MISCHKOPF

Description

[0001] The invention relates to a mixing head for processing reactive plastic components into a plastic mixture, in particular for processing a polyol material and an isocyanate material into a polyurethane material.

[0002] Document DE19515039A1 discloses a mixing head with a cylindrical mixing chamber, a control piston, and injection nozzles through which the plastic components can be introduced into the mixing chamber. The plastic mixture can be discharged from the mixing chamber via a discharge pipe connected to the mixing chamber. Furthermore, a cleaning piston is provided, which can be moved within the discharge pipe. The cleaning piston can be moved by means of a hydraulic fluid between two end positions defined by mechanical stops: a rear end position in which the mixing chamber is fluidically connected to the discharge pipe, and a front end position in which the front surface of the cleaning piston lies in the same plane as the front surface of the discharge pipe.The front surface of the cleaning piston and the front surface of the outlet tube must be cleaned periodically of adhering plastic mixture, especially adhering polyurethane. Documents CN112045880 A, US3189325 A, and EP1449592 A2 also disclose mixing heads with a front and rear end position for the cleaning piston.

[0003] For certain applications, a mixing head may be required in which the cleaning piston can be extended, at least partially, from the discharge tube. This might be the case, for example, when a plastic mixture is dispensed into a mold and a hole subsequently needs to be created in the dispensed plastic mixture, such as for screwing a screw into the plastic material. With such a mixing head, cleaning the discharge tube and cleaning piston is relatively complex. To thoroughly clean all surfaces, intricate arrangements of brushes are necessary to remove all adhering plastic mixture, such as polyurethane.

[0004] Based on this, the invention aims to provide a mixing head in which the cleaning piston can be extended at least section by section from the outlet pipe, whereby the removal of adhering plastic mixture on the cleaning piston and outlet pipe can be carried out with minimal effort.

[0005] This problem is solved by a mixing head having the features of claim 1.

[0006] By allowing the cleaning piston to be extended at least partially from the outlet tube and simultaneously moved into an intermediate position where the front surface at the end of the cleaning piston lies in the same plane as the front surface of the outlet tube, the desired cleaning effect can be achieved by extending the piston, while simultaneously simplifying the cleaning of both the piston and the outlet tube. This intermediate position is defined by a mechanical stop, which holds the front surfaces of the cleaning piston and outlet tube axially fixed in a common plane. Simply passing a brush or scraper over this plane is sufficient to clean both front surfaces.

[0007] According to an advantageous embodiment, the cleaning piston can be moved between two end positions: a rear end position in which the cleaning piston releases the mixing chamber towards the outlet pipe, and a front end position in which the cleaning piston has been extended at least partially out of the outlet pipe. The intermediate position for cleaning the front surfaces of the cleaning piston and the outlet pipe is located between these two end positions.

[0008] Preferably, the two end positions are each defined by a mechanical stop.

[0009] According to an advantageous embodiment, the cleaning piston can be in operative connection with a drive piston movable in a cylinder, wherein the drive piston can be moved between the two end positions by means of the hydraulic fluid in the cylinder, and wherein a mechanical stop for approaching the intermediate position is provided in the cylinder.

[0010] In particular, a hydraulically movable auxiliary piston can be provided in the cylinder as a mechanical stop for the drive piston.

[0011] The cylinder can have a first, front section with a first diameter D1 and a second, rear section with a second diameter D2, where D2 is larger than D1. The transition from D2 to D1 can be stepped, and an annular stop surface orthogonal to the longitudinal axis of the cylinder can be located at the transition. The auxiliary piston can be designed as a stepped piston, which has a first, rear section with a diameter corresponding to D2 and a second, front section with a diameter smaller than D1. The auxiliary piston can be brought into contact with the stop surface at its rear section.

[0012] A mechanical stop has the advantage that the intermediate position is precisely defined. The stop is positioned such that the front surface at the front end of the cleaning piston lies in the same plane as the front surface of the outlet pipe.

[0013] The invention will now be described using an exemplary embodiment and with reference to the Figures 1 to 4 will be explained in more detail. It shows: Fig. 1 Mixing head with cleaning piston in rear end position Fig. 2 Mixing head with cleaning piston in front end position Fig. 3 Mixing head with cleaning piston in intermediate position Fig. 4 Part of the mixing head according to the section line AA in Figure 1

[0014] The mixing head, designated overall by reference numeral 1, has a mixing chamber 2, a control piston 12 which is reversibly guided in the mixing chamber 2, and injection nozzles 3 and 4 (see Figure 4In the mixing position of the control piston 12, the reactive plastic components, such as a polyol material and an isocyanate material, can be introduced into the mixing chamber 2 via the two injection nozzles 3 and 4, where they can react to form a plastic mixture. The mixing chamber 2 is in fluidic communication with a discharge pipe 5 via a mixing chamber outlet opening 13, through which the finished plastic mixture can be discharged. The discharge pipe 5 has a discharge opening 5a and an annular front surface 5b at its front end. A cleaning piston 6 can be moved within the discharge pipe 5 to remove any remaining residues of plastic components and / or the plastic mixture. The cleaning piston 6 has a section at its front end with a ribbed outer surface 6a and a generally flat front surface 6b.The cleaning piston 6 is operatively connected to a drive piston 9 which can be moved in a cylinder 8. By means of a suitable hydraulic fluid, in particular a hydraulic oil, the drive piston 9 can be moved in the cylinder 8, namely between a rear end position ( . Figure 1 ) and a front end position ( Figure 2 ). In the rear end position ( Figure 1 ) the cleaning piston 6 has a position in which the mixing chamber outlet opening 13 is open towards the discharge pipe 5, thus allowing the plastic mixture to be discharged via the discharge pipe 5 and the discharge opening 5a. In the front end position ( Figure 2 ) the cleaning piston 6 has been extended out of the outlet pipe 5, at least partially.

[0015] In addition, a hydraulically movable auxiliary piston 10 is provided in the cylinder 8, the front surface of which forms a mechanical stop 7a for the drive piston 9 when the auxiliary piston 10 has been brought into a suitable position which corresponds to the intermediate position for the cleaning piston 6 or its drive piston 9.

[0016] The cylinder 8 has a first, front section 8a with a first diameter D1 and a second, rear section 8b with a second diameter D2, where D2 is larger than D1. The transition from D2 to D1 is stepped, and consequently, an annular stop surface 7b is located at the transition, perpendicular to the longitudinal axis of the cylinder 8. The auxiliary piston 10 is designed as a stepped piston and has a first, rear section 10a with a diameter corresponding to D2 and a second, front section 10b with a diameter smaller than D1. The auxiliary piston 10 can be brought with its rear section 10a to a stop against the stop surface 7b. In this position, the front surface of the auxiliary piston 10 forms a stop surface 7a as a mechanical stop for the drive piston 9, as shown in the Figure 3As shown, in this position the cleaning piston 6 is in an intermediate position in which the front surface 6b at the front end of the cleaning piston 6 lies in the same plane as the front surface 5b of the outlet pipe 5. This facilitates the cleaning of the front surface 5b, as simply passing it with a brush or scraper is sufficient for cleaning.

[0017] To insert the cleaning piston 6 into the Figures 1 to 3 To bring the hydraulic connections 11a, 11b and 11c and the pressure medium chambers connected to them into the positions shown, they are to be positioned as shown in the Figures 1 to 3 specified as being pressurized with a suitable hydraulic pressure or switched to depressurized mode. Reference symbol list

[0018] 1 Mixing head 2 Mixing chamber 3, 4 Injection nozzles 5 Outlet pipe 5a Discharge opening 5b Front surface of outlet pipe 5 6 Cleaning piston 6a Ribbed outer surface 6b Front surface of cleaning piston 6 7a First stop surface 7b Second stop surface 8 Cylinder 8a Front section of cylinder 8 with diameter D1 8b Rear section of cylinder 8 with diameter D2 9 Drive piston 10 Auxiliary piston 10a Rear section of auxiliary piston 10 10b Front section of auxiliary piston 10 11a Rear hydraulic connection 11b Middle hydraulic connection 11c Front hydraulic connection 12 Control piston 13 Mixing chamber outlet opening

Claims

1. A mixing head (1) for the processing of reactive plastic components to a plastic mixture, in particular for the processing of a polyol material and of an isocyanate material to a polyurethane material, with a mixing chamber (2), a control piston (12) guided reversibly in the mixing chamber (2), and with injection nozzles (3, 4), via which the plastic components can be introduced into the mixing chamber (2), with an outlet pipe (5) in fluidic connection with the mixing chamber (2), via which the plastic mixture exiting from the mixing chamber (2) can be discharged from the mixing head (1), and with a cleaning piston (6) which can be moved in the outlet pipe (5) by means of a hydraulic fluid, characterized in that the cleaning piston (6) can be moved at least partially out from the outlet pipe (5), and that the cleaning piston (6) can be moved into an intermediate position, in which the front face (6b) at the front end of the cleaning piston (6) lies in one plane with the front face (5b) of the outlet pipe (5), wherein the intermediate position is defined by a mechanical stop (7a, 7b).

2. The mixing head according to Claim 1, characterized in that the cleaning piston (6) can be moved between two end positions, namely a rear end position in which the cleaning piston (6) frees the mixing chamber (12) in the direction of the outlet pipe (5), and a front end position in which the cleaning piston (6) is moved out at least partially from the outlet pipe (5), wherein the intermediate position is situated between the two end positions and wherein preferably the two end positions are defined by respectively a mechanical stop.

3. The mixing head according to Claim 2, characterized in that the cleaning piston (6) is in operative connection with a drive piston (9) movable in a cylinder (8), wherein the drive piston (9) can be moved by means of the hydraulic fluid in the cylinder (8) between the two end positions, and wherein a mechanical stop (7a, 7b) for moving to the intermediate position is provided in the cylinder (8).

4. The mixing head according to Claim 3, characterized in that in the cylinder (8) a hydraulically movable auxiliary piston (10) is provided as mechanical stop (7a) for the drive piston (9).

5. The mixing head according to Claim 4, characterized in that the cylinder (8) has a first, front portion (8a) with a first diameter D1, and a second, rear portion (8b) with a second diameter D2, wherein D2 is greater than D1, wherein the transition from D2 to D1 is configured in a stepped manner, and at the transition a circular ring-shaped stop face (7b) is present orthogonally to the longitudinal axis of the cylinder (8), wherein the auxiliary piston (10) is configured as a stepped piston which has a first, rear portion (10a) with a diameter corresponding to D2, and a second, front portion (10b) with a diameter smaller than D1, and wherein the auxiliary piston (10) can be brought with its rear portion (10a) to stop with the stop face (7b).