FIELD OF THE INVENTION

The present invention relates in general to metallic scrapers for reversible belt cleaning in bulk material handling, and in particular to an auto adjusting scraper, which is a metallic scraper mechanically connected with a pneumatic system. By controlling the pressure of the pneumatic cylinder shaft of the pneumatic system, the scraper assembly system can either be engaged with the conveyor belt or disengaged from the conveyor belt easily from remote locations automatically, as per belt direction. BACKGROUND AND PRIOR ART

Belt scrapers are used in bulk material handling belt conveyors to avoid material carry back, reduce spillage and keep belt clean . Clean belts help prevent material build up on snub pulley and return idlers and increase their life, thereby reducing cleaning cost, downtime cost and mis-tracking of the belt.

In first generation counterweight belt scrapers, single blades made from thick rubber strip (wider than belt width) are provided under the return belt and a counterweight is provided at the side of the belt scraper with a pivot point to provide contact with the belt. The initial load exerted to the belt is approximately 80 - 90 Kgs. With time when the cleaning effectiveness reduces, the weight is increased and it can go up to 150 Kgs. Cleaning efficiency is approx 60-68 % and always, it is necessary to increase the counter weight load on a regular basis to compensate for blade wear. It is very less effective and high maintenance is involved . Second generation fixed mount belt scrapers' segmented blades are made of hard alloy steel with rubber cushion at the bottom of blade mounted on a steel tube with both end having fixed mount. It does not have automatic adjustments against blade wear. It provides inconsistent contact pressure to the belt which is approximately 100 - 125 Kgs.

Cleaning efficiency is approx 70-85 % and always, there is need to lift- up of the fixed mount on a regular basis to guard against blade wear. This too is less effective and involves high maintenance.

Pneumatically operated third generation belt scrapers have segmented blades which are made of hard alloy steel with or without polymer cushion at the bottom, mounted on a steel tube with ratchet and pinion mount and adjustment done through compressed air at 7- 10 bars pneumatically. They provide inconsistent load to the belt of approximately 90 - 110 Kgs. Cleaning efficiency is approx 75-85 %. There is a need to pump air periodically to maintain the blade-to-belt contact due to drop in air pressure / leakage / chocking of air. Maintenance requirement is high .

In fourth generation belt scrapers with shock absorbers, semi automatic adjustments are present to some extent but, but there is a need for periodic manual adjustments against blade wear every 3 - 4 weeks interval. This type of belt scrapers have segmented type metallic blades with pivot point below the scraping edge mounted on a steel tube with both ends rubber shock absorber. It provides comparatively less load to the belt, which is approximately 24 - 80 Kgs.

Cleaning efficiency is approx 92-95 %. It provides less consistency against heavy duty, high speed, vibration and bi-directional belt operation.

Belt conveyor systems with reverse mode are generally equipped with scrapers located at both drop zones. When using non-reversible scrapers, the scraper may only be engaged in the operating position that corresponds to the direction of belt travel. The other scraper must like wise be disengaged. But in the running condition normally this type of engaging and disengaging is done manually at site. However, if both scrapers are in engaged condition for both the running directions (forward and reverse), belt may get damaged. It is may not always be possible to reach every conveyor's scraper zone on at a particular time at site.

US patent no. 4,969,553 discloses a belt scraper which has first and second pairs of scraper support arms as well as first and second actuator arms for each of the support arms, and includes a gear adjustment by which the position of the belt scrapers may be adjusted with respect to the belt and with respect to the actuator arms, from a convenient position alongside of the belt. US patent no. 5,799,776 discloses a conveyor belt scraper blade support assembly having an elongate support bar extending transversely in excess of the width of the conveyor belt, external foundation support brackets operatively arranged to engage each end of the support bar, extensible/retractable device located between the brackets and the support bar arranged for controlled reciprocal movement of the support bar toward and away from the support brackets, spring loaded piston/cylinder assemblies mounted spatially along the length of the support bar for urging the pistons toward the conveyor belt, a blade attachment device on the piston for attaching and supporting a scraper blade thereto, a scraper blade mounted in the blade attachment device, and shock absorbing device between the brackets and the support bar.

US patent no. 5,722,528 discloses a method and apparatus for cleaning a conveyor belt. The invention comprises locating a support bar under the return side of a . conveyor belt and positioning it transverse to the direction of travel of the conveyor belt. The support bar has mounted on it several individual piston-cylinder apparatus which have pneumatic or hydraulic connections to a manifold assembly. Support plates are connected to the extensible end of the piston-cylinder apparatus and cleaner blades are removably attached to the support plates. The cleaner blades and piston-cylinder apparatus are arranged adjacently with one another along the length of the support bar, and the blade assemblies have side edges with tongue and groove connections so that each adjacent cleaning blade has a sliding engagement with one another. Connecting to the manifold assembly on the support bar are pneumatic supply and return lines that emanate from a pressure source having a regulator and a two way valve. The method comprises locating the support bar assembly in the proper position and activating the two way valve so that pressure is applied to each of the individual piston cylinder apparatus. As wear occurs on the individual blades or as the conveyor belt becomes curved more in the middle, the blades are pressed against the belt in a uniform manner. When it is necessary to change the blades the two way valve may be switched and the piston cylinders are retracted from contact with the belt.

However, none of the above discloses a belt cleaning arrangement with mechanism for automatic engagement and disengagement of scrapers for reversible, or addresses the problem of belt damage and other associated mechanical hazards mentioned above, for which there has been a persistent need. The present invention meets the aforesaid long felt need.

All through out the specification including the claims, the words "conveyor belt", "scraper blade" "scraper holding arm", "spring", "washer", "stud", "blade", "blade tip", "blade tip assembly ", "spring", "locking ring", and "nut" are to be interpreted in the broadest sense of the respective terms and includes all similar items in the field known by other terms, as may be clear to persons skilled in the art. Restriction/limitation, if any, referred to in the specification, is solely by way of example and understanding the present invention.

OBJECTS OF THE INVENTION

The principal object of the present invention is to provide a metallic scraper which can either be engaged with the conveyor belt or disengaged from the conveyor belt easily from remote locations.

Another object of the invention is to provide an auto adjusting metallic scraper for reversible belt conveyors, which is substantially more durable and compact compared to comparable prior art devices.

Yet another object of the invention is to provide an auto adjusting metallic scraper which ensures positive engagement with the belt in both forward and reverse directions and can operate under harsh operating conditions. A further object of the invention is to provide an auto adjusting scraper which can be fixed at several points in any zone of a plant or site, but scraper operating control is done from a central place. Another object of the present invention is to provide a scraper with which working pressure on belt can be easily controlled from one control unit.

A further object of the invention is to provide an auto adjusting metallic scraper which is fixed on- both sides of a reversible belt and whose engagement and disengagement is controlled automatically by means of solenoid valve, relay switch etc. as per the requirement of belt operating direction, so that minimum spillage or carry back takes place.

A still further object of the invention is to provide an auto adjusting metallic scraper which requires minimum maintenance, thereby ensures minimum downtime. How the foregoing objects are achieved will be clear from the following description. In this context it is clarified that the description provided is non-limiting and is only by way of explanation.

SUMMARY OF INVENTION

Accordingly, the present invention provides an auto adjusting scraper, at least one of which is provided at each of two discharge ends of a reversible conveyer belt assembly having a forward direction or a reverse direction of conveyance. Each of the auto adjusting scrapers is operatively connected to a pneumatic cylinder. The latter is equipped with suitable features to automatically disengage or engage the respective scraper with the return side of the belt alternately, depending upon the forward direction or the reverse direction (15') of conveyance of the belt.

Preferably, each scraper is connected to an arm holding plate connected to the distal end of a movable shaft of the pneumatic cylinder, whereby the shaft can move either in or out and the plate can consequently move inwards or outwards, for automatic disengagement or engagement of the scraper, by means of alteration of air pressure in the pneumatic cylinder.

More preferably, the pneumatic cylinder has an air flow circuit and a control unit.

Even more preferably, the control unit is provided with push buttons and is located at a central convenient place for remote operation of said scrapers.

Most preferably, the scraper is provided with metallic scraper blade on its top portion for scraping the return side of the belt.

The present invention also provides a reversible conveyer belt assembly comprising of a troughing side, a return side, discharge pulleys and at least one auto adjusting metallic scraper provided at both its discharge ends according to the present invention as described hereinbefore.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The nature and scope of the present invention will be better understood from the accompanying drawings, which are by way of illustration of a preferred embodiment and not by way of any sort of limitation. In the accompanying drawings: - Figure 1 shows a side view of auto adjusting scraper assembly with reversible conveyor running in one direction.

Figure 2 shows a side view of auto adjusting scraper assembly with reversible conveyor running in reverse direction.

Figure 3 shows a side view of auto adjusting scraper assembly during engaged condition. Figure 4 shows a side view of the same scraper assembly during disengaged condition.

Figure 5 shows a front view of auto adjusting scraper assembly during engaged condition along with control unit.

Figure 6 shows a rear view of auto adjusting scraper assembly during engaged condition.

DETAILED DESCRIPTION OF THE INVENTION

Having described the main features of the invention above, a more detailed and non-limiting description of a preferred embodiment will be given in the following paragraphs with reference to the accompanying drawings.

In all the figures, like reference numerals represent like features. Further, the shape, size and number of the devices shown are by way of example only and it is within the scope of the present invention to change their shape, size and number without departing from the basic principle of the invention. Further, when in the following it is referred to "top", "bottom", "upward", "downward", "above" or "below", "right hand side", "left hand side" and similar terms, this is strictly referring to an orientation with reference to the apparatus, where the base of the apparatus is horizontal and is at the bottom portion of the figures. The number of components shown is exemplary and not restrictive and it is within the scope of the invention to vary the shape and size of the apparatus as well as the number of its components, without departing from the principle of the present invention.

All through the specification including the claims, the technical terms and abbreviations are to be interpreted in the broadest sense of the respective terms, and include all similar items in the field known by other terms, as may be clear to persons skilled in art. Restriction or limitation if any referred to in the specification, is solely by way of example and understanding the present invention .

The auto adjusting scraper according to the invention can be best used under the following conditions :

i) With belt widths of 1000 - 1800 mm ii) At conveyor belt speeds <4.5 m/s. iii) Suitable for an operating/control voltages of 240v/60 Hz AC. iv) With conveyor belt switching cycles of min. 10 seconds (interval time between disengagement and re-start). v) Where it is possible to fasten mounting assemblies on torsion resistant, low vibration structural components or brackets outside of the transfer chute. vi) With unrestricted swivel movement of the mounting assembly components. As the name suggests, a reversible belt conveyor runs its belt in both forward and reverse directions.

Figures 1 and 2 show a reversible conveyer belt assembly ( 10) which comprises of a troughing side (11), a return side (12), discharge pulleys ( 13, 13') and auto adjusting metallic scraper (A, A') according to the present invention provided at both its discharge ends ( 14, 14'). The drive arrangement of the conveyor is not shown here. The material is discharged at the two discharge ends (14, 14') alternately, depending upon whether the belt is moving in the forward direction ( 15) or in the reverse direction ( 15'). The auto adjusting metallic scrapers (A, A') according to the present invention fixed on both ends of the conveyor, are engaged or disengaged on the return side ( 12) of the belt alternately, depending upon the forward direction ( 15) or the reverse direction ( 15') of conveyance of the belt.

When the conveyor is moving in the forward direction ( 15), the material is discharged at the discharge end ( 14) and vice-versa. During the forward conveyance of the conveyor belt the auto adjustable scraper (A) is engaged with the return side ( 12) of the belt and the auto adjustable scraper (Α') remains disengaged. This allows the carry back materials at the discharge end ( 14) to be scraped by the scraper (A). For the reverse direction of conveyance, the opposite takes place. These two figures clearly show the engagement and disengagement of the scrapers (A, A') depending upon the direction of the belt.

Figure 3 shows the details of mechanical arrangement of the auto adjusting scraper (A) according to the invention. The scraper has been shown in the engaged position. The auto adjusting scraper device (A) consists primarily of modified parallel elastomount. The left and right parallel elastomount arms, best shown in figure 5, with locking ring (8) hold the actual scraper blade (4) with its tube base. The scraper is engaged and disengaged ^* by extending or retracting the pneumatic cylinder shaft adjuster (2), the working of which is described below. A pneumatic cylinder ( 1) has a movable shaft (2) which is either moved in or out depending upon the air pressure in the cylinder ( 1). When the shaft is pushed out, it moves an arm holding plate (3) outwards, which is pivoted on a threaded spindle (5) and connected to said scraper (A) . The arm holding plate is at an angle to the threaded spindle (5) of the mechanism, which is either suspended or fixed. This movement moves the scraper into the "engaged" position, where the scraper blade (4) is pressed against the return side ( 12) of the moving belt. Figure 4 illustrates the "disengaged" position of the scraper (A) . For this position, the air pressure in the pneumatic cylinder ( 1) is altered, whereby the shaft (2) is drawn inwards. The arm holding plate assumes a position which is parallel to the threaded spindle (5) . In this position, the scraper blade (4) is disengaged from the return side ( 12) of the moving belt of the conveyor.

The threaded spindle of the mounting assembly can be suspended or fixed in place. The stroke of the pneumatic cylinder (1 ) is 150mm max. When the shafts of the pneumatic cylinder (1) are fully retracted, the difference in height between the scraping blade (4) and the return side ( 12) of the belt is minimum 50 mm, which is achieved based on the position of the locking ring (8).

Figure (5) shows a front view of the conveyor. It shows the scraper (A) in engaged position. It also shows the left and right parallel elastomount arms, a control unit (6) connected with a pneumatic circuit having a plurality of pneumatic pipes (7) which supply compressed air to the pneumatic cylinders ( 1) of the scraper mechanisms.

Figure 6 shows a rear view of auto adjusting scraper assembly (A) in the engaged position.

The main components of the mechanism are pneumatic cylinder ( 1) with its air flow circuit (7) and the control unit (6), best shown in figure 5. The control unit is provided with push buttons (not shown) and is located at a central convenient place for remote operation of the scrapers (A, A') . The exact operating position and pressure as well as the retracted position of the cylinder shafts (2), of each end must be set. This is done to ensure proper stroke length and proper position of the scraper blade (4). This also compensates for minimum variations in synchronization between the two pneumatic cylinder shaft adjusters while the device is disengaged.

The scrapers are alternatively engaged and disengaged automatically by the control unit (6), based on the direction of conveyance of material on the belt conveyor. The control unit (6) controls the automatic operation of the auto adjusting scrapers (A, A'). In the automatic mode of operation, the control unit (6) ensures that the proper scraper is either engaged or disengaged based on which direction the conveyor belt drive motor is turning . It also ensures that a wrong scraper is not left engaged in any direction of the belt. For example, for the direction shown in figure 1, scraper (Α') must be in disengaged position to save the belt from damages and the scraper (A) is engaged automatically by controlling unit (6) by means of relay switch or other device as per the belt direction whenever the conveyor belt is started. This function too is ensured by the controller (6). Pneumatic cylinder ( 1) air pressure is reviewed from time to time and fixed for a certain period in consideration of the blade wear. Some of the non-limiting advantages of the present invention are :

1. The auto adjusting scrapers according to the invention are more durable and compact when compared to the scrapers in the prior art.

2. They provide near zero spillage / carry back during operation of the conveyor.

3. They enhance profitability for reversible conveyor under harsh operating conditions through enhanced service life.

4. They reduce cost of manpower and annual maintenance and replacement.

5. They reduce belt damage due to automatic engaging and disengaging system of the scrapers at both ends of a reversible conveyor belt.

6. No ceramic dislodges during operation.

The present invention has been described with reference to some drawings and a preferred embodiment purely for the sake of understanding and not by way of any limitation and the present invention includes all legitimate developments within the scope of what has been described herein before and claimed in the appended claims.