NZ202401A - Automatic cut-off of powder flow for bag filling machine - Google Patents

Description

20240 1 Priority Datefs): .. f f. 7 J 11?/........

Complete Specification Filed: -f.'Jl Class: i PublHiation DM* 31 ■ J'*'> • • «PfOi Journal, Not •••••«•/.»"• .

Patents Form No.5 NEW ZEALAND PATENTS ACT 195 3 W < 5N0V/9^ »> f,' COMPLETE SPECIFICATION "SELF ADJUSTING WEIGHING SYSTEM FOR FLUX-P ACKER" ^'WEF.L, SMIDTH & CO. A/S, organized and existing under the laws of Denmark, of 77, Vigerslev Alle, DK-2500 Valby, Copenhage Denmark, a Danish company, hereby declare the invention, for which/%./we pray that a patent may be granted to ^le/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- - 1 - ^ 202401 Self-adjusting weighing system for Flux-packer.

The invention relates to a method of filling pulverulent material, e.g. cement, into valve sacks by means of a sack filling machine comprising a number of filling spouts suspended from their separate weighing systems which are preset to cut off the material flowing from the filling spout in question when a sack on the filling spout has attained a certain weight.

A sack filling machine of the above kind may be a rotat-20 able, automatic machine with its filling spouts distributed evenly along a circle and rotatable about the vertical axis of the machine. In principle, such a machine operates in the following way.. After placement, manual or automatic, of a sack on a filling spout, the weighing system of the filling spout is tared for the weight of sack, dust deposits etc., after which the filling of the pulverulent material in the sack starts. When the weighing system ascertains that the desired weight in the valve sack has been attained, the supply to the filling spout is cut off, and the sack is discharged. All this happens while the filling spout moves along 20 its circular path about the axis of the filling machine.

If the filling of a sack could be measured as an even and rectilinear curve, a weighing system - be it mechanical, electronical or combined electro-mechanical - would be capable of cutting off the filling process exactly when the desired weight in the sack had been attained.

The continuous measuring does not, however, follow an even curve because of the dynamic mass forces deriving from the filling process, i.e. from the forceful outflow of pulverulent material through the filling spout and into the sack. Consequently, the 30 cutting off of the filling process rarely takes place when the desired weight in the sack has been attained, but more often when in total load of the weight in the sack and the dynamic mass forces co k* equal the desired weight. ,7j| It is known to dampen the fluctuations from the dynamic ^ forces in a way which makes it it possible to state the filled in '•/ , ^.material weight on a comparatively even curve. Such dampening, however, entails a delay in the actual weight measuring, and consequently it is also known by check weighing the filled sacks to compensate the weighing system for such a delay as well as for 4q other systematical deviations in the weighing system. 202401 Check weighings of filled sacks must be made in respect of each filling spout at regular intervals, partly because two filling spouts with appertaining weighing systems do not react exactly alike although they have the" same construction, partly because the material filled into the sacks acts differently during the filling process from filling spout to filling spout and from hour to hour.

A manual check weighing of the filled sacks to correct the weighing systems of the filling machine, is considerably work consuming. An automatic check weighing made after the filling 10 machine calls for extra equipment to control from which filling spout the individual check weighed sack is discharged.

Thus, it is the object of the invention to devise a method eliminating the above disadvantages of the known sack filling machines.

According to the invention this object is achieved by a method of the kind described in claim 1, characterized in that the filled sack is check weighed while hanging on its filling spout, and that the result of the check weighing, immediately and before discharge of the sack from the filling spout, is used for adjusting the set-20 ting of the weighing system.

By this check weighing of the filled sack on the filling spout after a terminated filling process and after the weighing system has settled down, it is possible to measure statically, and thus more exactly, the weight of the material in the sack, and make the necessary adjustments of the weighing system without risking to make wrong adjustments for the weighing systems of other filling spouts; futhermore it is made impossible through a filling spout to fill more sacks with wrong material weight before the weighing system has been adjusted.

Particularly advantageous for carrying out the method accord ing to the invention are sack filling machines with electro-^ r.~^mechanical weighing systems and consequently the invention relates sack filling machine comprising electro-mechanical weighing ^ s^ktems, characterized in that each weighing system comprises a vr load cell, a control unit, a comparator and a feed-back unit for instantaneous, automatic adjustment of the preset weight setting of 1—^the weighing system according to the actual weight of the just fill ed sack.

As compared with sack filling machines in which the check 40 GB -2- 202401 weighing takes place outside the machine, thus demanding extra separate weighing equipment, it is an additional advantage of a machine according to the invention that the check weighing and the appertaining equipment form an integral part of the weighing process and the weighing system, respectively.

In the following the invention is described in more detail by means of an example of a sack filling machine according to the invention, references being made to the drawing which shows Fig. 1 a diagram of the circular path of a filling spout, 10 with indication of certain process stages.

Fig. 2 a diagrammatical side view of part of a rotating sack filling machine with a filling spout and an appertaining weighing system, and Fig. 3 and 4 weight/time diagrams describing the mode of operation of the weighing system.

Figure 1 illustrates the travel of a filling spout along a circular path during the rotation of the sack filling machine. Various process stages are indicated along the path, of which only 20 stages important for understanding the invention are provided with reference numerals.

At stage 1 a sack is placed - in the example automatically - on a filling spout, and between stages 2 and 3 the weight of the sack per se is tared in the weighing system of the filling spout in such manner that the said sack weight does not influence upon the measurement of the weight proper of the material filled into the sack. At stage 3 starts the filling of the material into the sack, and this filling is cut off when the weighing system ascertains that the preset weight has been attained. At the latest at stage 4, 30 the filling of the sack has been completed, and at stage 6 the filled sack is discharged after which the filling spout in question is ready for receiving a new empty sack.

In a sack filling machine according to the invention a check weighing stage 5 is inserted between stages 4 and 6, at which stage the filled sack is check weighed while still hanging on its filling spout, having settled down and no longer being exposed to dynamic impacts from the filling process. If the result of this check weighing deviates from the preset weight an instantaneous adjustment automatically takes place for the setting of the weighing 40 system. ^401 In Fig. 2, 7 is the rotating material container of a sack filling machine, the material being e.g. cement to be filled into sacks, and 8 is one filling spout out of a number of filling spouts mounted along a circle, evenly distributed about the container 7. The filling spout 8 is, as indicated, connected to the container 7 via a pipe or a hose with a valve 9, and is furthermore in a manner known per se suspended from a weighing system illustrated by a load cell 10 on the container 7.

On the filling spout is shown a sack 11 which is to be filled with a cettain weight of material from the container 7.

When the sack 11 has been placed on the filling spout 8 at stage 1 in Fig. 1, and the weighing system has been tared for the weight of the sack, dust deposits etc. between stage 2 and 3, the valve 9 opens at sta^e 3 in Fig. 1, and the filling starts.

In Fig. 2, 12 is an electro-mechanical setting unit, being set according to the preset weight in the sack. 13 is a comparator currently receiving a signal from the load cell 10 during the filling process and comparing this signal with the signal from the setting unit 12. The signal from the load cell 10 passes a damper unit 14 which dampens fluctuations in this signal deriving from dynamic mass forces which arise during discharge of the material into the sack 11.

When the comparator 13 ascertains concord between the actual weight of the sack 11 and the weight set on the setting unit 12, a cut off signal is sent to the valve 9.

At the latest at stage 4 in Fig. 1, the filling is completed, and between stages 4 and 5 the weighing system settles down whereupon at stage 5 a check weighing is made which is not influenced by dynamic forces in the system. In a comparator and feed-back unit 15 the result of the check weighing is compared with the preset sack weight. If the actual weight in the sack 11 deviates from the one desired, adjustment of the setting unit 12 is made automatically in accordance herewith through the feed-back mit 15, and the weighing system is ready for a more precise v^ighing of the next sack to travel along the circular path in Fig. iO ta!j tjjj The check weighing system can in a simple way form an J^ntegral part of the weighing system measuring the material weight in the sack 11 during the filling process.

Figs. 3 and 4 are weight/time-diagrams in which the GB -4- 202401 ordinate indicates the actual weight of material in the sack whereas the abscissa indicates the time by markings corresponding to the previously mentioned process stages. The dotted, horizontal line 16 indicates the preset weight of material in the filled sack.

Fig. 3 shows a rectilinear ideal curve 17 of the weight of material filled into the sack at any time between stages 3 and 4. If the signal from the load cell 10 followed this curve exactly, the attainment of the desired weight would be very simple, as the 10 filling could be cut off precisely when the curve 17 reached or intersected the horizontal line 16.

As the filling process entails the occurrence of dynamic mass forces in the system, the signal from the load cell 10 will not be rectilinear and even, but a strongly fluctuating curve as indicated by 18 in Fig. 3. The intersection point between the horizontal line 16 and the curve 18 consequently does not every time coincide with the intersection point between the horizontal line 16 and the ideal curve 17 and thus the signal for closing the valve 9 may occur before or after the material weight in the sack 20has reached the preset weight. This may entail that sacks from the same filling spout do not contain the same preset weight.

Consequently, as mentioned above and shown in Fig. 2, a damper unit 14 is inserted between the load cell 10 and the comparator 13 so that the signal from the load cell 10 to the comparator 13 follows a curve 19 as shown in Fig. 3. This curve is, however, as a consequence of the dampening delayed by a time lag t as compared with the ideal curve 17, and consequentially the valve 9 closes too late, i.e. the time lag t, after the sack has attained its desired weight.

If the time required for filling a sack always was the same for the individual filling spout and the corresponding weighing system it would be possible to compensate for the delayed closing of the valve 9, and consequently to avoid excess weight in the sack 11 by a suitable setting of the setting unit 12.

The filling time is, however, not constant, and therefore a computer unit 20 is additionally inserted between the load cell and the comparator 13 after the damper unit 14, the said computer unit being programmed, during the filling process, currently 40 to compensate for the time lag t in Fig. 3 so that the signal GB 202401 received by the comparator 13 does not follow the curve 19 (Fig. 4), but a curve 21 which during the filling process approximates to the ideal curve 17 prior to the latter intersecting the horizontal line 16.. In this way is achieved" a cutting off of the filling exactly when the preset weight has been attained.

In practice, however, the counter pressure to the outflow of material in the sack increases with the degree of filling of the latter; as a result the filling, instead of following the ideal curve 17 the last distance before intersecting the horizontal line 16, follows a curved segment, as indicated by a dotted line 22 in Fig. 4; this entails the risk of incorrect material weight in the sack in spite of the above meausres.

This problem is, as mentioned, solved according to the invention by check weighing each filled sack on its filling spout, and comparing this weighing signal in the comparator and feed-back unit 15 (Fig. 2) with a signal corresponding to the preset weight after which the result of this comparison is immediately used for an adjustment of the control unit 12.

GB 203401

Claims (5)

WHAT WE CLAIM IS:

1. A method of filling pulverulent material, e.g. cement, into valve sacks by means of a sack filling machine comprising a number of filling spouts suspended from separate weighing systems, each system being preset to cut 5 off the material flowing from its filling spout when a sack on the filling spout has attained a certain weight, characterized in that the filled sack is check weighed while hanging on its filling spout and that the result of the check weighing, immediately before discharge of the 10 sack from the filling spout, is used for adjusting the setting of the weighing system.

2. A sack filling machine according to claim 1 comprising electro-mechanical weighing systems, characterized in that each weighing system comprises a load cell, a 15 control unit, a comparator and a feed-back unit for instantaneous, automatic adjustment of the preset weight setting of the weighing system according to the actual weight of a just filled sack.

3. A sack filling machine according to claim 2, 20 characterized in that each weighing system also comprises a damper unit for dampening fluctuations in the signal from the load cell and a computer unit to compensate for a delay of the said signal caused by the damper unit.

4. A method of filling pulverulent material, e.g. cement, 25 into valve sacks by means of a sack filling machine substantially as described herein with reference to the accompanying drawings. - 7 - 2024VI

5. A sack filling machine substantially as herein described with reference to the accompanying drawings. IDTH & CO. A/S