GB2155645A

GB2155645A - Filling bags

Info

Publication number: GB2155645A
Application number: GB08504762A
Authority: GB
Inventors: Gerhard Feldhans
Original assignee: Haver and Boecker OHG
Current assignee: Haver and Boecker OHG
Priority date: 1984-03-03
Filing date: 1985-02-25
Publication date: 1985-09-25
Also published as: CH667247A5; IT1186832B; FR2560580A1; IT8512437A0; DE3408005A1; FR2560580B3; GB2155645B; GB8504762D0

Abstract

Bags are to be filled so that a uniform volume is introduced into each bag. Consequently, the weight is dependent on the respective density of the filling material. Increase in weight is detected by a load carrier (7) and measuring means (8) during the operation of filling a bag. By means of continuous evaluation of the measurement values, the stream of filling material through a nozzle (1) is cut off by a slider (6) as soon as no further increase in weight can be detected or the rate of increase in weight falls below a given value. <IMAGE>

Description

SPECIFICATION Method and apparatus for filling bags The invention relates to a method of filling bags and to apparatus for carrying out the method.

Various filling materials which are packed in bags or sacks have the property that, due to environmental influences, they undergo a change in their specific weight which is generally referred to in the relevant art as the 'litre weight'. That applies for example to insulating materials which are used in the building industry, hygiene straw for domestic animals and like substances. Such substances are generally referred to as being hygroscopic.

Their specific weight or 'litre weight' also varies due to the absorption of moisture. Also known are substances which undergo a change in their grain size due to the effect of pressure, whereby once again the specific weight changes. Substances of that kind are used for example as filling agents for filling out hollow spaces or cavities when packaging articles. They are made from styropor and are of an irregular geometrical shape, which further causes them to be broken down more readily.

If now a given amount, in accordance with a predetermined weight, of a filling material of the above-mentioned kind is put into a bag or sack, the accommodation volume of a bag or sack is not fully utilised if the 'litre weight' is greater than was assumed when calculating the dimensions of the bag or sack. Consequently, when using such filling materials, the bags or sacks are filled to different degrees.

That may cause a purchaser who normally purchases the same article at certain intervals of time to adopt a particularly critical attitude, on the assumption that the specified amount is not actually contained in the bag. That assumption is even correct, in regard to volume.

In order to counter such aspects, a bag filling method for such filling materials is already known, wherein a uniform amount, with respect to volume, is introduced into each respective bag. Before the material is introduced into the bag, a measuring container is first filled, the material in the container is scraped off flush with the filling opening of the container and the amount of material which is then still contained in the measuring container is then put into the bag.

Although the use of that method ensures that, irrespective of the particular specific weight of the filling material, each bag or sack is virtually always apparently uniformly filled, in terms of volume, nonetheless in practice twp filling operations are required to fill a bag, which means that only a low level of filling output can be achieved so that the method cannot economically be used industrially.

According to one aspect of the invention there is provided a method of filling bags comprising the steps of introducing filling mterial into each successive bag, detecting the increase in weight of the bag during the bag filling operation, continuously evaluating the measurement values and interrupting the filling stream of filling material as soon as no increase or only a slight increase in weight is detected, thereby to obtain filling of a uniform volume of filling material into each successive bag.

According to another aspect of the invention there is provided apparatus for filling bags comprising first means to introduce filling material into each successive bag, second means for detecting the increase in weight of the bag at small intervals in respect of time during the filling operation, third means for determining the respective difference between each measure value and the previously detected value, and fourth means to stop the filling operation as soon as no difference in weight is determined thereby to obtain filling of a uniform volume of material into each successive bag.

The invention can ensure that each bag is fully filled with the material to be packaged therein, since the bag, in addition to its transporation and protective function, now also acts as a measuring container. As long as the bag is not yet completely filled, it can be assumed that, with a filling stream which remains the same, the filling material which is introduced in a given unit of time is the same or approximately the same, in terms of weight, so that the detected increase in weight is also the same or approximately the same, irrespective of the respective weight of the partly filled bag. That serves as a signal that the filling operation is not yet to be shut off. However, as soon as the interior of the bag is fully filled, the increase in weight detected per unit of time becomes substantially less or can no longer be ascertained.

That may be taken to be a signal to switch off the filling stream. The switching off of the stream of filling material is consequently to be seen as a signal which is given by the bag when it is already filled.

In a particularly advantageous fashion, the increase in weight may be detected in analog or digital manner, as in that case it is possible to use components which are tried and tested in the measuring and regulating art.

Another advantage in the use of the method of the invention is that by detecting the increase in weight, by measuring the actual weight, it is possible to ascertain whether a predetermined mixture ratio of a filling material which comprises a plurality of components is being observed. Such materials are for example finished mixtures which are used in the building industry for producing mortar, concrete, floor finish materials and the like, with a particularly high proportion of quartz.

The specific weights of the individual components are particularly different so that fluctuations in weight of the fully filled bag, beyond an admissible tolerance, can only be cuased by an unintensional and undesired change in the mixture. That therefore eliminates complaints.

The apparatus of the invention can be used as a control means not only for filling bags or sacks on the basis of the volume principle but also in regard to filling machines which operate in accordance with the gravimetric process. In the case of filling machines which operate on a gravimetric basis, the flow or stream of filling material is interrupted as soon as the bag or sack to be filled reaches a predetermined reference weight. For that purpose, the actual weight is ascertained and, as soon as that weight is the same as the reference weight, the filling operation is terminated. When filling bags or sacks, it happens occasionally that a bag which is hanging on the filling nozzle of the filling machine bursts.

The unfilled amount of filling material still to be introduced into the bag or sack is then blown into the area around the filling machine. That results in the operating personnel being subject to extraordinary trouble and strain, as well as resulting in the area around the machine being fouled. If the apparatus of the invention is installed as an accessory apparatus, besides establishing the actual weight, it can additionally detect increase in weight. If such increase no longer occurs, prior to reaching the reference weight, or if it occurs only to a slight degree, that can be taken as a signal that a bag has burst and the stream of filling material can be immediately interrupted.

It may also happen that a bag or sack to be filled is not fitted onto the filling nozzle in the proper fashion, so that only a part of the stream of filling material goes into the bag, with the rest passing into the area around the machine. In that case, the detected rate of increase in weight will be below the usual value. That can also be taken as a signal for cutting off the stream of filling material. The use of the apparatus as a control device in relation to machines which operate on the basis of the gravimetric principle is particularly advantageous as that process is predominantly used for filling materials in dust or finegrain conditon.

The invention is diagrammatically illustrated by way of example with reference to the accompanying drawing, in which: Figure 1 is a graph showing the detected actual weight of a bag to be filled, weight G being shown in the ordinates and filling time t shown in the abscissae; Figure 2 shows differentiation of the curve shown in Fig. 1, wherein the increase in weight per unit of time, dG/dt, is shown in the ordinates and time is shown in the abscissae; and Figure 3 shows a view of part of an embodiment of a turbine-type packaging machine, to be operated in accordance with the method of the invention.

As can be seen from Fig. 1, filling of a bag begins at the point of intersection of the abscissae and the ordinates. Consequently, the weight curve firstly rises in a straight line and then goes into a curve as soon as the bag or sack is filled to a substantial degree. As soon as the bag is completely filled, the weight curve extends parallel or approximately parallel to the abscissae, that is to say, the pitch of the curve is virtually zero. The filling operation is then concluded.

Fig. 2 shows the increase in weight in graph form. As will be clearly seen, the curve in respect of the increase in weight first extends parallel to the abscissae, that is to say, the pitch is zero, and it then falls very steeply towards zero. The cut-off time for the flow of filling material may be fixed in the region of the lower end of the falling curve.

Fig. 3 is a purely diagrammatic view of part of a filling machine for valve-bearing sacks or bags. A valve-bearing sack or bag (not shown) is fitted onto a filling nozzle 1 in a manner which is not described in detail herein, and is clamped firmly in position by means of a holder 2 which is disposed above the filling nozzle 1. The filling material is introduced into the bag from a bunker (also not shown) by way of a filling hopper, by means of a filling turbine 3. The filling turbine 3 is provided with a discharge tube 4, the free end of which is flanged to the filling nozzle 1. For the purposes of cutting in and cutting out the stream of filling material, the discharge tube 4 can be opened and closed respectively by a slider 6 which can be actuated by an actuat ing means 5 which is not described in detail herein.

The bag or sack to be filled, which hangs from the filling nozzle, co-operates in a man ner which is also not described herein with a load carrier 7 of which only part is shown.

The force produced by the sack or bag acts on a measuring means 8, the detailed features of which will not be described herein. The mea suring means 8 may comprise a measuring capsule or cell for detecting the respective actual weight, the signals of which are applied to a weight proportioning means for the pur poses of detecting the increase in weight. The evaluated measurement values are then used by way of control means (not described herein), for actuating the slider 6.

Claims

1. A method of filling bags comprising the steps of introducing filling material into each successive bag, detecting the increase in weight of the bag during the bag filling oper ation, continuously evaluating the measurement values and interrupting the filling stream of filling material as soon as no increase or only a slight increase in weight is detected, thereby to obtain filling of a uniform volume of filling material into each successive bag.

2. A method according to claim 1, in which the increase in weight is detected in analog or digital fashion.

3. Apparatus for filling bags comprising first means to introduce filling material into each successive bag, second means for detecting the increase in weight of the bag at small intervals in respect of time during the filling operation, third means for determining the respective difference between each measured value and the previously detected value, and fourth means to stop the filling operation as soon as no difference in weight is determined thereby to obtain filling of a uniform volume of material into each successive bag.

4. Apparatus according to claim 3, in which for the purposes of detecting the increase in weight, the bag is suspended on a load carrier, the second means comprises measuring means to detect the weight of the bag, associated with the measuring means is the third means in the form of weight proportioning means for feeding in signals obtained by the measuring means, and the fourth means comprises actuating means for cutting off the flow of filling material, and is controlled by the output signals of the weight proportioning means.

5. A method of filling bags as claimed in claim 1 and substantially as hereinbefore described.

6. Apparatus for filling bags substantially as hereinbefore described and illustrated with reference to the accompanying drawing.