IE20000089A1

IE20000089A1 - High Pressure High Temperature Apparatus

Info

Publication number: IE20000089A1
Application number: IE20000089A
Authority: IE
Inventors: Claes Mannerfelt; Stefan Ederyd
Original assignee: Sandvik Ab
Priority date: 1999-02-19
Filing date: 2000-02-14
Publication date: 2000-10-04
Also published as: SE9900594D0; KR20010006648A; CN1263793A; SE9900594L; JP2000237575A

Abstract

The present invention relates to a cemented carbide annular die for high-pressure, high-temperature (HPHT) processes such as synthesis of diamond or cubic boron nitride (cBN). Said die is provided with cooling channels. A dramatic and unexpected increase in performance has been obtained.

Description

present invention relates to a high pressure high temperature (HPHT) apparatus, which basically comprises an 5 annular die and a pair of tapered punches. By providing the annular die with cooling channels a dramatic and surprising increase in performance has been obtained.

Punch-and-die apparatus are favoured in industrial manufacture of synthetic diamond and CBN(cubic boron nitride), or for making PCD (polycrystalline diamond compacts) and PCBN (polycrystalline cubic boron nitride compacts) for their simplicity in general of construction and a relatively large volume available for the processing part. It consists of an annular die and a pair of tapered punches in opposed and axial Alignment therewith. The inner diameter of the die is generally T3|bout 5 cm and the outer diameter about 15 cm. The punches and the die are generally made of cemented carbide. The composition **··· i O<|f the dies and the punches are chosen so that the hardness of tjhe dies is more than 1100 HV and that of the punches higher T tjhan 1500 HV. Both die and punches are shrunk into a steel ring v|ith an outer radius of about 35 cm. Such apparatuses generally ^.cperate at pressures and temperatures where diamond or cBN is Potable i.e. pressures of the order of 60 kilobars simultaneously Ο j «»?at temperatures of several hundreds above 100 0 °C. Such processes δ J ^qre herein referred to as HPHT-processes. Heating is obtained by ^.rpassing an electrical current through the cemented carbide punches and the diamond or cBN charge. Although the heat generated in the diamond or the cBN charge is thermally and electrically isolated from the die a certain increase in temperature of the cemented carbide can not be avoided. The part of the cemented carbide close the charge may very well reach a temperature of about 200 °C. This may affect the strength of the cemented carbide tools used in HPHT process, i.e. die and punches. In order to keep a controlled temperature of the die it is generally subjected to cooling with water on the end surfaces.

Because of the extreme conditions subjected to the punches and the die these only can be used for a limited number of cycles before they have to be replaced. Generally the reason for replacement is cracks in the outer part of the die or spalling.

IE 000089 The punches are relative cheap and easy to replace. The die however is because of its larger volume far more expensive than the punches. It is also more difficult to replace. It is therefore an object of the present invention to provide an annular die with improved properties.

Fig 1 shows a punch-and-die-apparatus in which A - punch B - annular die Fig 2 shows an annular die according to the invention in which cooling channels have been placed into the cemented carbide die. The orientation of the cooling channels is in the axial direction of the die.

Fig 3 shows an alternative solution to place cooling channels in the outer cylindrical surface of the die.

It has now surprisingly been found that an unexpected and an almost tenfold increase in performance of a die is achieved if the die is provided with cooling channels extending from the top to the bottom surface of the die. These cooling channels seem not to affect the strength of the die but instead the temperature is lowered below some critical point. The cooling channels shall be located at a certain distance from the centre of the die. They shall not be too close because then the strength may be affected.

According to the invention the die shall be provided with 525 cooling channels equidistantly located on a circle with a diameter in the range: outer diameter (OD) to two times the inner diameter (ID). Channels located on the outer diameter of the die are of course present as grooves in the outer cylindrical surface. The dimensions of these channels shall be such that they occupy an area up to 2000 mm2 of the end surface of a typically dimensional die. The cooling channels can be straight but they can also be helical or twisted.

The cooling channels can be obtained by several methods known in the art. They can be drilled or milled in the presintered state. They can also be made by placing some material or metal that melts during sintering. They can also be made by making the die of two rings of which the inner has grooves in its external surface.

The invention also relates to a method of synthesising diamond or CBN under high pressure/high temperature conditions IE 000089 using a cemented carbide annular die. The method is characterised in using an annular die, which is cooled by being provided with cooling channels. Preferably the temperature of the cooling medium shall be <10 °C.

Example A number of six annular dies were tested. The dies were made of cemented carbide with dimensions: OD=127 mm, ID=40 mm. The composition of the cemented carbide was 11% Co and 89% WC with a hardness of 1330HV. In the presintered state 15 holes 06 mm were drilled regularly distributed on a circle with diameter 105 mm.

The dies were tested in an 1800 ton diamond press and it was found that they lasted 22460 runs in average. Similar prior art dies i.e. without cooling channels only last 3200 runs.

Claims

1. Annular die for HPHT processes c h in being provided with cooling channels or from the top surface to the bottom surface 5

2. Annular die according to the previous claim characterised in being made of cemented carbide.

3. Annular die according to the previous claims 1 and 2 characterised that said channels are straight.

4. Annular die according to claim 1 and 2 10 characterised that said channels are helical or twisted.

5. A HPHT process performed in an apparatus consisting of an annular die and two opposing punches characterised in that said annular die is cooled by being provided with 15 cooling channels.

6. A process according to claim Scharacterised in that said annular die is cooled by a cooling medium with a temperature <10 °C.

7. Annular die for HPHT processes substantially as herein described with reference to the accompanying drawings.