EP2198970A1 - Cartridge piston - Google Patents

Abstract

The piston (51) has a body including a drive side (54) transverse to a longitudinal axis and opposite a conveying side (53) of the body. A circumferential piston jacket (5) of the body connects the sides and merges into a projection (56) on the conveying side. An annular guide element (57) of the jacket is placed in a plane transverse to the axis and spaced a distance from conveying side. An annular scraper element (58) extends from the jacket. The element includes a surface in a plane transverse to axis and spaced another distance from the conveying side smaller than the former distance. An independent claim is also included for a discharge apparatus comprising a cartridge having a longitudinal axis.

Description

The invention relates to a piston for a cartridge, in particular for the discharge of solids containing fillings. The fillings may contain multicomponent mixtures.

Such a piston is for example from the DE 200 10 417 U1 known. The piston has a first piston part, which is provided with a sealing lip. The sealing lip abuts the cartridge wall.

Another prior art piston is in the EP1 165 400 B1 disclosed. This piston is made of a soft plastic, for example LDPE (low density polyethylene), in order to achieve the required sealing effect towards the cartridge wall. Such a piston can be only partially compatible with materials which form the filling of the cartridge. In order to avoid that the piston comes into contact with such materials along its delivery side, a cover plate is used, which consists of a plastic which is resistant to the filling. The cover plate covers a majority of the cross-sectional area on the delivery side, with the exception of the edge region, which is adjacent to the cartridge wall. The edge region is formed by a leg which extends outside the cover disk along the outer circumference of the piston in the direction of the delivery side. The leg is separated from the cover by a V-shaped groove. Although the leg is in contact with the filling in this embodiment, the remaining regions of the piston are shielded by the cover. For most fillings, contact with the piston material will result in swelling of the piston material, thus widening in the region of the leg. This has the advantage that the sealing effect is possibly enhanced. Alternatively, several sealing lips on Be arranged piston circumference, which for example made CH 610 994 is known.

However, these prior art pistons have proved unsuitable for the discharge of solids containing fillings. Solids may enter the gap between the end of the leg and the sealing lip and remain trapped in the gap. If the discharge process continues, the sealing lip sweeps over the solid particle grain lying on the cartridge wall. The contact of the sealing lip with the cartridge wall is lost, accordingly, the sealing effect is no longer present.

One solution to this problem is to provide a sealing lip located at the extreme end of the leg. However, such a sealing lip is not suitable for practical use because it is easily damaged when inserting the piston into the cartridge. This problem can be remedied by the piston itself is designed deformable, such as the piston of the CH 610 994 ,

However, the piston is the CH 610 994 only with an adapted to the geometry of the piston Ausdrückstössel usable when viscous or pasty media to be discharged with this piston from a cartridge. This means that this piston is not compatible with standard dispensers.

The object of the invention is to provide an improvement to said piston, so that solids containing material can be discharged with the piston, wherein the tightness of the piston is ensured. Furthermore, the piston should be displaceable by means of commercial dispensing devices in the cartridge.

This object is achieved by a piston which contains a stripping element which serves for stripping solid particles from the piston wall. The piston comprises a piston body, which is surrounded by a delivery side, an opposite drive side and the circumference of a piston skirt, wherein the piston skirt a connection formed between the delivery side and the drive side, wherein the piston skirt is disposed about a piston axis, wherein the piston skirt on the delivery side merges into a projection having a guide element for guiding the piston in a cartridge, which is used to make a sealing contact with a wall of the Cartridge is suitable. The projection comprises a stripping element, which has a smaller distance to the delivery side, than the guide element. The distance to the delivery side is determined in the direction of the piston axis. The delivery side is the surface of the piston which is in contact with the charge. The filling is located in a cartridge in which the piston is displaceable. The surface is usually part of a plane that is normal to the piston axis. The surface need not coincide with this plane, but may deviate therefrom, if the piston has a curvature, or recesses and projections for receiving stiffening elements, protective elements, venting elements and the like. To determine the relative distance between the conveying element and the stripping element, a reference surface is assumed which lies in a plane which is normal to the piston axis and which contains the point (s) of the piston which project furthest into the filling. In other words, if one were to place the piston with its delivery side on a flat surface and align it so that its piston axis is normal to this surface, this flat surface forms the reference surface.

According to this definition, the stripping element has a smaller distance to the reference surface than the guide element. As a result, solid particles are detected by the scraper and discharged from this or deflected in the direction of the piston axis when discharging the filling from the cartridge, so that the solid particles are completely discharged with the filling.

The scraper element has an edge which contains points of the scraper element farthest from the piston axis in the radial direction. The guide element has a distance from the piston axis in the radial direction, which is greater than the distance of the edge of the piston axis. This means that the guide element has a larger diameter has as the edge. The guide member contacts the wall of a cartridge when the piston is in the cartridge. The guide element may even have a diameter which is greater than the inner diameter of the cartridge, that is to say have an excess in relation to the inner diameter of the cartridge. By means of the guide element thus takes place the sealing of the filling containing the delivery-side piston chamber from the drive side.

The edge of the stripping element has a radial distance R1 from the piston axis and the guide element has a distance R2 from the piston axis, wherein the difference is at most 0.5 mm, preferably 0.3 mm, particularly preferably 0.2 mm. Because the wiping element thus has a smaller radial extent than the guide element, it is not damaged during assembly of the piston with the cartridge. Once the wiper element is inserted into the cartridge, the piston is centered by the wiper element and canting can be avoided. If the piston is moved further into the interior of the cartridge, the guide element comes into contact with the circumference of the wall of the cartridge. Since at most small inclinations of the piston are possible by the centering of the stripping, the force exerted by the wall on the guide element contact pressure will distribute evenly over the circumference of the guide element. As a result, damage to the guide element can be avoided. The guide element can thus exert its sealing function as soon as it is in contact with the wall of the cartridge.

The edge defines a bearing surface, which is arranged between 80 ° and 110 °, in particular substantially normal to the piston axis. Thus, a bearing surface of the scraper element adjoins the edge. This support surface receives during the discharge of the proportion of the compressive forces which are exerted by the filling on the piston when the filling is to be discharged from the cartridge. The forces acting on the bearing surface pressure forces have a resultant, which extends in the direction of the piston axis. If the support surface is arranged at an angle of 80 ° to 110 ° to the piston axis, the compressive forces cause the the projection belonging to the stripping element is deformed in such a way that the edge of the stripping element comes into contact with the wall of the cartridge.

In the known from the prior art projections, as for example in the EP 1 165 400 B1 are shown, the projection has an inclined surface instead of an edge. The inclination thereof is designed such that the distance between the projection and the cartridge wall increases in the direction of the delivery side. This inclined surface has the advantage that the piston can be better inserted into the cartridge. In particular, if the projection has a diameter which is larger than the inner diameter of the associated cartridge, the piston can be easily positioned in the bore of the cartridge. At the beginning of the assembly process of the piston in the cartridge, the end of the projection is in contact with the cartridge wall. The farther the piston is inserted into the bore, the farther the line of contact between the projection and the cartridge wall moves away from the end of the projection. At the same time the projection receives an ever greater bias. The diameter of the projection increases more and more along the inclined surface. However, since the inner diameter of the cartridge wall is predetermined, the projection is deformed such that it can engage in the interior of the cartridge. It also follows that the projection is pressed with an increasing contact pressure against the wall, the further the assembly process progresses. This has the result that in the end position, when the piston is pushed so far into the interior of the cartridge that the sealing lip comes to rest on the inner wall, the end of the projection comes to lie at a distance from the cartridge wall. The inclined surface remains. When the piston is displaced to discharge the filling with a discharge device, that is, for example, a plunger, the internal pressure of the filling exerts a force on the inclined surface in the direction of the piston axis. This force can be decomposed into a force component directed normal to the inclined surface and into a force component directed in the direction of the inclined surface. From the force diagram it follows that the force normal to the inclined surface seeks to move the projection away from the cartridge wall.

When a solid particle gets between the inclined surface and the cartridge wall, the solid particle supports this tendency. The solid particle is trapped on the one hand by the pressure of the filling more and more in the gap between the inclined surface and the cartridge wall. Since the piston and the sealing lip made of soft material, the piston material gives way and the solid particles can pass through the sealing lip. As a result, the contact between the sealing lip and the cartridge wall is interrupted, thus the solid particles and further filling material can escape. This leakage is a problem that often occurs in the prior art solutions, particularly in processing fillers containing solid particles.

Advantageously, the support surface on a portion which encloses an angle of up to 80 °, preferably up to 60 °, more preferably up to 45 ° to the support surface. The angle can be determined as follows. By the piston axis facing edge of the support surface is a plane normal to the piston axis. This normal plane is cut with a plane extending in the direction of the piston axis, which contains the edge, so that there is a line of intersection. The angle is spanned between the line of intersection and the line of intersection of the section with the plane extending in the direction of the piston axis.

The section is located on the side of the projection which is aligned with the piston axis, ie on the inside of the projection. On the section also acts a compressive force, which is due to the filling. This force may in turn be broken down into two force components, a normal component which is normal to the portion and a component which extends in the direction of the portion. Due to the normal component, the section and thus the projection including the edge is pressed against the cartridge wall. Thus, the way for the solid particles is blocked, it can therefore be avoided that solid particles come to rest between the cartridge wall and projection. It follows that by means of the projection, a redirection of any solid particles in the piston interior takes place.

The same advantage results for an annular piston. Such an annular piston additionally comprises an inner piston skirt, wherein the inner piston skirt defines the piston body on an inner side facing the piston axis, comprising an inner projection comprising an inner guide element for guiding the piston along the piston axis, wherein the inner guide element for producing a sealing Contact with a wall of the inner tube is suitable. The inner projection comprises an inner stripping element, which has a smaller distance to the delivery side than the inner guide element.

The inner wiper element has an inner edge, the inner edge containing the points of the inner wiper element that are least distant from the piston axis in the radial direction.

The inner guide member has a distance from the piston axis in the radial direction, which is less than or equal to the distance of the inner edge of the piston axis.

The inner edge has a radial distance R3 from the piston axis and the guide element has a radial distance R4 from the piston axis, the difference between R3 and R4 being at most 0.5 mm, preferably 0.3 mm, particularly preferably 0.2 mm.

The piston can be configured such that a protective element is attached to the piston body on the delivery side. Such a protective element may be made of a material having a higher resistance to filling than the piston material. Thus, the protective element can develop a protective function for the piston material.

The piston body or the protective element may include a venting element. This venting element, serves to remove gases from gas inclusions, which arise for example when inserting the piston into the cartridge wall, from the piston interior. In particular, the gas may be air.

On the drive side of the piston stiffening ribs may be arranged. The provision of stiffening ribs ensures that the piston remains dimensionally stable, even when the discharge of the filling of the piston is placed under pressure by means of a discharge device.

On the drive side of the piston, a Kippsicherungselement may be arranged, which serves to improve the guidance of the piston in a cartridge. The piston is guided non-tilting by the anti-tip element, which is in contact with the wall of the cartridge, that is, the axis of the piston body coincides with the piston axis. By the anti-tip element is ensured that the delivery side is arranged in a plane normal to the piston axis, or if the delivery side is not flat, that points of the delivery side piston surface, which are characterized by a certain radius and a certain height, along the circumference in substantially the same Normal level lie. If the piston tilted, the condition for such points would not be met. Through such a tilt protection element, a peripheral contact with the wall of the cartridge can be maintained during the entire discharge process, so that a deflection of the piston can be prevented together with the guide element described earlier.

The advantages of the particular features which the ring piston may have correspond to the advantages as mentioned in connection with a piston for a cylindrical interior or an interior of another geometric shape without internals in the earlier place.

A discharge device comprises a piston according to one of the preceding embodiments. The discharge device comprises a cartridge for discharging a plurality of components, wherein the components are arranged in juxtaposed or coaxial cavities of the cartridge. Furthermore, the discharge device may comprise a discharge device, by means of which the piston is connectable on the drive side.

Particularly advantageous is the piston according to one of the preceding embodiments use for the discharge of solids-containing fillings, as well as pasty or viscous masses.

Fig. 1

einen Kolben gemäss des Standes der Technik

Fig. 2

einen Ausschnitt aus Fig. 1

Fig. 3

eine Darstellung des Beginns des Austrags einer feststoffhaltigen Füllung mit einem Kolben gemäss Fig. 1 nach dem Stand der Technik

Fig. 4

eine Darstellung des Austrags einer feststoffhaltigen Füllung mit einem Kolben gemäss Fig. 1 nach dem Stand der Technik

Fig. 5

einen Kolben gemäss eines ersten Ausführungsbeispiels der Erfindung

Fig. 6

ein Detail der Fig. 5

Fig. 7

eine Darstellung des Beginns des Austrags einer feststoffhaltigen Füllung mit einem Kolben gemäss Fig. 5

Fig. 8

eine Darstellung des Austrags einer feststoffhaltigen Füllung mit einem Kolben gemäss Fig. 5

Fig. 9

einen Ringkolben gemäss eines weiteren Ausführungsbeispiels der Erfindung.

The invention will be explained with reference to the drawings. Show it:

Fig. 1

a piston according to the prior art

Fig. 2

a section from Fig. 1

Fig. 3

a representation of the beginning of the discharge of a solids-containing filling with a piston according to Fig. 1 According to the state of the art

Fig. 4

a representation of the discharge of a solids-containing filling with a piston according to Fig. 1 According to the state of the art

Fig. 5

a piston according to a first embodiment of the invention

Fig. 6

a detail of Fig. 5

Fig. 7

a representation of the beginning of the discharge of a solids-containing filling with a piston according to Fig. 5

Fig. 8

a representation of the discharge of a solids-containing filling with a piston according to Fig. 5

Fig. 9

an annular piston according to another embodiment of the invention.

Fig. 1 shows a piston, as it is known from the prior art. The piston 101 comprises a piston body 102, which is usually made of plastic by means of an injection molding process. The piston 101 is preferably used to fill in particular of fluid or pasty media out of a cartridge. A wall 116 of the cartridge 117 is shown. The piston 101 slides along the wall 116 and during this movement pushes the filling out through a discharge opening (not shown). The media-side side of the piston 101 will be referred to below as the delivery side 103. In order to set the piston in motion and to keep moving a compressive force is applied by means of a discharge device. The discharge device, of which a plunger element 118 is shown, is located on the side of the piston, which lies opposite the delivery side 103. This page is referred to below as the drive side 104.

The piston body 102 is thus limited by the drive side 104, the delivery side 103 and a piston skirt 105. The piston skirt 105 forms the connection between the drive side 104 and delivery side 103. In most cases, the piston body has a plurality of recesses or is constructed as a hollow body. Already for reasons of material savings and because of the difficulties that the injection molding of thick-walled components entails, such pistons are already made from diameters of a few centimeters as thin-walled components. The required dimensional stability of the piston is obtained by stiffening ribs 115. In addition, the piston can contain a protective element 113. A protective element 113 may be formed as a cover, the function of which is to shield the piston body from the filling. A cover is used when the filler tends to attack the piston material. This is especially true for soft plastic pistons such as LDPE. For example, LDPE is attacked by polyester resins and swells up.

The piston may also contain a venting element. Such a venting element 114 is in Fig. 1 shown. By means of this venting element, gas which is located in the interior of the cartridge 117 between the filling and the piston 101 can escape outwards, that is to say escape to the drive side 104, without the filling emerging. The venting element 114 is closed as long as the cartridge is stored in the filled state. If the filling is to be discharged, the discharge device 118 is brought into contact with the piston on its drive side 104. Here comes that Dispensing device with a pin 119 of the venting element 114 in contact. The pin protrudes beyond the surface which comes in contact with the discharge device on the drive side, so that the pin lifts off its seat 120 when the discharge device 118 comes into contact with the drive side 104. In this case, a flow path for the gas is opened. The gas enters the space between the valve body 122 and the piston body 102 via the flanks 121 of the valve body 122 in the form of a cover disk and leaves the piston via the opened flow path through the opening between the pin 119 and the seat 120.

The flanks 121 are engaged via latching connections with the piston body 102. For this purpose, the flank 121 engages, for example, in a circumferential groove 123 of the piston body 102 on the delivery side 103. In Fig. 2 this is shown in detail. The flank can also have a sealing lip 124, which engages in a recess 125 of a projection 106 of the piston 101. For the gas usually several small recesses are provided in the flank. Subsequent to these recesses, a labyrinthine connection path between the piston body 102 and the cover plate 113 may be provided. Any filling material passing through the recesses is deposited along this labyrinthine communication path. This connection is not shown in detail.

The piston 101 must otherwise have means against the discharge of charge to the drive side. For this purpose, at least one sealing lip is usually provided along the sliding surface on the wall of the cartridge. In the present embodiment, this sealing lip is shown as a guide member 107, see in particular also Fig. 2 , The guide member 107 is located on a projection 106 which extends between the groove 123 and the wall of the cartridge. The protrusion 106 is formed as an arm communicating with the piston body 102. What is not visible in the sectional view is the fact that the arm belongs to an annular bead which extends along the entire circumference of the piston body 102 and forms a fluid-tight connection with the wall 116 of the cartridge 117.

Fig. 2 is a section of Fig. 1 , which in particular the projection 106 shows enlarged. The projection comprises a guide element 107, which is intended to rest on the wall 116 of the cartridge 117. In the direction of the delivery side 103, an edge 110 adjoins the guide element and a support surface 111. A further edge or a section 112 can adjoin the support surface, which protrudes into the filling. The support surface is inclined with respect to the wall of the cartridge, in such a way that the distance of the support surface from the wall increases with increasing distance from the guide element. The edge 110 is the end of the support surface that is the smallest distance from the wall of the cartridge, the portion 112 includes the opposite end of the support surface, which has the greatest distance from the wall of the cartridge. The inclination of the support surface is chosen for the reason that the piston can be easily inserted into the interior of the cartridge. The piston must not tilt during insertion into the cartridge and should not tilt, as in this case the sealing lip may be damaged. For this reason, the support surface 111 is tilted to keep the piston in the correct position relative to the wall 116 of the cartridge. In the correct position, the piston axis 109 is parallel to the wall 116 of the cartridge.

Fig. 3 shows a representation of the beginning of the discharge of a solids-containing filling with a piston according to Fig. 1 according to the prior art and Fig. 4 a representation of what the discharge may look like at a later date. In Figure 3 the projection 106 is already inserted into the interior of the cartridge. The piston rests with the guide element 107 on the wall 116 of the cartridge. The filling 124 is located on the delivery side 103 of the piston. Only a portion of the piston 101 is shown to better discern the details. The projection is the same as in Fig. 1 or Fig. 2 described. Now, if the piston body 102 is moved by a discharge device, not shown, in the direction of the piston axis 109 against the filling, a pressure force from the filling acts on the piston. This pressure force also acts on the projection and in particular on the bearing surface 111. The resultant of the pressure force, which is represented by an arrow 125, counteracts the discharge direction. The resultant of the compressive force can be translated as vectorial greetings into a tangential component 126 and a normal component 127 are decomposed. The normal component of the force can cause deformation by bending the projection 106. From the Fig. 3 it follows immediately that the projection 106 tends to be moved away from the wall of the cartridge by the normal component 127.

The position of the projection in advanced discharge is in Fig. 4 shown. Due to the internal pressure so the gap between support surface 111 and wall 116 is possibly greater. If the filling now contains solids that are in 3 or 4 As particles 128 are shown, individual particles can enter the gap between the bearing surface and the wall. As the discharge progresses, the particles will continue to penetrate the gap. In particular, if the particles have a greater hardness than the plastic of the piston, the particles damage the plastic, in particular the sealing lip or are bypassed by the plastic, that is, the sealing lip bulges, thus losing contact with the wall and the particle can - together With filling material from the interior of the cartridge leak, as in Fig. 4 shown.

Fig. 5 shows a first embodiment of a piston according to the invention. The piston 1 comprises a piston body 2, a delivery side 3, a drive side 4, and a piston skirt 5. The delivery side 3 is the boundary of the piston to the filling, the drive side 4, the boundary in the direction of the discharge. The piston skirt connects delivery side 3 and drive side 4 and represents the boundary to the wall 16 of the cartridge 17.

The function of the protective element 13, a venting element 14 and the stiffening ribs 15 does not differ from the prior art, therefore, with respect to these elements, reference is made to the description of the prior art.

The piston 1, the piston body 2, which is surrounded by a delivery side 3, an opposite drive side 4 and the circumference of the piston skirt 5, is preferably a plastic component, which has been advantageously produced by injection molding. The piston skirt 5 forms a connection between the delivery side 3 and the Drive side 4, wherein the piston skirt 5 is arranged around a piston axis 9. In particular, the piston skirt is rotationally symmetrical when the piston is intended to be received in a cylindrical cartridge. The piston skirt 5 merges into a projection 6 on the delivery side 3. The projection 6 is a thin-walled rotationally symmetrical body in the embodiment, which is visible in the sectional view as an arm of the piston body 2. The projection 6 has a guide element 7 for guiding the piston in a cartridge 17, which is suitable for producing a sealing contact with a wall 16 of the cartridge 17. The guide element may be formed in particular as a sealing lip. If necessary, a plurality of sealing lips may be provided. The projection 6 comprises a stripping element 8, which has a smaller distance to the delivery side 3 than the guide element 7. To determine the distance, the dimension of the piston is determined which is closest to the filling or even extends into the filling. This dimension may be the piston surface in simple pistons, or the protective element 13 covering the piston surface, for example a cover plate.

On the drive side 4 of the piston, a Kippsicherungselement 18 may be arranged, which serves to improve the guidance of the piston in a cartridge. The piston is guided by the anti-tip element 18, which is in contact with the wall 16 of the cartridge 17, non-tilting, that is, the axis of the piston body 2 coincides with the piston axis 9. By the anti-tip element 18 ensures that the delivery side 3 is arranged in a plane normal to the piston axis 9, or if the delivery side 3 is not a flat surface or contains portions that are not in a plane that points the delivery-side piston surface by a certain Radius and a certain height are located along the circumference in substantially the same normal plane. If the piston 1 tilted, the condition for such points would no longer be satisfied. Through such a tilt protection element 18, therefore, a circumferential contact with the wall 16 of the cartridge can be maintained throughout the discharge process, so that a deflection of the piston can be prevented together with the guide element 7 described earlier.

According to Fig. 5 it is the delivery end of the piston skirt 5, which is formed as a projection 6. By the end of the piston skirt or possibly another point that meets the above criterion, a normal plane to the piston axis 9 is placed. The normal distance between this normal plane to the stripping element 8 is compared with the normal distance between the guide element 7 and this normal plane. In particular, the point of the guide element 7 is selected, on which the guide element 7, the wall 16 of the cartridge 17 touches. Due to the rotational symmetry of the piston, this point is representative of all points of contact of the guide element 7 with the wall 16. The distance between the point of contact of the guide element and the conveying side characterizing plane is therefore greater than the distance of any point of the stripping element 8 to the aforementioned plane ,

The filling therefore "sees" during the discharge only the stripping element 8, which rests against the wall 16 as soon as a pressure force is exerted on the piston. In the direction of the filling on the piston, the stripping element 8 is thus in front of the guide element 7. This feature already has the advantage that the filling is guided during discharge along the support surface 11 in the direction of the piston axis. Due to the proximity of the stripping element to the wall, solid particles contained in the filling can not pass through the stripping element 8. In particular, the stripping element 8 has an edge 10. The edge 10 contains the points of the stripping element 8 farthest from the piston axis 9 in the radial direction. The term proximity to the wall is understood to mean the contact of the edge 10 of the stripping element with the wall or a small distance from the wall, the distance being smaller is the average expected particle diameter.

The guide element 7 has a distance from the piston axis 9 in the radial direction, which is greater than or equal to the distance of the edge 10 from the piston axis 9. The guide element rests against the wall of the cartridge and seals the interior of the cartridge containing the filling against the environment, so that leakage of the filling onto the drive side is prevented. The edge 10 has a radial distance R1 from the Piston axis and the guide member 7 has a radial distance R2 of the piston axis, wherein the difference between R1 and R2 is at most 0.5 mm, preferably 0.3 mm, particularly preferably 0.2 mm. This distance corresponds to the distance of the edge 10 from the wall 16 of the cartridge, as long as no pressure force has been applied to the piston, that is, in a state in which the discharge has not yet begun.

The edge 10 defines a support surface 11, which is arranged between 80 ° and 110 °, in particular substantially normal to the piston axis 9. The bearing surface is thus arranged such that any solid particles detected by means of the scraping element 8 are discharged together with the filling. If the support surface is arranged substantially normal to the piston axis, the solid particles can migrate in the direction of the piston axis. An accumulation of solid particles in the near wall region can thus be prevented.

Particularly advantageous has been found when the support surface 11 has a portion 12 which encloses an angle 19 of up to 80 °, preferably up to 60 °, more preferably up to 45 ° to the support surface. The angle 19 can be determined as follows. By the piston axis 9 facing edge 30 of the support surface 12 a plane normal to the piston axis 9 is placed. This normal plane is cut with a plane extending in the direction of the piston axis, which contains the edge 30, so that there is a line of intersection. The angle 19 is spanned between the cutting line and the section line of the section 11 with the plane extending in the direction of the piston axis. The slope of the section is towards the drive side, that is, each point of the section 11 remote from the edge 30 is closer to the drive side than the point at which the edge 30 intersects the cutting plane of the drawing. The inclination of the section 12 thus takes place in the direction of the drive side.

Fig. 6 shows a section of the piston, the Fig. 5 in which the details concerning the projection 6 can be seen even better. From the piston body 2 projects an arm in the direction of the wall 16 of the cartridge 17, which the Projection 6 forms. On the function of the parts which have the same reference numerals as in Fig. 5 should not be further discussed, since they are not from Fig. 5 different. In addition to the illustration according to Fig. 5 an additional sealing lip 31 was provided. This further sealing lip 31 is particularly advantageous when the piston has a tendency to assume an inclination with respect to the piston axis. By providing a further sealing lip or a plurality of sealing lips, possible leaks resulting from this inclination can be prevented. The attachment of a further sealing lip also has the advantage that, even if the guide element 7 or the first sealing lip attached thereto is damaged, there is still another sealing lip, so that it is ensured that the filling can not escape onto the drive side 4 with certainty.

Furthermore, in Fig. 6 a stripping element 8 is shown, which has a small distance from the wall 16 of the cartridge 17. This stripping element 8 comprises a support surface 11, which extends almost over the entire width of the projection 6. The support surface 11 extends in the sectional view from the edge 10 to the edge 30. For a rotationally symmetrical piston is that this support surface 11 is annular. To the support surface 11 of the section 12 connects. This section 12 includes with the plane passing through the edge 30 normal plane on the piston axis a large angle, which is between 60 and 90 °.

The choice of the inclination of the section can influence how strongly the wiper element 8 is pressed against the wall 16 during dispensing.

FIGS. 7 and 8 show two different positions of the piston 1, in Fig. 7 is a rest position shown. This rest position takes the piston before the start of the discharge and it corresponds to the position in which the filled cartridge can be transported and stored.

Fig. 8 shows a position at a time during which emptying, so a discharge of the filling takes place from the cartridge.

To illustrate the forces acting on the piston and thus also on the stripping element 8 during the discharge, the forces on the support surface 11 and the section 12 are drawn. On the support surface 11, which is aligned substantially normal to the piston axis 9, a compressive force acts 32. The compressive force generates a compressive stress in the interior of the projection 6. In addition, a bending moment can be introduced into the projection when the pressing force 32 does not act on the support point , but this is offset. As a support point here the point of the shoulder 34 is defined, which corresponds to the center of gravity of a plane passing through the shoulder cutting plane. The cutting plane is laid so that it divides the shoulder into two substantially equal parts, measured at the smallest cross-section.

Since a soft, compliant plastic is preferably used as the piston material, the projection deforms under the effect of the compressive force in such a way that a compression and a bend occur around the support point. As a result of the attacking bending moment, depending on the wall thickness of the projection 6, deformation of the projection and of the stripping element is either already caused or the tendency for deformation is intensified.

In addition, a compressive force engages along the section 12. As already related to FIG. 3 and FIG. 4 As shown, this compressive force can be decomposed into a tangential component 35 and a normal component 36. The normal component 36 can in turn be decomposed into a radial component pointing in the direction of the wall 16 and into an axial component which is arranged parallel to the piston axis 9. It follows that the stripping element is displaced by this radial component against the wall 16 until the edge 10 comes into contact with the wall.

Fig. 9 shows an annular piston 51, as used for example for coaxial cartridges are used. In a coaxial cartridge two or more coaxially arranged cylindrical cavities are arranged. Each of these cavities is filled with a component. The one or more internal cavities are completely surrounded by the outer cavity, which is formed as a cylindrical cartridge.

The annular piston 51 comprises a piston body 52, which is usually made of plastic by means of an injection molding process. The annular piston 51 is preferably used to discharge a filling in particular of fluid or pasty media from a cartridge. The filling may in particular also contain solid particles. A wall 16 of the cartridge 17 is shown. The annular piston 51 slides along the wall 16 and pushes in this movement, the filling through a discharge opening, not shown. The media-side side of the piston 51 will be referred to below as the delivery side 53. In order to set the piston in motion and to keep moving a compressive force is applied by means of a discharge device. The dispenser, which is not shown here, is located on the side of the piston, which is the delivery side 53 opposite. This page is referred to below as the drive side 54.

The piston body 52 is thus bounded by the drive side 54, the delivery side 53 and an outer piston skirt 5 and an inner piston skirt 55. The outer piston skirt 5 may have the same structure as under Fig. 5 to Fig. 8 described. The inner piston skirt 55 forms the inner connection between the drive side 54 and the delivery side 53. The inner piston skirt 55 delimits the piston body 52 on an inner side 59 facing the piston axis 9.

The inner piston skirt 55 merges into a projection 56 on the delivery side 53. The projection 56 is in the embodiment, a thin-walled rotationally symmetrical body, which is visible in the sectional view as an arm of the piston body 52. The projection 56 has an inner guide element 57 for guiding the piston along, ie in the direction of the piston axis 9, for example along an inner tube 67. The guide member 57 is suitable for making a sealing contact with a wall 66 of the inner tube 67. The guide member 57 may be formed in particular as a sealing lip. If necessary, a plurality of sealing lips may be provided. The projection 56 comprises a stripping element 58, which has a smaller distance to the delivery side 53 than the guide element 57. To determine the distance, the dimension of the piston is determined which is closest to the filling or even reaches into the filling. This dimension can be simple Piston be the piston surface, or the piston surface covering protective element 63, for example, a cover. By the conveyor-side surface of the protective element 63 is placed a normal plane to the piston axis. The normal distance between this normal plane to the stripping element 58 is compared with the normal distance between the guide element 57 and the normal plane. In particular, the point of the guide element 57 is selected, on which the guide element 57 contacts the wall 66 of the inner tube 57. Due to the rotational symmetry of the piston, this point is representative of all points of contact of the guide member 57 with the wall 66. The distance between the point of contact of the guide member 57 and the conveying side characterizing plane is therefore greater than the distance of any point of the stripping member 58 to the aforementioned Level. The filling therefore "sees" during discharge only the stripping element 58, which rests against the wall 66 as soon as a pressure force is exerted on the piston. In the direction of the filling on the piston, the stripping element 58 thus lies in front of the guide element 57. By this feature, there is already the advantage that the filling is guided during discharge along the support surface 61 in the direction of the piston axis. Due to the proximity of the stripping element 58 to the wall 66, solid particles contained in the filling can not pass the stripping element 58. In particular, the stripping element 58 has an edge 60. The edge 60 includes the closest of the piston axis 9 in the radial direction points of the stripping element 58. The term proximity to the wall is the abutment of the edge 60 of the stripping element 58 on the wall or a small distance thereof to the wall understood, the distance smaller than average expected particle diameter is.

The guide element 57 has a distance from the piston axis 9 in the radial direction, which is less than or equal to the distance of the edge 60 from the piston axis 9. The guide member 57 abuts against the wall 66 of the inner tube and seals the interior of the cartridge, which contains the filling, against the environment, so that leakage of the filling is prevented on the drive side. The edge 60 has a radial distance R3 from the piston axis 9 and the inner guide member 57 a radial distance R4 from the piston axis, wherein the difference of R3 and R4 is at most 0.5 mm, preferably 0.3 mm, particularly preferably 0.2 mm. This radial distance corresponds to the distance of the edge 60 of the wall 66 of the inner tube, as long as no pressure force has been applied to the piston, that is, in a state in which the discharge has not yet begun.

The edge 60 defines a support surface 61, which is arranged between 80 ° and 110 °, in particular substantially normal to the piston axis 9. The bearing surface is thus arranged such that any solid particles captured by the wiping element 58 are discharged together with the filling. If the support surface is arranged substantially normal to the piston axis, the solid particles can migrate in the direction of the piston axis. An accumulation of solid particles in the near wall region can thus be prevented.

To be particularly advantageous has been found when the support surface 61 has a portion 62 which includes an angle 69 of up to 80 °, preferably up to 60 °, more preferably up to 45 ° to the support surface 61. The angle 69 is measured from the bearing surface 61 or the normal plane to the piston axis, which contains the edge which forms between bearing surface 61 and section 62. The slope of the section is in the drive-side direction, that is, each point of the section 61 remote from the edge 80 is closer to the drive side 54 than the point at which the edge 80 intersects the cutting plane of the drawing. The inclination of the section 62 thus takes place in the direction of the drive side 54.

The annular piston may also contain a venting element, which is not shown here in the drawing. The piston body may also have stiffening ribs 65 or a tilt protection element (18, 64).

Claims (15)

Piston (1, 51) comprising a piston body (2, 52) surrounded by a delivery side (3, 53), an opposite drive side (4, 54) and the periphery of a piston skirt (5, 55), wherein the piston skirt (5, 55) forms a connection between the delivery side (3, 53) and the drive side (4, 54), wherein the piston skirt (5, 55) is arranged around a piston axis (9), the piston shell (5, 55) on the delivery side (3, 53) merges into a projection (6) having a guide element (7) for guiding the piston in a cartridge suitable for making a sealing contact with a wall of the cartridge, characterized in that Projection (6) comprises a stripping element (8), which has a smaller distance from the delivery side (3) than the guide element (7). Piston according to claim 1, wherein the wiping element (8) has an edge (10), wherein the edge (10) contains the points of the wiping element (8) farthest from the piston axis (9) in the radial direction. Piston according to claim 2, wherein the guide element (7) has a distance from the piston axis (9) in the radial direction, which is greater than the distance of the edge (10) from the piston axis (9). Piston according to claim 3, wherein the edge (10) has a radial distance R1 from the piston axis and the guide element (7) has a radial distance R2 from the piston axis, wherein the difference between R1 and R2 at most 0.5 mm, preferably 0.3 mm, particularly preferably 0.2 mm. Piston according to one of claims 2 to 4, wherein the edge (10) defines a bearing surface (11) which is arranged between 80 ° and 110 °, in particular substantially normal to the piston axis (9). Piston according to claim 5, wherein the support surface (11) has a portion (12) which encloses an angle (19) of up to 80 °, preferably up to 60 °, more preferably up to 45 ° to the support surface (11). Piston (51) according to one of the preceding claims, comprising an inner piston skirt (55), wherein the inner piston skirt (55) delimits the piston body (52) on an inner side (59) facing the piston axis (9), comprising an inner projection (56 ), which comprises an inner guide element (57) for guiding the piston along the piston axis (9), wherein the inner guide element (57) is suitable for making a sealing contact with a wall of an inner tube, characterized in that the inner projection (56 ) comprises an inner scraper element (58), which has a smaller distance to the delivery side than the inner guide element (57). The piston of claim 7, wherein the inner wiper member (58) includes an inner edge (60), the inner edge (60) including the least radially spaced points of the inner wiper member (58) from the piston axis (9). Piston according to claim 8, wherein the inner guide element (57) has a distance from the piston axis (9) in the radial direction, which is less than or equal to the distance of the inner edge (60) from the piston axis. A piston according to claim 9, wherein the inner edge (60) has a radial distance R3 from the piston axis (9) and the inner guide element (57) has a radial distance R4 from the piston axis (9), the difference between R3 and R4 being at most 0.5 mm , preferably 0.3 mm, more preferably 0.2 mm. Piston according to one of the preceding claims, wherein on the delivery side (3, 53) a protective element (13, 63) is mounted. Piston according to one of the preceding claims, wherein the piston contains a venting element (14). Piston according to one of the preceding claims, wherein on the drive side (4, 54) stiffening ribs (15, 65) are arranged and / or a Kippsicherungselement (18, 64) is arranged. Discharge device comprising a piston according to one of the preceding claims. Discharge apparatus according to claim 14, comprising a cartridge (17) for discharging a plurality of components, wherein the components are arranged in juxtaposed or coaxially arranged cavities of the cartridge.

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