How To Check The Performance Of A Composite PDC Cutters?

1. Wear resistance

The wear resistance of the PDC Cutters is generally measured by the wear ratio, but so far there is no unified test standard in the world, and several major PDC producing countries have their own test methods.

For example, the method adopted by GE in the United States is to use PDC to turn a granite rod with a uniform structure, the cutting speed is 180 m/min, the depth of cut is 1 mm, and the feed rate is 0.28 mm/r. Use a dynamometer to measure the force of the PDC during turning. After turning a certain amount of granite, the wear amount of the PDC was observed.

The wear amount is measured by the projection microscope of the length and width of the worn part, and then the volume is calculated by a computer for comparison.

The UK's DeBeers approach is similar to GE's. The former Soviet Union's determination of PDC wear resistance is to use PDC to plan the quartz sandstone from the designated area. Quartz sandstone was mined from the Torrez open-pit mine in the Donets region, with dimensions of 500mmx300mmx250mm.

The PDC is fixed on the cutter of the planer. During the test, the cutting speed is 0. 55m/s, the depth of cut is 0. 5mm, the lateral feed is 2. 8m/stroke, and the cutting length of each PDC sample is 501 m. . The PDC wear value is the line height (measured with a tool microscope, the error is 0.03 mm) of the center portion while the diamond layer is worn.

These two methods have their own advantages. The grinding wheel can be used to standardize the standard. Even if the standard cannot be completely standardized, the difference is not big, and the more accurate grinding value can be obtained through calculation. Using granite is more in line with the scope of application.

But their shortcomings are also obvious: only the partial test of the PDC Cutters can not judge the quality of the entire PDC Cutters; only the wear resistance of the PDC Cutters can be judged, and the reason for the wear ratio cannot be found, which is a destructive experiment.

The PDC Cutters synthesized by the 6-sided top in China were initially measured by a tool grinder, but the error was very large. Abrasion ratio tester and measurement method commonly used now. This detection method has a high degree of automation, high detection efficiency, and can greatly reduce labor intensity.

At present, there is also a test method, which is mainly to comprehensively test the PDC Cutters through XRD, Raman spectroscopy and SEM. The comprehensive use of this method can accurately judge the wear resistance of the diamond layer of the PDC Cutters, not only to judge the PDC Cutters It can also give reasons for the advantages and disadvantages of the wear resistance of the diamond layer of the PDC Cutters and the improvement method, which has not been widely used.

2. Thermal stability

Since the performance of the PDC Cutters will be greatly affected after being heated, it is natural to study its thermal stability from the change of the performance of the PDC Cutters before and after heating. At present, measuring the change in properties of the PDC Cutters after heating has become the main method to determine its thermal stability.

At present, in the world, there are mainly the following three test methods for measuring the heat resistance of PDC Cutters:

(1) The British DeBeers company heated it in the air with a muffle furnace, and at the same time placed it in a reducing atmosphere (95%H2+5%N2) and heated it to a certain temperature with a reducing furnace, and kept it for a period of time, Then measure its weight loss, wear resistance, degree of graphitization and impact resistance;

(2) The British DeBeers company also uses a thermogravimetric-differential thermal analyzer (DSC-DTA) and a high-temperature microscope to measure its initial oxidation temperature to determine the degree of oxidation and heat resistance;

(3) The GE company of the United States used a scanning electron microscope for fracture analysis and turning test of the heated sintered body. The cutting speed was 107~168 m/min, and the feed rate was 0.13 mm/r. Most of the domestic test methods are similar to method (2), using the differential thermal-thermogravimetric method.

The differential thermal-thermogravimetric curve is mainly used to analyze the temperature points to determine the oxidation temperature and graphitization temperature of the PDC Cutters. Moreover, most of the heating methods used to test the thermal stability of the PDC Cutters are heating in a furnace.

3. Test method for impact resistance

Due to the characteristics of the PDC Cutters own structure and the way it is damaged in actual use, the PDC Cutters is generally damaged by impact and fails. Therefore, the impact resistance is also an important indicator to measure the quality of the PDC Cutters. More and more attention is paid to it,

,and the detection method of impact resistance is also constantly improving.

3.1 High-speed moving particle erosion method

(1) Basic principles. Using silicon powder or glass powder as the projectile material, these particles obtain kinetic energy by the principle of capacitive discharge, and then form a high-speed particle flow, which impacts the surface of the tested sample, causing erosion and damage, and measuring the mass loss of the sample before and after the impact.

According to the type of spray used in the test, the velocity of the particle flow and the mass loss ratio curve, it is used as the standard index of its impact resistance performance.

(2) Test instruments. High-energy capacitor banks, launch devices, high-speed sub-speed cameras and projectiles.

(3) Disadvantages. The requirements for equipment are high, and it is not easy to popularize and apply.

(4) Actual use. It is mainly used by GE Company of the United States to measure the impact resistance of its products.

3.2 PDC turning grooved granite bar-turn-impact method

(1) Basic principles. First, the PDC is made into a turning tool, and the granite bar with axial grooves is transversely cut at a certain speed and feed force.

(2) Disadvantages. It is difficult to find granite rods with the same performance indicators, which greatly reduces the reliability of the test results; in addition, the PDC must be welded on the tool holder during the test, which is troublesome.

(3) Actual use. The British De Beers company uses silicon aluminum alloy as the material to make a circular workpiece. There is a V-shaped groove every 180 degrees on the workpiece. The cutting speed is 100 mm/min and the single cutting depth is 1 mm. The impact resistance and bonding quality of PDC were compared with the number of times the sample passed through the V-groove when it failed as the test index.

3.3 Heavy weight impact method

(1) Basic principles. The heavy weight impact is carried out on the hanging wire impact frame, which is composed of -polished steel plate and hydraulic system. The hydraulic system can be adjusted smoothly to generate an axial pressure of 500~1000N on the sample; the weight can move along the tensioned steel wire, and the dynamic load is generated by different weights, and its range is 0.1~500J.

The test parameters used in the test are generally, the axial pressure is 1 000N, and the single impact energy is 0.6J. During the test, the sample is placed on the steel plate of the impact frame, and a steel rod with a diameter of 20mm is applied to the sample. 1000N axial pressure, and then drop the hammer several times until the sample is completely destroyed. The number of drops (total impact energy) when the sample is damaged is used as an index to measure the impact resistance of PDC.

(2) Disadvantages. This method measures the number of impacts or impact energy that the sample is completely broken under certain conditions, but in fact, when the PDC cutting tool is working in the well, it is often affected by the impact shear force and partially or edge failure, rather than Therefore, this method cannot simulate the actual stress state of PDC well.

3.4 Variable impact energy falling ball impact method

(1) Basic principles. The steel ball is dropped freely at a certain height, the potential energy of the steel ball is converted into kinetic energy (impact energy), and the test is carried out by using this energy to impact the sample. During the test, make the rushing ball smash the edge of the PDC successively (single impact energy is generally 0.2J), and when visible cracks or breakage appear on the surface of the sample, the impact energy value is obtained as a measure of its impact resistance. Quantitative index, expressed in impact energy, in joules.

(2) Disadvantages. It is completely feasible in principle, and the test error can also meet the requirements (<5%). It is an ideal test method. However, with the continuous progress of PDC manufacturing technology, the quality of PDC has been greatly improved.

Testing - a sample often requires hundreds or even hundreds of shocks. Although this method is easy to operate, the repetitive workload is too large, and it is also cumbersome to manually record the number of impacts. All of the above methods have their limitations

4. Ultrasonic testing

The internal sintering quality of diamond compacts, that is, whether the diamond layer and the cemented carbide layer are firmly bonded, has always been a concern of PDC manufacturers and users.

As a new type of superhard material product, the output of domestic PDC is constantly expanding, the application field is getting wider and wider, and the export of large batches has also begun to appear. Under this circumstance, how to better detect the internal quality of PDC and produce more reliable products has become a new problem that needs to be solved for PDC manufacturers.

Now, some domestic manufacturers have begun to study and find solutions. At present, ultrasonic testing methods are used in foreign countries to detect the internal quality of PDC.

The detection principle is: using ultrasonic to detect the internal quality of PDC is actually the process of using ultrasonic technology for flaw detection. Among the ultrasonic flaw detection principles currently used, the pulse reflection method is the most widely used.