DE19756328C2 - Hydraulic tensioning device for belt conveyor - Google Patents

Abstract

The most reliable moving tensioners for belt conveyors are weight-loaded. However, if the use of such a weight-loaded tensioning device is not possible for specific spatial, safety-related or structural reasons, external energy sources are used. In order to be able to achieve a similarly reliable functional effect as with weight-loaded devices with a hydraulic tensioning device with simple means, one or more tensioning cylinders (8) which are functionally connected to the tensioning drum (6) are integrated into a hydraulic system in such a way that both short-term pressure differences within one Tolerance range and pressure differences beyond this tolerance range are automatically compensated. To ensure that the belt conveyor functions continuously and to avoid damage, these pressure corrections must be carried out quickly. This is achieved by the following technical requirements: DOLLAR A Z The hydraulic unit is installed in the immediate vicinity of the clamping cylinders (8) in order to achieve short switching distances. DOLLAR A Z To compensate for sudden, low pressure fluctuations, a pressure accumulator (13) designed as a gas spring is provided. DOLLAR A Z To compensate for pressure fluctuations beyond a larger specified tolerance range, if the pressure drops, the pump (15) is automatically activated by a pressure switch (16) until the belt pretension ...

Description

The invention relates to an automatically acting hydraulic tensioning device arranged in the lower strand of a belt loop Belt conveyor, with the at least one hydraulic tensioning element either a constant or one according to the respective load on the belt conveyor Tension can be achieved and changing Belt tension due to internal and external influences a safe and fast Correction or change is possible.

The most reliable movable tensioners for belt conveyors are weighted. The tension weight used is always one constant tractive power functionally and equal to ensure the the pretension required by calculation automatically stretches the belt. However, if from specific spatial, security or constructive reasons the use of such a weight-loaded Tensioning device is not useful or possible, mainly come electrically, pneumatically, hydraulically or electrohydraulically driven for Commitment. In general, it should be noted that with a comprehensive assessment important application criteria such as functional reliability, reliability, response time, Costs and technical effort compared to the weighted Tensioner also disadvantages have to be accepted. An advantage of these tensioning devices, which are additionally fed with external energy must, however, is that with them different clamping forces are reachable.

In order to ensure the safe operation of a belt conveyor Belt pretensioning force must be maintained during the entire operation various manually or automatically operated devices are known. them What is common is that the current load situation is based on a striking Measured size on a significant component, recorded the size and with a, compared by an upper and a lower target range an increase or decrease when a limit value is exceeded  the belt pretensioning force is brought about by an actuating element until the Target range is reached again.

According to DD 216 431, this is a device for monitoring and controlling the Preload force of a belt conveyor known, in which two regardless of Belt conveyor biased monitoring devices, one with the permissible full load belt tension and the other with the required Idle belt tensile force are arranged on the belt conveyor, the Monitoring device for the permissible full load belt tension on the deflection and at the same time discharge drum, which corresponds to the area of the maximum belt tension, and the monitoring device for the required idle belt tensile force at the Tension drum, which corresponds to the area in which the only when idling Idle belt tensile force occurs as a maximum value, are arranged and these Monitoring devices are in operative connection with switching devices. This device is made movable by means of a self-drive Clamping device completed.

The conveyor belt is placed on the tensioning drum using this tensioning device the necessary idle belt tension is tensioned when not loaded Conveyor belt on the drive, the tensioning and the deflection drum almost the same belt tension available. However, the load changes when the conveyor belt is loaded Belt tension on these drums not in the same proportions, but it increases to the maximum value at the maximum load on the deflection drum while on the opposite, at the beginning of the conveyor arranged tension drum falls to the minimum value. The pulley side monitoring device for the full load belt tension is set so that the switch assigned to it when the maximum is exceeded Belt tension responds. In contrast, the tension drum side Monitoring device for the idle belt tensile force tuned so that you assigned switch when the maximum idle belt tensile force is exceeded appeals. Thus, a further increase in the clamping force is achieved by both switches avoided.

According to DD 221 436, there is also a process for process size-dependent Tension control of belt conveyors known, in the case of several Conveyor sections measuring devices for belt loading, belt slip and  the belt tensioning force is provided and the measured values thus determined in one Computer evaluated according to a program and using a Control device the belt tension is changed if necessary. there depending on the loading of the conveyor belt with the material to be conveyed Tension is determined and adjusted, which is just necessary to get one to ensure safe operation of the system. Through this Belt tension conveyors can be controlled by process sizes operate in a manner that is gentle on the wear.

Another control device for tensioning a belt conveyor in the underground mining and tunneling is known from DE 38 11 393. With her it will Belt strap during the start-up phase and continuous operation Pneumatic cylinder clamped. So that those occurring in underground operations abrupt loads on the belt conveyor not over the tension cylinder the pneumatic system are transferred back, a check valve is provided. For quick pressure equalization is between the clamping cylinders and the Non-return valve positioned a pressure relief unit.

From the patent DE 35 31 552 C2 is a hydraulic Tensioning device for belt conveyor known, in which the tension cylinder in Structure of the belt conveyor between the upper and lower run are arranged. Through this tensioning cylinder the tensioning pulley becomes the same time The pulley is tensioned with the intended force. To the tension pulley in this Able to hold sufficiently stable telescopic beams that are attached to the Belt framework are connected, extended in the tensioning direction and through Locking devices kept constant in the clamping position. If the Conveyor belt has stretched so much that the existing tension for one proper operation is no longer sufficient, this process of Retensioning by means of the tension cylinders and the locking of the beams repeated.

A hydraulic belt tensioning device with tension levels depending on the process size is known from the patent AT 368 469. She doesn't work around the facility to claim more than necessary when the conveyor belt is loaded in the Persistent operation with an almost constant clamping force. When starting and Braking the band, however, is the tension force against this Normal value increased by approximately 50% and by approximately when the system is at a standstill 25% reduced. For this purpose, a hydraulic system is provided in which a constant pressure is generated by a hydraulic pump. This pressure is the one Maximum system pressure. It is constantly in the system during operation Piston chamber of the tensioning cylinder and corresponds to the belt tensioning force for the Start-up and braking of the belt in the order of approximately 50% above the predetermined normal value is required. During normal operation of the Plant, the steady state with a loaded conveyor belt, is in the Piston rod space of the clamping cylinder is the same compared to the piston space large back pressure generated. Due to the smaller size of the piston rod A force difference arises on the surface on the side of the piston rod space. she is dimensioned so large that the predetermined for the steady-state operation of the system Normal clamping force is reached. The control of the pressure in the clamping cylinder is done by pressure control valve, which is hydraulically controlled by its own control circuit is piloted. When the system is at a standstill, the back pressure in the Complete piston rod space by actuating the relevant valves reduced and the pressure in the hydraulic system by about 25% of the Normal value reduced.

The solutions used as prior art above require all based on the method used or the one used provided technical means a certain response time. That is why you are not suitable for use in belt conveyors where one quick response to suddenly changing conditions is required. The especially applies to belt conveyor systems that are under high load, relatively have short conveyor lengths, work with a high conveyor speed and are subject to high dynamics.

The invention has for its object to provide a simple, functional structure, automatic and reliable hydraulic clamping device for Belt conveyor to create either constant Belt pretensioning force or to certain load situations in stages  adjusted required belt pretensioning forces can be achieved on the one hand to enable a slip-free drive and, on the other hand, an unnecessary one Avoid overloading the conveyor system. All should occurring operating situations, among other things a sudden Result in a reduction or increase in the pretensioning force, automatically a quick correction of the preload to the nominal value the hydraulic system may be possible.

The task for a hydraulic tensioning device for belt conveyor will be solved by the combination of known features according to the first claim. The for the Belt conveyor required pretension force introduced by tension cylinder and in amount by automatic detection, evaluation and immediate Correct the specified pressure in all operating conditions. This will overload or overdimension the Conveyors avoided.

When using at least two clamping cylinders, one of them fed common line. This is in the annulus of the Clamping cylinders each at the same pressure. The existing pressure is on Conveyor control panel displayed. The pressure range and thus the The working range is within the tolerance range specified for the nominal pressure. As soon as the pressure in the annulus of the clamping cylinder drops, which is a decrease the belt pretension means the pressure reduction through the pressure accumulator eliminated, in which the reservoir automatically replenishes hydraulic oil.

If, on the other hand, the pressure drops below the tolerance value, this is caused by the Pressure switch detected and the pump activated, which the system back on Pump up nominal value. When the nominal pressure is reached again, the Pressure switch one contact and the pump is switched off again.

In the opposite case, when the pressure increases and the belt tension increases, the pressure relief valve speaks at a pressure above the Tolerance value on and the excess hydraulic oil splashes over this. This extreme case will mainly only occur when the conveyor is braked.  

In normal operation there are only small movements and small movements associated with them Pressure fluctuations, which are automatically compensated by the pressure accumulator become available.

The tensioning device designed and functioning in this way works automatically without additional measuring, control and regulating circuits.

With this hydraulic tensioning station, the advantageous properties a movable weight clamping station with constant clamping force, relatively long span and automatic response to Maintain changes in length of the webbing. Negative characteristics of a Movable weight clamping station with constant clamping force like the larger one Inertia of the system in the event of sudden changes or crashes Tensioning masses in the event of a belt break occur with this movable weight tensioning station constant clamping force not.

By using the pressure accumulator and the arrangement of the Hydraulic unit and the pressure accumulator in the immediate vicinity of the Clamping device will respond quickly to the clamping device Corrections or changes in the pretensioning force achieved. Advantageous embodiments of the invention are the subject of Subclaims.

If for different operating conditions such as starting and Decelerate the conveyor or deviate from the horizontal conveying path Rising or falling directions achieved these adjusted clamping forces should be, this can be due to the design of the hydraulic system two or more pressure levels can be achieved.

Further details and advantages of the subject matter of the invention emerge from the following description and the associated drawings, in which a preferred embodiment is shown. Show it:

Fig. 1 is a schematic representation of the web guide of a belt conveyor with a clamping device,

Fig. 2 is an automatically acting hydraulic clamping device in a side view for schematically illustrated in Fig. 1 webbing conveyor,

Fig. 3 is a hydraulic circuit diagram for a constant pressure system of the clamping device with two clamping cylinders,

Fig. 4 is a hydraulic circuit diagram for a constant pressure system of the clamping device with a clamping cylinder and

Fig. 5 is a hydraulic circuit diagram for a two-stage pressure system of the clamping device with two clamping cylinders.

In Fig. 1, the belt guide of a belt conveyor with two-drum head drive and direct ejection and with a tensioning device is shown schematically. The conveyor belt 1 is driven by the drive drums 2 and 3 , which are also deflection drums. Another, non-driven deflection drum 4 is located at the beginning of the conveying path on the side of the conveyed goods. The direction of movement 5 of the conveyor belt 1 is indicated by an arrow. The belt is tensioned in the lower run of the belt conveyor in a tension loop by the tension drum 6 . The tensioning direction 7 of the conveyor belt 1 shows another arrow. The tensioning drum 6 and conveyor belt 1 shown in broken lines represent a tensioning state with a tensioning path, as is required, for example, in the case of prolonged operation after belt stretching.

The tensioning device works hydraulically. Their constructive structure is shown in Fig. 2. The drawing shows a hydraulic clamping cylinder 8 . He is in pin joints on the one hand over the housing base 8 a with the belt structure 9 and on the other hand through his piston rod 8 b in the piston rod head 8 c with a moving carriage 11 movable along a guide 10 either directly or via a region of the clamping path predetermined by the stroke of the clamping cylinder 8 changing coupling element 22 connected. The tensioning drum 6 is mounted on the frame of the tensioning carriage 11 . Instead of the tensioning carriage 11 , two sliding blocks can also be provided, which are supported on both sides directly on the axis of the tensioning drum 6 . The guide 10 on the belt stand 9 is then to be designed accordingly. When the tensioning drum 6 is tensioned, the tensioning cylinder 8 generates a sufficiently large tensile force.

In order for the hydraulic system to react as quickly as possible to changes in the belt tension, three technical conditions must be met:

• - The hydraulic switching paths must be short.
• - Since hydraulic oil is not compressible, there must be an additional option be created to sudden, external changes in the Hydraulic system to respond through elasticity.
• - The actual belt tensioning force must be constantly monitored and under or Exceedings must trigger impulses for automatic regulation become.

The first condition is met by the arrangement of the hydraulic unit 12 in the immediate vicinity of the tensioning device 7 . As a result, the hydraulic system manages with short lines.

The fulfillment of the second and third conditions is shown on the basis of the hydraulic circuit diagram according to FIG. 3 and explained in more detail below. This drawing shows a first embodiment variant of a hydraulic belt tensioning device with a constant pressure system and two tensioning cylinders 8 arranged parallel to one another, which are connected directly to the axis of the tensioning drum 6 in an articulated manner. As described above, the tensioning drum 6 can be guided by sliding blocks or by a tensioning carriage 11 . In the hydraulic circuit diagram, the symbols and designations are used for the individual functional elements, as they are binding for such circuits and disclose the principle of the circuit to the person skilled in the art in this field. This eliminates the need for extensive explanations of these functional elements and how they work in the hydraulic system. The hydraulic circuit diagram for the tensioning device is structured as follows: the annular spaces 8 d of the two tensioning cylinders 8 are connected to a pressure accumulator 13 without leakage oil and their piston spaces 8 e to a tank 14 . In terms of its functional design, this pressure accumulator 13 is designed as a bladder accumulator and can thus automatically compensate for pressure differences in a very short time.

The pressure of the hydraulic oil previously determined for the necessary belt tensioning force is monitored by a pressure switch 16 and additionally secured against overload by a pressure limiting valve 17 . This pressure limiting valve 17 also takes over the monitoring function for the maximum clamping pressure occurring and thus the limitation of the maximum clamping force. The third condition for a rapid reaction of the hydraulic system of the belt tensioning device is thus also fulfilled.

The two flow control valves 18 and 19 installed in opposite directions between the pressure accumulator 13 and the annular spaces 8 d of the two clamping cylinders 8 ensure a vibration-free system.

The pump 15 is only required for the initial filling and the refilling of the hydraulic oil. This refilling may be necessary due to hydraulic oil losses, which occur either due to leakage or the hydraulic oil being sprayed off via the pressure relief valve 17 when the overload safety device responds when the load is too high.

Since both clamping cylinders 8 are fed by a common line, the same pressure is present in their annular spaces 8 d.

The existing pressure is used to control the conveyor control panel displayed.

The operation of this hydraulic tensioning device constructed in this way is the following:

The different forces that act on the tensioning drum 6 , depending on the operating state, cause corresponding pressure changes in the two cylindrical annuli 8 d. With increasing pressure in the hydraulic system, the hydraulic oil is pressed against the gas spring in the pressure accumulator 13 and the gas is thus compressed. If, on the other hand, the pressure drops as a result of decreasing forces, the gas spring relaxes and presses the hydraulic oil back into the annular spaces 8 d of the two clamping cylinders 8 . The pressure changes slightly depending on the memory size, but is still within the desired pressure range. If, on the other hand, the pressure falls below the lower limit of the tolerance, this is detected by the pressure switch 16 and the pump 15 is activated. When the nominal pressure is reached again, the pressure switch 16 makes a contact and the pump 15 is switched off again.

If the pressure increases and the belt pretension increases, which can occur when the conveyor brakes, the pressure relief valve 17 responds when the upper limit of the tolerance of the pressure is exceeded and the excess hydraulic oil is fed back into the tank 14 , it splashes over the pressure relief valve 17 onwards.

A compared to the first simplified second variant of the embodiment example is shown in Fig. 4. Since only one clamping cylinder 8 is used, the hydraulic circuit diagram can be carried out easily. The clamping cylinder 8 is articulated by a bolt 20 to the clamping carriage 11 used here. The tensioning carriage 11 itself can be moved on the belt stand 9 by means of its wheels 21 along the guide 10 consisting of rails. The details are shown in the drawing of FIG. 2.

A hydraulic circuit diagram for a two-stage pressure system of the tensioning device with two tensioning cylinders 8 is shown as a third embodiment variant according to FIG. 5. Such a solution can be used where the conveyor belt 1 of the belt conveyor is to be tensioned when starting with a higher force than in the later continuous conveying process in order to avoid unnecessary wear of the conveyor belt 1 and the linings of the drive drums 2 and 3 due to slippage.

The structure and function are basically the same as in the constant pressure system. However, in order to be able to set a second, lower pressure level, hydraulic oil is drained to the tank 14 via a switching valve 23 and a flow limiting valve 24 until the pressure switch 25 makes contact. The pressure switch 16 is no longer in operation. With the contact of the pressure switch 25, the switching valve is switched to another position 23, and hence is no longer the pressure relief valve 17 but the pressure-limiting valve 26 active.

With the "band stop" command, the switching valve 23 is reactivated and at the same time the pressure switch 16 is activated and the pressure switch 25 is reactivated. Since the pressure switch 16 is set higher than the pressure switch 25 , its minimum contact responds immediately. With this contact, the pump 15 is activated until the maximum contact from the pressure switch 16 responds. The starting position for starting the belt conveyor again is thus established. The variable system can also be used for more than two pressure levels. In such a case, further hydraulic switching stages would be integrated into the hydraulic system in the manner described above. In a departure from the arrangement of the tensioning station described above with a tensioning drum 6 and a tensioning carriage 11 or two sliding blocks in a belt loop, the tensioning station can also be designed as a rear or drive station for belt conveyors. In these two latter arrangements, the clamping cylinders 8 can also be used as pushing elements instead of as pulling elements.

reference numeral

1

Conveyor belt

2nd

Drive drum

3rd

Drive drum

4

Deflection drum

5

Direction of movement of the conveyor belt

1

6

Tension drum

7

Clamping direction

8th

Clamping cylinder

8th

a housing foot

8th

b piston rod

8th

c Piston rod head

8th

d annulus

8th

e piston chamber

9

Band structure

10th

guide

11

Tension wagon

12th

Hydraulic unit

13

Pressure accumulator

14

tank

15

pump

16

Pressure switch

17th

Pressure relief valve

18th

Current limiting valve

19th

Current limiting valve

20th

bolt

21

wheel

22

Coupling link

23

Switching valve

24th

Current limiting valve

25th

Pressure switch

26

Pressure relief valve

Claims (3)

1. Hydraulic tensioning device for belt conveyor, which works automatically with a constant pre-tensioning force for all operating conditions, so that the different belt strains in the individual operating conditions are automatically compensated for as in a weight-loaded tensioning device, consisting of

• - a tensioning drum ( 6 ) arranged in the lower run of the belt conveyor in a belt loop and connected on both sides with a sliding block or a tensioning carriage,
• - A right and left slide guide or rail, along which the tension drum ( 6 ) in the belt stand ( 9 ) is longitudinally displaceable or movable,
• - At least one hydraulic tensioning cylinder ( 8 ) articulated between the belt stand ( 9 ) and the tensioning drum ( 6 ),
• - A hydraulic line connecting the tank ( 14 ) filled with hydraulic oil and the annular space ( 8 d) as the pressure space of the tensioning cylinder ( 8 ) with a pump ( 15 ) which is functionally connected to a pressure switch ( 16 ),
• two flow limiting valves ( 18 and 19 ) integrated in this hydraulic line with opposite directions of action,
• - A pressure accumulator ( 13 ) connected to the hydraulic line leading from the pump ( 15 ) to the clamping cylinder ( 8 ) near the clamping cylinder ( 8 ),
• - One from the piston chamber ( 8 e) of the clamping cylinder ( 8 ) to the tank ( 14 ) leading, almost pressure-free hydraulic line.

2. Hydraulic tensioning device for belt conveyor according to claim 1, characterized in that in the formation of the belt tensioning device as a two-stage or multi-stage pressure system for each additional, lower pressure stage, each with a switching valve ( 23 ) and a flow limiting valve ( 24 ) are provided, through which After switching off the pressure relief valve ( 17 ) designed for a higher working pressure, a lower pressure and thus tensioning level can be continuously achieved depending on the belt load in the steady state and after switching off the belt conveyor drive the higher pressure level required for starting is automatically applied. 3. Hydraulic tensioning device for belt conveyor according to claim 1, characterized in that between the tensioning cylinder ( 8 ) and the tensioning drum ( 6 ) or with the tensioning drum ( 6 ) receiving tensioning carriage ( 11 ) one or more extending coupling members ( 22 ) can be arranged .