Barrier seal for conveyor skirtboard

Abstract: A conveyor belt assembly for conveying particulate material is provided with a rigid primary seal (34) mounted between the inboard loading zone (22C) and each outboard region (22A,22B) of the belt (22). A flexible secondary seal (36) is mounted between the primary seal (34) and the outboard region (22A,22B), and includes a flexible sheetlike member having a sealing portion (36B) resting with light sealing pressure in sliding contact with the upper belt surface.

Description: The present invention relates to a barrier seal assembly for use in combination with a skirtboard in a conveyor belt installation. The invention is of use in controlling spillage of particulate material in conveyor systems. Most belt conveyors have a flexible endless belt comprising a load bearing body protected by top and bottom covers of a rubberlike material. The belt is supported at intervals by rollers. The belt is therefore supported against deflection as it curves about each roller, but flexes and sags between the rollers according to the variable load conditions. This flexing and sagging is most severe in the loading zone, because of the impact of the falling particulate material. The quasi-fluid characteristics of the material being loaded causes the material to flow laterally with considerable force upon impact against the belt. In such conveyor belt systems, it is customary to provide stationary lateral skirtboards above the belt along the sides of the loading zone to retain the material on the belt as the material accelerates to the speed of the belt. The skirtboards usually are extensions of the loading chute, with lower edges positioned some distance above the belt on either side of and extending the length of the loading zone. The gap between the lower edge of each skirtboard is usually sealed by a rubber strip attached to the outer surface of the skirtboard and positioned such that the lower thin edge of the rubber strip engages the belt surface. With this construction it is possible to maintain a seal only if the seal strip is forced down with sufficient pressure to force the belt down to the point of lowest sagging deflection when the belt is loaded. This requires a force approaching that of the impacting material, and therefore exerts considerable pressure between the strip and the belt when the belt runs empty or lightly loaded. This excessive contact pressure leads to formation of grooves on the belt surface, which can cause separation and destruction of the belt. Consequently, frequent adjustment is necessary to compensate for wear of the strip and the belt surface. In another type of seal, for example as shown in U.S. Patent 4,641,745, a flexible seal strip has an upper edge attached to the outboard side of a metal skirtboard, and has a lower sealing portion deflected inwardly and curled under the skirtboard and engaging the conveyor belt load surface on the inboard side of the skirtboard. In that configuration, the inwardly deflected seal strip defines a longitudinal pocket in which load material accumulates. Such accumulation of load material creates an undesirably high pressure between the lower contacting surface of the seal strip and the upper belt surface which leads to rapid abrasion and wear of the seal strip and the upper belt surface. Another limitation on the use of the inboard deflected sealing arrangement of Patent 4,641,745 is that the accumulation of load material within the longitudinal seal strip pocket reduces the flexibility of the seal strip and increases the frictional engagement between the seal strip and the conveyor belt. Moreover, the metal skirtboard is spaced vertically above the belt and seal strip, thereby defining a gap in which rocks or other consolidated load material can become wedged. The wedging of consolidated load material between the stationary skirtboard and the rapidly moving conveyor belt, which may be moving at a high velocity, for example as much as 1,000 feet per minute, may cause catastrophic destruction of the conveyor belt. In the inboard deflected sealing arrangement of U.S. Patent 4,641,745, a large gap must be maintained between the top surface of the flexible strip and the lower edge of the metal skirtboard to accommodate lateral rippling excursions of the conveyor belt which are produced in response to impact forces of the discharged load material which strike the surface of the conveyor belt at random locations, thereby causing lateral shifting and rippling flexure of the conveyor belt within the loading zone. If the lower edge of the metal skirtboard is positioned closely to the surface of the flexible seal strip to limit the escape of load material into the longitudinal pocket, the seal strip will suffer abrasion damage as the belt shifts laterally. Consequently, the inwardly projecting seal strip will become torn. On the other hand, if the metal skirtboard is spaced far enough away from the flexible strip to avoid abrasion damage, for example a gap distance of two inches, a considerable amount of load material will escape into the longitudinal pocket, thereby increasing frictional engagement. Moreover, consolidated load material such as rocks will become wedged between the lower edge of the metal skirtboard and the flexible strip. US-A-2665795 discloses a barrier seal assembly for a conveyor belt installation comprising a relatively rigid primary seal having a lower end defining a gap between the load bearing surface of the conveyor belt and the primary seal, and a vertically movable secondary seal for surface engagement against an outboard apron of the conveyor belt. SU-A-962130 discloses a barrier seal assembly for use in combination with a skirtboard in a conveyor belt installation comprising an elongated retainer wall defining a relatively rigid primary seal having an upper end portion adapted for suspended attached to a skirtboard; an elongated, flexible sheetlike secondary seal having a length substantially co-extensive with the length of said primary seal and having a first end portion suspended adjacent to said retainer wall, and having a second flexible sealing end portion for surface engagement against an outboard apron of a subjacent conveyor belt, with said flexible sealing end portion being deflected by its engagement against the outboard apron of the subjacent conveyor belt and laterally spaced with respect to said retainer wall when said retainer wall is positioned above the subjacent conveyor belt, said secondary seal forming a flexible web which extends angularly outwardly from said first end portion adjacent said retainer wall to said sealing end portion spaced outwardly from said retainer wall; and whereby said primary seal provides a relatively rigid barrier for containing load material on an inboard side of the subjacent conveyor belt, and the secondary seal in combination with the primary seal defines an elongated tunnel for confining fine particulate load material which escapes past the primary seal, so that said fine particulate load material will be conveyed through said tunnel along the subjacent conveyor belt apron beneath the flexible secondary seal on the outboard side of said primary seal. The present invention is characterised in that the primary seal has a lower end portion adapted for placement above the load bearing surface of a subjacent conveyor belt, thereby defining an elongated gap therebetween; said first end portion of the secondary seal is in contact with the retainer wall, and the second flexible sealing end portion includes a raised tapered rib adapted for surface engagement against the outboard apron of the subjacent conveyor belt. The function of the primary seal is to absorb the impact and turbulence of the material being loaded onto the conveyor belt. A small volume of material will leak through the primary seal. The function of the flexible secondary seal is to conform with the flexing of the belt edge. This prevents the escape of the material which has leaked through the primary seal. The material trapped by the secondary seal continues on the conveyor belt apron through the tunnel formed between two seals. The present invention will be understood and appreciated by those skilled in the art upon reading the detailed description which follows with reference to the attached drawings, wherein: FIGURE 1 is a side elevational view of a conveyor system incorporating the present invention; FIGURE 2 is a sectional view of the preferred embodiment of the invention, taken along the line 2-2 in FIGURE 1, as applied to a troughed conveyor belt; FIGURE 3 is a perspective view, partly broken away, of the embodiment shown in FIGURE 2; FIGURE 4 is a perspective view of a troughed conveyor belt installation, showing adaptation of the preferred embodiment to an angular transition; FIGURE 5 is a perspective view similar to FIGURE 3, showing adaptation of the preferred embodiment to a flat conveyor belt; FIGURE 6 is a sectional view of a flexible primary seal constructed according to one aspect of the present invention; FIGURE 7 is a sectional view of a secondary seal which is adapted for attachment to the primary seal shown in FIGURE 6; FIGURE 8 is a side elevational view, partially broken away, which illustrates deflection of a conveyor belt in response to loading by falling particulate material; FIGURE 9 is a view similar to FIGURE 8 in which the gap between the skirtboard and the conveyor belt is continuously sealed by the secondary seal member of the present invention; FIGURE 10 is a sectional view, partially broken away, which illustrates a first alternative assembly of primary and secondary seals in combination with a troughed conveyor belt; FIGURE 11 is a sectional view similar to FIGURE 10, illustrating a second alternative embodiment in which the primary and secondary seal members are integrally formed; and, FIGURE 12 is a sectional view similar to FIGURE 11 which illustrates engagement of the secondary apron seal member against a troughed conveyor belt which is subject to lateral displacement. Detailed Description of the Preferred Embodiment Referring to FIGURE 1 and FIGURE 2, the barrier seal assembly 10 of the present invention is incorporated in a conveyor system 20 of the type having a belt 22 moving along its longitudinal axis Q between tail or inlet roll 24 and head or outlet roll 26. Idler rolls 28 between rolls 24 and 26 provide additional support for the belt 22. Particulate material is dropped through a chute 30 onto the upper surface S of belt 22 in a loading zone LZ, and is transported therefrom toward the head roll 26 (to the right as viewed in FIGURE 1). Skirtboards 32A, 32B are positioned on laterally opposite sides of the chute 30 above the upper surface S of belt 22 and extend along the length of the loading zone. The barrier seal assembly 10 includes a primary seal 34 in the form of a barrier wall and a flexible secondary seal 36, together with mounting means as described herein. Each primary seal 34 is mounted by any convenient means along the outboard (away from the axis Q of belt 22) lower edge of its associated skirtboard 32, and comprises a downwardly extending retaining wall 38 having an inside surface 40 exposed to the inboard working region LZ and an external side surface 42 exposed to a clear outboard region 44. The primary seal 34 terminates in a lower edge 46 positioned above the upper surface S of the belt 22 to define therewith a small gap G. The primary seal 34 (FIGURE 7) is formed from a relatively rigid material such as molded nylon polymer, rigid polyurethane, or rigid neoprene elastomer. The durometer of the primary seal material is in the range of 50-90 ( Shore "D"), and preferably has a durometer of 80. Each primary seal 34 accordingly separates the central inboard working region 22C of belt 22 from lateral belt aprons 22A, 22B, each of which extends outwardly from its respective gap G to its respective longitudinal belt edges 22D, 22E. As thus described, the primary seal 34 confines the bulk of the particulate material falling down chute 30 to the central working region 22C of belt 22, with only a small portion of the material leaking through gap G onto the lateral belt aprons 22A, 22B. According to one method for attaching the secondary seal 36 onto the primary seal 34, the primary seal 34 is provided with a longitudinal mortise cavity 48 which is adapted to receive a dovetail strip 49 which is formed on the secondary seal 36. While the primary seal 34 is illustrated as a separate element attached to the skirtboard 32, it could be eliminated as a separate element if the skirtboard 32 is positioned close enough to the upper surface of belt 22 to confine the bulk of the falling material to the central working region 22C, in which case the skirtboard 32 would function as the primary seal. However, a separately mounted primary seal 34 is preferred to facilitate adjustment of the gap G. In accordance with the invention, the flexible, sheetlike secondary seal 36 cooperates with the primary seal 34 to prevent the escape of load material out of the central working region 22C into the clear regions 44. Each seal 36 is formed from a flexible material, having a high resistance to abrasion, preferably either natural or synthetic resins. For example, various known thermoplastic polymer resins such as polyurethane, preferably having a lower resistance to wear than the upper belt surface, and having a durometer of from about 50-70 (Shore "D"), may be used to good advantage. Each flexible seal 36 has an upper attachment end portion 36A mounted a given distance above the upwardly facing surface of belt 22, as by the illustrated dovetail joint 48, 49 to the outboard surface of its associated primary seal 34. The flexible seal 36, like the primary seal 34, has a length dimension extending along the direction of belt travel at least as long as the loading zone LZ. Each seal 36 has a width dimension extending from its upper attachment end portion 36A to the opposite free end portion 36B of seal 36, and a thickness dimension separating respective first and second opposite major seal surfaces 36C and 36D. Each secondary seal 36 has its length dimension extending along and overlying a band along each conveyor apron 22A, 22B. As illustrated, the band has a width extending laterally from the gap G to the outer free end portion 36B of secondary seal 36. The portion of the apron 22B to the right of free end portion 36B as viewed in FIGURES 2 and 3 forms a part of the clear region 44 where it is desired to prevent particulate material from reaching. The thickness of secondary seal 36 is less than either the length or the width of the secondary seal, and is less than the width of the band overlain by secondary seal 36. The width of seal 36 is greater than the distance from the upper attachment end portion 36A to the upper surface of belt 22, such that the seal 36 in the vicinity of free end portion 36B is deflected by contact between apron 22B and the lower major surface 36D. Accordingly, a contacting portion of lower major surface 36D spaced from free end portion 36B rests with light sealing pressure in sliding contact with part of the band between gap G and the clear region 44, thus preventing material leaking past the primary seal 36 from entering clear region 44. The secondary seal 36 in combination with the primary seal 34 defines an elongated tunnel T for confining fine particulate load material which escapes through the gap G, so that the fine particulate load material will be conveyed through the tunnels along the subjacent conveyor belt aprons 22A, 22B beneath the flexible seal 36 on the outboard side of each primary seal 34. In the exemplary embodiment, the contacting portion is one or more ribs 50 extending along the length of secondary seal 36. The ribs 50 are optional in the FIGURES 2 and 3 embodiments, and provide for increased wear life before the secondary seal 36 must be replaced. The invention is not limited in applicability to the loading zone, but is useful in other locations such as the angular transition region as illustrated in FIGURE 4. The invention may also be used to good advantage in combination with a flat conveyor belt as shown in FIGURE 5. While secondary seal 36 is preferably a separate element mounted on the primary seal 34, it can be integrally formed therewith, as shown in FIGURES 11 and 12. The barrier seal assembly 10 is preferably clamped onto the skirtboards 32A, 32B by releasable wedge plates 52 as shown in FIGURE 3, or by standoff clamp plate 54 as shown in FIGURE 4. Referring now to FIGURE 8 and FIGURE 9, it should be understood that the conveyor belt 22 is flexible and slightly elastic. The conveyor belt 22 is very often tensioned by a gravity take-up roller which applies tension on the belt. In this situation, the belt 22 is suspended on spaced rollers. Therefore, the conveyor belt can sag between the idler rollers. The sag is normally designed to be limited to about two percent of idler roll spacing. Idler roll spacing is typically three to four feet. In the loading zone as illustrated in FIGURE 1, FIGURE 8 and FIGURE 9, the sag deflection A in the belt as the particulate material R is loaded onto the belt can be as much as 1/2 to 3/4 inch or maybe even slightly more. That means that as the material is being loaded, the conveyor belt will open up a as much as 3/4 inch or more between the top surface of the belt and the lower end portion 32E of the skirtboard. Such a large gap A will permit a large quantity of load material to escape out of the loading zone LZ. As shown in FIGURE 9, the primary seal 34 and the secondary seal 36 effectively block the escape of particulate load material R, which may be impacting onto the conveyor belt 22 randomly and with great force. Moreover, the load zone becomes a positive pressure region which tends to cause fine particulate load material to squirt through such small openings as the sag gap A shown in FIGURE 8. The escape of bulk, consolidated load material is blocked by the rigid primary seal wall 34 which is positioned closely adjacent to the top of the belt 22, for example by about 1/16 inch. The lower edge 46 of the fixed primary seal 34 is positioned closely enough to the top surface of the belt 22 to avoid contact by flexure movement of the belt, while at the same time preventing the escape or wedging of rocks or other consolidated material. The small amount of fine particulate load material which does escape through the gap G is trapped beneath the flexible seal 36 and is carried along the belt apron 22A, 22B. While neither the skirtboard 32 nor the primary seal 34 can conform and maintain a seal against the sagging belt 22, the flexible seal member 36 is well adapted to follow and seal against the sagging belt 22. Because of the concave deflected orientation of the flexible sealing members 36, and because of the weight of the seal, a spring bias force is developed which maintains positive engagement of the sealing portions of the flexible seal against the sagging belt. The flexible seal 36 is made of a material which is soft enough to conform to the sagging belt surface, but will not be forced open by the very low volume of fine particulate load material which manages to escape through the gap G beneath the primary seal wall 34. The small amount of fine particulate load material which does escape through the gap will be conveyed along the belt apron beneath the flexible seal 36. Referring again to FIGURE 2 and FIGURE 6, the flexibility of the seal member 36 is increased by the reduced thickness of the member near its upper attachment end 36A as compared with the thickness of the lower end 36B. Preferably, the thickness of the seal member 36 increases linearly from the upper attachment end 36A to the lower free end 36B. The spring tension applied by the flexible seal member 36 is reduced slightly by reducing its thickness along its upper end. The ribs 50 are formed on the flexible seal member 36 to reduce the area of frictional engagement, thereby extending the life of the flexible seal 36. The dovetail interlock shown in FIGURE 2, FIGURE 3, FIGURE 6 and FIGURE 7 facilitates installation of the barrier seal assembly 10, particularly while adjusting the gap clearance G. The primary and secondary seals 34, 36 may be integrally formed together, as shown in the barrier seal assembly 60 of FIGURE 11 and FIGURE 12. However, the primary and secondary seals may be completely separate and clamped together as shown in FIGURE 10. Referring now to FIGURE 12, the belt 22 tends to wander laterally on the rollers 28 in response to the impact forces applied by the falling load material. That is, the belt does not always run perfectly true and in alignment with the idler rollers 28. Excessive loading on one side of the trough causes the belt to tend to run in the direction of the uneven loading. As the uneven loading is reduced, the belt tends to return to its centered position. As this lateral shifting occurs as indicated by the arrows in FIGURE 12, the belt is shifted laterally (left arrow) until the flexible seal 36 and rib 50 extend over the belt edge 22E. To avoid damage to the flexible seal 36 as a result of such lateral belt shifting, the ribs 50 have a tapered inside surface 50T which will permit the belt edge 22E to ride in and out without snagging, binding or cutting the flexible secondary seal 36.

Claims: A barrier seal assembly (10) for use in combination with a skirtboard (32A, 32B) in a conveyor belt installation (20) comprising an elongated retainer wall defining a relatively rigid primary seal (34) having an upper end portion adapted for suspended attachment to the skirtboard (32A, 32B) an elongated, flexible sheetlike secondary seal (36) having a length substantially co-extensive with the length of said primary seal (34) and having a first end portion (36A) suspended adjacent to said retainer wall, and having a second flexible sealing end portion (36B) for surface engagement against an outboard apron (22A, 22B) of a subjacent conveyor belt, with said flexible sealing end portion (36B) being deflected by its engagement against the outboard apron of the subjacent conveyor belt and laterally spaced with respect to said retainer wall (34) when said retainer wall is positioned above the subjacent conveyor belt, said secondary seal (36) forming a flexible web which extends angularly outwardly from said first end portion (36A) adjacent said retainer wall to said sealing end portion (36B) spaced outwardly from said retainer wall; and whereby said primary seal (34) provides a relatively rigid barrier for containing load material on an inboard side (22C) of the subjacent conveyor belt, and the secondary seal (36) in combination with the primary seal (34) defines an elongated tunnel (T) for confining fine particulate load material which escapes past the primary seal (34) so that said fine particulate load material will be conveyed through said tunnel along the subjacent conveyor belt apron (22A, 22B) beneath the flexible secondary seal on the outboard side of said primary seal; characterised in the said primary seal (34) has a lower end portion (46) adapted for placement above the load bearing surface (S) of the subjacent conveyor belt, thereby defining an elongated gap (G) therebetween; said first end portion (36A) of said secondary seal (36) is in contact with said retainer wall (34), and said second flexible sealing end portion (36B) includes a raised tapered rib (50) adapted for surface engagement against the outboard apron (22A, 22B) of the subjacent conveyor belt. A barrier seal assembly according to claim 1 wherein said secondary flexible seal (36) is integrally formed with said primary seal (34). A barrier seal assembly according to claim 1 wherein said primary seal (34) and said secondary seal (36) each have marginal end portions which are adapted to be clamped together for mounting onto a skirtboard (32A, 32B). A barrier seal assembly according to claim 1, wherein said primary seal (34) has a mortise cavity (48) extending along its length, and wherein said secondary seal (36) has a dovetail joint (49) extending along its length, said dovetail joint being received in interlocking engagement with said mortise cavity.

Inventors: VEENHOF WILLEM D, VEENHOF, WILLEM D.
Applicants: MARTIN ENG CO, MARTIN ENGINEERING COMPANY
Application year: 1991
Main classification: B65G21
IPC codes: B65G21