A new machine can automatically press together different refractory materials in a single working cycle.
Functional refractories made of different layered materials have long posed a challenge to manufacturers because of the manual labor involved. Either the different materials must be manually fitted together as finished components, or the molds must be manually filled before the refractories can be pressed into one piece (the technique primarily used with friction presses).
Figure 1. Typical wear damage to the working surface and bore lining on a compound sliding gate.
Functional refractories made of different layered materials have long posed a challenge to manufacturers because of the manual labor involved. Either the different materials must be manually fitted together as finished components, or the molds must be manually filled before the refractories can be pressed into one piece (the technique primarily used with friction presses). Both options are labor- and time- intensive, and therefore costly. Furthermore, the quality of the product depends on the daily individual performance of the different workers.
So why make layered refractories? When using elements such as sliding gates or nozzles, only the surface that comes in contact with the smelted steel must be composed of a highly wear-resistant-and therefore costly-material, while the basic structure of the element can be a less expensive material. In some cases, two different materials are used to provide different mechanical or thermal properties.
Recently, a new hydraulic press was developed to facilitate the production of compound sliding gates and nozzles. The machine fills the molds and presses the product in a single working cycle, which makes the process more economical and highly reproducible.
Figure 2. A double-layered sliding gate design.
The most common damage that occurs during the lifetime of a compound sliding gate includes bore enlargement, bore edge damage and sliding surface damage (see Figure 1). Taking this into account, a typical sliding gate design might be as shown in Figure 2.
Figure 3. A double-fill procedure for a sliding gate without a bore. (click to enlarge)
The top surface and the bore area are made of a different material than the basic structure. To achieve this combination, the mold in the new press is equipped with two different lifting devices and a pin. The pin locks the area holding the high-grade material into the bore area while the main filling charger box fills the core material. Master slave hydraulic servo axes keep the pin exactly at the level of the top surface of the mold at all times, even when the mold frame is lifted while the basic material is being suctioned in. A second filling charger fills the compound material. When this charger is above the cavity, the pin is lowered while the mold frame is simultaneously lifted, and the compound material is filled in. Both materials are pressed together in one step and are then ejected by the machine (see Figure 3).
Figure 4. A layout schematic of a double-layered pressing unit.
Figure 4 shows a sample layout of a press used for compound elements. The filling charger with the feeding hopper for the core material is located in the back, similar to a standard press, while the charger for the high-grade material is mounted on the left side of the press. Both chargers are equipped with a filling box mixer to homogenize the material during filling. Depending on the material type, the second charging system can be equipped with a material disintegrator, vibrating sieve or cellular valve. The press can also be configured with a vacuum pressing unit to avoid lamination and increase the product density.
Compared to a conventional pressing process, the new press increases the total cycle time by approximately 10 seconds due to the second charging process and increases the machine cost by about 12%. However, this is far less than the time and costs required to complete the fitting and/or filling processes manually.
Further advances are being developed for the production of sliding gates and nozzles, as well as for other shapes where the use of at least two different materials is useful. Technologies are also under way that will allow the modification of existing presses for co-pressing operations.
For more information about the new hydraulic press, contact:
LAEIS GmbH at Am Scheerleck 7, 6868 Wecker, Luxembourg
Phone: (352) 27612-0
Fax (352) 27612-109