Device For Insertion, Guidance And Evacuation Of Cylindrical Parts Such As Nuclear Fuel Pellets, In A Centreless Grinder

Abstract

The invention relates to a device (1) for the insertion, guidance and evacuation of cylindrical parts to be ground in a centreless grinder (10). According to the invention, micrometric means (4, 40, 41) for adjustment of the alignment of the guides at the entry (3) to and the exit (5) from the guide chute (2) are provided and these micrometric adjustment means are independent from each other. The invention enables very precise adjustment of the alignment and prevents any shift of the parts.

Description

TECHNICAL FIELD

The invention relates to a device for the insertion, guidance and evacuation of cylindrical parts such as nuclear fuel pellets in a centreless grinder.

It is particularly aimed at improving the reliability of centreless grinding.

The main application is grinding of nuclear fuel pellets for which quality is strict and imposes requirements to avoid generating defects on the pellets.

PRIOR ART

Centreless grinding is a known advantageous grinding process for grinding cylindrical parts, particularly for nuclear fuel pellets.

A centreless grinder usually includes two grinding wheels, one of which is a drive wheel used to rotate the pellets on themselves and making them advance on a guide rail called the guide chute in the case of nuclear fuel pellets, and the other is a grinding wheel with the function of grinding the pellet diameters by abrasion.

Obviously, the quality of ground nuclear fuel pellets depends on the efficiency of the centreless grinder itself, but also on the quality of the pellet transfer immediately on the entry side into the centreless grinder, in it, and immediately on the exit side from it, in other words the quality of insertion of pellets into the guide chute, of their guidance in the guide chute between the grinding wheel and the drive wheel and of their evacuation from the drive wheel when they have been ground.

The general purpose of the invention is to propose a solution to further improve the transfer quality of cylindrical parts such as nuclear fuel pellets, immediately on the entry side into a centreless grinder, in it and immediately on its exit side.

One particular purpose is to propose a solution that is easy to use in a glove box environment.

PRESENTATION OF THE INVENTION

To achieve this, the purpose of the invention is a device for the insertion, guidance and evacuation of cylindrical parts such as nuclear fuel pellets, in a centreless grinder comprising:

an insertion guide chute adapted to guide said cylindrical parts over the length of the grinding wheel and drive wheel of a centreless grinder,

a first guide called the entry guide arranged at one longitudinal end of the guide chute and adapted to allow the insertion of cylindrical parts one by one onto the guide chute from a conveyor system on the entry side of the centreless grinder,

mechanical means for adjustment of the entry guide relative to the guide chute,

a second guide called the exit guide arranged at the other longitudinal end of the guide chute and adapted to transfer parts from the chute to a conveyor system on the exit side from the centreless grinder,

mechanical means for adjustment of the alignment of the exit guide relative to the guide chute.

According to the invention, mechanical means for the micrometric adjustment of the alignment of the entry guide are independent from the alignment means of the exit guide.

In other words according to the invention, means of adjusting the alignment of the entry and exit guides are provided that enable a very precise alignment of the guides and the space between the grinding and drive wheels, to within the nearest micrometre. Making the two adjustment means independent enables an even more precise adjustment. This prevents any shifting of the parts to be ground such as nuclear fuel pellets, still present between the grinding wheels.

Thus, the parts (fuel pellets) may be inserted at the entry to the centreless grinder with no mechanical interference between them.

Similarly, there is a continuity in the contact line of the ground parts and the drive wheel at the exit from the grinder. This prevents grinding defects related to discontinuity in the contact as is possible in the state of the art.

Preferably, the guide chute is a single piece steel part on which surface and in-core annealing and quenching heat treatments have been made. These treatments may preferably be completed by surface treatments once the part (guide chute) has been finished, to increase some characteristics such as a better coefficient of friction and greater resistance to wear. This steel is preferably an XC 38 steel.

Guide chutes according to the state of the art for a centreless grinder application for nuclear fuel pellets are composed of a steel base on which a tungsten carbide plate has been added that forms the actual guide rail for the pellets, in other words the part in direct contact with the pellets to be ground.

The advantage of a tungsten carbide plate is that it has a very good resistance to wear. The major disadvantage is its brittleness under shocks and internal stresses in the steel base. Thus, the disadvantages of guide chutes according to the state of the art are avoided by making a single-piece steel chute with in-core and surface heat treatments providing wear resistance equivalent to tungsten carbide and good resistance to shocks and the relaxation of internal stresses in the chute.

According to one advantageous embodiment, at least one of the two guides is composed of two strips, one of which is fixed and parallel to the longitudinal edge of the chute placed on the grinding wheel side and the other is installed on a pivot that adjusts the space from the fixed guide facing it, the distance from the pivoting guide being varied by actuation of mechanical means for adjusting the alignment of said guide. Preferably, the entry guide and the exit guide are each composed of two strips, one of which is fixed and parallel to a longitudinal edge of the chute and the other is free to pivot to adjust the spacing of the guide from the fixed guide facing it.

Also preferably, the axis of the pivots of the adjustable guides is fitted with a polymer bearing. This makes the pivot axis compatible with the dust and splinters from pellets during grinding, and consequently eliminates the risk of seizure.

According to one advantageous variant embodiment:

the pivot axis of the pivoting strip of the entry guide and/or the exit guide is (are) mounted in a support,

the mechanical micrometric means for adjustment of the alignment of the entry guide relative to the guide chute and/or the mechanical adjustment means of the exit guide comprise a first screw screwed into the pivot axis support and a second screw nested into the first screw with a smaller pitch than the first screw and adapted to bear in contact with a part of the pivoting strip, screwing of the first screw into the support causing translation of the two screws while screwing the second screw into the first screw and bearing in contact with the part of the pivoting strip causes pivoting of the pivoting strip.

The pitch of the second screw is smaller than but sufficiently close to the pitch of the first screw to create a micrometric adjustment of the pivoting strips, so as to obtain the greatest possible precision. The device advantageously comprises a spring adapted to compensate for functional clearances of the device by guaranteeing permanent bearing between the second screw and the pivoting strip.

Each pivot axis and screw axis support is fixed to the guide chute, to facilitate assembly.

Each pivot axis and screw axis support is shaped in a turret with the two screws nested in each other and arranged in the upper part of the turret.

Due to a turret type arrangement, the alignment adjustments can be made manually by manipulating the screws from the top. This is perfectly suitable for a glove box environment in which the centreless grinder is installed.

The geometric shape and the length of the exit guide are preferably adapted to limit the number of ground cylindrical parts buffered at the exit from the wheels. In other words, this avoids the accumulation of pellets, some of which could collect between the grinding wheels and be machined beyond the required tolerances. The inclination of the exit guide and the inclined length cause the evacuation of the pellets while limiting their kinetic energy during evacuation to the conveyor on the exit side so that they remain in the horizontal position on the conveyor.

If their kinetic energy were not limited, they would be likely to tip on the conveyor which could damage their final quality.

The device preferably forms a single piece assembly to which adapted handles are fixed to enable its insertion into and evacuation from a centreless grinder in a glove box. Making it easy to remove the device manually facilitates maintenance operations on the centreless grinder.

The invention also relates to a centreless grinder comprising a device described above. Such a centreless grinder is adapted to grinding of nuclear fuel pellets.

Finally, the invention relates to a glove box in which a centreless grinder is arranged as above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics will become clear after reading the detailed description given below with reference to the following figures among which:

FIG. 1 is a perspective view of the side of the entry guide of a device according to the invention in a non-installed configuration,

FIG. 2 is another perspective view of a device according to the invention in a non-installed configuration but on the exit guide side,

FIG. 3 is a side view of a device according to the invention in its configuration installed in a centreless grinder for nuclear fuel pellets,

FIGS. 3A and 3B are cross-sectional views on lines A-A and B-B respectively of the device according to FIG. 3.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

The terms “lower”, “upper”, “below”, “above”, “entry side” and “exit side” should be considered in the installed configuration of device 1 according to the invention, in other words with the guide chute in the horizontal position between the grinding wheel and the drive wheel of a centreless grinder as shown in FIG. 3.

The device 1 according to the invention includes firstly a guide chute 2 adapted to guide pellets over the length of the grinding wheel 8 and drive wheel (not shown) of a centreless grinder 10 shown in FIG. 3.

The guide chute 2 is a single piece part made of XC 38 steel on which surface and in-core quenching and annealing heat treatments have been performed. The heat treatments were done to give the guide chute wear resistance equivalent to tungsten carbide, good shock resistance and so that the chute 2 has no internal stresses. This chute 2 comprises an upper part 20, the function of which is to guide the pellets P of nuclear fuel. As can be better seen in FIGS. 3A and 3B, the guide part 20 is inclined and is delimited by two longitudinal edges 200, 201.

An entry guide 3 is arranged at a longitudinal end of the guide chute 2: it is adapted to enable pellets P to be slid onto the chute 2 from a conveyor system not shown on the entry side of the centreless grinder 10. This entry guide 3 comprises a fixed strip 30 approximately aligned on the longitudinal edge 200 of the chute 2 and another strip 31 free to pivot to change the inclination relative to the other longitudinal edge 201 of the chute 2.

The strip 31 is installed free to pivot on an axis 310 fitted with a polymer bearing installed in a support 32 arranged as a turret.

The alignment of the pivoting strip 31 is adjusted relative to the edge 201 of the chute by mechanical means 4. These means are composed of two screws 40, 41, one nested into the other in the upper part of the turret 32 (FIG. 3A). The first screw 40 is screwed into the support 32. The second screw 41 has a smaller pitch which is similar to the pitch of the screw 40, and the screw 41 is fixed in rotation.

Rotating the screw 40 causes translation along its axis relative to the fixed support 32 (screw-nut connection). At the same time, this rotation of the screw 61 creates a second translation along its axis relative to the second screw 41. The difference in pitch results in a small translation of the bearing point of the screw 41 on the guide 31, which rotates the guide 31. Such adjusting means 4, 40, 41 make it possible to achieve very precise adjustment of the alignment of the pivoting strip 31, to the nearest micrometer.

A spring 42 compensates for functional clearances of the device to achieve permanent bearing between the screw 41 and the strip 31 in the pivoted position.

Due to the shape and dimensional characteristics of the entry guide 5 and the alignment adjustments of the pivoting strip described above, the nuclear fuel pellets P can be inserted with no mechanical interference between them.

An exit guide 5 is arranged at the other longitudinal end of the guide chute 2; it is adapted to enable transfer of pellets P from the chute 2 to a conveyor system not shown at the exit from the centreless grinder 10.

The assembly and arrangement of the entry guide 5 with the means of adjusting the alignment of the pivoting strip 31 are made in a similar manner for the exit guide 5, the adjustment means 6, 60, 61 of the pivoting strip 51 of the exit guide 5 being independent of the adjustment means 4, 40, 41 of the pivoting strips 31 of the entry guide 3.

Thus, the exit guide 5 comprises a fixed strip 50 approximately in line with the longitudinal edge 200 of the chute 2 and another strip 51 installed free to pivot to change the inclination relative to the other longitudinal edge 201 of the chute 2.

The strip 51 is installed free to pivot on an axis 510 provided with a polymer bearing installed in a support 52 arranged as a turret.

Mechanical means 6 are provided to adjust the alignment of the pivoting strip 51 relative to the edge 201 of the chute. These means are composed of two screws 60, 61 nested in each other in the upper part of the turret 52 (FIG. 3B). The first screw 60 is screwed into the support 52. The second screw 61 has a smaller pitch but similar to the pitch of the screw 60 and the screw 61 is fixed in rotation. Rotation of the screw 60 causes translation along its axis relative to the fixed support 52 (screw-nut connection). At the same time, this rotation of the screw 60 causes a second translation along its axis relative to the second screw 61. The difference in pitch results in a small translation of the bearing point of the screw 61 on the guide 51 which causes a rotation of the guide 51. Such adjustment means 6, 60, 61 are capable of achieving very precise adjustment of the alignment of the pivoting strip 51 to the nearest micrometer.

A spring 62 for compensation of functional clearances of the device is installed between the pivoting strip 51 and the support 52; it can thus provide a permanent bearing between the screw 61 and the strip 51 in the pivoted position.

As shown, the geometric shape and length of the outlet guide 5 are adapted to limit the number of ground pellets in the buffer and their exit speed. This prevents said pellets P from tipping on the conveyor system at the exit from the centreless grinder 10.

As shown in FIGS. 1 and 2, the device 1 according to the invention 1 forms a single piece assembly to which pivoting handles 70, 71 are fixed, adapted to enable the insertion into and withdrawal from a centreless grinder 10. This facilitates maintenance operations that are difficult in a glove box environment.

The assembly 1 is single piece because:

• • the turrets 32, 52 in which the pivoting strips 31, 51 are installed with adjustment means 4, 6 and
  • the supports 72 of handles 70, 71 to which the fixed strips 30, 50 are fixed, are fixed by screwing to the guide chute which is itself a single piece.

Although described as a reference to an application in a centreless grinder in which the functions of the device are insertion, guidance and evacuation of nuclear fuel pellets in a centreless grinder, any application that requires insertion, guidance and evacuation of cylindrical parts with very high precision to prevent any shift of the parts, could also be envisaged.

Claims

1. Device for the insertion, guidance and evacuation of cylindrical parts such as nuclear fuel pellets, in a centreless grinder, comprising: wherein the mechanical means for micrometric adjustment of the alignment of the entry guide are independent from the micrometric alignment means of the exit guide.

an insertion guide chute adapted to guide said cylindrical parts over the length of the grinding wheel and drive wheel of a centreless grinder,

a first guide, called the entry guide, arranged at one longitudinal end of the guide chute and adapted to allow the insertion of cylindrical parts one by one onto the guide chute from a conveyor system on the entry side of the centreless grinder,

mechanical means for micrometric adjustment of the entry guide relative to the guide chute,

a second guide, called the exit guide, arranged at the other longitudinal end of the guide chute and adapted to transfer parts from the chute to a conveyor system on the exit side from the centreless grinder,

mechanical means for micrometric adjustment of the alignment of the exit guide relative to the guide chute,

2. Device according to claim 1, in which the guide chute is a single piece part made of XC 38 steel, on which surface and in-core annealing and quenching heat treatments have been made and preferably surface treatments once the guide chute has been finished.

3. Device according to claim 1, in which at least one of the two guides is composed of two strips one of which is fixed and parallel to the longitudinal edge of the chute and the other is installed on a pivot that adjusts the space from the fixed guide facing it, the distance from the pivoting guide being varied by actuation of mechanical means for adjusting the alignment of said guide.

4. Device according to claim 3, in which the entry guide and the exit guide are each composed of two strips, one of which is fixed and parallel to a longitudinal edge of the chute and the other is free to pivot to adjust the spacing of the guide from the fixed guide facing it.

5. Device according to claim 3, in which the pivoting strip of the two guides is installed pivoting about an axis fitted with a polymer bearing.

6. Device according to claim 4, in which:

the pivot axis of the pivoting strip of the entry guide and/or the exit guide is (are) mounted in a support,

the mechanical micrometric means for adjustment of the alignment of the entry guide relative to the guide chute and/or the mechanical adjustment means of the exit guide comprise a first screw screwed into the pivot axis support and a second screw nested into the first screw, with a smaller pitch than the first screw and adapted to bear in contact with a part of the pivoting strip, screwing of the first screw into the support causing translation of the two screws while screwing the second screw into the first screw and bearing in contact with the part of the pivoting strip causes pivoting of the pivoting strip.

7. Device according to claim 6, in which the pitch of the second screw is smaller than but sufficiently close to the pitch of the first screw to create a micrometric adjustment of the pivoting strips.

8. Device according to claim 6, comprising a spring adapted to compensate for functional clearances of the device by guaranteeing permanent bearing between the second screw and the pivoting strip.

9. Device according to claim 7, in which each pivot axis and screw axis support is fixed to the guide chute.

10. Device according to claim 7, in which each pivot axis and screw axis support is shaped in a turret with the two screws nested in each other and arranged in the upper part of the turret.

11. Device according to claim 1, in which the geometric shape and the length of the exit guide are adapted to limit the number of ground cylindrical parts buffered at the exit from the wheels.

12. Device according to claim 1, forming a single piece assembly to which adapted handles are fixed to enable its insertion into and removal from a centreless grinder.

13. Centreless grinder comprising: wherein the mechanical means for micrometric adjustment of the alignment of the entry guide are independent from the micrometric alignment means of the exit guide.

an insertion guide chute adapted to guide said cylindrical parts over the length of the grinding wheel and drive wheel of a centreless grinder,

a first guide, called the entry guide, arranged at one longitudinal end of the guide chute and adapted to allow the insertion of cylindrical parts one by one onto the guide chute from a conveyor system on the entry side of the centreless grinder,

mechanical means for micrometric adjustment of the entry guide relative to the guide chute,

a second guide, called the exit guide, arranged at the other longitudinal end of the guide chute and adapted to transfer parts from the chute to a conveyor system on the exit side from the centreless grinder,

mechanical means for micrometric adjustment of the alignment of the exit guide relative to the guide chute,

14. Centreless grinder according to claim 13, adapted to grinding of nuclear fuel pellets (P).

15. Glove box in which a centreless grinder is arranged according to claim 13.

16. Device for the insertion, guidance and evacuation of cylindrical parts such as nuclear fuel pellets, in a centreless grinder, comprising: wherein the first plurality of screws for micrometric adjustment of the alignment of the entry guide are independent from the second plurality of screws for micrometric alignment means of the exit guide.

an insertion guide chute adapted to guide said cylindrical parts over the length of the grinding wheel and drive wheel of a centreless grinder,

a first guide, called the entry guide, arranged at one longitudinal end of the guide chute and adapted to allow the insertion of cylindrical parts one by one onto the guide chute from a conveyor system on the entry side of the centreless grinder,

a first plurality of screws for micrometric adjustment of the entry guide relative to the guide chute,

a second guide, called the exit guide, arranged at the other longitudinal end of the guide chute and adapted to transfer parts from the chute to a conveyor system on the exit side from the centreless grinder,

a second plurality of screws for micrometric adjustment of the alignment of the exit guide relative to the guide chute,

17. Device according to claim 15, in which the first plurality of screws and/or the second plurality of screws comprise a first screw and a second screw nested into the first screw.