner contour of the support tube. The mandrel is manufactured in multiple segments. The casting mold further comprises a shell for defining an outer contour of the support tube, the shell having a plurality of detachable and connectable segments.

[0002] Magnetic resonance imaging (MRI) scanners are imaging devices that use a strong external magnetic field to align the nuclear spins of a sample and then stimulate them to precess around this alignment using an alternating magnetic field. The precession, or return of the spins from this excited state to a lower-energy state, in turn generates an alternating magnetic field that is received by antennas.

[0003] Using magnetic gradient fields, a spatial coding is imprinted on the signals, which subsequently allows the received signal to be assigned to a volume element. The received signal is then evaluated, and a three-dimensional imaging representation of the object under investigation is generated. Local receiving antennas, so-called local coils, are preferably used to receive the signal; these are positioned directly next to the object under investigation to achieve a better signal-to-noise ratio.

[0004] The patient tunnel (bore) is limited by the dimensions of the field magnet and should therefore have the smallest possible thickness to allow as much space as possible for the patient. At the same time, it absorbs the patient's weight. The patient tunnel is therefore preferably designed as a rigid support tube. The support tube can be manufactured, for example, using a winding technique with fiberglass mats. Support tubes manufactured by vacuum casting are also known from German patent application DE 10219767 A1. Typically, the cores of the mold are machined from a solid body by turning.

[0005] In the current state of the art, undercuts in the interior are created by means of subsequent machining by milling or turning.

[0006] German patent application DE 10 2015 221 182 A1 describes a core system for the production of a fiber composite component. The core system comprises at least two core elements that are coupled to each other and can be displaced relative to each other. At least one core element has a surface inclined to a direction of displacement. Furthermore, the use of the core system as a core in the production of a fiber composite component, as well as a method for producing the fiber composite component, are described.

[0007] The publication DE 10 2014 217 042 A1 describes a method for manufacturing a hollow component made of fiber-reinforced plastic, which comprises the following process steps: - a construction step in which a multi-part core is built from a multitude of core elements, wherein at least one rigid core element is provided; - an application step in which reinforcing fibers are applied to the multi-part core; - an embedding step in which the reinforcing fibers are embedded in a matrix material made of plastic to form the hollow component; - a removal step in which, for the formation of the hollow component, at least the rigid core element is removed and at least one remaining core element, which cannot be removed non-destructively, remains in the hollow component; and - a final step in which the process is completed, with the remaining core element remaining in the hollow component beyond the final step.

[0008] From German patent application DE 10 2009 051 459 A1, a method for manufacturing a hollow profile is known. The hollow profile comprises a fiber composite component in which several layers of fibers are wound around a one- or multi-part core in a radial braiding process, then, for example, synthetic resin is injected and cured, and optionally, the core is at least partially removed. It is proposed that at least one preferably metallic reinforcing insert be integrated into the fiber composite component at at least one load-critical location. This reinforcing insert is designed either as a lost core or as an inserted reinforcing layer and is positioned, for example, by magnetic force.

[0009] Therefore, improving the manufacturing process for the support tubes is a task.

[0010] This problem is solved by a casting mold according to claim 1.

[0011] The casting mold according to the invention is intended for casting a support tube for a magnetic resonance tomograph, in particular by means of a vacuum casting.

[0012] The casting mold has a mandrel for defining an inner contour. The mandrel is the part of the casting mold that, during casting, defines the inner wall of the support tube, and is manufactured in multiple segments. The segments can be permanently welded or bonded together. It is also conceivable that the segments are detachably connected, as explained in more detail in the dependent claims.

[0013] The casting mold according to the invention further comprises a sleeve for defining an outer contour of the support tube. In the application position during casting, the sleeve surrounds the mandrel on its outer circumference and forms a closed cavity for receiving the casting compound. The sleeve also comprises a plurality of segments. The segments of the sleeve are detachably connectable to one another.

[0014] The multi-part mandrel advantageously enables simpler and more cost-effective manufacturing. Furthermore, the segmented casing allows for greater freedom in designing the outer surface of the support tube, as the casing does not need to be removed axially along the longitudinal axis, but rather the segments can be removed radially.

[0015] The casting mold according to the invention further comprises a loose part. A loose part is defined as a part of the casting mold that is neither part of the shell nor the mandrel, but nevertheless influences or modifies the shape of the support tube in a predetermined manner, in particular by being at least partially molded by the casting material. In a preferred embodiment, the loose part forms an end face of the support tube. The loose part is designed to be arranged in a cavity between the shell and the mandrel during a casting process, which is to be filled with a casting material. The loose part is detachably connected to the mandrel or the shell in order to fix it in a predetermined position during casting.

[0016] The detachable loose part advantageously makes it possible to create undercuts during casting and yet to separate the casting from the mold without damage using the loose part.

[0017] Further advantageous embodiments are described in relation to the dependent claims.

[0018] In one possible embodiment of the casting mold according to the invention, the shell, the mandrel, or the shell and the mandrel together comprise a plurality of segments. Segments are understood to be, in particular, approximately equal-sized parts which, when joined together, form the whole, here the shell and / or the mandrel. The segments are permanently or detachably connected to one another. In particular, the connection of the segments is fluid-tight for the casting of the support tube.

[0019] The segments are arranged along the circumference of the support tube to be cast. Preferably, the segments extend in the direction of the longitudinal axis of the support tube, which runs centrally between the two openings of the support tube. Preferably, the segments are made in one piece. However, it is also conceivable that a segment is made of several parts joined together along the longitudinal axis.

[0020] The mandrel segments are arranged in the application-specific position along the inner circumference of the support tube on an inner surface of the support tube to be cast. The number of mandrel segments is preferably three, four, or more.

[0021] The advantageous design of the mandrel in individual segments, as opposed to a one-piece mandrel made of solid material, allows for significant material and weight savings. This results in easier handling, faster production, and energy savings due to shorter heating and cooling times.

[0022] The segments of the jacket are arranged in the application-specific position around the outer circumference of the support tube to be cast. The number of jacket segments is preferably two, three, or four.

[0023] A multi-part, detachable jacket advantageously allows for a more flexible design of the outer contours of the support tube.

[0024] In one conceivable embodiment of the casting mold according to the invention, a first segment of the mandrel has a radially conically decreasing contour at a contact surface with the adjacent second segments. In other words, the distance between the contact surfaces perpendicular to the longitudinal axis between two points with the same radial distance to the longitudinal axis decreases with increasing radius in the application-specific arrangement.

[0025] The adjacent second segments of the mandrel exhibit a corresponding radially increasing contour. In other words, the distance perpendicular to the longitudinal axis between two points of the contact surfaces with the same radial distance to the longitudinal axis on the adjacent segments decreases in the application-specific arrangement.

[0026] The outer contours of the first segment and the adjacent segments are designed in such a way that the first segment of the mandrel can be moved radially inwards after the casting of the support tube and detached from the adjacent segments, and then removed axially along the longitudinal axis of the support tube.

[0027] Advantageously, the corresponding conically increasing and decreasing contours allow the core segments to be removed inwards, instead of having to remove the core in one piece in the axial direction. This allows the inner surface of the support tube to be made more flexible during casting, for example, by incorporating undercuts.

[0028] In one possible embodiment of the casting mold according to the invention, the loose part has several segments. For example, the loose part can be designed as a multi-part ring. The segments of the loose part are attached to segments of the mandrel, so that the segment of the loose part can advantageously be removed from the cast support tube together with the segment of the mandrel.

[0029] In one conceivable embodiment of the casting mold according to the invention, the mold includes fastening means for the detachable attachment of the loose part to the mandrel. The fastening means can be detached when the support tube is mounted on the mandrel. The loose part, or in the case of a segmented loose part, the segments, can, for example, be attached to the mandrel from the inside by means of screws through a segment of the mandrel.

[0030] The internally detachable fastening of the loose part to the mandrel advantageously allows the loose part to be detached from the mandrel after potting, the mandrel to be removed axially, and the loose part to be removed from the inside of the support tube.

[0031] In one possible embodiment of the casting mold according to the invention, the mold is vacuum-tight in the application-specific configuration. For this purpose, the individual segments of the shell and / or mandrel are either permanently and airtightly connected to one another, for example, by welding, bonding, or soldering. In the case of detachable connections, the respective corresponding contact surfaces of the shell, mandrel, and / or segments are each designed so that they lie against one another without gaps or cracks in the application-specific arrangement. Sealing agents such as gaskets and / or a highly viscous sealing fluid are also conceivable. In particular, the shell, mandrel, and loose part are designed so that no gaps or other leaks form during the temperature changes during casting and subsequent cooling.

[0032] The vacuum-tight casting mold advantageously allows for precise and void-free casting of the support tube.

[0033] In one conceivable embodiment of the casting mold according to the invention, the mandrel, in the configuration suitable for application, encloses a cavity that extends along a longitudinal axis of the support tube. In other words, the mandrel is not formed from a solid body, but as a hollow body. The minimum radius of the cavity in the radial direction perpendicular to the longitudinal axis is greater than the maximum thickness of a segment of the mandrel in the radial direction.

[0034] In conjunction with the segmentation of the mandrel, the cavity advantageously allows for the provision of a lightweight casting mold with minimal material expenditure.

[0035] The properties, features and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings.

[0036] They show: Fig. 1 a schematic representation of a magnetic resonance imaging scanner with a support tube as a patient tunnel; Fig. 2 a longitudinal section through an embodiment of a casting mold according to the invention; Fig. 3 a cross-section through an embodiment of a casting mold according to the invention; Fig. 4 a schematic representation of the manufacture of the mandrel from a plurality of raw blocks; Fig. 5 a schematic representation of an embodiment of a mandrel of a casting mold according to the invention.

[0037] Fig. Figure 1 shows a schematic representation of an exemplary embodiment of a magnetic resonance tomograph 1 with a support tube as a patient tunnel 16, as can be produced with the casting mold according to the invention.

[0038] The magnet unit 10 comprises a field magnet 11 that generates a static magnetic field B0 for aligning the nuclear spins of samples or patients 100 within a receiving area. The receiving area is arranged in a patient tunnel 16, which extends longitudinally 2 through the magnet unit 10. The patient tunnel 16 is formed by a support tube 17, which is preferably produced by vacuum casting using the casting mold 60 according to the invention. The support tube 17 has a cylindrical shape with a circular, elliptical, or more complex cross-section. A prism shape or hybrid shapes are also conceivable. The support tube 17 further comprises a multitude of details that serve to secure the support tube 17 itself within the field magnet 10 and to secure components described below, such as the patient bed 30 or the body coil 14. For example, the support tube provides running surfaces or rails for the patient bed 30.The support tube 17 must have high rigidity in order to absorb the forces of the components and the weight forces of the patient during operation and not to vibrate.

[0039] A patient 100 can be moved into the reception area using the patient table 30 and the patient table's transfer unit 36. The field magnet 11 is typically a superconducting magnet capable of generating magnetic fields with a magnetic flux density of up to 3 T, and even higher in the latest devices. However, for lower field strengths, permanent magnets or electromagnets with normal-conducting coils can also be used.

[0040] Furthermore, the magnetic unit 10 includes gradient coils 12, which are designed to superimpose variable magnetic fields in three spatial directions onto the magnetic field B0 in order to spatially differentiate the captured imaging areas in the investigation volume. The gradient coils 12 are typically coils made of normally conducting wires that can generate mutually orthogonal fields in the investigation volume.

[0041] The magnetic unit 10 also includes a body coil 14, which is designed to radiate a high-frequency signal supplied via a signal line 33 into the examination volume and to receive resonance signals emitted by the patient 100 and transmit them via a signal line. Preferably, however, the body coil 14 is replaced for receiving by local coils 50, which are arranged in the patient tunnel 16 close to the patient 100. It is also conceivable that the local coil 50 is designed for both transmitting and receiving, and therefore a body coil 14 can be omitted. The body coil 14 can be arranged directly on the support tube 17.

[0042] A control unit 20 supplies the magnet unit 10 with the various signals for the gradient coils 12 and the body coil 14 and evaluates the received signals. A magnetic resonance imaging (MRI) control unit 23 coordinates the subunits.

[0043] The control unit 20 thus has a gradient control 21 which is designed to supply the gradient coils 12 with variable currents via supply lines, which provide the desired gradient fields in the investigation volume in a time-coordinated manner.

[0044] Furthermore, the control unit 20 includes a high-frequency unit 22, which is designed to generate a high-frequency pulse with a predefined temporal profile, amplitude, and spectral power distribution to excite magnetic resonance of the nuclear spins in the patient 100. Pulse powers in the kilowatt range can be achieved. The individual units are interconnected via a signal bus 25.

[0045] The high-frequency signal generated by the high-frequency unit 22 is fed to the body coil 14 via a signal connection and transmitted into the patient's body 100 to excite the nuclear spins there. However, it is also conceivable to transmit the high-frequency signal via one or more local coils 50.

[0046] The local coil 50 preferably receives a magnetic resonance signal from the patient's body 100, because the signal-to-noise ratio (SNR) of the local coil 50 is better than that of a body coil 14 due to the short distance. The MR signal received by the local coil 50 is processed within the local coil 50 and transmitted to the radio frequency unit 22 of the magnetic resonance imaging scanner 1 for evaluation and image acquisition. Preferably, the signal connection 33 is used for this purpose, but wireless transmission is also conceivable, for example. Fig. Figure 2 shows a longitudinal section through an embodiment of a casting mold 60 according to the invention.

[0047] The casting mold 60 is shown in an application-specific arrangement with the mandrel 70 in the sleeve 80. The sleeve 80 and the mandrel 70 seal a cavity 61 in a vacuum-tight manner. During casting, the cavity 61 is filled with a thermoset, preferably a synthetic resin, via channels in the sleeve 80 or mandrel 70. Channels are also provided in the sleeve 80 and / or mandrel 70 for venting.

[0048] To make the cavity vacuum-tight apart from the channels, the shell has sealing lips 81, 82 which correspond to the shape of the mandrel 70 in a contact area between the sealing lips 81, 82 and the mandrel 70, ensuring full-surface contact without gaps. When casting a support tube, the casting mold is preferably rotated 90 degrees counterclockwise relative to the illustration in Fig. 2. If the contact surfaces of mandrel 70 and sleeve 80 are conically shaped, such that the sleeve 80, with its weight and correspondingly conically chamfered sealing lips 81, 82, rests on the mandrel 70, which is conical at the contact surfaces or tapers upwards, alignment and sealing of the cavity occur almost automatically. This can be further supported by preferably heat-resistant plastic or highly viscous sealants on the contact surface. The term "conical" here is not limited to a circular cross-section, but also includes other cross-sections such as ellipsoid or polygon, or combinations thereof.The term "conical" should also be generalized here to mean that the lateral surface does not necessarily form a straight line when cut with a plane in which the axis of the longitudinal direction 2 lies, as in the case of a geometric cone, but can also be curved, provided that the radius around the axis decreases along the longitudinal direction 2.

[0049] In a preferred embodiment, the mandrel 70 is withdrawn axially in the longitudinal direction 2 or upwards after casting, without having to disassemble it into parts. Therefore, the outer radius of the mandrel 70 is either constant or decreases in this direction, or the outer contour of the mandrel has a curve on each plane through the axis or longitudinal direction, the distance of which to the longitudinal direction is constant or decreases with the longitudinal direction or upwards.

[0050] However, the support tube 17 to be cast preferably also has contours on its inner side, the spacing of which increases in this longitudinal direction; these are called undercuts. Such an undercut would, however, prevent the support tube 17 from being pulled off the mandrel 70 without damage. For this purpose, the casting mold 60 according to the invention has, in one embodiment, one or more loose parts 90. Fig. Figure 2 shows a simple form of the loose part 90, which is placed ring-shaped and tightly around the surface of the mandrel 70. The cross-section of the loose part 90 is shown here as a triangular example, with an outer radius increasing in the longitudinal direction 2, so that the cast support tube 17 subsequently has a chamfered inner edge.

[0051] The loose part 90 is preferably detachably attached to the mandrel 70 for the casting process to prevent movement or floating. The attachment is releasable before the support tube 17 is removed from the mandrel 70, for example, by screws, pins, or a clamping device that can be loosened from an end face opposite to the longitudinal direction 2 or from the inside of the mandrel 70. It is also conceivable that the loose part 90 is fixed between the sleeve 80 and the mandrel 70 and can be removed from the mandrel 70 after the sleeve 80 is removed. Another possibility is a loose part 90 that can be attached to the mandrel 70 from the inside, through the mandrel 70, for example, with one or more screws or pins. After casting, the attachment could be loosened, the support tube 17 with the loose part 90 pulled off the mandrel 70, and then removed from the inside of the support tube 17.In the case of a loose part 90 that surrounds the mandrel 70 in a ring shape, the loose part 90 necessarily consists of several segments which, as explained below in relation to the mandrel 70 itself, can be individually removed inwards.

[0052] Fig. Figure 3 shows a cross-section through an embodiment of a casting mold according to the invention along line A - A in Fig. 2. The cross-sectional image in Fig. Figure 2 corresponds to a longitudinal section along line B - B. The circular cross-section of mandrel 70 and sleeve 80 are shown here, as already explained, only as examples and are not limiting. The sleeve 80 is shown here as an example with 4 segments, recognizable by the dividing lines. Each segment forms a 90-degree segment around the axis or longitudinal direction 2. The segments of the sleeve 80 can, for example, be screwed together. An external clamping device such as clamping bands or clamping jaws is also conceivable, which releasably fix the segments in a predetermined position relative to each other. The relative position of the sleeve segments can be determined by additional aids such as guide pins and holes or corresponding projections and recesses.

[0053] It is also conceivable to use fewer segments of the sheath 80, for example 3, in order to reduce the number of segments to be joined. Conversely, a larger number of sheath 80 segments can reduce the material required for manufacturing the sheath 80, as will be shown below. Fig. 4 for the Dorn 70 will be explained in more detail.

[0054] It is evident in Fig. 3. It is also noted that the mandrel 70 is hollow. The wall thickness of the mandrel is preferably thin, e.g., less than the radius of the recess around the axis. The thin wall thickness makes the mold easier to handle and reduces the time and energy required to heat the casting mold 60 for curing the resin. Cooling is also faster.

[0055] Fig. Figure 4 shows a schematic representation of how a hollow mandrel 70 according to the invention can be manufactured from a plurality of cast blocks as raw material. The individual cast blocks 83 are arranged here to form a rectangular hollow body that encloses a cuboid cavity. The mandrel 70 is inscribed within this hollow body. The segments of the mandrel 70 can thus be produced from the cast blocks 83, for example, by milling. Compared to manufacturing from a solid block or cylinder, this allows for a considerable saving of raw material.

[0056] In Fig. Figure 5 shows a schematic representation of an embodiment of a mandrel 70 of a casting mold 60 according to the invention, in which an undercut on an inner surface of the support tube 17 can be produced during casting even without a loose part 90.

[0057] The Dorn 70 of the Fig.The mandrel 5 has first segments 71 and second segments 72 that are detachably connected to each other, for example by screws, as already explained in more detail for the sleeve 80 or the loose part 90. However, the first segments 71 and the second segments 72 of the mandrel 70 must be moved inwards towards the axis of the longitudinal direction 2 to clear undercuts on the inside of the support tube 17. This is only possible if the contact surface 74 between the first and second segments has special properties. The distance d between points of the two opposing contact surfaces of a first segment 71 on a line perpendicular to a radial inwards movement for removing the first segment 71 and perpendicular to the axis of the longitudinal direction 2 must be constant or decrease with increasing radius.

[0058] The contact surfaces 74 of the second segments 72 are complementary, so that the first segments 71 and the second segments 72 can be assembled to form a complete mandrel 70. The distance d between points of the two opposing contact surfaces of a second segment 72 on a line perpendicular to a radial inward movement for removing the first segment 71 and perpendicular to the axis of the longitudinal direction 2 must increase with increasing radius by a measure predetermined by the geometry of the first segment 71 and the mandrel 70.

[0059] Preferably, the distance between the contact surfaces 74 on the outside of the mandrel 70 is still greater than zero, so that the second segments 72 can also be moved radially inwards after the first segments 71 have been removed, in order to be free of undercuts and then removed from the support tube 17 in longitudinal direction 2.

[0060] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples and other variations can be derived by the person skilled in the art without leaving the scope of protection of the invention.

Claims

[1] Casting mold for casting a support tube (17) for a magnetic resonance imaging scanner (1), wherein the casting mold (60) comprises: a mandrel (70) for defining an inner contour of the support tube (70), wherein the mandrel (70) is manufactured in multiple parts from a plurality of segments (71, 72); a sheath (80) for defining an outer contour of the support tube (17), wherein the sheath has a plurality of segments that can be detachably connected to one another, characterized by , that the casting mold (60) has a loose part (90) that can be detachably connected to the mandrel (70) and / or the sleeve (80), wherein the loose part (90) is designed to be arranged during a casting process in a cavity (61) between the shell (80) and the mandrel (70), which is to be filled with a casting material, wherein the detachable loose part is designed to create undercuts already during a casting and to separate the casting from the casting mold non-destructively with the loose part. [2] Casting mold according to claim 1, wherein the majority of the segments of the mandrel (70) and / or the sleeve (80) are arranged along the circumference of the support tube (17). [3] Casting mold according to claim 2, wherein the segments (71, 72) of the mandrel (70) are detachably connectable to one another, wherein a first segment (71) of the mandrel (70) has a radially conically decreasing contour at a contact surface (74) to adjacent second segments (72) and the adjacent second segments (72) of the mandrel have a corresponding radially increasing contour, so that the first segment (71) of the mandrel (70) can be moved radially inwards after the casting of the support tube (17) and then removed axially along a longitudinal axis of the support tube (17). [4] Casting mold according to one of the preceding claims, wherein the loose part (90) has several segments which can be detachably connected to each other. [5] Casting mold according to one of claims 1 to 3, wherein the casting mold (60) has a fastening means for releasably fastening the loose part (90) to the mandrel (70), wherein the fastening means is releasable when the support tube (17) is applied to the mandrel (70). [6] Casting mold according to one of the preceding claims, wherein the casting mold (60) is vacuum-tight in the application position. [7] Casting mold according to one of the preceding claims, wherein the mandrel (70) in application configuration encloses a cavity extending along a longitudinal axis of the support tube (17), wherein the minimum radius of the cavity in the radial direction perpendicular to the longitudinal axis is greater than a maximum thickness of a segment of the mandrel (70) in the radial direction.

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