Large Pit Furnace Hanging Plate

What Is a Large Pit Furnace Hanging Plate?

A large pit furnace hanging plate is the core supporting and lifting tool for pit‑type heat treatment furnaces. It is primarily used to vertically suspend and carry various shaft‑type workpieces, gears, and other components inside the furnace during processes such as carburizing, quenching, annealing, and tempering.

A pit furnace is a batch‑type furnace with a cylindrical, deep‑well structure. Its hearth diameter typically ranges from 0.5 to 4.5 metres, with depths reaching up to 30 metres, and charge capacities generally between 10 and 20 tonnes. Workpieces are vertically loaded into the furnace using specialised lifting tools. This vertical suspension method effectively prevents slender workpieces from bending or distorting during heating. The large pit furnace hanging plate is the critical load‑bearing component in this process, and its quality directly determines the success of the heat treatment operation and workplace safety.

Material Selection for Large Pit Furnace Hanging Plates

Material choice is the primary consideration in hanging plate design. Since the plate operates under prolonged high temperatures and severe thermal cycling (rapid heating and cooling), it must exhibit excellent high‑temperature resistance, creep resistance, and thermal shock resistance.

Mainstream Heat‑Resistant Steel Grades

2520 (ZG40Cr25Ni20Si2) is the most commonly used material for pit furnace lifting tools. It contains 24–27% chromium and 19–22% nickel, with silicon added for strengthening. Its continuous service temperature reaches 1100–1150°C, with short‑term peaks up to 1350°C. It offers excellent high‑temperature tensile strength and creep resistance, maintaining dimensional stability under full loads without elongation, bending, or sagging.

Higher‑grade materials include 1838, 2535, and 2848. For higher furnace temperatures, critical parts such as the base can be made from these grades for enhanced durability. For example, 2848W5 (ZG45Cr28Ni48W5Si2) withstands even more extreme temperatures. ZG3Cr24Ni7N, through the synergistic effect of chromium, nickel, and nitrogen, achieves oxidation resistance above 1000°C.

Material Selection Guide

Material Grade	Continuous Service Temp.	Recommended Applications
2520 (310S)	1100–1150°C	General pit furnace heat treatment
1838	~1100°C	Higher‑temperature duties
2535	~1150°C	High‑temperature, heavy‑load conditions
2848	~1200°C	Ultra‑high temperature applications

When selecting the material, consider furnace temperature, workpiece weight, frequency of use, and overall cost.

Structural Design of Large Pit Furnace Hanging Plates

Common Structural Types

Integral disc‑type bottom tray is the most widely used design, often with segmented fan‑shaped plates. Its flat structure helps control workpiece distortion during heat treatment. However, this type suffers from large dimensions, more casting defects, and relatively short service life.

Support‑frame tray is an improved design consisting of a central sleeve and 5–10 radial supports cast integrally with the sleeve. Honeycomb fan‑shaped plates are mounted between adjacent supports. This structure offers simplicity, lower self‑weight, fewer failure points, reduced heat absorption, and easier casting.

Double‑layer or multi‑layer configurations are used for very large pit furnaces. They comprise a bottom plate, intermediate plates, spacers, suspension rods, and honeycomb panels. A complete large pit furnace hanging assembly can weigh about 8 tonnes and accommodate up to 50 tonnes of workpieces.

Adjustable‑spacing hanging plates represent a recent development, allowing flexible loading of different‑sized workpieces through expandable designs.

Key Design Considerations

1. Strength verification: Rigorous strength calculations must be performed based on total workpiece weight to ensure load capacity at elevated temperatures.
2. Honeycomb panel design: The honeycomb structure reduces dead weight and heat absorption while maintaining adequate strength.
3. Modular design: When workpiece shapes change, only the hanging plate or fixture needs replacement rather than the entire assembly, extending service life and reducing material consumption.
4. Hole layout: The hanging plate consists of multiple sector pieces, each with several suspension holes – typically 6‑, 10‑, or 15‑hole configurations.

Manufacturing Processes

The manufacturing process directly influences product quality and service life. Mainstream techniques include:

• Investment precision casting: high accuracy and good surface finish
• Sand casting: suitable for large castings, with single pieces weighing up to 3 tonnes
• Lost‑foam casting: ideal for complex geometries with tight dimensional tolerances
• Centrifugal casting: dense microstructure with fewer defects
• Integral casting: no seams or weld points, eliminating the risk of weld cracking or rod breakage common in welded designs

Reputable manufacturers perform spectral material analysis and penetrant (PT) inspection on every batch to eliminate porosity, sand inclusions, cracks, and other casting defects. Finished products undergo full stress‑relief annealing to remove internal casting stresses.

Core Advantages

1. Exceptional high‑temperature deformation resistance

High‑quality heat‑resistant steel hanging plates maintain dimensional stability under heavy loads at high temperatures – no elongation, distortion, or fracture.

2. Outstanding thermal fatigue resistance

Specially optimised for frequent heating/cooling cycles in quenching and carburising processes, these plates resist cracking, peeling, and fracture even after repeated furnace entries and exits.

3. Wide adaptability and modular compatibility

They can be used with matching‑material baskets, trays, and tiered racks for integrated batch loading and unloading, greatly improving furnace utilisation and throughput.

4. Extended service life

Compared with ordinary carbon‑steel lifting tools, premium heat‑resistant steel plates last 3–5 times longer. Modular design also allows replacement of only worn components, further reducing operating costs.

Application Range

Large pit furnace hanging plates are widely used in:

• Furnace types: Aichelin, Ipsen, Huisen, Fengdong, and other major brands of large pit carburising, quenching, and annealing furnaces
• Processes: carburising, carbonitriding, quenching, annealing, tempering, solution treatment, etc.
• Workpieces: various shafts, gears, automotive parts, bearing components, fasteners, precision hardware, mould forgings, and more
• Base diameter range: 1000–3000 mm

Usage and Maintenance Guidelines

Before use:

• Remove dirt and debris from the plate surface.
• Inspect the lifting tool and check the furnace cover lifting mechanism for proper operation.
• Ensure the plate is dry – any moisture may cause molten media splashing.

During use:

• Do not touch the lifting tool by hand to prevent accidents.
• Monitor rod creep to avoid clamping deformation.

Maintenance tips:

• Regularly inspect for cracks, especially at stress concentration points like slots.
• Temper promptly after quenching to prevent cracking.
• If suspension rods show thinning due to elongation, scrap and replace them immediately.

Customisation and Selection Advice

Large pit furnace hanging plates are available for non‑standard customisation. When selecting, customers should provide the following key parameters:

1. Pit furnace inner diameter and depth
2. Total workpiece weight and dimensions
3. Heat treatment process temperature
4. Loading/unloading frequency
5. Overhead crane hook specifications

Professional manufacturers can design the plate size, rod length, number of lifting eyes, thickness, and finger configuration according to these parameters, supporting single‑layer, multi‑layer, and other special structures.