Method of Filling a Weighing Container for Plastics Granulate

Abstract

The method of filling a weighing container (10) for plastics granulate (12), wherein the granulate is dropped from a supply tube (26) into the weighing container (10) via a shutter (22), wherein the weighing container (10) is closed-off on the top side by a wall having a conical part (16) that reaches directly up the shutter (22), and in that the weighing container is filled with granulate up to the level of the shutter (22).

Claims

1. A method of filling a weighing container for plastics granulate, comprising the steps of: closing off the weighing container at a top side thereof by a wall having a conical part that reaches directly up to a shutter, dropping the granulate from a supply tube into the weighinq container via the shutter, and filling the weighing container with granulate up to the level of the shutter.

2. The method according to claim 1, wherein the conical part has a cone angle which is selected as dependent upon the consistency of the granulate.

3. The method according to claim 2, wherein the granulate in the weighing container has an upper surface with an angle of repose, and the cone angle is larger than the angle of repose of the granulate.

4. A weighing system for carrying out the method according to claim 1, comprising: a weighing container, a supply tube opening out into the weighing container via a shutter, and a wall having a conical part which closes off a top side of the weighing container, with the conical part of the wall reaching directly up to the shutter.

5. The weighing system according to claim 4, wherein the weighing container has a top wall with a conical configuration in its entirety.

6. The weighing system according to claim 4, wherein the conical part of the wall reaching up to the shutter is separate from the weighing container and is held independently of the weighing container.

Description

[0014] An embodiment example will now be described in conjunction with the drawings, wherein:

[0015] FIG. 1 is a vertical section of a part of a weighing system, comprising a weighing container for plastics granulate, during a fill operation;

[0016] FIG. 2 shows the weighing container in a state completely filled with granulate;

[0017] FIG. 3 shows the weighing container in a condition when a shutter has been closed; and

[0018] FIG. 4 shows the weighing container during an emptying process.

[0019] FIG. 1 shows a top part of a weighing container 10 which, as a whole, has an essentially cylindrical shape and which is being filled with plastics granulates 12.

[0020] On the top side the weighing container 10 is closed-off by a conical wall which has an outer and lower part 14 rigidly connected to the weighing container, and an inner and upper part 16 which is separate from the weighing container 10. The two parts 14 and 16 are separated by a gap 18 which is surrounded by a collar 20 formed at the part 14. The top part 16 is disposed directly adjacent to a shutter 22 which is formed by a slide plate and an associated drive mechanism 24. The shutter 22 and the top part 16 of the closure wall are commonly held at a lower end of a supply tube 26 from which the granulate drops into the interior of the weighing container 10.

[0021] In the condition shown in FIG. 1, the shutter 22 is open, i.e. an opening 28 of the slide plate is aligned with the internal cross-section of the supply tube 26, so that the granulate drops into the weighing container 10 and forms a repose cone 30.

[0022] The cone angle a of the conical closure wall formed by the parts 14 and 16 of the weighing container is larger than the repose angle of the granulate, i.e. the angle of inclination of the repose cone 30, so that, when the fill level in the container increases, the granulate can completely fill also the top part of the weighing container 10 that is limited by the conical closure wall.

[0023] FIG. 2 shows the condition where the weighing container has completely been filled with granulate 12 up to the level of the shutter 22. In this condition, the interior of the weighing container, including the conical top part, is filled with granulate practically completely, so that practically no dead space remains in the weighing container. Now, in this condition, the shutter 22 is closed, as has been shown in FIG. 3. Any possible granulate dust that may adhere to the slide plate of the shutter 22 due to electrostatic charge will be stripped off by the horizontal movement of the slide plate.

[0024] The bottom end of the weighing container 10, which has not been shown here, is funnel-shaped and is connected to a conveyer with which the material is discharged continuously. As long as the shutter is closed, the fill level of the granulate in the weighing container 10 decreases, since no further granulate is fed via the supply tube 26. Thus, as has been shown in FIG. 4, an empty space forms in the conical top part of the weighing container 10, and this space becomes larger while the granulate exits at the bottom end of the weighing container.

[0025] The weighing container 10 is supported on a weighing cell with which the decrease in weight of the container and the granulate 12 contained therein is measured continuously. In this way, the amount of material that leaves the weighing container can be determined with high precision.

[0026] The cone angle a of the parts 14, 16 of the top closure wall of the weighing container has been selected such that the granulate that has been in contact with the part 16 in the condition shown in FIG. 3 can drop down freely without being restrained in its downward movement by the conical part 16. In this way, it is assured that the entire weight of the granulate, including the portion that is accommodated within the part 16, always rests on the weighing cell, so that the result of the weight measurement is not compromised.

[0027] When a certain amount of granulate has exited the weighing container 10, the shutter 22 is opened again, so that a new fill cycle may start.

[0028] In a transition phase between the condition shown in FIG. 3 and the condition shown in FIG. 4 the granulate 12 will gradually sink downward in the weighing container 10, and granulate particles will move along the internal wall of the part 14 and the part 16 of the closure wall, so that any dust that may adhere to these walls will be stripped-off.

[0029] Thus, the accumulation of larger amounts of dust or angel hair in the top part of the weighing container 10 may be prevented by performing, at least in certain time intervals, fill cycles in which the entire interior of the weighing container 10 is filled with granulate up to the level of the shutter 22, as shown in FIGS. 2 and 3. In between, it is possible to perform fill cycles in which the interior of the weighing container is filled only up to a lower level.

[0030] When the type of granulate is changed, the last fill cycle before the weighing container is emptied completely should in any case be performed in the manner shown in FIGS. 2 and 3 in order to minimize the amount of dust and angel hair that remains in the weighing container 10 and could therefore mix with the new granulate material. In most cases it is possible in this way to completely dispense with a manual cleaning of the weighing container and the part 16 of the closure wall. Only in those cases in which the granulate type is changed from a very dark material to a brighter material, a manual cleaning may be useful in order to avoid a perceptible change in the colour of the plastics.