EP1033213A2

EP1033213A2 - Assembly and method for generating a compacting movement in a concrete product casting machine

Info

Publication number: EP1033213A2
Application number: EP00660038A
Authority: EP
Inventors: Paavo Ojanen
Original assignee: Valkeakoski X-Tec Ltd Oy
Current assignee: Valkeakoski X-Tec Ltd Oy
Priority date: 1999-03-02
Filing date: 2000-03-01
Publication date: 2000-09-06
Also published as: EP1033213A3; CN1265962A; FI990451A; FI990451A0; FI115618B

Abstract

The present invention aims to provide a method and apparatus suited for advantageously generating the reciprocating compacting movement needed in a concrete casting machine so as to offer a simple technique of adjusting or changing the amplitude of the compacting movement as required. The invention is based on generating the compacting movement with the help of two rotary shafts (14, 12) of which the primary shaft (14) has a primary eccentric member (18) adapted thereon and the secondary shaft has a secondary eccentric member (20) adapted thereon. The movement of the primary eccentric member (18) is transmitted to the secondary eccentric member (20) by means of a lever (19), whereby the eccentricity of both eccentric members determines the angle of the reciprocating rotation of the secondary shaft (12) and, thus the stroke length of one or more crank levers (11) mounted thereon. The crank levers (11) are connected to the members that are desired to perform a reciprocating movement, e.g., swinging levers (5) moving the core-forming trowel members (4).

Description

Elongated concrete products such as hollow-core slabs are conventionally made using extruder-type casting machines or slip-form casting machines. The casting machine is comprised of a conical feed hopper having one or more spiral feed augers adapted thereunder. The auger is frequently followed by a core-forming trowel member which further has an extension serving as the final trowel member that supports the core cavity formed into the product. The core-forming trowel member incorporates a vibrator or similar compacting arrangement for the compaction of the cast concrete into the shape determined by the casting mould and the core-forming trowel members. Furthermore, the casting machine has an upper trowel beam acting as the upper edge of the mould and, frequently, the sides of the mould are also designed to perform as the side trowel beams. The trowel beams compact the concrete mix during casting and give the cast product a neat surface finish. In addition to trowelling or for augmentation thereof, vibration can also be employed for compaction. Extruder-type casting machines are designed to operate as continuous-casting machines, which are transferred forward on the mould top by the reaction forces imposed by the feed augers.
The compaction of cast concrete mix is accomplished, among other methods, by means of vibrating the mould surfaces that define the product being cast or, in the case of hollow-core slab production, vibrators adapted into the core-forming trowel. Instead of vibration, compaction has also been achieved by relatively slow movements of the different parts of the casting machine that work the cast concrete mix. Such compacting movement has been implemented by means of either a sideways deflected rotational movement of the core-forming trowel member that is secured to the end of the feed auger and/or cyclic deformation of said trowel member, whereby the compaction of the concrete is attained through varying the cross section of the trowel member. For trowel members of noncircular cross section, cyclically reversible rotational movement has been used for compaction. All of these casting machines have been characterized in that the compaction of concrete has been achieved by means of mechanical movements at a low frequency, whereby the movement of aggregate particles relative to each other results from the shear stress caused by the movement of the machine components, not by the impact of the aggregate particles on each other.
In the art, the above-described compacting method is generally called working compaction or shear compaction, and one of its benefits is that the movements and displacements of aggregate particles will be large already at a low number of strokes, that is, at a low frequency of the machine component movements resulting in noiseless operation of the machine.
The principle of low-frequency compacting movements has been further developed in a casting machine in which the core-forming members are provided with conical or wedge-shaped surfaces, whereby concrete is compacted by means of slow movements of the core-forming members performed in the direction of the casting flow. In practice, compaction is carried out using reciprocating movements with an amplitude of 5 - 50 mm and a frequency of 1 - 10 Hz, which are slow in regard to the amplitudes and frequencies used in vibrating. To improve the compacting friction, the machine uses wedge-shaped or conical surfaces which provide flaring or tapering spaces in the direction of the casting flow, said spaces acting as compacting spaces.
Compaction has a great impact on the final quality of the product. In the compaction process it is essential to make the concrete mix particulates, that is, the aggregates move relative to each other so as to allow them assume mutual positions of maximum packing density, whereby the concrete becomes compacted. This goal is attained by means of pressure imposed through the mechanical machine parts and by gravitation. The amplitudes and frequencies of the compacting movements may vary widely inasmuch the target is to use the most appropriate compacting method for a particular product and concrete mix being cast. In casting machines equipped with mechanical compacting means, the compacting movement may have a frequency of 1 - 200 Hz and amplitude of 50 - 0.005 mm. Generally, the higher the frequency the lower the amplitude and vice versa.
The effect of the compacting movement on the concrete mix being cast may vary within wide limits and good results under different conditions may be obtained by using different amplitudes. In the compaction of concrete mix, it is typical that large aggregates can be compacted with large-amplitude movements performed at very low frequencies and, respectively, small aggregates require high vibrating frequencies at low amplitudes for good compaction. The composition of a normal concrete mix contains particles of a wide size distribution starting from entirely dust-like binder particles up to aggregates as large as 16 - 32 mm. By varying the size and type of particulate matter, as well as their amount in the mix, it is possible to fabricate products suitable for all kinds of applications. However, to make an end product with best possible properties from a concrete mix produced for a given application, the mix must be compacted in a manner optimized for said mix, which means that each given mix should be compacted using compacting movements having a correct amplitude and frequency. The compaction of the concrete mix has a significant impact on the strength and homogeneity of the end product.
Currently, the adjustment and change of compaction frequency is relatively easy, because electric motors used as drive sources for vibrating means may be controlled over a large rpm range using frequency converters, for instance. In practice, however, compromises must be made in concrete compaction by accepting such a compaction frequency and amplitude that give an acceptably good end result. Typically, compaction parameters are kept unchanged without paying attention to the concrete mix composition in regard to its different design proportions, that is, the relative proportions of its components and the aggregate size distribution of the concrete mix used or other mix properties or changes therein. As compaction is performed without any regard to the properties of the concrete mix being cast, the compaction outcome is either poor or a very high specific compaction energy must be consumed to attain a desired compaction effect. Use of high compaction power causes wear and stress in the machinery, thus necessitating a more frequent maintenance thereof and requiring the casting machine to be dimensioned already at its design stage for high stresses.
Conventionally, the compaction efficiency is controlled by altering the frequency of the compacting movement. As the amplitude of the compacting movement is not changed simultaneously with the frequency change, the frequency control can chiefly affect the compacting power level alone, that is, the amount of energy transferred into the concrete mix. Frequency control does not pay any attention to the properties of the concrete mix nor the aggregate sizes or size distribution thereof. Consequently, current control methods cannot provide full control of the compaction process so that the properties of different concrete mixes could be utilized in an optimum manner without the need for using an unnecessarily large amount of energy in order to achieve a good compaction result.
It is an object of the present invention to achieve a method and an apparatus capable of advantageously generating the reciprocating compacting movement needed in a concrete casting machine so as to offer a simple technique of adjusting or changing the amplitude of the compacting movement as required.
The goal of the invention is achieved by means of generating the compacting movement with the help of two rotary shafts of which the primary shaft has a primary eccentric member adapted thereon and the secondary shaft has a secondary eccentric member adapted thereon. The movement of the primary eccentric member is transmitted to the secondary eccentric member by means of a lever, whereby the eccentricity of both eccentric members determines the angle of the reciprocating rotation of the secondary shaft and, thus the stroke length of one or more crank levers mounted thereon. The crank levers are connected to the members that are desired to perform a reciprocating movement, e.g., swinging levers moving the core-forming trowel members.
More specifically, the assembly according to the invention is characterized by what is stated in the characterizing part of claim 1.
Furthermore, the method according to the invention is characterized by what is stated in the characterizing part of claim 11.
The invention provides significant benefits.
The invention makes it possible to optimize the compaction power and application technique for different concrete mixes. By complementing conventional frequency control with the stroke amplitude control according to the invention, the compaction process can be governed in different ways. Should the properties or component proportions of the concrete mix vary, the amplitude and frequency of the compacting movement can be readjusted quickly to optimal values for the new composition of the mix. If the aggregate components or other constituents of the concrete mix are changed, the compaction parameters can be readjusted so that no products need to be dumped, but instead, it is possible to make products of good quality immediately or almost directly after a change in mix design. Due to the improved compaction result, raw materials of more advantageous pricing can be used without compromising the quality of end products, because the raw material deficiencies can be compensated for by the improved outcome of compaction. Hence, the invention can provide savings in production costs. Less compaction power is needed, which means lower energy costs, as well as less stress and wear on the machine. The lower compaction power level also gives less noise. The invention is more cost-efficient to implement than constructions providing the compacting movement from, e.g., hydraulic cylinders. While hydraulics can be used for implementing a reciprocating variable-amplitude compacting movement, the arrangement would need a high-capacity pressure system and a complicated control system.
The invention is next examined with the help of the appended drawings, in which
Fig. 1 shows a side view of an embodiment of the invention;
Fig. 2 shows a sectional view of Fig. 1 taken along line S - S;
Fig. 3 shows a side view of another embodiment of the invention;
Fig. 4 shows a detail Fig. 3;
Fig. 5 shows an adjustment flange used in the embodiment illustrated in Fig. 3;
Fig. 6 shows a partially sectional top view of the apparatus illustrated in Fig. 3; and
Fig. 7 shows a table of the adjustment flange position and the corresponding stroke length of the compacting movement.
Now referring to Fig. 1, therein is shown an extruder-type casting machine in which one of the compacting movements is provided by the rockingly reciprocating movement of the core-forming trowel members 3. The compacting movement and the function of such an extruder is described in EPO Pat. Appl. No. 0,677,362, whose copy is annexed with this application. To the framework 1 of the casting machine is connected a casting mould 2 defined by mould walls 7, said mould having thereon an infeed opening 8 for introducing concrete mix into the moulding space. The infeed opening 8 is delineated by a rear wall 9 through which shafts 10 of feed augers 3 can pass. To the ends of the feed augers 3 are connected core-forming trowel members 4 having a shape capable of forming core cavities of a desired cross section to the interior of hollow-core slabs to be cast. While in this type of apparatus embodiment, the compaction is particularly implemented with the help of the compacting movement of the trowel members 4, such products as pillars or solid-core slabs must be made using some other member for imposing the compacting movement inasmuch this kind of casting does not use core-forming trowel members.
The rocking movement of the core-forming trowel members 4 is achieved with the help of a swinging member 5. The swinging member 5 is adapted to support the shaft 10 of the feed auger 3 and it is connected by two levers 6 to the framework 1 of the apparatus. The typical rocking movement of the core-forming trowel members 4 can be attained under the guidance of said levers 6 as described in cited EPO Pat. Appl. No. 0,677,362. To the swinging member 5 is connected a crank lever 11 which is mounted on a shaft 12 by means of an eccentric member 13. The shaft 12 serves as the secondary shaft of the power transmission chain and is mounted on the framework 1 on bearings adapted to rotate in bearing blocks 15. A primary shaft 14 is mounted above the secondary shaft 12 on the framework 1 in a similar manner on bearings adapted to rotate in bearing blocks 16. The primary shaft 14 includes at its other end suitable means 17 for connecting the shaft to an electric motor or the like power source. While in the illustrated embodiment said means 17 are V-belt pulleys, any conventional power transmission means can be used as well for driving the shaft.
To the opposite end of the primary shaft 14 in regard to the V-belt pulleys 17, there is adapted a primary eccentric member 18 having a crank lever 19 mounted thereon on a bearing. Also mounted on a bearing, the other end of the crank lever 19 is connected to an eccentric member 20 adapted to the end of the secondary shaft 12. The primary eccentric member 18 has an eccentricity a, and in the illustrated embodiment, the eccentricity of the eccentric member 18 is made adjustable. The eccentricity adjustment can be implemented as a screw adjustment, for instance, either so that the center of rotation of the eccentric member in regard to the center axis of the primary shaft is arranged adjustable by means of coaxial eccentric disks, whose mutual position can be changed, or using an adjustment flange to be described later in the text. Generally, it is sufficient to arrange the compacting movement amplitude to be manually adjustable when necessary. Obviously, the eccentricity control may be arranged if so required to be remote-controlled or controllable from the machine control panel during operation provided that the adjustable eccentric member is complemented with a suitable actuator device. Naturally, the machine construction cost will be elevated by such a remote control facility, but it can be implemented in a simple manner if so desired by the machine operator. The secondary eccentric member 20 has an eccentricity b and this value must be greater than the eccentricity of the primary eccentric member 18.
The function of the apparatus is as follows. The primary shaft 14 is rotated by means of an electric motor, for instance. The speed of rotation of the primary shaft 14 determines the compacting frequency, whose adjustment may be readily implemented with the help of, e.g., a frequency converter connected to supply an electric motor drive. The end (first end) of the lever 19 connected to the primary eccentric 18 rotates about the center axis of the primary shaft 14 along a trajectory determined by the eccentricity a and actuates the end of the lever 19 that is connected to the secondary eccentric member 20. The trajectory of the end of lever 19 connected to the secondary eccentric member 20 is determined by the eccentricities of both eccentric members, the lever length ratios between the eccentric members and the positions of the eccentric members. In the illustrated case, the eccentricity b of the secondary eccentric member 20 is slightly larger than the eccentricity a of the primary eccentric member 18, whereby the end (second end) of the lever 19 connected to the secondary eccentric 20 cannot traverse over the center axis of the secondary shaft 12, but instead, is forced to move in a reciprocating manner. This reciprocating movement is transmitted to levers 11, which are mounted on the secondary shaft by third eccentric members 13, whereby the levers are at their other ends connected to the swinging member 5. In this manner, the rotary movement of the primary shaft 14 is converted into a rockingly reciprocating movement of the swinging member 5 and, subsequently, of the core-forming trowel member 5 and the feed auger 3 connected thereto. The lever mechanism 6 of the swinging member 5 controls the movement of the core-forming trowel members in the fashion described in cited EPO Pat. Appl. No. 0,677,362.
The angle α of reciprocating rotation of the secondary shaft 12 is determined by the eccentricity a of the primary eccentric member if the other eccentricity b is fixed and vice versa. Further, for a given setting of these variables, the amplitude of the swinging member stroke is determined by the lever ratio between the lever 11 connected to the swinging member 5 and the eccentric member 13 mounted on the secondary shaft 12 that actuates the lever. Also the position of the swinging lever 11 in regard to the secondary shaft 12 is a variable that affects the stroke length of the swinging member 5. This possibility is utilized in an exemplifying embodiment described later in the text.
In the above-described example, rotation of the primary shaft 14 at a speed of 1500 r/min gives a compacting stroke frequency of 25 Hz. The adjustment range of the screw or slit adjuster adapted on the primary eccentric member 18 for setting the eccentricity a thereof can be, e.g., 0 - 15 mm, combined with 20 mm eccentricity of the secondary eccentric member. Then, the lever ratio between the swinging levers 11 and the eccentric members 13 mounted on the secondary shaft 12 is determined so that when the eccentricity a of the primary eccentric member is set at its maximum value, also the desired maximum amplitude of the compacting stroke is attained. Then, setting said eccentricity a of the primary eccentric member to zero causes the ends of the lever 19, which is connected to the primary and secondary eccentric members 18, 20, to remain stationary inasmuch the center points of the rotary movement of the primary eccentric member and the secondary eccentric member coincide with each other. In this fashion, a stepless control facility between zero and the maximum stroke amplitude of the compacting movement can be accomplished.
In the apparatus shown in Figs. 3 - 6, the stroke amplitude control is implemented in a slightly different manner. In this embodiment, the eccentricities a, b of the primary eccentric member 18 and the secondary eccentric member 20 are made fixed, and the amplitude control is accomplished by changing the position of the secondary shaft 12 and the swinging levers 11 mounted thereon in regard to the secondary eccentric 20. For other details, this apparatus embodiment is similar to that described above, except for an adjustment flange 21 mounted on the secondary eccentric member 20. Fig. 6 shows the connection of the swinging levers 11 via the eccentric members 13 to the secondary shaft 12. The number of the secondary levers 11 depends on the number of feed augers 3 and core-forming trowel members 4. Generally, a plurality of feed augers are used, and a greater number of feed augers is required in wider casting machines to make them suitable for producing slabs with multiple core cavities. In the exemplifying embodiment illustrated in Fig. 3, the swinging levers 11 are adapted to move in cycles of offset phases, and when required, the movements of the feed augers 3 and their core-forming trowel members 4 can be varied in regard to each other by changing their actuator connection angle on the secondary shaft 12.
In Figs. 4 and 5 is illustrated the adjustment principle of the stroke length of the core-forming trowel member by means of an adjustment flange 21. Herein, both the secondary eccentric member 20 and the adjustment flange 21 have rings of holes 22 and 23 made on their periphery. The holes are staggered by their mutual distances so as to make the holes coincide in different angular settings when the adjustment flange 21 or, respectively, the secondary eccentric member 20 is rotated. The zero angle between the adjustment flange 21 and the secondary eccentric member 20 is the angle in which the desired direction of the swinging member stroke is parallel to the line drawn via the center of rotation of the eccentric member 13 mounted on the swinging lever 11 and via the center axis of the secondary shaft 12. Then, the rotary movement of the secondary shaft causes the minimum possible movement of the swinging member 5. In practice, this means an adjustment aligned into or essentially into the horizontal plane. In the illustrated embodiment, the lever-eccentric mechanism rotates about the secondary shaft 12 always by a fixed angle α that in the illustrated construction is 49.24°.
The stroke amplitude of the swinging member 5 and the core-forming trowel member 4 actuated thereby is determined by the position of the swinging lever 11 mounted on the secondary shaft. When the center line of the eccentric member actuating the swinging lever 11 is parallel to the movement of the swinging member 5 at the center of the angle α of rotation, the rotation of the secondary shaft 12 actuates the swinging lever 11 chiefly in the lateral direction in regard to the desired longitudinal direction of compacting movement, whereby the amplitude of the compacting stroke remains small as the lever-eccentric mechanism is in its dead-center point that in the illustrated case is the top dead-center point. In turn, when the center line of the eccentric member 13 mounted on the secondary shaft 12 forms a large angle with the direction of the compacting movement, the swinging lever 11 connected to said eccentric member moves chiefly in a direction parallel to the compacting movement thus causing a large stroke amplitude. This can be utilized for stroke amplitude control so that the secondary shaft 12 with the adjustment flange 21 mounted thereon is made rotatable in regard to the secondary eccentric member 20. Then, the locking holes 22, 23 made to the secondary eccentric member 20 and the adjustment flange 21 permit the secondary shaft 12 to be locked in different positions so that a suitable position can be found in which the eccentric members mounted on said shaft convert the angle α of the reciprocating movement of the secondary shaft 12 into a desired stroke amplitude of the compacting movement. The zero angle position of stroke adjustment can be selected to be, e.g., either the top or bottom dead-center point of the mechanism formed by the eccentric member 13 of the secondary shaft with the swinging lever, whereby the adjustment angle β is defined as the angular deviation of the adjustment flange 21 from said zero angle position.
In Fig. 7 is plotted the dependence of the stroke length on the adjustment angle β for the mechanism dimensions given in Fig. 5. Obviously, these dimensions are depicted as an exemplifying case, and the adjustment ranges may vary between different machine and actuator mechanism designs.
In addition to those described above, the invention can be implemented in alternative embodiments.
The eccentric members used in the above-described embodiments can be replaced by, e.g., crank mechanisms or other types of mechanisms capable of generating an equivalent actuating movement. In this text, the term eccentric mechanism must be understood broadly to refer to any type of assembly suited for converting the rotary motion of at least one machine part into the forced movement of a point, such as the connection point of a cranking lever, along a predetermined trajectory. In the second above-described embodiment of the invention, the adjustment flange attached to the secondary eccentric member can be disposed with by mounting all the eccentric members actuating the swinging levers 11 with the help locking means onto the secondary shaft. While this arrangement makes the adjustment of the casting machine more difficult, it on the other hand offers the possibility of setting different stroke lengths for each of the core-forming trowel members. Obviously, the invention may be used for generating compacting movements for other purposes than the actuation of core-forming trowel members alone. If the compacting movement is needed only for one compacting element such as a top trowel beam, the lever or arm actuating said element can be connected directly to the secondary eccentric member that in this case serves as both the secondary eccentric member and the actuating eccentric member of the swinging lever. If a cranking lever mechanism is used to replace the eccentric member mechanism, the primary and secondary eccentric mechanisms can be located centrally between the shafts. Obviously, a plurality of eccentric mechanisms can be mounted in parallel where substantially large compacting power levels must be used. The shafts of the assembly can be substantially shorter than those shown in the diagrams when, e.g., the compacting movement needs to be transmitted to one compacting member alone.

Claims

Assembly for generating a compacting movement in a concrete casting machine, said assembly comprising

a primary shaft (14),

a primary eccentric mechanism (18) adapted on the primary shaft (14),

means (17) for rotating the primary shaft (14),

at least one member (4) adapted to perform said compacting movement, and

means (18, 19, 20, 12, 13, 11, 5, 10, 3) for transmitting the movement of the primary shaft (14) to the members (4) adapted to perform said compacting movement,

characterized by

a secondary shaft (12),

a secondary eccentric mechanism (20) adapted on the secondary shaft (12),

at least one first lever (19), which is connected to said first eccentric mechanism (18) and said second eccentric mechanism (20) for transmitting the movement of said first eccentric mechanism (18) to said second eccentric mechanism (20), and

at least one eccentric mechanism (13) adapted on the secondary shaft (12) for transmitting the movement of said secondary shaft (12) to the members (4) adapted to perform said compacting movement.
Assembly according to claim 1, characterized in that the eccentricity (b) of said secondary eccentric mechanism (20) is larger than the eccentricity (a) of said primary eccentric mechanism (18).
Assembly according to claim 1 or 2, characterized in that the eccentricity (a) of said primary eccentric mechanism (18) is made adjustable.
Assembly according to claim 1 or 2, characterized in that the eccentricity (b) of said secondary eccentric mechanism (18) is made adjustable.
Assembly according to claim 1 or 2, characterized in that both the eccentricity (a) of said primary eccentric mechanism (18) is made adjustable and the eccentricity (b) of said secondary eccentric mechanism (18) is made adjustable.
Assembly according to claim 1, characterized by at least one locking member (21) suited for adjusting the angular position relative to the secondary eccentric member (2) of at least one of the eccentric mechanisms (13) which are adapted on at least one of the secondary shafts (12) and are connected to said members (4) adapted to perform a compacting movement.
Assembly according to claim 6, characterized by an adjustment flange (21) mounted on the secondary shaft (12), said flange serving to connect said secondary eccentric mechanism (20) to said secondary shaft (12) and to permit the adjustment of the angular position of said shaft in regard to the said secondary eccentric mechanism (20).
Assembly according to claim 6, characterized by at least one locking means for mounting said eccentric mechanism (13), which is connected to said members (4) adapted to perform said compacting movement, on said secondary shaft (12) so as to permit the adjustment of the angular position of said mechanism on said shaft (12).
Assembly according to claim 6, characterized in that the eccentricity (a, b) of said primary eccentric mechanism (18) or of said secondary eccentric mechanism (20) or of both is made adjustable.
Assembly according to claim 9, characterized by a remote-control device for adjusting the eccentricity of at least one of said eccentric mechanisms.
Method for generating a compacting movement in a concrete casting machine, the method comprising the steps of

rotating a primary shaft (14),

converting the rotary movement of the primary shaft (14) into a first eccentric movement, and

transmitting the movement of the primary shaft (14) to members (4) performing a compacting movement,

characterized in that

the first eccentric movement is converted by means of an eccentric mechanism into a rotary movement,
and

said rotary movement is converted by means of an eccentric mechanism into a reciprocating movement that is transmitted to actuate said members performing said compacting movement.
Assembly according to claim 11, characterized in that the eccentricity of at least one eccentric movement is varied for adjusting the stroke amplitude of said compacting movement.