The use of polycrystalline material DCHRM in the drilling impregnated crowns
The practice of drilling geological exploration wells on the solid minerals testifies that there can be no single universal rock drill instrument, capable to achieve excellent results, with drilling in rocks with different physical and mechanical properties.In the context of specific rock categories tools are developing, which are equipped with certain super hard materials. For example, for drilling soft rock (from I to V categories for drill ability) the instrument equipped with hard-alloy elements is used. For medium-hard rock drilling (from VI toVIII categories on drill ability) the instrument equipped with large natural and synthetic polycrystalline diamonds is used. In the solid rocks (from IX to XI categories on drill ability) the instrument equipped with small natural and high tensile monocrystal synthetic diamonds is used.
In the institute of super hard materials named after V.N. Bakul (ISM) a wide range of drilling tools, equipped with high tensile monocrystal synthetic diamonds for drilling in hard rock has developed.
With the development by ISM of diamond composite heat-resistant material (DCHRM), the opportunity to work on creating a tool for drilling in rocks of medium hardness appeared.
The thermal stability of DCHRM material is quite high with 1500 K. It allows to use ligament with a high temperature for the manufacture of drilling tools sintering, which provides high strength retention of super hard cutting insertions. For more lasting retention in the bundle insertion from DCHRM it is necessary to provide reliable connection between DCHRM and the matrix of the solid alloy. To obtain reliable connection between DCHRM and matrix and in some spots manufacturing technology provides DCHRM metallization, or application on carbide - forming element, such as titanium, that provides a reliable adhesion link between DCHRM and matrix, or produces agglomeration of hard alloy in conjunction with inlays DCHRM.
In design development of a crown with a cutter (insets) DCHRM the angle of cutting inserts and the number and their position on the working position of the crown are important. As we reduce the angle of cutting the destruction process of the rock is more efficient, the depth of cut is increasing, and a large sludge is formed. As a result, the mechanical drilling speed increases. However, with a decrease in the angle of cutting tool (box) DCHRM becomes more sensitive to impact loads appeared in crack rock drilling. Increasing the angle of cutting improves the work reliability of the inserts DCHRM in solid rock and the growth of the resource tool, but it leads to the mechanical drilling speed of decrease.
The important element of the crown design is the number of insertions on the rock drill part of the instrument. If you increase their number the effectiveness of cleaning the bottom hole from the sludge decreases, that has negative affects on the mechanical speed of drilling. With the increase in the number of insertions decreases the value of the insertion unit load on the single box, which also leads to the mechanical drilling speed of decrease.
The size of diamond crystals in the layer and the size of inserts must be in the certain ratio. If this ratio is less than optimal, then formed in the process of prefracture the rock sludge particles will be larger as compared with crystals of diamond in the crown layer, and will hang on these particles until they over mill in size at which they can go through between the distinguished crystals of diamond from the layer and washed out by washing liquid on the surface of the well. On the process of over milling additional cost power will be spent, speed of drilling will fall and drilling efficiency will decline.
In the case where the ratio of box sizes and diamond crystals in the layer is more than optimal, sludge particles will be significantly less than the value of the diamond crystals distinguished from the layer, and therefore will be fully got out by washing liquid from the flat end, which is insufficient for normal wear of the matrix and the exposure of crystals of diamond in the layer. This process will lead to a gradual polish of diamonds layer and, consequently, to halt the destruction of the rock. The crown work in these conditions will be ineffective because it will be necessary to spend time on the additional process of diamond crystals exposure.
With the optimal ratio of the size of diamond crystals in the layer and DCHRM inserts, the particles of sludge while in constant contact with the matrix, wear it on the need for continuous exposure of diamond value crystals. Sludge can go through in the gap between them and the drilling takes place without any additional cost to the power and time.
The correct setting mode by rock drilling tool achieves high drilling rates. Optimum operational parameters are the following if to the maximum mechanical speed of drilling and minimal wear of the tool are provided.
In the Institute for super hard materials named after V.N. Bakul tests were performed in the production conditions. The purpose of the tests was to establish and clarify the ability of the cutting tool of DCHRM and comparative data with base serial tool.
The diamonds surface to receive studying after rock drilling allows to separate two typical kinds of wear: brittle fracture and abrasive wear.
With the introduction in the rock the diamond grains have compressive and bending pressure. In addition, in the process of rock destruction by the action of cyclic loads in the diamond grains the fatigue phenomenons occur. Under their influence on cleavage planes, as well as emerging fatigue cracks micro pitting local sites of crystals occur. In this case we should consider that the force is transmitted by diamond to bearing rock by means of not the whole area of contact, but its local sites. In such areas of diamond grain loads may occur to exceed the critical value and cause the micro-and macro spading of local area.
Taking into account the cyclical character of ground destruction, the potential for uneven distribution of load on contact area «diamond - rock», it can be assumed that in the drilling the situations the total load on the diamond grain does not exceed normal when constantly take place. When loads do not exceed the critical value, the diamond grains retain their shape, have high overhang from the matrix and effectively destroy the rocks.
With the growth of the mechanical drilling speed caused an increase of the introduction depth of the diamond in the rocks the loads on the diamonds increase. In this case the situations can be created where the voltage on a separate part of diamonds outweighs the critical ones. As a result, micro cracks at these local stations on diamond surface begin to develop so it is the cause of the grain chipping or the complete destruction.
Moreover, on the local surface of some diamonds the raw of parallel slots is seen, elongated in the direction of the diamond grain movement. It can be assumed that the appearance of slots is a consequence of the abrasive effect on the diamond surface, weakening under the influence of high contact temperature, solid inclusions of rock-forming minerals, rocks and destroyed micro-diamonds.
The completed observation allowed to come to the conclusion that the predominant mode of wear of synthetic diamond in the drilling process is brittle failure with cleaving their grain distinguished parts.
Accordingly in order to improve efficiency rock the most useful tool is the use of its facilities for high - strength synthetic diamonds.
By studying the picture of wear, presented in Figure 1 and 2, we can remark the following: diamonds in the crown (Fig.1a) most of them are worn out and have a large number of blunted sites. Grooves on the surface of the contact matrix with slaughter shallow wells are not deep, which indicates the formation of sludge in the contact area the sludge of a small size. The availability of sludge with a small size indicates inefficient processes of rock destruction.
The character of the wear crowns (Fig.1b) differs from the character wear of the crown. The number of entire diamonds on the surface of the friction in the first case is large than in the second one, and the grooves are much deeper. It is possible to prove that the insertion protects the diamonds and the destruction of species occurs more efficiently.
The character of the wear sector (Fig. 2a) is largely similar to the character of wear ( Fig.1b). As the intensity of wear crown is the most stable as shown in Fig.2a, but the polish off sites on diamonds are nearly absent.
Fig. 1a |
 Fig.1b
|
Fig. 1. The character of rock wear crown of sectors №1
Fig. 2a |
 Fig.2b
|
Fig. 2. The character of rock wear crown of sectors №2
The character of crown wear is presented on Fig.2.
On the surface of the matrix contacted with the rock, there are a lot of holes from the out-of-its diamond grains. This shows crown work of such design in vibration regime. At the last stage of the tests the lowest work capability of the crown is indicated compared with other tools.
DCHRM material in the form of grains and in the form of cylindrical inserts, is capable to destroy rocks. This tool made from DCHRM in shape of cylindrical cutting inserts in combination with the matrix, incorporated with synthetic mono crystal diamond, allows you to increase the productivity of drilling in the 1.8 - fold compared with existing types of instrument in the rocks of VII - IX (partly) categories of the research drill ability. Further the research will be continued to improve the design crowns with inserts of DCHRM and to make a new one, capable of efficiently drilling in stronger rocks (IX - X category of drill ability).
Библиотека