A pressurized screw feeder for powder injection
- PDF / 269,155 Bytes
- 3 Pages / 603.28 x 783.28 pts Page_size
- 54 Downloads / 216 Views
I
I
I
I
I
41
A Pressurized Screw Feeder for Powder Injection
"E
L.R. FARIAS and G. A. IRONS
v
,I
E
3
The injection of solids into liquid metals is a prominent feature of many metallurgical processes such as desulfurization and dephosphorization of iron and steel, and copper smelting and refining. Precise control over the injection conditions is essential for smooth injection and control of metallurgical properties. ] The most common dispenser design consists of a pressurized tank with a conical bottom section, often with bottom injectors to prevent the packing of the solids. The gas and solids flow rate are controlled by the dispenser bottom orifice diameter, the pressure drop across the tank, and the distribution of gas supplied to the bottom of the tank and that supplied to the conveying line. Figure 1 shows the operating characteristics for such a feeder. One can see that it is difficult to control independently the gas and solids flow rate. Screw feeders are widely used for the accurate control of feed rate, but there were none commercially available that could operate under high pressure necessary for pneumatic conveying and injection deep into liquid metals. Therefore the pressurized screw feeder was designed and constructed. A schematic diagram of the equipment is shown in Figure 2. The screws were commercially available drill bits in 12.7, 19.0, and 25.4 mm diameter. They were matched with three interchangeable flanges at the powder exit. The powder was directed to the screw by a sheet metal powder container which sits inside the pressurized chamber. A 0.19 kW (0.25 HP) motor with solid-state control was used to drive the screw. A load cell was used to weigh continuously the dispenser and motor so that the solids feed rate could be determined. The gas flow was metered by a mass flow meter and controlled by a needle valve. Three pneumatically-activated piston valves were used to divert the gas. For the injection of gas alone, valves A and B are closed and C is opened. This is reversed for powder flow. In order to ensure that the screw controls the solids rate, the gas pressure must be uniform in the dispenser. Therefore, two equalization lines were installed to the discharge flange and dispenser top. Figure 3 shows the operating characteristics of the feeder for sinter fines. Note that the solids rate increases linearly with screw speed up to approximately 600 revolutions per minute (rpm). Apparently at higher speeds there is not enough time for complete filling of the drill bit flutes. Figure 4 demonstrates that the solids feed rate is essentially independent of gas flow rate over a wide range of gas flow rates and screw speeds. Figure 5 shows the influence L. R. FARIAS, formerly with McMaster University during the course of this work, is Research Metallurgist with HyL Research and Development Center, Monterrey, N.L., Mexico. G. A. IRONS is Associate Professor, Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. Manuscript s
Data Loading...
