GB2030505A - Installations for obtaining continuous blocks of polyurethane - Google Patents

Abstract

A conveyor belt 15 providing the floor of a foaming tunnel 2 is enclosed by an insulating housing which is divided into an upstream chamber and a downstream chamber by transverse partitions 19, 20, 21 each of which can assume an open or closed condition. Between the downstream end of the tunnel and means 14 for collecting a web laid on the conveyor at the upstream end of the tunnel, there is means 22, 23, 24 for drying the surface of the bottom of the block. <IMAGE>

Description

SPECIFICATION Installations for obtaining continuous blocks of polyurethane This invention deals with further improvements in or relating to an earlier improved installation for obtaininc blocks of polyurethane foam which constitutes the subject matter of our British Patent Application No.

16068/78.

The differences which the earlier improved installation, subject of Application No. 16068/78, displayed in relation to a conventional installation for producing blocks of polyurethane foam were constituted by amendments made to the housing surrounding the endless conveyor belt of the foaming tunnel, on which the foam is formed.

Said conveyor belt was surrounded by a large-sized heat-insulated box-like housing, in which the upper surface of the upper run of said conveyor belt was flush with the open upper part of said box. Likewise, in the principal embodiment, according to which said housing was heated by hot air, the space defined by said box was divided by a single transverse partition into an upstream chamber and a downstream chamber, both of constant volume. In association with said box arrangement, application No. 16068/78 described and claimed heating means other than hot air, as well as cooling means, which allowed control of the temperature existing on the upper or conveying surface of the endless belt.Said heating means, in addition to the hot air recirculated through the inside of the box, which constituted the preferred embodiment, could be an arrangement of coils with steam, infrared radiation devices, or resistors in the plates. According to the type of heat source, the housing of the box required a plurality of more or less complex elements and devices.

The further improvements which are the subject matter of the present application relate not only to the housing of the conveyor belt of the foaming tunnel, but also to parts of the installation situated downstream from said foaming tunnel.

For a better understanding of the further improvements provided by the present invention, a brief description will first be given below of the elements comprised by a standard installation for producing blocks of polyurethane foam.

The basic elements or parts of said standard installation are: a foaming tunnel constituted by a sloped conveyor belt, formed by plates hinged together, the floor of the foaming tunnel being constituted by the upper run of said conveyor belt. The rest of the parts of said tunnel are formed by side walls and a ceiling, provided with ducts for evacuating the gases which are formed and/or released during the reaction which results in the foam, such as CO2 and blowing agent. At the upstream end of said foaming tunnel there is a mixer-feeder device, in which the various reactants which form the foam are mixed and from which they are fed onto a web, preferably paper, which covers and travels with the upper part of the conveyor belt of the foaming tunnel.After the endless conveyor belt of the foaming tunnel there are several drawing conveyors which move the block formed in the foaming tunnel towards an arrangement of idle rollers, from which the block passes on to be cut and stored.

The aforementioned paper web is interposed on the upper surfaces of all the conveyor belts, being fed from a supply device located upstream from the foaming tunnel and being removed by a collecting device located downstream from the last drawing conveyor and before the idle roller arrangement. Naturally, in the installation there are also tanks for reactants, pumps, motors for actuating the conveyors and other necessary devices for its operation.

According to a first aspect of the further improvements subject of the present invention, instead of a single partition as in our earlier improvement, there are provided inside the box-like enclosure or housing at least two transverse partitions capable of assuming two conditions, the first of which, called "open", allows air to flow through them, and the second, called "closed", does not allow air to flow, forming substantially complete airtightness, whichever partition is in closed condition constituting the division between the two aforementioned "upstream" and "downstream" chambers. The number of these partitions is at least two, preferably three, and when the installation is operating only one of them is in the closed condition.Thus one can have, according to the type of foam manufactured, a given constant volume of the upstream and downstream chambers, but these volumes are variable from one foam to another by opening the closed partition, and closing another, which was not possible in the earlier improved installation, where both chambers were of constant volume. It is to be noted that, according to this first aspect of the invention, the formation of these two chambers which are variable from one type of foam to another is applicable to all the heating means considered, and not only to hot air, as occurred in Application No. 16068/78.

According to a second aspect of the further improvements subject of the present invention, at a place located downstream from the foaming tunnel, between the conveyor belt of the foaming tunnel and the first drawing conveyor, between two drawing conveyors, or between the last drawing conveyor and the idle roller arrangement, but before the web collecting device, there are arranged at least some means for drying the surface of the bottom of the block, in which relatively high temperatures are attained.

Said two essential aspects of the subject matter of this invention will be described in further detail in relation to the accompanying drawings, where: Figure 1A is a schematic side view of one installation, embodying this invention, where the insulated housing of the conveyor belt is heated according to the preferred embodiment of the invention, that is, by hot air.

Figure 1B is a plan view of the complete installation of Figure 1 A.

Figure 2A is a side view, on a larger scale, of only the conveyor belt arrangement of the foaming tunnel of Figure 1A.

Figure 2B is a plan view of the arrangement of Figure 2A.

Figure 3A is a side view of the conveyor belt arrangement of the foaming tunnel in a second embodiment of this invention, according to which heating is effected by infrared rays.

Figure 3B ia a plan view of the arrangement of Figure 3A.

Figure 4A is a side view of the conveyor belt arrangement of the foaming tunnel in a third embodiment of this invention, according to which heating is effected by electrical resistors.

Figure 4B is a plan view of the arrangement of Figure 4A.

Figure 5A is a side view of the conveyor belt arrangement of the foaming tunnel in a fourth embodiment of this invention, according to which heating is effected by coils through which steam circulates.

Figure 5B is a plan view of the arrangement of Figure 5A.

Figures 6A and 6B are cross-sectional views, further enlarged, along line A-A of Figure 2A and along line C-C of Figure 3A, respectively, and show a front view of one of the aforementioned transverse partitions which are capable of assuming two conditions, that is, open and closed.

Figure 6C and 6D, respectively, are cross-sectional views, also further enlarged, along lines B-B of Figures 4A and 5A, respectively, and show a front view of one of the aforementioned transverse partitions, in the embodiments according to which heating is effected by electrical resistors and coils with steam, respectively.

Figure 7 is a cross-sectional view, yet more enlarged, along line D-D of Figure 6A.

Figure 8 is a fragmentary view, highly enlarged, of a detail of the arrangement shown in Figure 4.

Figure 9 is a cross-section view along line B-B of Figure 3A.

Figure 10 is a fragmentary view of another detail of the arrangement shown in Figure 4A.

Figure 11A is a plan view of an embodiment of surface drying means for the bottom of the block.

Figures 11B and 11C are cross-sectional views along line A-A and along line B-B, respectively, of Figure 11A.

Figure 12A is a plan view of another embodiment of surface drying means for the bottom of the block and, finally Figures 12B and 12C are cross-sectional views along line A-A and along "B" of Figure 1 2A.

The process carried out in each of the installations involves obtaining three different heat levels on three surface areas of the installation which are in contact with the web, preferably paper, which is placed between the surfaces of the floor of the foaming tunnel and of the drawing conveyors, and the bottom of the block of foam.

On the floor surface of the foaming tunnel, in a first reaction area located in an upstream part of the tunnel, a temperature TR is maintained throughout foaming. This temperature varies from one foam to another. The extent of said reaction area, which depends on the reactivity of the formulation, likewise varies from one foam to another. In Figure 1A of the drawings, 3, 4 and 5 identify the slope of the growth curves of the foam for three formulations of different reactivity. The most reactive foam is that for which the growth curve is identified as 3, whereas the least reactive is that for which the growth curve is identified as 5.

Subsequently, a temperature Tc higher than TR is maintained in a second surface area of the floor of the foaming tunnel, called the consolidation area. The value Tc is also kept constant throughout foaming, varying from one foam to another. It is readily realised that since the floor of the foaming tunnel constitutes the reaction and consolidation area, once the former is defined to match the reactivity of the foam, the extent of the latter is obtained.

In Figure 1 A of the drawings, the longitudinal edges of the reaction and consolidation areas for three types of foam would be as indicated in the following table: Reaction Consolidation Area Area High Reactivity Foam AB BF Medium Reactivity Foam AC CF Low Reactivity Foam AD DF The third area, called the drying area, is downstream from the foaming tunnel, between the foaming tunnel and the first of the drawing conveyors 16, or between two drawing conveyors (a second conveyor is shown in Figure 1A as 17), or between the last drawing conveyor and the idle roller arrangement 25. There may be more than one such area, and it is always before the place where the paper removing device 14 is located. In said area, the bottom of the moving block E is subjected to a drying temperature Ts, much higher than TR and Tc, for a very short time. The mentioned Figure 1 A shows three of these drying areas as 22, 23 and 24.

Thus, the installation in Figure 1A makes it possible to obtain the three mentioned temperatures Tn, Te and Ts, which fulfill the condition TR < TC < < Ts. Additionally, the areas of surface of the floor of the foaming tunnel is, reaction area (TR) and consolidation area (Tc), may vary according to the reactivity of the foam.

The remaining parts of the installation of Figure 1A are as follows: 1 is the mixer-feeder head, 2 is a side wall of the foaming tunnel, 13 is the paper web supplying device, 15 is the conveyor belt of the foaming tunnel, formed by plate-like members identified as Pin Figure B, 18 are ducts for exhausting the gases formed and/or released during the reaction in the foaming tunnel, such as CO2, freon, etc. RA is the driving wheel of the conveyor belt 15 and RG is the guiding wheel of said belt. the remaining parts of the installation shown in Figure 1A will be described hereinafter in relation to other Figures of the drawings where they also appear.

The elements of the arrangements of the conveyor beltforthe foaming tunnel which are common to thedifferent heating means and which are shown in Figures 1A to 5B are described below.

Said conveyor belt 15 is surrounded by a large-sized heat-insulated box-like housing 35, the upper surface of the conveying run of said conveyor belt being arranged flush with the open upper part of said box. Said box-like housing 35 is formed by a bottom 10, located at a very short distance from the lower or return- run of said conveyor belt 15, vertical sides CV1 and CV2, also located at a very short distance from the side edges BL1 and BL2 of said conveyor belt 15 and of a height such thattheir upper edges are flush with the upper surface of the conveying run of said belt over its entire length, and vertical end plates PE1 and PE2 located close to the end parts of said conveyor belt 15.The plate located upstream from the belt, that is, PE2, is of a height equal to that of said sides CV1 and CV2, whereas the plate PE1 is of a height less than thatof said sides CV1 and CV2. The parts forming said housing 35, that is the bottom 10, the vertical sides CV1 and CV2, and the end plates PE1 and PE2, are totally or partially made of heat insulating material.

In the inside of said housing, that is the volume defined by said conveying and return runs of the belt and between the sides of said housing, there are three cross separating partitions 19, 20 and 21 capable of assuming closed and open conditions, only one being in the closed condition during the operation of the installation, the other two being in the open condition. Whatever the heating means may be, it is thus possible to divide the inside of the housing into an upstream and a downstream chamber, or reaction and consolidation chambers, as indicated above, which may be varied in volume according to the reactivity of the foam which it may be desired to produce. In fact, if it is desired to manufacture a high reactivity foam, the partition means 19 will be in the closed condition, whereas the partition means 20 and 21 will be in the open condition.When an intermediate reactivity foam is involved, the partition means 20 will be closed, and 19 and 21 open. When a low reactivity foam is involved, the partition means 21 will be closed, and 19 and 20 open. Naturally, only the partition means which are closed will cause an airtight division between the two: chambers, thereby obtaining, with the programmed use of the heating means, the two different heat levels on both sides of the closed partition means, in such a way that the temperatures TR and Tc are attained on the surface of the endless conveyor belt. Said separating partitions, the conditions whereof are changed by rod means 30, will be described hereinafter in detail in the explanation of Figures 6A, 6B, 6C, 7, 8 and 9.

Between the end plate PE2, close to the mixer-feeder head 1, and the first partition- 19, that is, in a part of the housing which always forms part of the reaction chamber, there isa fan 11 in the side CV1, the purpose whereof is to start operating and drive cold air into the upstream- or reaction chamber when a temperature exceeding the pre-set temperature TR is reached.

According to the preferred embodiment, the heating means are constituted by hot air recirculated in a closed circuit from an installation located outside the conveyor belt arrangement of the foaming tunnel. This embodiment is shown in Figures 1A, 1 B, 2A and 2B.

Outside said housing 35 there is hot air blowing means 12, the outlet whereof is connected with a main hot air supply duct 26 which, passing beneath the housing 35, subsequently branches-off into two secondary supply ducts 6 and 6' at a point located halfway along the conveyor belt 15, each of said secondary ducts 6 and 6' running towards the respective end of said housing, adjacent to the side. Starting from each of said secondary ducts 6 and 6' there is a plurality of branches G, at the outlet whereof there are air inlet control valves 8. These branches open through the side CV2, some of them ending in the reaction chamber and others in the consolidation chamber. Starting from the opposite side, that is CV2, there is a plurality of branches G', at the outlet whereof there are air outlet control valves 9.Said branches G' lead to two air outlet collecting ducts 7 and 7', which meet at a point located halfway along said conveyor belt, in order to form a single main air outlet duct 27. This is connected in turn with the intake of the blowing means 12, thereby obtaining closed circuit circulation of the hot air into and out of the housing 35.

At the point where the mentioned main hot air supply duct 26 divides to form the-secondary supply ducts 6 and 6', there is a directing valve 29 which allows distribution of the flow of hot air fed by the blowing means 12 to the respective secondary ducts 6 and 6', equally or differently. Likewise, at the point where the outlet collecting ducts 7 and 7' meet to form the collecting duct 27 there is another directing valve 28, which performs a similar function on the return flow of air. Control of the valve 28 is linked to that of the aforementioned valve 29.

In Figure 2B the extreme positions of said valves 29 and 28 are shown as H, I, J and K, respectively.

The aforementioned fan 11 is on the side CV1, in communication with the reaction chamber through a flow control valve 31. On the opposite side CV2 there is an assembly 32 of air outlet means also provided with-a flow control valve. Said cooling air inlet and outlet flow control valves can adopt any position, between a completely closed and a completely open position, operating in mutually dependent form if ever an excessive temperature is detected in said reaction chamber, above a preset limit value, which might be ietrimental for the foaming of the material on the conveyor belt 15, if said belt were to stop as a result of a breakdown, for example.

Each secondary duct 6 and 6' for supplying hot air to the inside of said housing 35 is prolonged at its end nto ducts CE1 and CE2 adapted to feed said hot air to the inside of the mentioned housing through the end warts of the latter, said ducts being provided with several hot air feeding outlets (not shown) distributed over he entire breadth of the corresponding end plates PE1 and PE2.

Inside said housing, at one point located to the left of the partition 19 and another to the right of the partition means 21, that is, at places which are always in a reaction area and in a consolidation area, respectively, there are temperature sensing and controlling devices 34 and 33, the mission whereof is to control the position of the valves 28 and 29 directing the air outlet and supply, as well as the position of the salves 8 and 9. The sensor 34 can also actuate the fan 11 when the closing of the directing valve 29 and the salves 8 are insufficient to reduce the temperature of the reaction chamber and it also becomes necessary to inject cold air.

Figures 3A, 3B and 9 schematically show a second embodiment of the invention, in which the upper and lower runs of said conveyor belt 15 are heated by incorporating, inside said housing 35, heating means constituted by a plurality of infrared radiation heating elements arranged in two planes, an upper one from which said elements are directed to radiate heat towards the lower face of the upper run of said conveyor belt, and another lower plane from which said elements are directed downwards to radiate heat towards the back of the return run of the mentioned conveyor belt. In said Figures 3A and 9 the heating elements in the upper plane of the reaction area are shown as 36, those in the lower plane of said area as 40, the heating elements in the upper plane of the consolidation area are shown as 50, and those in the lower plane as 51.

The elements 42 and 47 in the upper plane may belong to the reaction or the consolidation area, depending on which of the partition means 19,20 or 21 is closed. Similarly, the heating elements 41 and 52 in the lower plane may belong to the reaction or the consolidation area for the same reason. As can be seen in the Figures, there ia a dividing partition 37, 37a, 37b and 37which runs horizontally over the entire length of said belt, at mid height, in said housing.

Nine temperature sensing-controlling devices 34,38,39,43,44,45,46,48 and 49 can be seen in Figure 3A.

The one shown as 34, located in the reaction area, performs the same function as in the embodiment of Figure 2A, that is, on detecting a temperature value exceeding the pre-set temperature TR it actuates the fan 11, injecting cold air which flows out through exhaust means not shown in Figure 3B. Those devices shown as 38,43, and 45, located in the reaction area above the partition 37, 37a, 37b, will serve to connect and disconnect the heating elements,36,42 and 47 to maintain the pre-set temperature TR when the partition means which are closed are those shown as 21. Since the sensors-controllers 43 and 45 may belong to the consolidation area, according to which partition means 19 or 20 are closed, their pre-setting to TR or to Tc will depend on the type of foam produced.The sensors-controllers 39,44 and 46, located below the partition 37, 37a, 37t), are pre-set to a temperature below TR because, when the partitions 19 and 20 are open, the lower chamber, which is known as the approach to the reaction area, requires a lower temperature than TR.The same as 43 and 45, the sensors-controllers 44 and 46 may belong to the reaction or the consolidation area, depending on which of the partitions 19 or 20 is closed, and their pre-setting will thus depend on the type of foam to be produced. The device 48 will connect and disconnect the heating elements 50 to maintain the pre-set temperature Tc. The devices 43 and 45 will be equally adjusted in the event that the closed means are those shown as 19.Finally, the device 49 will actuate the heating elements 51 to maintain an intermediate temperature between Tc and TR on the surface of the return run on the back of which the radiation falls.

The electric power controls actuated by the sensing-controlling devices are shown in Figure 3B. The device 38 actuates 53, the device 43 actuates 53', the device 45 actuates 54 and the device 48 actuates 55. The electric power controls for the heating elements 40,41, 52 and 51 of the lower chamber parts are not shown, but their location and operation will be readily realised. As has been indicated, the device 34 only actuates the fan 11.

In the heating embodiment shown in Figures 4A, 4B and 10, said heating is effected by heating means constituted by individual electrical resistor elements R incorporated in each of the plate-like members P forming the conveyor belt. In this embodiment said elements R are duly insulated from the members P to prevent faults through passing of electric power to the belt 15.

Electric power is fed to each of said electrical resistor heating elements R through an arrangement (see Figure 10, enlargement of detail L in Figure 4A) which comprises two trolleys T, one being arranged at each end of a member P of the conveyor belt, each of said trolleys T sliding in contact with a power supply track T', arranged following a trajectory which is adapted to that of the conveyor belt over its entire contour, close to its edge parts.

In an alternative of this embodiment, said two trolleys Tare arranged at the same end of each of said members P of said conveyor belt, in which case said power supply tracks T' are in mutually adjacent arrangement, close to one or the other edge of said conveyor belt, over its entire contour.

Apart from the separating partition means 19,20 and 21, said FIGURES 1/2A and 4B show the sensing-controlling device 34 which actuates the fan 11, which drives cold air into the reaction enclosure, said air flowing out through outlet means which are not shown. As has been indicated earlier, this aspect is common to the four embodiments of heating means considered. Said figures likewise show four sensing-controlling devices 56, 57, 58 and 59. The first of them,56, actuates the feeding of the resistors of the reaction area to connect or disconnect the electric power depending on the pre-set temperature TB. Device 59 actuates the feeding of the resistors of the consolidation area to maintain the pre-set temperature Tc.The sensing-controlling devices 57 and 58 belong to the reaction or the consolidation area depending on which partitions 19, 20 or 21 are closed and, consequently, they will be programmed the same as 56 or as 59. Said resistor connecting-disconnecting points are shown as 60, 61, 62, 63, 64 and 65.

Figures 5A and 5B show the embodiment according to which the heating means are constituted by coil-like conduits, inside which steam circulates under high pressure and at high temperature, from a supply source (not shown) outside the installation. The mentioned Figures 5A and 5B show the coils 66 of the reaction area, those located between the partitions 19 and 20, shown as 67, others located between the partitions 20 and 21, shown as 68, and those 69 located in the consolidation areas. The inlet of steam to said coils is controlled by electrovalves 74, 75,76 and 77, the positions whereof are controlled by temperature sensing-controlling devices 70,71,72 and 73.As can be seen, said steam coils are arranged on two planes, an upper one and another lower one, the coil sections being located on each plane, respectively, close to the back of the upper run of the conveyor belt and close to the back of the lower run of said belt. With this arrangement, the output of heat from the coils is distributed over the entire breadth and length of the backs of said runs of the conveyor belt. Depending on which partitions 19, 20 or 21 are closed, the electrovalves 74, 75,76 will be programmed in such a way that the steam passing through them products heat radiation resulting in TR or Tc.

As has been indicated earlier, in the description of the elements common to all the heating embodiments, in the embodiment which is being considered now the sensing-controlling device 34 controls the operation of the fan 11.

A detailed description is given below of one of the cross separating partitions shown as 19,20 or 21 in Figures 1A to 5B. Said description is made with reference to Figures 6A, 6B, 6C, 6D, 7 and 8 of the drawings.

drawings.

As has been indicated earlier, Figures 6A, 6B, 6C and 6D correspond to sections along the previously indicated lines of Figures 2A, 3A, 4A and 5A, respectively, and show a front view of said separating partition.

figure 7 is a cross-sectional view of the partition of Figure 6A along line D-D of said Figure 6A. Figure 8 is a fragmentary view of the detail identified as M in Figure 4A.

Said partitions are each constituted by two equal upper and lower parts 78, formed by a rectangular metal plate or sheet, the edges whereof are bent at right angles towards the same side, forming pairs of flanges 78a, directed towards the back of the plates of the conveyor belt, the width of the flanges 78a being relatively small in comparison with the width of the part 78 from which said flanges 78a project. A fork-like cross-sectional part 78b is affixed from the longitudinal central halfway line of the part 78, in a direction parallel to and opposite said flanges 78a. This part 786 may be affixed to the main portion of the part 78 by welding or by another mechanical means which ensures a perfect connection between both portions of said part 78.Respective rectangular parts 79 of flexible plastics material are connected to each of the flanges 78a.

There are closure means 80 between the two parts 78b, resting on the channel portions thereof.

Said closure means 80 are constituted by two juxtaposed rectangular plates of sheet metal 81 and 82 (perpendicular to the moving direction of the conveyor belt), which are provided with equal window-like openings, which are rectangular in Figures 6A, 6B, 6C and 6D, of a width approximately equal to the distance between adjacent sides of two successive windows, although they may be of another shape. One of said plates, that shown in Figure 6A of the drawings as 81, can slide in a direction perpendicular to the length of the tunnel, being actuated by the rod means 30. On the other hand, the other rectangular metal plate, that is, the one whose rectangular windows are represented by dotted lines in the Figures, is of fixed position.As can be seen in the drawings, the arrangement of said windows of both plates, in alternating position, is such that there is a position of the slidable metal plate 81, that called "closed", which does not allow air to flow through the closure means 80, because the windows of both plates 81 and 82 are not in register. Naturally, the "open" position, in which both windows of both plates are in register, allows air to flow through them. It is thus clear how the "closed" and "open" positions of the partitions 19, 20 and 21 are attained. As has been indicated earlier, in use only one of said three partitions will be operating in the closed position, the other two being in the open position. The function of the parts 79, which are of flexible plastics material as has been indicated, is to provide airtightness on the two portions, upper and lower, of said partition.As can be seen in Figure 7, said parts 79 of a resilient nature will be depressed by the two short sides of the cross-section of the moving plates P, recovering their position thanks to said resiliency, thus forming substantially complete airtightness.

A description is given below of the surface drying means, located downstream from the foaming tunnel, which are shown in general as22, and 24 in Figure 1A of the drawings. The drying tem peraru re Ts for the bottom of the block of foam is obtained in said surface drying means.

The description of said surface drying means will be made with reference to Figures 11A, 11 B, 11 C and 12A, 12B, 12C. The first three Figures relate to an embodiment which uses infrared radiation elements as heating means, whereas the last three Figures relate to another embodiment which uses steam coils as heating means.

Said surface drying means, whatever may be the heating means used, comprises the following parts: a smooth-surfaced rectangular metal plate 83, the longer side whereof is equal to or slightly larger than the breadth of the block of foam; a housing N adjacent to one side of said plate 83, inside which the means for heating and for cooling said plate are arranged. Said housing is constituted by a shell 84 and a heat insulation 85. The longitudinal central portion of said housing constitutes the space in which the heating means are arranged, whereas the end parts are occupied by the cooling means.Said cooling means are constituted by a cold air supply duct shown as 86, adjacent to one of the longitudinal edges of said housing, and the side thereof adjacent to the central area occupied by the heating means is provided with orifices 91 which distribute the cold air which enters through said duct 86 throughout the enclosure of the heating means. On the side opposite said supply duct 86 there is a collecting duct 87, also provided with orifices 92, which exhausts the air which has cooled the enclosure of the heating means. An electrovalve 89 is in an inlet to the duct 86 and an electrovalve 90 is in an outlet from the collecting duct 87.

Said electrovalves 89 and 90 are of the type which start operating when there is an electric power failure. In this specific case, during normal operation said valves would be closed. As soon as there were an electric power cut they would open, injecting compressed air, from an installation which is not shown, into the enclosure of the heating means. The need for said cooling means is imposed by the fact that the surface drying of the bottom of the block of foam coated with the paper web is caused by contact of said bottom of the block moving over the plate 83 heated by the heating means. As has been indicated earlier, said surface drying is caused by a very high temperature Ts applied for a very short time. Said time is that which the bottom of the block of foam takes to cross the breadth of the plate 83.If there is an electric power failure, the whole installation stops, and even if the feeding of the heating means is also cut off (which may not always occur), at the bottom of the block resting in contact with the plate 83 there would be excessively high temperatures which could result in the combustion of the foam. This risk is eliminated with the arrangement of cooling means which has just been described.

Inside the enclosure where the heating means are located there is a temperature sensing-controlling device 88, the specific function whereof will be explained in description of the heating means in the embodiments shown in Figures 11 and 12.

In the embodiment of the surface drying means shown in Figures 1 1A, 1 1 B and 1 1C, heating is attained with infrared radiation elements 93 uniformly distributed in the central part of the housing N, which are fed from a source 94. In this embodiment, on detecting a temperature value above the scheduled one in the vicinity of the plate 83, the temperature sensing-controlling device 88 cuts off the feed 94, which is reconnected, by the action of said device 88, when a value below the desired one is reached. In this way, by the action of said device 88, the temperature Ts on the plate 83 is controlled within the desired range.

In a second embodiment ofthe surface drying means shown in Figures 12A, 12B and 12C, heating is attained with coils 95 through which steam or hot oil circulates. The feed of the fluid which circulates through said coils is controlled by an electrovalve 96, located at the inlet to the coils. Figure 12A shows, as 97, the outlet of said coil.

As can be seen in Figure 12A, in this embodiment the sensing-controlling device 88 controls the operation of the electrovalves 89 and 96. In Figure 12A the electrovalve 96 which controls the flow of hot fluid (steam or oil) has a function similar to that of the electric power supply source 94, for which reason both devices 94 and 96, with similar functions, in the two heating embodiments, are governed by the temperature sensing controlling device 88. However, in the embodiment of Figure 12A the device 88 also governs the electrovalve 89, which will additionally start operating when there is an electric power failure. This is due to the fact that the steam coil system has more inertia and a slower response than the infrared ray system.It may thus occur that the device 88 senses a temperature Ts above the desired one and orders the valve 96 to close altogether, but this may be insufficient owing to the inertia of the system, for which reason the device 88 is also programmed to actuate the electrovalve 89, allowing the intake of cold air to cool the enclosure N.

In a third embodiment of the heating means of the surface drying means, not shown in the drawings, said heating means are constituted by electrical resistors suitably arranged in the enclosure N. However, this is the least preferred embodiment because it is the one which presents the greatest heat inertia and where temperature control on the plate 83 is more difficult.

In the preceding description it is not intended to limit the improved installation subject of the invention to manufacture of only three types of foam, since all types, with their corresponding reaction times, as well as the length of their growth curve, are comprised within the three types which have been mentioned above. In any event, changes in position of the cross partitions 19, 20 and 21 also come within the scope of the invention.

Claims (7)

1. An installation for obtaining continuous blocks of polyurethane, comprising; a foaming tunnel defined by a ceiling and side walls, together with an endless belt conveyor, an upper run of which constitutes the floor of the tunnel, the conveyor comprising plates hinged together, and being enclosed by a housing having heat-insulating walls; the housing being divided transversely into two chambers, one upstream of the other when related to the direction of travel of the upper run of the conveyor, the division being by means of at least two transverse partitions, which are spaced along the housing in the up and downstream direction, and each of which can assume an open or a closed condition, and a selected one of which is closed, while the other or others are open; the installation further comprising at the upstream end of the tunnel a mixter-feeder device for reactant materials and a device for supplying a web to rest on the upper run of the conveyor, and downstream of the tunnel at least two drawing conveyors spaced in the up-and-downstream direction, followed by a device for collecting the web; and, between the downstream end of the tunnel and the collecting device, at least one means for drying the surface of the bottom of the block of foam which has been formed in the tunnel by contact of the drying means with the web.

2. An installation according to claim 1, in which there are three partitions in all, and there is one drying means in all.

3. An installation according to claim 1 or claim 2, in which said partitions are each constituted by: (a) two upper and lower parts formed by a rectangular metal plate or sheet, the edges whereof are bent at right angles toward the same side, forming pairs of flanges directed toward the back of the plates of the conveyor belt, the width of said flanges being relatively small in comparison with the rest of the part; (b) two fork-like section parts which are connected by welding or by screws, in the central portion of the upper and lower parts, perpendicular thereto and in a direction parallel to and opposite said flanges; (c) rectangular parts of flexible plastics material affixed to the longitudinal edges of said flanges, the function whereof is to form airtightness with the backs of the plates which constitute the upper and lower runs of the conveyor belt, which plates, in their travel, depress along their short vertical sides said rectangular parts of plastics material, which subsequently recover their position until they are again depressed by the following short side of the plate; (d) shutting means formed by two juxtaposed rectangular plates which rest on their longer sides in the channels formed by the fork-like section parts and on their shorter sides in the sides of the housing, one of said plates being fixed and the other slidable on being actuated by rod means connected thereto, in a direction perpendicular to the sides of the box-like housing, the surfaces of said plates being provided with equal rectangular window-like openings, in such a position that when said plates are totally parallel the openings of one are in register with continuous parts of the other, constituting the closed condition of the partition, and when the slidable plate is actuated by the rod means, the windows of both plates are in register, constituting the open condition of the partition.

4. An installation according to any of claims 1 to 3, in which said means for drying the surface of the bottom of the block of foam is constituted by a rectangular plate, the longer side whereof is equal to or slightly larger than the breadth of the block of foam, there being arranged to one side of said plate a housing in the longitudinal central portion whereof there are arranged heating means and a temperature sensing-controlling device, and in two side longitudinal areas thereof there are provided two cooling ducts namely an inlet duct and an outlet duct, which are provided with orifices which communicate with the central part in which the heating means are located, there being in the inlet to the cooling means an electrovalve connected to a conduit which communicates with a compressed air tank, said electrovalve being of the type which opens when there is an electric power cut.

5. An installation according to claim 4, in which said heating means are constituted by electric infrared radiation elements uniformly distributed in the housing, radiating heat towards the back of the rectangular plate, the front side whereof is in contact with the web, the supply to the radiating elements being connected and disconnected by the action of the temperature sensing-controlling device.

6. An installation according to claim 4, in which said heating means are constituted by a coil located in the housing, which coil is fed by hot oil or steam, the amount of heat being controlled by the position of an electrovalve located in an inlet conduit, which valve is governed by the temperature sensing-controlling device located in the housing.

7. An installation according to claim 6, in which the temperature sensing-controlling device also controls the opening of the electrovalve located in the inlet conduit of the cooling means.