Equipment for uniformly spreading anti-sticking powders on bituminous membranes for building coverings

The present invention pertains to an equipment adapted to uniformly spread anti-sticking powders, such as talc in an aqueous suspension, on bituminous membranes for water-repellent coverings in the building field. Said equipment comprises a series of rollers on which the membrane runs. During the feed motion the membrane passes through a suspension-applying station and a drying station. Downstream of the suspension-applying station, a flattened jet of compressed air eliminates the liquid in excess and creates a homogeneous liquid film on the membrane. Afterwards, the membrane reaches a rotating drum provided with suitably disposed shaped reliefs which, on the membrane itself, create a homogeneous distribution of the particles suspended in the liquid film.

FIELD OF THE INVENTION 
The present invention relates to an equipment for uniformly spreading 
anti-sticking powders on bituminous membranes used for accomplishing 
water-repellent coverings in the building field. 
BACKGROUND OF THE INVENTION 
It is known that, due to stockage and transport necessities, the bituminous 
membranes in question are delivered in the form of rolls that are 
subsequently unwound by the users at the moment of their laying down. 
In order to avoid undesirable glueing phenomena between two coils in a 
roll, due to the nature of the material (mainly consisting of bitumen), 
before the rolling step the membranes are coated with appropriate 
anti-sticking powders. 
The application of said anti-sticking powders is carried out only on one 
side of the membrane (that is the one that during the laying step is 
turned outwardly) while the other side (the one in contact with the laying 
surface) is coated with a protective plastic film. 
The anti-sticking powders applied on the membrane may be of various types. 
However the most preferred ones are mineral powders and, among them, talc 
powder which exhibits the best anti-sticking characteristics. 
It is known that the currently-used methods for spreading powders on 
membranes can substantially be divided into dry methods and wet methods. 
The application of powders using a dry method is carried out by means of 
appropriate vibrating nets that, being loaded with the powders, execute 
the spreading thereof on the underneath continuously running membrane 
which is transferred on rotating rollers. 
This method however has some drawbacks. First of all it causes pollution in 
the work environment due to the dispersion of the powders in the air and 
furthermore it does not allow a homogeneous and optimum spreading of the 
powders themselves on the membrane. The pollution problem can be partially 
solved by the use of strong aspirators, which however results in a 
disadvantage from an economical point of view owing to the construction 
costs of the aspirators that evidently adversely affect the cost of the 
finished product. 
The dry method used in order to obviate the above mentioned pollution 
problem provides the application of powders in an aqueous suspension. The 
application of the aqueous suspension on both sides of the membrane 
(obviously if the use of the protective plastic film is not provided) is 
carried out plunging the membrane itself into a suitable bath followed by 
a drying step which can be achieved by causing the membrane to move 
forward on entraining rollers for a given time. 
Should the application of said suspension be needed only on one side of the 
membrane, said membrane is kept in a vertical position and caused to move 
in contact with and along a horizontal cylinder transverse thereto. The 
area disposed above the cylinder and defined by the cylinder itself and by 
the moving membrane is flooded with the aqueous suspension so that the 
aqueous suspension itself is distributed on the membrane surface in 
contact with the cylinder. As in the previous case, this step is followed 
by a drying step. 
It is known that in both cases, however, it is not possible to reach the 
optimum spreading of the powders on the membrane. In fact, before and 
after the drying steps said powders tend to gather on preferential and 
rather broad areas threby creating other wide areas that, being 
unconcerned with the anti-sticking powders, give rise to the localized 
glueing of the roll coils. 
OBJECT 
The main object of the present invention is therefore to obviate the above 
mentioned drawbacks relative to the hitherto known art by providing an 
equipment for spreading anti-sticking powders on bituminous membranes 
which allows the accomplishment of a perfectly homogeneous and excellent 
spreading of the powders themselves on the membrane and which also has a 
low construction and operative cost. 
SUMMARY OF THE INVENTION 
The foregoing and still further objects are attained by the equipment of 
the present invention, of the kind using anti-sticking powders in an 
aqueous suspension and comprising a series of rotating rollers on which 
the bituminous membrane provided with a continuous feed motion runs and 
further comprising a station in which the aqueous suspension is applied to 
the membrane as well as a drying station and wherein, downstream of the 
suspension-applying station and upstream of the drying station relative to 
the membrane feed direction, provision is made for a rotating drum on 
which the membrane runs said rotating drum having its cylindrical surface 
disposed in contact with said membrane, provided with shaped reliefs and 
wherein, downstream of the suspension-applying station and upstream of 
said rotating drum provision is also made for a compressed air duct placed 
in the vicinity of the membrane transversely to the feed direction of the 
latter and provided with a longitudinal slit turned toward the membrane 
surface so that it generates a flattened air jet adapted to eliminate the 
liquid in excess on the membrane and to form a liquid film thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, it has been indicated at 1 a bituminous membrane 
for building coverings. Said membrane 1, which is provided with a 
continuous feed motion according to the direction shown by the arrows in 
the figures, comes from the manufacturing station A and is sent to the 
final station B where it is wound into rolls. 
On its way from A to B it passes through the equipment of the invention 
globally identified at 2 where the application and spreading of the 
anti-sticking powders on one of the sides thereof take place. 
The equipment 2 comprises a series of rotating rollers 3, 4, 5 and 6 (which 
can be idler or powered rollers in accordance with requirements) disposed 
at different heights so that the membrane passing thereon may follow the 
route shown in FIG. 1. 
The application of the anti-sticking powder takes place by wet process, 
using the aqueous suspension 7 (talc powder mixed with water) in the 
application station 8. 
In such a station 8 the membrane 1 is ketp in a substantially vertical 
position by virtue of the presence of the idler roller 4 and is caused to 
slide being in contact with a horizontal cylinder 9. The area above the 
cylinder 9 defined by the cylinder 9 itself and by the membrane 1 is 
flooded with the suspension 7 coming from a feed piping 10 connected to a 
tank 11 which is provided with a mixer 12. 
At the ends of the cylinder 9 the suspension 7 overflows into an underneath 
reception basin 13 connected to the tank 11 by a recycle piping 14. 
The surface of the membrane 1 downstream of the cylinder 9 is therefore 
covered with the water suspension 7. 
In traditional equipments, this suspension-applying step is immediately 
followed, as already mentioned, by a drying step during which the membrane 
1 is caused to run on entraining rollers, over a predetermined lapse of 
time, along a path of suitable length. 
In the equipment 2 in question, the suspension-applying step is followed by 
a further step during which the anti-sticking powders are uniformly 
spread. 
Downstream of station 8, close to the membrane 1 there is a compressed air 
duct 15 connected to a blower. Said duct 15, disposed transversely to the 
feed direction of the membrane 1, has a quadrangular section (but 
obviously any section can suit the purpose) and is provided, on its corner 
turned towards the membrane 1, with a slit 17 adapted to create a 
flattened air jet designed for eliminating the excess liquid present on 
the membrane 1 itself. By effect of the flattened air jet, a liquid film 
rich in suspended talc particles is left on the membrane 1. 
Downstream of the compressed air duct 15 provision is made for a rotating 
drum 18 on which the membrane 1 is partially wound. The cylindrical 
surface of the drum 18 is provided with many shaped small reliefs 19 each 
of them exhibiting a substantially flat top 20 (actually it is a slightly 
convex top having a bending radius equal to one half of the nominal 
diameter of the drum section). Said reliefs 19 are of substantially 
rhomboidal form and are defined by grooves 21 extending in a crossed 
helical manner (see FIG. 2), obtained on the cylindrical surface of the 
drum 18. 
The rolling of the membrane 1 on the drum 18 results in the formation, on 
the surface of the membrane 1 itself, of a particular configuration and 
distribution of the talc particles present in the liquid film. Such 
distribution is shown on the surface of the membrane 1 seen in FIG. 2. 
By examining each impression corresponding to the action exerted by each 
relief 19 on the liquid film present on the membrane 1, it is possible to 
notice three distinct talc-distribution areas: a first dark area 22 almost 
devoid of talc particles and substantially in the form of a C; a second 
white area 23 of circular form, rich in solid particles; a third grey area 
24 in the form of rectilinear perimeter segments, in which an intermediate 
amount of talc is present. 
The second area 23 is produced by effect of the surface tension of the 
liquid which, as the membrane 1 detaches from the top 20 of the relief 19, 
gives rise to the formation of a small drop (thence the circular form). 
The formation of said drop is achieved by removal of liquid from the 
surrounding area and particularly from the second area 22 which therefore 
is left almost devoid of liquid and consequently, as already said, of talc 
particles. 
The third area 24, on the contrary, corresponds to the position of the 
grooves 21 which, as they do not come in contact with the surface of the 
membrane 1, leave the distribution of the liquid film unchanged. 
Afterwards, downstream of the drum 18 the membrane 1 passes through a 
drying station 25 consisting of a pair of burner sets 26 aligned 
transversely to the same and disposed upstream and downstream of the 
roller 5 respectively, which burners allow a quick evaporation of the 
liquid film present on the membrane 1. 
Downstream of the drying station 25 the distribution of the talc particles 
on the membrane 1 remains unchanged as seen in FIG. 2. 
It is to be noted that the storage of talc particles on the second area 23 
due to the greater amount of aqueous suspension stored thereon constitutes 
an advantage to the ends of the anti-sticking effect. 
In fact, since in the long run the solid particles tend to be absorbed by 
the bitumen present on the surface of the membrane 1, it is important that 
on the surface itself areas with talc in excess should be provided and 
that said areas should be distributed as homogeneously as possible. 
In the case shown each area 23 has such a feature. 
As a result, even if the memberane 1 should be left rolled up for long 
periods, the anti-sticking effect would be always ensured. 
It is also to be noted that for the optimal achievement of the above 
described effects each top 20 of the reliefs 19 should preferably have an 
extension ranging from 10 to 100 mm.sup.2 and each groove 21 should be 1 
to 3 mm long and about 1 mm deep. 
The invention attains the intended purposes. 
Obviously the equipment according to the invention can, in practical forms 
of embodiment, also differ constructionally from what has been outlined 
above. Furthermore all of the details may be replaced by technically 
equivalent elements and the component members can be of any nature and 
magnitude in accordance with requirements.