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The application of ultrasonic cleaning in the pretreatment of electroplated diamond bits

Abstract: the adaptability of introducing ultrasonic cleaning into the pretreatment process of rigid diamond bits before plating is analyzed, the scope of application of ultrasonic treatment is analyzed, and the production process and process are designed

key words: ultrasonic cleaning, electroplated diamond bit, acidification etching, deoxidization coating

1 Introduction

low temperature mm; Electroplated diamond bit technology has been more and more used in bit manufacturing. The performance of diamond bit depends largely on the matrix connecting diamond and rigid body (see Figure 1). In the process of drilling, the bit is subjected to torsion, compression, bending and other functions, and its working state is extremely complex. In the electroplating diamond bit process, the connection strength between the matrix and the rigid body largely depends on the cleanliness of the rigid body surface cleaning in the pretreatment process. The rigid body surface with high cleanliness can ensure a good coupling force between the rigid body and the matrix. If the connection strength fails to meet the requirements, the matrix will be separated from the rigid body, resulting in the scrapping of the whole drill bit. In production, there are often several pretreatment and cleaning processes, but the effect is still unsatisfactory, which has become a bottleneck affecting the quality of drill bits

2 ultrasonic cleaning

as a kind of physical cleaning, ultrasonic cleaning has a good cleaning effect for materials with hard texture and high acoustic impedance (i.e. strong acoustic reflection) such as metals. In the pretreatment process of electroplated diamond bit, the plane of concrete foundation can be leveled by ultrasonic cleaning technology, which can achieve good results. The main objects in the pretreatment of electroplated diamond bits are burrs, molding sand, oil stains, oxide scales and rust products on the surface of rigid bodies. Ultrasonic cleaning belongs to fine cleaning, and the main treatment objects are oil and oxide skin

2.1 cavitation of ultrasonic wave

ultrasonic wave propagates in the form of density wave in the medium. When a certain frequency of ultrasonic wave passes through the liquid, the pressure generated in the sparse and dense stages of ultrasonic wave is greater than the structural strength of water, and a "cavitation core" is generated in the water, which is shown as small bubbles. The small bubble resonates with the ultrasonic wave, and in the sparse stage of the ultrasonic wave, the small bubble expands and becomes larger; In the dense phase, small bubbles are compressed until they collapse. When a small bubble is suddenly compressed, the surrounding liquid fills the hole at a great speed, and the nearby liquid or solid is under great pressure, that is, cavitation. Cavitation and its side effects are the main mechanism of ultrasonic cleaning, and the side effects include the second-order phenomenon caused by oscillation

2.2 ultrasonic deoxidization coating

45 carbon steel pipe is often used as drill bit rigid body. When carbon steel is processed, it will form oxide skin with complex structure, which has three layers of Fe3O4 and FeO from the outside to the inside. FeO, which accounts for 90% of oxide skin, has loose texture and weak protective effect. Fez03 has two forms: first, fez03 is formed at room temperature and has a cubic structure, which can be removed by general mechanical treatment; A-fez03 is formed above 400~c, which is a rhombic hexahedron structure with dense structure, which can prevent further oxidation of the matrix. Fe3O4 is composed of FeO and fez03. The main removal object of ultrasonic wave is a-fe203. The commonly used method to remove a-fez03 is acid etching, but it can not achieve good results. The combined effect of ultrasonic and acid etching is discussed below

ultrasonic removal of oxide scale is the result of the combined action of physics and chemistry. Physical effects mainly include:

(1) impact and vibration: small bubbles expand and compress under huge pressure, which will inevitably impact the oil on the surface of the rigid body. In the sound field, the maximum shock oscillation acceleration Amax of the medium caused by the action of sound waves is:

from the above calculation, it can be seen that the cavitation effect of ultrasonic waves will produce a huge shock oscillation effect on the surface

(2) fatigue effect: ultrasonic wave will impact the surface of rigid body once in a very short time. The common fatigue strength of metal is 10% - 20% of its design strength. The oxide skin will appear fatigue fracture under repeated ultrasonic impact

(3) circulation effect: the cavitation bubble itself will be accompanied by a series of second-order phenomena (such as radiation torsion) in the oscillation process. Radiation torsion acts on the liquid itself in a uniform liquid, resulting in the circulation of the liquid itself (called acoustic flow). It can make the vibrating bubble surface under high velocity gradient and viscous stress, which is in the order of megapascals, enough to destroy the rigid oxide skin and cause it to fall off

ultrasonic cleaning of oxide scale is combined with acidic conditions. The powerful impact and oscillation of ultrasonic makes the oxide skin on the surface of the rigid body loose and fall off, so that the etching solution can penetrate into the inner layer of the oxide skin in time for reaction. If the etching solution breaks through the barrier of fez03, it will quickly penetrate the non dense FeO layer and contact the substrate, and the generated hydrogen will escape from the interior of the oxide film, which has the effect of mechanical top cracking and spalling on the oxide skin. In addition, ultrasound also plays the role of stirring the etching solution at high speed, so that the invalid etching solution on the surface of the rigid body leaves the surface of the rigid body, and the effective etching solution can be added to the surface of the rigid body in time to react with the oxide skin

2.3 ultrasonic oil removal mechanism

ultrasonic oil removal mechanism includes chemical mechanism and physical mechanism. The chemical mechanism is to obtain the material characteristics by using water-soluble metal detergent: the indoor temperature of the model experiment is basically maintained at 2025e lotion, which mainly depends on the action of surfactant to reduce the surface tension, and has the effects of penetration, emulsification, solubilization, dispersion, convolution, dissolution and so on. The physical mechanism is that ultrasound can strengthen the chemical action of surfactants

(1) emulsification: the impact oscillation force generated in the cavitation promotes the oil to disperse and penetrate into the molecules of the cleaning fluid with very small particles, forming an emulsion, which accelerates the emulsification of oil

(2) dispersion effect: the high temperature effect (the heat generated by the liquid rubbing the metal surface and the shrinkage of cavitation bubbles) and the oscillation effect produced in the cavitation effect disperse the oil contamination into the cleaning fluid as tiny particles to form a suspension, which helps the oil contamination to diffuse into the cleaning agent finely, accelerates the removal process, and prevents the dirt separated from the surface of the parts from reattaching to the parts. The cavitation effect of ultrasonic wave and its mechanical and thermal effects make new material characteristics form in the interface between liquids, solids, solid-liquid interface and gas-liquid interface, which increases the chemical action of surfactants to varying degrees

3 ultrasonic cleaning process

ultrasonic cleaning equipment is mainly composed of ultrasonic generator, transducer and ultrasonic cleaning tank. As the power source of transducer, ultrasonic generator provides electromagnetic oscillation energy for the whole system; The transducer converts the electrical energy (electromagnetic oscillation) generated by the generator into mechanical energy (ultrasonic vibration); The cleaning tank is used to hold cleaning fluid and hang workpieces. The basic method of ultrasonic cleaning is cleaning in the tank, that is, the workpiece is immersed in the cleaning tank containing cleaning agent, and the ultrasonic vibration generated by the ultrasonic generator through the transducer is radiated from the bottom of the cleaning tank or the side wall of the cleaning tank (or both bottom and side walls) to the cleaning solution for ultrasonic cleaning

because ultrasonic cleaning is fine cleaning, the drill bit rigid body must be pre cleaned by other methods first. When using ultrasonic cleaning method to remove oxide skin, only indirect method can be used, that is, first put the cleaning medium and the rigid body to be cleaned into the beaker or other corrosion-resistant containers, and then put the containers into the ultrasonic cleaning tank for cleaning

the water-based cleaning solution trichloroethylene (c2hc13) is selected as the ultrasonic cleaning solution. Trichloroethylene has strong fat dissolving ability, high safety in use at room temperature, low surface tension and good cleaning effect; Phosphoric acid (h3vo4) is used as the etching solution. As a medium strong acid, phosphoric acid has strong binding force with iron, has no oxidation at any concentration, and has low volatility

in order to effectively inhibit the occurrence of "Hydrogen Permeation", the ultrasonic oscillation frequency should be reasonably selected in the process of ultrasonic cleaning oxide skin, so as to minimize the possibility of "hydrogen embrittlement" of metal. The drill bit rigid body, which is sensitive to "hydrogen embrittlement", can be cleaned by ultrasonic etching with 22 ~ 23khz ultrasound. The cavitation threshold of the cleaning fluid is low. Although the bubble is small, the cleaning force is high, which is suitable for cleaning larger or heavier workpieces. The ultrasonic cleaning process is shown in Figure 4

4 cleaning effect

generally, the effect inspection after cleaning adopts the method of combining indoor inspection and field test inspection. For electroplated diamond bits, if the on-site drilling test method is used for inspection, a large number of data need to be counted, and a small amount of data is too random, the detection cost is high, and the formation condition is changeable, while the bits have strong adaptability to the formation, so it is not easy to obtain the detection parameters under the same working conditions

indoor inspection mainly adopts pre plating inspection, that is, direct inspection after ultrasonic cleaning and before electroplating. The water drop method is a commonly used simple method for qualitative evaluation of cleanliness. Its principle is to use the contact angle to evaluate the cleanliness of rigid bodies. When the volume of water drops dripping on the surface is certain (it can be considered that the volume of each drop of water gushing out of the dropper is the same), the larger the diameter of water drops unfolding on the surface, the smaller the contact angle, and the higher the cleanliness. When there is residual material on the surface of the tested object, the shape of water droplets on the surface of the tested object is irregular, then the contact angle is large; If the shape of water droplets on the surface is round, the contact angle is small and the cleanliness is high. If quantitative detection is required, precise analysis methods such as IRRs, FXS, EPMA, etc. should be used

Table 1 lists the effect comparison between common decontamination cleaning methods and ultrasonic cleaning methods. The data in the table are obtained by precision analysis method FXS (X-ray fluorescence analyzer with low indication). It can be seen from table 1 that ultrasonic plus acid etching is the most effective pretreatment method for diamond rigid bodies

5 conclusion

ultrasonic cleaning simplifies the pretreatment process of electroplated diamond bits, with high speed. This method has remarkable oil removal effect, good cleaning effect and little environmental pollution. The combined action of ultrasonic cleaning and acidification etching table is suitable for the pretreatment process of electroplated diamond bits with high requirements for surface cleanliness. (end)

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