EP0514352A1

EP0514352A1 - A machine for conditioning and distributing cement mixes, in particular for plaster spraying

Info

Publication number: EP0514352A1
Application number: EP92830211A
Authority: EP
Inventors: Giuseppe Pattarini; Enrico Gadioli
Original assignee: AZ SERVICE Srl
Current assignee: AZ SERVICE Srl
Priority date: 1991-05-08
Filing date: 1992-05-07
Publication date: 1992-11-19
Also published as: ITMI911253A1; ITMI911253A0; IT1248303B

Abstract

In a plaster spraying machine (1), the particles of a cement mix are screened and sized by means (2) comprising a supporting frame (11) secured to the pan (3) that contains the mix during operation, and affording an internal conditioning chamber (15a) of which the top part connects with an inlet (16) in receipt of the mix and the bottom part discharges into the pan (3); the sizing action is produced by a pair of mutually tangential profiled rollers (19) positioned internally of the chamber (15a), which are supported rotatably by the frame (11) in such a way as to turn on parallel axes spaced apart at a selected distance one from the other. One of the two sizing rollers (19) is coupled to a motor (29), and the two rollers themselves are also permanently interconnected by a transmission link (22) in such a way as to rotate in mutually opposed directions when the motor is activated.

Description

The present invention relates to a machine by means of which to condition and distribute cement mixes, in particular for plaster spraying.
Conventionally, a plastered surface consists in one or more coats of a cement mortar applied to a wall or a ceiling to the end of affording protection and providing a smooth finish. Cement mortars used for plastering are the same as for general brickwork, but with a greater proportion of binder in the mix.
Once applied and dried, the traditional type of plastered surface obtained with such compositions will tend to exhibit hairline cracks, produced as the cement contracts and cures, with the result that the plaster presents a poor appearance and is structurally unsound.
Such a plaster offers insufficient guarantees of strength and stability, especially when the mix is applied to an appreciable thickness.
In an attempt to avoid such problems and provide greater strength and stability, recourse has been made to the use of reinforced plasters, that is, plasters incorporating an embedded metal or plastic mesh, or impregnated with synthetic microfibres of specially treated polypropylene.
Currently, fibres are preferred to mesh since the difficulty of positioning the mesh on the surface is eliminated, as also are the high costs of the mesh material itself; moreover, the reinforcement provided by the fibres is three-dimensional whereas that of the mesh is two-dimensional.
The plaster can be applied to the surface manually, or sprayed mechanically with a machine by which the cement mortar is projected in a pressurized jet.
Plaster spraying machines currently in general use essentially comprise a pan in which to collect and hold mortar, prepared previously by a cement mixer, and a motor-driven feed screw at the bottom of the pan by which the mortar is directed into an outlet duct terminating with a nozzle. Once in the outlet duct, the mortar is invested with a stream of air supplied from a compressor driven by the same motor as that which operates the screw, and thus forcibly ejected.
Projecting the mix at high velocity onto a surface in this manner, the plaster acquires properties of adherence, imperviousness to water and mechanical strength superior to those obtainable when applying the mix by hand.
In addition, plaster sprayers allow a considerable reduction in job times, thereby saving on labour and limiting costs.
Plaster spraying machines currently in use betray certain drawbacks, however, one of which being the frequency with which the spraying operation needs to be interrupted; in effect, notwithstanding the materials utilized in the mix are granulometrically selected, it happens often that the nozzle becomes blocked as the result of foreign matter finding its way into the ingredients accidentally. To contain this problem as far as possible, most conventional machines are equipped with a screen fitted over the pan.
The purpose of the screen, consisting generally in a mesh of square holes 1 cm across, is to prevent larger foreign bodies from entering the pan. Nonetheless, it is still possible for bodies of dimensions smaller than the mesh size, and capable of blocking the nozzle, to pass through the screen and occasion a stoppage in the operation of the machine.
The operation of the machine must also be suspended periodically to clean off the material retained by the screen.
The presence of the screen brings further problems when handling microfibre-impregnated mixes as used for the fibre-reinforced type of plaster mentioned above.
More exactly, these fibres are between 19 and 64 mm or thereabouts in length, according to different building requirements and uses, and must be added to the mix in precise proportions if the desired level of reinforcement is to be achieved.
By reason of their structure, the microfibres tend to accumulate and cling to the mesh over the pan.
Consequently, the surface to be plastered does not receive a mix containing the fibres in a percentage proportion considered optimum for the purpose of reinforcement. Neither is it advantageous, however, simply to add greater quantities of the microfibre to the mix in an attempt to obtain a given minimum percentage in the plaster.
The object of the present invention is to overcome the drawbacks typical of the prior art as outlined above, by providing a machine for conditioning and distributing cement mixes such as will be capable of sizing ingredients uniformly and investing them with suitable properties in terms of granulometry and of the percentage content of microfibres, if added, and which can eliminate the risk of blockage affecting the spray outlet nozzle and/or the screen associated with the collection pan.
Another object of the invention is to enable the embodiment of such a machine by the simple addition of determined components to a conventional plaster spraying machine, though without substantially modifying the existing machine.
The stated objects are realized according to the present invention in a machine for conditioning and distributing cement mixes in particular as used for plastering, of the type comprising a collection pan in which to deposit a previously blended mixture of aggregates and binders destined to be applied to a wall as a coat of plaster, a feed screw positioned at the bottom of the pan and driven by a motor, an outlet duct into which the mix is directed from the pan by the feed screw, a compressor by which air is directed forcibly into the outlet duct, a nozzle associated with the end of the outlet duct from which the mix is expelled in a jet of compressed air produced by the compressor, and screening means positioned over the collection pan and serving to ensure a uniform particle size of the ingredients utilized in the mix, which is characterized in that the screening means comprise:

a supporting frame secured to the collection pan and affording an internal conditioning chamber of which the top part connects with an inlet admitting the mix and the bottom part connects with the pan;
a pair of mutually tangential sizing rollers, positioned internally of the conditioning chamber and anchored to the supporting frame in such a way as to rotate about parallel axes spaced apart one from the other by a predetermined distance;
means of interconnection, with which the sizing rollers are associated and constrained to rotate in respectively opposed directions;
at least one motor, to which one of the sizing rollers is coupled and by which both rollers are caused to rotate in such a way that mix introduced by way of the inlet is directed into the collection pan by way of the passage between the rollers.

A preferred embodiment of the present invention will now be described in detail by way of example and with the aid of the accompanying drawings, in which:

fig 1 is the perspective of a machine according to the invention for conditioning and distributing cement mixes;
fig 2 is a perspective view of the screening means in the machine disclosed;
fig 3 illustrates the screening means in a section through III-III, fig 2;
fig 4 is an enlarged sectional detail illustrating the profile of the peripheral surface of one of the rollers of the screening means.

With reference to the accompanying drawings, and in particular to fig 1, the present invention relates to a machine, denoted 1 in its entirety, by means of which to condition and distribute cement mortar mixes typically as used in plastering.
The machine 1 consists essentially in a collection pan 3 and, fitted to the bottom of the pan, a feed screw not illustrated in any of the drawings, being conventional in embodiment and incidental to the invention. The pan 3 is filled with a mixture of fine aggregates and binders blended previously by a cement mixer, likewise not illustrated other than by the presence of a chute denoted 4, and destined ultimately to be applied to a wall as plaster. From the pan 3, the mix is directed by the rotation of the screw into an outlet hose 6 terminating in a nozzle 7; the screw is driven by a motor denoted 5.
The same motor 5 also drives a compressor 8, also of conventional embodiment, by which air is forced into the hose 6 in such a way that the mix can be expelled under pressure from the nozzle 7.
In the machine disclosed, the collection pan 3 is surmounted by screening means, denoted 2 in their entirety, of which the purpose is to ensure that the ingredients of the mix are reduced to a uniform maximum particle size before entering the pan 3.
As discernible from figs 2, 3 and 4, such screening means 2 comprise a supporting frame 11 secured to the pan 3 by fastening means such as bolts 12, and thus removable from the machine.
The supporting frame 11 in turn comprises a base 13 embodied as a substantially rectangular plate-like element 13a affording a central void 13a through which the mix is allowed to pass into the pan 3; this same plate-like element 13a also incorporates two end flanges 14 positively engaging the rim of the pan 3.
Also forming a part of the frame 11 is a hollow structure or casing 15 rigidly associated with the base 13 and encompassing a conditioning chamber 15a of which the top part communicates with an inlet 16 admitting the mix, and the bottom part communicates with the pan 3 by way of the void 13b.
The inlet 16 is framed and surmounted by an infeed hopper 17 fitted with an internal grille 18 for the safety of the user.
Advantageously, the casing 15 affords handles 15b, one on either side, allowing the screening means 2 to be lifted clear and distanced from the machine 1 whenever their removal becomes necessary.
The screening means 2 further comprise a pair of sizing rollers 19 associated with the casing 15, and more exactly a first roller 19a and a second roller 19b positioned face to face internally of the conditioning chamber 15a. The sizing rollers 19 are anchored rotatably to the casing 15 in such a way as to turn on respective parallel axes spaced mutually apart by a predetermined distance.
The peripheral surfaces of the first roller 19a and the second roller 19b each exhibit a plurality of first corrugations 20, consisting in a succession of circumferential grooves 20a alternated with corresponding circumferential projections 20b.
These first corrugations 20, for example produced by machining, serve to invest the surfaces of the rollers 19 with a substantially wedge-like profile.
In addition, the rollers 19 exhibit substantially hemispherical second corrugations 21 distributed randomly over the first corrugations 20, as shown in fig 4. To advantage, such second corrugations might be produced by the simple application of welding spots.
In the embodiment illustrated by way of example, the two sizing rollers 19 are associated with means of interconnection denoted 22, and constrained by them to rotate in mutually opposite directions.
Such means of interconnection 22 comprise at least one pair of gears 23 and 24 engaged in constant mesh, positioned externally of the casing 15 and keyed to respective first ends 25a and 26a of two corresponding shafts denoted 25 and 26 which span the casing and are rotatable about their respective axes. Each shaft 25 and 26 carries one of the two sizing rollers 19a and 19b, and the gears 23 and 24 serve thus to transmit rotation from one roller to the other.
The sizing rollers 19 are driven by a motor 29 mounted to the supporting frame 11 externally of the casing 15, to which the first sizing roller 19a is coupled mechanically by means of at least one drive belt 30. Three belts 30 are shown in the example of the drawings, looped around a driving pulley 31 associated with the motor 29 and a driven pulley 32 keyed externally of the casing 15 to a second end 25b of the shaft 25 carrying the first roller 19a, in such a way that the rotation of the motor 29 is transmitted to the first roller 19a.
The motor 29 is connected to a power source, in this instance the electrical power supply, by way of a control switch 33.
Embodied in the manner thus described, a machine according to the present invention for conditioning and distributing cement mixes, and in particular the screening means of such a machine, will operate in the following manner.
The screening means 2 are activated by supplying power to the motor 29, in such a way that rotation is transmitted by way of the driving pulley 31, the belts 30 and the driven pulley 32 to the shaft 25 of the first roller 19a. The shaft 25 in its turn causes rotation to be transmitted from the relative gear 23 to the gear 24 associated with the shaft 26 of the second roller 19b; the two rollers 19a and 19b are thus set in rotation, the one clockwise and the other anticlockwise.
Mortar obtained from the materials introduced into the cement mixer will contain fine aggregates of varying granulometry, not always appropriate for the requirement in hand. Accordingly, having been poured into the hopper 17 and through the inlet 16, the mix passes between the two rollers 19a and 19b, whereupon any particles exceeding the prescribed granulometry are crushed and reduced to the correct dimensions. Thus it becomes possible to ensure that regular particle sizes are maintained in the mix.
Having passed through the rollers, the mix drops into the collection pan 3 of the machine 1 and is directed by the screw into the hose 6; air is then directed forcibly into the hose by the compressor 8 and the resulting stream of fluid is projected from the nozzle 7 onto the surface being plastered.
It will be noted that, when the machine is used in the application of a fibre-reinforced rendering, microfibres added to the mix encounter no obstacle whatever in their passage to the collection pan 3 and can therefore be incorporated into the plaster in the percentage proportion required to produce the desired results.
The objects stated at the outset are thus fully realized according to the present invention.
Directing the mix between the rollers, in effect, it becomes possible to prevent the passage of any material consisting in particles exceeding the granulometry prescribed for the plaster, and likely as a result to block the nozzle attached to the end of the outlet hose.
Advantageously, according to the present invention, blockage of the nozzle is avoided without utilizing screens as fitted to machines of the conventional, prior art type; accordingly, it becomes possible to achieve a considerable reduction in the time taken to complete plastering jobs by virtue of the fact that pauses for cleaning of the nozzle and screen are eliminated, and work can proceed uninterrupted. The result is an appreciable reduction in operating costs.
Since there is no obstacle to the passage of the microfibres, moreover, their incorporation into the mix will be absolute, with no loss or damage, and the required percentage of fibres in a reinforced plaster can therefore be maintained uniform.
Advantageously, the invention can be carried into effect simply by addition of the screening means described above to a conventional plaster spraying machine, replacing the usual mesh screen; neither does such a step require significant modification of the existing machine.
With this end in view, the fact that the screening means are removable from the collection pan will be seen to be especially advantageous.
The screening means disclosed can also be utilized independently of the plaster spraying machine in sizing fine aggregates destined for a variety of uses.

Claims

1) A machine for conditioning and distributing cement mixes, in particular as used for plaster spraying, of the type comprising: a collection pan (3) in which to deposit a previously blended mixture of aggregates and binders destined to be applied to a wall as a coat of plaster; a feed screw positioned at the bottom of the pan and driven by a motor (5); an outlet duct (6) into which the mix is directed from the pan by the feed screw; a compressor (8) by which air is directed forcibly into the outlet duct (6); a nozzle (7) associated with the end of the outlet duct (6), from which the mix is expelled in a jet of compressed air produced by the compressor, and screening means (2) positioned over the pan (3) and serving to ensure uniform particle size in the ingredients of the mix,
characterized
in that the screening means (2) comprise:

- a supporting frame (11) secured to the collection pan (3) and affording an internal conditioning chamber (15a) of which the top part connects with an inlet (16) admitting the mix and the bottom part connects with the pan (3);

- a pair of mutually tangential sizing rollers (19), positioned internally of the conditioning chamber (15a) and anchored to the supporting frame (11) in such a manner as to rotate about parallel axes spaced apart one from the other by a predetermined distance;

- means of interconnection (22), with which the sizing rollers (19) are associated and constrained to rotate in respectively opposed directions;

- at least one motor (29) to which one of the sizing rollers (19) is coupled and by which both rollers are caused to rotate in such a way that cement mix introduced by way of the inlet (16) is directed into the collection pan (3) by way of the passage between the rollers.

2) A machine as in claim 1, wherein the peripheral surface of each of the sizing rollers (19) affords a plurality of first corrugations (20) consisting in a succession of circumferential grooves (20a) alternated with corresponding circumferental projections (20b).

3) A machine as in claim 2, wherein the transverse profile exhibited by the first corrugation (20) is essentially wedge-like.

4) A machine as in claim 1, wherein the peripheral surface of each of the sizing rollers (19) affords a plurality of first corrugations (20) consisting in a succession of circumferential grooves (20a) alternated with corresponding circumferental projections (20b), and a plurality of essentially hemispherical second corrugations (21) distributed randomly over the first corrugations (20).

5) A machine as in claim 4, wherein the second corrugations (21) are fashioned by the deposition of welding spots.

6) A machine as in claim 1, wherein the supporting frame (11) comprises a base (13) consisting in a substantially rectangular plate-like element (13a) affording a central void and two end flanges (14) positively engaging the rim of the pan (3), and a hollow structure or casing (15), secured to the base (13) and encompassing the conditioning chamber (15a) with the pair of sizing rollers (19).

7) A machine as in claim 1, further comprising an infeed hopper (17) associated with the inlet (16) by which the cement mix is admitted.

8) A machine as in claim 7, further comprising a protective grille (18) positioned internally of the infeed hopper (17).

9) A machine as in claim 1, wherein the motor (29) is secured to the supporting frame (11), externally of the conditioning chamber, and coupled mechanically to one of the sizing rollers (19).

10) A machine as in claim 1, wherein the means of interconnection (22) comprise at least one pair of meshing gears (23, 24) positioned externally of the conditioning chamber (15a) of the screening means, each keyed to a respective first end (25a, 26a) of a corresponding rotatable shaft (25, 26) spanning the chamber and carrying one of the two sizing rollers (19a, 19b), in such a way that rotation is transmitted from one roller to the other by way of the two gears (23, 24).

11) A machine as in claim 1, wherein the motor (29) is coupled mechanically to the sizing rollers (19) by way of at least one drive belt (30) looped around a driving pulley (31) associated with the motor (29) and a driven pulley (32) keyed externally of the conditioning chamber (15a) to the second end (25b) of a rotatable shaft (25) spanning the chamber and carrying one of the two sizing rollers (19a, 19b).

12) A machine as in claim 6, wherein the hollow structure or casing (15) of the supporting frame affords a pair of handles (15b) for the purposes of lifting and transporting the screening means (2).