Mineral glass (MG) is a scratch and impact-resistant glass most commonly used in watchmaking. It has excellent reflective properties, strength, and clarity. Mineral glass crystals are coated with a hard material which makes them resistant to scratch marks. The advantage of mineral glass is that a scratch can be easily polished out. Currently, we are using mineral glass with the compositions as shown below:
Transparency: above 95%
Grade 1: 1.518
Grade 2: 1.520
Grade 1: 550 ~ 650 HV
Grade 2: 600 ~ 700 HV
In order to lower the production costs, we wish to replace mineral glass with alternate cost-effective material. We would expect the new material to be less brittle which is one of the limitations of the mineral glass. The dimensions of the watch cases vary from 18 mm to 38 mm in diameter and 1mm to 1.1mm in thickness.
Plastic was tried as an alternative. This, however, could not be assembled with O-rings using the normal process. The gaskets had to be ultrasonically welded or glued. This reduces the application of plastic material with metallic cases or water-resistant watches. Also, plastic is less scratch-resistant compared to mineral glass.
- The watches with alternate material should have comparable or better properties than Mineral Glass in terms of transparency, water resistance, scratch resistance, and refractive index.
- The material needs to pass the Impact strength test and should be capable to withstand up to 3, 5 and 10 atm pressure during testing of the assembled watch.
- To ensure easy assembling with Brass cases, the top and bottom surface of the material needs to be provided with chamfer. Thus, the alternate material should be machinable to produce chamfer on either side.
- The alternative material should be used with all metallic cases and water-resistant watches.
- In case the glass joint is made using adhesives, the alternate material being proposed should be compatible with transparent glues.
- It should not hamper the assembly process.
- In order to ensure sustainability, we are looking for recyclable material. However, a solution which is bio-degradable is also preferred.
- It must be environmentally safe and should pose no health hazards to operators during any phase of operation.
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