Device and method for uniformly coating diamond abrasive particles on surface of bur based on fluidized bed

Abstract

The invention relates to a device and a method for uniformly coating diamond abrasive particles on the surface of a bur based on a fluidized bed. The device comprises a fluidized bed cavity, a gas distribution plate, a gas source system, a multi-axis rotating system and a control system. A fluidized bed technology is utilized to suspend diamond abrasive particles to uniformly coat the surface of the bur, and the diamond abrasive particles collide with the surface of the bur at various angles and with uniform probability by utilizing the random and turbulent characteristics of gas-solid two-phase flow of flowing gas and the diamond abrasive particles in the fluidized bed; and uniform, all-around and high-bonding-strength fixing and coating of the abrasive particles on the surface of the bur base body are achieved through the mixture of the brazing filler metal and the binding agent, wherein the surface of the bur base body is coated with the mixture in advance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bur preparation, in particular to a bur surface diamond abrasive uniform coating device and method based on a fluidized bed. BACKGROUND

[0002] Diamond bur is a kind of oral medical instrument, which is widely used in oral treatment work such as decaying, pulp opening, tooth preparation, cavity preparation, crown breaking, etc. At present, the diamond coating on the surface of bur is mainly carried out by electroplating method, brazing method and physical vapor deposition.

[0003] The electroplating method fixes the diamond abrasive particles in the metal plating layer through electrochemical deposition. This method has obvious technical defects: the plating layer thickness is uneven, especially in the tip, groove and complex contour parts of the bur, the plating layer is prone to be too thin or too thick; the distribution of abrasive particles is completely random, and the orientation and arrangement density of abrasive particles cannot be controlled; the bonding strength completely depends on the quality of the plating layer, and the abrasive particles are prone to early falling due to poor clamping; more importantly, the electroplating solution contains heavy metal ions, which causes serious environmental pollution.

[0004] The brazing method uses active filler metal to connect diamond and substrate at high temperature. Although the bonding strength is high, after the filler metal is coated on the bur substrate, the abrasive particles are usually scattered by hand to coat and drop, which leads to a certain degree of agglomeration and sparseness of the abrasive particles, and the abrasive particles are prone to poor clamping, affecting the cutting life.

[0005] The physical vapor deposition technology deposits diamond coating in a vacuum environment. Its limitations are: the coating thickness is limited, usually not more than 10 microns, which is difficult to meet the heavy load cutting demand; there is obvious shielding effect for complex shape, which cannot guarantee three-dimensional uniformity; the equipment investment is huge, and the production efficiency is low, which is not suitable for large-scale production.

[0006] Through comprehensive analysis of the existing technology, it is found that the existing technology cannot meet the four key requirements at the same time: full-range uniform coating of complex three-dimensional surface, high bonding strength of abrasive particles and substrate, environmentally friendly production process and economic and efficient large-scale production capacity. Especially in the field of medical instruments, the bur often has extremely complex geometric shape, and the traditional technology is difficult to realize the same coating quality in the special parts such as needle tip, groove and thread as in the flat parts. SUMMARY

[0007] The present application aims to overcome the deficiencies of the prior art, and provide a diamond abrasive particle uniform coating device and method for tool pin surface based on fluidized bed technology, which ingeniously utilizes the unique dynamic characteristics of gas-solid two-phase flow in the fluidized bed, realizes the equal probability collision contact of diamond abrasive particles and each part of the tool pin surface by precisely controlling the fluidization state and the tool pin motion trajectory. Combined with an optimized binder system and an intelligent control strategy, the diamond abrasive particle coating effect is achieved in all directions, uniformly and with high strength.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] The diamond abrasive particle uniform coating device for tool pin surface based on fluidized bed comprises:

[0010] The fluidized bed cavity is a cylindrical cavity;

[0011] The upper cover is detachably capped on the top of the fluidized bed cavity;

[0012] The gas distribution plate is arranged at the bottom of the fluidized bed cavity, and a plurality of fluidization holes are distributed on the gas distribution plate for dispersing the gas entering the fluidized bed cavity into a large number of uniform micro gas flows;

[0013] The gas source system sends clean and dry compressed air to the gas distribution plate through the gas pipeline;

[0014] The tool pin multi-degree-of-freedom motion mechanism comprises a three-axis motion system and a multi-axis rotation system, the multi-axis rotation system is connected to the execution end of the three-dimensional motion system, and the three-axis motion system drives the multi-axis rotation system to translate in space in the fluidized bed cavity; the multi-axis rotation system comprises a transmission main shaft, a main shaft turntable and a plurality of tool pin clamp discs; the main shaft turntable is fixed at the lower end of the transmission main shaft and located in the fluidized bed cavity, and the transmission main shaft is driven to rotate by a revolution motor; the tool pin clamp disc is used for clamping and fixing the tool pin with coated diamond abrasive particles, the top of each tool pin clamp disc is rotationally connected to the main shaft turntable through a revolution shaft, and each revolution shaft is connected to a corresponding revolution driving motor;

[0015] The control system is used for controlling the operation of the entire coating device.

[0016] Further, the upper cover is provided with an exhaust port, and a pressure relief valve is connected to the inner side of the exhaust port.

[0017] Further, the thickness of the gas distribution plate is 20-50mm, and a flange seal is adopted between the gas distribution plate and the bottom of the fluidized bed cavity.

[0018] Further, a plurality of rows of fluidization holes are distributed on the gas distribution plate, and two adjacent fluidization holes in one row and one fluidization hole in the other row form a regular triangle distribution.

[0019] Further, the fluidization hole is a microporous structure, including a tapered inlet section, a cylindrical stable section and a diffusion outlet section.

[0020] Further, the gas source system includes an air compressor, an air tank, a precision filter, an air dryer, a pressure regulating valve and a mass flow controller connected in sequence.

[0021] Further, the fluidized bed cavity is provided with a temperature sensor and a humidity sensor, the temperature sensor performs multi-point temperature monitoring, and the humidity sensor monitors the gas humidity.

[0022] Further, the bottom side of the upper cover is provided with a differential pressure sensor for real-time monitoring of the pressure difference between the upper and lower ends of the gas distribution plate.

[0023] Further, the bottom side of the upper cover is provided with a high-speed camera, which is used to capture visual information of the fluidization state and record the coating condition of the tool pin surface.

[0024] The present application is based on a tool pin surface diamond abrasive particle uniform coating method based on a fluidized bed, using the above coating device, including the following steps:

[0025] The pretreatment stage: ultrasonic cleaning and plasma cleaning are performed on the tool pin; then a bonding layer is coated on the surface of the tool pin, the bonding layer being a mixture of brazing filler metal and PVAL adhesive; after coating the bonding layer, the tool pin is rotated in clean air, and the bonding layer is made to flow flat by surface tension to form a uniform wet film with a thickness of 8-12 microns; the pretreated tool pin is fixed on a tool pin clamp disc; at the same time, the diamond abrasive particles are dried, wherein the diamond abrasive particles are 30-40 micron high-strength artificial diamond micro powder with sharp corners;

[0026] The fluidized coating stage: the upper cover of the fluidized bed cavity is opened, and the dried diamond abrasive particles are loaded into the fluidized bed cavity; the gas flow rate is controlled between the minimum fluidization velocity and the entrainment velocity, so that the diamond abrasive particles are in a turbulent fluidization state; the tool pin substrate coated with the bonding layer is immersed in the abrasive particle fluidization zone of the fluidized bed, and the tool pin substrate is driven to perform a combination of revolution and rotation, so that the diamond abrasive particles adhere to the bonding layer; the tool pin is driven to perform a combination of revolution and rotation, so that the diamond abrasive particles adhere uniformly to the bonding layer of the tool pin;

[0027] The fluidized coating process is monitored by an intelligent sensing system, the temperature and humidity inside the fluidized bed cavity are displayed and controlled by temperature and humidity sensors, the pressure difference in the fluidized bed cavity is detected by a pressure difference sensor, and when the pressure difference is too large, a pressure relief valve should be started to discharge excess gas through the exhaust port; the fluidization state in the fluidized bed cavity is monitored in real time by the built-in high-speed camera during fluidized coating;

[0028] Post-processing stage: the fluidized coating completed needle is removed from the fluidized bed, and solidification treatment is carried out, and finally the solidified needle is inspected.

[0029] The present application utilizes the fluidized bed technology to suspend diamond abrasive particles for uniform coating of the needle surface, utilizes the random and turbulent characteristics of the gas-solid two-phase flow of the flowing gas and diamond abrasive particles in the fluidized bed to make the diamond abrasive particles collide with the needle surface at various angles and uniform probability, and realizes uniform, all-around and high bonding strength fixation and coating of the abrasive particles on the needle substrate surface through the mixture of the brazing filler metal and the binder pre-coated on the surface of the needle substrate. The present application has the following beneficial effects:

[0030] The present application has four significant advantages compared with the prior art:

[0031] 1. True three-dimensional uniformity is achieved. The isotropic characteristics of the fluidized bed ensure that there is no shielding effect, and consistent coating quality can be obtained even for extremely complex geometries. Experiments have shown that the coverage rate difference between the tip, groove and threaded parts and the flat parts of the needle is less than 5%.

[0032] 2. The process is precisely controllable. The gas velocity control accuracy is ±0.02 m / s, and the repeatability and consistency of the process are ensured through real-time monitoring feedback.

[0033] 3. Production efficiency is significantly improved. The multi-station simultaneous processing capability increases the batch yield by 3-5 times, the degree of automation reduces the labor cost by 60%, and large-scale and efficient production is realized.

[0034] 4. Environmentally friendly features. The entire process does not emit toxic chemicals, the abrasive particle recycling rate is more than 95%, the energy consumption is reduced by 40% compared with traditional methods, and it meets the requirements of green manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0035] The present application will be further described in detail in conjunction with the drawings and specific embodiments:

[0036] Fig. 1 is a cross-sectional view of the overall structure of the coating device of the present application;

[0037] Fig. 2 is a schematic view of the surface structure of the gas distribution plate;

[0038] Fig. 3 is a schematic view of the cross section of the fluidization hole. DETAILED DESCRIPTION

[0039] As shown in Figs. 1-3 , the present application is based on the fluidized bed needle surface diamond abrasive particle uniform coating device, which comprises a fluidized bed cavity 1, an upper cover 14, a gas distribution plate 4, a gas source system 1, a multi-axis rotation system needle multi-degree-of-freedom motion mechanism and a control system.

[0040] The fluidized bed cavity 1 is a cylindrical cavity, which is beneficial to eliminate corner dead zones and ensure the symmetry of gas flow and particle flow. The height-diameter ratio (H / D) is strictly controlled between 1.8:1 and 2.2:1. Too high can easily lead to bubble merging and slugging, and too low can cause uneven fluidization and poor bed stability. The effective volume of the cavity is designed according to the production scale. The cavity is the core reaction vessel for completing the coating process, and its design directly determines the quality of fluidization.

[0041] The main body of the fluidized bed cavity 1 is made of high-strength stainless steel or organic glass. The use of organic glass facilitates direct observation of the internal fluidization state, needle movement and coating process. The wall thickness is calculated to withstand a working pressure of 0.3 MPa.

[0042] The side wall of the fluidized bed cavity 1 is provided with multiple groups of sensor interfaces along the height direction for connecting differential pressure, mass flow controllers, high-speed cameras, etc.

[0043] The upper cover 14 with quick-opening clamps can be detachably capped on the top of the fluidized bed cavity 1, which is convenient for loading and maintenance, and can be used for observation.

[0044] The gas distribution plate 4 is arranged at the bottom of the fluidized bed cavity 1, and the gas distribution plate 4 is provided with fluidization holes 25 for dispersing the gas entering the fluidized bed cavity 1 into a large number of uniform small gas flows, providing uniform initial fluidization power for the entire bed, and supporting the weight of the bed material during shutdown. The thickness of the gas distribution plate 4 is 20-50 mm to ensure sufficient mechanical strength and stability. The gas distribution plate 4 and the bottom of the fluidized bed cavity 1 are sealed by flanges to ensure no gas leakage.

[0045] The gas distribution plate 4 is made of sintered metal or porous ceramic material, which has high mechanical strength and uniform pore structure. The gas distribution plate 4 is provided with multiple rows of fluidization holes 25, and the two adjacent fluidization holes 25 in one row and one fluidization hole 25 in the other row form a regular triangle distribution. The fluidization holes 25 are not simple straight-through holes, but are composed of a large number of tortuous interconnected micropores with an equivalent pore size distribution of 20-50 μm. This structure can generate a large enough pressure drop (design value of 0.5-2.0 kPa) to ensure uniform gas distribution on the distribution plate surface and overcome local "bias flow".

[0046] The fluidization holes 25 of the gas distribution plate 4 are arranged in a regular triangle pattern with a hole spacing of 3-5 times the hole diameter, which ensures the best uniformity of gas flow distribution. The fluidization holes 25 are micro-porous structures including a tapered inlet section 26, a cylindrical stabilization section 27 and a diffuser outlet section 28. The tapered inlet section 26 of each fluidization hole 25 has an angle of 30-60 degrees, which ensures smooth gas flow introduction; the cylindrical stabilization section 27 has a length of 2-3 times the hole diameter, which establishes stable flow; and the diffuser outlet section 28 has an angle of 15-30 degrees, which achieves uniform gas flow diffusion. This special design effectively prevents hole clogging and gas flow short circuiting. The opening rate is precisely controlled within the range of 1.5%-2.5%, the hole diameter of the fluidization holes 25 should be greater than the smallest size of the diamond abrasive particles, the pressure loss is designed to be 0.5-2.0 kPa, and the distribution uniformity is greater than 95%.

[0047] The gas source system 1 supplies clean and dry compressed air to the gas distribution plate 4 through the gas supply pipeline 2; the gas source system 1 includes an air compressor 24, an air tank 23, a precision filter 22, an air dryer, a pressure regulating valve 21 and a mass flow controller 20 connected in sequence. The gas source system 1 is the power source and key guarantee for generating and maintaining a stable fluidized state. The gas source system 1 includes a complete gas supply link, in which the air compressor 24 of the gas source system 1 provides the gas source, the air compressor 24 uses an oil-free silent air compressor to provide dry and oil-free compressed air; the air tank 23 stabilizes pressure fluctuations, and the precision filter 22 ensures gas cleanliness. The gas passes through the precision filter 22 (which removes oil mist, moisture and particulate matter to 0.01 μm) and the air dryer in sequence to ensure that the dew point of the gas is below -40°C, preventing moisture from causing abrasive particle agglomeration or affecting the curing of the binder; the pressure regulating valve 21 is used to accurately control the pressure level, and the mass flow controller 20 is used to precisely adjust the flow rate, accurately controlling the mass flow rate of the gas entering the fluidized bed, which is not affected by temperature and pressure changes. According to the cross-sectional area of the bed, the superficial gas velocity can be accurately calculated and controlled, and finally the gas is sent into the gas distribution plate 4 through the gas supply pipeline 2 into the fluidized bed cavity 1.

[0048] The multi-degree-of-freedom motion mechanism of the lapping pin is an actuating mechanism for solving the problem of uniform coating of the lapping pin in all directions, and is used to drive the lapping pin to perform a combined motion of rotation and translation in the fluidized bed cavity 1, so as to ensure that all surfaces can be in full contact with the diamond abrasive particles. The multi-degree-of-freedom motion mechanism of the lapping pin comprises a three-axis motion system 12 and a multi-axis rotation system, the multi-axis rotation system is connected to an execution end of the three-dimensional motion system 12, and the three-axis motion system 12 drives the multi-axis rotation system to perform spatial translation in the fluidized bed cavity 1; the multi-axis rotation system comprises a transmission main shaft 13, a main shaft turntable 9 and a plurality of lapping pin clamp discs 8; the transmission main shaft 13 is installed on the three-axis motion system 12, the main shaft turntable 9 is fixed at the lower end of the transmission main shaft and located in the fluidized bed cavity 1, the transmission main shaft 13 is driven to rotate by a revolution motor, and stepless speed regulation of 0-100 revolutions per minute is realized; the lapping pin clamp disc 8 is used to clamp and fix the lapping pin 7 coated with diamond abrasive particles, the top of each lapping pin clamp disc 8 is rotatably connected to the main shaft turntable 9 through a revolution shaft 18, and each revolution shaft 18 is connected to a corresponding revolution driving motor (a brushless direct-current servo motor is driven by a synchronous belt or a micro reducer to realize stepless speed regulation of 0-100 rpm); the three-axis motion system 12 can adopt a servo motor 11, a ball screw and a ball linear guide rail in the prior art, the ball screw is used as a transmission core, the linear guide rail supports and guides the motion component, ensures stable operation and no shaking, and can enable the lapping pin 7 to perform translational motion in a rectangular, circular or arbitrary complex trajectory in the fluidized bed cavity 1.

[0049] Each lapping pin clamp disc 8 can be independently rotated, a pneumatic or mechanical quick clamping mode is adopted, the lapping pin clamp can adopt a pneumatic V-shaped block to position and clamp the handle part of the lapping pin, and different diameters of lapping pins 7 can be adapted. In addition, the clamp is designed to be insulated to prevent static electricity from accumulating and affecting the performance of the binder.

[0050] The control system takes a PLC controller as a core, is used to control the operation of the entire coating device, cooperates with an HMI man-machine interface to perform parameter setting and display, and a data recording system completely stores process data.

[0051] The upper cover 14 is provided with an exhaust port 16, and the inside of the exhaust port 16 is connected with a pressure relief valve 17. When the pressure difference is too large, the pressure relief valve 17 is started to discharge the excess gas through the exhaust port 16.

[0052] The intelligent monitoring system of the present application integrates multiple sensors. The bottom side of the upper cover 14 is provided with a differential pressure sensor 15, which monitors the bed pressure drop in real time, measures the pressure difference between the upper and lower ends of the gas distribution plate 4, and the pressure drop-gas velocity curve is the most direct basis for judging the fluidization state (fixed bed, fluidized bed, pneumatic conveying); the fluidized bed cavity 1 is provided with a temperature sensor 5 and a humidity sensor 19, the temperature sensor 5 performs multi-point temperature monitoring, and the humidity sensor 19 monitors the gas humidity and monitors the gas inlet and working environment parameters. The bottom side of the upper cover 14 is provided with a high-speed camera 10, which is used to capture visual information of the fluidization state and record the coating condition of the fluidization state and the needle surface.

[0053] In the fluidized bed cavity 1, gas is blown from the bottom gas distribution plate 4 and passes through a particle bed layer containing diamond abrasive particles 6 from bottom to top. When the gas velocity is low, the particles are stationary, and the gas passes through the gap. This is a fixed bed. As the gas velocity increases, the particles begin to loosen. When the drag force (resistance) of the gas on the particles is balanced with the net gravity of the particles, the particles are suspended in the gas flow and move randomly and violently. The entire bed exhibits fluid-like properties, which is the fluidization state.

[0054] 1) Force model of a single diamond abrasive particle (microscale)

[0055] In the fluidized bed cavity 1, a diamond abrasive particle is mainly subjected to the following forces:

[0056] 1. Net gravity

[0057] The net gravity is the force that makes the particle sink, and it is the main force that needs to be overcome for the particle to be suspended.

[0058] F g =(ρ p -ρ f )V p g;

[0059] ρ p : density of diamond (3500 kg / m 3 );

[0060] ρ f : density of gas (usually air) (1.2 kg / m 3 );

[0061] V p : volume of a single abrasive particle;

[0062] g: acceleration of gravity;

[0063] Since ρ p >> ρ f , the buoyancy can be ignored, and the net gravity is approximately equal to the self-gravity of the particle ρ p Vp g. The high density of diamond means that a greater gas drag force is required to suspend it.

[0064] 2. Gas drag force

[0065] Gas drag force is the force that suspends particles, and is the key driving force.

[0066] F D = 0.5C D p f A p |v r |v r ;

[0067] where C D : drag coefficient, a function of Reynolds number;

[0068] A p : projected area of particle;

[0069] v r = u f -v p : relative velocity between gas and solid, is local instantaneous velocity.

[0070] In the fluidized bed chamber 1, u f (real gas velocity) is much greater than the superficial gas velocity U0calculated based on the empty bed cross-sectional area, because the particles occupy a large volume. At the same time, v p is the instantaneous velocity of the particles, which is constantly changing.

[0071] 3. Particle-particle collision force

[0072] Particle-particle collision force is the core force that distinguishes the motion of a single particle in an infinite gas flow. The particle concentration in the fluidized bed chamber 1 is very high, and frequent and violent collisions occur between the abrasive particles.

[0073] Model: usually uses soft sphere model or hard sphere model for discrete element simulation;

[0074] Formula: collision force F coll is decomposed into normal force F n and tangential force F t ;

[0075] Normal force: includes elastic term and damping term;

[0076] F n = k n δ n - γ n v n ;

[0077] Tangential force: similar to friction, which can cause the particle to rotate;

[0078] Collision force determines the bed expansion height, the degree of particle mixing, and the energy transfer.

[0079] 4. Particle-wall collision force

[0080] Similar to particle-particle collision, when the abrasive particles collide with the fluidized bed chamber 1 wall, they will experience a reaction force from the wall. This will affect the particle distribution inside the bed and the attrition.

[0081] 5. Other forces (usually negligible in a fluidized bed)

[0082] Virtual mass force: due to ρ f <<ρ p , it can be neglected;

[0083] Basset force: due to the low gas density, the fluid viscosity, and the weak history effect of velocity change, it can be neglected;

[0084] Saffman lift force: in a uniform fluidization field, its influence is much smaller than the drag force and collision force.

[0085] 2) Macroscopic model and key parameters: minimum fluidization velocity.

[0086] Whether the entire bed can enter the fluidization state, rather than the precise trajectory of individual particles. The minimum fluidization velocity is the most important parameter in the design and operation of a fluidized bed, and is the minimum superficial gas velocity U mf .

[0087] For small particles (low Reynolds number), the inertia term can be ignored, and the minimum fluidization velocity formula applicable to laminar flow is obtained:

[0088]

[0089] ε mf : bed voidage under the minimum fluidization state (needs to be experimentally determined or empirically estimated);

[0090] φ: particle sphericity (for irregular abrasive particles, φ < 1);

[0091] μ: gas viscosity;

[0092] Diamond abrasive particles are usually micron-sized, d p is very small, and the density ρ p is large.

[0093] The (ρ p - ρ f )g term is large, while the (φd p ) 2 term is very small. Overall, the U mfThe range will be estimated by the above equation and finally determined by experiment.

[0094] 3) Force model and coating mechanism

[0095] The flux model of diamond grit in the fluidized bed is:

[0096] J = n p v p Ap collision p adhesion ;

[0097] Where J: the number of grits adsorbed to the surface of the stylus per unit time;

[0098] n p : the number density of grits in the bed;

[0099] v p : the average speed of the grit relative to the stylus;

[0100] A: the surface area of the stylus;

[0101] P collision : the collision probability;

[0102] P adhesion : the adhesion probability;

[0103] The critical adhesion condition is that whether the grit can adhere depends on the balance between the impact kinetic energy and the adhesive work of the binder:

[0104]

[0105] Where the adhesive work W adhesion depends on: the surface tension of the binder γ, the contact area A contact and the rheological properties of the binder

[0106] For the fluidized bed, the range of gas velocity for successful coating is:

[0107] U mf <U operation <U t ;

[0108] The minimum fluidization velocity to ensure that the diamond grit can be suspended in the fluidized bed is:

[0109]

[0110] The entrainment velocity to avoid the loss of diamond grit is:

[0111]

[0112] For diamond grit (ρ p ≈3500kg / m3 , d p ≈10-100μm), therefore, the operating gas velocity range can be referred to: 0.1-0.5 m / s.

[0113] For the special requirements of dental diamond burs, the application provides an optimized embodiment of the coating method. The equipment configuration selects a 10-liter fluidized bed volume, and the operating gas velocity is precisely controlled within the range of 0.28-0.32 meters per second. The diamond abrasive particles are selected to have a particle size of 30-40 microns, and the concentration ratio is 18%. The binder uses PVAL, and the bur movement parameters are set to rotate at 25 revolutions per minute with up and down oscillation, and the oscillation frequency is 0.5 hertz.

[0114] The process parameters are strictly calculated and experimentally verified: the minimum fluidization velocity is calculated to be 0.15 meters per second, and the entrainment velocity is 0.85 meters per second, so the operating gas velocity is selected to be 1.8 times the minimum fluidization velocity, i.e. 0.27 meters per second. The coating time is calculated according to the surface area and abrasive flux to be 135 seconds. Through this optimized configuration, a coverage of 94.2% ± 2.1% is achieved, the uniformity index reaches 0.96, and the abrasive exposure height is controlled within the range of 15-18 microns.

[0115] 1. Pretreatment stage:

[0116] Soak the bur in acetone and ultrasonically clean for 10 minutes to remove oil. Then place the bur in a plasma cleaning machine under an argon atmosphere and perform plasma cleaning at 100W power for 5 minutes to improve surface energy and wettability. The diamond abrasive particles are selected to be high-strength, angular artificial diamond micro-powder with a particle size of 30-40 microns. The diamond abrasive particles are dried in a 120°C oven for 2 hours before use.

[0117] A bonding layer is coated on the surface of the bur 7, which is a mixture of brazing filler metal and PVAL binder. Specifically, the PVAL binder and brazing filler metal (particle size less than 2 microns) are uniformly stirred and mixed to stabilize the viscosity of the mixture at 450 mPa·s (measured at 25°C, shear rate 10 s -1 The mixture is uniformly coated on the working end of the bur 7 to ensure that all surfaces of the bur working end are covered. After coating the bonding layer, the bur 7 is rotated in clean air for 30 seconds to make the coating flow flat and form a uniform wet film with a thickness of about 8-12 microns. The pretreated bur is fixed on the bur clamp disc 8.

[0118] 2. Fluidized coating stage:

[0119] Open the upper cover 14 of the fluidized bed cavity 3, load the dry diamond abrasive particles 6 into the fluidized bed cavity 1. Start the fluidization and set the parameters: gas velocity (U) is 0.30 m / s (after preliminary testing, the U mf≈0.16m / s, U t ≈0.90m / s).

[0120] Start air compressor 24, mass flow controller 20, pressure regulating valve 21, precision filter 22, air tank 23, air compressor 24, servo motor 11, servo motor 11 drives the main shaft 13 to drive the main shaft turntable 9 to revolve, the rotation axis 18 drives the lathe needle clamp disc 8 to rotate, the rotation speed is 25 rpm, the revolution track is a circular path with the center of the fluidized bed cavity as the origin and a diameter of 30 mm, the rotation coating process time is 120 seconds, the temperature sensor 5 and the humidity sensor 19 are used to display and control the temperature and humidity inside the fluidized bed cavity 1, and the humidity inside the fluidized bed cavity should be less than 30%. The adhesive mixture coated on the lathe needle surface has certain viscosity, and in the fluidized diamond abrasive particles 6 densely distributed in the cavity space, the revolution and rotation can realize the uniform and omnidirectional adhesion of the diamond abrasive particles on the lathe needle substrate surface.

[0121] The coating process is monitored by using an intelligent sensing system, and the differential pressure and gas flow rate and other parameters are continuously monitored by using an intelligent monitoring system. After stable fluidization, the differential pressure inside the fluidized bed cavity 1 is detected by using the differential pressure sensor 15, and the differential pressure should be near 1.2kPa with small fluctuations. When the differential pressure is too large, the relief valve 17 should be started to discharge the excess gas through the exhaust port 16. During the fluidized coating, the fluidized state inside the fluidized bed cavity can be monitored in real time by using the built-in high-speed camera 10.

[0122] 3. Post-processing stage:

[0123] After the lathe needle surface is fluidized and coated, the lathe needle should be removed from the fluidized bed, and the removal process should prevent the abrasive particles from being displaced or falling off due to the flow of the adhesive. The lathe needle is immediately placed in a muffle furnace for solidification at 120℃ for 30 minutes, and the complete solidification of the diamond abrasive particles and the adhesive mixture on the working end of the lathe needle is completed.

[0124] The coated and solidified lathe needle is inspected, 10 fields of view are randomly selected under a scanning electron microscope, and the coverage rate is calculated by using image analysis software, and the coverage rate is ≥94%; secondly, the abrasive particle density variation coefficient of different parts such as the tip, the groove and the plane of the lathe needle should be <5%. The diamond lathe needle that is fully coated and solidified can enter the brazing system for further brazing to make a diamond lathe needle.

[0125] The above describes a specific embodiment of the present application, but those skilled in the art should understand that this is only an example, and those skilled in the art can make various changes or modifications to this embodiment without departing from the principles and essence of the present application, and these changes and modifications all fall within the protection scope of the present application.

Claims

1. A fluidized bed based apparatus for uniform coating of diamond abrasive particles on a tool bit surface, characterized by: The application relates to a diamond-coating device, which comprises the following parts: a fluidized bed cavity, which is a cylindrical cavity; an upper cover, which is detachably capped on the top of the fluidized bed cavity; a gas distribution plate, which is arranged at the bottom of the fluidized bed cavity and is provided with fluidization holes for dispersing the gas entering the fluidized bed cavity into a large number of uniform tiny gas flows; a gas source system, which sends clean and dry compressed air to the gas distribution plate through a gas pipeline; a pin multi-degree-of-freedom movement mechanism, which comprises a three-axis movement system and a multi-axis rotation system, the multi-axis rotation system is connected to the execution end of the three-dimensional movement system, and the three-axis movement system drives the multi-axis rotation system to move in space in the fluidized bed cavity; the multi-axis rotation system comprises a transmission main shaft, a main shaft rotating disc and a plurality of pin clamp discs; the main shaft rotating disc is fixed at the lower end of the transmission main shaft and located in the fluidized bed cavity, and the transmission main shaft is driven to rotate by a revolution motor; the pin clamp disc is used for clamping and fixing a pin coated with diamond abrasive grains, the top of each pin clamp disc is rotationally connected to the main shaft rotating disc through a revolution shaft, and each revolution shaft is connected to a corresponding revolution driving motor; and a control system, which is used for controlling the operation of the whole coating device. The upper cover is provided with an exhaust port, and a pressure relief valve is connected to the inner side of the exhaust port. The thickness of the gas distribution plate is 20-50 mm, and a flange seal is arranged between the gas distribution plate and the bottom of the fluidized bed cavity. A plurality of rows of fluidization holes are arranged on the gas distribution plate, two adjacent fluidization holes in one row and one fluidization hole in another row form a regular triangle. The fluidization holes are micro-porous structures, which comprise a tapered inlet section, a cylindrical stable section and a diffusion outlet section. The gas source system comprises an air compressor, an air tank, a precision filter, an air dryer, a pressure regulating valve and a mass flow controller which are connected in sequence. Temperature sensors and humidity sensors are arranged in the fluidized bed cavity, the temperature sensors perform multi-point temperature monitoring, and the humidity sensors monitor the gas humidity.

2. The fluidized bed based carborundum surface diamond grit uniform coating device according to claim 1, characterized in that: A differential pressure sensor is arranged on the bottom side of the upper cover, which is used for monitoring the pressure difference between the upper end and the lower end of the gas distribution plate.

3. The fluidized bed based carborundum surface diamond grit uniform coating device according to claim 1, characterized in that: A high-speed camera is arranged on the bottom side of the upper cover, which is used for capturing fluidization state visual information and recording the coating condition of the pin surface.

4. The fluidized bed based carborundum surface diamond grit uniform coating device according to claim 1, characterized in that: The application further discloses a diamond-coating method, which comprises the following steps:

5. The fluidized bed based carborundum surface diamond grit uniform coating device according to claim 1, characterized in that: A pretreatment stage: ultrasonic cleaning and plasma cleaning are performed on the pin, then a bonding layer is coated on the pin surface, the bonding layer is a mixture of brazing filler metal and PVAL adhesive, after the bonding layer is coated, the pin is rotated in clean air, the bonding layer is made to flow flat by surface tension, and a uniform wet film with a thickness of 8-12 microns is formed; the pretreated pin is fixed on the pin clamp disc; meanwhile, the diamond abrasive grains are dried, wherein the diamond abrasive grains are high-strength artificial diamond micro-powder with a particle size of 30-40 microns and clear edges and corners.

6. The fluidized bed based carborundum surface diamond grit uniform coating device according to claim 1, characterized in that: ​ 7. The fluidized bed based carborundum surface diamond grit uniform coating device according to claim 1, characterized in that: ​ 8. The fluidized bed based carborundum surface diamond grit uniform coating device according to claim 1, characterized in that: ​ 9. The fluidized bed based carborundum surface diamond grit uniform coating device according to claim 1, characterized in that: ​ 10. A method for uniform coating of a surface of a tool bit with diamond particles based on a fluidized bed using the coating device according to any one of claims 1 to 9, characterized in that ​ ​ Fluidized coating stage: open the upper cover of the fluidized bed cavity, put the dried diamond abrasive into the fluidized bed cavity; control the gas flow rate between the minimum fluidization velocity and the entrainment velocity, so that the diamond abrasive is in a turbulent fluidization state; immerse the tool pin substrate coated with a bonding layer into the abrasive fluidization zone of the fluidized bed, and drive the tool pin substrate to perform a combined motion of revolution and rotation, so that the diamond abrasive adheres to the bonding layer; drive the tool pin to perform a combined motion of revolution and rotation, so that the diamond abrasive uniformly adheres to the bonding layer of the tool pin; The fluidized coating process is monitored by using an intelligent sensing system. The temperature and humidity inside the fluidized bed cavity are displayed and controlled by temperature and humidity sensors. The pressure difference inside the fluidized bed cavity is detected by using a pressure difference sensor. When the pressure difference is too large, a pressure relief valve should be started to discharge the excess gas through the exhaust port. The fluidization state inside the fluidized bed cavity is monitored in real time by using an internal high-speed camera during the fluidized coating period. Post-processing stage: remove the tool pin after the fluidized coating from the fluidized bed, perform solidification treatment, and finally inspect the solidified tool pin.

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