CA1080928A

CA1080928A - Twin belt system

Info

Publication number: CA1080928A
Application number: CA258,935A
Authority: CA
Inventors: Olof Hellsund
Original assignee: Sandvik Conveyor GmbH
Current assignee: Sandvik Conveyor GmbH
Priority date: 1975-08-12
Filing date: 1976-08-12
Publication date: 1980-07-08
Also published as: JPS5241371A; SE7608905L; FR2348135A1; DE2636170A1; GB1508534A

Abstract

Abstract of the Disclosure A system for treating a continuous sheet of a product by passing it around a series of drums with endless twin belts extending around them. A layer of the product is fed between the belts and it is treated to form a continuous product sheet. Each of the belts has one or more V-ropes or guide strips mating with annular beveled surfaces around the periphery of each of the drums. Those V-ropes hold the belts in precise alignment with the drums and overcome the problems created by the tendency for the outer belt moving from a drum to bulge away from the other belt when passing to the next drum.

Description

This invention relates to processing equipment having endless twin metal belts which move together while holdin~ a product captive between them, and relates particularly to improvements in systems for the manufacture of products in continuous sheet form and of the types which require such treat-ment by heat and/or pressure.
An object of this invention is to provide improved methods and apparatus for treating materials between two belts. Another object is to provide improved systems for treating products between metal belts. A
further object is to provide for the above in a manner which overcomes difficulties which have been encountered with such systems in the past. These and other objects will be in part obvious and in part pointed out below.
The present invention involves producing products by feeding a layer of materials into the nip between two metal belts as the belts pass on-to and around a series of drums. The illustrative embodiment of the present invention involves a twin-belt system for producing a continuous sheet of a product from a filler and a material which requires heat-treatment under pressure. The continuous sheet is heat treated to perform the curing or re-acting of the product while holding the sheet captive between the pair of steel belts and passing the belts around a series of hollow heating drums.
One system is disclosed in U.S. Patent No. 2,069,589 to J. Meijling et al.
It has been found that the present invention overcomes difficulties which were encountered with such systems.
According to the invention, there is provided guide means between each belt and the drum upon which it rests which forms a combination of the drum and the belt, said ~uide means comprising guide structures a~tached to the respective belts and presentin~ guide surfaces which are spaced from the belt surface which contacts the drums and extend toward the drum axis and guide surfaces on the drum which are parallel with and mate with the first-..
named ~uide surfaces, respectively, said guide surfaces on said guide structures and on said drums forming a first set of cooperating guide sur-faces which prevent movement of the belt in one direction parallel to the drum axes and another set of guide surfaces which prevent such movement in the opposite direction whereby said guidc structuresact thro-ughout the length of each belt contacting one of the drums to exert continuous forces opposing deviation of the belt movement from true alignment.
'. Referring to the drawings:
, Figure 1 is a schematic side elevation of a system constituting one embodiment of the invention;

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Figures 2 and 3 are enlarged plan and sectional views of a portion of one of the belts of Figure l;
Figure 4 is a view similar to Figure 2 but showing another embodiment of the invention;
, 5 Figure 5 is a greatly enlarged sectional view of ? the central portion of one of the drums in the system of Figure 1, showing a belt resting on the drum; and, Figure 6 is an enlarged somewhat schematic view of a portion of Figure 1 showing the steel belts passing from one drum to another.
? . In manufacturing certain sheet products it is . .
desirable to hold the materials captive between two belts during a curing or finishing process. That is particularly important in certain processes for manufacturing sheet products which require heating and/or cooling under pressure. With some such processes, a continuous product sheet or strip may be passed from a hopper type tank as shown in U. S. Patent No.

2,069,589 or it may pass from a roll on an unwinder or from a tank and then is fed between two mating steel belts. The belts ~ ~
20 with the product sheet held captive between them pass around a -series of hollow cylindrical drums or rolls. The product sheet is heated by supplying steam to the one or more drums, and there may be a drum upon which the product is cooled. The product can then pass to a winder or other receiving means thus com-pleting the process.
The present invention overcomes a very serious problem which was encountered in a system of that type. In -~
~: passing around the drums in a series, the two belts alternate between being the inner belt which wraps directly against the :
drum, and being the outer belt which wraps around the layer of the product sheet. That is, when the two belts approach -the '' .', ',.

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first drum, the product sheet is fed between them and one belt is the inside belt and contacts the drum, while the other belt is the outside belt and presses the product sheet against the inside belt. And when the belts pass from that first drum to the second drum, the relative positions of the belts on the drum are reversed so that the belt which contacted the first drum is the outside belt on the second drum and holds the product sheet against the other belt which lies on the second drum.
~hen passing around each drum, the inside belt is at a lesser radius than the outside belt, so that the outside belt tends to move at a more rapid rate than the inside belt.
But the inside belt is drawn away as the outside belt on the next drum so that it is the belt which tends to move around the next drum at the more rapid rate. That difference in the - relative rates of the movement of the two belts tends to cause : the outside the belt leaving a drum to bulge outwardly away from the other belt. Also, it was found that there was a very -marked tendency for at least the outside belt to move axially with respect to the drums, i.e., depart from the tracking position on the drums. When such a condition developed, it :
was found to be impractical to try to adjust the axis of the drum because adjusting one drum disturbed the relationship ; between the belts and the next adjacent drum and subsequent ;~
!;25 drums. For solving that problem there was a proposal to hold the belts in alignment by flanges on the pulleys and drums around which the belts pass. However, it has been found that `
flanges on the pulleys or drums will not overcome the problems referred to above. The belts still tend to depart from true alignment so that the belt edges become seriously damaged by ;scraping on the flanges and the belts even tend to ride up on :.
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, . top of the flanges thus rendering the machine completely ~ inoperative. The result was that the belts would not remain :. in tracking relationship with respect to the drums, and the product sheet also deviated from true alignment and developed i 5 bulges w~ich became large enough to produce folds or pleat$
in the edge portion of the product sheet. The present ~$ invention overcomes that difficulty, and insures that the product sheet will be of uniform high quality.
Referring to Figure 1 of the drawings, a system is represented schematically for fabricating a continuous sheet or strip of glass-fiber reinforced plastic. The system of this embodiment includes two hollow cylindrical drums 6 and 7 and a pair of endless steel belts 14 and 16 ; which pass around the drums together with the product strip held captive between them. Drum 6 is a heating drum which is mounted at its ends upon axial stub shafts (not shown).
This drum is supplied with steam through a line 5 from a boiler 9 and the condensate is returned through a line 11, lines 5 and 11 being concentric and extending through one of ~ 20 the stub shafts. Drum 7 is a cooling drum and cold brine is -:i ` delivered to it from a chiller 13 through a line 19 and the ~ brine is returned to the chiller through a line 17, lines 19 :s and 17 being concentric tubes through one of the stub shafts j ~ of the drum.
Belt 14 passes from drum 7 to pulley 18 and thence upwardly around the pulley and to the left and around a pulley 20. Belt 16 moves with belt 14 to pulley 18, and then onto a pulley and downwardly around a pulley 22 and thence some-what downwardly and to the left and around pulley 24. The belts move from their respective pulleys 20 and 24 somewhat ~, ::
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downwardly and they converge and move together as they approach drum 6. The product strip 15 is fed between them and the belts pull the strip captive as they move around drum 6 and thence around drum 7.
The drums and pulleys are mounted on a frame structure (not shown), and are enclosed with the belts in a housing represented at 26. A product strip 15 is drawn from a tank 28 upwardly around a pulley 30 and thence down-wardly and to the right of the bite between belts 14 and 16 as the belts move onto drum 16. Strip 15 is compressed between the belts and is first heated as it passes around drum 6 and is then cooled as it passes around drum 7. The product is further cooled as it is held captive between the belts while moving from drum 7 to pulley 18. Belt 14 is peeled away from the product strip at pulley 18, and the product strip is carried by belt 16 to pulley 22 where belt 16 is also peeled from the product strip. The finished product strip 32 is discharged ~rom housing 26 and is further treated or packed for storage.
Separate electric motor and gear units 23 and 25 drive belts 14 and 16, respectively, through pulleys 18 and 22 and the tension on each of the belts is controlled by units 23 and 25, respectively. The drive and tension control units are of known construction.
As indicated above, with a system of the general type of the illus~rative embodiment, the outer belt passing ` from one drum to the next drum of a series tended to bulge out away from the outer belt and from the product sheet, and tended to move from its true alignment path. The basis of the difficulty was that the inner belt 14 on drum 6 was pulled onto drum 7 at a more rapid rate than belt 16, whereas belt 16 ' ,, .

,: , .. . , :, tended to move around drum 6 at a more rapid rate than belt 14. It was found that that difficulty was avoided by providing a belt-guiding system to maintain both belts in exact alignment at all times. For that purpose, each of the belts 14 and 16 has a V-rope 50 (see Figure 5) extending along its center line and projecting into a peripheral groove 52 in each of the drums which the belt contacts. Also, there is an identical groove in each of the pulleys. That is, the V-rope 50 on belt 14 projects into an annular groove 52 in : ;
drum 6, and the V-rope on belt 16 projects into groove 52 in drum 7. Each of the V-ropes is generally triangular in cross-section and is formed by a continuous spiral ~see Figures 2 and 3) of a thin narrow stainless steel strip.
Each of the flat sides 54 of the V-rope is spot-welded to the belt at 56, so that each loop is attached to the belt at both of its ends, and the other two sides (Figure 5) 58 and 60 are free and resilient. The arrangement is such ~ ;
; that when belt 14 is held snuggly against surface 70 of the drum, portions 58 and 60 of the V-rope are held firmly against surfaces 66 and 68 so as to provide a fixed relationship between the V-rope and those surfaces. With the belt posi-, tioned as shown in Figure 1 and a layer 15 between them, the ~ -belts and layer 15 form a rigid stable construction around each drum. That is, each groove 52 provides two tapered annular or peripheral surfaces 66 and 68, each of which mates with a surface portion of each spiral of its V-rope 50.
Each of those two pairs of mating surfaces at each spiral of the V-rope throughout the length of each belt contacting a drum or a pulley provide balanced opposite forces tending to hold the belt in egact alignment.
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~ IV~9V9Za The belts and the product layer between them act in the nature of a single structure in that they are held together in hugging relationship against drums and the pulleys.
Hence, while the belts move continuously, a rigid construction of unchanging configuration is provided which is formed by the . belt and the drums and pulleys. Throughout that construction the V-ropes resist the tendency for the belts to deviate from the true alignment path. For example, belt 14 is held in ; exact alignment when it passes around drum 6 and pulleys 18 10 and 20, and that alignment is maintained by the cylindrical -forms as it passes around drum 7. Simultaneously, belt 16 is held in exact alignment when passing around the drum 7 and pulleys 22 and 24 and the cylindrical forms maintain it in ; alignment while passing aro~nd the drum 6.
The maintenance of the belts in exact alignment ~
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has overcome the above-mentioned difficulty which was encoun-tered in a system of the general type disclosed herein which did not have the V-ropes on the belts and the mating grooves in the drums and pulleys. With the present system, the belts ; 20 do not tend to bulge out, and in fact the belts and product ~ -layer stay together as they pass from one drum to the next.
An explanation for the achievement of that result will now be discussed.
As pointed out above, the optimum posture of the : 25 belts is for each of them to be formed into a series of partial cylinders and with each partial cylinder being connected to each adjacent partial cylinder by a flat belt portion which is tangential to the two partial cylinders.

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Referring to Figure 6, the belts are formed into partial cylinders extending around drum 6 from tangential point 80 to tangential point 82, and then the belts move away from drum 6 to tangential point 84 on drum 7. The belts i 5 have portions 86 between points 82 and 84 which are flat and tangential to their respective partial cylinders on the adjacent drums.
The portion 86 of belt 14 is under tension because it is being drawn into drum 6 at a lesser radius than is belt 16, and portion 86 of belt 16 tends to be slack because it has moved at a greater radius than belt 14 around drum 6.
The above-mentioned bulging effect is avoided only because the belts are forced to move around both drums at the same rate. It is believed that the flat portion 86 of belt 16 j 15 acts in effect as a column to exert forces at the tangential zone of point 82, those forces are of a magnitude to retard the movement of belt 16 around drum 6. As long as portion 86 of belt 16 does not buckle or bulge and is under compression at the nip at 84 between drum 7 and belt 14, belt 16 cannot move forwardly from drum 6 any faster than the surface of drum 7 is moving. Nevertheless, it is held against the drum and is being pushed forwardly from drum 6 at point 82. However, even a thin belt can withstand longitudinal compression forces when acting as a column, provided the forces are below the limit at which the belt would buckle when acting as a column.
That limit is based upon the physical characteristics of the belt, i.e., its cross-section and length and the material of .
i which the belt is constructed. Accordingly, belts 14 and 16 are ` caused to move around drum 6 at the same rate so that between , '' :, - 8 - ~

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points 80 and 82, there is preogressive relative longitu-dinal movement between the belts with belt 16 lagging behind belt 14.
Similarly, if the system were to include a third drum in the series downstream from drum 7, in moving around drum 7, belt 14 would be restrained from moving freely beyond point 88 because of compression forces ex- ;
erted by the portion 92 of the belt. It is thus seen that the inside belt on each drum is caused to lag behind the 10 outside belt. However, the belts would alternate as the inside and outside belts on successive drums so that neither belt moves more than "one step" ahead of the other. The total amount that one belt lags behind the other on a drum . ~ equal the difference between the mean circumferential 15 lengths of the two partial cylinders of the belts.
V-rope 50 cooperates with the other belt and drum structure to provide adequate heat transfer between , the heat exchange fluids in the drums and the product layer. Other forms of V-ropes may be used, for example~
` 20 in the embodiment of Figure 4 the V-rope is in the form of individual triangular clips 100 spot welded to .:` the belt.
" The invention contemplates that additional drums ;~
~; for heating or for cooling may be added to the series, and 25 that the number of drums and the construction will be such as to produce the desired results. Various heat ~ransfer ; and/or pressure effects may be produced upon the product, for example, by changing the belt tension to control the i~ pressure and by changing the temperature of the heat exchange ;
30 fluids to control the heat transfer rates. Also, if the _ g _ ,:
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product is to be frozen, the drums can be evaporators of a refrigeration system. The single V-rope attached along . the center line of each of the belts can be replaced by two V-ropes on each of the belts mating with V-grooves at the ends of the drums and pulleys. Also, the belts can , overhang the ends of the drums with a V-rope at each edge ',. of each of the belts, and with the drums and pulleys j beveled at their ends to produce surfaces identical with surfaces 66 and 68 in Figure 5. With that arrangement, the V-rope at the left-hand edge of the belt (as in Figure 5) would mate with a beveled surface like 68, and at the right-hand edge of the belt, the V-belt would mate with a : surface like 66. It is understood that other modifications ~` in the constructlon and other embodiments may be provided within the scope of the claims.
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Claims

1. In apparatus for treating products, the combination of, a plurality of drums having parallel axes, a pair of metal belts which are adapted to move coextensively with a product between them while passing around cylindrical surfaces of said drums in series wherein a first belt of said pair rests upon a first drum of said series and the other belt of said pair presses the product against the outer coextensive surface of said first belt and the belts with the product between them pass around the next drum of said series with said other belt resting upon said next drum and said first belt presses the product against the outer coextensive surface of said other belt, and wherein a longitudinal portion of each of said belts passing around each drum is a portion of a cylinder with the same axis as the drum and wherein said belts pass from one drum to the next drum through a zone wherein that portion of each belt is substantially tangential to the respective drum, and guide means between each belt and the drum upon which it rests which forms a combination of the drum and the belt, said guide means comprising guide structures attached to the res-pective belts and presenting guide surfaces which are spaced from the belt surface which contacts the drums and extend toward the drum axis and continuous guide surfaces on the drum which are parallel with and mate with the first-named guide surfaces, respectively, said guide surfaces and continuous guide surfaces forming a first set of cooperating guide surfaces which prevent movement of the belt in one direction parallel to the drum axes and another set of guide surfaces which prevent such movement in the opposite direction whereby said guide structures act throughout the length of each belt contacting one of the drums to exert continuous forces opposing deviation of the belt movement from true alignment.

2. A system as described in claim 1 wherein said portion of each belt is not greater than a portion of the circumference of one of said drums.

3. A system as described in claim 1 wherein said guide means includes a guide structure for each of said belts comprising a continuous series of resilient loop portions each of which is attached at its ends to its belt and annular surfaces on said drums.

4. A system as described in claim 1 wherein said guide means comprises V-belts attached to said belts and grooves in said drums.

5. A system as described in claim 1 wherein said guide means comprises a pair of V-belts and grooves which mate with said V-belts, each of said V-belts comprising a continuous series of metal loops attached to their belt and having converging side portions which provide contact surfaces which mate with drum surfaces.

6. In a system as described in claim 5 wherein, each of said grooves is a V-groove with annular side surfaces which diverge radially-outwardly to lines of intersection with the peripheral drum surface.

7. In a system for treating products, the combination of, a plurality of drums having cylindrical outer surfaces positioned with parallel axes, means mounting said drums to rotate, a pair of metal belts mounted on said drums in coextensive relationship with one belt being in direct contact and forming a segment of a cylinder in a hugging relationship with said cylindrical surface of one drum and the other belt being in direct contact and forming a segment of a cylinder in hugging relationship with said cylindrical surface of a next drum, and said belts being adapted to hold a product captive between them along a path in alignment around said drums in series, each of said belts having guide means attached to the belt surface which is opposite the surface facing the other belt, each of said drums having contact surfaces which extend from the respective belt in a radial direction toward the axis of the respective drum and which contact surfaces mate with said guide means and prevent said belts from deviating from their alignment positions, each of said belts having a portion between the portions which extend around the adjacent drums which in each of said belts is a portion tangential to both of said adjacent drums.

8. In a twin belt system for treating products, the combination of, a pair of endless metal belts, means to support said belts upon a series of rigid cylindrical surfaces of rotating units and to move the belts along a product treating path through which they are coextensive and between which the product is held captive and subjected to the desired treatment, said belts being held under tension around said rigid cylin-drical surfaces of said units along which the belts pass to-gether with the product between them from one cylindrical surface to the next to thereby maintain coextensive portions of said belts with one belt being the inner belt when passing around said one cylindrical surface with a portion being tangential thereto and with the other belt being the inner belt when passing around said other cylindrical surface with a portion being tangential thereto, and guide surfaces upon each of said units and guide means mounted upon the side of each of said belts opposite the other belt which guide means presents guide surfaces which mate with said guide surfaces on the respective unit within a zone adjacent the cylindrical surface of said unit and extending toward the axis thereof thereby to maintain said belts in precise alignment, said cylindrical surfaces being positioned so that said portion of said other belt will act as a column and withstand the longitudinal compressive forces without buckling or bulging.

9. In a system for treating products, the combination of, a drum assembly comprising a plurality of drums with cylindrical outer surfaces and means mounting said drums to rotate on parallel axes, a metal belt assembly comprising a pair of endless belts and pulley means mounting said belts to move in coextensive relation-ship around said drums in series and to hold said belts under pre-determined tension against said cylindrical surfaces, means to drive said belts at a controlled rate, means to feed a product to be treated between said belts as they approach the first of said drums in the series, and guide means comprising beveled surfaces on each of said drums within a zone between the cylindrical surface and the axis of the respective drum and guide means on said belts presenting surfaces which mate with said beveled surfaces and which hold said belts in precise alignment, wherein the belt moving at the greater radius around the first drum of said series has a portion extending tangentially to said first drum and the second drum of said series and said portion is placed under compression by the restraining of its movement onto said second drum by the clamping action of the other belt against said second drum whereby said belts tend to move around said first drum at the same rate.

10. A system as described in claim 9 wherein said belts are steel belts and which includes means to circulate heat exchange fluid through said drums to produce a temperature treatment modifi-cation of said material.

11. In a twin belt system wherein two metal belts are held under tension and move together around a plurality of drums in series with one belt resting upon the surface of one drum of the series and the other belt resting upon the next drum of the series and wherein a product is held captive between the belts and the tension on the outer belt on each drum causes said outer belt to compress the product tightly against the belt resting on that drum, whereby a longitudinal portion of each of said belts is a portion of a cylinder with the same axis as the one drum and said pair of belts pass from said one drum to said next drum through a zone wherein a portion of each belt is substantially tangential to the two drums, each of said drums having two drum-guide surfaces which are positioned radially inwardly with respect to its cylindrical surface, and guide means mounted upon each of said belts and pro-jecting from the surface which is opposite to that facing the other belt, each of said guide means presenting belt-guide surfaces each of which is positioned parallel to and in contact with the respective one of said drum-guide surfaces when the belt is positioned in contact with the cylindrical drum surface, said drum-guide surfaces cooperating with said belt-guide surfaces to oppose any forces tending to cause that belt to move parallel to the drum axis whereby each belt is held in precise alignment.

12. In a twin belt system wherein two metal belts are held under tension and move together around a plurality of drums in series with one belt resting upon the surface of one drum of the series and the other belt resting upon the surface of the next drum of the series, and wherein a product is held captive between the belts and the tension on the outer belt on each drum causes said outer belt to compress the product tightly against the belt resting on that drum, the combination of, a plurality of drums having parallel axes, a pair of belts which are adapted to have a product between them with a first belt of said pair resting upon said one drum and the other belt of said pair pressing the product against the outer coextensive surface of said first belt whereby a longitudinal portion of each of said belts is a portion of a cylinder with the same axis as said one drum, and with said belts then passing around said next drum whereby a longitudinal portion of each of said belts is a portion of a cylinder with the same axis as said next drum and said pair of belts passes from said one drum to said next drum through a zone wherein a portion of each belt is substantially tangential to the two drums, and guide means comprising a V-belt structure mounted upon the drum-contacting surface of each of said belts and extending continuously throughout the longitudinal extent thereof and each of said drums having a groove which is adapted to snugly receive the V-belt structure on the belt which rests upon that drum surface and which presents a pair of continuous opposed guide surfaces which mate with guide surfaces of the V-belt structure without interfering with the contact between the belt and the drum, whereby each of said longitudinal portions of said belts is maintained in precise alignment with the respective of said drums upon which it rests.

13. In a twin belt system, the combination of, a plurality of drums having parallel axes, a pair of metal belts which are held under tension and move together around said drums in series with one belt resting upon the surface of one drum of the series and the other belt resting upon the next drum of the series, and wherein a product is held captive between the belts and the tension on the outer belt on each drum causes said outer belt to compress the product tightly against the belt resting on that drum, and wherein a longitudinal portion of each of said belts is a portion of a cylinder with the same axis as said one drum, and with said belts then passing around said next drum whereby a longitudinal portion of each of said belts is a portion of a cylinder with the same axis as said next drum and said pair of belts pass from said one drum to said next drum through a zone wherein a portion of each belt is substantially tangential to the two drums, and guide means comprising a guide structure mounted upon each of said belts and projecting from the drum-contacting belt surface and presenting guide surfaces positioned radially inwardly from said drum-contacting surface with respect to the drum axis, each of said drums having two continuous guide surfaces which cooperate with the respective guide surfaces of said guide structure so as to exert opposing forces parallel to said axes which act continuously to resist axial movement of the respective of said portions of cylinders contacting that drum so that said belts and said drums maintain a stable cooperative relationship with each of said belts including said portions of cylinders and with said guide means acting to maintain the belts in precise alignment.