CA1103295A - Devices for pre-heating concrete before pouring - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A device according to the invention for pre-heating concrete before pouring comprises: at least one bucket with a vertical axis which comprises, in a known way, at its upper part, an opening for introducing concrete to be pre-heated and at its lower part, a clos-able opening for pouring: a mobile horizontal plate capable of closing off said opening for introducing the concrete and a set of several elongated electrodes fixed to the lower face of said plate so as to hang vertically from this plate around a central vertical axis, means for vertically moving said plate with said elctrodes between a high position, in which it disengages said introduction opening for loading the bucket with concrete to be pre-heated and a low position in which said electrodes plunge into the concrete to be pre-heated contained in the bucket and the introduction opening is stopped up by said plate, said central vertical axis arriving in the position of said vertical axis of the bucket.

Description

The present invention concerns -the pre-hea-ting o~ concrete and has more particularly f~an ob~ect an improved device for pre-hca-ting concre-te just before pourillg .
I-t is known tha-t i-t is advan-tageo-ls, ~or improving the set-ting o~ concrete, to pre-hea-t i-t be~ore pouring into shuttering or moulds. Generally -this heating is achieved with steam.
Recently, it has been suggested to heat~he concre-te in a horizontal bucket on a worlcing site, before its use, by means of metal plates forming electrodes between which is applied an electric current, the mass o~ the concrete between these electrodes acting as an electric resistor and so hea-ting up by Joule effect. In this case an electric current is passed through the concrete for ten minutes or so to bring it to a tempera-ture o~ about 50C, the concrete thus pre-heated being directly poured into the usual shuttering.
The electrical pre-heating of concrete is particularly advantageous for it permits ar. excellent use of the electrical energy, the kilo~atts used being transformed, with a yield substantially equal to unity, into heat for directly heating the concrete whose temperature may thus rap~dly reach 50, as indicated previously. Furthermore, if the concrete thus pre-heated to 50 is poured into lagged shuttering, the dismantling of the shut-tering can be carried out in a~ory short time while avoiding heating in the mass or through the shuttering which has overall an inferior yield.
Present devices for the electric heating of concrete use horizontal buckets which it is necessary to set uprigh-t again be~ore the pouring o~ the pre-heated concrete ; now this setting upright requires the use of a crane which may break down and in this case the concrete sets in the bucket which becomes unusable and which must be overhauled at great cost. Moreover, known devices use parallel electrodes which do not allow homogenous curren-t dens~ties to be obtained through-out -the mass of fresh concrete, which leads to the formation of hot points and even the risk of causing the water contained in -this concrete to boil, resulting in a reduction o~ the water con-tent in the fi~al concrete, and consequently a pOOI' ,: : .: -~3~

quality thereof.
The present invelltion has nn object to overcome the above-mentioned disadvc~ltages o~ ~nown devices for pre-heating concrete before pouring.
A device for pre-lleatillg concrete before pouring according to the invention is characterised by the fact that it comprises, in combination:
at least one bucket with a vertical axis which comprises, in a known way, at its upper part, a filling opening for introducing concrete to be pre-heated and, at its lower part, a closable discharge opening for pouring; a mobile horizontal plate capable of closing off said filling opening for introducin~
the concrete and a set of several elongated electrodes fixed to the lower face of said plate so as to hang vertically from this plate around a central vertical axis; means for vertically moving said plate with said electrodes between a high position, in which it disengages said filling opening for introducing concrete to be pre-heated and a low position, in which said electrodes plunge into the concrete to be pre-heated contained in the bucket and the filling opening is stopped up by said plate, said central vertical axis arriving in the position of said vertical axis of the bucket; and means for supplying these electrodes with current and for earthing the bucket.
Preferably, the electrodes have different lengths and sections, the longest electrode having the smallest section.
In a first application, the device serves for pre-heating concrete before pouring into shuttering on a working site and in this case it comprises furthermore a horizontal platform on which there is permanently disposed at least one bucket of the above-mentioned type, the platform having a discharge hole in register with the discharge opening of the bucket, a gallows which comprises a vertical upright fixed on the platform and a horizontal arm slid-able on said upright, a free end of the arm carrying said set of electrodes;
in the preferred embodiment, the platform carries two buckets and, in this case, it has two discharge holes, the horizontal arm of the gallows being not only slidably but also rotatably mounted on the upright, so that the set of :J. ~ ~ .

~ 3~

electrodes may plunge at will into one or the other of the two buckets.
In a second application, the device serves for pre-heating concre-te in an installation Eor producing concrete castings and in this case it com-prises, in combination with a set of vertically mobile electrodes of the above-mentioned type, several buckets, aLso oE the above-mentioned type, which are hori70ntally movable so as to be able to come in turn underneath said set of electrodes, and means for collecting the pre-heated concrete leaving a bucket underneath a said set of electrodes, for subsequent transport oE this concrete to the place for casting said parts.
The concrete pre-heating device of the invention enables perfect homogeneity of heating of the concrete to be achieved since the arrangement provided for the electrodes affords an excellent distribution of the equi-potential lines in the mass of the concrete, the electric field and so the current density being uniform in the mass of the concrete, The invention will, in any case, be well understood from the detail-ed description which follows considered in combination with the accompanying drawings, which are, of course> given especially by way of illustration.
Figure 1 shows, in perspective, an embodiment of a device according to the invention for pre-heating concrete before pouring on a working site.

2~ Figure 2 is a section, along II-II of Figure 1, showing the arrange-ment of the electrodes.
Figure 3 illustrates, similarly to Figure 2, a variation of the shape of the electrodes.
Figure 4 shows the distribution of the equipotential lines in -the neighbourhood of an electrode of the type illustrated in Figures 1 and 2.
Figure 5 shows, in side elevation, a device according to the invention for pre-heating concrete in an installation for producing concrete castings in a workshop manufacturing such parts.
Figure 6 shows, schematically and in elevation, another modification of the electrodes.

, ~, .
....

F:igure 7 shows, :in section the arrangement of the electrodes of Figure 6.
~ ith referellce to Figures 1 to 4, there will first of all be described an embodiment of the invention for the electric pre-heating of concrete before pouring on a working site.

- 4a -7he clevice properly spea~ing is mountr[.l Orl a nori~ontal platr-~ or plat-form l. This platforrnlnay carry one or more vertical buckets, particularly two Duckets. as illustrated in Fig. l, in which one of the buckets (bucket 2) is shown in continuous lina and the ot;her (bucket 3) schematically with a Droken line. Netting 4 surrounds the cievice -for saFety's sake, netting 4 enclosing two chambers or boxes 5 and 6 in each o-f which is placed a bucket, respectively 2 and 3. On the input: face is provided a sliding door 7 which may close either chamber 5 or chamber 6. In practice one of buckets 2 or 3 is in operation and the other in preparation, sliding door 7 being normally in front of the bucket in operation so as to ensure the saFe-ty oF the workmen.

- Platform 1 is provided therethrough with holes 8, 9, i.e. a hole opposite each bucket 2, 3. Around each hole 6, 9 there is disposed a support 10 for supporting a bucket such as 2 or 3.

A bucket such as 2 or 3 comprises essen-tially an upper cylindrical part 11a and a lower conical part 11b, part 11b -Finishing in an aperture 12 which may be closed by means o-F a hood 13 operable by means of a wheel 13a. A hook 15 allows to move bucket 2 of axis 13v.
The concrete pre-heating device comprises also, in addition to bucket 2 or 3, a set of elec-trodes 14 with three electrodes 15a, 15b and 15c, made for example from stainless steel, whose arrangement can be seen in Fig. 2: these electrodes, in the form of glove fingers (i.e. closed at their lower end), are sectionally in the form of hollow circular sectors, with an angle at the apex a equal to 120 in the case where there are three electrodes, as in -the illustrated embodiment. These electrodes are carried by an upper circular shaped plate 16, which is pierced at right angles to the electrodes for the fixing of these latter.
Assembly 14 is suppor-ted by a gallows.17 comprising a vertical upright 18 fixed on platform 1 and a horizontal arm 19 vertically slidable on upright 18 for liF-ting or lowering assembly 14 out oF bucke-t 2 or into bucket 3. Furthermore, in the ease where two (or more) buckets sueh as 2 and 3 are provided, mounted on platForm 1, the same gallows 17 may serve For both buekets, the assembly of eleetrodes 14 being eommon -to both buekets. In this case arm 19 may not only slide vertieally along upright 16 but may also rotate about this upright, so that ~ssembly 14 n~ay cooperate with olle or other of the -two bucke-ts.
From the electrical point of view, electrodes 15a, 15b and 15c are supplied with electric currcnt, for example 50t) amps at 380 vol-ts, by a cable 20, whereas bucket 2 is connected to tile electric"l neutral which is connected to ear-th for ensllring the safety of the workmen.
The unit illustrated in Fig. 1 is for continuous operation, one of the buckets 2 being in operation while the other bucket 3 is being prepared for later operation In one of the buckets (bucke-t 2) is fed the cement to be pre-heated, the opening 21 of this bucket being disengaged by removing assembly 14 from the bucket. Then once the bucket 2 is filled assembly 14 is lowered and electrodes 15a, 15b and 15c are suppliea with current for five to ten minutes, for example to bring the cement to about 50C. lYhen the operation is finished, wheel 14 is actuated to move hood 13 and free ope~ing 12 at the bottom of bucket 2. The cement flows through hole ~ and is collec-ted by means such as a tip-wagon or truck for transporting it to the desired place or preferably is fed airectly into a shuttering.
During the operation for heating -the concrete in bucket 2, the other bucket (buclset 3) is char~ed with concrete. At the end o~ -the operation for heating bucke-t 2, assembly 14 is raised by vertical movement of arm 19, then this arm is rotated so that assembly 14 is brought opposite the other bucket (bucket 3) then lowered and electrodes 15a, 15b and 15c are again supplied with curren-t for pre-heating the concrete in bucket 3. ~leanwhile, -the cement is ~ischarged from bucket 2, then this latter is again charged with concrete.
It can then be seen that continuous operation is effectively achieved by emptying, then loading one bucket whilst, in the other, the heating of -the concrete is carr:ied out.
In Fig. 3 are illustrated electrodes 35a, 35b and 35c having a hollow elliptical shape, also in the form of glove fingers closed at the lower part, which may be provided instead of electrodes 15a, 15b and 15c of Figs. 1 and 2.
In Fig. 4 are shown the equipotential lines E in a third o-f the drawing around electroc~e 1~a an(l arollnd centre O. The equipotential l-ines in the whole drawing may be readily deduced there~rom. These curves show that the heating ol th concre-te is very homogenous.
Thcre will now be described with re~erence to Fig. 5 an embodiment of the device according to the invention for tl1e electric pre-heating of concrete in a worlcshop producing concrete castin~s In such a shop beams~ flagsstones, ~rontage blocks, shaped sections and similar pieces may be prefabricated ~rom concrete. In this embodiment also there are provided several buckets, e.g. three buckets A, B and C , two only of which (buckets C and A respectively in positions 22 and 23) can be seen in Fig. 3 and a single set of electrodes 2~. Buckets A, B and C are of the type shou~ at 2 in Fig. 1, whereas the set o~ electrodes 24 may be of the type shown at 1~ in Fig. 1 and comprisesthree electrodes 25a, 25b and 25c having, in section, -the shape shown in Fig. 2 (electrodes 15a, 15b and 15c of this Fig. 2) or the shape shown in Fig. 3 (electrodes 35a, 35b, 35c o~ this Fig. 3.
me unit shown in Fig. 5 comprises also an overhead crane 26 provided with a hopper 27 which goes and fetches aggregates and cement from storage hoppers not shown. The preparation of the concrete takes place in a mixer 28, of known type, which receives the cement and the aggregates from hopper 27 when this latter is brought by overhead crane 26 above mixer 28. Instead of overhead crane 26, a belt may be provided for bringing the aggregates and the cement to mixer 28. Once the concrete is mixed in mixer 28, the lower opening 2g of this latter is disengaged and -the freshly mixed concrete is collected in bucket A
at position 23.
The three buckets (onl~ two o-~ which at 22 and 23 are shown) may move in a closed circuit, for example by means of a rail 30.
Bucket A in position 23 once filled wi-th mixed concrete moves in the direction o~ arrow f to assume position 22 which was occupied by bucket C in Fig. 3, whereas bucket C moves to take up a third position in which it cannot be seen and bucket B comes to 23. Once bucket A is in place in position 22, , ~

the set of elec-trodes 2~1 is lowered in-to this bucket in posi-tion 22 by means of a hoist 31. Then, for -the desired time, elec-tric cuxrent is applied to the electrodes, bucke-t .~ a-t 22 being ear-thed The pre-hea-ting of the concrete in the bucket a-t 22 finished, -the lower opening -thereof is opened so as to let the pre-heated concrete, e g a-t 50C~ flow in-to a distribu-ting vehicle 32. This vehicle, once filled, is brought -to -the casting moulds or shuttering, such as mould 33, in-to which it discharges a part of its charge through an endless screw distribution system 3~.
It will be noted that in Fig. 5, for simplification thereof, the distributing vehicle 32 feeds mould 33, whereas it is underneath the bucket at 22, but in general vehicle 32 moves from the position illustrated in Fig. 5 to the position for CaSting in mould 33, as previously indicated.
After closing the lower hole of bucket A at present at 22, this latter is moved to take up the third position not shown in which it ~ay, for example, be cleaned by means of a shower type device. Meanwhile a new bucket ~bucket B) which has been charged in the position illustrated at 23 is brought into the position illustra~ted at 22. ~hen the concrete, in bhis new bucket B at position 22, has beell pre-heated by electrodes 25a, 25b and 25c, then discharged into a dis-tributing device 32, this bucket B is brought under the "shower" whereas bucket A which was originally at 23 and which was under the shower comes back to this position ; finally bucket C comes back to position 22 illustrated in Fig. 5.
So that the arrival of each of the three buckets A, B and C in the three successive positions : filling position (illus-trated at 23), pre-hea-ting and emptying position (illustrated at 22) and cleaning position (not shown);may take place in the best conditions possible it is advantageous for the three buckets travelling in a closed circuit on rail 30 to be rigidly interlocked so that the automa-tic positioning a-t the three working stations is very accurate (one being in position, the o-ther two being automatically so), whereas if the three buckets wexe independent it would be necessary to position each of the buckets at each of the stations.

_... _. ;. .. .~

Th-- assfn1~ly of Fig. ~, enables the o~leratiorl o-F mixing, pre-heating and pre-neated concrete castingg to be automated whilst only heating the concrete at the last moment.
The starting o-f the heating, i.e. the switching on Of~ electrodes 25a,25b and 25c, may be controlled directly from vehicle 32; when the ciriver of this latter sees that his charge of pre-heated concrete, ready to be cast, will soon be e~hausted, he controls the pre-heating oF the concrete in the bucket which is at position 22: as the time 1`or heating is o-f the order o~f` five minutes, there is no storage of hot concrete and so no loss. Moreover, the driver may control, for example also trom vehicle 7, -the raising of unit 24 and the movement of the buckets from one position to the next position, after he has emptied the contents of the bucket at position 22; he will then control the lowering of unit 24 into the bucket which has just arrived at position 22 and the emptying in-to the bucket which has just arrived at position 23 of concrete coming from mixer 28; it is also the driver who may control the actuation of the "shower" which cleans the third bucket (not shown), which is the cleaning position.
It can then be seen that the device of the invention is particularly appropriate for heating concrete, whether it is to be used on a work site, in shuttering or in a shop manufacturing concrete parts.
As is evident and as it follows moreover already from what has gone before, the invention is in no wise limited to those of its embodiments and modes of application which have been more especially considered; it embraces, on the contrary, all variations thereof.
For example it is possible to have the elec-trode arrangement of Figs 6 and 7 with three electrodes 45a, 45b, 45c,-two of which (45a, 45b) are shorter but of larger diameter than the third elec-trode (45c). These three electrodes are located around a vertical axis of trace O on Fig. 7 and they are pending from plate 16. In this embodiment of Figs 6 and 7, bucket 2a has a dissymetrical shape, the opening 12 being excen-trical.
With such an arrangement of the elec-trodes. a better distribution o-f the electric current:s and an improved heatir;g is obtained in the lower portion o-f the bucket.

Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A device for pre-heating concrete before pouring, characterised by the fact that it comprises in combination:
at least one bucket with a vertical axis which comprises, in a known way, at its upper part, a filling opening for introducing concrete to be pre-heated and, at its lower part, a closable discharge opening for pouring;
a mobile horizontal plate capable of closing off said filling opening for introducing the concrete and a set of several elongated electrodes fixed to the lower face of said plate so as to hang vertically from this plate around a central vertical axis;
means for vertically moving said plate with said electrodes between a high position, in which it disengages said filling opening for introducing concrete to be pre-heated and a low position, in which said electrodes plunge into the concrete to be pre-heated contained in the bucket and the filling opening is stopped up by said plate, said central vertical axis arriving in the position of said vertical axis of the bucket;
and means for supplying these electrodes with current and for earthing the bucket.

2. A device according to claim 1, characterised by the fact that it comprises several buckets as defined in claim 1 and a single set of electrodes, the set of electrodes or the buckets being movable so as to be able to cause the set of electrodes to cooperate with each of the buckets.

3. A device according to claim 1, for pre-heating concrete in an installation producing concrete castings, characterised by the fact that it comprises, in combination with a set of vertically mobile electrodes, of the above-mentioned type, several buckets, also of the above-mentioned type, which are horizontally mobile so as to be able to come in turn under said set of electrodes, and means for collecting the pre-heated concrete discharging from a bucket under a said set of electrodes.

4. A device according to claim 1, 2 or 3, characterised by the fact that said set comprises three electrodes in the shape of glove fingers closed at the lower end and having, in section, the shape of hollow circular sectors.

5. A device according to claim 1, 2 or 3, characterised by the fact that said set comprises three electrodes in the form of glove fingers closed at the lower part and having, in section, the shape of hollow ellipses.

6. A device according to claim 1, 2 or 3, characterised by the fact that said electrodes have different lengths and sections, the longest electrode having the smallest section.

7. A device according to claim 1 for the pre-heating of concrete before pouring into shuttering on a work site, characterised by the fact that it comprises furthermore a horizontal platform on which is permanently disposed at least one bucket according to claim 1, the platform having a discharge hole in register with the discharge opening of the bucket, a gallows which comprises a vertical upright fixed on the platform and a horizontal arm being slidably mounted on said upright, a free end of the arm carrying said set of electrodes.

8. A device according to claim 7, characterised by the fact that the platform carries two buckets and that it has two discharge holes, the hori-zontal arm of the gallows being not only slidably but also rotatably mounted on the upright, so that the set of electrodes may plunge irrespectively into one or other of the two buckets.

9. A device according to claim 3, characterised by the fact that it comprises three buckets able to travel on a rail or similar means in a closed circuit, the buckets being preferably rigidly interconnected.

10. A device according to claim 3 or 9, characterised by the fact that it comprises three operational positions for the buckets, viz. a position for filling these buckets from a mixer, a pre-heating and emptying position and a cleaning position, the set of electrodes being vertically mobile above the pre-heating position of the bucket.

11. A device according to claim 3 or 9, characterised by the fact that it cooperates with a distributing vehicle capable of receiving the concrete from a bucket in the pre-heating position and of distributing the pre-heated concrete into moulds, this vehicle comprising means for controlling the pre-heating of the bucket which is at that moment in the pre-heating position.