Title of Invention

METHOD AND APPARATUS FOR METERING STARING SUBSTANCES IN BATCHES INTO A MIXER ON A PLASTICS-PROCESSING MACHINE

Abstract An apparatus and a method for inetering two or more than two starting substances intended for products made of thermoplastic froe storage containers in batches and in selectable concentrations, into a mixer for mounting onto a plastics-processing machine, in particular an injection-tolling machine. Each storage container has an outlet with which is associated a scale with a weighing cell Africa has an inlet communicating with the outlet of the storage container and which has an outlet, blockable by means of blocking member, which communicates with an inlet of the mixer. A control device is provided, on which the selectable concentrations can be set and to which the weighing results are transmitted from the scales, after the selected concentrations have been reached in the respective weighing cells, their blocking members are activated. There is additionally provided a volumetrically operating metering device which is linked to the control device.
Full Text The present invention proceeds from an apparatus and a method for metering
two or more than two starting substances intended for products made of
thermoplastic. An apparatus of this kind is known from DE 22 43 298 Al.
In this known apparatus two or more than two starting substances intended
for products made of thermoplastic are metered in selectable weight
proportions from storage containers into a mixer that is present on a plastics-
processing machine. The starting substances are typically a thermoplastic
raw material in the form of pellets, a regenerated plastic, adjuvants and
fillers, and coloring agents. In order for the product manufactured in the
plastics-processing machine to have consistent quality, the starting
substances must be metered in consistent concentrations, i.e. weight
proportions, into the mixer that is present on the machine. For this purpose,
it is known to weigh the starting substances in batches and introduce the
weighed quantities into the mixer. For this purpose, according to DE 22 43
298 Al a weighing cell, which is attached to a scale beam and is weighed
along with its contents, is


provided under the outlet of the storage container of each starting substance. The weighing cell is allowed to fill up from the reservoir until the desired weight is reached, and inflow is then stopped. A blocking flap or similar blocking member can then be opened so that the weighing cell empties into the mixer arranged below. The principal components of the starting substances flow freely from the reservoir into the weighing cells; the additional components used in smaller proportions, in particular coloring agents, are according to DE 22 43 298 A1 delivered into the weighing cell by means of a metering screw.
Although the concentrations can, in principle, be weighed very accurately with scales, the known metering apparatuses which operate in batches are unfortunately highly subject to interference, due primarily to the fact that the environmental conditions are unfavorable for exact weighing conditions. For example, the weighing cells suspended from the scale beam can be caused to oscillate not only by the inflowing starting substances, but also by vibrations generated during operation of the plastics-processing machine itself or generated by machines located in the vicinity and transferred via the floor. Even passing forklift trucks, trucks traveling on a nearby road, or rail vehicles can transfer vibrations to the scale, leading to considerable indication errors and thus to incorrect metering results.
DE 22 47 518 discloses the individual weighing of substances using a discontinuous weigher for smaller quantities and a belt weigher for larger quantities. The susceptibility to interference here is even greater than in the case of DE 22 43 298.
From DE 28 06 103 C2, 28 57 739 C2, and 28 57 740 G2, it is known to meter pelleted and powdered starting substances into the mixer of a plastics-processing machine by means of star feeders. Metering apparatuses of this kind which meter volumetrically are less sensitive to vibrations, but have the disadvantage that metering accuracy can be no better than the volume of one chamber of the metering wheel, and that

changes in bulk density and flow characteristics result in changes in the weight metered.
From DE 21 49 242 it is known to deliver a principal component gravimetrically by means of a belt weigher, and an auxiliary component in volumetrically metered fashion, to a plastics-processing machine. In this context, each of the metering methods used has the disadvantages discussed above.
It is the object of the present invention to indicate a way to reduce the susceptibility to interference which occurs in the gravimetric metering of starting substances for products made of thermoplastic.
This object is achieved by means of an apparatus having the features indicated in Claim 1, and by means of a method having the features indicated in Claim TO. Advantageous developments of the invention are the subject of the dependent claims.
The metering apparatus according to the invention has, for each starting substance to be metered into the plastics-processing machine, a storage container from which the starting substance in question passes into a weighing cell of a scale. The weighing cell has an outlet with a controllable blocking member. Also provided is a control device at which the selectable concentration (parts by weight) of the various starting substances can be set. The scales transmit the weighing results to the control device, and after the selected quantities have been reached in the respective weighing cells, the control device activates their blocking members. In contrast to the related art in which the control device activates the blocking members exclusively on the basis of the weighing results, according to the invention the control device is also linked to the volumetrically operating metering devices in such a way that the respective blocking member is not activated until the control device has determined that the volumetrically operating metering device in question has metered a predefined volume into the associated weighing cell.

This yields substantial advantages:
Incorrect weighing results caused by vibrations or similar sources of interference, which simulate attainment of the preselected weight before it has actually been attained, are ignored if it is known, by way of the volumetrically operating metering device, that it has not yet completely metered the preselected volume and that the preselected quantity therefore cannot yet have been attained.
If the volumetrically operating metering device should rheter incorrectly in an isolated case, for example occasionally delivering an empty volume or not completely filling or emptying its metering chamber, this is discovered by the fact that the scale indicates an incorrect amount which can then be metered again. It is improbable that the metering scale and the associated volumetrically operating metering device will simultaneously operate incorrectly. The probability of this event can be further reduced by performing the weighing for each filling of the weighing cell several times in succession, e.g. three times in succession. Normal fluctuations in the weighing result can thereby be compensated for by averaging. Deviations in a weighing result which are so great that they cannot be explained by normal weighing inaccuracy will preferably be ascribed to external sources of interference, e.g. vibrations, acting on the metering apparatus; these "outliers" among the measured values are preferably discarded and left out of consideration when comparing the weighing result with the volumetrically operating metering system.
Deviations between the weighing result and the volumetrically operating metering system do not always lead to an adjustment of the setpoints on the control device. The setpoints on the control device are preferably not adjusted until deviations between the volumetric metering system and the weighing results are noted, in the same direction, in several successive metering cycles, so that a systematic deviation can be assumed which might indicate, for example, a change in bulk density, a drift in the scale's

zero point, or a change in the sensitivity of the scale. A zero point drift can be easily eliminated by resetting the scale to zero each time the weighing cell is emptied. A change in the sensitivity of the scale can be eliminated by selecting a suitable weighing technology and by means of calibrations performed from time to time. Scales that operate with strain gauges are particularly suitable in the present case. The principal remaining source of systematic errors is the interaction between the starting substances and the volumetrically operating metering device; systematic errors of this kind can be counteracted by gradually adjusting the default setting of the volume to be metered to the weighing result as a function of the actual deviation of the weighing result.
The invention is a very simple way of achieving a substantial improvement in the accuracy and reliability of the metering of starting substances into a plastics-processing machine, and thus more uniform quality in the plastic products manufactured with the machine. The invention is suitable for both extrusion machines and injection-molding machines, but particularly for the latter because they process the material in batches. They moreover have the advantage that in them, the weighing operation can occur in a working phase with minimal vibrations, for example while adding or holding pressure'after the injection operation. The injection-molding machine could also easily be shut down briefly for the weighing operation; for example, the weighing operation could take place after ejection of the molded part manufactured by injection molding, before the injection-molding die is closed again.
When a plastics-processing machine is first set up for the manufacture of a certain product, the default settings on the control unit for metering the starting substances are preferably first determined in test runs, advantageously by presetting the weight proportions of the individual starting substances on the control unit and then checking to see how many chamber volumes or how much metering time the selected metering device requires, under standard conditions, to meter into the weighing cell a quantity of the starting substance having the predefined weight. This

experimentally predetermined value is then entered as the volume setpoint, or the number of chamber volumes or rotations on the metering unit, or the metering time of the control device, with the consequence that the particular metering operation cannot end until this setpoint has been reached.
The invention is particularly suitable for pourable powdered or pelleted substances. The latter are metered volumetrically out of their storage containers into the associated weighing cell, preferably by means of a star wheel as know from DE 28 06 103 C2, DE 28 57 739 C2, and DE 28 57 740 C2. The star wheels have a number of identical chambers or cells, distributed at regular intervals around the star wheel, into which the starting substance flows under its own weight from the storage container, and from which, when the cells are pointing downward, it falls out into the weighing cell. Uniform filling of the cells can be promoted by the means cited in the three aforementioned patent documents, in particular by means of wipers which are arranged above the star wheel and prevent overfilling; the discharge of starting substances with a tendency to back up can be promoted by scrapers which engage into the cells and act on the lower region of the star wheels.
Liquid or pasty substances can also be metered volumetrically into a scale, in particular using a piston pump with a predefined displacement volume. The greater the number of individual volumes that must be introduced into the weighing cell in order to reach the predefined weight of starting substance, the more accurate the volumetric metering system. The volume of one cell of the star wheel and the displacement volume of a piston pump that Is used should therefore be small as compared with the capacity of the associated weighing cell, preferably less than 1/100, even better less than 1/500 of the capacity of the associated weighing cell.
In some circumstances, liquid and pasty substances cannot readily be removed by flowing out of the weighing cell; in order to promote outflow it may be advisable, as proposed in DE 22 42 298, to empty one of the

pourable principal components of the plastic into the mixer through the weighing cell for the liquid or pasty starting substance.
For pourable starting substances the weighing cells are preferably funnels; for liquid or pasty starting substances they are preferably cylinders, from which the starting substances can flow out particularly easily.
The weighing cell can comprise a base which serves as a weighing tray and is decoupled from the peripheral walls of the weighing cell, so that the peripheral wails do not also need to be weighed. Friction and even jamming can, however, occur between the base and the peripheral walls, and falsify the weighing result. It is therefore preferable to weigh the entire weighing cell. In the interest of high weighing sensitivity, the weighing cell should be as light as possible so that the weight of the substance rather than its own weight predominates. The weighing cell should therefore be free of physical elements that do not absolutely need to be installed on the weighing cell. This applies in particular to the actuation member that is required in order to open, and optionally to close, the blocking member of the weighing cell. A compressed-air cylinder is advantageously used here, but it does not need to be installed on the weighing cell but can be installed, for example on the support of the metering apparatus or on the mixer into which the weighing cell is emptied. It is sufficient if the compressed-air cylinder pushes on the blocking member, for example a flap. The compressed-air cylinder then does not need also to be weighed.


Accordingly, the present invention provides an apparatus for metering two or more than two starting substances intended for products made of thermoplastic from storage containers, in batches and in selectable concentrations, into a mixer for mounting onto a plastics-processing machine, in particular an injection-molding machine, such that each storage container has an outlet with which is associated a scale with a weighing cell which has an inlet communicating with the outlet of the storage container and which has an outlet, blockable by means of a blocking member, which communicates with an inlet of the mixer and a control device is provided, on which the selectable concentrations can be set and to which the weighing results are transmitted from the scales and which, after the selected concentrations have been reached in the respective weighing cells, activates their blocking members, characterized in that there is additionally provided, between each storage container and the associated weighing cell, a volumetrically operating metering device which is linked to the control device in such a way that the control device does not activate the respective blocking member until it has detected the metering of a preselected volume by the volumetrically operating metering device in question.
Accordingly, the present invention also provides a method for metering two or more than two starting substances intended for products made of thermoplastic from storage containers (23, 24, 25), in batches and in selectable concentrations, into a plastics-processing machine (1), in particular an injection-molding machine, such that the particular starting substance is weighed into a weighing cell (15, 16) out of its storage


container (23, 24, 25), and after the desired weight has been attained is delivered as a batch to the plastics-processing machine (1), wherein the particular starting substance is metered volumetrically into the weighing cell (15, 16) and the starting substance is not permitted to flow out of the weighing cell (15, 16) until metering of a preselected volume has been completed.
An exemplified embodiment of the invention is shown with reference to the
accompanying drawings, in which
Fig. 1 shows an apparatus for metering three different starting substances in
batches into a mixer on a plastics-processing machine, in a partly sectioned
view;
Fig. 2 shows, as a detail, a portion of the apparatus according to Fig. 1,
namely a weighing cell on the mixer and, above the weighing cell,

"^1


a volumetrically operating metering device for one of the starting substances, with the weighing cell blocked, partly in section; and
Fig. 3 shows a portion similar to Fig. 2, but with a metering apparatus pulled away from the mixer.
Fig, 1 shows a plastics-processing machine 1, symbolically shown by means of a barrel 1 with a screw 2 arranged therein. Barrel 1 has on its upper side a filler opening 3 on which is located a funnel-shaped mixer 4 in which is arranged a stirrer 5 that is driven by a motor 6 which is located on a cover 7 of mixer 4. Pairs of guide rods 8 that project approximately radially from the mixer are installed near the upper edge of mixer 4 on its peripheral wall. A shoe 9 is mounted slidingly on each pair of such guide rods 8 and, in the working position, attached with wing nuts 10 to a mounting plate 11 installed on the outside of mixer 4.
Shoe 9 has a support plate 12 on which a scale 13 operating with a strain gauge is installed. Provided on scale 13 by means of a bent mounting panel 14 is a funnel-shaped weighing cell 15 or 16, two examples of which are shown in Fig. 1, while a third weighing cell is located behind motor 6 and is concealed by it. Weighing cells 15 and 16 are made of thin sheet metal and have at the lower end an outlet 17 which can be blocked by means of a blocking member 18 in the form of a flap which is attached to weighing cell 15 or 16 so as to pivot about a horizontal shaft 19. A compressed-air cylinder 20, the piston rod 21 of which is directed against an extension 18a of the flap and, when the weighing cell is closed (see Fig. 2), is at a distance from the said extension, is provided on shoe 9 in order to open flap 18. When compressed-air cylinder 20 is actuated and its piston rod 21 is thus extended, it strikes against extension 18a of the flap so that the latter pivots and uncovers opening 17 (see Fig. 3). Closing of flap 18 can be effected by the fact that the torque exerted by extension 18a is greater than that of flap 18 on which the weight of the weighing cell contents is acting. Closing of flap 18 can be assisted by a return spring, which for reasons of clarity is not shown in the drawings.

Outlet 17 is located above a hole 22 in top 7 of the mixer (see Fig. 2).
A storage container 23 for one of the starting substances is arranged above weighing cell 15. A further storage container 24 is arranged above weighing cell 16, and a third storage container 25 for a third starting substance is arranged above the weighing cell concealed by motor 6. A suction conveyor device 26 and 27, with which storage containers 23 and 25 can be refilled from reservoirs 28 and 29, is located as a top attachment on storage containers 23 and 25, respectively. The third storage container 24 is the smallest of the storage containers and contains, for example, a color pigment powder that is added only in small quantities. Storage container 24 can be refilled manually as needed.
Storage containers 23, 24, and 25 each have a pedestal 30, 31, and 32, in which a star wheel feeder 33 and 34, as a volumetrically operating metering device, is arranged, as will be described using the example of Figs. 2 and 3.
Star wheel feeder 33 shown in Figs. 2 and 3 consists of a predominantly cylindrical recess 35 in pedestal 30, in which a star wheel 36 is rotatably mounted. An electric motor 37 (Fig. 1) is provided to drive the star wheel. Star wheel 36 has a plurality of cells 38, identical to one another and distributed over the periphery of the star wheel. An outlet 39 of storage container 23 opens into recess 35 from above, laterally next to the vertex of recess 35. On the opposite side of the lower vertex of recess 35, the latter is equipped with an outlet opening 40 that is located directly above inlet opening 41 of weighing cell 15.
Star wheel 36 rotates clockwise as shown in Fig. 2. The wall of recess 35 is located - viewed in the direction of rotation - in the portion betweea outlet opening 40 and outlet 39 of storage container 23, sufficiently close to the walls of star wheel 36 that the starting substance present in storage container 23, shown as pellets 42, cannot reach the weighing cell by

falling freely and bypassing star wheel 36, but can reach it only as a result of the delivery action of star wheel 36, which is effected by the fact that cells 38 below outlet 39 are filled with starting substance 42 (overfilling being prevented by a wiper 46 delimiting outlet 29), and that the filled chambers 38 rotate toward outlet opening 30 where they then empty in response to gravity, assisted if necessary by a scraper (as disclosed in DE 28 06 103 C2, DE 28 57 739 C2, and DE 28 57 740 C2). To ensure that starting substance 42 placed in cells 36 does not cause clogging, portion 35a of the inner wall of recess 35 extending - viewed in the rotation direction - between outlet 39 and outlet opening 40 is set back from the walls of star wheel 36 (see Fig. 2).
A level sensor 43, operating for example by capacitance, is also installed in cover 7 of the mixer.
Lastly, a control unit 44, which is connected via electrical lines (not further designated) to drive motors 37 of star wheels 33, 34, to level sensor 43, to strain-gauge scales 13, and to a solenoid valve in a compressed-air line to compressed-air cylinder 20, is provided.
The metering apparatus shown is operated as follows:
Before a specific plastic product is first manufactured on machine 1, the desired concentrations (parts by weight) of the individual starting substances are entered numerically into control unit 44. The volumetrically operating metering devices constituted by star wheel feeders 33 and 34 are then gravimetrically calibrated. To do so, wing nuts 10 are loosened and shoes 9, with the equipment arranged on them, are pulled away from mixer 4 into the position shown in Fig. 3, in which outlet 17 of weighing cell 15 is no longer located above mixer 4, but rather next to it. Several test runs are then made to determine how many revolutions of star wheel 36 are needed to dispense into weighing cell 15, 16 a quantity of the starting substance present in storage container 23 which has the weight per batch previously entered into the control unit. In the case of a star

wheel 36 operating at constant speed, it is also possible instead to determine the time required for the star wheel to meter into weighing cell 15 or 16 a quantity having the desired weight. Attainment of the desired weight is determined by means of scale 13 under controlled, quiet conditions, to ensure that the scale is displaying correctly. The respective batch of starting substance dispensed into weighing cell 15 is emptied through outlet 17, and collected in a bucket 45. The collected material can be recycled back into the production process. Once the number of rotations, or the running time, of star wheel 36 required for the desired weight has been determined from several measurements and by averaging, this value is also entered into control unit 44, and the arrangement is returned to the working position shown in Fig. 2.
Under operating conditions, star wheel 36 is then rotated for the preset time or for the preset number of revolutions, and the starting substance is thereby dispensed in the corresponding quantity out of storage container 23 into weighing cell 15, which is additionally weighed, along with its contents, by means of scale 13, If the specific weight determined, preferably from three successively performed and averaged weighings, agrees with the preset weight within a predefined tolerance, the control unit activates blocking member 18, provided level sensor 43 indicates that the level in mixer 4 has dropped below a preset value.
If the result of the weighing deviates from the preset weight by more than the predefined tolerance, metering is repeated by means of star wheel feeder 33 until the result of the weighing agrees with the preset weight within the predefined tolerance. Flap 18 is then opened by control unit 44 by means of compressed-air cylinder 20, and weighing cell 15 is emptied into mixer 4 as soon as level sensor 43 has signaled a need for refilling.
If three successive filling operations yield a systematic deviation between the measured and preset weight, the calibration of the volumetrically metering star wheel feeder 33 is then gradually adjusted, specifically by

always readjusting by only a portion of the measured error, e.g. by half the error, in order to prevent control oscillations.
Individual measured values from scale 1 3 which deviate so greatly from the other measured values that the deviation cannot be explained by normal measurement inaccuracies are considered "outliers," e.g. caused by vibrations, and are not taken into account when averaging the measured weight.


WE CLAIM:
1. An apparatus for metering two or more than two starting substances intended for products made of thermoplastic from storage containers (23, 24, 25), in batches and in selectable concentrations, into a mixer for mounting onto a plastics-processing machine (1), in particular an injection-molding machine such that each storage container (23, 24, 25) has an outlet (39) with which is associated a scale (13) with a weighing cell (15, 16) which has an inlet (41) communicating with the outlet of the storage container (23, 24, 25) and which has an outlet (17), blockable by means of a blocking member (18), which communicates with an inlet (22) of the mixer (4) and a control device (44) is provided, on which the selectable concentrations can be set and to which the weighing results are transmitted from the scales (13) and which, after the selected concentrations have been reached in the respective weighing cells (15, 16), activates their blocking members (18), characterized in that there is additionally provided, between each storage container (23, 24, 25) and the associated weighing cell (15, 16), a volumetrically operating metering device (33, 34) which is linked to the control device (44) in such a way that the control device (44) does not activate the respective blocking member (18) until it has detected the metering of a preselected volume by the volumetrically operating metering device (33, 34) in question.
2. The apparatus as claimed in claim 1, wherein the volumetrically operating metering devices (33, 34) for pourable substances are star wheel feeders.

3. The apparatus as claimed in claim 1, wherein the volumetrically operating metering devices for pasty and for liquid substances are piston pumps.
4. The apparatus as claimed in claim 2 or 3, wherein the volume of one cell (38) of the star wheel (36), or the displacement of the piston pump, is small compared to the capacity of the associated weighing cell (15, 16).
5. The apparatus as claimed in claim 4, wherein the volume of the cell (38) of a star wheel (36), or the displacement of the piston pump, is less than 1/100, preferably less than 1/500, of the capacity of the associated weighing cell (15, 16).
6. The apparatus as claimed in any one of the preceding claims, wherein the
weighing cells (15, 16) are funnels.
7. The apparatus as claimed in any one of the preceding claims, wherein the blocking member (18) is actuated by an actuation member (20) that is not mounted on the weighing cell (15, 16).
8. The apparatus as claimed in any one of the preceding claims, wherein the preselected volume is equal to the selected concentration (weight proportion) divided by the bulk density of the particular starting substance.
9. The apparatus as claimed in any one of the preceding claims, wherein the arrangement made up of storage containers (23, 24, 25), volumetric metering

device (33, 34), and associated weighing cell (15,16) rests on guides (8) that project from the mixer (4).
10. A method for metering two or more than two starting substances intended for products made of thermoplastic from storage containers (23, 24, 25), in batches and in selectable concentrations, into a plastics-processing machine (1), in particular an injection-molding machine, such that the particular starting substance is weighed into a weighing cell (15, 16) out of its storage container (23, 24, 25), and after the desired weight has been attained is delivered as a batch to the plastics-processing machine (1), wherein the particular starting substance is metered volumetrically into the weighing cell (15, 16) and the starting substance is not permitted to flow out of the weighing cell (15, 16) until metering of a preselected volume has been completed.
11. The method as claimed in claim 10, wherein the volumetric metering occurs in partial volumes which are small compared with the capacity of the associated weighing cell.
12. The method as claimed in claim 11, wherein the preselected
concentration by weight of the particular starting substance, divided by its
bulk density, is selected as the preselected volume.
13. The method as claimed in any one of claims 10 to 12, wherein the
volumetrically operating metering devices (33, 34) are first calibrated by
means of the scales provided for the various starting substances.

14. The method as claimed in any one of claims 10 to 13, wherein the weight determination for each batch is performed several times in succession, and an average is calculated therefrom.
15. The method as claimed in claim 14, wherein measured values that deviate to an unusual degree from the other measured values are not considered in calculating the average.
16. The method as claimed in any one of claims 10 to 15, wherein the
weight-related calibration of the volumetric metering system is readjusted if
a systematic deviation between the volumetrically metered quantity and the
predefined weight occurs in several successive batches.
17. An apparatus for metering two or more than two starting substances
intended for products made of thermoplastic substantially as herein
described with reference to the accompanying drawings.
18. A method for metering two or more than two starting substances
intended for products made of thermoplastic substantially as herein
described with reference to the accompanying drawings.


Documents:

448-mas-1997 abstract.pdf

448-mas-1997 claims.pdf

448-mas-1997 correspondence others.pdf

448-mas-1997 correspondence po.pdf

448-mas-1997 description (complete).pdf

448-mas-1997 drawings.pdf

448-mas-1997 form-1.pdf

448-mas-1997 form-26.pdf

448-mas-1997 form-4.pdf

448-mas-1997 petition.pdf


Patent Number 194268
Indian Patent Application Number 448/MAS/1997
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date
Date of Filing 05-Mar-1997
Name of Patentee WERNER KOCH MASCHINENTECHNICK GMBH
Applicant Address INDUSTRIESTRASSE 3 D-75228 ISPRINGEN
Inventors:
# Inventor's Name Inventor's Address
1 WERNER KOCH INDUSTRIESTRASSE 3 D-75228 ISPRINGEN
PCT International Classification Number G01G13/24
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA