FI63071B - ANORDNING FOER VAERMEHAERDNING AV FIBERMATTOR - Google Patents

Description

- PATENT PUBLICATION, χ n „.

tV * PATE NTS K Rl FT θόϋ / 1 3¾¾¾ (51) Kv.lk3lnt.CI.3 D 04 H 1/58, D 06 C 7/02 (21) Patent application - Patentansöknlng 781824 ^ ^ (22) Application cloud - Ansökningsdag 07.06.78 (23) Starting line - Giltighettdtg 07.06.78 FINLAND —FINLAND (41) Becoming a lullse - Blivit offentlig 10.12.78 / pi \ (44) Date of issue of NShtSviksipanon | ^ kriften publiccrad 31.12.82 (45) Patent granted - Patent meddelat 08.08.84

Patent and Registration Office

Patent- och registerstyrelsen (32) (33) (31) Privilege requested —Begird priorttet 09.06.77

France-France (FR) 7717642 (73) Saint-Gobain Industries, 62, Bd Victor-Hugo, F-92209 Neuilly sur Seine, France-France (FR) (72) Jean A. Battigelli, Rantigny, Francois Bouquet, Rantigny,

France-France (FR) (74) Berggren Oy Ab (54) Non-woven thermal hardener - Anordning för värmehärdning av f i bermattor

In the manufacture of fibrous insulating mats, especially mats made of glass or similar mineral fibers, it is customary to first form the mat by depositing the fibers on a perforated, conveying conveyor, usually by means of suction boxes arranged under the conveyor on which the fibers are deposited. It is also customary to deposit a fibrous binder on the fibers either before or after the carpet is built on a conveyor having adhesive properties, and usually consists of a thermosetting material or a thermosetting resin, for example a phenol formaldehyde resin sprayed on the fibers .

A layer of relatively loose fibers on the layering conveyor, i.e. a cover, is then usually delivered to a device commonly referred to as a carpet curing oven, through which the carpet is fed by a second torn conveyor, usually comprising two endless conveyors with adjacent runs facing each other. thickness. Such a mat may be more or less dense 63071, depending on the degree of compression that this pair of conveyors applies to the mat in the curing oven.

A variety of methods have been used to cure the binder, but quite commonly a method of passing hot air through the mat for the purpose of the path followed by the mat through the curing oven is fitted with recycling boxes in pairs on each side of the mat, and such furnaces quite usually include a plurality of such pairs of recycled boxes, provided with the possibility of arranging different high temperatures in succession along the set of boxes, to different zones of the mat in its passageway through the curing oven to control the curing temperature.

It is a main object of the present invention not only to provide heating to cure the binder by a primary heating system in the general manner previously known, but also to provide a second, independent heating system comprising at least one pair of relatively small distributors / collectors operating relatively in small local areas on both sides of the carpet path, the distributor / collector pair being responsible for passing hot gas through the carpet at a pressure and temperature high enough to raise the temperature of the carpet core to a value higher than that reached in the local areas. In addition, the hot gas from the "secondary" binder curing system is preferably passed through the mat in a local area located in the middle or downstream portion of the feed path where the surface layers of the mat have already cured and stabilized due to the primary heating system. The initial stabilization of the surface layers of this mat makes it possible to use a relatively high pressure in the secondary heating system without tearing the fibers of the mat apart.

Although the system of the invention can be applied to curing a wide variety of mats and fibrous layers, for the above reasons the invention is particularly advantageous in curing the binder in relatively dense mats because the pressure and temperature conditions used in the secondary heating system of the present invention provide rapid heat penetration. even inside this thick fiber product, and because this secondary 3,63071 high-pressure air is applied to the mat after its surface layers have already stabilized, resulting in rapid penetration without tearing the fibers apart.

In a typical plant where the primary thermal curing system uses pairs of hot air recirculation manifolds arranged sequentially along a feed passage through the furnace, the invention uses at least one additional pair of hot air recirculation manifolds / collectors with relatively small local areas. inside. In this plant, the purpose is that the hot air pressure of the secondary system operating in the local area is higher than the pressure of the air used in the primary system. When used in this form, the primary air recirculation system not only provides the heat necessary to cure the binder, but also acts as a device to prevent the loss of air leaking from the secondary system operating at higher pressure into the atmosphere.

When using both the primary and secondary systems, ’and kur. the secondary system uses a higher pressure, the rapid penetration of the flap into the interior of the mat to be cured in said local area of the secondary distributor (s) is excellent in accelerating the curing temperature of the binder in the inner or core part of the mat, high to initiate the exothermic reaction of the binder resin. Achieving this exothermic temperature results in the binder continuing to cure even if the subsequent steps of the curing oven are not maintained at the same high temperature. As a result, the use of a secondary high-pressure system in local, downstream curing zones provides overall savings in the fuel required to achieve curing throughout the curing phase.

Another object of the invention is to provide novel structural adaptations for adapting secondary high pressure manifolds / collectors to local areas of primary system recycle bins, which structural reductions result in a reduction in leakage and leakage and in addition automatically result in the release of certain guards without m that resin or other deposits accumulate on those conveyors whose function is to convey the carpet through the curing furnace.

The present invention therefore relates to an apparatus for treating a nonwoven fiber containing a thermosetting fiber binder with heat, comprising a conveyor mechanism for conveying the nonwoven along a treatment passage, gas recycling boxes arranged on opposite sides of the mat in said passageway and forming treatment zones recycling bins and cause the heated gas to pass through the nonwoven in said treatment zones. The objects of the invention are achieved by such a device, characterized in that in the downstream part of the treatment passage there are supply gas and exhaust gas recirculation distribution pipes located inside the recycle bins, forming a local secondary treatment zone , which is connected to the manifolds of the secondary treatment zone and circulates the heated gas through the nonwoven at a pressure higher than the pressure of the gas which is passed through the nonwoven between the respective pair of recycling boxes.

How the above-mentioned and other objects and advantages will be achieved will become more apparent from the following description and the accompanying drawing, in which: Figures 1a and 1b, taken together, form a longitudinal sectional view of a carpet curing oven according to the invention comprising six pairs of hot air recirculation boxes for heat treatment, i.e. curing, and furthermore a secondary system comprising two pairs of local high pressure distributors / collectors, one pair placed in each of the last two primary or low pressure recycling boxes; Fig. 1c is an enlarged sectional view of a portion of Fig. 1b, and shows an alternative embodiment in which two pairs of high pressure or secondary recycling boxes are enclosed within one pair of low pressure recycling boxes; Fig. 3 is a longitudinal sectional view on the scale of Fig. 2 and shows one pair of primary or low pressure recycle boxes with one pair of secondary or high pressure distributors / collectors, Fig. 4 is on the same scale as Figs. 2 and 3, and shows a cross-section taken along section line 4-4 of Fig. Ib, and Fig. 5 is a fragmentary view on a smaller scale than Fig. 4, and shows a modification of the high pressure air recirculation system.

In the drawing, reference numeral 6 denotes the housing structure of the carpet curing oven as a whole, to which the conveyor equipment and the hot air recirculation systems are arranged.

As can be seen from Figures 1a and Ib, the lower part of the furnace has rotating support members, i.e. rollers 7-7, supporting a subordinate endless conveyor, the upper and lower runs of which are shown in Figures 1a and Ib with 63071 6 line-point lines, and the conveyor runs at 8a and 8b in Figures 2, 3 and 4. Figures 1a and Ib also show rotating rollers, i.e. supports 9-9 for a conveyor above, which is shown in Figures 1a and Ib only by dashed dotted lines, but whose upper and lower runs are shown in more detail at 10a and 10b in Figures 2, 3 and 4. Each conveyor consists of a series of loops articulated to each other and supporting rollers adapted to ride on rails marked 13. The loops have transverse ribs 1. These types of conveyors are driven by means of their support rollers.

The rollers 9 of the upper conveyor and also the rails 13 are attached to a frame structure 14 consisting of longitudinal and transverse members connected to each other so as to allow the upper conveyor to be positioned adjustably relative to the lower conveyor. This arrangement can be carried out by means of barbs, numbered 15, in a manner known in the art and not within the scope of the present invention.

Due to the superficial position of the conveyor, the distance between the conveyor runs 8a and 10a, which are the conveyor runs which are against the nonwoven mat, can be varied to give the desired density or thickness to the product to be manufactured.

At the upstream or feed end of the furnace, there is a conveyor schematically shown in point 16. The conveyor shown here represents a perforated conveyor of the type commonly used for collecting fibers to form a mat. The suction boxes shown in section 16 can be used to promote the collection of fibers and to keep them in place on the conveyor. The suction fans 17a are connected to suction boxes. This conveyor 16 delivers the nonwoven conveyor to the gluing rollers R1, R2, which are preferably adjustable to adjust the thickness of the mat to be fed to the oven, and after the rollers R1 and R2 have handed over the partially glued mat, the mat passes between the curing oven conveyor runs.

Primary or low-pressure air recirculation boxes are paired inside the furnace. In the embodiment shown in Figures 1a and Ib, there are six such pairs of low pressure boxes, the zones or areas of the pairs of which are generally denoted by the letters A, B, C, D, E and F. Each such pair of boxes comprises two generally rectangular box-like structures 18 and 19. , which are closed on all sides except the side facing the conveyor runs 8a or 10a. Each box 18 is fixed to a stationary structure below the upper run 8a of the lower conveyor, and each box 19 is fixed to a vertically adjustable frame 14 of the upper conveyor so that the upper boxes move with the upper conveyor when its position is set.

Each box is also provided with an opening connected to either the supply or exhaust line for the process gases, and these openings are marked with the number 20. The inlet and outlet openings and the outlet or outlet openings are marked with the plus and minus symbols "+" or Note, respectively. in the first pair of boxes, the feed opening 20 is arranged in the lower box 18 near the upstream end of this box with respect to the product feeding direction through the oven, and the outlet opening is arranged in the upper box of this pair, close to its downstream end.

The same general pattern is repeated in the second pair of B boxes. In the third pair of boxes C, the supply opening is in the upper box 19, at the upstream end, and the outlet opening is in the lower box of this pair, at its downstream end.

In zone D of the fourth pair of drawers, the pattern of the inlets and outlets is the same as in pairs A and B. In box pair E, the arrangement of the inlets and outlets is as above for zone C, and in pair F the arrangement is similar to boxes D. the ratios can be varied to vary the manner in which curing occurs, and different flow conditions can be used for different types, thicknesses, and densities of products, as is known in the art. In addition, a smaller or larger number of recycling boxes and treatment zones may be used depending on the nature of the product to be manufactured. In addition, the flow through certain boxes can be shut off if desired.

Before considering the structure and operation of the high pressure air recirculation system of the present invention, it should be noted that the furnace universal housing 6 is provided with a degassing system comprising ducts 21 and an exhaust fan 22 which delivers the exhaust gases from the furnace to a suitable purifier 23 and through to separate the solid particles suspended in the gas. The furnace walls 6 in fact form a hood surrounding the furnace's internal components, including the hot gas recirculation and distribution boxes, and the leakage is removed from the furnace housing by a freshly described removal system.

Figure 2 shows on a larger scale a cross-section of the low pressure boxes in zone C. It can be seen that the gas supply line 24 is connected to the upper or supply box 19 and that the outlet line 25 is connected to the lower or outlet recirculation box 18. The purpose of the vanes 19a is to distribute the incoming gas over the entire width of the conveyor and thus the entire width of the mat to be treated. The gases leaving line 25 are supplied to a heater 26 with a burner 27 and these gases are sucked through the heater by a fan 28 which supplies them to a supply line 24. This gas heating and recirculation system can be used for more than one pair of small pressure boxes, or use separate recycling systems.

To accommodate the upper conveyor and the parts attached thereto for vertical movement, the feed line 29 inserts through an oversized opening 29 in the furnace wall, and a flexible closure bellows 30 can be used to substantially seal the connection between the feed line and the furnace wall. In addition, the line 24 is provided with a sliding connection 24a to allow a vertical arrangement.

When considering a high-pressure gas recirculation system, attention should first be paid to certain structural properties of the conveyors. As mentioned above, these conveyors consist of loops 11 articulated to each other in an endless loop, so that one such loop forms each conveyor. The private loops (see, for example, Figures 2 and 3) extend over the entire width of the conveyor and are associated with rollers 12, as mentioned above, and each loop has a base plate 31 with holes spaced apart from the width of the conveyor (as clearly shown in Figure 2), and protruding ribs 32 forming transverse channels extending through the loops for the flow of gases from the low pressure supply boxes or high pressure supply manifolds, through the mat conveyed by the conveyors and then through the holes and channels in the loops of the second conveyor to the discharge boxes, or the headers.

As can be seen from the embodiment of Figures 1a and Ib, the high pressure distributor / collector system HP1 is associated with a low pressure box pair E, the high pressure system and the low pressure box pair E shown in an enlarged longitudinal section in Figure 3 and an enlarged cross-section in Figure 4. / collector system is substantially smaller than low pressure boxes, and in addition that the high pressure distributor / collector system is located inside the low pressure boxes. The high pressure feed divider is denoted by 33, and comparing Figures 3 and 4, it was found that this divider extends over the entire width of the conveyor above the run 10a and above the mat to be treated, but is relatively short in the direction of the path of the mat. The supply line 34 is connected to a high pressure supply manifold and this line passes through an oversized opening 35 in the wall of the furnace, and this opening is closed by a flexible bellows closure 36. The line 34 has a sliding connection 34a for vertical movement. Inside the high pressure feed manifold there are vanes 37 to ensure the distribution of the high pressure gases over the entire width of the conveyor. Below the downstream conveyor run 8a there is a high pressure exhaust manifold 38, and this exhaust manifold is connected to a line 39 for the removal of high pressure gases after they have passed through the mat in question. Line 39 directs the removed gases to a heater 40 having a burner 41 from which the gases are sucked out by a fan 42 which circulates the gases back to the supply line 34.

As with the low pressure system, the High Pressure Line and recirculation system, including heater 40 and fan 42, may be used for more than one high pressure system, or, if desired, separate heaters and fans may be used for different high pressure systems.

Although the feed manifold 33 has manifold blades 37, they are not needed in the discharge manifold 38 and are preferably omitted therefrom.

Figure 5 schematically shows an alternative embodiment of a heater that can be used to heat the high pressure gases of a recirculation system. Here, there is schematically shown at 43 a heat transfer device located in the exhaust manifold 39 before the gases pass through the fan 42. Figure 5 also shows an alternative arrangement of the high pressure feed manifolds 33 and outlet manifolds 38, and in this representation the feed manifold 33 is located below the mat in question and the outlet manifold 38 is located above the mat.

Because relatively high pressure gases are used in the high pressure system, it is important to minimize gas leakage, and this requires the use of special sealing devices, an example of which is shown in particular in Figure 3. It can be seen , one of which is on either side of the divider 33. Both of these wall members are articulated as indicated at 46 so that the wall members can pivot, i.e. move upwards, from the upper surface of the conveyor run 10a. At the point opposite the joint 46, the wall member 45 is provided with a flange which cooperates with a stop, i.e. a stop 47, which serves to limit the downward movement of the wall member and thus prevents the wall member from contacting the upper surface of the conveyor run 10a. Both of these wall members 45 are trough-shaped in shape and extend over the entire width of the conveyor, and according to the invention these wall members have a planar lower surface and are mounted very close to the upper surface of the conveyor run 10a so as to interact flow transversely, i.e. leakage. In a typical plant, in the normal operating position of each wall member 45, the member is a few millimeters, for example about 3-5 millimeters, from the top surface of the run 10a.

These movable sealing wall members are arranged so that the sealing members can normally be placed much closer to the conveyor than would be possible if they were fixed. Moving away from the conveyor easily occurs in the event that irregular layers of resin or fibers have accumulated on the conveyor, as tends to occur from time to time during the use of such equipment. Since the members 45 move automatically if a lump or deposit comes forward, no damage to the equipment will occur even if the wall members are mounted very close to the surface of the conveyor for normal operation.

The members 45 located above the conveyor operate automatically by gravity, returning to their position very close to the conveyor after being moved by some layer of resin or fibrous material. The width of the planar bottom surface of each trough-shaped member 45 is preferably at least equal to the channel between any two adjacent ribs of the conveyor, so that the desired sealing effect is achieved regardless of the position of the conveyor relative to the wall member in the conveyor path.

Similar movable wall members 48 are also associated with the lower conveyor run 8a, and these wall members are adapted to move downward, away from the lower surface of the conveyor run 8a, and are forced upward by springs 49. These sub-members 48 have similar joints and restraint responses when they encounter obstacles as the conveyor runs past the high pressure system, springs are used instead of gravity to return the wall member 48 to its normal operating position.

Each wall member 45, 45 and 48, 48 has an oblique surface 50 on the upstream side of the member, to facilitate movement during the action of foreign bodies carried by the conveyor.

It can be seen from Figures Ib, 3 and 4 that in the high pressure distributor / collector system, the HP1 supply distributor 33 is located above the conveyor in the low pressure recycle box with which the low pressure gas supply line communicates, with the high pressure system outlet in this low pressure system outlet box.

Figure Ib also shows that in the low pressure zone F the high pressure system HP2 is inverted compared to the arrangement shown in the zone E. Thus, in Fig. 1b, the high pressure supply manifold 33 is located below the mat in the low pressure supply box and the high pressure outlet size 38 is located above the mat in the low pressure discharge box.

An alternative arrangement of Figure 1E shows two high pressure recirculation systems installed within a single pair of low pressure boxes 12 63071. In this case, the high-pressure supply manifolds 33a and 33b are located in parallel so that a sealing wall member similar to the sealing members described in connection with Fig. 3 must be moved between them, and the cooperating high-pressure relief manifolds 38a and 38b are mounted inside the low pressure relief box below, so that there is a movable wall member of the type shown above in connection with Figure 3 between the two high-pressure discharge collectors. The external, movable wall members also relate to the divider-collector system of Figure 1e in a manner that is now understood.

Although the high pressure air recirculation systems of the present invention can be used with any treatment zone AF, it is particularly preferred to use these high pressure recirculation systems with low pressure recirculation boxes downstream of the center of the feed path and preferably two thirds of the length of the feed path. from the inlet end. Thus, according to a preferred embodiment shown in Figures 1a and Ib, the two high pressure recirculation systems are generally indicated at HP1 and HP2 located in the low pressure zone E and F, respectively, which are the last two zones in the embodiment of Figures 1a and Ib.

When two high pressure systems are incorporated into a single pair of low pressure boxes, both high pressure supply manifolds are preferably placed on the same side of the mat and preferably inside the low pressure supply box, as this minimizes leakage problems that cause heat loss.

As will be appreciated, the operating conditions will vary depending on many factors, including the thickness of the mat to be formed, the composition and properties of the binder used, and also the amount of binder used. However, some general guidelines for operating conditions are presented below.

First, the invention requires that the low pressure circuit formed by the recycling boxes 18 and 19 in zones A to F include some zones in which gases pass upwardly through the mat and some zones in which gases pass downwardly through the mat 13,63071. It is also required that the gases recirculated through the boxes 18 and 19 in different zones may be at different temperatures, depending on the properties of the binder used, as is already known in carpet curing ovens with several treatment zones. The appropriate temperature range for the gas fed to the recycle bins 18 and 19 is from about 150 ° C to about 300 ° C when conventional types of fiberizing agents such as phenol-formaldehyde binders are used.

The prevailing pressure conditions can also vary and the pressure conditions can be measured in different ways. The pressure in the supply box and the pressure in the discharge box are, of course, different due to the pressure drop due to the passage of gas through the mat. Under typical operating conditions, the pressure in the supply boxes of low pressure systems can be on the order of about 5-30 mm.

With respect to high pressure recirculation systems, when more than one such system is used, for example in the embodiment shown in Figure Ib, where one high pressure system HP1 is located in low pressure zone E and another high pressure system HP2 is located in low pressure zone F, one of these high pressure systems is required to conduct treatment gas through the mat in one direction, and one of these high pressure systems is adapted to conduct the gas through the mat in the opposite direction. Thus, as indicated by the arrow in Figure Ib, the high pressure system HP1 is shown to supply gas downwards and the high pressure system HP2 is shown by the arrow to supply gas upwards. The purpose of this is to maintain a substantially uniform handling throughout the thickness of the mat.

With regard to the pressure and temperature used in a high pressure system, it should also be noted that some advantage can be obtained by using both a low pressure and a high pressure system combined in the same curing furnace, even if the high pressure system temperature is not higher than or even lower than the low pressure system. The reason for this is that high pressure causes faster and more efficient heat penetration into the inside of the mat than a low pressure system.

14 63071

The high pressure system can be operated at quite a wide range of pressures, but in general the pressure should be at least several times, preferably at least ten to twenty times as high as the pressure in the low pressure system. For example, the pressure in the high pressure systems can be up to about 300-600 mm

In the typical case where the air temperature in the low pressure systems is from about 150 ° C to about 300 ° C, the temperature in the high pressure systems may suitably be from about 200 ° C to about 350 ° C.

In a typical plant, the total flow of recirculated gases in low pressure recirculation systems can be about 30,000 Nm / h. In such a typical case, high pressure systems can use hot gas at about 5000 Nm ^ / h.

High pressure gases are concentrated in local, relatively small areas compared to low pressure gases, and these local areas can typically comprise about 10% of the area of the treatment zones formed by the low pressure boxes.

Temperatures and pressures also vary depending on the rate of advance of the mat being formed and the number of treatment zones included in the mat curing oven. The method of using both high pressure and low pressure air recirculation systems according to the invention is particularly effective in many respects, including that a certain curing effect can be achieved with fewer treatment zones and a substantially shorter overall curing oven length. This is because high pressure systems are particularly effective in bringing the interior of the mat to a curing temperature in a short time. It is also advantageous that high pressure systems rapidly raise the temperature of the binder to the level at which the exothermic reaction takes place even in the core part of the mat, and this temperature is then more easily maintained, even after the local areas of the high pressure distributors.

Claims (9)

15 63071 An apparatus for heat treating a nonwoven fabric containing a thermosetting fiber binder by heat, comprising a conveyor mechanism for conveying the nonwoven along a treatment passageway, gas recycling boxes arranged on opposite sides of the mat in said passageway and forming treatment zones, providing for the passage of heated gas through the non-fibrous in said treatment zones, characterized in that in the downstream part of the treatment passage there are recirculation manifolds for the feed gas (33) and the exhaust gas (38) located inside the recycle boxes (18, 19) forming a local secondary treatment zone, smaller than and located within the primary treatment zone of the corresponding pair of recycle bins, and a heated gas recirculation device connected to the distribution pipelines (33, 38) of the secondary treatment zone and recycled ä heated gas through the fibrous mat at a pressure greater than the pressure of the gas passed through the nonwoven between the respective pair of recycling bins. Apparatus according to claim 1, wherein the conveyor mechanism comprises two perforated, endless conveyors, the conveyor runs of which are spaced apart and turned against the nonwoven mat, in contact with the mat and conveying it along the treatment passage, the gas recycling boxes being located outside said conveyor runs (8a, 10a) provided with openings opening in the conveyor runs for circulating heated gas through the non-fibrous mat between the perforated conveyors and said runs, characterized in that the recirculation manifolds (33, 38) form part of a wall member (45, 48) very close to the perforated conveyor run (10a), 8a), and that their fastening structure (44) allows the wall member (45, 48) to move freely away from the conveyor run. 16 63071 Device according to claim 2, characterized in that the wall member (45) above the conveyor run (10a) can move upwards, away from the conveyor run, and downwards towards the conveyor run by gravity and that the stop (47) is adapted to limit the downward movement of the wall member. per conveyor run. Device according to claim 2, characterized in that the wall member (48) located below the conveyor run (8a) can move downwards, away from this conveyor run (8a), and that devices are adapted to force the wall member upwards towards the conveyor run (8a) and abutments ( 49) adapted to limit the upward movement of the wall member towards the transport run. Device according to claim 1, characterized in that it comprises at least two pairs of gas recirculation manifolds (33, 38) forming at least two local secondary treatment zones, both within and smaller than the respective primary treatment zones, and that these manifolds are at a distance from each other in the direction of the non-fibrous processing passage. Device according to Claim 5, characterized in that the supply manifolds (33) of the gas recirculation manifold pairs are located in the recirculation boxes (19) on one side of the treatment passage and in that the discharge collectors are located in the recirculation boxes (18) on the other side of the treatment passage. Device according to Claim 5, characterized in that the supply manifolds (33) for the gas recirculation pairs are located in the supply recirculation boxes (19) on one side of the treatment passages and the discharge collectors in the discharge recirculation boxes (18) on the other side of the treatment passages. Device according to Claim 1, characterized in that a plurality of recycling box pairs (18, 19) are arranged on opposite sides of the treatment paths and in that the device has a plurality of recycling distribution pipe pairs (33, 38), at least one of which is arranged in one recycling box pair (18). , 19) and at least one is housed in a second pair of recycling bins (18, 19). Device according to Claim 2, characterized in that the dimension of the movable wall element (45, 48) in the direction of the processing path is at least twice as large as the distance between two adjacent ribs (11) of the conveyor joint.