VOL. 13 March ISSUE YEAR 2012
in Vol. 13 - March Issue - Year 2012
Tailored Solutions For Technological Problems.
Technological sandblasting treatment plant for surface preparation
Example of typical components for surface preparation
Typical surface profile for surface preparation
Norblast designs and manufactures sandblasting and shotblasting systems and, with over 6000 machines sold worldwide, has covered the vast majority of the industrial fields. Norblast offers a wide range of solutions, from those designed with a modular concept, able to adapt itself to specific technological needs, to the most special cases entirely designed ad hoc. Peen Service is a research, development and application center of shot peening for third parties. It has been working with the major Italian universities for over 15 years, either on base research issues or on specific customer’s topics. The high quality level, certification according to EN 9100, and the technical support Peen Service is able to provide in the design phase of the process are certainly the strength points of the company.
Norblast group is a small Italian group of SMEs that for over thirty years has been working in the world of surface treatment either as a manufacturer of shot blasting and sand blasting machines or as a job shop for shot peening. In many areas, among which, just to name a few, the energy and biomedical fields, it is necessary to coat the surfaces of the mechanical components. Each coating has its own characteristics and purpose that best suits the needs of each single component. Proper surface preparation ensures coating success.
Turbine blades are usually coated with metal coatings to be preserved by mechanical wear induced by condensation droplets in steam turbines, or by impurities of exhaust gas in gas turbines. The latter can be coated by ceramic layers to reduce thermal stress of the hot blades of gas turbines or can be treated up to multilayer coatings to add different features. In biomedical components, for totally different purposes, coatings can be applied to encourage osseointegration such as in the case of permanent implants or even reduce it in the case of temporary ones. Each case has its own peculiarities and, of course, its own needs. No matter what they are, a characteristic of all coatings is the need for an adequate preparation of the surface on which they must be deposed. The right preparation that ensures proper cleaning and morphology of the surface is without any doubt one of the keys to success of the deposition and the adhesion of a technological coating. Surface morphological characteristics are usually characterized by appropriate surface roughness parameters among which are the best known average roughness Ra, the maximum values ??of roughness valley Rv and peak Rp, or the more common total peak-valley Rz. In some cases, there may be particularly useful lesser-known parameters such as the bearing surface or the value of average slope Rdq. To ensure proper performance of the various coatings, each of those parameters must be first properly evaluated and then strictly kept within very tight tolerances. Based on those principles, during a recent period, Norblast has developed a fully automated system of surface preparation for biomedical components, totally unattended by personnel, with a high production capacity. Once the optimal process parameters are known, to ensure the continuity of plant performance, the company runs a detailed preventive FMEA (Failure Mode Effects Analysis). Through this type of analysis, it is possible to identify the criticality of the process and design the system so as to minimize the effects of potential malfunctions. Four global areas of analysis were identified.
• Quality requirements of the technological process
• Production capacity of the plant
• Biological compatibility of materials used in the process
• Environmental compatibility of the plant and its emissions
For each of these areas, the most critical situations were identified, and then specific sensors were introduced into the system. In addition, some of those sensors were adapted or even re-engineered to resist abrasive aggression and simultaneously meet the needs of biological compatibility or to ensure compliance with environmental compatibility. The most important work was in any case, the satisfaction of the specific quality issues under very high work volumes. It is well known that, in the same way as shot peening, even in blasting technology, the result of the treatment is directly related to the energy of the treatment. Once again, as in shot peening, the energy of the abrasive stream is directly proportional to the size of the abrasive and to its speed. In a compressed air sandblasting machine, it is relatively easy to control the speed of the abrasive stream while controlling the grain size, especially that of an abrasive grit, and it is an operation that hides many pitfalls. To control the size of the abrasives, vibrosieves as used, as in shot peening plants. In the case of abrasive grits, the lower sieve, deputized to discard the crushed grains, tends to become "blinded" by those grits that remain trapped in the net. In the long run then, the lower sieve tends to lose its effectiveness and the average size of the working abrasive decreases. To reduce the problem of "blind sieves" it is possible to use "self-cleaning" systems, but usually they are aggressive towards the nets of the sieves often causing the net breakage, adding an additional problem. To solve this problem, Norblast has worked in synergy with Peen Service, as a matter of fact its research center, to design and develop an innovative self-cleaning system that is at the same time non-aggressive and effective, ensuring the correct life of the system. As it is quite clear, the technological level of those plants is nowadays comparable to that of the most advanced shot peening systems. That is the reason why Norblast likes to define such types of treatments as "technological sandblasting treatments."