EP0172052A1 - Process for metallising relatively flat work pieces, electrode obtained by this process and X-ray multiple detector comprising such an electrode - Google Patents

Abstract

Process for covering a steel electrode with a uniform deposit of lead. A steel metal plate (11) of an area which is larger than the piece (12) to be covered is used and this piece is precut in the metal plate without separating it completely from the latter so that an electrical contact remains between the plate and the piece; the lead is then deposited by electroplating. Application to the manufacture of the electrodes of an X-ray multidetector for a tomodensitometer. <IMAGE>

Description

The invention relates to a method of metallizing a relatively flat part, in particular a method for obtaining a uniform deposit of lead on such a part forming the electrode of an X-ray multidetector with ionization chambers, usable in a tomodensitometer. The invention also relates to any electrode obtained by this method and any multidetector incorporating such electrodes.

There is known an X-ray multidetector specially designed for absorption measurements in a CT scanner and comprising a plurality of essentially flat metal electrodes, placed side by side along an arc of a circle so that their front fields are parallel converge on a common axis on which is placed the focus of a source of X-rays emitting a fan-shaped beam.

Such an arrangement is for example described in French patent n ° 2.114.699.

The electrodes are electrically connected to supply means so as to define a succession of anodes and cathodes delimiting between them ionization chambers. These electrodes must preferably be of a sufficiently dense material to limit the crosstalk between the ionization chambers which they delimit. This is how many such multidetectors are fitted with tungsten electrodes. This material is very expensive and difficult to machine. The invention aims to solve these drawbacks.

The invention firstly proposes a new type of electrode for an X-ray multidetector, said electrode being characterized in that it comprises a steel core covered on each of its faces by a layer of lead.

It is possible, for example, to apply this lead layer by electrodeposition using the future electrodes as cathodes immersed in an appropriate electrolytic bath and placed opposite one or more soluble lead anodes. We can nevertheless observe side effects resulting in an excess thickness of lead around the cathode plates.

• - à prédécouper au moins une telle pièce dans une plaque métallique de surface plus importante sans la dissocier de ladite plaque pour qu'un contact électrique subsiste entre ladite plaque et ladite pièce,
• - à effectuer la phase d'électrodéposition proprement dite sur l'ensemble de ladite plaque portant ladite pièce prédécoupée, puis
• - à achever la séparation entre ladite pièce et ladite plaque métallique.

This is why the invention also relates to a method of metallizing a relatively flat part, by electrodeposition, characterized in that it consists

• - pre-cutting at least one such part in a metal plate with a larger surface area without dissociating it from said plate so that an electrical contact remains between said plate and said part,
• - to carry out the actual electrodeposition phase on the whole of said plate carrying said precut part, then
• - to complete the separation between said part and said metal plate.

Thus, by leaving a "frame" around the part defining the future electrode of the multidetector, the extra thickness occurs on the edge of this frame and not on the edge of the part itself.

The invention finally relates to any X-ray multidetector characterized in that it comprises a plurality of ionization chambers delimited by adjacent partitions forming electrodes and in that these electrodes have been metallized by an implementation of the process defined above. above.

• - la figure 1 représente une plaque métallique dont la partie centrale a subi un prédécoupage conforme à l'invention, pour matérialiser une électrode d'un multidétecteur ;
• - la figure 2 représente schématiquement l'étape d'électrodéposition proprement dite au cours de laquelle la plaque métallique de la figure 1 est recouverte de plomb.

The invention will be better understood and other advantages of it will appear better in the light of the following description of a metallization process in accordance with its principle, given only by way of example and made with reference to the drawing annexed in which:

• - Figure 1 shows a metal plate whose central part has undergone a precut according to the invention, to materialize an electrode of a multidetector;
• - Figure 2 schematically shows the actual electrodeposition step during which the metal plate of Figure 1 is covered with lead.

Referring to the drawings, there is shown a metal plate 11 in the center of which appears an electrode 12 of an X-ray multidetector. This electrode has been precut without being dissociated from the plate so that an electrical contact remains between the electrode and the rest of the plate 11. In the example shown, the separation between the edge 13 of the electrode and the plate 11 is effective over almost the entire periphery of said electrode in the sense that a strip of metal has been removed. , the internal contour of which delimits the perimeter of the electrode, leaving a limited number of small connecting bridges 14 between the electrode and the rest of the plate.

This precut configuration can be obtained by various conventional methods such as par. example electrochemical cutting, laser cutting or even punching using a tool of suitable shape. In the latter case, the punch having the shape of the contour of the electrode comprises notches allowing the formation of the bridges 14. It is also possible to envisage materializing the contour of the future electrode by incomplete punching without elimination of material (therefore retaining the electrical contact) but of sufficient depth to allow subsequent separation by simple pressure, of the electrode and the frame. In the example, the metal plate is of steel of type XC 75.

When the precut is completed, the actual electrodeposition phase is carried out, in accordance with FIG. 2. The plate 11 is immersed in an electrolytic bath 15, for example lead fluoborate and plays the role of cathode with respect to a or several soluble anodes 16, of lead. The intensity delivered by the current source 17 connected between anode and cathode and the immersion time of the plate 11 determine the thickness of the lead deposit. By doing so, the extra thicknesses due to the effects of edge are located in the vicinity of the outer edge 18 of the plate 11, and the deposit of lead on the future electrode 12 is substantially uniform. The electrode 12 is then separated from the metal plate 11 by any suitable mechanical operation (not shown), for example punching eliminating the connecting bridges 14.

Of course, the invention is not limited to the above description. In particular for industrial exploitation of the process, it will be possible to use metal plates 11 with a larger surface area on which several electrodes 12 will be precut. This means that the invention covers the technical equivalents of the means involved if these are within the scope of the claims which follow.

Claims (8)

1. A method of metallizing a relatively flat part, by electrodeposition, characterized in that it consists: - pre-cutting at least one such part (12) in a metal plate (11) with a larger surface area without dissociating it from said plate so that an electrical contact remains between said plate and said part, to carry out the actual electrodeposition phase on the whole of said plate carrying said precut part, then, - to complete the separation between said part and said metal plate. 2. Metallization process according to claim 1, characterized in that lead is deposited on said metal plate (11) carrying said part (12) precut. 3. Metallization process according to claim 1 or 2, characterized in that the aforementioned metal plate (11) is made of steel. 4. metallization process according to one of the preceding claims, characterized in that the aforementioned precut consists of removing a metal strip whose internal contour substantially delimits the perimeter of said piece (12) leaving a limited number of bridges of connection (14) between said part and the rest of said plate, the aforementioned separation consisting in subsequently removing said connecting bridges. 5. Metallization method according to one of the preceding claims, characterized in that the aforementioned precut materializes an electrode of a multidimensional X-ray detector with partitions usable in particular in a CT scanner. 6. Multidetector X-ray electrode, in particular for a CT scanner, characterized in that it comprises a steel core covered on each of its faces with a layer of lead. 7. X-ray multidetector electrode according to claim 6, characterized in that it is obtained by implementing the method according to claim 5. 8. X-ray multi-detectors for CT scanners, characterized in that it comprises a plurality of ionization chambers delimited by adjacent partitions (12) forming anodes and cathodes and in that these electrodes have been metallized by implementing the method according to claim 5.

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