ABSTRACT

Making of an artistic piece usually includes a number of different technologies. It implies that for understanding of eventually present irregularities one should knows a lot of technical details. Brazing tehnology is one of them, inspection of integrity, also. Brazing technology generally has evolved on empirical manner, mainly by trial and error(s). The basic difficulty in this technology is that the real situation is highly complex due to the presence of large number of variables, some of them may not be easy to recognize. The great problem is the appearance of crack(s) in postcleaning periode, i.e after brazing is finished, it means over years or decades. A good braze joint must be both physically and chemically bounded. One of the available method for investigation is radiographic testing, when the thickness of testing components commonly does not represents a problem. Here provided radiographic testing has revealed the existence of some indications only at leaves. The indications usualy mean discontinuity in material homogenity. Penetrant testing is a next step for investigation of surface. Registration of indications and their locations are necessary steps in any further approach for removing such discontinuities. Choosing the repair method always is particular problem, however in entire technique, especially on sensitive artistic component(s). Every action in repairing or restauration may led to more or less visible traces. Unadequate actions may permanently change the appearance or usage of treated artefact. Here is shown one irregularity (crack) at one brazed leaf from an artistic desk lamp.

Due to its excellent mechanical, chemical and optical properties, also on fatigue, polymethilmetacrylate (PMMA) is widely used for many purposes. PMMA has a reputation as a material that cannot be machined well, but, its elasticity and toughness enable its shaping by the deformation processes. Laser drilling and cutting are also available techniques for PMMA sheets shaping, used when both mechanical and optical PMMA properties must be preserved. In this work, the influence of CO 2 laser cutting/drilling on transparent and coloured PMMA surfaces is investigated, as well as by the other laser systems. The cut surfaces were investigated by a light microscopy and, on those surfaces, the average surface roughness R a was measured. The material zone affectted by the laser beam during the cutting process was monitored by a thermal imaging, and theoretical simulations of temperature distribution in this area were performed using the various versions of COM-SOL packages.