Project leader: Maria Lang
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.
You can read the second report here.


Polishing trials
After the introductory attempts made using an existing pump at the "Swedish Waterjet Lab" it was confirmed that higher pressure is needed to achieve shiny surfaces. During November 2009 a new pump was installed, which means that we can conduct tests with up to 30 bar of pressure.

The test bench has been developed so that we are able to vary the pressure of the slurry (a mixture of water and polishing agent), the speed of the nozzle over the surface of the glass, the angle of the nozzle and the distance between the nozzle and the glass to be polished.

The test bench.

We have purchased six different nozzles so far, but there are many more that may be worth testing.

We also use various types of polishing agent. So far we have tested Regipol (cerium oxide), Sillitin (aluminium silicate), aluminium oxide and iron oxide.

A statistical experiment schedule for these parameters has been drawn up using "Modde" software for designing experiments. The results from trial runs are entered into the software. This allows you to see which parameters have the most effect and which work well together.


The Ra value, which is a measurement of surface roughness on the polished samples, has been entered into the experiment design software Modde.
The lowest Ra value (= the finest surface) is in the blue area up to the left.
This shows that on the samples run so far, a low speed nozzle over the surface of the glass had the biggest effect in producing the smoothest possible surface.

With some of the nozzles it seems that at high pressures there is blasting of the shiny surface. Continued optimisation of the various parameters is ongoing.


Results of the tests performed to date show that we have more developing to do.
We can see that it is possible to achieve a shiny surface but the results are not sufficiently good to look at. The measurements we have got so far using a stylus profilometer do not really match what we see with our own eyes.

Selection and purchase of analysis equipment
When the various analysis methods were compared, what determined the choice was that the interferometer can also provide a good image of the surface to be analysed.

Bruker and Topnova have been asked to supply quotes for optical interferometers.
An interferometer can produce both an image and a calculation of the surface structure.

With Bruker’s equipment it is also possible to use a confocal objective, which means that it is possible to carry out measurements on gently curved surfaces and on certain edges.

Samples are sent to all suppliers for sample measurement, and these measurements, along with the price, determine which equipment we will choose.

Further work
Another nozzle is to be purchased and tested.

Until now, polishing experiments have been carried out on float glass, which is harder than crystal. Now there will also be tests polishing ground plates of crystal.

Work is continuing on optimising the various polishing parameters.

Evaluation of the various instruments continues.

We will be testing the polishing of surfaces that have a finer ground surface to start with than we have tested before.