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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to the preparation of adhesive compounds intended to
be sprayed on mineral fibers constituting fleeces or felts, especially for
thermal and acoustic insulation. These compounds give the felts which are
formed their cohesion and, in a more general manner, their mechanical
properties. The compounds in question can vary quite appreciably depnding
on the purpose of the felts, even when, as in the most common forms, the
base resin for these compounds is still the amino plastic, phenolic
plastic and especially formo-phenolic (amine modified or otherwise) type.
2. Background of the Prior Art
In addition to the resin, in general, the compound which is sprayed on the
fibers thus traditionally comprises various ingredients which either
improve the former's action or which add supplementary properties. In
addition, it is known to add constituent in addition to the resin which
also act as bonding agents. This is the case, for example, with carbamide
or ammonium lignosulfonate. It is also customary to add an oil emulsion to
the compound which acts as a softener and dust-proofer. Certain
glass-resin "coupling" agents are also added, which facilitate the bonding
of the resin to the fibers. These include amino-silanes, for example.
Filler materials, coloring, waterproofing agents such as silicones, etc.
are also added.
A catalyst must also be added for the cross linkage of the resin which will
promote the subsequent processing. Of course, this constituent cannot be
added very long before the adhesive is applied to the fibers when its
nature is such that it initiates an evolution towards cross linkage under
surrounding conditions. Finally, in addition to the fact that the resin
can run the risk of premature transformation if produced in very large
quantities and increase the time periods between production and
consumption (taking into account the proportion of water needed and the
volume these compounds reach), it is preferably for reasons of storage
convenience not to prepare the adhesive until immediately before it is
used.
For example, it is generally preferable to limit storage time to a few
hours. For some compounds, this period does not exceed 24 hours but can be
shorter for certain compounds, for example, about 1 hour, or even less.
Moreover, products prepared on the same production line can quite often
vary. In the hypothesis in which each adhesive would be prepared
independently of immediate consumption, access to a complete range of
adhesives would be necessary. This becomes less desirable as the variety
of adhesives utilized increases.
For these reasons, the adhesives are usually prepared gradually as they are
consumed. The problem is to ensure continuous preparation under
economically satisfactory conditions. It is especially necessary to reduce
operator intervention as much as possible. The cost of the special
equipment used must also remain compatible with the economic objective
established for the adoption of these techniques. In other words, simple
solutions are needed which require a small number of personnel and
moderate-cost equipment, while of course maintaining the quality of the
adhesives prepared.
The traditional preparation method consists of placing the various
constituents together in a tank, the proportions of which are measured by
an operator when they are added. Taking into account the need for operator
control, the preparation operations tend to be spaced and relatively large
quantities are involved for each of these preparations. These two factors
constitute an obstacle against frequent changes of the type of adhesive
and require large storage capacities.
More recently, it was attempted to automate the preparation sequences
allowing them to occur more frequently and thus involve smaller
quantities.
It was proposed to prepare the adhesive compounds by adding the different
constituents of the mixture using dosing pumps set to add these
constituents in the required proportions. Even if it was proposed to
prepare the compound continuously, as a direct function of its
consumption, the most widespread solutions consist of making successive
small-volume lots, with a previously prepared lot being consumed while the
subsequent lot is being prepared.
A problem with this preparation method is related to the fact that the
dosing pumps used must be very precise. Volumetric piston pumps are
especially used. This equipment requires frequent maintenance. The
equipment is also relatively expensive.
Moreover, the use of these volumetric pumps involves problems with respect
to their automatic adjustment. It is known to modify their flow rate by
changing the piston cycle or by modifying the operating speed, for
example, but each of these methods involves its own problems. Speed
modification, which is done especially using speed variators, does not
allow a great degree of precision to be maintained over long periods of
use. To modify the piston cycle, the pump must be connected to complex
electromechanical equipment. For these reasons, the adjustment of prior
equipment is rarely automated and operator intervention is limited by
avoiding frequent production changes. But this obviously does not respond
perfectly to practical needs.
An object of the invention is to propose a method for the preparation of
the adhesive compound which is both reliable and precise, a preparation
which is done in small quantities for each operation.
Another object of the invention is to propose such a method of preparation
in which the constituents are measured preferably with a number of
measuring devices which is smaller than the number of constituents used.
Another object of the invention is to allow the quantities of constituents
utilized to be controlled instantaneously and automatically in the method
for the preparation of the adhesive involved.
Another object of the invention is to allow an assessment of available
compound to be prepared simultaneously so as to adjust the amount of
compound being prepared to the quantity of felt of a given quality
remaining to be prepared in the production sequence in progress. This
assessment can also be combined with that of each of the constituents in
stock to facilitate the management thereof.
Another object of the invention is to propose an installation which makes
it possible to greatly reduce operator intervention for the adjustment of
maintenance thereof.
SUMMARY OF THE INVENTION
According to the invention, the preparation apparatus for the adhesive
compound comprises, in addition to storage tanks for the various
constituents, a group of conduits and circulation pumps leading to valves
connected to a single common conduit or to a limited number of common
conduit(s) on which equipment to measure the mass of the product
circulating in the conduit(s), is installed, with this (these) common
conduit(s) carrying the constituents circulating sequentially to a
preparation tank, in which the compound is prepared in definite
quantities, then transferred by pumping into a distribution tank, from
which it is finally taken by one or several pumps and sent to the device
which sprays it on the fibers.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in detail, with reference to the
drawings, in which:
FIG. 1 is a schematic view of a traditional assembly to supply the various
constituents of the adhesive up to the preparation tank;
FIG. 2 is a schematic diagram showing a part of the preparation and
distribution installation for the adhesive compound according to the
invention;
FIG. 3a is a diagram of the measuring device used in the installation
according to the invention in a perspective view;
FIG. 3b illustrates a surface view of the phenomenon of bending which is
the basis for the measurement using the device in FIG. 3a.
DETAILED DESCRIPTION OF THE INVENTION
In prior methods and in the method according to the invention, the
constituents intended to form the adhesive are stored and taken to
utilization tanks in a similar manner.
FIG. 2 shows the part of the installation which corresponds to the storage
and transfer of a constituent to the utilization tank. Analogous
arrangements are used for each of the constituents under the conditions
indicated below for some of them. This part of the installation is not
shown in FIG. 1.
The individual constituents (resin, carbamide solution, emulsion, oil,
ammoniac, silane hydrolysate. . .) are stored in large capacity tanks (1)
in the utilization areas to allow a sufficient autonomy. Especially when
the isolated constituents are prepared on the site, the tanks can have a
smaller capacity, since risks of running out of supply are smaller.
These tanks (1) are kept under the required conditions for each constituent
so as to ensure a clearly defined quality. They are, for example, equipped
with homogenization and devices and are thermostatically controlled.
It is obviously preferable to introduce the water needed to complete the
compound directly into the circuit at the level of the measuring device
discussed below.
It may be preferable to transfer products added in very small proportions
directly from their container to the utilization tank (2).
The constituents are each taken to a utilization tank (2) through the use
of a transfer pump (3). It can be advantageous to install a filter (4) on
the transfer conduit, upstream from the pump, to protect the latter.
During operation, the utilization tank (2) is kept filled between the
maximum and minimum levels. Level detectors control the activation of each
transfer pump (3). The utilization tank (2) constitutes a convenient
small-capacity intermediary in the immediate proximity of the adhesive
preparation area. It allows a constant feed to be ensured for the circuits
which follow it. Each utilization tank can also feed several preparation
complexes if necessary.
When the installation of various elements calls for it, especially when the
storage area is close enough to the adhesive preparation area (and thus
when the conduit system needed is not too extensive), the circulation loop
can be placed directly after the storage tank (1). In other words, the
utilization tank (2), the transfer pump (3) and its filter (4) can be
eliminated.
The constituent is tapped from the utilization tank to pass into a circuit
which leads to a preparation tank.
This circuit is quite appreciably different if one considers the
conventional structure shown in FIG. 1 and that according to the
invention, an embodiment of which is shown in FIG. 2.
According to the conventional method, the circuit has a set of filters (5)
and volumetric dosing pumps (6), which push the constituents, in definite
quantities, back into the preparation tank (7) which is common for all
constituents and in which they are mixed. The circuit also usually has
shutdown valves and drains.
The most precise traditional volumetric pumps are piston pumps whose
movement establishes a constant volume. The speed and amplitude of this
movement, caused by a connecting rod-crank engine, can be adjusted.
The amplitude or the cycle of the piston correspond to a change in the
shape of the rod-crank complex. In addition, although this modification
may be controlled automatically as indicated above, this automation
requires relatively complex equipment which greatly increases the cost of
the installation. For this reason, manual control is often preferred but
involves problems inherent in this method, namely slowness of operation,
risk of error, etc.
The variation of the speed obtained, for example, using speed variators is
not problem-free either. As stated, the operation of the variators is not
precise enough to ensure a satisfactory preparation.
The adhesive compound prepared in the tank (7) next passes into a
distribution circuit which is presented in detail with respect to the
installation according to the invention.
FIG. 2 shows an embodiment according to the invention.
In this installation, the part pertaining to storing the constituents and
transferring them to the utilization tanks is as described above. The
subsequent part, which is peculiar to the embodiments according to the
invention, must be considered in detail.
Each constituent taken from a utilization tank (2) passes into a feed loop
which comprises a circulation pump (8), a filter (9) to protect the pump
(8) and, located upstream from the latter, a three-way valve (10), a
return conduit (11). In this circuit, the operating parameters are
determined so that the flow rate of the pump is greater than that required
to feed the preparation tank (12) mentioned below. As such, the
constituent constantly runs through the feed loop.
Indeed, for the proper operation of the circulation pump (8), it should
preferably run continuously. Under these conditions, depending on the
position of the three-way valve (10), the constituent is either completely
returned to the utilization tank (2) through the conduit (11), or is
partially returned and partially sent into the circuit feeding the
preparation tank (12).
It is also possible according to the invention to replace the feed loop
with a one-way circuit to the utilization tank (2). As such, this method
implies that the pump is discontinuous, which is less favorable,
especially because of the risks of deenergizing as the result of a even a
brief shutdown. Moreover, this also involves a circulation pump flow rate
which is relatively similar to the flows actually necessary. On the
contrary, in the case of a feed loop, there is a great degree of latitude
in choosing the characteristics of the pump, provided that the circulation
generated be greater than the necessary flow rate.
According to the invention, it is not necessary to use a pump with a very
precisely controlled flow rate. The dosage is not done by the pump, but
directly on the amount of constituent circulating in preparation tank (12)
feed conduits.
For these reasons, a wide variety of pumps can be used, especially
centrifugal pumps, gear pumps, propeller pumps or slide vane rotary action
pumps. Since the function of these pumps is not to measure the quantities
of the constituents, they can be chosen according to their sturdiness more
so than their precision, which allows the reliability of the installation
to be improved appreciably and limits the delicate maintenance operations
compared to what occurs when following the traditional technique in which
the volumetric pump itself does the measuring.
In FIG. 2, the feed loops for the various constituents (only one of them is
fully shown) are shown connected to a single circuit to measure and feed
the preparation tank (12). This arrangement is advantageous because it
makes it possible to greatly simplify the installation. We shall see that
it can be preferable to divide this part into two or more [sections]. But,
generally, according to the invention, it is not necessary to provide a
separate measuring circuit for each constituent while, on the contrary,
the most widely used traditional method consists of having a dosage
circuit with a volumetric pump for each constituent.
When, as shown in FIG. 2, several connections are made on a same measuring
circuit, an effort is made to limit the volumes of the conduits separating
the three way valves of the common conduit (13) as well as the length of
the common conduit (13) coming before the measuring device (14) as much as
possible.
In the installation according to the invention, the constituents are
measured by a mass flow meter-type device such as those marketed by the
MICRO-MOTION company. These devices operate as described below.
The measured liquid circulates in a U-shaped tube (20) which is given a
vibrating movement imposed in a direction located outside of the plane of
the U-. The vibration of the tube causes the liquid circulating in the
U-shaped tube to accelerate in the direction of arrows a. The
instantaneous direction of these vibrations is illustrated in FIGS. 3a and
3b by arrows V. Conversely, the liquid resists the acceleration imposed on
it due to inertia. This resistance creates two forces in opposite
directions on each leg of the U, shown by arrows F in FIG. 3b. These
forces are a direct function of the mass of the liquid circulating in the
tube. These forces and subsequently the mass of the liquid are measured by
measuring the bending of the tube, which occurs as shown in FIG. 3b. The
bending is inversely related to the direction of the vibration.
The bends are measured, for example, magnetically.
Mass measurements done using these flow meters has a precision of about 0.5
to 1%, which is totally satisfactory for its use according to the
invention. Moreover, has about the same magnitude as that obtained with
very high quality volumetric pumps.
We have stated that the same measuring circuit can serve for the various
constituents of the adhesive. In practice, the masses of the constituents
used to prepare a single adhesive can be very different. This can involve
a few problems.
Indeed, the cross section of the mass flow meter is chosen to allow maximum
precision for a given flow range. The loading time for each product is
determined according to the choice of this range. When constituents are
used in very different proportions while using a same flow meter, the time
sequences are also very different. This can cause certain problems. If a
low flow rate is chosen, the most abundant constituents will take a long
time to pass, so that the speed at which the adhesive is used may not be
satisfied. If, on the contrary, a high flow rate is chosen, the sequence
is rapid and demand is satisfied, but the passage time for small
proportion constituents is much less and measurement precision for them
can decrease in an undesirable manner, for example, due to the inertia of
the valves.
When the adhesive formula contains constituents which are added in very
different proportions, it can be advantageous to construct two or more
measuring circuits, with each circuit being chosen to correspond to the
best measuring conditions corresponding to the products considered.
Of course, it is possible to assemble a measuring circuit for each
constituent, but this greatly increases the cost of the installation. The
improvement resulting from such an arrangement is generally insufficient
to compensate for this additional investment.
It is remarkable that only one measuring device (or, if need be, two) can
suffice for all of the various constituents, regardless of their nature.
This becomes more advantageous as the number of constituents increases.
There are usually 6 to 10, but there can be more. One advantage of mass
flow meters is that they operate independently of the volume mass of the
products treated. Possible variations are smaller than the general
accuracy of the measuring indicated above. Moreover, the volume masses of
the various constituents used are essentially similar, which further
increases the accuracy of the measurements.
The similarity of by-volume masses of the constituents also prevents the
dead volume formed by the conduit located between the three-way valves and
the intake of the flow meter from appreciably distorting the measurements
made although a fraction of the time period in which a constituent is
circulating is used to measure the rest of the preceding constituent
filling this part of the circuit. However, it is preferable to limit this
dead volume as much as possible by placing the three-way valves as close
as possible to the flow meter. Of course, when products having very
different volume masses are involved, a systematic correction allows
precision to be further increased. For the most common operating
conditions and, by following the precautions indicated below, it is
nonetheless possible to operate without corrections. In the hyoothesis in
which the compounds are prepared automatically according to a programmed
control, the systematic correction is advantageously included in the
program.
The use of only one flow meter (or a small number of them) in the operation
of the installation implies that it receives the products in a sequence to
measure them one after the other.
The choice of the sequence is not necessarily arbitrary. It can be
determined by the mixture to be made. It can also depend on whether the
constituents are made to pass through a common circuit. It is especially
preferable to rinse the preceding elements in the sequence once or twice
with water at the end of the sequence, which can involve all of the water
added or only a fraction of it. As such, each passage of the constituent
can be separated by a rinse using a fraction of the water necessary.
Rinsing at the end of the sequence has a twofold interest. On the one hand,
it ensures that all of the constituents, the introduction of which was
controlled by the opening and closing of the different valves, was indeed
transferred to the preparation tank and thus the proportions are
respected. On the other hand, in the event of a change in composition from
one operation to the next, it ensures that the constituents from the
preceding compound are eliminated.
For the same reasons, in the schematic circuit shown in FIG. 2, it is
preferable to place the water feed at the end of the conduit 13, so that
the wash covers all of this conduit.
The drawing in FIG. 2 shows a feed circuit for the measuring device
comprising 7 three-way valves. This is only an example. The number of
feeds and consequently the number of different constituents is unlimited.
Moreover, since a same installation can serve in the preparation of
different types of adhesives, all of the feeds are not necessarily
utilized during the sequence for the preparation of a given adhesive.
The constituents placed in the preparation tank are homogenized with an
agitator (15). They are next transferred into the distribution tank (16).
The command to pass from tank (12) to tank (16) is determined by the level
measurement in the latter. When the minimum level detector activates the
transfer, the whole preparation in the tank (12) is decanted. This is done
either by simple gravity, as shown in the figure, or with a circulation
pump. When the tank (12) is emptied, another adhesive preparation sequence
is begun.
Provisions are made so that the preparation time is still less than the
consumption time for the compound, so that the process continues in an
uninterrupted manner. Under this condition, it is seen that a relatively
small volume can be prepared in each sequence, which limits the quantities
of products immobilized. Even if it requires the multiplication of
preparation operations, this method does not involve any measuring
problems to the extent where these operations are completely automated, as
we will see below.
Moreover, the small volume of adhesive prepared in each sequence allows a
more rapid rotation, in other words, a shorter average standby time before
a utilization period. This is especially advantageous when the compound
prepared changes quickly under surrounding conditions.
The small volume on standby also facilitates changing the adhesive in
operation by reducing the time between two successive preparations. As we
have indicated, the compound is changed in the case of the invention
without interrupting production, by simply changing the constituent feed
sequence.
When the compound is changed, the tank (12) is emptied completely. In other
words, the fraction of compound which is located under the minimum level
is either consumed or removed by the drain (19).
Various methods can be used to distribute the adhesive to the spraying
stations. Advantageously, the compound coming from the distribution tank
(16) is sent by dosing pumps to the spray devices (18). These dosing pumps
must be stable, but they do need to be highly precise.
At this point in the installation, it is not a question of preparing a
compound from constituents in highly rigorous proportions, but of coating
the fibers forming the felts with a constant amount of the adhesive.
The dosing pumps can also be replaced temporarily or permanently by a
volume mass-type measuring complex associated with means to control the
flow rate such as proportional valves. If the cost of these devices makes
this type of solution less attractive for a permanent industrial
application, it can nonetheless present great advantages in the capacity
of occasional checks done on the production line.
Propeller pumps, for example (like MOINEAU type pumps) are used to feed the
spray devices.
A circulation loop (16) can be installed connecting the distribution tank
(16) and the dosing pumps (17). This arrangement, which is not shown in
FIG. 2, is useful especially when the distribution tank (16) is relatively
far from the place of use and when the type of compound is to be changed
frequently. In this case, as above, the circulation loop has a filter,
with a circulation pump ensuring a flow rate which is greater than that
corresponding to the feed for the dosing pumps (17).
When a circulation loop is used, the measuring of the adhesive distributed
can be controlled using simple rotameters regulating controlled-opening
electrovalves, or with similar devices.
A considerable advantage of the installation according to the invention
presented above is related to the fact that the proportions of each
constituent in the compound is controlled without any modifications to the
level of the measuring device, contrary to the operating method using
dosing pumps. Indeed, according to the invention, materially, the
modification of the proportions or the constituents themselves results
from a change in the opening and closing sequence for the three-way
valves. The mechanical complex is thus unchanged.
This simplification is appreciable when the preparation sequence is
operator-controlled. The latter can remote monitor the preparation and
intervene instantaneously for urgent modifications. The provisions
according to the invention are still more appreciable for automated
operation. The latter is increasingly advantageous as production lines are
more varied and modified more often.
The automated complex does not require other information inputs than those
established in any event, namely, the measuring of the levels of the
constituents in the storage tanks and vats, that of the levels in the
preparation, utilization and distribution tanks and the information
provided by the device(s) which measure the masses of the constituents
feeding the product.
Automated or not, the complex also generally has measuring devices which
verify that the necessary pressures are present in the circulation loops.
All of this information is sent preferably to a processing complex which
also receives programmed instructions. In response, this complex controls
the operation of the various elements of the installation: valves, pumps
which control the preparation of the adhesive etc. In FIG. 2, the data
processing and control complex is represented by the block (22). For
example, the connections for the processing complex have been shown in
dotted lines, on the one hand, with the measuring device (14), and, on the
other hand, with a three-way valve (10). Of course, connections are
installed with all of the measuring and control equipment in the
installation.
If necessary, the information coming from the various measuring instruments
also allows the storage of the constituents of the adhesive compound to be
managed by determining the cumulative consumption thereof.
For example, an adhesive preparation utilized for the production of glass
fiber felts for insulation includes the following different constituents
added in this order:
water,
modified or unmodified formo-phenolic resin,
carbamide in aqueous solution,
ammonium sulfate in solution,
ammonia solution,
oil emulsion,
hydrolyzed silane,
water.
As indicated above, the circulation of water at the end of the sequence
allows the feed conduits to be rinsed. The water introduced at the
beginning of the sequence allows the proper homogenization of the compound
gradually as the different constituents are added. The water introduced on
these two occasions can be divided, for example, in half.
In the case of a single measuring device, the constituents are introduced
separately.
Like the manual control, the automated control allows not only the
following of the introduction of the different constituents in the
required proportions, but also allows the total quality of the compound
prepared to be modulated. As such, the quantity of the adhesive can be
adjusted precisely to the amount necessary when a production change
occurs.
The preparation time for the adhesive is adjusted to follow the rate of
consumption. Advantageously, a sufficient margin is maintained to allow
intervention on the preparation installation. For example, the length of
the preparation period is adjusted to half of the consumption cycle.
As we have indicated, the quantity of the adhesive compound prepared for
each cycle can be very small. For reasons of convenience and if needed to
provide for brief interventions on the installation without having to
interrupt production, it is nonetheless preferable for the capacity of the
distribution tank to be sufficient so that, between the maximum and
minimum levels, the quantity of adhesive corresponds at least to 15
minutes of consumption.
The capacity of the distribution tank is not related to that of the
utilization or preparation tank. Of course, the only limit is that the
volume of the distribution tank be sufficient to accommodate all of the
largest load to be prepared in the preparation tank.
The above described invention for the preparation of adhesives can be used
to prepare compounds which are sprayed under the same conditions on
fibers, even if the latter are not intended, or are not essentially
intended to bond the fibers together. The invention can especially be used
to prepare softening compounds whose main role, for example, is to make
the fibers pleasant to the touch, or to prevent the emission of dust. In
the same manner, a combination of several liquid constituents is used in
the preparation of these softening compounds. The same process and the
same type of installation as that described for adhesives thus can be
utilized.
Obviously, numerous modifications and variations of the present invention
are possible in light of the above teachings. It is therefore to be
understood that within the scope of the appended claims, the invention may
be practiced otherwise than as specifically described herein.
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