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In the metallurgical, heat‑treatment, and steel‑processing industries, hearth rollers and cantilever roller heads are two core conveying components that are easily confused yet serve distinctly different purposes. One carries steel strips through the furnace chamber, while the other guides billets in and out of the furnace. Both directly withstand temperatures above 800°C, oxidising atmospheres, and continuous wear. The performance of each directly affects product quality, production continuity, and overall operating costs.
However, because they look similar and have comparable names, many practitioners are often puzzled when selecting them. This article provides a comprehensive analysis of the key differences and selection criteria for hearth rollers and cantilever roller heads from four perspectives: function, material selection, structural design, and maintenance.
1. Hearth Roller vs. Cantilever Roller Head – Different Roles Despite Similar Names
What Is a Hearth Roller?
A hearth roller is a critical load‑bearing and transmission component in continuous annealing lines, roller‑hearth furnaces, and similar equipment. Installed at the bottom of the furnace chamber, it serves as the key component that supports and drives steel strips or plates through the furnace with precision. Its operating condition is the decisive factor in whether the annealing furnace can operate normally.
Hearth rollers operate in furnace chambers at 850°C to 1200°C, withstanding high‑temperature oxidation, corrosion, cyclic thermal stress, mechanical loads, and wear. Their core tasks are to carry the weight of the strip, maintain roller straightness, and convey the strip stably, ensuring uniform heating and smooth travel through the furnace.
Hearth rollers have diameters ranging from Φ60 mm to Φ2000 mm and are made from either heat‑resistant alloy steels or fused‑silica ceramics. They are widely used in the annealing of silicon steel, stainless steel tubes, carbon steel tubes, oil‑well pipes, as well as in glass‑tempering furnaces and the photovoltaic industry.
What Is a Cantilever Roller Head?
A cantilever roller head is the core working component of a cantilever roller table that extends directly into the furnace chamber and contacts the high‑temperature billet. Cantilever roller tables feature a cantilevered structural design – the support and drive mechanisms are arranged on the same side of the roller table, and the roller head projects into the furnace like a cantilever, used for conveying and guiding billets during charging and discharging.
Cantilever roller heads are widely used in the steel, metallurgical, paper, and chemical industries to support and drive rollers under severe conditions such as high temperature, high pressure, and heavy loads. In rolling production, reheating furnaces generally adopt side‑charging and side‑discharging, which requires cantilever roller tables inside the furnace to convey billets.
Key Differences at a Glance
| Aspect | Hearth Roller | Cantilever Roller Head |
|---|---|---|
| Installation position | Bottom of furnace chamber (load‑bearing surface) | Side of furnace body (cantilevered into the furnace) |
| Core function | Supports and drives strip through the furnace | Guides billets in and out of the furnace |
| Support method | Supported at both ends | Single‑side cantilever support |
| Load characteristics | Uniform load + thermal stress | Large cantilever bending moment, complex loading |
| Primary applications | Continuous annealing furnaces, hot‑dip galvanising lines, silicon‑steel annealing furnaces | Reheating furnace charging/discharging ends, bar/section rolling mills |
2. Hearth Roller – The “Load‑Bearing Backbone” of Continuous Annealing
Core Functions
1. Supporting and conveying strip
As the key load‑bearing and transmission component that supports and drives steel strip through the furnace, the hearth roller directly carries the full weight of the strip. In large continuous annealing furnaces, hearth rollers must operate stably for extended periods to ensure the strip passes through at a constant speed.
2. Ensuring strip surface quality
The surface quality of the hearth roller directly determines the quality of the steel plate and production efficiency. Roll surface nodules, oxidation, or wear can cause scratches, indentations, and other defects on the strip surface, seriously affecting the yield.
3. Withstanding severe operating conditions
Hearth rollers must operate stably under harsh conditions including high temperature, oxidation and corrosion, cyclic thermal stress, mechanical loads, and wear. Furnace temperatures typically range from 850°C to 1200°C, imposing demanding requirements for high‑temperature strength, oxidation resistance, and creep resistance of the material.
Material Selection
The material for hearth rollers should be determined based on furnace temperature, furnace atmosphere, and load requirements:
| Furnace Temperature | Recommended Material | Key Characteristics |
|---|---|---|
| 650–850°C | ZG35Cr24Ni7Si2N, ZG30Cr26Ni12 | Medium‑temperature heat resistance, cost‑effective |
| 950–1050°C | ZG30Cr25Ni20Si2, ZG45Cr25Ni35 | Good high‑temperature strength, excellent oxidation resistance |
| 1050–1200°C | ZG45Cr28Ni48W5 (2848W5) | Tungsten‑strengthened, excellent creep resistance |
| 1200–1400°C | ZG45Cr33Ni50W16 | Ultra‑high‑temperature heat resistance, top‑tier creep resistance |
Common materials for hearth rollers include high‑nickel‑chromium alloys such as ZG40Cr25Ni20Si2 (2520/310S), with special heat treatments to enhance overall performance.
Structural Design
Double‑layer composite structure: Large‑diameter heat‑resistant steel hearth rollers for continuous annealing lines often adopt a double‑layer composite structure – an inner core of centrifugally cast carbon steel / low‑alloy steel with an outer cladding of high‑performance heat‑resistant steel. This design improves rigidity and load capacity.
All‑ceramic hollow roller structure: Fused‑silica ceramic hollow rollers are mainly used in non‑oriented silicon steel lines and galvanising‑line annealing furnaces. They offer high strength, high‑temperature resistance, low thermal expansion, good chemical stability, no deformation, a smooth and fine surface, and good wear resistance – making them an ideal replacement for traditional graphite sleeves and ceramic‑coated rollers.
Manufacturing Processes
Hearth rollers are generally produced by casting, with the roller body mainly manufactured by centrifugal casting. The shafts are machined from a lower‑grade material than the roller body, assembled by shrink fitting, and welded with filler material of the same grade as the roller body.
3. Cantilever Roller Head – The “Charging/Discharging Messenger” of Reheating Furnaces
Core Functions
1. Guiding billets into and out of the furnace
Cantilever roller tables are primarily used at the charging and discharging ends of reheating furnaces, feeding billets into the roughing mill or guiding them into the furnace. In bar‑mill reheating furnaces, the cantilever roller table consists of multiple charging cantilever rollers and multiple discharging cantilever rollers.
2. Withstanding cantilever bending moments
The cantilever structure is subject to complex forces with large bending moments. The roller head (fixed end) must bear the huge load from the cantilever end without plastic deformation.
3. Adapting to different temperature zones
The charging and discharging cantilever roller heads are located in different positions and subjected to different temperatures, requiring correspondingly different materials and structures.
Material Selection – Zone‑Based Matching Principle
The material for cantilever roller heads should be matched according to the temperature of each furnace zone:
| Furnace Zone | Temperature | Recommended Material | Structural Form |
|---|---|---|---|
| Charging end | ~650°C | ZG4Cr25Ni35Si2 | Curved/arc structure |
| Discharging end | ~1100°C | ZG4Cr28Ni48W5Si2 (2848W5) | Tapered structure |
Common material grades for cantilever roller heads include:
- ZG45Cr28Ni48W5Si2 (2848W5): 1300°C, top choice for ultra‑high temperatures
- ZG40Cr25Ni35NbW (2535W2): 1200°C
- ZG40Cr25Ni20Si2 (2520/310S): 1200°C
- ZGCr26Ni12: 1100°C
2848W5 is currently the leading high‑end material for high‑temperature cantilever roller heads. It contains approximately 28% chromium for oxidation resistance, 48% nickel for austenitic matrix stability, and 4–6% tungsten for solid‑solution strengthening, greatly improving creep resistance above 1100°C. 2535 (ZG40Cr25Ni35) is particularly valued for its excellent resistance to carburisation and coking, performing exceptionally well in controlled‑atmosphere furnaces.
Structural Design
Curved/arc structure: Charging‑end cantilever roller heads use an arc shape to keep the billet as close as possible to the centreline of the roller table during charging, avoiding impacts and collisions.
Tapered structure: Discharging‑end cantilever roller heads generally use a tapered design.
T‑shaped clad structure: The roller head consists of a shaft and a disc, with a ceramic material layer (0.5–1 mm thick) applied to the opposing faces. This design offers high strength, prevents the ceramic layer from peeling off, and effectively extends service life.
Water‑cooled design: The roller shaft is a thick‑wall seamless steel tube. Cooling water is delivered through an inlet pipe to the front end of the shaft and returns through the hollow cavity, cooling the hollow shaft. Water‑cooled rotary joints can extend equipment life by 2.3 times.
Manufacturing Processes
Manufacturing processes for cantilever roller heads include: centrifugal casting, investment casting, sand casting, lost‑foam casting, machining, and welded assembly. Investment casting reduces internal defects and improves structural density.
4. Selection Guide – Five Steps to the Best Solution
Step 1: Identify the equipment type and application
- Load‑bearing and conveying in continuous annealing furnaces, hot‑dip galvanising lines, silicon‑steel annealing lines → Hearth roller
- Billet guiding and conveying at reheating furnace charging/discharging ends → Cantilever roller head
Step 2: Determine the temperature range
- For hearth rollers, refer to the temperature‑zone material table above.
- For cantilever roller heads, select materials separately for the charging end (~650°C) and discharging end (~1100°C).
Step 3: Evaluate the loading characteristics
- Uniform load and thermal stress dominate → hearth roller, focus on creep resistance and oxidation resistance
- Large cantilever bending moment and complex loading → cantilever roller head, focus on high‑temperature yield strength and bending capacity
Step 4: Choose the structural form
- Large diameter, heavy load → hearth roller with double‑layer composite structure or all‑ceramic hollow roller
- High‑temperature charging/discharging → cantilever roller head with arc/tapered structure and water‑cooled design
Step 5: Consider manufacturing processes and maintenance
- High quality, long service life → centrifugal casting (roller body) + investment casting (roller head)
- Quick‑change requirements → modular design
5. Usage and Maintenance Highlights
Hearth Roller Maintenance
Nodule treatment: Hearth rollers are prone to nodule formation at high temperatures, causing roller failure. Typically, they must be removed for nodule cleaning every 3–6 months. Online treatment methods can also be used to control nodules.
Regular inspection: Regularly check roller‑body diameter changes, and monitor the stability of the oxidation‑resistant layer and high‑temperature creep limits.
Surface protection: Hearth roller surfaces are often aluminised or coated with ceramics to enhance oxidation resistance.
Cantilever Roller Head Maintenance
Regular inspection: Check roller heads for cracks or deformation, paying special attention to the connection between the head and the shaft.
Water‑cooling system maintenance: Ensure the water‑cooling system is clear to prevent overheating deformation of the roller head due to inadequate cooling.
Timely replacement: Replace roller heads promptly when severe wear or cracking is found to avoid damage to billet surfaces.
Measures to Extend Service Life
- Select high‑quality heat‑resistant steel: Premium materials such as 2848W5 significantly improve high‑temperature creep resistance.
- Optimise structural design: Use ceramic coatings, water cooling, and other features to enhance heat resistance.
- Zone‑based material matching: Choose different materials for different temperature zones instead of a one‑size‑fits‑all approach.
- Standardised operation: Avoid thermal‑fatigue damage from frequent start‑stop cycles.
- Regular maintenance: Promptly remove nodules and replace worn parts.