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Since 1971, Lema has devoted itself exclusively to the production of machinery and equipment
for the processing, treatment and production control of glass and organic lenses.
World leader in developing systems for the chemical tempering of glass lenses,
Lema caters both for optical lens industry as well as the sunglasses sector.
With modern ovens for chemical and physical tempering, the fruit of years of development,
Lema provides what’s necessary to make glass lenses reliable, top quality objects.
We ask Mr. Alessandro Rivaroli, the company’s assistant manager,
to explain in detail the importance of a treatment such as chemical tempering for the world of glass.
We are here today with Mr. Alessandro Rivaroli, assistant manager of the company Lema.
Can glass be considered unbreakable?
Nowadays, the only kinds of glass considered unbreakable are those that have undergone a tempering process.
Chemical tempering, the field of specialisation for LEMA S.r.l.,
provides the best results possible in breakage tests, guaranteeing unrivalled breakage resistance.
Unlike traditional tempering, chemically tempered glass is used in many other sectors besides optics where the breakage factor is central, such as aeronautical, military, naval and high speed trains
- all the fields in which breakage resistance is much, much more than just criteria, it is an absolute necessity.
How important is chemical tempering for glass lenses?
To date, chemical tempering has proven itself to be an indispensable treatment for the production of both lenses for prescription glasses as well sunglasses.
In fact, the ion exchange that occurs during the treatment guarantees resistance of up to 2.5 times higher
than that achieved through thermal tempering and 2 times higher than a lens in CR39 resin, making lenses thus tempered reliable and proof-tested.
Furthermore, after the treatment, the surface compression is just a few microns in penetration, avoiding the formation of stresses inside the glass and thus reducing the risk of breakage and maintaining perfect optical quality by not exceeding 450° C during the process.
Not to be underestimated is the possibility to temper also curved glass,
thinner than 2mm in thickness and also glass of different size and shape in a single cycle.
What properties can glass boast following this process?
As already mentioned, mechanical resistance of chemically tempered glass is higher than that produced by traditional tempering,
not to mention higher resistance to heat and bending, according to several tests.
It must also be highlighted how glass thus treated can be then perforated, cut or processed without any risk of breakage, chemical tempering being the treatment that affects only the glass surface, not producing internal stresses.
What’s the difference between the two treatments, chemical and thermal tempering?
Chemical tempering differs from thermal tempering in many ways.
We have already listed the differences in results in our answers to the previous questions, but here are the differences between the various ways in which the treatment is carried out.
Chemical tempering is a process that thanks to our ovens requires only the use of electricity and potassium nitrate,
reducing production costs insofar as once the salt is molten, consumption to maintain a temperature of 450° C is minimal, while salt consumption is negligible.
Each tempering cycle requires a standard time of about 16 hours,
which can vary depending on the type of glass used, but no operator is necessary apart from in the loading and unloading phase.
Lastly, and of particular importance for the lenses sector, chemical tempering, unlike thermal tempering guarantees full respect for the optical quality of the glass.
It does not create any distortion and maintains the response to light unchanged in tinted lenses.
Why can glass be considered the material of the future, compared to other materials?
From many viewpoints, glass is one of the most versatile materials for a range of different applications, not just lenses.
We know that it is used as reinforcement, given its remarkable resistance, in various products such as fibreglass and in telecommunications thanks to optical fibres.
Chemical tempering of glass is thus the treatment of the future for glass, increasing its positive qualities and maintaining its most useful natural properties.
That is precisely why LEMA, after 40 years of business, can boast clients in the most wide ranging sectors:
from the optical to the naval and aeronautical sector, from architecture and safety glass as well as in the IT and telecommunications field.