RH Ruhrstahl Heraeus Vacuum Degassing Refining Furnace 80T~320T
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Product Summary
Product Details
RH Vacuum Degassing Refining Furnace
,Ruhrstahl Heraeus Refining Furnace
,Refining Furnace 80T
Product Description
I. Overview
The RH vacuum circulation degassing process (RH process) is a highly efficient secondary refining technology for molten steel. It was jointly developed by Ruhrstahl and Heraeus in Germany in 1957, with the equipment name derived from the initials of the two companies. This technology utilizes the vacuum circulation principle to perform various refining treatments on molten steel, including degassing, decarburization, desulfurization, composition fine-tuning, and temperature compensation. It is one of the core pieces of equipment for producing high-quality clean steel in modern steel plants.
The RH process was originally primarily used for hydrogen removal to prevent white spot defects in steel, with the treatment range limited to steel grades with strict gas content requirements such as large forging steels, heavy plate steels, silicon steels, and bearing steels. Since the 1980s, with increasingly stringent requirements for molten steel quality in the automotive industry, RH technology has developed rapidly, gradually transforming from a single-function degassing device into a multi-functional secondary refining equipment incorporating vacuum decarburization, oxygen blowing decarburization, powder injection desulfurization, temperature compensation, and homogenization of temperature and composition.
II. Working Principle
An RH vacuum degassing unit mainly consists of a refractory-lined vacuum vessel and two snorkels (an up-leg and a down-leg). Its working principle is based on the air-lift pump principle, with the specific process as follows:
1. The two snorkels (up-leg and down-leg) at the bottom of the vacuum vessel are immersed into the molten steel in the ladle, with an immersion depth of generally 150-200mm.
2. The vacuum pump system is started to evacuate the vacuum vessel, reducing the pressure inside to approximately 50-100Pa.
3. Argon gas (lifting gas) is injected into the molten steel through nozzles in the side wall of the up-leg snorkel. This argon rapidly expands under the high temperature of the molten steel and the low pressure in the vacuum vessel.
4. The expansion of argon reduces the density of the gas-liquid mixture in the up-leg snorkel. Under the pressure difference caused by this density difference, molten steel is continuously drawn into the vacuum vessel. Inside the vessel, the molten steel releases gases under high vacuum and is dispersed into fine droplets. The degassed molten steel then returns to the ladle through the down-leg snorkel.
5. The molten steel rises at approximately 5 m/s and descends at 1-2 m/s, circulating rapidly between the vacuum vessel and the ladle. Typically, degassing is completed after 3 cycles (about 10 minutes), with an additional 5 minutes for alloying and other operations, resulting in a total treatment time of approximately 20 minutes.
III. Equipment Composition
1. Vacuum Vessel: A refractory-lined cylindrical container, divided into upper vessel and lower vessel, serving as the main site for degassing and decarburization reactions.
2. Snorkels: Consisting of an up-leg and a down-leg, installed at the bottom of the vacuum vessel, used for circulating molten steel between the vacuum vessel and the ladle, with the interior fully lined with refractory materials.
3. Vacuum Pump System: Generates and maintains the vacuum degree within the vacuum vessel; can use steam ejector pumps or dry mechanical pumps.
4. Alloy Feeding System: Used to add alloy materials into the vacuum vessel under vacuum conditions for precise composition control.
5. Top Lance System: Multi-functional top lance capable of oxygen blowing decarburization, post-combustion, powder injection desulfurization, etc.
6. Ladle and Ladle Lifting System: Used to carry the molten steel to be treated; immersion of the snorkels can be achieved by either lifting the ladle or lowering the vacuum vessel.
7. Vessel Preheating Device: Preheats the vacuum vessel before treatment to reduce temperature drop during processing.
IV. Metallurgical Functions
After decades of development, the RH vacuum circulation treatment process can accomplish the following functions:
| Function | Performance Indicator | Description |
|---|---|---|
| Dehydrogenation | [H] ≤ 1×10⁻⁶ (1 ppm) | Under vacuum conditions, hydrogen in the molten steel escapes and is removed by the vacuum pump. Degassed steel can achieve approximately 65% hydrogen removal, while non-degassed steel can achieve approximately 70%, with hydrogen content in the steel reduced to below 2×10⁻⁶. |
| Deoxidation | [T.O] ≤ 10×10⁻⁶ (10 ppm) | Utilizing the deoxidation effect of carbon under vacuum, when treating non-degassed ultra-low carbon steel, oxygen content can be reduced from (200-500)×10⁻⁶ to (80-300)×10⁻⁶. |
| Decarburization | [C] ≤ 10×10⁻⁶ (10 ppm) | By blowing oxygen onto the molten steel surface in the vacuum vessel under reduced pressure, the carbon content of the molten steel can be reduced to below 10×10⁻⁶, meeting the production requirements for ultra-low carbon steels such as IF steel. |
| Desulfurization | [S] ≤ 30×10⁻⁶ (30 ppm) | By injecting synthetic slag onto the molten steel surface in the vacuum vessel, sulfur content can be reduced to below 30×10⁻⁶, or even as low as 3×10⁻⁶. |
| Denitrogenation | [N] ≤ 10×10⁻⁶ (10 ppm) | When the initial nitrogen content in the steel is high (>100×10⁻⁶), the denitrogenation rate can reach 10-20%; when the initial nitrogen content is low (<50×10⁻⁶), there is little change in nitrogen content before and after treatment. |
| Composition Fine-tuning | High analysis hitting rate | After vacuum circulation treatment, the molten steel is in a good reducing state, allowing for accurate composition adjustment during fine-tuning, with high alloy yield. |
| Steel Heating | Chemical heating | Using methods such as oxygen blowing for chemical heating can compensate for temperature drop during processing and precisely control molten steel temperature to meet the strict superheat requirements of continuous casting. |
| Inclusion Removal | Significantly improve molten steel cleanliness | The dispersion of molten steel into fine droplets within the vacuum vessel promotes the flotation and removal of non-metallic inclusions, significantly improving molten steel cleanliness. |
V. Process Characteristics and Advantages
| Characteristic | Description |
|---|---|
| Short treatment cycle | The total treatment time is about 20 minutes, which can coordinate well with the converter smelting rhythm, resulting in high production efficiency. |
| Fast reaction rate | The apparent decarburization rate constant kC can reach 3.5min⁻¹, resulting in a short treatment cycle and high production efficiency. |
| Small temperature drop | The general treatment temperature drop is only 30-50℃, and chemical heating can be used to compensate for the temperature drop. |
| Large treatment range | The same equipment can treat molten steel of different capacities, with treatment capacity reaching up to 400t. |
| High analysis hitting rate | Good reproducibility of metallurgical results, high composition hitting rate, and high alloy yield. |
| Flexible operation | Snorkel immersion can be achieved through either vacuum vessel lifting or ladle lifting, with various equipment configurations available. |
| Strong adaptability | The treatment of steel grades is unrestricted, ranging from ultra-low carbon IF steel to high-carbon bearing steel and high-alloy stainless steel, all of which can be treated. |
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