US3604641A

US3604641A - Apparatus for hydraulic crushing

Info

Publication number: US3604641A
Application number: US7853A
Authority: US
Inventors: Joseph Dodman Wilson; Bertram Reginald Donoghue; John Lester Waddingham
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1969-02-10
Filing date: 1970-02-02
Publication date: 1971-09-14
Anticipated expiration: 1988-09-14
Also published as: GB1289121A

Abstract

The apparatus is for crushing samples in preparation for analysis. A support vessel receives and supports a comparatively thin walled sample container, which may be filled and sealed separately from the crushing apparatus. A clamp clamps the sample container in the support vessel and effects electrical connection between electrodes molded in situ in the sample container and plates connected across capacitors for providing high-voltage pulses. The thin walled sample container is disposable so that cross-contamination is avoided by using a new sample container for each sample to be crushed.

Description

United States Patent [72] Inventors Joseph Dodman Wilson Oxford;

Bertram Reginald Donoghue, Didcot; John Lester Waddingham, Abingdon, all of,

England Appl. No. 7,853 Filed Feb. 2, 1970 Patented Sept. 14, 1971 Assignee United Kingdom Atomic Energy Authority London, England Priority Feb. 10, 1969 Great Britain 7 168/69 APPARATUS FOR HYDRAULIC CRUSHING 8 Claims, 1 Drawing Fig.

US. Cl 241/301 Int. Cl 1302c 19/18 Field of Search 241/1 46,

[56] References Cited UNITED STATES PATENTS 3,208,674 9/1965 Bailey 241/l 3,352,503 l1/1967 Maroudas... 24l/30l 3,529,776 9/1970 Meszaros 241/301 X Primary ExaminerGranville Y. Custer, Jr. An0rneyLarson and Taylor ABSTRACT: The apparatus is for crushing samples in preparation for analysis. A support vessel receives and supports a comparatively thin walled sample container, which may be filled and sealed separately from the crushing apparatus. A clamp clamps the sample container in the support vessel and effects electrical connection between electrodes molded in situ in the sample container and plates connected across capacitors for providing high-voltage pulses. The thin walled sample container is disposable so that cross-contamination is avoided by using a new sample container for each sample to be crushed.

APPARATUS FOR HYDRAULIC CRUSHING BACKGROUND OF THE INVENTION The invention relates to apparatus for electrohydraulic crushing of samples for analysis.

A spark discharge taking place in a liquid causes intense shock waves to be set up in the liquid and, in electrohydraulic crushing, it is these shock waves which are used for crushing materialin the liquid. The technique is particularly useful .for crushing hard materials such as carbides or oxides which are difficult to crush by conventional techniques.

The present invention is based upon the appreciation that by making provision for avoiding or controlling contamination, the electrohydraulic crushing technique is particularly suitable for preparing samples of material, difficult to crush by conventional techniques, for subsequent analysis.

SUMMARY OF THE INVENTION The invention provides apparatus for electrohydraulic crushing of samples for analysis, which apparatus comprises a support adapted to receive a separately formed sample container having spaced electrodes therein, means for clamping the sample container in the support, and means for connecting the electrodes across a high-voltage source.

It is an important feature of the invention that the apparatus is constructed and arranged so that a sample container is supported over the whole, or substantially the whole, of its outer surface, whereby the sample container is supported against the explosive forces of electrohydraulic crushing therewithin. The sample container may thus be constructed of thin material such as may conveniently. be disposed of after use in crushing one sample. A new sample container may therefore be used for each analysis and the possibility for cross-contamination significantly reduced.

Preferably the support comprises a vessel, the internal shapeand dimensions of which correspond with the exterior shape and dimensions ofthe sample container. Preferably the clamping means includes a member which overlies the lid of a sample container when positioned in the support, the arrangement being such that the clamping pressure when applied,

serves to press the lid of the sample-container into tightly sealed engagement with the sample container body.

Preferably the arrangement is such that the clamping means simultaneously serves to press the lid as aforesaid and to press into electrical contact with the electrodes electrical contact members adapted for electrical connection to the high voltage source.

Preferably the high-voltage source provides'high-voltage pulses and comprises one or more capacitors, means for charging the capacitors and means for intermittently discharging the capacitors through the electrodes of a sample container clamped in the apparatus. Preferably the means for intermittently discharging the capacitors comprises an air, or other gas, gap between further electrodes in series with the electrodes of the samplecontainer. When thepotential across the capacitors has built up to a predetermined level, the airgap breaks down and discharge through the sample container is initiated. When the capacitors have discharged, arc discharge through the air gap ceases and recharging commences.

The invention also provides apparatus for electrohydraulic crushing of samples for analysis comprising opposed rigidly supported electrically conducting plates, one of which has an aperture therethrough, one or morecapacitors disposed between the plates and electrically connected across the plates, a support vessel of electrically insulating material received in the said aperture and having a flange overlying part of the plate, clamping means comprising a member adapted to overlie the lid of a sample container supported in the support vessel, and means for pressing the clamping member towards the said apertured plate, an electrical contact member provided in the support vessel and electrically connected, preferably via a switchable means such as an airgap, to the other of the said plates, an electrical contact member provided in or by the clamping member, the arrangement being such that when clamping pressure is applied with a sample container supported in the support-vessel,the clamping member applies sealing pressure to the lid of the sample container and electrical contact making pressure between electrodes in the sample container and the respective electrical contact members.

The invention includes a sample container for samples to be electrohydraulically crushed prior to analysis, which container comprises electrodes around which plastics material is molded, preferably injection molded, to form the container.

Specific constructions of apparatus for electrohydraulic crushing embodying the invention will now be described by way of example and with reference to the accompanying drawing, which is a diagrammatic sectional view of the apparatus.

In the example shown in the drawing the apparatus is for electrohydraulic crushing of small quantities of material for subsequent analysis. The apparatus comprises two

circular brass plates

11 and 12 between which are arranged five capacitors in a ring. Two of these

capacitors

13, 14 are visible in the drawing. Each of the capacitors has a working voltage of 60 kv. and a capacity of 0.005 microfarads. The capacitors are mechanically secured between the

plates

11 and 12 and are electrically connected across these plates. The plate 11 forms an earthed plate and means is provided at 15 for connecting the plate 12 to an l-LT. supply through a charging resistor (not shown).

The plate 11 has a centrally located aperture in which is received a support vessel 16. The support vessel 16 is cylindrical with an outside diameter of 2 inches and has an annular flange 17, of outside diameter 3 inches, for overlying the plate 1 l to locate and support the support vessel 16 in the aperture in the plate 11. The overall length of the support vessel l6'is, in this example, 2 7/16 inches and the upper end (as seen in the drawing) has an internal bore 18 of diameter 1 H2 inches extending 1 1/8 inches along the length of the support vessel 16. The bore 18 tapers to a bore 19 of diameter 7/ l 6 inches. A bore 21 of diameter 5/ 16 inches extends from the bottom end (as seen in the drawing) of the support vessel 16 into the bore 19, leaving an annular shoulder between the

bores

19 and 21.

The support vessel 16 is formed from an acetyl based plasticsv material such as Delrin (registered trade mark) by injectionmolding.

Extending out of the bore 21 in the support vessel 16 is -a brass electrical contact member 22 which is retained by its head 23 engaging the shoulder between the

bores

19 and 21, The brass contact member 22 is screw-threaded and has screwed on to it a dome-shaped electrode 24. Disposed opposite this electrode 24 is a similarly dome-shaped electrode 25 screwed into the plate 12. The

electrodes

24 and 25 both comprise brass in this example and define an airgap between them, the width of which is adjustable, to a limited extent, by-- screwing the electrode 24 up or down-the contact member 22. r

The

electrodes

24 and 25 and the airgap at 26 are enclosed within a tube of plastics material 27'which extends fromthe bottom of the support vessel 16 to the plate 12.

Received within the support vessel 16 is a sample container 28 which comprises a comparatively thin-walled container, the external shape and dimensions of which correspond to the internal shape and dimensions of the support vessel 16. In this example, the container is formed by injection molding from an acetyl based plastics material which, like that of the supportvessel 16, may be Delrin (registered trade mark). In this exam ple, the wall thickness of the sample container 28 is approximately Aainches. Secured in the bottom of the container 28 is an electrode 29. The electrode 29 is secured in position by molding the container 28 around the electrode in situ in the mold. The container 28 has an outwardly projecting annular flange 31 at the top for overlying the top of the support vessel The container 28 has a lid 32, also injection molded from acetyl based plastics material. The lid 32 is injection molded around an electrode 33 in situ in the mold. A sealing ring 34 is located in an annular groove in the part of the lid 32 which abuts against the outwardly protruding flange 31 of the sample container 28.

A cylindrical brass cap 35 fits over the sample container 28 and is adapted to be pressed into firm contact with the plate 1 1 by a toggle clamp 36. The dimensions of the support vessel 16 and the sample container 28 are arranged so that when the cap 35 is so clamped, the top of the cap 35 applies pressure upon the lid 32 to effect a firm seal between the lid 32 and the container 28 and also to make electrical contact from the plate 11 via the cap 35 to the electrode 33. The pressure is also transmitted through the sample container 28 to the electrode 29 to press this into contact with the contact member 22. It will be appreciated that the brass cap 35 provides an electrical contact member for the top electrode 33.

The whole apparatus is enclosed within a box-shaped enclosure 37 having a hinged lid 37a. A safety device 38 comprises an electrically conducting rod 39 slidable through an aperture near the edge of plate 11 and having a contact member at 41 aligned with a contact member 42 on the plate 12. A spring 43 biases the rod 39 in a sense tending to bring the

contact members

41 and 42 into contact with one another. With the lid 37a in position on the apparatus, the rod 39 is pressed downwardly against the action of spring 43 so that the

contact members

41 and 42 are spaced apart. When the lid is opened, the spring 43 moves the rod 39 upwardly, bringing the

contact members

41 and 42 into contact with one another and thereby discharging the capacitors.

' In operation, a sample to be crushed is contained, together with a suitable liquid, usually water, within the sample container 28 clamped in position. The l-LT. supply at 15 is switched on so that the

capacitors

13, 14 begin to charge up. The airgap 26 operates as a triggerable switch which triggers when the voltage appearing across it becomes high enough for disruptive discharge to occur across the airgap. When this happens, discharge across the

electrodes

29 and 33 in the liquid in the sample container 28 is initiated and continues until the capacitors are discharged to an extent such that the arc discharge across the airgap 26 can no longer be maintained. Recharging then commences and the cycle repeats.

It will be appreciated that the arrangement of this example in which the sample container 28 and airgap 26 are arranged centrally between two

plates

11 and 12 with the capacitors for charging the plates arranged around these operative components provides for a low inductance circuit. Cable strap connections are avoided, thus further reducing inductance, while the making of electrical connection between the

electrodes

29 and 33 with the

respective plates

12 and 11 is simply achieved by the clamping operation which also serves to secure and support the sample container. The importance of minimizing inductance is referred to in Patent Specification No. 1,021,786 in which it is explained that fast rise time is an important factor in securing the most rapid crushing to fine particle sizes. Within limits, for a given apparatus, the finer the ultimate particle size required, the longer the apparatus will have to be operated upon the particular sample.

it will be further appreciated that the sample container 28 with its lid 32 comprises a scalable enclosure readily removable from or insertable into the apparatus. Thus a container 28 may be filled with a sample at some remote location and sealed for subsequent treatment in the apparatus and, if desired, removed to a remote location before unsealing after crushing has been carried out. Further, as explained above, the removable sample container 28 and lid 32 does not have to be sufficiently robust to withstand explosive forces of the electrohydraulic crushing. Thus, the container-28 and lid 32 may be made thin enough and small enough to comprise an item which it is reasonable todispose of after using only once in the apparatus. In this example, the dimensions of the container 28 and lid 32 are chosen so that the container isself-supporting.

An important advantage of this example which provides a disposable sample container is that the risk of cross-contamination from one sample to the next is avoided or reduced.

The material for the

electrodes

33 and 29 is chosen according to the elements which are to be searched for in the sample for analysis and also depending upon the method in which the sample is to be analyzed. The electrode material must, of course, not comprise hard or brittle material likely to be seriously damaged by the electrical discharge. For example, where the sample is subsequently to be analyzed spectrographically by introducing the sample into an are between copper electrodes, then the material selected for the

electrodes

29 and 33 of the electrohydraulic crusher will be high purity copper. Another material frequently employed istitani um.

In a modification of the apparatus a slightly different clamping and safety system has been employed. in the modification an earthed casing encloses all the components below the plate 11.- The clamping system and the support vessel 16 are accessible on the top of the casing, without having to lift a lid. The clamping system comprises a clamp arm, pivoted on one side of the support vessel to a releasable locking mechanism. A downwardly extending toothed arm on the end of the clamp arm remote from the pivot is engageable in the releasable locking mechanism, which is fixed to the casing. Pressure is applied manually to the clamp arm and is maintained by the engagement of the toothed arm in the releasable locking mechanism. The releasable locking mechanism can be released only with a special key, the releasing movement of which is also operative to earth the lower plate 12. The same key is used for turning on a separate switch to the high-voltage power supply. The key cannot be removed from this switch without turning it off. Thus, the clamp cannot be released without turning off the power supply and discharging the capacitors.

The invention is not restricted to the details of the forcgoin examples. For instance, the material of the support vessel 16 and sample container 28 need not necessarily comprise Delrin (registered trade mark) but may for example comprise any other tough, shock-resistant, nonconducting and noncontaminating material such as, for example, nylon.

We claim:

1. Apparatus for electrohydraulic crushing of samples for analysis, which apparatus comprises support means for supporting a separately formed sample container comprising a lid and a body and having spaced electrodes therein, means for clamping the sample container in the support, and means for connecting the electrodes across a high-voltage source.

2. Apparatus as claimed in claim 1, wherein the support comprises a vessel, the internal shape and dimensions of which correspond with the exterior shape and dimensions of the sample container.

3. Apparatus as claimed in claim 2, wherein the clamping means includes a member which overlies the lid of the sample container when positioned in the support vessel, the clamping pressure serving to press the lid of the sample container into tightly sealed engagement with the sample container body.

4. Apparatus as claimed in claim 3, wherein the clamping means simultaneously serves to press the lid as aforesaid and to Press into electrical contact with the said electrodes electrical contact members connectable to the high-voltage source.

5. Apparatus as claimed in claim 1, wherein the high-voltage source provides high-voltage pulses and comprises one or more capacitors, means for charging the capacitors and means for intermittently discharging the capacitors through the electrodes of a sample container clamped in the apparatus.

6. Apparatus as claimed in claim 5, wherein the means for intermittently discharging the capacitors comprises a gas gap between further electrodes in series with the electrodes of the sample container.

7. Apparatus for electrohydraulic crushing of samples for analysis comprising opposed rigidly supported electrically conducting plates, one of which has an aperture therethrough,

one or more capacitors disposed between the plates and electrically connected across the plates, a support vessel of electrically insulating material received in the said aperture and having a flange overlying part of the plate, clamping means comprising a member adapted to overlie the lid of a sample container supported in the support vessel, and means for pressing the clamping member towards the said apertured plate, an electrical contact member provided in the support vessel and electrically connected to the other of the said plates, an electrical contact member provided by the clamping member, whereby when clamping pressure is applied with a sample con-

Claims

7. Apparatus for electrohydraulic crushing of samples for analysis comprising opposed rigidly supported electrically conducting plates, one of which has an aperture therethrough, one or more capacitors disposed between the plates and electrically connected across the plates, a support vessel of electrically insulating material received in the said aperture and having a flange overlying part of the plate, clamping means comprising a member adapted to overlie the lid of a sample container supported in the support vessel, and means for pressing the clamping member towards the said apertured plate, an electrical contact member provided in the support vessel and electrically connected to the other of the said plates, an electrical contact member provided by the clamping member, whereby when clamping pressure is applied with a sample container supported in the support vessel, the clamping member applies sealing pressure to the lid of the sample container and electrical contact making pressure between electrodes in the sample container and the respective electrical contact members.

8. A sample container for samples to be electrohydraulically crushed prior to analysis, which container comprises electrodes around which plastics material is molded to form the container.