A DEVICE IN A MINERAL WOOL PRODUCTION LINE

Abstract: The object of the invention to provide a mineral wool mat with a surface weight as constant as possible. The mineral wool is produced in a line, in which a mineral melt converted into fibres is collected so as to form a thin primary wool mat on a conveyor, which leads to a suspended swing tray conveyor (2) depositing the primary wool mat on a receiving conveyor so as to form a secondary wool mat comprising several layers. The object is achieved by providing the receiving conveyor (1) with means (4) for weighing a surface weight of the secondary wool mat (6) formed on the receiving conveyor (1) and by connecting the weighing means (4) through a regulator to a driving motor (5) of the receiving conveyor (1) for the control of the speed of the motor.

Description: A device in a mineral wool production line The present invention relates to a device in a mineral wool production line, in which production 'V 5 line a mineral melt converted into fibres is collect¬ ed so as to form a thin primary wool mat on a convey¬ or, which leads to a suspended swing tray conveyor depositing the primary wool mat on a receiving con¬ veyor so as to form a secondary wool mat comprising 10 several layers. In the manufacture of mineral wool, a mineral melt is converted into fibres by means of a spinning machine provided with a blow-off blowing the fibres formed into a fibre collecting chamber, while unde- 15 fibrated solidified small melt particles, called beads, are separated from the fibre. The formed fibre is collected on a conveyor so as to form a thin fibre mat, called primary wool mat, which is transported further to a suspended swing tray conveyor depositing 20 it on a slow moving receiving conveyor. Through this is formed a secondary wool mat comprising many lay¬ ers. The intention of pendulous deposition is to re¬ duce the variations in volume weight of the secondary 25 wool mat in order to provide an even wool distribu¬ tion across the breadth of the whole production line. The primary wool mat with a surface weight of 200 to 400 g per m 2 is deposited pendulously so as to form a secondary wool mat having usually at least six 30 layers on a receiving conveyor, which moves at a 90° angle towards the arriving wool mat and runs at syn¬ chronous speed with the subsequent line. In connection with a given product thickness, the volume weight or the surface weight is one of the 35 most important quality parameters to be kept within certain given limits at the manufacture. On account of the variations in the melt flow to the spinning machine, the fibre production varies per time unit and thus also the surface weight of the primary mat. The speed of the receiving conveyor is control¬ led in order to compensate for these variations in the primary mat, for which compensation have been used different measuring signals, such as power con- sumption of the spinning machine, underpressure in the wool collecting chamber etc., in order to obtain an early indication of changes in the momentary vol¬ ume of the fibre production per time unit. These aux¬ iliary signals are not absolute and there is no sta- ble connection between these signals and the fibre production. Attempts have been made to weigh the primary wool mat, but owing to the low surface weight and the high speed of the primary mat, a weighing accuracy better than ±5 % cannot be reached, and therefore it is not possible to control the speed of the receiving conveyor in such a way that an appreciably better accuracy of the surface weight of the pendulously de¬ posited wool mat would be reached than when weighing the primary wool mat. Another known method is to weigh the pendulous¬ ly ready-deposited secondary wool mat and to regulate the speed of the receiving conveyor by means of pre¬ viously mentioned auxiliary signals, which are cor- rected by means of the surface weight signal from the pendulously deposited wool. A subsequent weighing of the deposited wool mat has a rather long time delay, till it can give a cor¬ rection signal to a surface weight regulator, whereby several metres of deposited wool mat can have an in- correct surface weight. Normally it is expected that a surface weight accuracy of ±3-4 % can be reached by above regulating methods. Moreover, for starting and stopping the fibre production or the primary wool mat, a sophisticated computer programme is required so as to calculate when the primary wool mat is deposited on the receiv¬ ing conveyor so that this can start and stop at the correct moment to avoid a too big accumulation of wool or an idle running of the receiving conveyor. The object of the invention is to provide a new device, by means of which above drawbacks can be avoided and a higher accuracy of the surface weight of the pendulously deposited secondary wool mat can be achieved. The device according to the invention is mainly characterized in that the receiving conveyor com¬ prises a portion positioned substantially below the suspended swing tray conveyor and provided with means for weighing the surface weight of the secondary wool mat formed on said portion and that the weighing means are connected through a regulator to a driving motor of said portion in order to control its speed in such a way that, in spite of variations in the surface weight of the primary wool mat, a secondary wool mat with an accurately constant surface weight is obtained. The speed of the portion of the receiving con¬ veyor weighing according to the invention can be reg- ulated in such a way that the surface weight of the pendulously deposited wool mat is all the time kept constant on an adjusted level with an accuracy better than ±1 %. According to a preferred embodiment of the in- vention, the weighing portion of the receiving con- veyor, i.e. the so-called weighing conveyor, is in a mechanically balanced way suspended from below the suspended swing tray conveyor so that the point of suspension will be on the rear side of the middle line of the suspended swing tray conveyor. The front portion, i.e. that portion of the weighing conveyor in which the pendulously deposited wool mat is fed forward to subsequent conveyors taking it further to a tempering furnace, is suspended from weight sensing load sensors, which will thus sense the weight of the pendulously deposited wool mat only and be irrespec¬ tive of the own weight of the weighing conveyor. In the construction suggested, the own weight of the whole weighing conveyor is appr. 400 kg and the weight of the wool mat maximally appr. 30 kg and minimally appr. 4 kg. The load sensors have a maximum accuracy of 0,1 % and can in above cases be chosen for a measur¬ ing range of 0 to 40 kg, whereby the measuring accu- racy, even in connection with the lightest wool mat, will be ±1 % instead of ±10 %, if the whole weighing conveyor were supported by load sensors. By regulating the speed of the weighing con¬ veyor in such a way that the weight is kept constant thereon, a deposited wool mat with constant surface weight is all the time fed onward so that the speed corresponds to the wool amount fed down on the weigh¬ ing conveyor from the swing tray, irrespective of • variations in the surface weight of the primary mat coming from the suspended swing tray conveyor. With the lowest surface weight of about 2 kg per m 2 of the pendulously deposited wool, mat, exposing the load sensors to a weight of about 4 kg, the weighing conveyor and the subsequent conveyors move at a maximum speed of about 20 m/min or 0,33 m/s. A 10 % change in the surface weight, which is approxi¬ mately 300 g per m 2 in the primary wool mat, is sensed by the load sensors in 1 second as an error of about 1,5 % and in 3 seconds as an error of about 5 % in order to come out in 6 seconds as an error of fully 10 % in the surface weight of the pendulously depos¬ ited wool, if the weighing conveyor has a constant speed. By letting a regulator control the speed of the weighing conveyor immediately when the measuring sen- sors sense an error in the surface weight, in order to eliminate the error in the weight of the deposited wool mat, it is possible to control the speed by a simple PID regulator so that the variations in the surface weight are kept within ±1 %, within a length of 0,5 m of the pendulously deposited wool mat, which cannot be achieved by previously known and described methods. If the primary wool mat comes to an end, the load sensors will sense within one second in above cases that the pendulously deposited wool mat has become 15 % too light and can give a signal for stop¬ ping the weighing conveyor so that no greater distur¬ bance arises in the surface weight of the pendulously deposited wool mat. When pendulous deposition of a primary wool mat starts again, the weighing conveyor can be run up to the correct speed quickly, when the load sensors sense that the weight corresponds to the surface weight adjusted. The method of weighing the wool mat directly under the swing tray on the weighing conveyor allows to compensate for a change in the volume weight of the primary wool mat while the secondary wool mat is formed, whereby the variations in the volume weight thereof can be kept within very narrow tolerances. A preferred embodiment shown schematically in the enclosed drawing will be described in greater detail in the following. The drawing shows a lateral view of the lower end of a suspended swing tray conveyor of the produc¬ tion line and the subsequent receiving conveyor. The suspended swing tray conveyor is designat¬ ed 2 in the drawing. The receiving conveyor comprises a weighing conveyor 1 positioned substantially below the suspended swing tray conveyor 2, a battery 7 of wheels and a subsequent line conveyor 8. The middle line of the swing motion is designated 2a and the end lines of the motion, i.e. edges of the primary wool mat, 2b. The weighing conveyor is suspended from a cross-formed spring 3 behind the middle line 2a of the swing motion on both sides of the conveyor in such a way that it is almost fully balanced mechani¬ cally. When the conveyor is empty, load sensors 4 positioned between the cross spring 3 and the outlet end of the conveyor, preferably one of these sensors also positioned on each side, shall only sense a tare load of appr. 20 % of the measuring range of the load sensors, which load is tared away in the weighing electronics. The weighing electronics gives a control signal to a regulator, which is not shown in the drawing, but controls the speed of a motor 5 driving the weighing conveyor so that the weight of the depo¬ sited wool mat, sensed by the load sensors 4 along the distance between the cross spring 3 and the end wheel of the weighing conveyor at the transition to the subsequent battery 7 of wheels, is kept constant all the time. The load sensors 4 are preferably posi¬ tioned at least substantially at the place where the secondary wool mat 6 has reached its final thickness, thus preferably at or at the end of the weighing con- veyor 1, before the battery 7 of wheels. However, it is also possible to carry out the weighing earlier. The subsequent line conveyor 8 and the battery 7 of wheels are driven by a separate motor synchronously with the motor 5 driving the weighing conveyor 1. The motor 5 is attached to the frame of the weighing con¬ veyor 1. The frame 9 to which the cross spring and the load sensor means are fastened is kept at a con¬ stant height by a support 10 at the end which is sit- uated closer to the suspended swing tray conveyor, while a device 11, e.g. a hydraulic cylinder, can lift or lower the other end of the frame 9, which also supports the battery 7 of wheels and one end of the subsequent line conveyor 8. The drawing shows the weighing conveyor in its lowest adjustment position, i.e. adjusted for the slowest speed and the highest surface weight of the pendulously deposited wool mat 6. The inclination of the frame 9 is adjusted by means of the device 11 so that the upper surface of the pendulously deposited wool mat 6 is parallel to the lower edge 12 of the suspended swing tray con¬ veyor 2. The pendulously deposited wool mat 6 will be about 80 cm thick in the lowest adjustment position shown in Figure 1 and about 15 cm in the highest ad- justment position, by means of which adjustment the weighing conveyor 1 moves at its highest speed.

Claims: Claims : 1. A device in a mineral wool production line, in which production line a mineral melt converted into fibres is collected so as to form a thin primary wool mat on a conveyor, which leads to a suspended swing tray conveyor (2) depositing the primary wool mat on a receiving conveyor so as to form a secondary wool mat comprising several layers, c h a r a c - t e r i z e d in that the receiving conveyor comprises a por¬ tion (1) positioned substantially below the suspended swing tray conveyor and provided with means (4) for weighing the surface weight of the secondary wool mat (6) formed on said portion (1) and that the weighing means (4) are connected through a regulator to a driving motor (5) of said portion (1) in order to control its speed in such a way that, in spite of variations in the surface weight of the primary wool mat, a secondary wool mat (6) with an accurately constant surface weight is obtained. 2. A device according to claim 1, c h a r ¬ a c t e r i z e d in that the weighing portion of the receiving conveyor consists of a weighing con¬ veyor (1), whereby the receiving conveyor further comprises a battery (7) of wheels and a subsequent line conveyor (8). 3. A device according to claim 1, c h a r - a c t e r i z e d in that the weighing means (4) are positioned at least substantially at the place where the secondary wool mat (6) has reached its final thickness. 4. A device according to claim 2 or 3, c h a r a c t e r i z e d in that the weighing means (4) are positioned substantially at or at the outlet end of the weighing conveyor (1). 5. A device according to any of the claims 2 to 4, c h a r a c t e r i z e d in that the weighing conveyor (1) is suspended in a mechanically balanced way, in order to minimize the effect of its own weight. 6. A device according to claim 5, c h a r¬ a c t e r i z e d in that cross springs (3) on each side of the weighing conveyor (1) form suspension devices. 7. A device according to claim 5 or 6, c h a r a c t e r i z e d in that the middle line (2a) of the swing motion of the suspended swing tray conveyor (2) lies between the suspension devices (3) of the weighing conveyor (1) and the outlet end of the weighing conveyor, preferably closer to the sus¬ pension devices (3) than to the outlet end.

Inventors: LAUREN HENNING, LAUREN, HENNING
Applicants: PAROC OY AB
Application year: 1992
Main classification: C03B37
IPC codes: D04H1