Matilda Schander and Christina Stålhandske operating Glafo’s optical profilometer. The profilometer performs extremely detailed analyses of surface smoothness. Photo: Dick Gillberg
Scratch resistance of flat glass
Published 2012-04-12
New functions of flat glass require it to undergo complex production processes. The RISE institute Glafo Glass Research Institute has investigated the scratch resistance of flat glass and of modified flat glass.
In buildings, flat glass has traditionally provided a transparent barrier against weather conditions. In other applications, it has served mainly to protect some enclosed object that is intended to be viewed by users or others. Development of new functions of flat glass requires it to undergo increasingly complex production processes, such as the manufacture of multifunctional laminates or the application of coatings. Glass can also be used as a surface for information and/or carrier of communication in applications such as displays, smart phones and touch screens. In other words, glass is becoming a material that is not merely "just there", but which is also increasingly handled and subject to wear and tear.
It is probable that more and more parts/surfaces in buildings and the domestic environment will be made from, and/or covered by, multifunctional glasses. The opportunities for utilising previously unused surfaces, such as worktops, walls, doors and furniture in order to improve the quality of life in society are endless.
As these changes and applications evolve, flat glass is moving from being simply a barrier to a material with one or more additional functions. Glass and persons will inter-react more actively, which means that the performance of flat glass, in terms of resistance to contact and abrasion will have to be improved.
Equipment for investigating scratch resistance
The Glafo project has identified different types of scratches, equipment necessary for their investigation and various methods of testing. In this context, "scratch resistance" is used as an umbrella concept for various types of wear of surfaces. Scratches occur in many forms, examples include scratching, scuffing, chipping, abrasion, scraping, engraving, cloudiness, delamination, erosion, cracking, robustness and scraping.
Various types of apparatus and equipment have been developed in order to simulate natural processes, and to optimise the accuracy of the apparatus. Examples of tests for investigation of various types of scratches include:
- Nano indentation
- Cloth test
- Scanning probe microscopy
- Linear scratch testing
- Rotational scratch testing
- Oscillating abrasion test
- Standard pencil test
Companies manufacturing such equipment include Taber Industries, Sheen Instruments, Elcometer, Gardner and others.
Other parts of SP Technical Research Institute of Sweden whose work include scratch resistance and wear of various materials, such as those working with the automotive industry and in the field of electronics, have also been brought into the project.
Glafo has recently purchased an advanced optical profilometer, which is capable to perform extremely detailed analyses of surface smoothness. It is hoped that this equipment will enable different types of scratches and materials to be identified.
How resistant is a resistant surface?
Scratch resistance and wear resistance are material properties that are more qualitative than quantitative. However, a common feature of all forms of wear and tear is that the process results in loss of mass or volume from the body subject to it. In practice, and in analysis, it may well be clear that a material or surface is very resistant, but this often presents a challenge to find a quantified measure of by just how much one material is better than another. It also means that direct comparisons between the results of different investigations are not always possible.
With the optical profilometer, it is possible to obtain values of surface smoothness - Ra values - that can be used for comparison of the results of scratch tests.
The project, which is being carried out in conjunction with the School of Glass Technology at Linnæus University in Växjö, concluded during the latter part of 2011. Flat glass that has been modified by various methods at the university will be evaluated using equipment from SP in Borås, after which Glafo will analyse the samples, with particular emphasis on the optical profilometer.
