GB2256709A - Quantometer sample holder - Google Patents

Abstract

The holder (24) comprises a cylindrical housing (28) having an open first end (32) and a second end (34). The first end is positionable around an aperture (18) in a table (10) of a quantometer within which an electrode (20) is fixed in position; a chuck (30) positioned within the housing adjacent the second end and movable relative thereto, the chuck having jaws (38) directed towards the first end of the housing, the jaws being capable of gripping a sample; adjusting means (42, 44) for adjusting the separation of the jaws in order to move the jaws towards one another to grip the sample to be analysed therebetween, the adjusting means extending through the second end of the housing; and securing means (50) for securing the chuck in the housing, the adjusting means and/or the securing means being actuable to position the end of a gripped sample a predetermined distance from the first end of the housing. <IMAGE>

Description

QUANTOMETER SAMPLE HOLDER This invention relates to a device for holding samples for analysis in a quantometer.

A quantometer is an instrument that shows by spectrographical analysis the percentage of the various elements present in a metallic sample (Chambers English Dictionary - published in 1988).

In such a known instrument, a tungsten or other suitable electrode is fixed in position in an aperture of predetermined diameter (usually 16mm) in a table a predetermined distance (which is less than the radius of the aperture) below the upper surface of the table. A sample to be analysed is placed across the aperture in the table, with an analytical gap (due to the predetermined distance) between the lower surface of the sample and the tungsten electrode. An electrical contact is brought into contact with the upper surface of the sample. An inert atmosphere is formed around the sample and tungsten electrode by flowing argon across the analytical gap to eliminate any air present.The electrical contact and tungsten electrode are connected to a source of electrical energy in a pre-integration step in which a high-energy spark is generated across the analytical gap between the sample and the tungsten electrode, which spark melts and thus homogenises a small part of the sample's surface (approximately 4 to 5 mm diameter). This is followed by an integration step in which sparking takes place with less energy so as to spark a smaller surface than previously and to have a more homogenous plasma during integration. During this period the light emitted is analysed by a spectrometer.

This arrangement works well for samples which have a diameter which is greater than that of the aperture. However, for samples of a diameter which is less than that of the aperture, a problem arises. Simply reducing the size of the aperture in the table is not feasible as this brings the table closer to the tungsten electrode, and generates a risk of the spark passing between the tungsten electrode and the table, rather than the sample.

Moving the tungsten electrode nearer the sample does not rectify this problem, as the predetermined distance between the sample and the tungsten electrode must be great enough to produce a spark which is of a size that is adequate for analysis. To overcome this problem of the smaller sized samples, the size of the aperture has been reduced using an annular insert of electrically insulating material, such as a ceramic. However, such annular inserts have the disadvantages of a very short working life (the inner edge is eaten away very quickly by the spark), and also have a limitation on the size of the sample that can be analysed. In these known arrangements, samples above 16mm diameter can be placed directly on the table, and samples between 7mm and 16mm diameter can be analysed using the annular insert. However, samples below 7mm diameter cannot be analysed.

It is an object of the present invention to overcome the above disadvantages due to size limitations, and remove/reduce the need to use an annular insert.

To this end, a quantometer sample holder in accordance with the present invention comprises a cylindrical housing having a first end which is open and a second end, the first end being positionable around an aperture in a table of a quantometer within which an electrode is fixed in position; a chuck positioned within the housing adjacent the second end and movable relative thereto, the chuck having jaws directed towards the first end of the housing, the jaws being capable of gripping a sample; adjusting means for adjusting the separation of the jaws in order to move the jaws towards one another to grip the sample to be analysed therebetween, the adjusting means extending through the second end of the housing; and securing means for securing the chuck in the housing, the adjusting means and/or the securing means being actuable to position the end of a gripped sample a predetermined distance from the first end of the housing.

With this arrangement, samples having substantially any size below 16mm diameter can be held by the chuck for analysis in the quantometer.

In practice, due to restrictions of sparking characteristics and design, samples below 3.5mm diameter are unlikely to be analysed as an area of not less than 3.5mm diameter is usually melted by the spark. However, the present invention may be used for smaller sized samples should the need arise.

This invention removes the need for an annular ceramic insert to be placed in the aperture, and also allows samples of a smaller size to be analysed. The upper limit of 16mm diameter could be increased, where required, dependent on the size restrictions of the chuck.

In usual circumstances, the chuck would be secured in position and the adjusting means actuated such that the end of a gripped sample is aligned with the first end of the housing.

Preferably, the chuck comprises a main body portion; and the adjusting means comprises an actuating body which is screw-threaded in the main body portion and which engages the jaws for adjustment thereof, and a rod secured to the actuating body. In this case, the second end of the housing is preferably substantially closed, and the rod of the adjusting means passes though an opening in the second end.

The securing means is preferably a grub screw passing through a threaded aperture in a wall of the housing.

Preferably, a vent opening is formed in a wall of the housing.

The chuck can preferably grip samples having a diameter in the range 3.5mm to 16mm.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a table and tungsten electrode in a quantometer; Figure 2 is a cross-sectional view of a quantometer sample holder in accordance with the present invention placed in position on the table of Figure 1; and Figure 3 is a cross-section view of an alternative chuck for a quantometer sample holder in accordance with the present invention.

Referring to Figure 1, a table 10 of a quantometer is shown in which a plate 12 is positioned in a suitable slot 14 in the table surface 16. The plate 12 has an aperture 18 therein above a tungsten electrode 20. The electrode may be made of any other suitable material. The aperture 18 has a preferred diameter of 16mm, and the upper end of the tungsten electrode 20 is preferably 6mm below the upper surface 22 of the plate 12. The upper surface 22 of the plate 12 and the table surface 16 lie in substantially the same plane. The remaining features of the quantometer are well known to those skilled in the art. In use, a metallic sample to be analysed, and having a diameter of more than 16mm, is placed across the aperture 18. An electrical contact is brought into contact with the upper surface of the sample.The atmosphere around the sample and tungsten electrode 20 is replaced by an inert atmosphere (preferably argon), and the tungsten electrode and electrical contact are connected to a suitable electrical power source. As the power from the source is increased, a high-energy spark is generated between the sample and the tungsten electrode across the 6mm gap, and this spark melts and thus homogenises a small part of the surface of the sample. This is followed by an integration step in which sparking takes place with less energy so as to spark a smaller surface than previously and to have a more homogenous plasma during integration.

During this period the light emitted is analysed by a spectrometer to determine the percentage of the various elements present in the metallic sample. The above described arrangement is well known to those skilled in the art, and will not be described in greater detail. Whilst this arrangement works well for samples having a diameter of more than 16mm, problems obviously arise with smaller samples, especially those below 7mm in diameter.

The present invention overcomes these problems by providing a new and improved quantometer sample holder 24, as shown in Figure 2. The quantometer sample holder 24 is positioned on the table 10 above the aperture 18 in the plate 12 such that its longitudinal axis 26 is aligned with the centre of the aperture. Such alignment can be achieved by any suitable means, such as pegs or V-blocks (not shown) positioned on the table 10. The quantometer sample holder 24 comprises a cylindrical housing 28 made from electrically conducting material; and a chuck 30 also made from electrically conducting material. The housing 28 has a wall 29 defining a bore 31; and a first end 32 which is open, and which in use rests on the table 10. The other (second) end 34 of the housing 28 is substantially closed.The chuck 30 comprises a main body 36 and a number of jaws 38 (preferably three, which provide self-centring) which are movable relative to the main body into and out of a tapered central bore 40. The chuck 30 is positioned inside the bore 31 of the housing 28 with the jaws 38 directed towards the first end 32. The jaws 38 are biased away from one another to remain in contact with the surface of the tapered central bore 40. As the jaws 38 are moved downwards, out of the tapered central bore 40, the jaws move towards one another and can grip a sample therebetween. With the present invention any suitable sized samples may be gripped for analysis.

However, sparking restrictions usually mean that the lower limit is samples down to 3.5mm in diameter.

The jaws 38 are moved relative to the main body 36 by adjusting means comprising an actuating body 42, which is screw-threaded in the main body 36, and a rod 44 which has a tapered end 45 which makes a friction grip in a correspondingly tapered bore in the actuating body. The rod 44 extends through an opening 46 in the closed end 34 of the housing 28, and has a hand-grip portion 48 outside the housing for manual operation of the adjusting means. The actuating body 42 engages the jaws 38. Rotation of the rod 44 rotates the actuating body 42 relative to the main body 36, and moves the actuating body along the longitudinal axis 26, such longitudinal movement causing the jaws 38 to move in a similar direction into or out of the tapered central bore 40.

The chuck 30 is secured in the bore 31 of the housing 28 adjacent the closed end 34 by securing means comprising a grub screw 50 which passes through a threaded aperture 52 in the wall 29 of the housing.

This arrangement allows the position of the chuck 30 relative to the first end 32 of the housing 28 to be adjusted if required. For most samples there is an optimum position for the chuck 30 within the housing 28 which is set by the grub screw 50. Once in position, the chuck 30 rarely needs to be moved relative to the housing 28. A sample is cut to a known length, placed in the chuck 30, and lightly gripped. The quantometer sample holder 24 is then placed on a smooth flat surface, and the sample is released allowing the end of the sample to become aligned with the first end 32 of the housing. The adjusting means of the chuck 30 are then tightened to grip the sample, thereby automatically centring the sample, and placing its end at the preferred predetermined distance from the tungsten electrode 20 when the housing 28 is placed on the table surface 16.The position of the chuck 30 relative to the housing 28 is usually only adjusted by actuation of the grub screw 50 when non-standard samples are to be analysed. In such cases, when a sample for analysis is gripped by the jaws 38, the position of the chuck 30 can be adjusted such that the gap between the sample and the tungsten electrode 20 is at the preferred predetermined distance of 6mm. In most cases, this means the end of the sample is aligned with the first end 32 of the housing 28.

In use, the quantometer sample holder 24 is positioned as shown in Figure 2, with a sample to be analysed gripped by the jaws 38 of the chuck 30 a predeteremined distance from the tungsten electrode 20. An electrical contact 54 is brought into contact with the housing 28, and the housing and the chuck 30 provide an electrically conductive path between the electrical contact and the sample. The normal atmosphere around the sample and the tungsten electrode 20 is replaced by an inert atmosphere, such as argon - a vent opening 56 through the wall 29 of the housing 28 assists in the flushing of the normal atmosphere out of the housing by its replacement, argon.Electrical power from a suitable power source is then applied between the electrical contact 54 and the tungsten electrode 20, and increased to generate a spark between the sample and the tungsten electrode which can be analysed in the usual way.

It will be appreciated that the present invention can be used to grip samples having any suitable diameter, up to (and beyond, if required) 16mm; that is, within the limits imposed by the chuck and by operation of the quantometer.

Figure 3 shows a modified version of the chuck 30 shown in Figure 2, and like parts have been given the same reference numeral but with the addition of a prime ('). In this modified version of the chuck 30', the jaws 38' are biased away from one another, and into contact with the surface of the tapered central bore 40', by helical springs 58.

Various other modifications could be made to the above described embodiment. For example, the grub screw could be replaced by any other suitable means for securing the chuck in position.

Claims (7)

Claims:

1. A quantometer sample holder comprising a cylindrical housing having a first end which is open and a second end, the first end being positionable around an aperture in a table of a quantometer within which an electrode is fixed in position; a chuck positioned within the housing adjacent the second end and movable relative thereto, the chuck having jaws directed towards the first end of the housing, the jaws being capable of gripping a sample; adjusting means for adjusting the separation of the jaws in order to move the jaws towards one another to grip the sample to be analysed therebetween, the adjusting means extending through the second end of the housing; and securing means for securing the chuck in the housing, the adjusting means and/or the securing means being actuable to position the end of a gripped sample a predetermined distance from the first end of the housing.

2. A quantometer sample holder as claimed in Claim 1, wherein the chuck comprises a main body portion; and wherein the adjusting means comprises an actuating body which is screw-threaded in the main body portion and which engages the jaws for adjustment thereof, and a rod secured to the actuating body.

3. A quantometer sample holder as claimed in Claim 2, wherein the second end of the housing is substantially closed, and the rod of the adjusting means passes though an opening in the second end.

4. A quantometer sample holder as claimed in any one of Claims 1 to 3, wherein the securing means is a grub screw passing through a threaded aperture in a wall of the housing.

5. A quantometer sample holder as claimed in any one of Claims 1 to 4, wherein a vent opening is formed in a wall of the housing.

6. A quantometer sample holder as claimed in any one of Claims 1 to 5, wherein the chuck can grip samples having a diameter in the range 3.5mm to 16mm.

7. A quantometer sample holder substantially as hereinbefore described with reference to, and as shown in, Figure 2 or Figure 3 of the accompanying drawings.