EQUIPEMENT FOR THE GRINDING OF MATERIAL SAMPLES

Abstract: Equipment for the grinding of material samples, for instance the grinding of a rock sample assembled on a microscope slide includes a console and a frame structure (1) with a turntable (3) which is arranged to hold a number of material samples. Above the turntable is arranged at least one vertical moveable grinding spindle (2). A programmable control unit (4) controls the grinding process.

Description: Equipment for the grinding of material samples The present invention relates to equipment for the grinding of material samples, for instance microstructure grinding of a rock sample assembled on a microscope slide. By extraction of oil and gas from an underground formation (rock) it is of basical importance to obtain knowledge of the nature of this formation. This is obtained inter alia by studying microstructures of the rock in question in a microscope to form an idea of the rock's porosity and structure. A grinding is produced at first by cutting a piece of the rock and impregnate it. Then the impregnated piece is surface ground before it is assembled on a microscope slide and finally ground. The most common grinding method is based on so-called "patching", i.e. that silicon carbide grain in water suspension is supplied to a rotary cast iron disk, the material samples (the microscope slide with the samples) are assembled to one or more rotary holders and are pressed towards the rotary cast iron disk. By this type of equipment and method the silicon carbide grains as such act as grinding compound and the thickness is reduced gradually to about 30 μm. The known method and equipment is, however, encumbered with several disadvantages. Firstly, the grinding grains are pressed into the epoxy plastic in the material samples during the "patching"-process and appear as black particles in the pores in the ground material samples. This, in the worst case, may make samples unsuitable for further analyses. Secondly, the rotary cast iron disk may obtain an oblique surface during the grinding operation and has to be adjusted frequently. This involves considerable more work. The obliquity in the cast iron disk may also lead to considerable unevenness in the material samples and therefore cannot be used for further testing. A further disadvantages of the known equipment is that it require supervision of an operator and is therefore expensive to use. By the present invention there is provided an equipment for grinding material samples where the disadvantages mentioned above are eliminated, i.e. which is essentially easier to use, gives essentially greater precision during the grinding operation, avoids the penetration of the grinding grains in the material samples, involving minimal contribution of the operator, gives essentially finer and smoother surface of the finished, ground material samples, saves time in connection with later polishing of the surface of the material samples, has greater grinding capacity. The equipment according to the invention is characterised in that it includes a rotating table (a turntable) on which the material samples are realisably provided whereby the grinding takes place in at least one step by the means of at least one vertically moveable grinding spindle arranged above the turntable, as defined in claim 1. The independent claims 2-10 defines preferred features of the invention. The invention will now be further described by means of examples and with reference to the drawings where: Fig. 1 shows a) a front view, b) a side view and c) a top view of the grinding equipment in accordance with the invention, Fig. 2 shows in a larger scale a support for the grinding spindle which is included in the equipment, and Fig. 3 shows seen from the top and on an enlarged scale a turntable according to the invention. Fig. 4 shows two examples of material samples which are ground by the means of a) grinding equipment according to the invention and b) known equipment by "patching" respectively. The equipment according to the invention includes as shown in the Fig. 1 four main components, namely a frame- and a console structure 1, a grinding spindle arrangement 2, a turntable 3 and a control unit 4. The frame- and console structure 1 is designed to absorb great energies during the grinding operation when the equipment is used and is therefore made of strong steel beams and - stiffeners 5, 6, 7 to secure sufficient stability and prevent unevenness of the grinding samples. Concerning further details about the frame- and console structure, it is submitted that such details would lay within the competence of a person skilled in the art and will therefore not be further described here. The grinding spindle arrangement 2 comprises, as shown in Fig. 1, two grinder spindles provided above the turntable 3, one rough- and one fine spindle, each being driven by an electric motor 8. Each spindle and motor unit 2,8 are supported by a sledge or a carriage 9 which is movable in the vertical direction along rails 10 in the console structure. The carriage 9, and with the spindles 2, can be moved up or down by means of a high precision nut/screw arrangement 11 which is operated by a servomotor 12. The equipment according to the invention is as mentioned above designed to be able to finely grind material samples to a thickness of 20-30 μm and with a precision of ± 1 μm. To avoid deviations of the grindings by reason of thermal expansion the grinding spindle is supported in a special support 13 on the sledge 9 which is further shown in an enlarged scale in Fig. 2. In detail is shown Teflon packings 14, angular contact ball bearing 15 and 16, cup springs 17, radial contact ball bearing 18, lock nut 19, spindle shaft 20 and a centring ring. In the support is used bearings as mentioned above with different dimension and ball numbers because this will prevent that the ball raceway from producing undesirable patterns in the grinding surface of the material samples. The cup springs produce a constant pressure towards the bearing 18, respectively the low trust bearings 15, 16 which result in that any overheating of the spindle does not create inaccuracy toward the grinding surface. The spindle shaft is in other worlds free to expand in the direction upwards. The Teflon seal has low friction which creates low heat generation in the spindle house. As to the grinding spindles as such, they consist of diamond particles bound in a metal material formed as disks 21 , preferably formed as a cup to obtain good cooling during the grinding operation. The use of diamond disks represents an essential advantage of the invention, since the material samples get entirely clean and free from unwanted particles in the structure of the ground material. In Fig. 4 it is shown two examples of material samples which are ground by the means of a) grinding equipment according to the invention and b) known equipment by "patching" respectively. From Fig. 4 b) it follows that there is several unwanted particles 30 in the material structure. The material samples shown in Fig. 4 a) have no such particles. The turntable 3 (see Fig. 2) which constitutes the third important element in the invention, comprises a circular disk which via a belt 22 or the like is driven by an electric motor 23. The disk 3 with drive gear 22, 23 is arranged on a carriage, sledge or the like 24 which is movably provided on rails 25 on the frame structure 5. The carriage can suitably be driven by means of a servomotor via a nut/screw arrangement similar the solution which is used for the raising and lowering of the grinding spindles 2. By arranging the turntable 3 movable as mentioned above, there is provided combined oscillatory and rotary grinding motion for the material samples which give a smooth and exact (cover totally) grinding of these. The material samples to be ground are releasably held in position on the turntable 3 by means of vacuum. Fig. 3 shows on an enlarged scale a turntable 3 in accordance with the invention seen form the top. The turntable is made of brass, free from material tension, and has several holes 28 communicating with grooves or recesses 31 which are arranged in a pattern at some distance form one other and which are connected to a vacuum source (not shown). Totally the table shows forty of such holes with grooves which can hold an equivalent number of such samples. During the grind process water is supplied to the turntable to cool the material samples via one or more nozzles provided above the table. This is not further shown in the figures. The fourth important part which is included in the present invention is a programmable logic control (PLC) which constitutes the control system 4 for the solution. The operation of the PLC-unit can suitable take place via a so-called "touch screen display" where different menus with touch buttons are used to control the grinding equipment. The whole control system is provided in connection with a control board arranged on the grinding equipment, or preferably on a separate control board providing easy access for the operator. This kind of PLC-unit which is used, does not as such represent anything patentable since it is available on the market, and therefore the technical solution of the PLC-unit will not be further described. However, in the following a brief description will be given with regard to how the grinding machine can be operated by means of the PLC-unit. When the main switch is turned on all the "axis" which are showing the turntable and the grinding spindles will move to zero point called "origo". Simultaneously the text "origo search" will be displayed at the operator display. When the equipment is ready to be used a main menu will be displayed on the display. For instance one can choose between automatic grinding of rock samples, automatic grinding of sheet of glass or manual grinding. By choosing manual grinding in the main menu, a sub menu will appear with choices related to the running of the turntable and choices of which grinding motor is desirable to use. If fine or rough- grinding is chosen, another sub menu will appear where manual running of the grinding procedure is carried out. It is here also possible to get into and save (memorise) reference points which later can be used for fully automatic grinding with the machine. I.e., by grinding a sample and by saving the reference points, the machine can automatically execute a repetition of the grinding procedure. Choice of end positions for the oscillating movements of the turntable is performed on a separate menu. On this menu the speed for automatic grinding also can be programmed. Before automatic grinding is chosen, the material sample are at first placed on the turntable and vacuum and cooling water is turned on. Thereafter automatic glass sample grinding or automatic rock sample grinding is chosen from the main menu. When this is done the respective sub menus appear and it is possible to start and stop the grinding procedure wherever in the program. Here the whole grinding procedure can be executed with rough and fine grinding and with simultaneous oscillation of the turntable until the grinding operation is finished. Then the turntable will move back to the starting point and the material samples are ready for further treatment and analyses. As to the grinding operation it should be noted that it is preferable to use two grinding wheels as described above, since the grinding time is reduced. In this case the material samples are rough-grinded to a suitable thickness at first, for instance 100 μm, with the rough grinding disk, before they are ground by the fine grinding disk to the desired thickness, for instance about 30 μm. The invention as defined in the claims is, however, not limited to two grinding disks, but can be provided with only one, or more than three disks of this kind.

Claims: Claims 1. Equipment for the grinding of material samples, for instance micro structure grinding of rock samples assembled on a microscope slide, characterised in that it includes a console- and a frame structure (1) with a turntable (3) which is designed to realisably hold a number of material samples, at least one vertical moveable grinding spindle (2) arranged above the turntable, and a programmable control unit (4) for controlling of the grinding process. 2. Equipment according to claim 1 , characterised in that it includes two grinding spindles (2), one for rough grinding and one for fine grinding of the material samples. 3. Equipment according to claim 1 or 2, characterised in that the grinding spindles are fitted with a grinding disk (21) of metal bound diamond particles. 4. Equipment according to claim 3, characterised in that the grinding disk (21) is formed as a cup. 5. Equipment according to the preceding claim 1-4, characterised in that the grinding spindle(s) are arranged on a carriage or a sledge (9) which is movable in the vertical direction along rails (10) by the means of a servomotor via a screw/nut arrangement. SUBSTITUTE SHEET 6. Equipment according to claim 1, characterised in that the turntable (3) is designed to oscillate laterally relative to the turntable and the grinding spindles. 7. Equipment according to claim 6, characterised in that the turntable is arranged on a carriage or a sledge (24) which is provided on and is movable along rails (25) by the means of a servomotor (27) via a screw/nut arrangement (26). 8. Equipment according to claim 6-7, characterised in that the turntable is designed to hold material samples by means of vacuum, in that it is supplied with a number of holes (28) which are connected to a vacuum source, and which are arranged in a pattern along the circumference of the turntable. 9. Equipment according to claim 1-8, characterised in that the shafts (20) for the turntable (3) and the grinding spindles (2) respectively are pre set relative to the trust bearings (15, 16) by the means of a spring arrangement (17) in such a way that the shaft is free to expand at heat influence without displacing of the turntable or the grinding spindle/s. 10. Equipment according to claim 9, characterised in that the shaft is supported in two trust bearings, one arranged towards the other, in that the bearings (16, 17) are of the angular contact ball bearing type with different diameter and number of balls.

Inventors: THORESEN BJOERN, THORKILSEN GEIR, THORESEN, BJOERN, THORKILSEN, GEIR
Applicants: NORSK HYDRO AS, THORESEN BJOERN, THORKILSEN GEIR, NORSK HYDRO A.S, THORESEN, BJOERN, THORKILSEN, GEIR
Application year: 1995
Main classification: G01N1
IPC codes: B02C7, B24B7, B24B27, B24B51, B24D7, G01N1