Mixers are more efficient than double-cone units
Ductil Iron Powder (DIP), Buzau, Romania, was established in 2000 as a spin-off of Ductil Steel. Its products are iron and alloyed powders for use in powder metallurgy and welding applications.
The plant for making the iron powders began operation in 1995, and by 2000 it reached its current capacity of 10,000 metric tons per year. DIP is owned by two other metals companies: Feralpi Siderurgica and Sider Sipe of Italy.
The DIP strategy calls for continuous improvement of its product range, with an emphasis on high-performance powders, such as those used to manufacture automotive parts. The strategy also calls for a gradual increase in capacity as the company meets its quality goals.
Making powder metals
Making iron powders starts with melting scrap iron and steel and then striking the stream of molten metal with high-pressure water jets. The jets solidify the metal into irregular particles, and a hydroclone and centrifuge then separate the particles from the water.
Next, a rotary dryer removes any remaining moisture, a screener sorts the particles by size, and a magnetic separator removes contaminants. The metal then enters an annealing furnace that heats the powder to 1,000°C in a hydrogen atmosphere. Annealing removes most of the oxygen and carbon from the metal and softens it so that it's easy to compact into the shape of a part. Annealing also forms the powder into a coherent cake, which is subsequently broken up and screened to eliminate oversize particles in the powder.
In the final processing step, a double-cone blender homogenizes the iron before packaging. The blender handles 5-ton lots that DIP then divides into 1-ton portions and packages in FIBCs. Many of DIP's powder customers are Western European manufacturers of sintered structural components.
Improving the operation
To help implement its marketing, quality, and growth strategy, DIP hired Per Lindskog as its managing director in 2000. He has more than 40 years' experience in powder metallurgy at several international companies and was president of the European Powder Metallurgy Association.
One of Lindskog's first tasks at DIP was to evaluate the efficiency of its blending process. The evaluation involved touring metal powder facilities in the USA and elsewhere, and he became interested in arotary batch blender made by Munson Machinery, Utica, NY USA.
The blenders use lifters and baffles inside a rotating mixing chamber to create a rapid but gentle mixing action that fluidizes the ingredients. According to the supplier, the rotary blenders create a better blend than double-cone blenders, and they are more efficient because they are easier to load, they require less space on the plant floor, and they work faster. Furthermore, the units maintain better homogeneity because the mixing chamber rotates during loading and unloading, which prevents the de-mixing, or segregation, common when ingredients have very different bulk densities. At DIP, the bulk density of metal powders is about 2,800 kilograms per cubic meter, while the bulk density of additives such as zinc stearate is about one-tenth of that.
In 2002, Lindskog approved the purchase of three rotary batch blenders. Two are lab-scale and pilot-scale units called Mini Mixers. One has a capacity of 10 kilograms and is used for testing in the lab. The other unit handles up to 600 kilograms and is used for testing production lots. The third blender, a Model 700-THCX-140, is a production unit that handles up to 10 metric tons and is equipped to accept liquid additions. DIP commissioned the production-size blender at the end of June 2003.
'The new installation will make it possible to serve our customers with press-ready pre-mixes,' Lindskog said.
'These can have different compositions. Usually, they contain one of our grades of iron powder as the main constituent, one or several alloying additions in powder form, and a pressing lubricant.'
Lindskog said DIP has relatively limited experience with the blenders, but he called them state-of-the-art machinery that ensure the utmost homogeneity. 'We have made quantitative studies of the mixing process and found that the Munson mixers give a very effective mixing action, better than other processes we have studied,' he said.
'We chose the mixers for a number of reasons: It is an effective mixer. It treats the powder gently. It is possible to vary the charge weight from 15 to 100 percent of the capacity, and it continues mixing during discharge.'