Address:
Glafo, PG Vejdes väg 15,
SE-351 96 Växjö
SWEDEN

Visitor's address:
Vejdes plats 3

Tel: +46 10 516 63 50
E-mail: info@glafo.se

You find a map at the
"about Glafo" page.

Project leader: Christina Stålhandske
Project status: on-going project


POLISHING GLASS BY MEANS OF WATER CUTTING TECHNOLOGY – CROSS-DICIPLINARY COLLABORATION FOR SUSTAINABLE DEVELOPMENT


The aims are:
- to develop an environmentally friendly polishing technique that produces the same finish as an acid-polished finish; for flat surfaces, cut edges and holes both in float glass and in crystal glass
- to create a network within this field
- to appoint a person in the area of water cutting
- to produce a prototype glass polishing installation
.

You can read the first report and the background of the project here.


Initial meeting
We held an initial meeting in February at which we gave information on the project and held a group discussion in order to gain ideas, requests and opinions on the possibilities of the technology. It was attended by representatives from the glass industry, water cutting industry and the university as well as financiers. The work group is taking the results of the discussions into account in the project work.

Development of plate glass polishing technology
A deeper literary study has been carried out to establish achievements within the area, and previous research results have been studied. A fine polishing agent must be used, and organisations with competence and experience in the area have been contacted. Existing equipment has been adapted to feed in a mixture of polishing agent and water. Static equipment was tested first and then equipment was built incorporating motion and with the capability of polishing angles.

Pilkington and Orrefors have provided test pieces of plate glass and lead-free crystal glass. Orrefors has contributed to the work by polishing test surfaces and providing polishing agent.

Even the initial tests show that the technology works, but polishing area demarcations are still evident. Various parameters such as time, distance, angle and nozzle have been varied. For example, solid cone, flat jet and point jet nozzles have been tried. A test has also been performed on a piece with a cut, with apparently already the same result as for a flat surface. To achieve acceptable polishing times in future tests, among other things, higher pressure is required, and a pump with a capacity of 24 bar has be ordered.


Initial test equipment for polishing glass using water-cutting technology.

We have also started a strategic sustainability analysis of the technology in cooperation with Blekinge Teknisk Högskola.

Polishing agent
Initially, two polishing agents, Regipol och Sillitin, which are presently used for crystal glass, will be used. The particle size and chemical composition of the agents have been analysed using a scanning electron microscope (SEM) as well as a laser method. The chemical compositions differ while the particle size is almost identical, being primarily between 5 and 10 mm.


SEM images of two polishing agents being tested in combination with water-cutting technology.

Evaluation of analysis methods
We are also working to find an objective method for evaluating and describing the polished surfaces. We need this in order to ascertain whether we are achieving the goal of obtaining surfaces of minimally the same quality as can be obtained using acid polishing. We have taken measurements at the Ytkemiska institutet, SP, and at a topography workshop arranged by Bruker AXS. The lead-free crystal test pieces were brush polished and acid polished; the acid-polished example was shiniest to the eye and corresponds to the quality we wish to obtain in the project. We have arrived at three main groups of techniques that show potential:

1) trailing stylus profilometry
2) optical profilometry
3) AFM (atomic force microscopy)

Trailing stylus profilometry entails a fine point sweeping over the surface along a line that is some tenths of a millimetre long. The method can be used to establish values for surface smoothness, for example in the form of R_a value (average deviation from the surface), and this should also work directly on a cut. Any inclination is subtracted and the largest surface wave lengths are filtered out.

The table shows the results for some of the test surfaces and, as reference, the value for a perfect plate glass surface. These show that the method is sufficiently sensitive to grade different acid polished surfaces also.

Optical profilometry, based on optical interference, and AMF technology have the advantage of providing an image which represents the topography of the surface. They show large differences in appearance between acid polished and brush polished surfaces, see photo. AFM provides a better resolution, laterally, but the area analysed is smaller.


Image with AFM, analysed surface about 80 x 80 mm. Brush polished surface to the left, and acid polished surface to the right.


Images with Optical profilometry 1, analysed surface about 250 x 250 mm. Brush polished surface to the left, and acid polished surface to the right.


Images with Optical profilometry 2, analysed surface about 260 x 350 mm. Brush polished surface to the left, and acid polished surface to the right.

Further work
We are also planning to perform a simple hole polishing test, e.g. holes of 5 and 20 mm diameter. While waiting for the pump, we are forming a test plan and ensuring that the installation is as prepared as it can be. We shall acquire and examine several polishing agents.

The evaluation of the analysis method is continuing, and we are planning for the taking of measurements at SP using trailing stylus profilometry. We are obtaining the prices of some selected pieces of analysis equipment.