EP0762952B1 - Method of separation of a piece from a volume of material by propagation of a single crack - Google Patents

Description

The present invention relates to a process for removing a piece from a block of material, by propagation of a single crack, following a predetermined area according to the first part of claim 1.

Such a process is disclosed in EP-A-0 294 267.

The problem of guiding cracks on large areas seems to have been very rarely addressed and it seems necessary to define a certain number of terms that we will use in this text.

By "crack" is meant a phenomenon of decohesion of the molecules constituting a material, to inside a block of this material. The propagation of a crack can lead to separation between a piece and the rest of said block of matter without removal of material.

By "material" is meant here a substance solid, coherent, rigid such as natural rocks, concrete, bricks and terracotta, glass, plastic rigid and even wood, cast iron and steel.

By "fissile material" is meant a material which has a cleavage plane direction, that is to say a plane direction having resistance to significantly lower traction, the tenth or even the hundredth, in this direction of plane than in any another neighboring direction.

By "material with natural cleavages" is meant a material which has cleavage planes at variable spacings.

By "homogeneous matter" is meant a matter of which the tensile strength in any direction of given plane, is greater than one tenth of that exists in a neighboring plane direction.

By "block" is meant a volume of material having roughly the shape of a section prism in the form of a quadrilateral, the actual line on one side of the section not deviating from a straight line by more than 20% of the length on this side.

"Flat separation surface" means a surface which deviates from an average plane only by small deviations due to defects in the homogeneity of the material, the differences reaching at most 5% of a dimension of the separation surface.

By "curved separation surface" is meant a relatively flat surface but at least one of which of edges is wavy and deviates from a straight line average of 5 to 25% of its length, or an area curved, concave or convex, or a curved surface with wavy edges. The importance of irregularities as well defined, however, makes it possible to define an average plan of separation.

By "median plane" of a block, a plane perpendicular to the mean plane of separation and passing through the middle of the start and finish lines of rift.

By "predetermined area" is meant "flat surfaces" or "curved surfaces".

By "propagation of a single crack", one indicates that the process will not generate cracks artificial in the block or piece, other than that propagated in the predetermined area except exceptionally in the particular case of materials containing very strong heterogeneities.

"Crack start line" means a line extending on one of the faces of the block called "crack starting face". It includes the whole points from which the rift. It can be straight or wavy around of a straight line.

"Crack finish line" means a line comprising all the points reached by the crack at the time of the separation of the piece and on the side of the block called "arrival face of crack "located opposite the starting face of rift. It can undulate like the starting line of rift.

For simplicity, the above terms will be replaced in this text by "starting line", "start face", "finish line" and "finish face".

"Intermediate lines" means the lines joining the end of the starting lines and of arrival and located on the other two sides of the prism, other than the start and end faces of rift.

By "ends" of the block, the two ends from the prism.

By "crack length" is meant the average distance between the starting line and the line of arrival.

By "separation width" is meant the distance separating the two "intermediate lines".

By "piece" is meant part of the block separated from the rest of the block and of thickness at most equal to half that of the original block; and by "piece side" of a block, the part of that block destined to become the piece that we want to separate from block.

By "thickness" is meant the dimension average of a piece or block in one direction perpendicular to the separation surface.

By "thick piece" is meant a piece of thickness at least equal to a quarter of its length.

By "thin piece" is meant a piece of thickness at most equal to a quarter of its length but most often equal to 1/5, even 1/10 of its length, even less in some favorable cases.

By "crack initiation" is meant a crack or a very shallow groove, a few millimeters, rarely a few centimeters, created locally or on a certain length on the surface of a block by known means such as shock, high pressure of a tool, etc., for a crack or diamond disc, etc., for a groove.

By "compressive force" is meant a force or a force component which is exerted parallel to the mean plane of the separation surface, towards the interior of the block.

"Separation force" means a set of two forces, or components of forces, equal and opposite, exercising on either side of crack start lines and lines intermediaries.

By "system of compressive forces" and "separation force system" means a set of forces or force components of compression or separation exerted on an area defined from the block by means of support elements.

"System of forces" means a set of forces, acting on a defined area of the block by means of support elements, and the resulting includes at least one component of compression.

By "supporting elements" of a force or force system, we mean a pusher or a set pushers transmitting this force to the surface of the matter. The support can be done in a very zone localized or point, an elongated and very narrow area or line, an area of determined shape, or finally, if nothing is not specified, an area of any shape. The area application of a force is the support zone of the pusher. By definition, the supporting elements are arranged to distribute as evenly as possible, in their area of action, the force on the block material.

"Fixed non-deformable assembly" means a chassis provided in a machine intended for setting process work. The existence of such a chassis is essential for absorbing force reactions put into play on the material block.

It has long been known to divide blocks of material by propagation of a crack at from a crack initiator prepared in advance. According to US-A-26319154, ORLOW has introduced corners in slots made in advance then subjected these corners to an abrupt impact, which fractures the block.

In documents FR-A-2432375 and EP-A-0050075, applying to fissile materials or natural cleavage plan, which cite as inventor the author of the present invention, one exercises on walls of the crack initiator liquid pressure or we exert a shearing force on both sides of the crack to advance.

These processes, of application limited to certain types of material, are only effective in certain well-defined configurations.

We commonly use, in the case where seeks to separate a thick piece of a block, a technique of tightly clamping the block between two tools applied on two opposite sides of the block, each tool generating a crack. Control of the exact shape of the separation surface is difficult. It is linked to a precise adjustment of the machine, and becomes impossible as soon as the supporting bodies are taking a game.

One can also cite among the documents of the prior art U.S. Patent No. 4,256,246.

In document EP-A-0294267, in the name of the same inventor that the present invention describes a process for separating a piece from a block of material along a predetermined area intersecting one of the faces of the block, called next crack starting face a line called the crack start line on which we created at least one crack initiator and intersecting an opposite face, called the arrival face of crack, along a crack finish line, the separation being effected by a single crack propagating from the crack starting line to the crack finish line, under the action of a separation force system, a process by which acts on the propagation of the crack by creating compressive stresses in the mass of the block, at vicinity of said crack.

More specifically, according to EP-A-0294267, and notably its figure 2, we use forces of separation created by a tool with small radius of curvature penetrating the crack initiator, and compensated for using a tool with a large radius of curvature acting opposite direction on the finish line, and we add to these compressive stress forces created in clamping the block, on the piece side, between two tools large radius of curvature. It is specified that the forces creating these compression constraints will have to be properly dosed, and furthermore, frequently prepare the separation surface in y creating areas of least resistance.

The studies made for the implementation of the method of EP-A-0294267, have shown that the dosage of forces applied to the chunk side should be very precise, and that, in the absence of surface preparation of separation, the crack tends to bend in direction of the song if the compression is too weak, and in the opposite direction if the compression is very strong.

We know that the direction taken by a crack propagating in a block is directly related to stress regime induced in this block in the vicinity immediately from the crack front. The difficulty lies in the fact that the cracks spread the most often very quickly; it is therefore advisable to create in matter, from the start of the propagation of the crack, the conditions that will cause the crack to be correctly guided throughout its journey. That is all the more difficult as the forces brought into play are very important. As an indication, the first experiences from which the patent EP-A-0294267 have shown that the piece side compression force reached, in a medium granite, an intensity of 4000 Newton per centimeter of width to separate a piece 3 centimeters thick. The present invention makes following long studies and experiments which have allowed to discover the very particular properties of constraint regime induced in a block by at least three force systems acting on two sides opposites of a block of prism-shaped material to quadrilateral section.

The object of the present invention is to provide a method for obtaining a surface of separation of the desired shape, without very control precise forces applied to the piece, and with a preparation of the separation surface which is more reduced than in the prior art.

• création d'au moins une amorce de fissure sur la ligne de départ de fissure;
• mise en action sur les faces du bloc autres que ses deux extrémités d'un ensemble de forces, agissant simultanément, symétriquement par rapport au plan médian du bloc et comprenant au moins:
• un système de forces de séparation agissant de chaque côté de cette ou ces amorces de fissure d'une intensité suffisante pour propager la fissure, intensité dont le minimum est lié aux caractéristiques géométriques du morceau et du bloc ainsi qu'à la matière constitutive du bloc;
• deux systèmes de forces de compression dont les zones d'application ont une surface suffisante pour ne pas propager une fissure sous leur propre zone d'action, comprenant:
• un premier système de forces de compression dont les éléments d'appui ont leur zone d'application sur la face d'arrivée de fissure, à une distance de la ligne d'arrivée de la fissure inférieure au 1/5 de la longueur de la fissure et de préférence sur la ligne d'arrivée de la fissure;
• un deuxième système de forces de compression dont les éléments d'appui ont leur zone d'application sur la face de départ de fissure, côté morceau, écartée en majeure partie de la ligne de départ de fissure mais à une distance de celle-ci inférieure à la longueur de la fissure, forces dont les composantes de compression ont une intensité supérieure à une valeur minimale au-dessous de laquelle la fissure se propage en s'incurvant sans atteindre la ligne d'arrivée de fissure,
  ce procédé étant caractérisé en ce qu'on met en action un troisième système de forces de compression dont les éléments d'appui ont leur zone d'application sur la face de départ de fissure, côté bloc, écartée en majeure partie de la ligne de départ de fissure mais à une distance de celle-ci inférieure à la longueur de la fissure, ces zones d'application ayant une surface suffisante pour ne pas provoquer une fissure sous leur propre zone d'action. L'ensemble des forces auxquelles est soumis le bloc étant en équilibre.

To obtain this result, the invention provides a method for separating a piece of a block of material along a predetermined surface intersecting one of the faces of the block called the crack starting face along a line called the crack starting line and cutting through the opposite face called the crack arrival face along the crack finish line, the separation being carried out by a single crack propagating from the starting line to the crack finish line, the method comprising the operations following:

• creation of at least one crack initiator on the crack starting line;
• actuation on the faces of the block other than its two ends of a set of forces, acting simultaneously, symmetrically with respect to the median plane of the block and comprising at least:
• a system of separation forces acting on each side of this crack initiator (s) of sufficient intensity to propagate the crack, intensity the minimum of which is linked to the geometrical characteristics of the piece and of the block as well as to the constituent material of the block ;
• two systems of compressive forces, the areas of application of which have a sufficient surface so as not to propagate a crack beneath their own area of action, comprising:
• a first system of compressive forces, the support elements of which have their area of application on the crack arrival face, at a distance from the finish line of the crack less than 1/5 of the length of the crack and preferably on the finish line of the crack;
• a second system of compressive forces, the support elements of which have their area of application on the crack starting face, piece side, spaced for the most part from the crack starting line but at a distance therefrom the length of the crack, forces whose compression components have an intensity greater than a minimum value below which the crack propagates by bending without reaching the crack finish line,
  this process being characterized in that a third system of compressive forces is put into action, the support elements of which have their area of application on the starting face of the crack, on the block side, largely separated from the line of starting from a crack but at a distance from it less than the length of the crack, these application areas having a sufficient surface not to cause a crack under their own area of action. The set of forces to which the block is subjected being in equilibrium.

Note first of all that the result of each of the force systems to which is subjected the block is located in the median plane and the conditions of equilibrium of the block are therefore those of a plate, one of the ribs of which is subjected to two forces and the rib opposite to at least one force. If, despite everything, he there is a slight component perpendicular to this plane due to an imperfect symmetry of the forces exerted on the block whose shapes are irregular, this component, parallel to the front line of the crack, will have no influence on the form taken by the crack and it will therefore be neglected in what follows.

The balance of all forces to which the block is subject, requires that we cancel not only the sum of the forces, but also the moment of a couple contained in the median plane, and therefore perpendicular to the mean plane of separation. The cancellation of this couple obliges to induce, in the block material, a couple of which, we will see more far, the value of the moment conditions the form taken by the separation surface.

Furthermore, we know that the duration of the crack propagation can be very small, for example less than 1/100 of a second. It is therefore not absolutely necessary that the block be in stable equilibrium during separation itself because the movement produced may be only very slight scope, and do not modify the induced constraints in the block.

We can therefore imagine devices brutally and perfectly reproducible the force systems described above and inducing in the material a regime of constraint perfectly similar to that explained below even if the block is not stabilized just before the operation of seperation. In this case part of the forces is used to give movement to the block and to overcome its inertia. The existence of this movement will not change in itself the constraints exerted in the material.

We will assume in all that follows that the block is in equilibrium just before the separation operation but we do not exclude from the process the case where we put in brutally operates the forces described thus allowing to perform shape separation operations even controlled on a moving block.

As mentioned above, the experiences previously conducted on the basis of the EP-A-0294267 have shown that in the operations of separation of thin pieces from a thick piece, the second compression force exerted on the piece side had to be dosed with great precision, especially in homogeneous materials. The intensity of this force, very important as indicated above, depends on the material, geometric characteristics of the piece and, to a lesser degree, from the block. If the value of the compression force is too high, the crack has tendency to decrease the thickness of the block, if it is too weak, it tends to decrease the thickness of the piece; unfortunately this trend is related to characteristics of the material, which are likely to vary within the same block, it also depends on the shape of the end of the block.

It should be emphasized that the compression forces put in works act by the constraints they induce in the matter. Precise analysis of forces and constraints they induce can only be done if we assume the block in stable equilibrium just before the separation, even if, during the separation operation, itself there is a slight relative movement of the block and of the piece, a movement which practically does not affect the stresses exerted in the block.

• l'existence d'un état de compression suffisant de la matière côté bloc agit comme une barrière et empêche la fissure de dévier de la surface prévue dans une large plage d'intensité relative des deuxième et troisième systèmes de forces de compression; l'intensité côté morceau pouvant même dépasser de 30% au moins celle strictement nécessaire, à la seule condition que la "barrière" créée côté bloc ait une intensité suffisante;
• la nécessité de maintenir le bloc en équilibre au moins juste avant l'opération de séparation permet d'introduire dans la matière du bloc un couple dont la valeur peut aisément être contrôlée tout en pouvant choisir librement la valeur la plus adéquate pour le deuxième système de forces de compression. Or, la valeur de ce couple, induisant à l'intérieur du bloc une for variable, perpendiculaire au plan joignant les lignes de départ et d'arrivée de fissure, va permettre, quelle que soit l'épaisseur du morceau à séparer, d'écarter plus ou moins rapidement la fissure du plan contenant les lignes de départ et d'arrivée de fissure puis de ramener la fissure vers la ligne d'arrivée de fissure.

The considerable progress brought by the introduction of a third compression force system, on the piece side, is due on the one hand to the fact that it allows to induce in the material, in the area where the crack progresses, a degree of high compression, a guarantee of a regular separation surface even in materials with significant homogeneity defects, but it essentially results from the discovery of the following double phenomenon:

• the existence of a sufficient state of compression of the material on the block side acts as a barrier and prevents the crack from deviating from the surface intended in a wide range of relative intensity of the second and third systems of compression forces; the intensity on the piece side can even exceed by 30% at least that strictly necessary, on the only condition that the "barrier" created on the block side has sufficient intensity;
• the need to keep the block in equilibrium at least just before the separation operation makes it possible to introduce into the material of the block a torque whose value can easily be controlled while being able to freely choose the most suitable value for the second system of compression forces. However, the value of this couple, inducing inside the block a variable for, perpendicular to the plane joining the lines of departure and arrival of crack, will allow, whatever the thickness of the piece to be separated, remove the crack more or less quickly from the plane containing the crack start and finish lines, then bring the crack back to the crack finish line.

This double feature therefore allows only to separate a piece or a succession of thin pieces of a block without having to settle with precision the second system of forces even if the block width varies, but also, whatever the thickness of the piece to be separated, to obtain surfaces with concavity or convexity perfectly determined, by the measurement of the torque introduced into the material. Considering the fact that there is always interest, even in separations of thick pieces, that the constraints of compression exerted in the block; in the neighborhood of the separation plan are as high as possible, we set a maximum indicative distance between the crack start line and application areas second and third force systems.

The flatness or curvature of the surface of separation are therefore linked to the intensity of the torque introduced into the material to keep the block in balanced; the solutions leading to this balance, very numerous, are studied by mechanics classic and can all be used in the limit of the constraints exposed above. We will however favor a certain number.

An advantageous way to produce very flat separation surfaces without having to adjust in a precise way the relative positions of the zones application of the first, second and third compression force systems and their intensities, consists in not inducing any torque in the block material, making sure that the resulting forces acting on the departure or arrival face crack between the support zones of at least two forces, acting on the opposite side, i.e. of arrival or departure of crack, and in that these support zones are arranged to prevent any rotational movement of the block around one of them.

Indeed, under these conditions, the block is in stable equilibrium since it rests on at least two points and the balance of forces to which is subjected the block is easily obtained without the material of the block is subject to a couple. There are obviously interest, whenever possible, in order to to have the greatest possible freedom for the adjustment of the relative intensities of the different forces, the distance between the support zones of the two above forces to be as large as possible.

On the other hand, an advantageous way of inducing in matter a couple of measurable intensity, consists of the support zone of at least one of the compression forces from the first system of forces; either from second or third system of forces, is a line fixed elongated parallel to the mean plane of separation desired and if the implementation of all of the forces applied tends to rotate the block around this line, we cancel this trend by exercising on at minus one of the supporting elements of the other forces put in play, a measurable force, perpendicular to this plane, effort whose meaning and intensity determine the form that we want to give to its separation surface. In effect, the cancellation of the rotational movement of the block by a force whose intensity is easily measurable induced in the matter of it, a couple which we have indicated the effect above.

• des amorces de fissure sont crées sur la majorité de la ligne de départ de fissure désirée;
• on fait agir les éléments d'appui du premier système de forces le plus régulièrement possible exactement sur la ligne d'arrivée de fissure désirée; et
• on exerce sur chacune des deux lignes intermédiaires, d'une façon symétrique, dans toutes les parties où on désire que la fissure suive exactement ces lignes, des systèmes de forces jouant le rôle d'appel de fissures, mais d'une intensité insuffisante pour propager seuls des fissures.

We have seen above how one can act on the general shape of the separation surface but the method also provides a means for the desired separation surface to cut across the four edges of the block along lines defined in advance, slightly different from those arising from the desired flat or curved surfaces inside the block. According to an advantageous way, one will force, in a homogeneous material, the crack to follow, during its development, the lines of departure and arrival of crack as well as the desired intermediate lines, even if each of these lines undulates around '' a straight or curved line by proceeding as follows:

• crack initiators are created on the majority of the desired crack starting line;
• the support elements of the first system of forces are made to act as regularly as possible exactly on the desired crack finish line; and
• one exerts on each of the two intermediate lines, in a symmetrical way, in all the parts where one wishes that the crack follows exactly these lines, systems of forces playing the role of call of cracks, but of an insufficient intensity for only propagate cracks.

According to this last feature of the method, known means are used to encourage a crack to follow a determined path on the surface of a block but the quality of the crack guidance during of its spread both inside the block and on its perimeter will provide separation surfaces better defined in advance and much more regular than by any known method. Remember that the means playing the crack calling role are known systems such that: crack initiation created by a shock or any other medium, force exerted exactly on the hotline desired, separation forces exerted on both sides and on the other side of the desired call line.

According to another interesting modality of the process, in addition to force systems described above, a system of compressive forces, acting exactly on the crack starting line and on the majority of its dimension, through scissor-shaped tools, force system of a sufficient intensity to initiate a crack according to its line of support and create at least part of the force of separation necessary for the propagation of the crack.

This latter process also has an implementation fast and almost as simple as the process classics. It allows to introduce into the material a compression as high as it appears desirable for achieve perfect separation, even in materials say homogeneous but having heterogeneities in their mass. It gives an excellent mastery of the couple introduced into matter and therefore concavity or convexity of the separation surface.

• limiter au strict minimum, une seule le plus souvent, le nombre et la dimension des amorces de fissure créées sur la ligne de départ; et
• appliquer le premier système de forces de compression, au voisinage de la ligne d'arrivée de fissure, sur la plus grande surface possible.

To obtain a separation in the plane of cleavage of a fissile material or with natural cleavages, it is preferable to limit to the strict minimum the zones of crack calling around the periphery of the block because these calling zones would risk being in outside the natural plane. Consequently, an advantageous way of carrying out such separations is to

• limit to the strict minimum, usually only one, the number and size of the crack tips created on the starting line; and
• apply the first system of compressive forces, in the vicinity of the crack finish line, over the largest possible surface.

The implementation of the process requires that be applied, on either side of the crack starting line, an effort of separation. Many solutions are possible including three are to be preferred if possible in combination with other.

An interesting modality of the process consists in that that at least part of the separation forces ensuring the crack propagation is generated by fluid pressure confined in all or part of the crack initiator (s) created on the crack starting line. this modality will give a very "soft" appearance on the separation surface in part of the "grain" of the "matter. This modality, where the propagation of the crack can be done without measurable spacing crack books at the starting surface, allows to carry out the separation even if all or part of the support means the second system of compressive forces on the one hand, the third force system on the other hand are linked together so as not to not being able to move away from each other, useful provision for make certain balancing arrangements. We can also provide a place of flexible and waterproof material, extending from on either side of the starting line of the crack, serves both to confine the fluid under pressure in the primer (s) of crack, and to transmit to the block the forces of the second and third systems of forces compression.

In some cases, on the contrary, it will be easier to ensure the propagation of the crack by spreading the lips of the crack, at the crack start surface, piece side on the one hand, block side on the other. This modality requires that the supporting elements of the second and third force systems compression while remaining fixed relative to the block and piece, can deviate freely from each other by a distance corresponding to the widening of the crack during its progression. This possibility of separation can also be advantageous in the case of other modes for the creation of separation forces.

Finally, in another method modality, we provides that at least one of the supporting elements of each of the second and third force systems of compression is confused with the supporting elements of minus part of the separation forces. This provision likely to simplify implementation of the process, can be used in many case.

Indeed, in the case of separation of thin pieces, experience, confirmed by calculation, shows that, in the vast majority of subjects, the separation effort is less than 60% of the effort minimum compression required on the piece side, what whatever the thickness of the piece. We can therefore very simple way, using a cylinder for example, without risk of inadvertent slipping, exert an effort to separation between all or part of the support elements of the compression forces on the block side on the one hand, piece side the other.

Anyway, in all cases, it should be noted that the supporting elements of the second and third system of compressive forces, forces whose lines - are located on either side of the line of action of the first system of forces, induce automatically in the material an effort of separation.

So we can see the flexibility of this process which allows you to choose, for each subject, for each geometric characteristic of the piece to be separated, optimum compression constraints while providing the necessary separation constraint.

Figure 1 est une vue schématique, en perspective, d'un bloc de matière avant traitement. Cette figure ainsi que les suivantes supposent que la face de départ de fissure se trouve à la partie supérieure du bloc. Dans la réalité, le bloc et sa face de départ de fissure peuvent prendre, dans l'espace, n'importe quelle disposition.

Figure 2 est une vue schématique en perspective d'un bloc et d'un morceau après séparation.

Figure 3 est le schéma, suivant une coupe établie dans le plan médian du bloc, plan passant par le milieu des lignes de départ et d'arrivée de fissure et perpendiculaire au plan moyen de séparation désiré, d'un dispositif permettant d'exercer les différents efforts prévus dans le texte ci-dessus et maintenant le bloc en équilibre stable avant le début de la progression de la fissure.

Figures 4 et 5 sont deux schémas explicitant les contraintes auxquelles va être soumise la matière du bloc de la figure 3, suivant l'intensité relative des différentes forces de mise en jeu.

Figures 6, 7, 8 et 9 sont des schémas, établis comme celui de la figure 3, de différents dispositifs permettant de mettre en oeuvre les systèmes d'effort prévus tout en maintenant le bloc en équilibre.

The invention will now be explained more precisely with the aid of practical examples illustrated by drawings among which:

Figure 1 is a schematic perspective view of a block of material before treatment. This figure and the following assume that the crack start face is at the top of the block. In reality, the block and its crack starting face can take, in space, any arrangement.

Figure 2 is a schematic perspective view of a block and a piece after separation.

Figure 3 is the diagram, along a section established in the median plane of the block, plane passing through the middle of the start and finish lines of the crack and perpendicular to the desired mean plane of separation, of a device making it possible to exercise the different efforts provided for in the above text and keeping the block in stable equilibrium before the crack progresses.

Figures 4 and 5 are two diagrams explaining the constraints to which the material of the block of Figure 3 will be subjected, according to the relative intensity of the different forces involved.

Figures 6, 7, 8 and 9 are diagrams, established like that of Figure 3, of different devices for implementing the force systems provided while keeping the block in balance.

Figure 1 shows a block 1 we want separate a piece 2, which represents the piece side of the block before separation while 3 designates the element which will remain after separation and constituting the block side of the initial block. The starting face of crack 4 carries the starting line of crack 11 undulating around the medium right 11A. The crack arrival face is designated by 5. The other two sides, designated by 6B and 6A are intersected by the separation plane curve along the intermediate line 13A. The end of the piece is designated by 7A, and that of the remaining block after separation by 7B.

Figure 2 shows piece 2 separated from the block remaining 3 along the curved separation surface 8 intersecting the block along the starting line 11 on the starting face of crack 4, the finishing line 12 on the crack arrival face 5, the lines intermediate 13A and 13B on the sides 6A and 6B (not represented). References 14 and 15 denote the separation length and the width respectively of seperation; while 16 and 17 represent respectively the thicknesses of the piece on the one hand, of the block remaining on the other.

Figure 3 is a sectional view of a block in balance and subject to several force systems. Her crack arrival face 5 rests along the line crack arrival 12 on a support 20 rigidly connected to a fixed non-deformable assembly 25 and on another support 21 also rigidly linked to the assembly 25. The support 20 will generate the first force system. On the face of start of crack 4, two support elements 22 and 23 transmit to the block the efforts produced by two rod-jack assemblies 26 and 27 connected by pins 28 and 29 to the same assembly 25. These support elements act on either side of the crack starting line whose trace is at 11. They respectively transmit the second and third compression force systems. The piece to detach is marked 2, the remaining block 3. Finally, the support element 23 prevents by a support 30, always connected to the non-deformable assembly 25, any lifting of the support block 21. Support zones for support means 20, 21, 22 and 23 cover all or part of the width of the block or piece even if the surface is irregular using the usual means at the solution of this type of problem.

Figure 4 is drawn in the median plane of the same block and analyzes the forces transmitted in the material by the support means 20, 21, 22 and 23 of the figure 3. We find in 11 and 12, the traces of the lines of departure and arrival of crack. In 2 and 3, the piece and the block which will remain after separation. We have schematized in 32 and 33 the respective result of the second and third compression force systems acting on the face of departure of crack with their intensity. Under the action of these forces, the supports 20 and 21 of FIG. 3 go generate forces schematically in 31 and 34 including the total intensity will be equal to the resultant 35, of forces 32 and 33. We see that 31 is the result of this which we called the first system of forces. In the case, the line of action of the resultant 35 forces 32 and 33 to which we will add, in the case figure shown, to be perfectly rigorous, the self-weight of the block not shown for the sake of simplification, is between the lines of the forces 31 and 34 generated by the supports 20 and 21 of figure 3. The block will be in equilibrium stable without being subjected to any torque. We will be able to obtain a separation along a plane joining 11 to 12. Let us study in more detail the constraints induced in the matter by these four force systems. We have schematically in 40 the trace of the crack front in progress of development. Force 32 generates an effort of compression 36 on the surface of the block and will induce, in the material, piece side, near line 40 a compressive stress, likewise force 33 will induce compression stress through its component 38. We see that, for a configuration given the intensities of the forces and their zones respective actions, we can always get balance of the block and adjust the induced stresses in the block above a given minimum. Calculations very complex theoretical allow to calculate these minimum but, in practice, some experiences allow to quickly determine these minima, which, we have seen, can then be exceeded without no downside. We can also play on directions of the resultants of the second and third compression force systems and on the location of their area of application.

Still on this figure 4, we have designated by 14 the length of the crack, by 41 the distance between the support line 12, crack arrival line, and the line of action of force 32. The support element of the force 32 will therefore induce a constraint, parallel to the separation force, intensity equal to 32 x 41:14. The force-bearing element 33 will induce a force of same nature and opposite direction. We understand how the supporting elements of the second and third systems compression forces induce on either side of the line of departure from crack, a force of separation. This strength is directly related to positions, directions and intensities of the second and third compression force systems that we can always fix so that they induce inside the block the constraints of compression desired and specified above before that they do not generate an intensity separation force sufficient to propagate the crack.

Now suppose that with the device shown diagrammatically in FIG. 3, acting on the same block, we want to create a curved separation surface with a piece side concavity. In Figure 5, showing the same block as that of figure 4, with the same ratings, we just varied the intensities of forces 32 and 33. The line of action of the resulting 35 now goes to the left of the line support 12. This set of forces alone cannot keep the block in balance. Therefore, as shown in Figure 3, prevents movement of lifting of the block by the reaction of the support 30 on the support means 23. This reaction of support 30 induce in the material, in the vicinity of the supports of 23 and 20 a intensity torque 43 (figure 5) which will have repercussions in the area where the crack is propagated by a force which will tend to spread the crack, in the first half of its path, of the plan joining the lines of departure and arrival of crack 11 and 12, then in the second half to bring it closer.

In Figure 6, we have a device identical to that of figure 3 but where the means support 23 slides between two supports 30 and 30A, all two linked to the rigid assembly 25. On the other hand, we have removed support 21. Analysis of Figures 4 and 5 allows immediately understand how such a device is going allow by simply playing on the intensities relative forces 32 and 33 to produce surfaces convex, flat or concave. The measurement, very easy to support reactions of 30 and 30A will allow to control the value of the torque and therefore the intensity of the curvature of the separation surface. The weight of block has an influence on the torque value. We will be able to always correct this influence by playing on relative intensities of forces 32 and 33 exerted by the support means 22 and 23.

In Figure 7, there is shown a device different in which a cylinder 50, connected by an axis 51 to the fixed non-deformable assembly 25 transmits the first force system through its means support 51 acting on the crack finish line 12, and pushes the block on two blades or sets of blades 22 and 23 constituting the support means for second and third compression force systems. These blades are rigidly linked to the fixed assembly 25. We see immediately that such a device does not introduce any torque in the material and will therefore ensure flat separations using only one cylinder or a single set of cylinders.

FIG. 8 represents a block 1 of material cleavable with separate cleavage plans, roughly parallel. We find a support 20, fixed, acting on either side of the finish line of crack 12 and the support means 22 and 23 transmitting the second and third systems of compressive forces. A cylinder 55, through its support means 50 consisting of a knife with a relatively acute angle, strongly presses on the starting line of crack 11 and create a crack initiation there will propagate while remaining in the cleavage plane chosen under the action of separation forces induced by 56 but also, as we saw above by the organs 22 and 23.

Figure 9 differs from Figure 7 by the presence of an element 60 of flexible material. The block is pressed on a face 61 of this element, which is supported by its opposite face 62 on a rigid part 63 linked to the fixed assembly 25. The support of the face 61 induced in the block material constraints equivalent to those forces 32 and 33 of FIG. 4; the direction of these forces is conditioned by the shape of the element of flexible material and / or the part 63. If the element 60 is waterproof, we can use the pressure it exerts on the block to confine a pressurized fluid, introduced by tubing 64 into all or part of the crack initiators created on the starting line of crack, generating all or part of the force of separation required.

The implementation of separation forces necessary to propagate the crack can be analyzed in Figures 3, 6, 7 and 8. For example in the Figures 3 and 6, we see that the support member 22 of the second system compression forces can deviate freely from the support member 23 of the third system of compressive forces thus leaving the crack free to open at as it progresses. We saw that the intensity, the situation of the application area, the relative inclination of the second and third systems compression forces create a force of desired intensity separation. Sometimes there can be disadvantage that separation occurs in have precisely checked the intensity beforehand the second and / or third system of compressive forces. In this case, we will complete the separation effort by having one or more sets of cylinder rods hydraulic connecting the support means 22 and 23 that will only act after giving other forces the desired value. This provision is particularly interesting in the case of separation of pieces thin where the intensity of the second system of forces of compression should be well controlled.

In FIG. 7, the blades 22 and 23 can be very rigid and prevent any separation significant between them. We can then favor separation by pressure of fluid confined in a or more crack starters of the starting line 11. We can also give a slight flexibility to blades 22 and 23 and we are brought back to the case previous.

It should be noted that the strength of separation, in the case of separation of pieces thin, will never exceed, according to all experiments carried out, confirmed by calculation, 60% of the minimum compression force required on the piece side and we can therefore always apply an effort of sufficient separation without risk of sliding supports 22 and 23. For thick pieces, setting work of the separation effort will not pose any problem.

No diagram illustrates how to control the shape of the four edges of the pieces. Respect for a perfectly regular shape and thickness is however very important each time that a succession of pieces intended to be assembled side by side side. This control indeed implements means perfectly known but whose effectiveness will be increased due to very good shape control average of the separation surface. Creation of crack initiators on the starting line to which giving the desired shape poses no problem. The forms supporting elements acting exactly according to the crack finish line either, but the irregularities around a straight line cannot reach a great scale. On both sides, we can operate straight or curved tools or waving slightly around these lines, pressed strongly along the desired line, the intensity of however, the effort must never initiate a crack at the end of the tool. Guidance to the lines desired intermediaries will be even stronger if we creates, along the desired lines, primers of crack on the lips of which one will exert a light separation effort. In general, all of these irregularities can never be very significant and will only slightly modify the general shape of the separation surface whatever the material. They however will eventually give an appearance original to the pieces obtained.

Claims (10)

1. A process for separating a piece (2) from a block of material (1) according to a predefined surface intersecting one of the block faces called the crack starting face (4) according to a line called the crack starting line (11) and meeting the opposite face called the crack finishing face (15) according to the crack finishing line (12), separation being achieved by a single crack propagating from the crack starting line (11) to the crack finishing line (12), the process involving the following operations:

   the making of at least one incipient crack on the crack starting line (4);

   the application on the faces of the block (1) other than its two ends (7A, 7B) of a set of forces, acting simultaneously and symmetrically in relation to the center plane of the block (1) and including at least:

   a system of separating forces acting from each side of this or these incipient crack(s) of sufficient intensity to propagate the crack, an intensity whose minimum is linked to the geometric characteristics of the piece (2) and of the block (1), as well as to the material making up the block (1);

   two systems of compression forces whose zones of application have a surface sufficient not to propagate a crack under their own zone of application, comprising:

   a first system of compression forces whose bearing devices (20, 51) have their zone of application on the crack finishing face (5), at a distance from the crack finishing line (12) of less than a 1/5 of the crack length (14) and preferably on the crack finishing line (12);

   a second system of compression forces whose bearing devices (23) have their zone of application on the crack starting face (4), on the piece (2) side, in the main away from the crack starting line (11) but at a distance from the latter of less than the length (14) of the crack, forces whose compressing components have an intensity greater than a minimum value below which the crack propagates by incurving without reaching the crack finishing line,

   the characteristic of this process being that a third system of compression forces is applied whose bearing devices (23) have their zones of application on the crack starting face (4), on the block (1) side, in the main away from the crack starting line (11) but at a distance from the latter of less than the length (14) of the crack, these zones of application having a surface sufficient not to provoke a crack under their own zone of application, the overall forces to which the block is subjected are in equilibrium.
2. A process as defined in claim 1, characterized by the resultant of the forces acting on the crack starting (4) or finishing face (5) passes between the bearing zones of at least two forces, acting on the opposite face, i.e.: crack finishing (5) or starting opposite face (4), and that the bearing zones are arranged in such a way as to prevent any rotational movement of the block about any one of them.
3. A process as defined in claim 1, characterized in the bearing zone of at least one of the forces either of the first system of compression forces, or of the second or third system of compression forces, being a fixed line extended in parallel to the required average plane of separation and if implementation of the overall applied forces has a tendency of making the block (1) turn about this line, this tendency is canceled by exerting on at least one of the bearing devices other forces put into play, a measurable stress, perpendicular to this plane, a stress whose direction and intensity determine the shape that is sought for the surface of separation.
4. A process as defined in one of the claims 1 to 3, characterized by:

   incipient cracks being created on the major part of the starting line (11) of the crack sought after;

   the bearing devices of the first system of compression forces being made to act, as uniformly as possible, precisely on the crack finishing line (12); and

   on each of the two intermediate lines (13A, 13B) being exerted, symmetrically, in all the parts where we want the crack to follow these lines precisely, systems of forces playing a crack call role, but which alone are of an intensity insufficient to propagate a crack.
5. A process as defined in one of the claims 1 to 4, characterized by a system of compression forces being applied, acting exactly on the crack starting line (11) and on the major part of its length, using tools of chisel form, a system of forces of sufficient intensity to start a crack according to its bearing line and to set up at least a part of the force of separation necessary for the propagation of the crack.
6. A process as defined in one of the claims 1 to 3 characterized by at least one incipient crack being created on the crack starting line (11), which happens to be in the cleavage plane of fissile material or material with natural cleavage, whose follow-through is sought, and the bearing devices of the first system of forces acting on a zone situated in the neighborhood of the crack finishing line (12) made up of the meeting line of the cleavage plane chosen and the crack finishing face.
7. A process as defined in one of the claims 1 to 6, characterized by at least a part of the separation forces ensuring the generation of crack propagation by a fluid under pressure confined in all or a part of the incipient crack(s) created on the crack starting line (11).
8. A process as defined in one of the claims 1 to 7, characterized by the bearing devices of the second and third systems of compression forces, while remaining fixed in relation to the block and the piece, being able to freely part one from the other by a distance corresponding to the widening of the crack during its advance.
9. A process as defined by one of the claims 1 to 8, characterized by at least one of the bearing devices of the second and third systems of compression forces being merged with a bearing device of at least a part of the separation forces.
10. A process as defined in claim 7, characterized by a pad of flexible and impermeable material (60) stretching here and there along and from the crack starting line, being used both to confine the fluid under pressure and transmit together the forces of the second and third systems of compression forces.

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