PVD vacuum coating for medical devices - frequently asked questions and answers.
PVD (Physical Vapor deposition) is a vacuum coating process in which a solid material is vaporized in a vacuum and deposited onto the surface of a part. This process improves 10 times the durability and performance compared with uncoated part. Nowadays, more and more PVD coated medical devices can be found in the hospitals.
Q1 | What is the role of PVD vacuum coating for medical devices?
PVD coating improve the aesthetic appeal of medical devices greatly. In addition, the manufacturers use the coating colors to differentiate the device models. A better edge retention is provided by PVD vacuum coatings to remain coated surgical instruments clear. For other devices, the coatings reduce wear between stainless steel components and help prevent oxidation and corrosion.
Q2 | Does PVD have an adverse effect on the sharp edges of the devices?
A cleaning that may adversely affect edge will not be made during PVD coating process if the part has sharp edges. To coat tiny or delicate parts, it’s required to reduce the heating and coating rate to ensure that the parts are not damaged during the process.
Q3 | What surface treatment gives the best result?
The typical thickness of PVD vacuum coating is 0.0025 – 0.013 mm. it’s so thin that it’s strongly recommended to have the surface grinded or polished instead of sandblasted or matte treated to get better results.
Q4 | What materials are applied to PVD coating?
PVD vacuum coating can be applied to most of metals that can withstand heating up to 430°C. Common medical materials include stainless steel #303, #440C, #17-4, Titanium and some tool steels. Since the melting point of aluminum is quite close, the coating process cannot be applied to this material.
Q5 | What kind of PVD coating is used for medical devices?
Four types of coating are commonly used for medical devices. They are:
- TiN (Titanium Nitride) with thickness of 0.0025 – 0.005 mm and hardness of 2400 – 2600 HV for golden surface.
- AlTin (Aluminum Titanium Nitride) with thickness of 0.0025 – 0.005 mm and hardness of 4000 – 4200 HV for carbon black surface.
- CrN (Chromium Nitride) with thickness of 0.0025 – 0.013 mm and hardness of 2200 – 2400 HV for silver surface.
- Alpha with thickness of 0.0025 – 0.005 mm and hardness of 4400 – 4600 HV. Alpha is a multi-layer coating with top layer is ZrN (Zirconium Nitride) for silver or golden surface. The lifespan of Alpha coating is 2-4 times longer than that of TiN coating due to its high hardness, lubrication and wear resistance.
Q6 | What are the advantages of PVD over CVD (Chemical Vapor Deposition)?
Compared to CVD, PVD is applied at a much lower temperature. In addition, heat treatment is not required for the parts after PVD coating. Moreover, The surface of the parts with PVD coating remains the original finish, while the CVD coated parts needs to be polished as an extra process.
Q7 | What are the advantages of PVD over Anodization?
Generally speaking, PVD is more wear resistant than Anodization and retains colour better over time.
For both PVD and CVD coating, the required vacuum is quite high. Therefore, dual stage rotary vane vacuum pumps are frequently used for this process.
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