EP1961517A1

EP1961517A1 - Polishing apparatus for concrete specimens

Info

Publication number: EP1961517A1
Application number: EP07380051A
Authority: EP
Inventors: Rafael Pedrajas Cid
Original assignee: Atme Menendez Sl
Current assignee: Atme Menendez Sl
Priority date: 2007-02-23
Filing date: 2007-02-23
Publication date: 2008-08-27

Abstract

The concrete specimen (9), which compression strength tests have to later be performed on, and which, for reasons of manufacturing, has on one of its bases (10) an irregular surface, is arranged on a support plate (8) rotatory via a motor (6), and receives through said surface (10) the action of an abrasive disk mounted on a second support plate (14), actuated simultaneously in rotatory direction by the corresponding motor (12), so that said abrasive disk acts on the surface (10) of the specimen causing the wear thereof until achieving a perfect polish. The system comes to replace the classic capping system using the sulphur mortar method, recommended by standard UNE-EN 12390-3, consequently eliminating the contaminating effects of this capping method and permitting a surface finish to be achieved for the specimen with greater safety, greater quality and less costs.

Description

OBJECT OF THE INVENTION

The present invention relates to a polishing system, especially devised for a perfect surface finish of the concrete specimens used in compression strength tests, in order to avoid that the surface irregularities could falsify the results of the test by causing fractures of the specimen with substantially lower pressures than the concrete can actually withstand.
Nevertheless, the system is equally valid for the treatment, prior to the relevant tests, of other materials such as brick, plaster, etc.
The invention is fundamentally situated within the field of construction, and more particularly within the field of methods and instruments for measuring the quality of the materials used in the works.

BACKGROUND OF THE INVENTION

In the field of practical application of the invention, basically two types of specimens are used for compression strength tests, cubic specimens and cylindrical specimens, which are produced from concrete in fluid phase and with the collaboration of moulds formally and dimensionally adapted to the specimens to be produced.
The quality of the moulds and a correct vibration of the concrete, enable producing in the specimen, in addition to a homogenous mass, a lower base and side walls which are perfectly finished, but the same does not occur with the area corresponding to the open surface of the mould, where irregularities are frequently produced of magnitude more than sufficient so that when the specimen is introduced in the test press, said press rests on restricted or specific areas of the upper base of the specimen, i.e. the compression strength is not uniformly distributed throughout the support surface of the specimen, but concentrated in certain points or areas thereof, which generates fractures which do not at all correspond to the fracture limit points due to the compression resistance of the specimen being analysed.
To avoid this problem, a capping system of the specimens is used, recommended by standard UNE-EN 12390-3, according to which the surface of the specimen should be dry, clean and all types of loose particles should be removed therefrom, performing the capping by commercial mixtures of sulphur and fine silica sand, in equal parts, a mixture which is heated until achieving a temperature which gives it the required consistency.
This capping system, despite its mass use, has extensive and varied problems, which are basically focussed on the following aspects:

Sulphur is highly contaminating, with the consequent and negative effects for the environment and the personnel that should participate in these capping manoeuvres.
The capping thickness, which according to said standard should be less than 5 millimetres, is difficult to attain.
Cavities frequently remain on the specimen surface, which ultimately negatively affect the fracturing thereof, a fracture which is deficient on many occasions, with the consequent falsifying of the results.

Capping systems are also known using sand box, which require very fine silica sand with complex apparatus and minimum tolerance, which are expensive and cause functional problems, especially as they need the aid of a vibrator mounted below the horizontal plane of a layout frame, a vibrator which is essential for the homogenous distribution and the compacting of the sand in the boxes, but whose vibration tends to negatively affect in the relative positioning between the specimen and said boxes. It also requires a compressed air system to loosen the boxes, and a container holding paraffin wax, a hot plate and thermostatically controlled for said wax, a receptacle calibrated to measure a predetermined volume of sand, and said paraffin wax with a melting temperature around 60°C.
It is due to the complexity of this system that the sulphur mortar system is mainly used, despite its contaminating effects.

DESCRIPTION OF THE INVENTION

The polishing system for concrete specimens that the invention proposes resolves in a fully satisfactory manner the aforementioned problem, since with an extremely simple structuring, with automatic functioning and in optimum productivity conditions, it enables an optimum polishing of the surface of the specimen that requires it, in the absence of contaminating products or residues, since it is exclusively based on the surface polishing system of the specimen with a suitable abrasive element.
More particularly, the system is based on supplying the specimen with a rotatory movement, resting on a support plate by its side opposite that which one wants to polish, said support plate of the specimen being parallel to a second upper support plate, it holding a conventional abrasive disk which is in charge of acting, also with circular and planetary movement, on the corresponding base of the specimen to polish, and around the axis of the latter.
In accordance with another of the characteristics of the invention, the spin axes of both plates are out of phase in a magnitude so that the periphery of the abrasive disk passes permanently through the axis or centre of the specimen, so that said abrasive disk instantaneously affects at least half of said base, but in time fully affects it due to the rotatory movement of the specimen around its own axis.
It has also been provided that the abrasive disk preferably has an abrasive surface in the form of a circular crown whose band width should not exceed half of the radius of the abrasive disk to achieve the best working conditions, reduction in production costs, and improving the efficacy of abrasion.
Finally, and in accordance with another of the characteristics of the invention, the support plate of the specimen is not only mechanized in the rotation direction but also in the direction of vertical displacement, in order to progressively move closer to the abrasive disk, as the specimen is polished.

DESCRIPTION OF THE DRAWINGS

To complement the description being made, and in order to aid towards a better understanding of the characteristics of the invention, in accordance with an example of preferred example of practical embodiment thereof, a set of drawings is attached as an integral part of said description wherein, with illustrative and non-limitative character, the following has been represented:

Figure 1.-: Shows, according to a schematic representation in side elevation, a machine resulting from the implementation of the polishing system for concrete specimens which constitutes the object of the present invention.
Figure 2.-: Shows a plan detail, also in schematic representation, of the two support plates, that of the specimen and that of the abrasive disk.

PREFERRED EMBODIMENT OF THE INVENTION

In light of said figures and particularly figure 1, it can be observed how the machine recommended incorporates a frame (1), enclosed within a casing, not represented in the figures and which will be commented below, establishing in said frame (1) a lower platform (2) whereon a motor (3) is positioned which, by a rack system (4) or any other conventional element of motor transmission, supplies a raising/lowering movement to a support (5), as shown in the arrows of figure 1, a support (5) which holds a second motor (6), with a vertical output shaft (7) whereto a support plate (8) of the specimen (9) is solidly joined, whose irregular surface (10) is intended to be polished.
At the upper end (11) of the frame (1) a third motor (12) is established, with vertical and descending output shaft (13), topped in a second support plate (14), in this case designed to admit the securing of an abrasive disk which acts on the surface (10) of the specimen (9), when it moves closer to said abrasive disk by the effect of the motor (3).
As is observed in any of the figures, and especially in figure 2, the axis of the support plate (8) of the specimen (9), and consequently the actual specimen (9), is out of phase with respect to the axis (13) of the support plate (14) of the abrasive disk, a disk whose abrasive area (15) is positioned on a wide perimeter band, in the form of a circular crown, whose width can be variable but never exceed half of the radius of the abrasive disk to achieve the best working conditions and efficacy in the smoothing and polishing of the specimen (9).
The rotatory and simultaneous movement of the abrasive disk mounted on the support (14) and of the specimen (9) mounted on the plate (8), via the respective motors (12) and (6), with independence of the rotation of said plates (8) and (14) whether in the same direction or opposite direction, generates a polishing effect on the upper base (10) of the specimen (9), that at each instant partially affects said specimen, but in time totally covers said surface (10), permitting a perfect finish and calibration of the smoothed area by the control which is exercised automatically at all times on the lifting movement of the support plate (5), i.e. in conditions of optimum quality, with a maximum absence of contaminating products and with low cost level.
The frame (1-2-11) is fully enclosed in a casing, not represented in the figures, provided with doors and airtight seal, in order to avoid the exit of the dust generated by the abrasive disk to the outside, dust which is suctioned by an extractor, connected to an outlet (16) of said casing, the machine not having externally more than one set of buttons (17) for the functional activation of all its elements, the polishing process being totally automatic.

Claims

Polishing system for concrete specimens, particularly for cylindrical specimens which are going to be subjected to compression resistance tests, and which require a perfect finish on their two bases, characterized in that it consists of providing said specimen with a rotatory movement around its own axis, accompanied by an axial and controlled travelling movement towards a conventional abrasive disk, whose spin axis is parallel to that of the specimen and is markedly out of phase with respect to the latter, specifically with a magnitude so that the perimeter edge of the abrasive disk is always positioned at the level of the specimen axis, the disk describing a planetary movement on the corresponding base of the specimen and around the axis thereof.
Polishing system for concrete specimens, according to claim 1, characterized in that the axial displacement of the specimen, automated as is its rotatory movement and that of the abrasive disk, is determined by the level of polishing or wear occurring in the specimen over time and due to the effect of the abrasive disk.
Machine for the implementation of the polishing system of claims 1 and 2, characterized in that therein there participates a bedplate (1), with a lower platform (2) whereon is positioned a motor (3) which, via a rack (4) or similar element, supplies vertical displacement to a support (5) for a second motor (6), with vertical axis (7) and solidly joined to a support plate (8) for the specimen (9), so that the first motor (3) raises the specimen (9) whilst the motor (6) supplies a rotatory movement thereto, the frame having, in its upper area, another platform (11) whereon a third motor (12) is positioned, with the vertical and descending output shaft (13) topped in a support (14) for the abrasive disk, which is superimposed on the specimen (9).
Machine, according to claim 3, characterized in that the axis (7) of the support plate (8) for the specimen (9) is out of phase laterally with respect to the axis (13) of the support plate (14) of the abrasive disk, so that the periphery of said abrasive disk is positioned markedly in correspondence with the imaginary axis of the specimen (9), i.e. with the centre of the upper base (10) to polish in said specimen.
Machine, according to claims 3 and 4, characterized in that the abrasive disk mounted on the support (14) has an abrasive surface (15) in the form of a circular crown, perimetral, whose width can be variable from the free edge of the disk without exceeding half of its radius.