WO1994029203A1 - Conveyor-belt scraper system - Google Patents

Abstract

A scraper (16) applies a blade of polyurethane (18) in scraping contact with an ore conveyor-belt (10) in a mine. A detector (29, 34) senses when the staples at a joint (23) in the belt (10) are approaching the blade (18), and signals the air actuation system (20) of the scraper to automatically cause the blade (18) to jump back momentarily. The scraper blade (18) is automatically eased back onto the belt (10) after the joint (23) has passed. The system is used when the blade (18) and associated components have enough inertia that the jerk from the passing joint (23) could cause damage. The system is used also in conjunction with sensors which detect an absence of ore on the belt, and/or when the belt (10) has stopped moving, and which signal a requirement to retract the blade from the belt (10).

Description

Title: CONVEYOR-BELT SCRAPER SYSTEM

This invention relates to scrapers for conveyor belts.

The conveyor belts to which the invention applies are typically of the kind used in mines for conveying crushed ore and the like. Often, the material that is to be scraped off the belt is caked onto the belt, and it is well known to be a difficult problem to keep belts clean on a continuous basis, day in, day out, over a long service period.

Recent developments in belt scrapers have made it possible to keep a scraper blade pressed against a belt with a heavy enough pressure to ensure high-performance scraping, and yet the scraper blade is highly conformable to the belt, and yet also the blade has a long service life. In the context of conveyor belt scrapers in mines, until recently a long service life has meant, if the scraper were performing effectively, at most a few weeks; now, a long service life is starting to mean a year or more.

This long service life places greater demands on the scraper mechanism, in that it would serve little purpose for the blade to last for a year if the scraper actuation mechanism would be needing repairs every few weeks. It is recognised that some aspects of scraper mechanism and operation that could formerly be ignored now need to be addressed.

One of the factors facing the designer of the scraper mechanism is the fact that a conveyor belt usually has at least one joint or junction. The seam at the junction, although the belt manufacturer makes every effort to keep the seam as unobtrusive as possible, nevertheless is thicker than the general thickness of the belt, and often the seam includes metal staples, clips, or other fasteners. As the seam traverses through the scraper, the blade of which is being pressed tightly against the belt, the seam therefore can give the scraper a sharp jolt. Repeated time after time over a long period, the shock loading caused by these jolts can have a deleterious effect on the scraper mechanism (and, of course, on the belt).

Another factor facing the designer is that when the belt is not actually conveying ore, the scraper is rubbing directly against the belt material. Often the scraper blade in fact wears away at a faster rate if the blade is pressed heavily against the belt when the belt is clean than when the belt is caked with debris; and again the belt is more vulnerable to being damaged by the scraper when the belt is clean.

Yet another factor facing the designer is the fact that belt scraper mechanisms are usually set up for operation with the belt moving in one direction. If the belt should stop, and especially if it should reverse, even if only under momentary roll-back conditions, the resulting reversal of forces can place undue strains on the scraper mechanism.

The invention provides a means for automatically retracting the scraper mechanism in response to a signal from a sensor. The sensor may be set up so as to detect, for example, the metal clips at a seam. Another example is a sensor that detects a sudden change in the thickness of the belt. Another example is a sensor that detects the absence of the sound of ore falling through a feed chute onto the belt. Another example is a sensor that detects whether the belt is moving at less than a certain speed, or when the belt is moving backwards.

In the invention, whatever the nature of the sensor and the source of the signal, the signal from the sensor is effective to cause the scraper mechanism momentarily to lose the force of activation: the mechanism may be arranged to make the blade actually jump clear of the belt, or it may be arranged just to relieve the pressure of the blade on the belt. Once the disturbance has passed, the scraper reverts, preferably automatically, to its normally activated status.

The period of time the blade stays retracted may be less than a second in the case where the belt retracts momentarily to clear the passing seam. In another case, it may be arranged that the scraper blade actuation mechanism is safety-interlocked with the conveyor belt drive, whereby the blade can only be forcefully applied to the belt when the belt is moving, and is moving forwards.

In some scrapers, the scraper blade is very light in weight. In this case the blade may be allowed to follow the change in thickness of the belt caused by the passing stapled-joint; the low inertia of the blade allows the blade to jerk and move quickly, whereby the jolt caused by the joint does not damage the blade. If the scraper blade is light enough to follow the thickness changes of the passing joint, the invention would not be required.

The invention provides a means for sensing when the joint is approaching, whereby the blade can be retracted before the joint reaches the blade. The invention is therefore of use when the blade, and its associated suspension and actuation systems, has a high enough inertia that the jolt caused by the passing joint would cause damage, at least over a long period.

It is becoming clear that the key to good scraping performance over a long service life is for the blade to be of a relatively soft material, which wears relatively quickly. The soft material conforms easily to the belt, and the scraping or cutting edge of the relatively soft material is constantly being renewed. Since the material wears quickly, and since the service life is long, a large quantity of blade material is required, which is heavy. Thus, the invention is most especially applicable to the case where the scraper includes a long length of relatively soft scraper blade material.

It may be noted that the scraped-off material is, as a general characteristic, highly abrasive. If the scraper is made of metal, the cutting edge of the scraper quickly becomes dulled, and it is not practically possible to make the scraper out of a material that is so hard that the blade retains its sharpness for more than a day or two. When the blade is soft and rapid- wearing, on the other hand, the cutting edge of the blade is constantly being renewed. Again, the invention is especially applicable to the case where the scraper includes a long length of relatively soft scraper blade material.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

By way of further explanation of the invention, exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Fig 1 is a diagram of a first system which embodies the invention, being a system for withdrawing a scraper blade from a moving conveyor belt;

Fig 2 is a diagram of a second system, which corresponds to Fig 1 ;

Fig 3 is an elevation of a conveyor belt scraper, a scraper blade of which is arranged for scraping contact with a moving conveyor belt, and which includes a means for withdrawing the blade from the belt.

The apparatuses shown in the accompanying drawings and described below are examples which embody the invention. It should be noted that the scope of the invention is defined by the accompanying claims, and not necessarily by specific features of exemplary embodiments.

Fig 1 shows a conveyor belt, of the type used for example in a mine to convey crushed mineral ore. The belt 10 is arranged to pass around a head pulley 12. The ore carried by the belt falls into a chute 14.

A residue of ore remains adhering to the belt. This residue may be a dust-like, which is relatively easily scraped off, or it may be consolidated and caked onto the belt and may be very difficult to scrape off. The residue adhering to the belt may be wet, dry, or moist; in all cases the residue is highly abrasive. Scraping the residue off the belt is, in general, a highly demanding task.

A scraper 16, having a blade 18, is arranged to scrape the residue from the return run of the belt. The blade is forced upwards against the belt by an actuation system, which in this case includes a pneumatic ram 20. It is desirable that the residue be scraped off the belt close to the head pulley 12, whereby the scraped-off material can pass straight into the chute 14.

The belt 10 includes a joint 23, which comprises metal (steel) staples or clips 25. Of course, different types of clips used to secure the joints of conveyor belts; typically, the clips are spaced 3 or 4 cm apart, and are 6 or 7 cm in length. The clips protrude 3 or 4 mm from the thickness of the belt.

Such a joint 23 going past the scraper blade 18 on a regular basis can be very damaging over a period of time. This is especially the case if the scraper is being pressed hard against the belt, and it is desired that the blade should be pressed hard if the scraper is to be effective. The jolt from the joint can cause pieces to be broken from the blade, or can distort the housing in which the blade is mounted, or can damage other components of the scraper and it actuation system. Also, it is possible for the clips to be damaged by the scraper blade.

Of course, the suspension system and actuation system of the scraper can cater for small variations in thickness of the belt, and can cater for the occasional lump of material adhering so firmly to the belt that the lump passes the blade; but the clips used at belt joints pose a substantial, threat, notwithstanding this capability, not so much because of the magnitude of the jolt delivered by the clips, but because the jolt is sudden, and is repeated regularly and often.

In accordance with the invention, a system for interrupting the actuation force on the scraper blade is provided. A pneumatic valve 27 is fitted with a trip arm 29, a roller of which bears against the upper side of the return run of the belt 10; that is to say, against the clean side of the belt. When the joint 23 passes, the trip arm 29 is forced upwards by the extra thickness of the belt, and activates the valve 27. Upon being activated, the valve 27 releases pressure from the line 30, which exhausts the ram 20, and withdraws the blade from the belt.

When the joint 23 has passed, the trip arm 29 returns to its normal position as shown in Fig 1 , and the line 30 is once more pressurised and the full actuation force on the scraper blade is resumed.

The positioning of the valve 27 should be such that the pneumatic ram 20 has time to exhaust sufficiently to allow the blade to move clear of the belt, or at least to withdraw far enough that the jolt from the joint is of no consequence.

Of course, while the scraper is clear of the belt, the scraper is not performing its function of scraping the belt. The blade should be actuated back onto the belt as quickly as possible after the joint has passed.

When the valve 27 is activated, the ram may be set to exhaust through the valve, or, if that is too slow, a conventional quick-exhaust valve 32 may be provided and the ram exhausts through that. Alternatively, the valve 27 may be set to pressurise a control line, which then activates a conventional five-port ram control valve. Alternatively again, the ram may be double acting, in which case the ram may be return- pressurised in order to force the blade clear of the belt quickly and cleanly. In some cases, where an air compressor is available close by for actuating the scraper, the designer can provide an interrupter system which dumps large quantities of compressed air, and he can therefore provide for rapid and vigorous withdrawal of the blade. In other cases however, especially where the scraper is pressed against the belt by means of gas pressure fed from a gas bottle, the designer should aim to waste as little of the pressurised gas as possible, and a more modest reduction in the blade actuation pressure is called for.

The trip valve 27 is located on the clean side of the belt 10. It would be unsatisfactory for the valve 27 to be on the dirty side of the belt, because, since the valve is positioned ahead of the blade 18, the valve might then be tripped by dirt on the belt.

In cases where the detector or sensor is to be positioned on the dirty side of the belt, a detector should be used which senses a feature other than mere thickness. In Fig 2, a proximity sensor 34 is provided. The sensor 34 is arranged to detect the proximity of the steel of the clips 25, for example by detecting the magnetism of the steel. The sensor 34 operates on electricity, and when activated the sensor is effective to issue an electrical voltage. This signal is passed, via suitable circuitry (not shown) to an electrically operated solenoid valve 35, which exhausts the ram 20 as in Fig 1. Of course, the system of Fig 2 is only of use when electrical power is available.

In cases where electrical power is indeed available, sensors or detectors may be provided for detecting other parameters. For example, a microphone may be provided, which is activated by the absence of the sound of ore falling into the chute 14.

One way in which the blade and/or the belt can be damaged is by pressing the blade hard against the belt when the belt is hardly moving, or is stopped, or is moving (slowly) backwards. Sensors can be incorporated into the belt, or into the pulleys etc associated with the belt, to detect when the belt is moving. For example, a movement sensor may be provided which detects the rotational speed (or absence thereof) and the rotational sense, of the head pulley 12. The output from this sensor can be used to dump air from the ram 20 when the head pulley ceases to maintain a predetermined forward speed. The movement sensor on the head pulley can be interlocked with the actuation system of the scraper, whereby the scraper cannot be actuated until the belt is moving at a substantial forward speed.

It will be understood that a particular system may include two or more detectors or sensors to provide for interruption of scraping, ie withdrawal of the blade from the belt, under different circumstances. Also, a manual over-ride of the interrupter system is useful for setting-up purposes.

Fig 3 shows an actual scraper 36, operating on a belt 38. The blade 40 of the scraper 36 is made of polyurethane, which is flexible, the flexible blade 40 being disposed in a spiral coil inside a housing 43.

The housing 43 is mounted on a suspension system, which includes a swing arm 45 pivoted at hinge point 47 to a fixed plate 49. The fixed plate 49 is welded or otherwise secured to the frame of the conveyor belt. An air actuator 50, in the form of an inflatable air-bag, urges the swing arm 45 and the housing 43 about the hinge point 47 so that the blade 40 is forced into scraping contact with the belt 38.

The pressure supplied to the air actuator 50 is controlled by means of a pressure regulator 52, the pressure setting of which is determined by the technician for optimum scraping under normal conditions. Once the technician has set the regulator, the pressure of the air supplied to the actuator 50 therefore remains substantially constant during operation of the scraper. The usual small variations in thickness of the belt are accommodated by the resilience of the pressurised air actuation system. The response of the swing arm, the housing, etc are sufficient to accommodate such small movements of the blade; that is to say, the components have a low enough inertia that they can physically follow such minor movements.

However, the gross movement of the housing required to accommodate the thickness change due to a passing stapled joint would be too much for the resilience and inertia of the suspension system. The designer should not allow the blade 40 to retract into the housing through the seal, as this would damage the seal. Accordingly, an interrupter system of the kind described with reference to Fig 1 or Fig 2 is provided in the pneumatic system, in order to allow the housing, and with it the blade, to perform the required gross retraction.

The interrupter system as described may be used not just when the actuation system is as described, but may be used alternatively with any type of actuation system for forcing a scraper blade against a belt, and may be used whether or not the actuation system includes a means, manual or automatic, for compensating or adjusting for wear of the blade.

The invention is particularly applicable to the actuation and adjustment system used in the Fig 3 design, however. The coiled polyurethane blade 40 is subject to relatively rapid wear: of the order of 1 or 2 mm per day during normal heavy- duty operation. Compensation for wear is provided by an automatic wear adjuster. The housing 43 is filled with a liquid, such as water, and a seal is provided between the housing and the blade 40. The presence of the liquid prevents the blade retracting into the housing. To compensate for wear of the blade, a compensatory charge of liquid is injected into the housing, in response to the accumulating wear of the blade.

The sensor (not shown) which signals the need for adjustment for wear measures the closeness of the approach of the housing to the belt. It is desirable that the housing should run close up to the belt, in order that the overhang of the blade out of the housing should be as short as possible; the blade, being flexible, might tend to buckle or fold over if the overhang were too large. The housing should preferably be kept within about 3 or 4 mm from the belt, and the adjuster system is set up accordingly. (Adjusting the scraper blade by injecting water into the housing is described in detail in patent application no GB 92/21426.1, filed 13 Oct 1992, to which attention is hereby directed.)

It may be noted that in Fig 3 the system for adjusting the blade to compensate for wear is independent of the system for keeping the blade actuated or pressed against the belt with a constant pressure. The actuation system is powered by supplying air pressure to the actuator: the adjustment system is powered by periodically injecting a make-up charge of water into the housing.

Thus, the air-operated actuation system may be maintained or interrupted without reference to the quantity of water in the housing; and equally, make-up water may or may not be injected into the housing, without reference to the pressure of the air in the actuation system.

The adjuster system seeks to maintain the overhang of the blade enough to keep the housing 3 or 4 mm from the belt. The adjuster sensor detects when the housing is approaching too close to the belt, and includes an injector (not shown) for injecting a charge of water into the housing when that happens. In case the adjuster system should malfunction, the apparatus includes a travel stop 54, which prevents the housing from actually touching the belt.

In the Fig 3 design, the interrupter system is effective to momentarily back-off the actuator system, not the adjuster system. The adjuster system remains unaffected by whether the actuation system has been interrupted and backed off. The invention however may be used in cases where the adjuster is either not separate from the actuator, or cases where the adjuster would be affected by backing off the actuator. In these cases, the designer should see to it that the (automatic) adjuster does not sense the gross backing-off movement as a requirement for adjustment, and try to compensate for that movement as if it were wear of the blade. This can be done by using the signal for interrupting the actuator also to temporarily disable the automatic adjuster.

As mentioned, the requirement to withdraw the blade from the belt can arise for other reasons, apart from accommodating a passing stapled-joint. For example, the sensor may be, as mentioned, a device for sensing the speed of the belt.

In these other cases, the sensor will generally be of the electrical type, in which the sensor requires to be supplied with a source of electrical power, and in which the signal issued by the sensor is in the form of an electrical voltage. When the sensor is electrical, the sensor can be simply substituted in place of the proximity sensor in the system of Fig 2. A non-electrical pneumatic sensor can be accommodated as shown in Fig 1.

It is recognised that the invention may be advantageously used with many types of sensor, including, as mentioned, speed sensors, ore-presence sensors, thickness sensors, and so on. Also, the skilled expert will appreciate that many different valve arrangements can be designed that would be more or less suitable for the function of withdrawing the blade from the belt, in response to the signal from the sensor. In the invention, the key feature is that the blade is automatically retracted from the belt when the abnormality is detected. When the sensor signals that the abnormality has passed, the blade may be re-actuated manually, but preferably the blade is re- actuated automatically.

It is recognised that by retracting the blade, even momentarily, while the abnormal condition lasts, the service life of the blade can be substantially prolonged. As mentioned, the problem with which the invention is concerned substantially does not arise in cases where the blade and its associated actuation and suspension system have a low inertia, since then the blade can follow the changes in thickness of the belt without jolting. It is mainly when the blade and the housing are large and heavy and have an appreciable inertia that the jolt can give rise to damaging stresses. As explained, it is this type of scraper, being most effective in the function of scraping, that is also most vulnerable to damage caused by abnormal conditions. One of the reasons, with previous designs of scraper, that abnormal conditions did not adversely affect the scraper, was that the scraper was in any event pressed only very lightly against the belt.

However, even if the scraper is light in weight, and is pressed only lightly against the belt, the need can still arise for a momentary withdrawal of the scraper blade. This need can arise, for example, especially if a clip is damaged or broken, or lying at the wrong angle, etc, as sometimes occurs.

Naturally, the scraper should be clear of the belt for only a minimum time. Therefore, for example when the abnormal condition is a stapled-joint in the belt, it is preferable if the scraper blade can be quickly jerked free from the belt by rapidly dumping the pressure from the ram, and if the air is then allowed to flow back more slowly into the ram. Thus, the blade is clear at the time the staples first pass the blade, but then the blade can be gradually fed back onto the blade. It does not matter so much if the blade contacts the staples as the blade is being gently lowered back onto the belt: the damaging aspect of staples is the jolt they cause when they first strike the blade.

The rate of dumping the air from the ram, and the rate of air flow into the ram to re-pressurise it, are set by the designer bearing in mind the inertia of the blade plus the housing plus the water inside the housing, in conjunction with the effects of gravity. (Preferably, for safety reasons, the scraper is set so that gravity urges the scraper blade clear of the belt, not towards the belt.)

As mentioned, the rate of wear of both the belt and the scraper might be increased when the belt is not conveying any ore. On the other hand, it would be operationally disruptive if the blade were to be retracted every time a brief lull occurs in, say, the noise of ore falling into the chute. Therefore, when the sensor is sensing the presence/ absence of ore on the belt, the sensor should include a timer, whereby the signal is only transmitted to the interrupter means if the abnormal condition lasts for more than a pre-determined interval.

Claims

Claims CLAIM 1. Conveyor belt scraper apparatus, wherein: the apparatus includes a scraper blade, which is arranged for direct scraping contact with a moving conveyor belt; the apparatus includes an actuation system, having an operable actuator means which is effective, when operated, to force the blade into scraping contact with the belt; the apparatus includes a blade suspension system, in which the blade is constrained and guided for actuation movement into and out of scraping contact with the belt; the apparatus includes a sensor or detector means; the detector means is effective, during operation of the scraper on the moving belt, to detect an abnormal condition of the belt, being a condition of the belt requiring the scraper blade to withdraw from the belt, and is effective automatically to issue a signal upon detecting, and in response to, said condition; the apparatus includes an interrupter means, which is effective, upon receiving, and in response to, the signal, to automatically de-operate the actuator means in the sense to relieve the contact force between the blade and the belt.

CLAIM 2. Apparatus of claim 1, wherein: the actuator means comprises a pneumatic actuator, and the actuation system includes a means for supplying compressed gas to the actuator; and the interrupter means is effective, upon receiving the signal, to exhaust compressed gas from the actuator.

CLAIM 3. Apparatus of claim 2 , wherein the sensor is connected to the pneumatic actuator by means of a gas line, and the sensor is adapted, upon detection of the abnormal condition, to issue the signal in the form of a change in the pressure of the gas in the line.

CLAIM 4. Apparatus of claim 1 , wherein the sensor is connected to the actuator means by an electrical connection, and wherein the sensor is adapted, upon detection of the abnormal condition, to issue the signal in the form of a change in the electrical condition of the connection.

CLAIM 5. Apparatus of claim 1, wherein: the sensor is adapted to detect the abnormal condition as an abnormal and sudden increase in the thickness of the belt; and the apparatus is so arranged that the detector means is effective to issue the signal a little before the sudden increase in thickness of the belt reaches the blade.

CLAIM 6. Apparatus of claim 1, wherein the apparatus is so arranged that when the abnormal condition has passed, the actuator means automatically resumes normal operation, thereby forcing the blade once more into scraping contact with the belt.

CLAIM 7. Apparatus of claim 1, wherein: the scraper blade comprises a length of relatively soft plastic material; the apparatus includes a housing, and the blade is arranged in a coil inside the housing; and the apparatus includes a suspension system, whereby the housing and the blade are guided and constrained together for movement in unison towards and away from the belt.

CLAIM 8. Apparatus of claim 7, wherein the apparatus includes an adjustment means for displacing the blade out of the housing to compensate for wear of the blade, and the adjustment means comprises means for injecting a liquid into the housing in a quantity to make up the volume of blade displaced from the housing.

CLAIM 9. Apparatus of claim 1, wherein the apparatus is suitable for use with a conveyor belt of the type that has metal staples or clips at a joint of the belt, and the sensor is of the kind that is effective to detect the approach of the staples or clips towards the blade as the abnormal condition.

CLAIM 10. Apparatus of claim 1, wherein the sensor is of the kind that is effective to detect the absence of material being conveyed by the conveyor belt as the abnormal condition.

CLAIM 11. Apparatus of claim 1 , wherein the sensor is of the kind that is effective to sense the speed of the belt, and is effective to detect a reduction in the forward speed of the belt as the abnormal condition.