SCREW PUMP AND ITS COMPONENTS

Abstract

The disclosure relates to a screw pump comprising: a casing with an inlet, an outlet and a flow chamber between the inlet and the outlet; and at least two screws housed in the flow chamber to force a fluid flow through the flow chamber from the inlet to the outlet; wherein at least one of the screws comprises a lubricated polymer material.

Claims

1. A screw pump, comprising: a casing with an inlet, an outlet and a flow chamber between the inlet and the outlet; and at least two screws housed in the flow chamber to force a fluid flow through the flow chamber from the inlet to the outlet; wherein at least one of the screws comprises a lubricated polymer material.

2. The screw pump according to claim 1, wherein the lubricated polymer material comprises polyphenylene sulfide.

3. The screw pump according to claim 1, wherein the lubricated polymer material comprises a fiber reinforced lubricated polymer material.

4. The screw pump according to claim 3, wherein the lubricated polymer material comprises a glass fiber reinforced polyphenylene sulfide.

5. The screw pump according to claim 1, wherein the casing comprises a shell within which an insert defining the flow chamber is housed.

6. The screw pump according to claim 5, wherein the flow chamber is defined by a tubular wall of the insert that has a substantially constant wall thickness.

7. The screw pump according to claim 5, wherein the insert comprises one or more anti-rotation protrusions which engage with the shell to inhibit relative rotation between them.

8. The screw pump according to claim 5, wherein the insert comprises a lubricated polymer material.

9. The screw pump according to claim 5, wherein the insert comprises a lubricated polyphenylene sulfide material.

10. The screw pump according to claim 5, wherein the insert comprises a fiber reinforced lubricated polymer material.

11. The screw pump according to claim 5, wherein the insert comprises a glass fiber reinforced lubricated polyphenylene sulfide.

12. The screw pump according to claim 1, wherein at least one of the screws comprises a center shaft made of a first material on which the screw is molded from a second material that is less stiff than the first material.

13. The screw pump according to claim 12, wherein the second material comprises lubricated polymer, such as a lubricated polyphenylene sulfide material.

14. The screw pump according to claim 13, wherein the second material comprises a fiber reinforced lubricated polymer material.

15. The screw pump according to claim 14, wherein the fiber reinforced lubricated polymer material comprises a glass fiber reinforced lubricated polyphenylene sulfide.

16. The screw pump according to claim 1, wherein at least one of the screws comprises threads with a helix angle of at least 60.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Other features and advantages of the disclosure will become apparent from the following detailed description, which will be understood in reference to the appended drawings, in which:

[0074] FIG. 1 illustrates a pump assembly according to one aspect of the disclosure;

[0075] FIG. 2 is an exploded view of the pump assembly in FIG. 1;

[0076] FIG. 3 illustrates a first side of the flow chamber insert of the pump assembly in FIGS. 1 and 2;

[0077] FIG. 4 illustrates a second side of the flow chamber insert in FIG. 3;

[0078] FIG. 5 illustrates the insert in FIGS. 3 and 4 housed in the shell of the casing and with the screws housed in the insert;

[0079] FIG. 6 illustrates the flexible coupling of the assembly in FIGS. 1 and 2, which couples the drive screw to the drive motor;

[0080] FIG. 7 illustrates the drive screw of the pump assembly in FIGS. 1 and 2;

[0081] FIG. 8 illustrates the center shaft of the drive screw in FIG. 7;

[0082] FIG. 9 illustrates a first side of the two driven screws of the pump assembly in FIGS. 1 and 2;

[0083] FIG. 10 illustrates a second side of the driven screws in FIG. 9;

[0084] FIG. 11 illustrates a pump assembly according to another aspect of the disclosure;

[0085] FIG. 12 illustrates a first side of the flow chamber insert of the pump assembly in FIG. 11;

[0086] FIG. 13 illustrates a second side of the flow chamber insert in FIG. 12;

[0087] FIG. 14 illustrates the insert in FIGS. 12 and 13 housed in the shell of the casing and with the screws housed in the insert;

[0088] FIG. 15 illustrates the screw assembly of the pump assembly shown in FIG. 11; and

[0089] FIG. 16 illustrates another screw assembly that can be used in the pump assembly in FIG. 11 instead of the screw assembly in FIG. 15.

DETAILED DESCRIPTION

[0090] Different aspects of different aspects of the disclosure are described in more detail below, in reference to FIGS. 1 to 16 appended hereto.

[0091] Referring now to FIGS. 1 and 2, a screw pump assembly 1 is shown, which comprises a motor 10 coupled to a screw pump 2 by a flexible coupling 11. The screw pump 2 comprises a casing 3 with 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, 6 are housed in the flow chamber 32 to force fluid flow through the flow chamber 32 from the inlet 30 to the outlet 31. Preferably, at least one of the screws 4, 5, 6 comprises a lubricated polymer material. In this specific example, all of the screws comprise a polyphenylene sulfide (PPS) material containing a solid or dry lubricant, such as polytetrafluorethylene (PTFE), molybdenum disulfide and carbon or graphite.

[0092] The casing 3 comprises a shell 33 within which an insert 34 defining the flow chamber 32 is housed. In this example, the insert 34 also comprises a lubricated polymer material, specifically a glass fiber reinforced PPS material containing a solid or dry lubricant, such as polytetrafluorethylene (PTFE), molybdenum disulfide and carbon or graphite.

[0093] The shell 33 is in the shape of a hollow cylinder with a closed end 33a from which the inlet pipe 30 protrudes. The outlet pipe 31 radially protrudes from the shell 33, next to an open end 33b. The screw pump 2 is reversible and, as such, the inlet pipe 30 and the outlet pipe 31 can be reversed by rotating the screw pump 2 in the opposite direction. However, for the sake of simplicity, the axial pipe 30 protruding from the closed end 33a will hereinafter be referred to as the inlet pipe 30 and the radial pipe 30 protruding from the open end 33b will hereinafter be referred to as the outlet pipe 31.

[0094] As shown in FIGS. 3 and 4, the flow chamber 32 is defined by a tubular wall 35 of the insert 34, which has a substantially constant wall thickness. The tubular wall 35 has three cylindrical lobes 35a, 35b, 35c which approximate the outer profile of the three meshing screws 4, 5, 6. More specifically, a center lobe 35a approximates the outer surfaces of a center drive screw 4, with an outer lobe 35b, 35c on each side of the center lobe 35a, each approximating the outer surfaces of a respective driven screw 5, 6. The flow chamber 32 provides minimal space between the screws 4, 5, 6, while allowing them to rotate freely.

[0095] The insert 34 also comprises a pair of anti-rotation tabs 36, 37 protruding axially from each of its ends. A first pair of anti-rotation tabs 36 protrudes from the upper and lower parts of the center lobe 35a at a first end of the insert 34. A second pair of anti-rotation tabs 37 protrudes from a circular flange 38, above and below the center lobe 35a at a second end of the insert 34. The circular flange 38 has a perimeter which approximates an inner surface of the shell 33, which makes it possible to position the insert 34 within the shell 33 and to create a space E between them, as more clearly shown in FIG. 5.

[0096] The casing 3 also comprises a pair of mounting discs 39a, 39b and a spacing interface 39c. The mounting discs 39a, 39b engage the anti-rotation tabs 36, 37 of the insert 34 and are attached inside the shell 33 to trap the screws 4, 5, 6 and the insert 34 between them. The spacing interface 39c sealingly closes the screw pump 2 and isolates the flow chamber 32 from the motor 10, but the interface between the shell 33 and the insert 34 is designed to allow, when in use, part of the circulating fluid to enter the space E.

[0097] In some examples, the first mounting disc 39a can be part of or integrated with the spacing interface 39c. In some examples, the second mounting disc 39b can be part of or integrated with the insert 34. When the second mounting disc 39b is part of the insert 34, the antirotation tabs protruding from the circular flange 38 can be omitted.

[0098] The presence of a space E between the shell 33 and the insert 34, which is filled with circulating fluid, provides a vibration-damping effect resulting from the interaction between screws 4, 5, 6. In addition, the person skilled in the art will understand that the use of a separate insert 34 makes it possible to manufacture the flow chamber 32 with great precision.

[0099] This also makes it easier to manufacture the insert 34 by injection molding, since it can be designed with a substantially constant wall thickness to optimize cycle time and part quality.

[0100] The flexible coupling 11, more clearly illustrated in FIG. 6, is substantially cylindrical and has a first coupling feature 12 at a first of its axial ends and a second coupling feature 13 at a second of its axial ends.

[0101] The first coupling feature 12 is a diametrical slot for designed to house a rectangular protrusion on a shaft of the drive motor 10. The second coupling feature 13 is a rectangular protrusion, which is rotationally offset by 90 degrees from the first coupling feature 12, to engage a cooperating feature of the drive screw 4.

[0102] In this example, the flexible coupling 11 is made of a lubricated polymer. The use of a flexible coupling between the drive motor 10 and the screw pump 2 makes it possible to accommodate minor angular and axial misalignment, while minimizing vibrations. The person skilled in the art will understand that this feature acts in synergy with the vibration damping effect of the space E between the shell 33 and the insert 34.

[0103] The drive screw 4 is more clearly shown in FIG. 7, and comprises a center shaft 40 and a body 41 molded on the center shaft 40. In this example, the body 41 comprises two diametrically opposite threads 42 along its length.

[0104] The center shaft 40 comprises anchoring features 43 embedded in the body 41 to anchor the center shaft 40 to the body 41. In this example, the anchoring features 43 comprise two groups of axial splines 44 that extend along part of the center shaft 40. The two groups of axial splines 44 are spaced apart from one another along the length of the center shaft 40.

[0105] The center shaft 40 also comprises a motor coupling 45 in the form of a diametrical slot designed to house the rectangular protrusion 13 of the flexible coupling 11, although it can directly house the rectangular protrusion of the shaft of the drive motor 10. In this example, the center shaft 40 is made of stainless steel and the body 41 is made of a lubricated polymer material, specifically a glass fiber reinforced PPS material containing a solid or dry lubricant, such as polytetrafluorethylene (PTFE), molybdenum disulfide and carbon or graphite.

[0106] There are several advantages to using a polymer screw body 41 molded on a stainless-steel center shaft 40. The presence of the center shaft 40 reduces the thickness of the material required to form the body 41. The person skilled in the art will understand that this significantly reduces the cycle time and mitigates the tendency of the molded body 41 to deform when the material solidifies. In addition, the stiffness of the center shaft 40 also prevents the screw 4 from bending or deforming under load when torque is applied to it by the drive motor 10.

[0107] The person skilled in the art will also understand that this feature acts in synergy with the flexible coupling 11 and the vibration-damping effect of the space E between the shell 33 and the insert 34.

[0108] FIGS. 9 and 10 show the driven screws 5 and 6. Each driven screw 5, 6 comprises a lubricated polymer material, specifically a PPS material that is devoid of fiber reinforcement containing a solid or dry lubricant, such as polytetrafluorethylene (PTFE), molybdenum disulfide and carbon or graphite. Advantageously, the type and/or concentration of the lubricant in the driven screws 5, 6 may be different to that of the body 41 of the drive screw 4 and/or different to that of the insert 34.

[0109] Each driven screw 5, 6 comprises a respective body 50, 60 with a pair of diametrically opposite threads 51, 61 along its length. Each driven screw 5, 6 also comprises a release coupling 52, 62 at one of its ends. Each release coupling 52, 62 is in the shape of a ring 53, 63 with a pair of notches 54, 64 aligned with the adjacent ends of the threads 51, 61. The notches 54, 64 form radial shoulders 54a, 64a to which torque can be applied.

[0110] The diameter of the ring 53, 63 of each driven screw 5, 6 is larger than that of the threads 51, 61 and holes 55, 65 are defined between the ring 53, 63 and the base of the threads 51, 61. Thus, a fluid passage is defined along the entire length of each driven screw 5, 6, between the threads 51, 61 and through the release coupling 52, 62. Each driven screw 5, 6 also comprises an axial protrusion 56, 66 in the center of each of its ends.

[0111] In this example, the threads 51, 61 of the driven screws 5, 6 are self-locking, in that their rotation is prevented if only an axial force is applied to the driven screws 5, 6 at the end of the molding cycle, while they are still in the mold cavity (not shown). As such, torque must be applied to the driven screws 5, 6 to remove them from the mold. The release coupling 52, 62 allows this torque to be applied to the driven screws 5, 6.

[0112] In this example, the insert 34 comprises an annular step 32a, 32b surrounding the part of the flow chamber 32 defined by each of the outer lobes 35b, 35c. These annular steps 32a, 32b act as recesses that accommodate the rings 53, 63 when the screws 4, 5, 6 are housed in the flow chamber 32.

[0113] It will also be appreciated that the screw threads 51, 61 can alternatively be designed to be non-self-locking. In such circumstances, the release coupling 52, 62 can be omitted, and the driven screws 5, 6 can be ejected at the end of the molding process by simply applying axial force to them.

[0114] For example, the threads can each have a pitch and/or a diameter and/or a configuration that enables them to be ejected from a mold by applying an axial force to it, without applying a rotational force to it. More specifically, the threads can each have a helix angle that enables them to be ejected from a mold by applying an axial force to it, without applying a rotational force to it.

[0115] By way of example only, the helix angle can be at least 60, for example at least 70, when the threads are made of a polymer, such as lubricated PPS.

[0116] Referring now to FIGS. 11 through 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 marked with like numbers incremented by 100. The screw pump assembly 1 in this example differs from that of the first example in that it comprises three driven screws 105, 106, 107 and that the drive screw has three threads 142, which is more clearly illustrated in FIG. 15.

[0117] Therefore, the tubular wall 135 has four cylindrical lobes 135a, 135b, 135c, 135d, which approximate the outer profile of the four meshing screws 104, 105, 106, 107. More specifically, the center lobe 135a approximates the outer surfaces of the center drive screw 104, with three outer lobes 135b, 135c, 135d evenly distributed around the perimeter of the center lobe 135a, each approximating the outer surfaces of a respective driven screw 105, 106, 107.

[0118] FIG. 16 shows another screw assembly 205, 206, 207 that can be used in the pump assembly in FIG. 11 instead of the screw assembly in FIG. 15. The screws 205, 206, 207 are similar to the ones in the previous example in that similar features are marked by like numbers incremented by 100. The screw assembly 205, 206, 207 in this example differs from the one in the previous example in that the helix angle is greater.

[0119] A person skilled in the art will be aware that several variants of the aforementioned aspects are conceivable without departing from the scope of the disclosure.

[0120] Throughout the description and claims of this specification, the words comprise and contain and their variations mean including but not limited to and are not intended for (and do not exclude) other parts, additives, components, integers or steps.

[0121] Any features, integers, characteristics, compounds or groups described in connection with a particular aspect, embodiment or example of the disclosure are to be understood as being applicable to any other aspect, embodiment or example described herein, unless inconsistent therewith. All of the features disclosed in this specification (including the abstract and accompanying drawings), and/or all of the steps of a method or of a process thus disclosed, can be combined in any combination other than combinations wherein at least some of such features and/or steps are mutually exclusive. The disclosure is not limited to the details of all of the preceding aspects. The disclosure extends to any new feature or any new combination of features disclosed in this specification (including the abstract and accompanying drawings), or to any new feature, or any new combination, of the steps of any method or process thus disclosed.

LIST OF REFERENCE SIGNS

[0122] 1 screw pump assembly [0123] 10 motor [0124] 11 flexible coupling [0125] 12 first coupling feature [0126] 13 second coupling feature [0127] 2 screw pump [0128] 3 casing [0129] 30 inlet pipe [0130] 31 outlet pipe [0131] 32 flow chamber [0132] 32a annular step [0133] 32b annular step [0134] 33 shell [0135] 33a closed end of shell [0136] 33b open end of shell [0137] 34 insert [0138] 35 tubular insert wall [0139] 35a cylindrical center lobe of the tubular wall [0140] 35b cylindrical outer lobe of the tubular wall [0141] 35c cylindrical outer lobe of the tubular wall [0142] 36 anti-rotation tabs [0143] 37 anti-rotation tabs [0144] 38 circular flange [0145] 39a mounting disc [0146] 39b mounting disc [0147] 39c spacing interface [0148] 4 drive screw [0149] 40 drive screw center shaft [0150] 41 drive screw body [0151] 43 anchoring features [0152] 44 axial splines [0153] 45 motor coupling [0154] 5 driven screw [0155] 50 driven screw body [0156] 51 driven screw threads [0157] 52 release coupling [0158] 53 release coupling ring [0159] 54 release coupling notch [0160] 54a radial shoulder [0161] 55 hole [0162] 56 axial protrusion [0163] 6 driven screw [0164] 60 driven screw body [0165] 61 driven screw threads [0166] 62 release coupling [0167] 63 release coupling ring [0168] 64 release coupling notch [0169] 64a radial shoulder [0170] 65 hole [0171] 66 axial protrusion [0172] E space between insert and shell [0173] 101 screw pump assembly [0174] 110 motor [0175] 102 screw pump [0176] 103 casing [0177] 130 inlet pipe [0178] 131 outlet pipe [0179] 132 flow chamber [0180] 133 shell [0181] 133a closed end of shell [0182] 133b open end of shell [0183] 134 insert [0184] 135 tubular insert wall [0185] 135a cylindrical center lobe of the tubular wall [0186] 135b cylindrical outer lobe of the tubular wall [0187] 135c cylindrical outer lobe of the tubular wall [0188] 135d cylindrical outer lobe of the tubular wall [0189] 136 anti-rotation tabs [0190] 137 anti-rotation tabs [0191] 138 circular flange [0192] 104 drive screw [0193] 140 drive screw center shaft [0194] 141 drive screw body [0195] 145 motor coupling [0196] 105 driven screw [0197] 150 driven screw body [0198] 151 driven screw threads [0199] 156 axial protrusion [0200] 106 driven screw [0201] 160 driven screw body [0202] 161 driven screw threads [0203] 166 axial protrusion [0204] 107 driven screw [0205] 176 axial protrusion [0206] 204 drive screw [0207] 240 drive screw center shaft [0208] 241 drive screw body [0209] 245 motor coupling [0210] 205 driven screw [0211] 250 driven screw body [0212] 251 driven screw threads [0213] 256 axial protrusion [0214] 206 driven screw [0215] 260 driven screw body [0216] 261 driven screw threads [0217] 266 axial protrusion [0218] 207 driven screw [0219] 276 axial protrusion