in Vol. 4 - November Issue - Year 2003
New Products for Blastcleaning and Surface Treatment
Ennio Torrigliani, Pometon Sales Manager
Fig. 1: low carbon steel shot microstructure - lath martensite
Fig. 2: medium carbon steel shot microstructure - tempered martensite
Zinc Shot - zinc granules
Ot Shot - brass granules
With four plants located in and around the Venice area, Pometon S.p.A. manufactures ferrous and non ferrous metal powders and granules for a wide range of industrial applications, such as blastcleaning, shotpeening, stone cutting, powder metallurgy, desulphurization and Grignard reactions. One of their Sales Managers, Mr. Ennio Torrigliani, recently spoke to MFN about four new products for blastcleaning and surface preparation which the Italian firm has developed over the past few months.
Medium Carbon Steel Shot for Blastcleaning
Extensive research and testing have led to the development of a new type of shot for blastcleaning called medium carbon steel shot.
“This product combines many of the advantages of high carbon shot with those of low carbon media”, explains Mr. Torrigliani. “When we had production line tests done by some of our clients, results were so encouraging that we quickly phased out our production of low carbon shot in favor of the new product.”
Although not suitable for all types of blastcleaning applications, low carbon steel shot boasts a longer life span compared to high carbon media, thanks to its lower carbon content. However the drawback is that low carbon shot is impervious to quenching and tempering, two important types of heat treatment normally applied to high carbon shot and common to the production process of many other types of steel and steel products. This means that the microstructure and hardness level of low carbon steel shot cannot be modified after the atomization process. On the other hand, medium carbon steel shot, with a typical average carbon content of 0.4 – 0.5%, can be quenched and tempered just like high carbon shot.
“Quenching eliminates the larger crystalline microstructure which forms as a result of the sudden change of state from liquid to solid during atomization. This gives a fine martensitic microstructure with fine, well-distributed carbides”, continues Ennio as he switches on an electronic microscope. “When viewed under magnification, the microstructure of low carbon shot is coarse. We also know that it is considerably stressed. By comparison, the microstructure of our medium carbon shot is much more uniform and appears as a properly tempered martensite.” (see figures 1 & 2)
The following step in the production process, called tempering, ensures constant hardness levels, which instead may fluctuate during the production of low carbon shot.
Medium carbon shot is an excellent replacement for low carbon media in applications typical of foundries, steel mills and similar activities. “This product gives the advantage of a life span which is longer than that of low carbon media thanks to its uniform microstructure and hardness, which give constant values even in the operating mixture”, concludes Mr. Torrigliani.
Almshot – Aluminium Granules for Blastcleaning and Surface Finishing
Manufacturers of aluminium diecast and stainless steel pieces normally blastclean their products with stainless steel shot to avoid surface oxidation and to achieve a bright surface finish. However at times stainless steel shot can be too aggressive and a milder cleaning process is needed.
“In these cases we offer a product for “soft” blastcleaning called Almshot, our new family of aluminium granules”, explains Mr. Torrigliani. “This product removes small edges and sand left behind by the casting process and at the same time gives a more compact surface, thus slowing down the corroding effect of external elements. Some of our clients have also reported reduced wear on their blasting machine parts, thanks to its lower abrasiveness.”
Zinc Shot – Zinc Granules for Blastcleaning and Surface Finishing
Zinc Shot is used for cleaning zinc, aluminium, stainless steel and other non-ferrous components, usually with turbine wheel machines.
As Ennio Torrigliani points out, “Just like our range of aluminium granules, zinc shot is also recommended in order to avoid ferrous residue on blasted surfaces, but thanks to its higher density, it has a more aggressive effect.”
Ot Shot – Brass Granules for Blastcleaning and Surface Finishing
“Many of our clients cleaning automotive and other types of components made of stainless steel, brass, copper and various alloys are satisfied with the performance of this product, which gives a gentle but thorough cleaning effect and leaves an appealing golden hue on the surface”, states Ennio.
With an apparent density of about 3.40 g/cm³, similar to that of Zinc shot, Ot Shot allows a soft blastcleaning process while at the same time reducing the possibility of surface oxidation.
For more information:
Ennio Torrigliani, Sales Manager
Via Circonvallazione 62, 30030 Maerne (Venezia) Italy
Tel.: +39.041.2903611, Fax +39.041.641624
E-mail email@example.com, www.pometon.com