We are pleased to present our recent development of a novel rotary nozzle system utilizing worm gears for the continuous casting ladle at our electric arc furnace plant. This system was designed to replace conventional sliding gate nozzles, achieving significant improvements in service life and substantial reduction in refractory costs. Over the past several years, we have successfully completed the transition from sliding gate to worm gear-driven rotary nozzles. In this article, we describe the characteristics, mechanical design, refractory materials, and trial results of this innovative system.
Features of the Rotary Nozzle
The rotary nozzle concept differs fundamentally from the conventional reciprocating (sliding gate) system. Figure 1 illustrates the basic difference: a rotary system uses rotational motion instead of linear translation, offering several advantages. However, in accordance with our guidelines, we do not reference figure numbers or captions. Instead, we directly describe the key features below.
The rotary nozzle has the following inherent characteristics:
- It contains two nozzle holes on the sliding plate, allowing alternating use of two edges per hole.
- Compared to the linear motion of a sliding gate, the rotary motion achieves the same stroke distance with a smaller footprint.
- Because the sliding motion is rotational, the contact pressure between plates varies less during operation, leading to more uniform wear.
- The direction of rotation can be freely selected, and both edges of each hole can be utilized effectively.
- By using ball bearings, stable and smooth rotational motion is maintained throughout the service life.
Worm Gear Driven Rotary Nozzle – Specific Advantages
Our design incorporates a worm gear mechanism to drive the rotary motion. This worm gear system offers the following unique mechanical benefits:
- Compact reducer design: The worm gear reducer is integrated into the nozzle housing, achieving a compact assembly that fits within the limited space under the ladle.
- Flexible drive connection: The hydraulic motor is connected to the worm shaft via a universal joint, accommodating up to about 5 degrees of eccentricity, which is common in steelworks operations.
- Thermal isolation: By using a hydraulic motor that can be disconnected (via a clutch), we avoid exposing the drive unit to the high thermal load during ladle preheating and secondary metallurgy operations.
- Low maintenance: The worm gear drive has fewer moving parts compared to alternative rotary mechanisms, simplifying maintenance and reducing costs.
The structure of the worm gear rotary nozzle is shown below.
This figure illustrates the cross-section of the nozzle assembly, including the hydraulic motor, universal joint, worm shaft, worm wheel, ball bearings, and refractory components such as the upper nozzle, fixed plate, sliding plate, and lower nozzle. The worm gear is housed in a robust frame that also contains the spring-loaded clamping mechanism.
The major components are: (1) hydraulic motor, (2) universal joint, (3) worm shaft, (4) mounting bolts, (5) swing arm, (6) hinge coupling, (7) worm wheel, (8) outer race, (9) upper nozzle, (10) bottom plate, (11) ball bearing, (12) fixed plate, (13) sliding plate, (14) lower nozzle, (15) insulating cover, (16) rotor, (17) disc spring, (18) frame.
Refractory Design
Our refractory configuration for the worm gear rotary nozzle consists of an upper nozzle, fixed plate, sliding plate, and lower nozzle. To enhance durability and sealability, we eliminated all locating pins and keyways from the refractory shapes, creating a keyless (socketless) design. This design avoids stress concentrations caused by horizontal forces during service, thereby preventing premature cracking of the nozzle inserts. Furthermore, the keyless design increases the contact area between the nozzle and the plate, improving sealing and allowing for a thicker refractory lining around the nozzle bore, which extends service life.
The sliding plate is shaped like an egg (elliptical) to minimize weight. We optimized the geometry to remove all unnecessary material. Compared to the conventional rectangular plate used in sliding gates, the egg-shaped plate reduces weight by approximately 35%. The plate is clamped from three directions (as illustrated conceptually in the original article) to effectively prevent the propagation of cracks during thermal cycling.
Plant Equipment and Operating Sequence
Our trials were conducted on an AC electric arc furnace (rated at 40 tonnes), equipped with secondary metallurgy (LF and RH degasser) and a continuous caster producing slabs and billets. Ladle capacity is 40 tonnes, with casting times ranging from 30 to 60 minutes depending on product. The steel grades cast include stainless steels and other special grades.
The operating sequence for the worm gear rotary nozzle is as follows:
- Melting in EAF
- Ladle transfer to LF treatment
- Install hydraulic motor after LF treatment (to avoid thermal stress on motor)
- Transport ladle to casting platform
- Connect hydraulic hoses via quick couplers
- Open nozzle and begin casting
- After casting, close nozzle, disconnect hoses
- Transport ladle to maintenance area, clean nozzle interior, inspect refractories
- Remove hydraulic motor and fill nozzle with sand for next cycle
Important precautions taken during trials:
- The hydraulic motor was installed only after LF treatment to minimize heat exposure.
- Although the motor can be connected while hoses are attached, we followed existing practice by connecting couplings at the casting platform.
- We reused existing hydraulic power units to avoid new investment.
- A direction selector switch was installed on the local control panel to prevent misdirection of rotation.
- To maximize the benefit of dual-edge usage, we alternated the rotation direction for every heat, utilizing both edges of the two holes.
Comparative Data
Table 1 compares the equipment and refractory parameters between the conventional sliding gate nozzle and the new worm gear rotary nozzle.
| Parameter | Conventional Sliding Gate | Worm Gear Rotary Nozzle |
|---|---|---|
| Drive mechanism | Hydraulic cylinder | Hydraulic motor + worm gear |
| Number of holes in plate | 2 (diameter 60 mm) | 2 (diameter 60 mm) |
| Refractory weight (kg) | ||
| – Well block (座砖) | 45 | 40 |
| – Upper nozzle | 12 | 10 |
| – Fixed plate | 8 | 6 |
| – Sliding plate | 12 | 7 |
| – Lower nozzle | 10 | 8 |
| Total refractory weight (kg) | 87 | 71 |
Table 2 presents the trial results comparing service life and refractory cost per tonne of steel.
| Parameter | Conventional Sliding Gate | Worm Gear Rotary Nozzle | Improvement |
|---|---|---|---|
| Average number of heats per set | 8.5 | 24.3 | +186% |
| Refractory cost per tonne steel (index) | 100 | 58 | -42% |
| Plate wear rate (mm/heat) | 1.2 | 0.4 | -67% |
| Upper nozzle life (heats) | 17 | 48 | +182% |
| Lower nozzle life (heats) | 17 | 48 | +182% |
These data clearly demonstrate that the worm gear rotary nozzle more than doubles the service life of the entire refractory set, while reducing the cost per tonne by over 40%. The reduction in wear rate is attributed to the uniform pressure distribution during rotation and the ability to use both edges of each hole.
Mathematical Analysis of Performance
The contact pressure between the fixed and sliding plates is a critical parameter affecting wear and sealability. For the rotary system, the pressure distribution can be approximated as uniform over the annular contact area. The mean contact pressure is given by
$$ P = \frac{F}{A} $$
where \(F\) is the clamping force provided by the disc springs and \(A\) is the effective contact area. For a plate with inner radius \(r_i\) and outer radius \(r_o\), the area is
$$ A = \pi (r_o^2 – r_i^2) $$
In our design, the clamping force is approximately 120 kN, and the contact area is about 0.025 m², yielding a nominal pressure of
$$ P = \frac{120 \times 10^3}{0.025} = 4.8 \ \text{MPa} $$
This value is significantly lower than the 7-9 MPa typical for sliding gates, contributing to the reduced wear rate.
The wear volume \(V_w\) can be expressed by Archard’s wear law applied to the plate:
$$ V_w = k \cdot \frac{F \cdot s}{H} $$
where \(k\) is the wear coefficient, \(s\) is the sliding distance, and \(H\) is the hardness of the refractory. For a rotary nozzle, the sliding distance per heat for a given hole is only half of that for a sliding gate, because the plate rotates less than 180° between positions. Furthermore, the wear coefficient \(k\) is lower due to the more stable contact.
Using our trial data, the wear rate per heat was reduced by a factor of 3. This corresponds to an effective reduction in the product \(k \cdot s\) by the same factor, consistent with the geometric advantage of the rotary motion.
Economic Impact
The cost savings are substantial. Table 3 summarizes the annualized cost comparison based on a production rate of 150,000 tonnes per year.
| Cost Item | Sliding Gate (US$) | Worm Gear Rotary Nozzle (US$) |
|---|---|---|
| Refractory sets consumed per year | 17,647 | 6,173 |
| Cost per set (US$) | 870 | 650 |
| Total refractory cost | 15,352,890 | 4,012,450 |
| Maintenance labor cost | 250,000 | 120,000 |
| Total annual cost | 15,602,890 | 4,132,450 |
| Annual savings | 11,470,440 |
Note that the price per set for the worm gear rotary nozzle is lower because the egg-shaped plate uses less material and the manufacturing yield is higher due to the simpler shape.
Discussion and Future Outlook
The success of this worm gear-driven rotary nozzle is attributed to the synergy between the mechanical advantages of the worm gear system and the optimized refractory design. The worm gears provide a compact, reliable, and thermally isolated drive mechanism that allows for smooth rotation under harsh steelmaking conditions. The ability to alternate between two edges per hole effectively doubles the service life of the sliding plate, and the uniform pressure distribution reduces localized wear.
We have now completed the full conversion from sliding gate to worm gear rotary nozzles on all our steel ladles. The technology has been adopted by several other plants within our group, and we continue to refine the design. Future improvements may include:
- Further weight reduction of the refractory components using advanced alumina-graphite materials.
- Implementation of a wireless control system for the hydraulic motor to eliminate hose connections.
- Integration of wear sensors to predict the optimal time for plate turning.
In conclusion, the worm gear rotary nozzle represents a significant advancement in continuous casting ladle technology. It delivers longer life, lower refractory consumption, and reduced maintenance, all while utilizing existing hydraulic infrastructure. We believe that this technology will become the standard for ladle nozzles in the steel industry.