A DEVICE COMPRISING A PLUNGER ASSEMBLY, A METHOD OF ASSEMBLING THE DEVICE AND A METHOD OF MAKING THE PLUNGER ASSEMBLY

Abstract

A device for dispensing a material, being provided with a plunger assembly which has a screw with a first thread portion and a second thread portion. The first and second thread portion differ in shape and, in combination, form one continuous screw thread. The plunger assembly further has a nut which engages the screw thread by a nut thread. The nut thread corresponds in shape to a negative shape of the first thread portion. The invention help minimizing efforts in the assembly of a device using the plunger assembly.

Claims

1. A device for dispensing a material, comprising a plunger assembly having a screw comprising a first thread portion and a second thread portion, the first and second thread portion differ in shape and, in combination, form one continuous screw thread, the plunger assembly further comprising a nut which engages the screw thread by a nut thread, wherein the nut thread corresponds in shape to a negative shape of the first thread portion.

2. The device of claim 1, wherein the difference in shape is based on a retention structure in the first thread portion which is absent in the second thread portion.

3. The device of claim 2, wherein the retention structure is a web which protrudes into the thread groove of the first thread portion.

4. The device of claim 2, wherein the retention structure is provided by a taper thread forming at least part of the first thread portion.

5. The device of claim 1, wherein the first and second thread portion are based on the same pitch and thread profile, the second thread portion being formed by an outer straight thread, and wherein the thread of the first thread portion and the thread of the second thread portion continue into one another.

6. The device of claim 1, wherein the screw has a seal adjacent the first thread portion and a handle adjacent the second thread portion, and wherein each of the seal and the handle are greater in outer diameter than the outer diameter of the screw thread.

7. The device of claim 1, wherein each of the screw and the nut are monolithically formed.

8. The device of claim 1, wherein the screw and the nut are molded from a plastic material and wherein the nut forms an overmold on the screw.

9. The device of claim 8, wherein the nut is made from glass-fiber reinforced material having a higher glass-fiber content per weight than the screw, wherein the screw preferably has a glass-fiber content per weight of zero.

10. The device of claim 1, further comprising a container having a front end with a dispensing opening and an opposite rear end with a rear opening, wherein the plunger assembly being attached with the nut in the container.

11. The device of claim 10, wherein the nut has an outer thread engaging with an inner thread of the container, wherein the container forms an inner chamber extending between the dispensing opening and the rear opening, inner chamber having a first chamber portion and a second chamber portion with the second chamber portion forming the inner container thread, and wherein a step is formed between the first and second chamber portion.

12. A method of assembling a device for dispensing material, comprising: providing the device of claim 1; turning the plunger assembly and/or the container relative to each other and thereby causing the nut and the container to screw into each other; upon the nut and the container being blocked from further rotation as the nut and the step contact each other, further turning the plunger assembly and/or the container relative other and thereby causing the screw and the nut to screw relative to each other.

13. A method of making a plunger assembly, comprising: molding a screw comprising a first thread portion and a second thread portion, the first and second thread portion differ in shape but form in combination one continuous screw thread; and overmolding the first thread portion and thereby forming a nut embracing the screw.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0049] FIG. 1 is a side view of a device according to an embodiment of the invention;

[0050] FIG. 2 is a perspective view of the device of FIG. 1 in use;

[0051] FIG. 3 is a perspective view of a device according to a further embodiment of the invention;

[0052] FIG. 4 is an exploded view of a device according to an embodiment of the invention;

[0053] FIG. 5 is a partial view of a plunger assembly according to an embodiment of the invention;

[0054] FIG. 6 is a partial view of a plunger assembly according to a further embodiment of the invention; and

[0055] FIG. 7 is a partial view of a plunger assembly according to still a further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0056] FIG. 1 shows an exemplary device 100 for dispensing a dental material as it may be used with the present invention. A similar device is disclosed in detail in WO 2014/179219 A1. The device 100 has a housing 101 which is formed of a cover 102 and a handle 103. The housing 101 houses a container in which the dental material is stored and within which a thrust screw or screw plunger (also referred to as screw herein) is accommodated for extruding the dental material from the container. Such a container and screw are described in further detail in FIGS. 4 ff. herein. For dispensing of the dental material the cover 102 has an opening 104 which can be selectively brought in alignment with an outlet for the dental material in the container by rotation of the cover 102 relative to the container. For closing the device 100 the cover 102 and the container can be rotated to misalign the opening 104 and the container outlet so that a wall of the cover 102 blocks the outlet. Accordingly, the cover 102 and the container of this example form a rotary slide valve in combination. In the example shown the opening 104 is closed. The handle 103 and the cover 102 are rotatably interconnected with each other so that dental material can be extruded from the device 100 by rotating the handle 103 and the cover 102 against each other. The device 100 is further adapted such that upon rotating the handle 103 and the cover 102 against each other the initially closed device 100 opens automatically. Therefore, the device 100 is adapted such that a rotation of the handle 103 and the cover 102 against each other first causes the closed device to automatically open, and a further rotation of the handle 103 and the cover 102 against each other causes dental material to be dispensed.

[0057] The device 100 is further adapted such that a rotation of the handle 103 and the cover 102 in the opposite direction causes the device 100 to close. Thereby any material extending through the valve is sheared off. In FIG. 2 the device 100 is shown in operation by a user.

[0058] FIG. 3 shows an alternative device 200 as it may be used with the present invention.

[0059] The device 200 has a screw plunger 210 which is received within a container 220. The container 220 stores a dental material which can be extruded through an opening 204 in the container 220. In the example the device 200 has a rotatable closure cap 202 for selectively opening or closing the device 200. The skilled person will recognize other devices which may be used with the present invention, like for example a screw syringe with a removable cap.

[0060] FIG. 4 illustrates the plunger assembly 10 for the device of the of the invention. The plunger assembly 10 has a screw 11 and a nut 12. The screw 11 has an outer thread 113 and the nut 12 has an inner thread (not visible in this view) engaging with the outer thread 113 of the screw 11. The screw 11 in particular has a first thread portion 111 and a second thread portion 112. The first and second thread portion 111, 112 differ in shape, as further to explained in detail in the following. In particular, the first thread portion 111 is formed by a taper thread which widens in a direction away from the second thread portion 112. In contrast, the second thread portion is formed by a straight thread. The first and second thread portion 111, 112 seamlessly transition into each other so that the first and second thread portion 111, 112 in combination form common outer thread 113. The pitch of the thread is constant over the first and second portion 111, 112. In the example the pitch is 1 mm. Therefore a full rotation of the screw 11 by 360 degrees relative to the nut 12 causes the screw 11 and the nut 12 to linearly displace by 1 mm. This results in a transmission providing for a relatively high force in the linear direction if rotated at an acceptable torque by hand.

[0061] The inner thread of the nut 12 corresponds in shape to a negative shape of the first thread portion. This can be achieved by manufacturing in the following manner: [0062] providing the screw 11 in a first step; and [0063] making the nut 12 by overmolding the first thread portion 111 of the screw 11 subsequently.

[0064] Thus, the inner thread of the nut 12 is replicated from the outer thread of the screw 11, in particular from the outer thread within the first thread portion. Although such method is preferred for the purpose of the present invention, the skilled person will recognize other methods of making a nut which has an inner thread which corresponds to the negative shape of the screw thread. For example, a nut made of two halves or multiple segments may be provided or a nut which is separately manufactured and screwed onto the screw.

[0065] Because the first thread portion 111 differs in shape from the second thread portion 112, the inner thread of the nut 12 replicated from the first thread portion 111 accordingly differs in shape from the negative shape of the second thread portion 112.

[0066] In the present example, however, the screw has a handle 114 and a rear end 116 and a seal 115 at a front end 117 of the screw 11. Each of the seal 115 and the handle 114 is enlarged in diameter with respect to the outer thread 113 of the screw. Because the screw 11 is monolithically formed with the seal 115 and the handle 114, screwing the nut 12 from outside on the screw 11 is not enabled.

[0067] The nut 12 further has an additional outer thread 123. The outer thread 123 is configured to form a screw connection with an inner thread 23 of the container 20. The container 20 forms an inner chamber 21 extending between a dispensing opening 22 and a rear opening 24 along a length L of the chamber 21. The inner container thread 23 extends only over a partial length L1 of the container length L. Over the remainder of the container length (L-L1) the chamber has an inward chamber surface 25 extending at a generally uniform cross-section, preferably at a circular cross-section. Further, the innermost diameter of the inner container thread 23 is equal or greater than the inner diameter of the chamber surface 25. Thus, the risk of any undesired deformation or damaging of the seal 115 during insertion of the front end 117 of the screw 11 into the container can be minimized.

[0068] FIG. 5 shows the nut 12 arranged on the first thread portion 111. In this example the first thread portion 111 has a retention structure 118 in the form of a web which protrudes into the thread groove of the first thread portion 111. The inner thread of the nut 12 replicates the retention structure 118 in the form of a corresponding negative retention structure 128, in the example a recess which accommodates the web. Accordingly, the web and the recess engage with each other and hinder the nut 12 and the screw 11 in a rotation relative to each other. A rotation of the nut 12 and the screw 11 relative to each other can however be achieved by urging the nut 12 and the screw 11 relative to each other at a torque which exceeds a certain threshold torque. Upon exceeding the threshold torque the screw 11 and/or the nut 12 typically deforms in the area of and adjacent the retention structure 118 and/or the negative retention structure 128. Thus, the retention provided by the retention structure 118 and negative retention structure 128 can be overcome. The threshold torque can be pre-determined by design of the retention structure 118, for example by the dimensions of the retention structure.

[0069] The negative retention structure 128 is arranged at or adjacent a front end 127 of the nut 12. Therefore, a rotation of the nut 12 and the screw 11 relative to each other in a direction which causes the nut 12 to axially move in a direction from the first thread portion 111 toward the second thread portion 112, a relatively small rotation angle provides for the nut 12 to axially move to a position in which the nut 12 is no longer in contact with the retention structure 118. This is advantageous because once the retention between the nut 12 and the screw 11 is overcome so that the nut 12 and the screw 11 rotate relative to each other, the retention structure 118 typically still causes a friction between the nut 12 and the screw 11 (and a corresponding torque required for the rotation) as long as the nut 12 is in contact with the retention structure.

[0070] The threshold torque required to break the screw 12 and the screw 11 lose for a rotation relative to each other can be used for assembling the nut 12 in the container 20 (FIG. 4). In particular, the nut 12 is preferably screwed with its outer thread 123 into the inner thread 23 of the container 20 by rotating the screw 11. Due to the retention between the nut 12 and the screw 11 the nut 12 is driven by the screw 11. Therefore, the nut 12 can be screwed into the container without the nut 12 and screw 11 moving relative to each other. However, once the nut 12 reaches the end of the inner thread 23 of the container any further rotation of the nut 12 relative to the container 20 is prevented. At this stage a further rotation of the screw in the same direction causes the threshold torque to be overcome and that threshold torque causes a tightening of the nut 12 within the container at a predetermined torque. Accordingly, for the assembly of the screw 11 and the nut 12 not additional torque control is required. Therefore, the assembly may be performed manually or automatically at the same quality.

[0071] FIG. 6 shows a further embodiment of the screw 11 and the nut 12. For ease of understanding the same reference numbers are used. In the example of FIG. 6 the first thread portion 111 is formed by (or comprises) a taper thread and the second thread portion 112 is formed by a straight thread. The lower diameter of the taper thread of the first thread portion 111 corresponds to the diameter of the straight thread of the second thread portion 112. Further, the lower diameter of the taper thread of the first thread portion 111 is arranged directly adjacent the second thread portion 112, and the taper thread widens in a direction from the second thread portion 112 toward the first thread portion 111.

[0072] The inner thread 124 of the nut 12 corresponds in shape to the outer shape of the first thread portion 111. In particular the inner thread 124 is a taper thread which corresponds to a negative of the taper thread of the first thread portion 111. Accordingly, a rotation of the nut 12 and the screw 11 relative to each other to axially move the nut 12 in a direction from the first portion 111 toward the second portion 112 causes the inner thread 124 to establish a lose fit with the outer thread 113 of the first thread portion 111. Therefore, the nut 12 and the screw 11 can be rotated relative to each other at a relatively low torque. A threshold torque required to break the nut 12 and the screw 11 lose from each other may be achieved due to an overmolding of the screw 11 by the nut 12. Typically during overmolding the nut 12 is initially formed by a ring-shaped melt of a plastic material. As the plastic material hardens and cools it typically shrinks onto the screw 11 so that the nut 12 finally forms a press fit on the first thread portion 111. In addition to the press fit a surface adhesion and/or a surface engagement may occur between contacting surfaces of the nut 12 and the screw 11. A surface engagement may be formed for example by a surface roughness present on the screw 11 which replicates as a negative shape of the nut 12, for example. Once the so formed threshold torque is overcome (during a rotation of the nut 12 and the screw 11 relative to each other to axially move the nut 12 in a direction from the first portion 111 toward the second portion 112) the torque to further rotate the nut 12 and the screw 11 rapidly reduces upon a rotation over only small incremental rotation angles because of the two taper threads move away from each other and form a lose fit with each other. Preferably the taper of the taper threads is such that the inner thread 124 at its greatest diameter still engages with the outer thread 113 of the second thread portion 112. Thus, the inner thread 124 of the nut 12 is sufficiently engaged with the outer thread 113 of the second thread portion 112 in a position in which the nut 12 is entirely positioned on only the second thread portion.

[0073] The taper thread may be used in combination with the retention structure described in the example of FIG. 5. In this embodiment any press fit, surface adhesion and/or surface engagement by overmolding is optional.

[0074] As described above, the threshold torque for breaking the nut 12 and the screw 11 lose from each other can be used for assembly of the nut 12 in the container 20 (FIG. 4).

[0075] FIG. 7 shows a further embodiment in which the outer thread 113 of the first portion 111 has a wider thread profile than the outer thread 113 of the second portion 112. Again, a threshold torque may be achieved identically as described in the example of FIG. 6 by overmolding so that the inner thread 124 of the nut 12 forms a tight fit or press fit with the outer thread 113 of the first thread portion 11. In this example, however, the torque required for rotation of the nut 12 and the screw 11 relative to each other only gradually reduces as the nut 12 axially moves toward the second thread portion 112. Only when the nut 12 is positioned entirely on only the second thread portion a full lose fit is formed between the inner thread 124 of the nut 12 and the outer thread 113 of the second thread portion. The example of FIGS. 5 and/or 6 may be combined with the present example as appropriate.