GB2140759A

GB2140759A - Chain-tensioning device for the conveyor chains of a drag chain conveyor

Info

Publication number: GB2140759A
Application number: GB08410344A
Authority: GB
Inventors: Walter C Egger
Original assignee: VT Verpackungstechnik Zurich
Current assignee: VT Verpackungstechnik Zurich
Priority date: 1983-06-02
Filing date: 1984-04-19
Publication date: 1984-12-05
Also published as: DE3416288A1; CH659048A5; GB8410344D0; ZA842915B; GB2140759B; FR2546859B3; FR2546859A3; DE3416288C2

Abstract

The chain-tensioning device contains a mounting plate (7), longitudinally displaceable on the casing (10) of the chain drive, for the chain wheel (2) at one end of the conveyor path. For the production of the chain-tensioning force a pneumatic or hydraulic power cylinder (15) is provided which acts through a linkage (12, 13, 14) on the mounting plate (7). By means of this power cylinder (15) the chain-tensioning force can be accurately adjusted and kept constant for determined load conditions. The end of the useful tensioning path is sensed by position detector (22) and indicated by an alarm device (23). The attention of the maintenance personnel is thereby drawn to the need to shorten or replace the conveyor chain (1). <IMAGE>

Description

SPECIFICATION Chain-tensioning device for the conveyor chains of a drag chain conveyor For the conveying of loose articles, for example bottles, in certain fields of application, e.g. in bottle-filling machines, use is made of drag chain conveyors which have two conveyor chains spaced apart and running in the same direction, oppositely directed carriers bounding a conveying channel being disposed on these chains.

A particular problem in such drag chain conveyors is the elongation of the conveyor chains under continuous load. This necessitates repeated retensioning and the occasional shortening of the conveyor chains,. If the chain tension is insufficient, the slack conveyor chains may damage the guides in the chain track and in extreme cases may run onto the teeth of the chain wheels, which usually results in damage to the conveyor chains or even in their destruction.

In order to achieve a long life for conveyor chains, it is therefore necessary to monitor the chain tension in an appropriate manner. Experience shows that the increase in length of a conveyor chain of ordinary commercially available types is relatively great (about 0.3%) in roughly the first 100 hours of operation.

Subsequently, during a lengthy period of operation the conveyor chain will stretch only to a slight extent. Increased stretching of the conveyor chain will occur again only with increasing wear of the chain, the chain pitch then beginning to vary so greatly that the conveyor chain must be replaced. Because of these varying stretching phases, which could not be determined accurately in terms of time, the'monitoring of chain tension in the manner customary hitherto and the checking of conveyor chains by maintenance personnel are very difficult. These checks are normally made only during the fixed stoppages of operation of the drag chain conveyor, which usually operates on a shaft basis.If the maintenance personnel do not make these checks sufficiently frequently and/or with adequate expertise, it may occur that a conveyor chain will fracture during the operation of the drag chain conveyor, and this, because of the possible consequences of an unintentional interruption of operation, must be avoided as far as possible. A lengthy stoppage of production, the need for premature replacement of conveyor chains, and/or the possible consequent damage to machines and to the articles being conveyed, as the result of an unexpected stoppage of the drag chain conveyor, may in certain circumstances give rise to considerable expense. There is consequently a need for more reliable monitoring of chains.

Hith'erto the chain-tensioning force has been adjusted by means of a chain wheel mounting adjustable longitudinally with the aid of a screw. With a manually operated tensioning device of this kind, however, the tension of a chain can only be adjusted roughly and cannot be adequately adapted to the load on the chain. Moreover, after an adjustment with the aid of the tensioning device, the tension of the chain will gradually decline with the elongation of the conveyor chain, until the next adjustment is made. Defects of this kind prevent optimal operation of the chain drive system, and this in turn has a detrimental effect on the life of conveyor chains.

The invention seeks to provide a chaintensioning device for the conveyor chains of a drag chain conveyor, with the aid of which the disadvantages indicated can be avoided.

According to the invention, for the production of the chain-tensioning force a pneumatic or hydraulic power cylinder is provided which is equipped with a position detector sensing the end of the useful tensioning path and cooperating with an alarm device.

This chain-tensioning device makes it possible, by selection of the pressure in the power cylinder, to adjust the chain-tensioning force as required and to keep it constant for determined load conditions. Even if the conveyor chains become longer, the chain tension will remain unchanged until the end of the useful tensioning path. In this end position the position detector will respond and operate the alarm device by means of a signal. The alarm signal warns the maintenance personnel to shorten the conveyor chains when the operation of the drag chain conveyor is next stopped, by removing one or more chain links and thus restoring the original chain length.

In order to prevent a breakdown even if the maintenance personnel do not notice the alarm signal, arrangements may be made for the long chain conveyor to be stopped automatically, after a predetermined delay time, as the result of an alarm signal. For this purpose the alarm device can, for example be connected by way of a time delay circuit to the devices for operating the drag chain conveyor.

The delay time can be so selected that the stopping of the drag chain conveyor is prevented before the end of an operating period (shift) and will occur only if the drag chain conveyor is restarted after a pause in operation and if the necessary shortening of the conveyor chains was not carried out during the pause in operation.

The power cylinder provided may also be a gas spring arrangement. An arrangement of this kind, with one or more gas springs, makes it possible for the chain-tensioning device to be operated independently of a pneumatic or hydraulic pressure source.

Particularly advantageous utilisation of the full capacity of the conveyor chains and hence more economical operation of the drag chain conveyor are achieved with a device for the automatic regulation of the chain-tensioning force in dependence on the load on the conveyor chains. Inappropriate chain-tensioning forces, such as may for example occur when changing over from partial load operation of the drag chain conveyor to full load operation, and in the reverse case, are thus reliably avoided.

The power consumption of the drive motors for the conveyor chains may be taken as the basis for the automatic regulation. However, torque and rotational speed transducers may also be provided for this purpose. The pressure required in the power cylinder for the correct chain-tensioning force will then be adjusted by the measured power, for example by means of a servo-controlled pressure regu lator. Automatic pressure regulation can also be achieved with gas springs.

One example of embodiment of the invention is illustrated in the drawing, which shows in longitudinal section the end of one of the two chain drives of a drag chain conveyor together with the chain-tensioning device, and also a diagram of the devices for monitoring the chain tension and automatic regulation of the chain-tensioning force.

The conveyor chain 1, shown in dash-dot lines, is guided at one end of the conveyor path over a chain wheel 2 which is displaceable along the conveyor path. Carriers are disposed in known manner on the conveyor chain 1; one such carrier 3 of conventional construction, which is fastened to a chain link 4, is shown in the drawing. The chain wheel 2 is mounted by rolling contact bearings 5 on a journal 6 forming part of a mounting plate 7. This mounting plate 7 is disposed for longitudinal displacement on the casing 10 of the chain drive by means of threaded bolts 8 and 9, the bolts being guided in a longitudinal slot 11 in the casing 10. A pull rod 12 acts on the bolt 9 and is connected by a crossbar 12 to the piston rod 14 of a diagrammatically indicated pneumatic power cylinder 1 5 producing the chain-tensioning force.

The pull rod 1 2 is guided axially in a support 16 mounted on the casing 10.

For the operation of the chain drive a controller 1 7 is provided, which controls the supply of current to the drive motor 1 8 for the chain drive and contains means for measuring the power consumption of the drive motor 18.

The measured power is transmitted in the form of a control signal to a servo-controlled pressure regulator 19, which is disposed in the compressed air supply pipe 20 to the power cylinder 1 5 and regulates the piston pressure in the latter and hence the chaintensioning force exerted on the chain drive through the pull rod 12.

At the end of the useful chain tensioning path the crossbar 1 3 on the pull rod 1 2 comes into contact with the sensor 21 of a position detector 22. As it responds, the latter transmits a signal to an optical and/or acoustic alarm device 23, which draws the attention of the maintenance personnel to the fact that at the next opportunity (stoppage of operation of the drag chain conveyor) the conveyor chain 1 must be checked and shortened or replaced. The alarm device 23 is connected to the controller 1 7 through a time delay circuit, which for example is incorporated in it, so that the alarm signal is transmitted with a time delay to the controller 1 7. After a predetermined delay time the chain drive can thus be automatically stopped as the result of an alarm signal.

Each of the two chain drives of a drag chain conveyor is preferably provided with a separate chain-tensioning device together with the appertaining control and regulating devices.

Claims

1. Chain-tensioning device for the conveyor chains of a drag chain conveyor, characterised in that for the production of the' chaintensioning force a pneumatic or hydraulic power cylinder (1 5) is provided which is equipped with a position detector (22) sensing the end of the useful tensioning path and cooperating with a an alarm device (23).

2. Chain-tensioning device according to Claim 1, characterised in that the power cylinder used is a gas spring arrangement.

3. Chain-tensioning device according to one of Claims 1 and 2, characterised in that a device (19) is provided for automatically regulating the chain-tensioning force in dependence on the loading of the conveyor chains (1).

4. Chain-tensioning device according to Claim 1, characterised in that the alarm device (23) is connected through a time delay circuit to the devices (17) for operating the drag chain conveyor, in such a manner that as the result of an alarm signal the drag chain conveyor is automatically stopped after a predetermined delay time.

5. A chain-tensioning device substantially as hereinbefore described with reference to, and as illustrated by the accompanying drawing.