Mesh Belt Furnace Applications: Sintering, Brazing, Annealing, and More

Mesh belt furnaces serve a critical role in modern manufacturing, handling heat treatment processes that demand continuous flow, consistent quality, and precise atmosphere control. Their applications span automotive, aerospace, fastener manufacturing, powder metallurgy, electronics, and general metalworking industries. This article examines the major applications in detail, including the specific requirements each process places on furnace design.

Powder Metallurgy Sintering

Sintering is the cornerstone application for many mesh belt furnace lines. In powder metallurgy, metal powders are compacted into a near-net shape and then heated in a controlled atmosphere to bond the particles — without melting the base material.

Process Requirements for Sintering

• Temperature: Typically 1120-1150°C for ferrous parts, 800-900°C for bronze and copper-based components
• Atmosphere: Nitrogen-hydrogen (typically 90% N₂ / 10% H₂) or endothermic gas to prevent oxidation and reduce surface oxides
• Belt loading: Parts are loaded at controlled density, typically 3-8 kg per square foot of belt area
• Time at temperature: Usually 15-45 minutes depending on part cross-section

Common Sintered Products

• Self-lubricating bearings (oil-impregnated bronze)
• Automotive transmission components (gears, sprockets, hubs)
• Valve seat inserts and valve guides
• Shock absorber components
• Home appliance gears and cams
• Lock and hardware components

Zhejiang Wannengda Furnace Industry designs sintering lines with multi-zone temperature profiling and precision atmosphere control to achieve consistent sintered density and dimensional accuracy.

Continuous Brazing

Brazing in a mesh belt furnace joins two or more metal components using a filler metal that melts at a temperature above 450°C but below the melting point of the base metals. The continuous conveyor format is particularly effective for high-volume brazing of small assemblies.

Brazing Process in Mesh Belt Furnaces

The brazing process in a continuous furnace follows this sequence:

1. Cleaning: Parts must be free of oil, grease, and oxides before loading
2. Loading and assembly: Components are assembled with brazing alloy pre-placed (as paste, foil, or preform)
3. Heat-up: Parts travel through the furnace preheat and high-heat zones
4. Brazing: Filler metal melts and flows into the joint by capillary action at peak temperature
5. Cooling: Parts exit through a controlled cooling section, allowing the filler to solidify

Typical Brazing Applications

• Carbide cutting tool brazing (carbide inserts to steel shanks)
• Automotive heat exchanger assembly
• Metal-to-ceramic brazing for electronic seals
• Diamond tool segments to steel bodies
• Hydraulic fitting and manifold brazing
• Brake pad backing plate assembly

The key advantage of mesh belt brazing is the ability to run thousands of identical assemblies through an identical thermal cycle, producing consistent joint strength and appearance without flux in controlled-atmosphere furnaces.

Bright Annealing of Fasteners and Stampings

Bright annealing is one of the most common mesh belt furnace applications. The process softens work-hardened metal parts while preserving a bright, oxide-free surface finish — eliminating the need for post-process cleaning or pickling.

Why Bright Annealing Matters

When steel is cold-formed — drawn, stamped, headed, or rolled — the material work-hardens. For fasteners, this creates a problem: the threads must be formed, but work-hardened material can crack or produce poor thread quality. Annealing restores formability without surface degradation.

Process Parameters

• Fastener annealing (carbon/low-alloy steel): 720-850°C in nitrogen-hydrogen atmosphere (typically 3-5% H₂)
• Stainless steel annealing: 1000-1100°C in dissociated ammonia or pure hydrogen
• Copper/brass annealing: 480-650°C in nitrogen or nitrogen-hydrogen
• Belt speed: Calculated to provide 15-30 minutes at temperature depending on part mass

Products commonly bright-annealed in mesh belt furnaces include:

• Screws, bolts, nuts, and washers
• Cold-headed rivets and pins
• Stamped brackets and clips
• Electrical terminals and connectors
• Bearing races and rings
• Wire-formed components

Spring Tempering

Springs present unique challenges in heat treatment. After hardening, springs are brittle and unsuitable for service. Tempering reduces hardness to a specified range while improving toughness and fatigue resistance.

Spring Tempering Process

• Temperature range: 200-450°C for most spring steels
• Time: 30-90 minutes depending on spring wire diameter and furnace temperature
• Atmosphere: Air atmosphere is common for tempering; nitrogen may be used for appearance-sensitive springs
• Belt considerations: Springs can tangle on the belt; careful loading and sometimes individual fixturing is needed

Types of Springs Processed

• Automotive valve springs
• Suspension coil springs (smaller sizes)
• Flat springs and spring washers
• Compression springs for industrial equipment
• Torsion springs
• Clip and retainer springs

Hardening of Small Parts

Mesh belt furnaces are widely used for hardening small components in a neutral or carburizing atmosphere. The continuous flow allows parts to be austenitized and then discharged directly into oil or polymer quench.

Hardening Process Chain

1. Heat to austenitizing temperature (800-950°C for carbon steels)
2. Soak at temperature to ensure complete transformation
3. Discharge into quench (oil, polymer, water, or salt)
4. Post-quench wash and temper

Common hardened parts include:

• Chain links and pins
• Bearing balls and rollers
• Small shafts and pins
• Cutting blades and knives
• Lock components and tumblers

Electronics Manufacturing

The electronics industry relies on mesh belt furnaces for several precision thermal processes:

• Thick film firing: Silver, palladium, or other conductive pastes are fired onto ceramic substrates at 600-900°C
• Soldering and reflow: Circuit board assembly in nitrogen atmosphere
• Ceramic capacitor electrode firing: Base metal electrode sintering in reducing atmosphere
• Metal-glass sealing: Hermetic seal formation for electronic packages
• Annealing of copper lead frames: Softening precision-stamped lead frames for semiconductor packaging

Application Selection Guide

Wannengda Furnace configures each mesh belt furnace line to match the specific process requirements, from the belt alloy specification to the atmosphere control system and cooling section design.

FAQ

Can one mesh belt furnace handle multiple applications?

While a furnace is typically optimized for one primary process (e.g., sintering), it can often handle related processes with recipe changes. A bright annealing furnace can also temper springs, provided the temperature range and atmosphere are compatible. However, switching between processes that require different atmospheres may involve purge time and is less common in high-volume production.

What is the minimum batch size for a mesh belt furnace?

There is no minimum batch size in the traditional sense — mesh belt furnaces process a continuous stream of parts. However, very short runs may not justify the time needed to stabilize temperature and atmosphere. For practical production, several hundred to several thousand parts per run is typical.

Do mesh belt furnaces work for non-ferrous metals?

Yes. Mesh belt furnaces are widely used for copper, brass, bronze, aluminum, and nickel alloys. Temperature and atmosphere requirements differ — copper alloys typically anneal at 480-650°C, while nickel alloys may require temperatures up to 1150°C.

How are parts fed into a mesh belt sintering furnace?

Parts are typically loaded via vibratory feeders, belt conveyors, or robotic pick-and-place systems. The loading system meters parts onto the belt at a controlled rate to achieve the desired belt loading density. For delicate green powder metal compacts, care is taken to minimize drop height and handling.

What atmosphere is best for brazing in a mesh belt furnace?

Nitrogen-hydrogen atmosphere (typically 90-95% N₂ / 5-10% H₂) is widely used. The hydrogen reduces surface oxides and promotes wetting of the brazing alloy. For stainless steel brazing, higher hydrogen content or dissociated ammonia may be used. The specific atmosphere depends on base metals, brazing alloy, and whether flux is used.

Looking for a mesh belt furnace configured for your specific application? Zhejiang Wannengda Furnace Industry Co., Ltd. has been engineering custom continuous heat treatment solutions since 1989. Call or contact at . Visit www.wndfurnace.com to learn more about our sintering, brazing, and annealing furnace lines.