Screw pump and its components

Abstract

The present disclosure relates to a screw pump 2, comprising a casing 3 having an inlet 30, an outlet 31 and a flow chamber 32 between the inlet and the outlet, and at least two screws 4, 5, 6 accommodated in the flow chamber and pushing out a fluid flow through the flow chamber from the inlet to the outlet, wherein at least one (4) of the screws comprises a central shaft 40 made of a first material, and the screw is formed from a second material on the central shaft 40.

Description

Technical Field

[0001] The present disclosure relates to the field of screw pumps and their components. More specifically, but not limited thereto, the present disclosure also relates to a cooling circuit for a vehicle, for example, comprising a screw pump.

Background Art

[0002] Known screw pumps comprise a casing and two or more screws accommodated within the casing and driven by a motor to extrude a fluid flow through the pump.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The present disclosure aims to improve the known design and performance of screw pumps.

Means for Solving the Problems

[0004] The present disclosure comprises a casing having an inlet, an outlet, and a flow chamber between the inlet and the outlet, and at least two screws accommodated within the flow chamber and extruding a fluid flow through the flow chamber from the inlet to the outlet, wherein at least one of the screws comprises a central shaft made of a first material, and the screw is molded from a second material onto the central shaft. The present disclosure relates to a screw pump.

[0005] For clarity, the first material and the second material can be separate materials from each other or similar materials.

[0006] The first material and the second material can be different. Advantageously, the first material is harder than the second material, for example such that at least one screw is strengthened. The first material can include a metal, such as steel like stainless steel, or a hard polymer. The second material can include a polymer, in which case the first material can include a polymer harder than the polymer of the second material. Thus, according to one aspect, the second material can be made not harder than the first material.

[0007] According to one aspect of the present disclosure, at least one of the screws comprises a central shaft made of a first material, and the screw is molded from a second material that is not harder than the first material on the central shaft.

[0008] As a variant, the first material and the second material can be the same or similar. The first material and the second material can each include a polymer, such as a similar polymer.

[0009] The first material and the second material can include one or more polymers. At least one of the polymers can include polyphenylene sulfide (PPS). The polymer, such as PPS, can be filled with fibers such as glass fibers. The polymer, such as PPS, can be lubricated. The first material and the second material can include the same polymer, such as PPS, which can be filled, additivated (with additives added), or neither, differently for each of the first material and the second material.

[0010] The central shaft can comprise one or more fixing features or fixing elements or fixing members. The single or plural fixing features can be embedded in the second material, for example so as to fix the central shaft within the second material.

[0011] The fixed feature or each fixed feature can comprise ribs or splines, such as axial ribs or splines. The fixed feature or each fixed feature can extend along at least a part of the central axis.

[0012] The single or plural fixed features can include at least two fixed features or at least two groups of fixed features that can be spaced along the length of the central axis.

[0013] At least one reinforced screw can include a drive screw, and the central axis of the drive screw can comprise, for example, a motor coupling (connection part) that receives torque from a drive motor.

[0014] The casing can comprise a shell in which an insert defining a flow chamber is received therein.

[0015] The present disclosure also relates to a method of manufacturing a screw for a screw pump, including providing a central axis made of a first material and molding a screw on the central axis using a second material.

[0016] For clarity, the first material and the second material can be distinct from each other or similar materials.

[0017] The first material and the second material can be different. The method can include inserting the central axis into a mold before molding the screw on the central axis. Advantageously, the first material is harder than the second material, for example, such that at least one screw is reinforced. The first material can include a metal or a hard polymer.

[0018] Thus, according to one aspect, the second material can be not harder than the first material.

[0019] As a modification, the first material and the second material can be similar. The first material and the second material can include a polymer. The method can include molding the central axis using the first material, for example, before molding a screw on the central axis using the second material. The method can include a two-stage molding process.

[0020] The present disclosure also relates to a screw pump comprising a casing having an inlet, an outlet, and a flow chamber between the inlet and the outlet, and at least two screws housed in the flow chamber and pushing a fluid flow through the flow chamber from the inlet to the outlet, the casing comprising a shell having an insert defining the flow chamber housed therein.

[0021] The flow chamber can be defined by the tubular wall of the insert. The tubular wall can be present with a substantially constant wall thickness or can have a constant wall thickness. The tubular wall can have a plurality of cylindrical lobes that approximate the outer shape of the meshing screws. The cylindrical lobes can include, for example, a central lobe that approximates the outer surface of a central drive screw. The cylindrical lobes can include, on both sides of the central lobe, outer lobes that approximate the outer surfaces of respective driven screws, for example. The flow chamber can provide a minimum space between the screws while allowing the screws to rotate freely.

[0022] The casing can comprise a space between the shell and the insert. The boundary between the shell and the insert can be designed such that, in use, a portion of the circulating fluid can enter the space. The space can be separated from the flow chamber and / or not be part of the flow chamber.

[0023] The insert can be provided with one or more anti-rotation protrusions that can engage with the shell to prevent their relative rotation. The anti-rotation protrusion or each anti-rotation protrusion can extend axially from the insert. The anti-rotation protrusion or each anti-rotation protrusion can include an anti-rotation tab. The insert can be provided with one or more anti-rotation protrusions extending from one or each of its ends. The insert can be provided with a flange or a clamp, such as a circular flange or clamp, at one end. The flange or clamp can have an outer periphery that approximates the inner surface of the shell, for example, to position the insert within the shell.

[0024] The pump can be provided with a flexible coupling. The flexible coupling can be connected to one of the screws to connect the screw to the drive motor. The flexible coupling can be connected to the motor coupling of the central axis of the drive screw.

[0025] The present disclosure also relates to a screw pump comprising a casing having an inlet, an outlet, and a flow chamber between the inlet and the outlet, at least two screws housed in the flow chamber and pushing a fluid flow through the flow chamber from the inlet to the outlet, and a flexible coupling connected to one of the screws to connect the screw to the drive motor.

[0026] The flexible coupling can be provided with a first side or end having a first coupling feature that engages with the shaft of the drive motor, for example. The flexible coupling can be provided with a second side or end having a second coupling feature that engages with the cooperating feature of the connected screw, for example.

[0027] The first coupling feature can be a slot that can be in the diametrical direction and / or a slot designed to accommodate a protrusion on the shaft of the drive motor or a protrusion on the drive motor. The second coupling feature can be, for example, a protrusion that engages with the cooperating feature of the drive screw. The protrusion can be rectangular. The second coupling feature can be offset, for example, rotated 90 degrees with respect to the first coupling feature.

[0028] The flexible coupling can include a polymeric material that can be lubricated, for example, within its mass and / or by oiling.

[0029] At least one of the screws can be non-self-locking. At least one screw can have one or more threads with a pitch and / or diameter and / or configuration that allows the screw to be removed from the mold, for example, by applying an axial force to the screw without applying a rotational force to the screw. At least one screw can have one or more threads with a twist angle that allows the screw to be removed from the mold, for example, by applying an axial force to the screw without applying a rotational force to the screw.

[0030] The twist angle can be at least 60 degrees, for example, at least 70 degrees. At least one screw can be made of a polymer, such as polyphenylene sulfide (PPS). The polymer, such as PPS, can be filled with fibers such as glass fibers. The polymer, such as PPS, can be lubricated.

[0031] The present disclosure also relates to a method of manufacturing a screw for a screw pump.

[0032] The present disclosure also relates to a method for manufacturing a screw for a screw pump, including molding the screw in a molding tool using a polymeric material and removing the screw from the mold by applying an axial force to the screw, wherein the material and threads of the screw are configured to allow the screw to rotate freely within the mold under the axial force.

[0033] Self-locking of the screw can be prevented by the configuration of the screw, in particular the twist angle of each of the single or multiple threads, and / or the coefficient of friction between the single or multiple threads and the surface of the mold.

[0034] The present disclosure also relates to a screw pump including a casing having an inlet, an outlet, and a flow chamber between the inlet and the outlet, and at least two screws housed in the flow chamber for pushing a fluid flow through the flow chamber from the inlet to the outlet, wherein at least one of the screws can be obtained by the above method.

[0035] As a variant, at least one of the screws can be of a self-locking type. At least one screw can include one or more threads each having a pitch and / or diameter and / or configuration that prevent the screw from being removed from the mold by applying an axial force to the screw without applying a rotational force to the screw. At least one screw can include one or more threads, and the one or more threads each have a twist angle that prevents the one or more threads from being removed from the mold by applying an axial force to the one or more threads without applying a rotational force to the one or more threads.

[0036] The twist angle can be less than 60 degrees. At least one screw can be made of a polymer, such as polyphenylene sulfide (PPS). The polymer, such as PPS, can be filled with fibers such as glass fibers. The polymer, such as PPS, can be lubricated.

[0037] According to one aspect of the present disclosure, at least one screw comprises a release coupling that restricts rotation of the screw when withdrawn from the molding tool.

[0038] According to one aspect of the present disclosure, each screw comprises a release coupling that restricts rotation of the screw when withdrawn from the molding tool.

[0039] Of course, in various modifications of the present disclosure, at least one screw or each screw, such as a self-locking screw or each screw, can comprise a release coupling. The release coupling can be used to restrict rotation of the screw when withdrawn from the molding tool.

[0040] The present disclosure also relates to a screw pump comprising a casing having an inlet, an outlet, and a flow chamber between the inlet and the outlet, and at least two screws accommodated in the flow chamber and pushing a fluid flow through the flow chamber from the inlet to the outlet, each screw comprising a release coupling that restricts rotation of the screw when withdrawn from the molding tool.

[0041] The insert can comprise at least one recess. The recess or each recess can be designed to accommodate one of the release couplings, for example when the screw is accommodated in the flow chamber. One of the release couplings can be accommodated in the recess.

[0042] In each of the above aspects of the present disclosure, the screw can include three or more screws or four or more screws. The screw can include at least one drive screw and at least one driven screw, such as at least two driven screws. Advantageously, the screw can include at least three driven screws that can be distributed, for example, evenly around the drive screw.

[0043] The present disclosure also relates to a method for manufacturing a screw for a screw pump, including molding a screw in a molding tool using a polymeric material and removing the screw from the mold by applying torque to a release coupling of the screw when unscrewing the screw from the mold.

[0044] At least one release coupling of the screw can comprise at least one radial shoulder. At least one release coupling of the screw can have a circular or non-circular structure. At least one release coupling of the screw can have an annular or partially annular structure.

[0045] The present disclosure also relates to a cooling circuit for a vehicle, comprising a screw pump as described above.

[0046] To avoid misunderstanding, all features described in the present disclosure apply to any aspect of the present disclosure.

[0047] It is explicitly defined that, as part of the present application, the various aspects, embodiments, examples, and alternatives disclosed in the above paragraphs and / or the following description and drawings, particularly their individual features, can be adopted independently or in any combination. In other words, all aspects and / or features of any aspect can be combined in any way, unless these features are incompatible.

[0048] To avoid misunderstanding, terms such as "can", "and / or", "for example", and any other similar terms used in the present disclosure should be construed as non-limiting, and thus, not every feature described in the present disclosure necessarily has to be present. In fact, any combination of optional features is explicitly contemplated without departing from the scope of the present disclosure.

[0049] Other features and advantages of the present disclosure will become apparent from the following detailed description, which should be understood in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0050]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

DETAILED DESCRIPTION OF THE INVENTION

[0051] The different aspects of the present disclosure will be described in more detail below with reference to FIGS. 1 to 16 attached hereto.

[0052] Referring to FIGS. 1 and 2, there is shown a screw pump assembly 1 including a motor 10 connected to a screw pump 2 by a flexible coupling 11. The screw pump 2 includes a casing 3 having an inlet pipe 30, an outlet pipe 31, and a flow chamber 32 between the inlet 30 and the outlet 31. Three screws 4, 5, and 6 are accommodated in the flow chamber 32 and push a fluid flow through the flow chamber 32 from the inlet 30 to the outlet 31.

[0053] The casing 3 includes a shell 33 having an insert 34 defining the flow chamber 32 accommodated therein. The shell 33 has a hollow cylindrical shape with a closed end 33a from which the inlet pipe 30 projects. The outlet pipe 31 projects radially from the shell 33 adjacent to the open end 33b. The screw pump 2 is reversible, so that the inlet pipe 30 and the outlet pipe 31 can be interchanged by rotating the screw pump 2 in the opposite direction. However, for simplicity, the axial pipe 30 projecting from the closed end 33a will be referred to hereinafter as the inlet pipe 30, and the radial pipe 30 projecting from the open end 33b will be referred to hereinafter as the outlet pipe 31.

[0054] As shown in FIGS. 3 and 4, the flow chamber 32 is defined by the tubular wall 35 of the insert 34 having a substantially constant wall thickness. The tubular wall 35 has three cylindrical lobes 35a, 35b, 35c that approximate the outer shapes of the three meshing screws 4, 5, 6. More specifically, the central lobe 35a approximates the outer surface of the central drive screw 4, and on both sides of the central lobe 35a, there are outer lobes 35b, 35c that approximate the outer surfaces of the respective driven screws 5, 6. The flow chamber 32 allows the screws 4, 5, 6 to rotate freely while providing a minimum amount of space between the screws 4, 5, 6.

[0055] The insert 34 also includes a pair of anti-rotation tabs 36, 37 that project axially from each of its ends. The first pair 36 of the anti-rotation tabs projects from the upper and lower portions of the central lobe 35a at the first end of the insert 34. The second pair 37 of the anti-rotation tabs projects upward and downward from the central lobe 35a from the circular flange 38 at the second end of the insert 34. The circular flange 38 has an outer circumference that approximates the inner surface of the shell 33, whereby, as more clearly shown in FIG. 5, the insert 34 can be positioned within the shell 33 and a space E can be formed therebetween.

[0056] The casing 3 further includes a pair of mounting disks 39a, 39b and a spacing interface 39c. The mounting disks 39a, 39b engage with the anti-rotation tabs 36, 37 of the insert 34 and are mounted inside the shell 33 to capture the screws 4, 5, 6 and the insert 34 therebetween. The spacing interface 39c seals the screw pump 2 and separates the flow chamber 32 from the motor 10, but the boundary between the shell 33 and the insert 34 is designed such that a portion of the circulating fluid can enter the space E during use.

[0057] In some examples, the first mounting disk 39a can be made part of or integrated with the space-forming boundary 39c. In some examples, the second mounting disk 39b can be made part of or integrated with the insert 34. When the second mounting disk 39b is part of the insert 34, the anti-rotation tab 37 protruding from the circular flange 38 can be omitted.

[0058] The presence of the space E between the shell 33 filled with the circulating fluid and the insert 34 brings about a vibration damping effect due to the interaction between the screws 4, 5, 6. Furthermore, those skilled in the art will understand that by using the independent insert 34, the flow chamber 32 can be manufactured with high precision. Moreover, this enables the insert 34 to be designed with a substantially constant wall thickness, optimizing the cycle time and part quality, thus making the manufacture of the insert 34 by injection molding easier.

[0059] The flexible coupling 11 clearly shown in FIG. 6 is substantially cylindrical and has a first coupling feature 12 at its first axial end and a second coupling feature 13 at its second axial end.

[0060] The first coupling feature 12 is a diametrical slot designed to accommodate a rectangular protrusion on the shaft of the drive motor 10. The second coupling feature 13 is a rectangular protrusion that engages with the cooperating feature of the drive screw 4, which is rotated 90 degrees and offset from the first coupling feature 12.

[0061] In this example, the flexible coupling 11 is made of a lubricated polymer. By using a flexible coupling between the drive motor 10 and the screw pump 2, vibration can be minimized while accommodating slight angular and axial misalignments. Those skilled in the art will understand that this feature acts synergistically with the vibration damping effect of the space E between the shell 33 and the insert 34.

[0062] The drive screw 4 is more clearly shown in Fig. 7 and includes a central shaft 40 and a body 41 molded on the central shaft 40. In this example, the body 41 has two threads 42 that are diametrically opposed along its length.

[0063] The central shaft 40 includes a fixing feature 43 embedded in the body 41 that fixes the central shaft 40 to the body 41. In this example, the fixing feature 43 includes two groups of axial splines 44 that extend along a part of the central shaft 40. The two groups of axial splines 44 are spaced apart from each other along the length of the central shaft 40.

[0064] The central shaft 40 further includes a motor coupling 45 in the shape of a diametrical slot designed to accommodate the rectangular protrusion 13 of the flexible coupling 11. However, the central shaft 40 may directly accommodate the rectangular protrusion of the shaft of the drive motor 10. In this example, the central shaft 40 is made of stainless steel and the body 41 is made of a polymer material. Using a polymer screw body 41 molded on a stainless steel central shaft 40 has several advantages. The presence of the central shaft 40 reduces the thickness of the material required to form the body 41. Those skilled in the art will understand that this significantly reduces the cycle time and reduces the tendency of the molded body 41 to deform when the material solidifies. In addition, the hardness of the central shaft 40 also prevents the screw 4 from bending or deforming under the load when torque is applied to it by the drive motor 10.

[0065] Those skilled in the art will understand that this feature acts synergistically with the vibration damping effect of the flexible coupling 11 and the space E between the shell 33 and the insert 34.

[0066] Figures 9 and 10 show the driven screws 5 and 6. Each driven screw 5, 6 includes respective bodies 50, 60 having a pair of threads 51, 61 that are diametrically opposed along its length. Each driven screw 5, 6 also includes release couplings 52, 62 at one of its ends. Each release coupling 52, 62 is in the form of a ring 53, 63 having a pair of notches 54, 64 aligned with adjacent ends of the threads 51, 61. The notches 54, 64 form radially directed shoulders 54a, 64a to which torque can be applied.

[0067] The diameters of the rings 53, 63 of each driven screw 5, 6 are larger than the diameters of the threads 51, 61, and holes 55, 65 are defined between the rings 53, 63 and the bases of the threads 51, 61. Thus, along the entire length of each driven screw 5, 6, a fluid passage is defined between the threads 51, 61 and through the release couplings 52, 62. Each driven screw 5, 6 further includes axial projections 56, 66 at the respective centers of its ends.

[0068] In this example, the threads 51, 61 of the driven screws 5, 6 are self-locking and their rotation is prevented only when an axial force is applied to the driven screws 5, 6 at the end of the molding cycle while they are still present within a molding cavity (not shown). Thus, torque must be applied to the driven screws 5, 6 to remove them from the mold. This torque can be applied to the driven screws 5, 6 by the release couplings 52, 62.

[0069] In this example, the insert 34 includes annular steps 32a, 32b that surround a part of the flow chamber 32 defined by each of the outer lobes 35b, 35c. These annular steps 32a, 32b act as recesses for receiving the rings 53, 63 when the screws 4, 5, 6 are received within the flow chamber 32.

[0070] Alternatively, it is also recognized that the threads 51, 61 can be designed in a non-self-locking manner. In such a situation, the release couplings 52, 62 can be omitted, and the driven screws 5, 6 can be removed by simply applying an axial force to them at the end of the molding process.

[0071] For example, the threads can each have a pitch and / or diameter and / or configuration that enables the thread to be removed from the mold by applying an axial force to the thread without applying a rotational force to the thread. More specifically, the threads can each have a twist angle that enables the thread to be removed from the mold by applying an axial force to the thread without applying a rotational force to the thread.

[0072] As a mere example, when the threads are made of a polymer such as glass fiber-filled polyphenylene sulfide (PPS), the twist angle can be at least 60 degrees, for example at least 70 degrees.

[0073] Referring to FIGS. 11 to 15, a screw pump assembly 101 according to a second example is shown, which is similar to the first example in that similar features are shown with numbers increased by only 100. The screw pump assembly 1 of this example is different from the first example in that it includes three driven screws 105, 106, 107 and the drive screw has three threads 142, which is more clearly shown in FIG. 15.

[0074] Accordingly, the tubular wall 135 has four cylindrical lobes 135a, 135b, 135c, 135d that approximate the outer shapes of the four meshing screws 104, 105, 106, 107. More specifically, the central lobe 135a approximates the outer surface of the central drive screw 104 and has three outer lobes 135b, 135c, 135d that approximate the outer surfaces of the respective driven screws 105, 106, 107 and are evenly distributed around the outer circumference of the central lobe 135a.

[0075] Figure 16 shows another screw assembly 205, 206, 207 that can be used in place of the screw assembly of Figure 15 in the pump assembly of Figure 11. Screws 205, 206, 207 are similar to those of the previous example in that similar features are shown with numbers increased by only 100. The screw assemblies 205, 206, 207 in this example are different from those of the previous example in that they have a larger twist angle.

[0076] Those skilled in the art will notice that a plurality of variations of the above aspects can be considered without departing from the scope of the disclosure.

[0077] Throughout the description of the specification and the claims of this application, the words "comprise" and "include" and their variations mean "including but not limited to" and do not contemplate (and do not exclude) other parts, additives, components, integers, or steps.

[0078] Any feature, integer, characteristic, compound, or group described in connection with a particular aspect, embodiment, or example of the present disclosure is to be understood as applicable to any other aspect, embodiment, or example described herein, as long as they are not mutually inconsistent. All features disclosed in this application (including the abstract and the accompanying drawings), and / or all steps of the methods or processes thus disclosed, can be combined in any combination other than combinations in which at least some of such features and / or steps are mutually exclusive. The present disclosure is not limited to the details of all the above aspects. The present disclosure also extends to any novel feature or any novel combination of features disclosed in this application (including the abstract and the accompanying drawings), or to any novel feature or any novel combination of features of any method or process step thus disclosed.

Description of Reference Numerals

[0079] 1 Screw pump assembly 10 Motor 11 Flexible coupling 12 First coupling feature 13 Second coupling feature 2 Screw pump 3 Casing 30 Inlet pipe 31 Outlet pipe 32 Flow chamber 32a Annular step 32b Annular step 33 Shell 33a Closed end of the shell 33b Open end of the shell 34 Insert 35 Tubular wall of the insert 35a Cylindrical central lobe of the tubular wall 35b Cylindrical outer lobe of the tubular wall 35c Cylindrical outer lobe of the tubular wall 36 Anti-rotation tab 37 Anti-rotation tab 38 Circular flange 39a Mounting disk 39b Mounting disk 39c Space-forming boundary 4 Driving screw 40 Central axis of the driving screw 41 Body of the driving screw 43 Fixing feature 44 Axial spline 45 Motor coupling 5 Driven screw 50 Body of the driven screw 51 Thread of the driven screw 52 Release coupling 53 Ring of the release coupling 54 Notch of the release coupling 54a Radial shoulder 55 Hole 56 Axial protrusion 6 Driven screw 60 Body of the driven screw 61 Thread of the driven screw 62 Release coupling 63 Ring of the release coupling 64 Notch of the release coupling 64a Radial shoulder 65 Hole 66 Axial protrusion E Space between the insert and the shell 101 Screw pump assembly 110 Motor 102 Screw pump 103 Casing 130 Inlet pipe 131 Outlet pipe 132 Flow chamber 133 Shell 133a Closed end of the shell 133b Open end of the shell 134 Insert 135 Tubular wall of the insert 135a Cylindrical central lobe of the tubular wall 135b Cylindrical outer lobe of the tubular wall 135c Cylindrical outer lobe of the tubular wall 135d Cylindrical outer lobe of the tubular wall 136 Anti-rotation tab 137 Anti-rotation tab 138 Circular flange 104 Drive screw 140 Central axis of the drive screw 141 Body of the drive screw 145 Motor coupling 105 Driven screw 150 Body of the driven screw 151 Thread of the driven screw 156 Axial protrusion 106 Driven screw 160 Body of the driven screw 161 Thread of the driven screw 166 Axial protrusion 107 Driven screw 176 Axial protrusion 204 Drive Screw 240 Central Axis of Drive Screw 241 Body of Drive Screw 245 Motor Coupling 205 Driven Screw 250 Body of Driven Screw 251 Thread of Driven Screw 256 Axial Protrusion 206 Driven Screw 260 Body of Driven Screw 261 Thread of Driven Screw 266 Axial Protrusion 207 Driven Screw 276 Axial Protrusion

Claims

1. Screw pump (2), A casing (3) having an inlet (30), an outlet (31), and a flow chamber (32) between the inlet and the outlet, At least two screws (4, 5, 6) housed within the flow chamber and pushing the fluid flow through the flow chamber from the inlet to the outlet, Equipped with, At least one (4) of the screws comprises a central shaft (40) made of a first material, and the screw is formed on the central shaft (40) from a second material. Screw pump (2).

2. The screw pump according to claim 1, wherein at least one of the screws includes a drive screw, and the central shaft of the drive screw is provided with a motor coupling (45) for receiving torque from a drive motor.

3. The screw pump according to claim 2, further comprising a flexible coupling (11) connected to the motor coupling of the central shaft of the drive screw.

4. The screw pump according to any one of claims 1 to 3, wherein the first material is harder than the second material so that at least one of the screws is reinforced.

5. The screw pump according to claim 4, wherein the first material includes a metal.

6. The screw pump according to any one of claims 1 to 3, wherein the first material and the second material each comprise a polymer.

7. The screw pump according to any one of claims 1 to 3, wherein the central shaft comprises one or more fixing features (43) embedded in the second material for fixing the central shaft within the second material.

8. The screw pump according to claim 7, wherein the fixed feature portion or each fixed feature portion comprises an axial rib or spline (44) extending along at least a portion of the central axis.

9. The screw pump according to claim 7, wherein one or more of the fixed feature portions include at least two fixed feature portions or at least two groups of fixed feature portions spaced apart along the length of the central axis.

10. The screw pump according to any one of claims 1 to 3, wherein the casing comprises a shell (33) and an insert (34) defining the flow chamber is housed within the shell.

11. A screw pump according to any one of claims 1 to 3, wherein each screw (4, 5, 6) is provided with a release coupling (52, 62) that restricts the rotation of the screw when it is withdrawn from the molding tool.

12. The casing comprises a shell (33) and an insert (34) defining the flow chamber is housed within the shell, The screw pump according to claim 11, wherein the insert (34) comprises at least one recess (32a, 32b), and one of the release couplings (45, 52, 62) is housed in the recess.

13. A method for manufacturing a screw for a screw pump, Prepare a central shaft made from the first material, A screw is formed on the central axis using a second material, Methods that include...

14. The method according to claim 13, wherein the first material is harder than the second material, and the method includes inserting the central shaft into a mold before forming the screw onto the central shaft.

15. The method according to claim 13, further comprising forming the central shaft using the first material before forming the screw on the central shaft using the second material.

16. The method according to claim 15, wherein the first material and the second material are similar.

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