Process and apparatus for elimination of densified areas in blocks of pliable polyurethane foam

The densified area commonly formed during the manufacture of blocks of pliable polyurethane foam on a web of continuous material in a foaming tunnel is eliminated by controlled heating of the conveyor belt in the tunnel to a range between the densification temperature and the cracking temperature of the foam during the reaction period. An improved apparatus for this purpose comprises an enclosed, insulated housing and means for heating the conveyor belt such as hot air, infrared radiation, steam coils or electrical resistors. A preferred embodiment comprises heating the bottom of the foam block after it emerges from the foaming tunnel to a temperature considerably higher than that in the foaming tunnel. This eliminates completely any need for trimming off irregularities after removal of the web of continuous material.

BACKGROUND OF THE INVENTION 
The present invention relates to an important improvement obtained in the 
manufacture of blocks of polyurethane foam, specifically the elimination, 
during manufacture, of the densified bottom of the blocks, obtained by the 
usual process. 
This invention also relates to an improved apparatus for manufacturing 
continuous blocks of polyurethane foam and, more particularly, to 
arrangements for heating the housing of the conveyor belt of the foaming 
tunnel and parts downstream of the foaming tunnel in an apparatus of this 
kind. 
As is known, polyurethane foam is a plastic which has acquired increasing 
importance over recent years, having many uses in such different fields as 
the automotive industry and the food industry. 
In the usual process, polyurethane foam is obtained by reacting, on a 
moving belt, a polyol and polyisocyanate as principal ingredients, 
together with catalysts, dyes, blowing agents, etc. The physical 
properties (stiffness, density, cell size, tensile strength, etc.) of the 
different kinds of polyurethane foam are a function of multiple 
parameters, the principal ones being the nature of the polyol and of the 
polyisocyanate, the ratio between both and the blowing agent. 
The components in liquid state are vigorously shaken immediately before 
being deposited on a mechanically operated endless band conveyor. Between 
this endless band and the poured liquids there is placed a paper web, 
which will follow the conveyor in its path, so that said liquids do not 
spill before they solidify following the reaction. 
The conveyor is given translatory motion, with suitable speed for each 
quality of foam. The liquids deposited on the paper web commence reacting, 
being introduced, by the movement of the band, into a tunnel having an 
approximate length of 20 meters, with completion therein of the exothermic 
chemical reaction, via which the foam is produced, increasing by several 
times (approximately 50) the initial volume of the liquids. Finally there 
is obtained a pliable and spongy solid which is the polyurethane foam. 
Naturally, the shape of the cross-section of said block will be that of 
the tunnel at its base and side walls. 
The reasons for manufacturing said polyurethane foam inside a tunnel are as 
follows: 
(1) To prevent dispersion of the toxic gases, principally the CO.sub.2 
produced in the reaction or, eventually, the toxic gases evaporated as a 
result of the heat produced. 
(2) To obtain the approximate shape of the cross-section of the block, 
achieving a body with an almost rectangular section. This is usually 
referred to in this art as "molding effect". 
Independently of the type of foam produced, a problem associated with the 
manufacture of the block is the densification occurring in the bottom 
thereof, as a result of which it is necessary to waste an important part 
of the finished material because its density is notably greater than that 
of the rest of the block. 
Experts in the art will admit that it is frequent for the percentage of the 
densified area to be 5% by weight, even reaching 7% in relation to the 
total weight of the block. This amount of wasted raw material can be of 
considerable importance, bearing in mind that the daily production of an 
average-sized polyurethane foam installation exceeds 20,000 kg. 
The formation of this dense area at the bottom is a serious drawback from 
the economical-industrial point of view because: 
(1) It requires a trimming operation of said densified bottom, which 
consumes time, energy and manpower and requires proper mechanical means, 
preferably saws designed specifically for this purpose. The densified 
layer of foam can have a length of more than 100 meters (the length of the 
block), a width of two meters and a thickness of 10-30 mm. 
(2) The trimmed by-product has to be marketed at a notably lower price than 
the rest of the foam, because of its unsatisfactory properties, its small 
thickness and irregular shape. 
(3) Since the raw materials of polyurethane foam are substances of 
petrochemical origin, their high cost under present energy crisis 
circumstances calls for maximum utilization of the finished products which 
are used for manufacture. 
The preceding problems are solved by the process of the invention, which 
provides a block without the densified area, thus attaining notable 
utilization of the raw materials and, consequently, a substantial saving 
in manufacturing costs. 
As far as the inventor is aware, in this field there is no process 
resulting in the production of blocks without the densified bottom, as 
attained with the process of the invention, which can be implemented by 
the improved apparatus which is also an object of the invention. 
SUMMARY OF THE INVENTION 
In one essential aspect, the process of the invention requires heating in a 
controlled manner all the parts of the system where manufacture is carried 
out which are in engagement with said reaction mass. Said parts are 
basically represented by the surface of the band in engagement with the 
paper and the walls of the tunnel. Although a block lacking a densified 
bottom is obtained in this way, this nevertheless does not eliminate the 
operation of mechanically treating the bottom part of the block to remove 
a certain roughness which remains there. 
Such roughness is produced as a consequence of the fact that when the web 
on which the block rests is withdrawn, part of the foam of the lower zone 
of the block remains irregularly stuck to the web. Consequently, while a 
block lacking a densified bottom is obtained, a trimming operation is 
necessary to cut away a small amount of foam to thus give the bottom 
surface a smooth and uniform appearance. 
As is well known by experts in the art, in the manufacture of blocks of 
polyurethane foam there rests, on the endless belt upon which the foam is 
produced, a web of continuous material such as paper, polyethylene film or 
the like, which web moves along with the endless belt. Said web, which for 
convenience will hereinafter be called "paper web", is fed from a 
continuous reel located upstream of the foaming tunnel and is taken up and 
wound on an appropriate reel downstream of the foaming tunnel. Said paper 
web is made necessary by the fact that the endless belt does not have a 
continuously smooth surface, but rather is formed by a series of hinged 
plates with spaces between them. The inevitable need of the web of paper 
or other material is easily understood if it is borne in mind that the 
foam ingredients deposited at the tunnel entrance are liquid at the moment 
of their mixture in the mixer head, so that if there were no paper web, 
said mixed liquid would pass into the hinges of the endless belt. 
The invention is partly based on the fact that the formation of the skin or 
compacting results from lack of a uniform temperature in the whole 
reaction mass because the elements of the system in engagement with the 
foam under formation are at ambient temperature, whereas the actual foam 
itself is at the reaction temperature. 
Another factor which, together with the temperature, leads to the formation 
of more compact peripheral areas, is the pressure exerted either by the 
bottom of the conveyor band, owing to the actual weight of the foam, or by 
the side walls counteracting the expansion of the foam during its growth. 
Both to counteract the differences in temperature and the pressure exerted 
either by the actual weight of the foam or by the side walls, heat is used 
to activate the reaction. The heating temperature must be carefully 
selected within the range comprised between 30.degree. and 100.degree. C., 
choosing the suitable value for each specific quality of foam. It must be 
taken into account that the materials forming the polyurethane foam are 
highly inflammable, this being a factor which additionally requires very 
exact control of the temperature. 
Surprisingly, it is now found that the best results are obtained not by 
maintaining a constant temperature T.sub.0 at all the points of the 
surface of the endless belt which actually constitutes the foaming tunnel, 
as was first thought, but rather by differentiating in said surface of 
this endless belt two zones of different temperatures, designated reaction 
zone and consolidation zone. In addition, downstream of the foaming 
tunnel, in the means for drawing the already-consolidated block, there is 
a third zone designated final heating zone, at a point prior to the 
withdrawal of the paper web. 
The first or reaction zone upstream of the belt is traversed by the forming 
foam during a period of time which varies according to the time 
predetermined for each mix. In this zone the surface of the endless belt 
is maintained at a constant temperature which varies from one foam to 
another. 
The consolidation zone is traversed by the foam during a period of time 
depending on the predetermined time in the reaction zone. 
The fundamental parameters constituting the objects of the invention are 
defined as follows: 
T.sub.R =Surface temperature of the reaction zone. 
T.sub.C =Surface temperature of the consolidation zone. 
T.sub.S =Surface temperature of the final heating zone. 
t.sub.R =The time it takes an element of the endless belt or the bottom 
part of the paper-lined block which rests on it to traverse the reaction 
zone, that is, from point Q to point C represented in FIG. 7 of the 
drawings. 
t.sub.C =The time it takes said element to traverse the consolidation zone, 
that is, from point C to point B represented in FIG. 7 of the drawings. 
t.sub.T =The time it takes said element to traverse the floor of the 
foaming tunnel, that is, from point Q to point B represented in FIG. 7 of 
the drawings. 
If it is borne in mind that the floor of the foaming tunnel traverses the 
reaction and consolidation zones, it is readily seen that 
EQU t.sub.T =t.sub.R +t.sub.C ( 1) 
and as the value of t.sub.R is predetermined for each type of foam, it is 
deduced that 
EQU t.sub.C =t.sub.T -t.sub.R ( 2) 
While the values of t.sub.R and T.sub.R are fixed for a given foam, they 
vary from one foam to another, since as will be understood by experts in 
the art, the exothermicity of the reaction of polyurethane formation 
varies accordingly to the nature of the principal ingredients, and of the 
ratio between them. As is known, the principal ingredients are polyol and 
polyisocyanate. However, the percentage of water in the mixture plays an 
important role. 
A fundamental characteristic of the improvements contributed by the present 
invention is that the surface temperatures of the three zones have the 
ratio 
EQU T.sub.R &lt;T.sub.C &lt;T.sub.S 
In general, the difference T.sub.C -T.sub.R =.DELTA.T ranges from between 
10.degree. and 15.degree. C., about 10.degree. C. being preferable. As was 
indicated in the parent patent application, a temperature above a maximum 
limit inside the foaming tunnel in the reaction zone can cause cracking of 
the foam, and even its combustion. Keeping in mind that this cracking 
temperature varies with the formula between approximately 45.degree. and 
70.degree. C., T.sub.R and T.sub.C fulfill the condition 
EQU T.sub.R &lt;T.sub.C .ltoreq.80.degree. C. 
The temperature of the final heating zone T.sub.S can reach apparently high 
values, ranging between 100.degree. and 250.degree. C., in very short 
periods of time. This is not contradictory with the reaction temperature 
range, if it is kept in mind that it is applied at a point outside the 
foaming tunnel, when the foam has already consolidated. 
Although in the foregoing only only one final heating zone has been 
mentioned, the invention is not necessarily limited to only one zone of 
this type and there can be several, although practical reasons limit their 
number to three. However, a single final heating zone is most preferable. 
As a consequence of the difference in the mentioned three thermic levels, 
once the final heating zone is passed and the paper web is removed, a 
block is obtained having a smooth and uniform surface and no densified 
bottom, a thin and uniform layer of foam of a density similar to that of 
the rest of the block having remained adhered to the paper web. 
The improved apparatus used according to the invention includes an enclosed 
insulated housing surrounding the conveyor belt and means for heating the 
conveyor belt both within the downstream of the foaming tunnel. 
As the heating means, it is possible to use any one which is suitable and 
attains exact control of the appropriate temperature, among which can be 
cited steam coils, infrared rays, suitably arranged electrical resistors 
or hot air obtained from a heat exchanger. In any event, said heating 
systems must be strictly controlled to prevent combustion of the foam. 
In the event the hot air system is used, the air can be projected 
longitudinally or transversely to the movement of the conveyor band. In 
the first instance, the air can be projected in the travelling direction 
of the band or in the opposite direction. 
For a better understanding of the improvements provided by the invention, a 
brief description will be given below of the elements comprised by a 
standard apparatus for producing blocks of polyurethane foam. 
The basic elements or parts of said standard apparatus are: A foaming 
tunnel constituted by a sloped conveyor belt, formed by hinged plates, the 
floor of the foaming tunnel being constituted by the upper run of said 
conveyor belt. The rest of the parts of said tunnel is formed by side 
walls and a ceiling provided with conduits for evacuating the gases which 
are formed and/or released during the reaction which results in the foam, 
such as CO.sub.2 and blowing agent. In the upstream part 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 toward 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 apparatus there are also tanks for reactants, pumps, 
motors for actuating the conveyors and other necessary devices for its 
operation. 
The conveyor belt is surrounded by a large sized heat insulated box-like 
housing, in which the upper surface of the upper run of said conveyor belt 
is flush with the open upper part of said box. Likewise, in one principal 
embodiment, according to which said housing is heated by hot air, the 
volume defined by said box is divided by a single cross partition into an 
upstream chamber and a downstream chamber, both of constant volume. In 
association with said box arrangement, are heating means other than hot 
air, as well as cooling means, which allow 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 constitutes the preferred embodiment, comprise an 
arrangement of coils with steam, infrared radiation devices and resistors 
in the plates. According to the type of heat source, the housing of the 
box requires a plurality of more or less complex elements and devices, 
which will be described and illustrated in the drawings. 
According to a first preferred embodiment, there are provided inside the 
box-like enclosure or housing cross separating partition means capable of 
acting in two positions, 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, the partition in closed 
position constituting the dividing line of the two aforementioned 
"upstream" and "downstream" areas. The number of these cross partitions is 
at least three and when the apparatus is operating only one of them is in 
the closed position, thereby attaining, according to the type of foam 
manufactured, a given constant volume of the upstream and downstream 
areas, but variable from one foam to another, which is not possible when 
using a single partition where both areas are of constant volume. It is to 
be noted that, according to this first preferred embodiment of the 
invention, the formation of these two chambers which are variable from one 
type of foam to another may be used for all the heating means considered 
and not only for hot air. 
According to a second preferred embodiment of the 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 paper web removing device, there are arranged 
at least some means for the final heating of the surface of the bottom of 
the block, in which relatively high temperatures are attained.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, it can be seen that the bottom area F, which, by the 
influence of a series of factors, among which the weight of the mass plays 
an important role, presents greater densification when prepared by the 
conventional process. Although it is not possible to establish an accurate 
figure, because experts in the art are aware that this can vary from one 
type of foam to another, the density of the bottom area in the usual 
process is approximately between 6 and 9 times greater than that of the 
rest of the block. 
The process according to FIG. 2 comprises, as a first step, running an 
endless belt for a period of time ranging between 15 and 90 minutes, at 
the same time as heating thereof is commenced, raising the temperature 
from ambient temperature (T.sub.a) to a defined value (T.sub.m) within the 
range comprised between about 40.degree. and about 80.degree. C. The 
second step commences on reaching point T.sub.m, at which movement of the 
belt is stopped, and at that moment the components of the foam are fed in 
intimately mixed form through the head, allowing a period of time 
(.DELTA.t.sub.p) to pass with the belt stopped, during which the 
temperature drops to point T.sub.o. On reaching point T.sub.o movement of 
the endless belt is resumed, continuing to feed the ingredients and 
maintaining the temperature T.sub.o on all parts of the belt with suitable 
control means. 
It is extremely important for the attainment of the object of the invention 
to work at a suitable temperature for each type of foam and to maintain 
the variation thereof in accordance with the graph of FIG. 2 of the 
drawings. 
Experts in the art will realize that once the temperature is established 
from point T.sub.o, it must be controlled within the range .DELTA.T.sub.s, 
because otherwise, if a value above the permitted maximum of said range is 
reached at any point of the belt, cracking of the block occurs and, on the 
contrary, if the temperature drops below the lower value densification 
occurs at the bottom. These densification and cracking areas are 
illustrated in the graph of FIG. 2 as Z.D. and Z.A., respectively. There 
is a third area, illustrated as Z.C., which is the combustion area of the 
foam. T.sub.m must be below this value. 
According to a preferred embodiment of one aspect of this invention, an 
apparatus for obtaining continuous blocks of polyurethane foam, of the 
type without "crust" or more compact layer at their bottom part, comprises 
a foaming tunnel with the bottom part thereof constituted by the upper or 
conveying run of a notably wide endless belt, formed in a known manner, by 
a plurality of plate-like cross members connected in hinged fashion and 
mounted between end driving and guiding wheels at the ends of the tunnel, 
and is characterized in that said conveyor belt is surrounded by a large 
sized heat insulated box-like housing, the upper surface of the upper run 
of said conveyor belt being arranged flush with the open upper part of 
said box, in that the inside of said box, particularly the space defined 
between said conveying and return runs of the belt and between the sides 
of said box, is divided into an upstream chamber and a downstream chamber 
by a cross partition which runs from side to side of said box-like housing 
and along the top thereof, between the lower and upper runs of said 
conveyor belt; in that there are hot air blowing means, outside said 
housing, the outlet whereof is connected with a main supply conduit which, 
passing beneath said housing, subsequently branches-off into two secondary 
conduits at a point located halfway along the length of said conveyor 
belt, each of said secondary conduits running toward the respective ends 
of said housing, each secondary conduit being provided with a plurality of 
bypasses, uniformly distributed over their length and ending, through 
adjustable opening outlets, at their associated chamber on one of said 
sides thereof and in that the opposite side of that same chamber has a 
plurality of air outlets, likewise uniformly distributed over the length 
thereof, said outlets also having adjustable openings; in that starting 
from each of said outlets there is a conduit, all the outlet conduits 
which start from the side of the upstream chamber meeting at a first air 
outlet collecting conduit which goes toward the midpoint of the length of 
said conveyor belt and all the outlet conduits which start from the side 
of the downstream chamber likewise meeting at a second air outlet 
collecting conduit which also goes toward said midpoint of said belt, to 
meet there with said first collecting conduit in order to form a single 
meain air outlet conduit which is connected in turn with the intake of 
said hot air blowing means, so that closed circulation of the hot air is 
obtained. 
This arrangement is likewise characterized in that at the branch-off of the 
mentioned main hot air supply conduit there is a directing valve to allow 
distribution of the flow of hot air fed by said blowing means to the 
respective secondary feeding conduits, equally or differently, and in that 
at the point where said first outlet collecting conduit and said second 
outlet collecting conduit there is another directing valve, the purpose 
whereof is similar to that of the first one and the orientation whereof 
depends on that of the latter. 
In an alternative arrangement, said belt is heated with heating means 
constituted by a coil arranged in said volume on two planes, inside which 
steam under pressure and at high temperature is circulated from a supply 
source outside the apparatus. 
According to another embodiment, the means used for heating said volume are 
constituted by a plurality of infrared radiation heating elements, 
arranged on two planes and directed to radiate heat toward the lower part 
of the upper run of the conveyor belt and toward the back of the return 
run of said conveyor belt, all the mentioned heating elements being 
uniformly distributed over the entire length and breadth of said conveyor 
belt. In this alternative embodiment there is a dividing partition which 
runs horizontally over the entire length and breadth of said belt, at 
mid-height, in said volume, so that it divides the latter into an upper 
chamber and a lower chamber. 
According to a yet further embodiment of the invention, the heating means 
are constituted by individual electrical resistor heating elements 
incorporated in each of the platelike elements which form the conveyor 
belt, which heating elements take the electric current from an arrangement 
constituted by current collector trolleys which slide in contact with 
current supply tracks arranged following a trajectory which is adapted to 
the contour of said conveyor belt. 
The invention is further characterized in that there are means for 
continuously sensing the temperature inside said space and in that these 
sensing means are adapted to generate control signals, adapted in turn to 
control, through known means, the operation of the means heating the 
mentioned space. 
Referring to the attached drawings and, in particular, to FIGS. 3A and 3B 
thereof, they show a conveyor belt embodiment heated according to the 
invention, designated in general as 1, constituted by a plurality of 
plate-like cross members 2, connected in hinged fashion, and mounted 
between end driving and guiding wheels, 3, 4, respectively, at the ends of 
the tunnel, which belt is surrounded by a large sized box-like housing 5, 
formed by a bottom 6, placed very close to the lower or return run of said 
conveyor belt, vertical sides 7, 8, also located very close to the side 
edges 9, 10 of said belt 1 and of a height such that their upper edges are 
flush with the upper surface of the conveying run of said belt over its 
entire length, and vertical end plates 11, 12 located close to the end 
parts of said belt 1, the plate located at the upstream end of the belt 
(marked 11 in this embodiment) being of a height equal to that of said 
sides 7, 8, since the plate of the downstream end of said conveyor belt 
(marked 12 in this embodiment) being of a height lesser than that of said 
sides 7, 8, said bottom 6, said sides 7, 8 and said end plates 11, 12 
being totally or partially made of heat insulating material M and the 
arrangement being such that the conveyor belt 1 is located inside said 
insulated housing 5 with the upper surface of its conveying run flush with 
the edges of said sides 7, 8 end of said upstream end plate 11. 
Inside said housing 5, the space defined between said conveying (upper) and 
return (lower) runs of the belt 1 and between the sides 7, 8 of said box 
is divided into an upstream chamber 13 and a dowmstream chamber 14 by a 
cross partition 15 which runs from one side to the other of said box-like 
housing 5 and along the top, between the lower and upper runs of said 
conveyor belt. 
Outside said housing 5 there are hot air blowing means S, the outlet 
whereof is connected with a main hot air supply conduit CP which, passing 
beneath the mentioned housing 5, subsequently branches-off into two 
secondary conduits CS1, CS2 at a point located halfway along said belt 1, 
each of said secondary conduits CS1, CS2, running toward the respective 
ends of said housing. Each of said secondary conduits CS1, CS2 has a 
plurality of bypasses D, uniformly distributed over their entire length 
and ending, through adjustable opening outlets 16, in their respective 
associated chamber 13, 14, on one of said sides, for example 7, and the 
opposite side, in this case 8, in each chamber has a plurality of air 
outlets 17, likewise uniformly distributed over the entire length thereof, 
said outlets 17 also having adjustable openings. 
A conduit 18 starts from each of said outlets 17, all the outlet conduits 
18 which start from the side 8 of the upstream chamber 13 subsequently 
meeting at a first air outlet collecting conduit, CCS1, which goes toward 
the midpoint of the length of said conveyor belt 1. For their part, all 
the outlet conduits 18 which start from the side 8 of the downstream 
chamber 14 likewise meet at a second air outlet collecting conduit, CCS2, 
which also goes toward said midpoint of said belt 1, to meet at 20 with 
said first conduit CCS1 in order to form a single main air outlet conduit 
CPS which is connected in turn with the intake A of the mentioned hot air 
blowing means S, so that closed circuit circulation of the hot air is 
obtained toward the inside of the box and toward the outside thereof. 
At the point where the mentioned main hot air supply conduit CP branches 
off to form the conduits CS1, CS2, there is a directing valve 21 which 
allows distribution of the flow of hot air fed by said blowing means S to 
the respective secondary feeding conduits CS1, CS2, equally or 
differently, and at point 20 where said first outlet collecting conduit 
CCS1 and said second outlet collecting conduit CCS2 meet there is another 
directing valve 22 which performs a similar function on the return flow of 
air, the orientation thereof depending on the valve 21 which directs the 
supply flow of hot air. 
Furthermore, in said upstream chamber 13 of said boxlike housing 5 there 
are ventilation means constituted by cooling air blowing means 19 in 
communication with said space through a flow control valve 23, on one side 
of said chamber, and air outlet means 24, provided on the opposite side of 
said chamber 13 and also having a flow control valve 25, and said 
ventilating air flow control valves 23 and 25 can adopt any position, 
between a completely closed position and a completely open position, 
operating in mutually dependent form when an excessive temperature is 
detected in said upstream chamber 13, above a preset limit value, which 
might be detrimental for the foaming of the material on the conveyor belt 
1, if this belt were to stop as a result of a breakdown, for example. 
Each secondary conduit CS1, CS2 for supplying hot air to the inside of said 
housing 5 is extended, at its end part, into a conduit 26 designed to feed 
said hot air to the inside of the mentioned housing 5 through the end 
parts of the latter, said end conduits being provided with several hot air 
feed openings (not shown) distributed over the entire breadth of the 
associated end plate 11, 12 of the mentioned housing. 
Inside each of said upstream and downstream chambers, 13, 14, respectively, 
there are temperature sensing means P designed to control, according to 
the temperature sensed in each of said chambers 13, 14, the position of 
the air supply and air outlet directing valves, 21, 22, respectively, as 
well as the opening of said supply outlets 16, on the sides of said 
housing, and 26 at the end parts thereof, and of said air outlets on the 
sides of the mentioned housing, these temperature sensing means being 
capable of actuating the ventilation means 19, 24 provided in said 
upstream chamber of the apparatus when said preset limit temperature value 
is exceeded. 
Referring now to FIGS. 4A through 4C, which illustrate a second embodiment 
of this invention. They show the heat insulated box-like housing 5 which 
surrounds the conveyor belt 1 on the upper run whereof the material is 
foamed. In this particular case, in the space defined between the upper 
and lower run of said belt 1 and the two sides 7, 8 of said housing 5 
there is a coil-like conduit V inside which steam circulates under high 
pressure and at high temperature from a supply source outside the 
apparatus (not shown) the inlet of steam being controlled with a control 
valve VR, the position whereof is controlled by the temperature sensor P. 
This steam conduit is arranged on two planes, an upper one and a lower one, 
the sections of the coil being placed on each plane, respectively, close 
to the back of the upper run of the belt 1 and close to the back of the 
lower run of the same belt, so that the output of heat from the steam 
conduit V is distributed over the entire breadth and length of the backs 
of said runs of the conveyor belt, in order to heat all the mentioned belt 
as uniformly as possible. On one of the sides of the housing 5 there is a 
fan, marked 200, adapted to provide movement of the mass of air inside the 
space to be heated. 
FIGS. 5A and 5B schematically show a third embodiment of the invention, 
where the upper and lower runs of said conveyor belt 1 are heated by 
incorporating, inside said space, heating means constituted by a plurality 
of infrared radiation heating elements 300 arranged on two planes, an 
upper one, where said elements 300 are directed to radiate heat toward the 
lower part of the upper run of said conveyor belt 1, and a lower one, 
where said elements are directed downward, to radiate heat toward the back 
of the return run of the mentioned belt 1. All these elements 300 are 
uniformly distributed over the entire length and breadth of the conveyor 
belt 1, as can be seen in the figures, there being a partition T which 
runs horizontally over the entire length and breadth of said belt, at 
mid-height, in said space, to divide the latter into an upper chamber 30 
and a lower chamber 31, there being at least one temperature sensing 
device P which actuates a device controlling the feed of electric power to 
said heating elements (not shown) in response to the temperature sensed in 
said upper chamber and in said lower chamber, to control the radiation 
strength of the elements 300 associated with each of said chambers. 
In a contemplated alternative of this third embodiment, in each of said 
chambers 30 and 31 the temperature could be sensed separately, and 
therefore, the electric power feed to the heating elements 300, upper or 
lower, would be controlled independently, with at least two sensing 
devices and corresponding control means, thus providing the apparatus with 
greater flexibility. 
Referring to FIGS. 6A through 6D, they show a fourth preferred embodiment 
of this invention. 
In this embodiment the conveyor belt is heated with heating means 
constituted by individual electrical resistor elements R incorporated in 
each of the plate-like members 40 which form the conveyor belt 1, duly 
insulated therefrom to avoid faults through passing of electric power to 
said belt 1. 
Electric current is fed to each of said electrical resistor heating 
elements R through an arrangement (see FIG. 6D) which comprises two 
trolleys T, one at each end of a plate-like member 40 of said belt 1, each 
of which trolleys slides in contact with a power supply track 41 arranged 
following a trajectory which is adapted to the trajectory of said belt 1 
over its entire contour, close to its edges. 
In an alternative of this fourth embodiment, said two trolleys T would be 
arranged at the same end of each of said plate-like members 40 of said 
belt 1, said power supply tracks 41 being placed in mutually adjacent 
position, close to one or the other edge of said conveyor belt 1, over its 
entire contour. 
As can be seen, FIG. 7 is an excessively simplified representation of the 
apparatus for producing polyurethane foam in blocks. Said simplification 
is deliberate, to give a better understanding of the preferred process of 
the invention. 
Seen in said FIG. 7 is the inclined endless belt 101, formed by hinged 
plates PP, which constitutes the floor of the foaming tunnel the walls of 
which are numbered 105. Following the belt 101 are the conveyors 102 and 
103, forming the means for drawing the already formed and consolidated 
foam. This Figure shows two of said conveyors, although there can be more. 
Interposed between the block of foam E and the upper surfaces of the 
conveyor belts 101, 102 and 103 is the previously mentioned paper web, the 
supply and take-up reels of which are represented by 104 and 104'. 
The sector of belt 101 constituting the reaction zone is represented by QC, 
CB being the longitudinal border of the consolidation zone. It will be 
seen from the foregoing that the location of point C, while fixed for a 
given type of foam, varies from one foam to another and can be to the 
right or to the left of the position indicated in FIG. 7. 
Beyond the foaming tunnel properly speaking there are three final heating 
zones; represented as S.sub.1, S.sub.2 and S.sub.3 in FIG. 7. Said drying 
final heating zones are generally of narrower width than the other two 
zones, the width (or what is the same thing, the time it takes a certain 
element of the consolidated block to pass through said final heating zone) 
being related to the temperature in inverse ratio. That is, a relatively 
narrow drying final heating zone (or its equivalent, a short time in 
passing that zone) will require a high temperature and vice versa. 
It can be seen in FIG. 8 how the horizontal length of FIG. 2 appears in two 
levels, corresponding to the differentiation of the two zones of reaction 
and consolidation inside the foaming tunnel. It is easily understood that 
the temperature transition between the cited two zones is not abrupt and 
thus the existence of the inclined length, point C remaining at a 
temperature which can be considered as intermediate between T.sub.R and 
T.sub.C. Once the plate element of reference has reached the point of 
return, the part of the block bottom in contact with said plate of 
reference undergoes, if the drying final heating zone S.sub.1 exists, a 
rise in temperature until the value T.sub.S1 is reached. If the drying 
final heating zone lies downstream, for example at S.sub.2 or S.sub.3, the 
temperature of the block commences to diminish, tending to equal that of 
the atmosphere. The dotted line represented by BF would be the temperature 
variation with respect to time if there were no drying final heating 
zones. It is also seen that the farther away the foaming tunnel, the 
higher the temperature will have to be in the drying final heating zone to 
counteract the decrease of the consolidation temperature. 
It must be noted that the start-up of the apparatus with the operation of 
the endless belt of the foaming tunnel in the empty state is absolutely 
identical to the description of the process shown in FIG. 2. Thus FIG. 8 
is directed toward emphasis of the double level of the horizontal length 
of said curve owing to the existence of the two zones of reaction and 
consolidation and the temperature variation of the bottom upon emerging 
from the foaming tunnel. 
In accordance with the foregoing and once the reaction temperature is 
reached, which corresponds to the optimum temperature T.sub.m of FIG. 2, 
and the paper web supply device is functioning, feeding begins of the 
ingredients which react to form the foam in the upper portion of the 
foaming tunnel, the temperature being controlled in the surface of the 
reaction zone to the value T.sub.R, and likewise the temperature in the 
consolidation zone being controlled to the value T.sub.C. With start-up, 
the conveyor belts constituting the floor of the foaming tunnel and the 
means for drawing the formed and consolidated block at the programmed 
speed, the temperature is carefully controlled so that its variation with 
respect to time follows the graph of FIG. 8. 
Upon arrival of the block at the final heating zone there is produced the 
aforementioned phenomenon according to which a thin, uniform film of foam 
remains adhered to the paper web, as can be verified when taking up said 
web in the drawing means represented by 104' in FIG. 7. After disengaging 
from the take-up means the block slides over the idle rollers 106 from the 
pushing action furnished by the drawing means 102 and 103. The block then 
passes to the vertical cutting means without having to undergo the once 
necessary bottom trimming, by reason of a bottom having been obtained of a 
density equal to that of the rest of the block and lacking surface 
irregularities. 
The removal of the paper web being one of the important aspects of the 
object improvements of the present application, it must be noted that 
while previous reference has been made to paper as the most common 
material used for the web inserted between the block of foam in formation 
and the rectangular hinged plates which form the endless belt, any other 
weblike material can be used which fulfills the same function. 
The extent of the reaction area, which depends on the reactivity of the 
formulation, varies from one foam to another. In FIG. 9A of the drawings, 
X, Y and Z 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 X, whereas the least reactive is 
that for which the growth curve is identified as Z. 
Subsequently, a temperature T.sub.c higher than T.sub.R is maintained in a 
second surface area of the floor of the foaming tunnel, called 
consolidation area. The value T.sub.c is also kept constant throughout 
foaming, varying from one foam to another. It is readily realized that 
since the floor of the foaming tunnel constitutes the reaction and 
consolidation areas, once the former is established by the reactivity of 
the foam, the extent of the latter is obtained. 
In FIG. 9A of the drawings, the longitudinal edges of the reaction and 
consolidation areas for the three types of foam would be as indicated in 
the following table: 
______________________________________ 
RE- CON- 
ACTION SOLIDATED 
AREA AREA 
______________________________________ 
HIGH REACTIVITY FOAM 
QB BF 
MEDIUM REACTIVITY FOAM 
QC CF 
LOW REACTIVITY FOAM 
QD DF 
______________________________________ 
It will be readily realized that the surface of the foaming tunnel, called 
reaction area here, corresponds to the upper or conveying run of the 
endless belt of the foaming tunnel of the so-called "upstream" chamber 
when only one partition is used. Naturally, the surface of the 
consolidation area corresponds to the upper run of the "downstream" 
chamber. As indicated above, an important preferred aspect of this 
application lies in the possibility of altering the volumes of the 
upstream and downstream chambers or, what amounts to the same, the 
surfaces of the reaction and consolidation areas to adapt them to the 
reactivity of the specific foam manufactured. 
The third area, called the final heating area, is downstream from the 
foaming tunnel, between the foaming tunnel and the first of the drawing 
conveyors 116, between two drawing conveyors (a second conveyor is shown 
in FIG. 9A as 117, or between the last drawing conveyor and the idle 
roller arrangement 125. There may be more than one such area and it is 
always before the place where the paper removing device 114 is located. In 
said area, the bottom of the moving block E is subjected to a temperature 
T.sub.S much higher than T.sub.R and T.sub.C for a very short time. This 
surface final heating temperature is attained precisely with the means for 
heating the surface of the bottom of the block. FIG. 9A shows three of 
these final heating areas as 122, 123 and 124. 
Thus, the improved apparatus for manufacturing blocks of polyurethane foam 
makes it possible to obtain the three mentioned temperatures T.sub.R, 
T.sub.C and T.sub.S, which fulfill the condition T.sub.R &lt;T.sub.C 
&lt;&lt;T.sub.S. Additionally, the surfaces of the foaming tunnel where the 
first two mentioned temperatures are attained, that is, reaction area 
(T.sub.R) and consolidation area (T.sub.C), may vary according to the 
reactivity of the foam. 
The remaining parts of the apparatus of FIG. 9A are as follows: 
111 is the mixer-feeder head, 112 is a side wall of the foaming tunnel, 113 
is the paper web supplying device, 115 is the conveyor belt of the foaming 
tunnel, formed by platelike members identified as PP in FIG. 10B, 118 are 
conduits for evacuating the gases formed and/or released during the 
reaction in the foaming tunnel, such as CO.sub.2, Freon, etc. In FIG. 10A 
RA is the driving wheel of the conveyor belt 115 and RG is the guiding 
wheel of said belt. The remaining parts of the apparatus shown in FIG. 9A 
will be defined hereinafter in relation to other figures of the drawings 
where they also appear. 
The elements of the improved arrangement of the conveyor belt of the 
foaming tunnel which are common to the different heating means and which 
are shown in FIGS. 9A to 13B are described below. 
Said conveyor belt 115 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 110, located at a very 
short distance from the lower or return run of said conveyor belt 115, 
vertical sides CV1 and CV2, also located at a very short distance from the 
side edges BL1 and BL2 of said conveyor belt 115 and of a height such that 
their 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 115. 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 lesser 
than that of said sides CV1 and CV2. The parts forming said housing 35, 
that is, the bottom 110, 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 box, that is, the volume defined by said conveying 
and return runs of the belt and between the sides of said box, there are 
three cross separating partition means 119, 120 and 121 capable of acting 
in closed and open positions, only one being in the closed position during 
the operation of the apparatus, the other two being in the open position. 
Whatever the heating means may be, it is thus possible to form the two 
upstream and downstream chambers, or reaction and consolidation chambers, 
which may vary 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 119 will be in the closed position, 
whereas the partition means 120 and 121 will be in the open position. When 
an intermediate reactivity foam is involved, the partition means 120 will 
be closed, and 119 and 121 open. When a low reactivity foam is involved, 
the partition means 121 will be closed, and 119 and 120 open. Naturally, 
only the partition means which are closed will allow an airtight 
insulation 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 
T.sub.R and T.sub.C are attained on the surface of the endless conveyor 
belt. Said separating partition means, the positions whereof are actuated 
by rod means 30, will be defined hereinafter in detail in the explanation 
of FIGS. 14, 15, 16, 18, 19 and 20. 
Between the end plate PE2, close to the mixer-feeder head 111, and the 
first separating partition means 119, on the side CV1, that is, in a part 
of the upstream chamber which always forms part of the reaction chamber, 
there is a fan 211, the function whereof is to start operating and drive 
cold air into the enclosure of the upstream or reaction chamber when a 
temperature exceeding the programmed temperature T.sub.R is reached. 
According to a 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 FIGS. 9A, 9B, 10A and 10B. 
Outside said housing 35 there are hot air blowing means 212, the outlet 
whereof is connected with a main hot air supply conduit 126 which, passing 
beneath the mentioned housing 35, subsequently branches-off into two 
secondary conduits 66 and 66' at a point located halfway along said 
conveyor belt 115, each of said secondary conduits 66 and 66' running 
toward the respective ends of said housing, adjacent to the side. Starting 
from each of said secondary conduits 66 and 66' there is a plurality of 
bypasses G, at the outlet whereof there are air inlet control valves 208, 
some of them ending in the reaction chamber and others in the 
consolidation chamber, on the side CV1. Starting from the opposite side, 
that is, CV2, there is a plurality of bypasses G', at the outlet whereof 
there are air outlet control valves 209. Said bypasses G' are inserted in 
two air outlet collecting conduits 107 and 107', which meet at a point 
located halfway along said conveyor belt, in order to form a single main 
air outlet conduit identified as 27, which is connected in turn with the 
intake of the blowing means 212, thereby obtaining closed circuit 
circulation of the hot air toward the inside of the box and toward the 
outside thereof. 
At the point where the mentioned main hot air supply conduit 126 
branches-off to form the secondary conduits 66 and 66' there is a 
directing valve 29 which allows distribution of the flow of hot air fed by 
the blowing means 212 to the respective secondary feeding conduits 66 and 
66', equally or differently. Likewise, at the point where the outlet 
collecting conduits 107 and 107' meet to form the collecting conduit 27 
there is another directing valve 28, which performs a similar mission on 
the return flow of air, the orientation thereof depending on that of the 
aforementioned valve 29. 
In FIG. 10B the extreme positions of said valves 29 and 28 are shown as H, 
I, J and K, respectively. 
The aforementioned fan 211 is on the side CV1, in communication with the 
volume of 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 completly closed and a 
completely open position, operating in mutually dependent form if an 
excessive temperature were detected in said reaction chamber, above a 
preset limit value, which might be detrimental for the foaming of the 
material on the conveyor belt 115 if said belt were to stop as a result of 
a breakdown, for example. 
Each secondary conduit 66 and 66' for supplying hot air to the inside of 
said housing 35 extends at its end part into the conduits CE1 and CE2 
adapted to feed said hot air to the inside of the mentioned housing 
through the end parts of the latter, said conduits being provided with 
several hot air feeding outlets (not shown) distributed over the entire 
breadth of the corresponding end plates PE1 and PE2. 
Inside said housing, at one point located to the left of the separating 
partition means 119 and another to the right of the separating partition 
means 121, that is, at places which are always a reaction and 
consolidation area, respectively, there are temperature 
sensing-controlling devices 34 and 33, the function 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 valves 208 and 209. The sensor 34 can also 
actuate the fan 211 when the closing of the directing valve 29 and the 
valves 208 are insufficient to reduce the temperature of the reaction 
chamber and it also becomes necessary to inject cold air. 
FIGS. 11A-11A', 11B-11B' and 20 schematically show a second embodiment of 
the invention, in which the upper and lower runs of said conveyor belt 115 
are heated by incorporating, inside said volume, heating means constituted 
by a plurality of infrared radiation heating elements arranged on two 
planes, an upper one on which said elements are directed to radiate heat 
toward the lower part of the upper run of said conveyor belt, and another 
lower plane on which said elements are directed downward to radiate heat 
toward the back of the return run of the mentioned conveyor belt. In said 
FIGS. 11A-11A' and 20 the heating elements of the upper plane of the 
reaction area are as shown as 36, those of the lower plane of said area as 
40, the heating elements of the upper plane of the consolidation area are 
shown as 50, and those of the lower plane as 51. The elements 42 and 47 of 
the upper plane may belong to the reaction or the consolidation area, 
depending on which of the partition means 119, 120 or 121 is closed. 
Similarly, the heating elements 41 and 52 of the lower plane may belong to 
the reaction or the consolidation area for the same reason. As can be seen 
in the Figures, there is a dividing partition 37, 37a, 37b and 37c which 
runs horizontally over the entire length of said belt, at mid height, in 
said volume, an upper chamber and another lower one thereby also being 
obtained. 
Nine temperature sensing-controlling devices 34, 38, 39, 43, 44, 45, 46, 48 
and 49 can be seen in FIGS. 11A-11A'. The one shown as 34, located in the 
reaction area, performs the same function as the embodiment of FIG. 10A, 
that is, on detecting a temperature value exceeding the programmed 
temperature T.sub.R it actuates the fan 211, injecting cold air which runs 
out through evacuation means not shown in FIGS. 11B-11B'. Those shown as 
38, 43 and 45, located in the reaction area on the upper plane, will be 
adjusted to connect and disconnect the heating elements 36, 42 and 47 to 
maintain the programmed temperature T.sub.R when the partition means which 
are closed are those shown as 121. Since the sensing-controlling devices 
43 and 45 may belong to the consolidation area, according to which 
partition means 119 or 120 are closed, their programming to T.sub.R or to 
T.sub.C will depend on the type of foam produced. The sensing-controlling 
devices 39, 44 and 46, located on the lower plane, are programmed to a 
temperature below T.sub.R because when the means 119 and 120 are open the 
lower chamber, which is known as the approach to the reaction area, 
requires a lower temperature than T.sub.R. The same as those of numbers 43 
and 45, the sensing-controlling devices 44 and 46 may belong to the 
reaction or the consolidation area, depending on which of the means 119 or 
120 is closed, and their programming will thus depend on the type of foam 
produced. The device 48 will connect and disconnect the heating elements 
50 to maintain the programmed temperature T.sub.C. The devices 43 and 45 
will be equally adjusted in the event that the closed means are those 
shown as 119. Finally, the device 49 will actuate the heating elements 51 
to maintain an intermediate temperature between T.sub.C and T.sub.R on the 
surface of the return run on the back of which the radiation falls. 
The electric power points actuated by the sensing-controlling devices are 
shown in FIGS. 11B-11B'. The device 38 actuates 53, the device 43 actuates 
53', the device 45 actuates 54 and the device 48 actuates 55. The electric 
power points for heating elements 40, 41, 52 and 51 of the lower chamber 
are not shown, but their location and operation will be readily realized. 
As has been indicated, the device 34 only actuates the fan 211. 
In the heating embodiment shown in FIGS. 12A-12A', 12B-12B' and 21, said 
heating is effected by heating means constituted by individual electrical 
resistor elements R incorporated in each of the plate-like members PP 
forming the conveyor belt. In this embodiment said elements R are duly 
insulated from the members PP to prevent faults through passing of 
electric power to said belt 115. 
Electric power is fed to each of said electrical resistor heating elements 
RR through an arrangement (see FIG. 21, enlargement of detail L in FIG. 
12A) which comprises two trolleys TT, one being arranged at each end of a 
member PP of the conveyor belt, each of aid trolleys TT 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 TT are arranged at 
the same end of each of said members PP 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 119, 120 and 121, said FIGS. 
12A-12A' and 12B-12B' show the sensing-controlling device 34 which 
actuates the fan 211, which drives cold air into the reaction enclosure, 
said air running 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 programmed temperature 
T.sub.R. Device 59 actuates the feeding of the resistors of the 
consolidation area to maintain the programmed temperature T.sub.C. The 
sensing-controlling devices 57 and 58 belong to the reaction or the 
consolidation area depending on which partition means 119 or 120 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. 
FIGS. 13A-13A' and 13B-13B' 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 outside the installation (not shown). The mentioned FIGS. 13A-13A' 
and 13B-13B' show the coils of the reaction area 166, those located 
between the partition means 119 and 120, shown as 167, others located 
between the partition means 120 and 121, shown as 168, and those located 
in the consolidation area 169. The inlet of steam to said coils is 
controlled by the electrovalves 74, 75, 76 and 77, the positions whereof 
are controlled by the 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 partition means 119, 120 or 121 are closed, the 
electrovalves 74, 75, 76 will be programmed in such a way that the steam 
passing through them produces heat radiation resulting in T.sub.R or 
T.sub.C. 
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 
211. 
A detailed description is given below of one of the cross separating 
partition means shown as 119, 120, or 121 in FIGS. 9A to 13B-13B'. Said 
description is made with reference to FIGS. 14, 15, 16, 17, 18 and 19 of 
the drawings. 
As has been indicated earlier, FIGS. 14, 15, 16 and 17 correspond to 
sections along the previously indicated lines of FIGS. 10A, 11A-11A', 
12A-12A' and 13A-13A', respectively, and show a front view of said 
separating partition means. FIG. 18 is a cross-sectional view of the 
partition means of FIG. 14 along line 18--18 of said FIG. 14. FIG. 19 is 
an enlarged fragmentary view of the detail identified as MM in FIG. 12A'. 
Said partition means are 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 toward the same side, forming pairs of flanges 78a, 
directed toward 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 
78b may be affixed to the main portion of the part 78 by welding or by 
another mechanical means which assures a perfect connection between both 
portions of said part 78. Respective rectangular parts 79 of flexible 
plastic material are connected to each of the flanges 78a. There are 
shutting means 80 between the two parts 78b, resting on the channel 
portions thereof. 
Said shutting 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 FIGS. 14, 15, 16 and 17, 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 FIG. 14 of 
the drawings as 81, can slide in a direction perpendicular to 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 of the drawings, 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 shutting 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 partition means 119, 120 and 121 are attained. As has been indicated 
earlier, only one of said three partition means 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 plastic material, as has been 
indicated, is to form airtightness on the two portions, upper and lower, 
of said partition means. As can be seen in FIG. 18, said parts 79 of the 
resilient nature will be depressed by the two short sides of the 
cross-section of the moving plates PP, recovering their position thanks to 
said resiliency, thus forming substantially complete airtightness. 
A description is given below of the surface final heating means, located 
downstream from the foaming tunnel, which constitute another aspect of the 
improvements provided by this application and which are shown in general 
as 122, 123 and 124 in FIG. 9A of the drawings. The drying temperature 
T.sub.S for the bottom of the block of foam is obtained in said surface 
final heating means. 
The description of said surface drying means will be made with reference to 
FIGS. 22A, 22B, 22C and 23A, 23B, 23C. 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 final heating means, whatever may be the heating means used, 
comprise 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 is 
constituted by 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 conduit 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 conduit 86 
throughout the enclosure of the heating means. On the side opposite said 
supply conduit 86 there is a collecting conduit 87, also provided with 
orifices 92, which evacuates to the outside the air which may have cooled 
the enclosure of the heating means. The electrovalve 89 is at the inlet of 
the conduit 86 and the electrovalve 90 is at the outlet of the collecting 
conduit 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 and 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 
final heating 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 
final heating is caused by a very high temperature 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 apparatus stops, and although the feeding of the heating 
means may also be 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 the description of the heating means, contemplated in 
the embodiments shown in FIGS. 22 and 23. 
In the embodiment of the surface final heating means shown in FIGS. 22 (A, 
B and C) 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, with the action of said device 88, the temperature 
T.sub.S on the plate 83 is controlled within the desired range. 
In the second embodiment of the surface final heating means shown in FIGS. 
23 (A, B and C), 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 of the 
coil conduit to the heating enclosure. FIG. 23A shows, as 97, the outlet 
of said coil from the heating enclosure. 
As can be seen in FIG. 23A, in this embodiment the sensing-controlling 
device 88 controls the operation of the electrovalves 89 and 96. In FIG. 
23A 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 it is realized that both devices 94 and 96, with 
similar functions, in both heating embodiments, are governed by the 
temperature sensing-controlling device 88. However, in the embodiment of 
FIG. 23A 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 T.sub.S 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 surface final heating 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 
apparatus of the invention to manufacture 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, the change in position of the cross 
partition means 119, 120 and 121 also comes within the scope of the 
invention. 
Examples of various foam formulations are given below: 
______________________________________ 
1. Foam. Density 23 kg/m.sup.3 supersoft 
Polyol 100 
Toluenediisocyanate 
29.5 
Water 2 
Dimethylaminoethanol 
1 
Silicone 1.3 
Freon-11 16.5 
Tin octoate 0.3 
2. Foam. Density 20 kg/m.sup.3 
Polyol 100 
Toluenediisocyanate 
51.3 
Water 4.1 
Dimethylaminoethanol 
0.4 
Silicone 1 
Freon-11 6.5 
Tin octoate 0.2 
Dye 0.3 
3. Foam. Density 25 kg/m.sup.3 
Polyol 100 
Toluenediisocyanate 
50 
Water 3.9 
Dimethylaminoethanol 
0.4 
Silicone 1 
Tin octoate 0.2 
Dye 0.3 
______________________________________ 
The value of t.sub.o (FIG. 2) was 41.5.degree. C.+1.degree. C. when using 
Formulation 2 and 45.degree. C..+-.1.degree. C. when using Formulation 3. 
It is preferable to modify the apparatus and process so that the above 
temperatures are maintained only in the first half of the belt, the 
reaction area, and to increase the temperature in the second half of the 
belt, the consolidation area, by about ten degrees. Even more preferable 
is the incorporation in the process of a final third heating zone. This 
process was used for Formulation 2 above. Maintaining the reaction zone 
temperature at a value T.sub.R =41.5.degree. C..+-.1.degree. C. and the 
consolidation zone temperature at a value T.sub.C 
=51.5.degree..+-.1.degree. C., with a time in the reaction zone t.sub.R =2 
to 3 minutes and a time in the consolidation zone t.sub.C =3 to 2 minutes, 
a block is obtained which after being subjected to a temperature of 
120.degree. C. in the final heating zone, and after the paper web has been 
removed from the bottom, has a uniform density throughout its volume of 20 
kg/m.sup.3 and a bottom without irregularities which does not require 
trimming.