Identify low-cost Engineering material as an alternative to Mineral Glass in watch cases.
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:
Grade 1
SiO2 |
Na2O |
CaO |
K2O |
MgO |
TiO2 |
ZnO |
BaO |
Sb2O3 |
||
69.3% |
8.0% |
6.7% |
8.7% |
0.4% |
0.4% |
4.0% |
2.0% |
0.5% |
Grade 2
SiO2 |
Na2O |
CaO |
K2O |
MgO |
TiO2 |
Al2O3 | P2O5 | Fe2O3 | ||
72.3% |
13.5% |
7.0% |
1.0% |
4.0% |
0.1% |
1.3% |
0.2% |
0.1% |
Transparency: above 95%
Refractive Index
Grade 1: 1.518
Grade 2: 1.520
Core Hardness
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.
Options Tried:
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.
Solution Requirements: