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Grinding and polishing of titanium

1. Mechanical grinding: Titanium has high chemical reactivity, low thermal conductivity, high viscosity, low grinding ratio, and is easy to react with abrasive tools. Ordinary abrasives are not suitable for grinding and polishing titanium, and it is best to use superhard abrasives with good thermal conductivity, such as diamond and cubic boron nitride. The polishing speed is generally 900-1800m/min. It is advisable, otherwise, the titanium surface is prone to grinding burns and microcracks.
2. Ultrasonic grinding: Through the action of ultrasonic vibration, the abrasive particles between the grinding head and the surface to be ground move relative to the surface to achieve the purpose of grinding and polishing. Its advantage is that grooves, pits, and narrow areas that cannot be ground by conventional rotary tools become easier, but the grinding effect of larger castings is not yet satisfactory.
3. Electrolytic mechanical composite grinding: Using conductive grinding tools, electrolyte and voltage are applied between the grinding tool and the grinding surface. Through the combined action of mechanical and electrochemical polishing, the surface roughness is reduced and the surface glossiness is improved. The electrolyte is 0.9NaCl, the voltage is 5V, and the speed is 3000rpm/min. This method can only grind flat surfaces, and the grinding of complex denture brackets is still in the research stage.
4. Bucket grinding: Utilizing the centrifugal force generated by the revolution and rotation of the grinding bucket, the dentures inside the bucket move relative to the abrasive, thereby reducing surface roughness. Grinding is automated and efficient, but it can only reduce surface roughness and cannot improve surface glossiness. The precision of grinding is poor, and it can be used for deburring and rough grinding before precision polishing of dentures.
5. Chemical polishing: Chemical polishing is achieved by the oxidation-reduction reaction of metals in a chemical medium to achieve the purpose of leveling and polishing. Its advantage is that chemical polishing is independent of the hardness, polishing area, and structural shape of the metal. All parts in contact with the polishing solution are polished without the need for special and complex equipment. It is easy to operate and is more suitable for polishing complex titanium denture brackets. However, the process parameters of chemical polishing are difficult to control, and it is required to have a good polishing effect on dentures without affecting their accuracy. A better titanium chemical polishing solution is prepared in a certain ratio of HF and HNO3. HF is a reducing agent that can dissolve titanium metal and play a leveling role. When the concentration is less than 10%, HNO3 plays an oxidizing role, preventing excessive dissolution and hydrogen absorption of titanium, while also producing a brightening effect. Titanium polishing solution requires high concentration, low temperature, and short polishing time (1-2 minutes).
6. Electrolytic polishing: also known as electrochemical polishing or anodic dissolution polishing, due to the low conductivity and strong oxidation performance of titanium, using aqueous acidic electrolytes such as HF-H3PO4 and HF-H2SO series electrolytes can hardly polish titanium. After applying an external voltage, the titanium anode immediately undergoes oxidation, making anodic dissolution impossible. However, using anhydrous chloride electrolyte at low voltage has a good polishing effect on titanium. Small specimens can achieve mirror polishing, but for complex restorations, complete polishing cannot be achieved. Perhaps changing the shape of the cathode and adding a cathode can solve this problem, and further research is needed.

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