The rugged task of carrying freight by road in Australia is a punishing one.
Trucks encounter, often over vast distances, some of the harshest conditions on the planet. Windscreen damage and impairment can cost road transport fleets significant overages every month.
More often than not the entire windscreen, when chipped or scratched, needs to be replaced.
In the age of integrated electronics, cameras, sensors and safety feature requirements can make windscreen exchanges even more expensive.
The subsequent downtime alone can represent costly disruptions to asset utilisation and delays to pressing duty cycles. There is a new solution at hand from SCHOTT.
The German glass specialist is providing BOROFLOAT 33 for innovative impact-resistant windscreens as the outer ply giving them superior stone impact resistance as well as a better abrasion resistance in comparison to conventional windscreens.
Conventional windscreens, typically made of soda-lime glass, are particularly susceptible to damage.
They have a high probability of chipping and tend to suffer from extensive damage patterns after stone impacts.
This fragility leads to frequent replacements and greater overall maintenance, not to mention near-mandatory equipment add-ons such as mesh stoneguards.
Select mechanical tests in which soda lime glass is directly compared to specialty glass BOROFLOAT 33 will leave no doubt as to the superior performance and durability of the latter product.
In the Vickers indentation test a diamond tip is pushed onto the glass surface [see picture above].
Afterwards the imprint is investigated under a microscope. For the soda lime glass at a load of 2 Newton, four cracks have occurred around the imprint, whereas BOROFLOAT 33, even at 4 Newton, does not crack.
In sum, the load applied to initiate a crack needs to be much higher in the specialty glass in comparison to standard soda lime glass.
“There are much fewer cracks, less necessary repairs and your truck can keep moving,” says Dr Juliane Brandt-Slowik, Manager Business Development & Sales – Doctor of Engineering – Material Scientist at SCHOTT.
“The benefit is an increase in reliability and durability.”
In the stone impact test (DIN EN ISO 20567-1) gravel is shot onto the surface with a certain pressure.
The damaged surface area at 1 bar is 10.7 per cent for soda lime glass, while it is only 2.5 per cent for BOROFLOAT 33.
At 2 bar the damaged surface area is 19.2 per cent for soda lime glass, while it is between 5.5 and 10.7 per cent for soda lime glass.
The stone impact resistance therefore is much higher for BOROFLOAT 33 in comparison to soda lime glass.
Windscreens that do not have to be regularly replaced because of superior scratch resistance will continue to provide good long-term vantages for the human eye, sensors and cameras especially in dusty environments like the outback and deserts.
The results of a typical abrasion test, which has its origin in the porcelain industry, the PEI (porcelain enamel institute) test is illustrative. Here loose grain is rotated above the materials surface.
The microscopy pictures show minor defects for the BOROFLOAT 33 surface, whereas the soda lime glass surface shows defects, which are longer, deeper and more pronounced.
BOROFLOAT 33 is particularly abrasion resistant.
Illustrated above in a simplified way are the glass structures of the two glass types. On the left soda lime glass; on the right BOROFLOAT 33.
One reason for the better performance is the special structure of the glass according to Juliane.
“Because of the high packing density and low network connectivity, the soda lime glass has a higher density and does have a higher elastic modulus, which does mean it is as brittle as normal glass is,” she says.
“Whereas because of the low packing density and the high network connectivity of the BOROFLOAT 33 glass, the density as well as the elastic modulus are low, which does mean that the glass behaves relatively elastic.”
The lower density of the BOROFLOAT 33 glass also enables it to produce lighter glazing solutions, which helps to save money and to reduce CO₂ footprint, two other major considerations for the modern Australian fleet.
