Mesh Belt Furnace Applications: Fasteners, Springs, Sintering, and Bright Annealing
The continuous mesh belt furnace is one of the most versatile pieces of heat treatment equipment in the industry. It runs fasteners at 1.5 tons per hour. It runs springs at 0.8 tons per hour. It sinters powder metallurgy parts at 0.5 tons per hour. It bright anneals stainless stampings at 0.3 tons per hour. The list of applications keeps growing as engineers find new ways to use the continuous flow concept. Let me walk through the major application areas, the process recipes, and what MONTE INTELLIGENCE has learned from working across these industries.
Fastener Manufacturing
The fastener industry is the largest user of mesh belt furnaces worldwide. Bolts, nuts, screws, washers, and threaded rod all run through continuous mesh belt furnaces for hardening and tempering. The throughput is high, the parts are small, and the process is well understood.
A standard fastener heat treatment line uses a 600 to 900 mm wide belt furnace with 6 to 8 zones. The parts are austenitized at 840 to 880 degrees Celsius (depending on the carbon content), quenched in oil or polymer, washed, and tempered at 400 to 600 degrees Celsius. The total residence time in the furnace is 45 to 75 minutes, and the throughput is 300 to 800 kg per hour.
The atmosphere is typically endothermic gas for carbon steel fasteners and nitrogen plus 1 to 2 percent natural gas for alloy steel fasteners. The carbon potential is controlled at the target value to prevent decarburization. Surface hardness is HRC 38 to 44 for grade 8.8 fasteners, HRC 33 to 39 for grade 10.9, and HRC 36 to 42 for grade 12.9.
MONTE INTELLIGENCE has supplied fastener heat treatment lines to multiple Chinese, Indian, and Southeast Asian fastener manufacturers. The largest installation runs 1.5 tons per hour of M8 to M16 bolts in a 1200 mm wide belt furnace.
Spring Manufacturing
Springs are another large application for mesh belt furnaces. The springs are loaded onto the belt in a single layer, austenitized, quenched, and tempered. The process is similar to fastener heat treatment, but the temperature uniformity requirement is tighter because the springs are more sensitive to non-uniform hardness.
A standard spring heat treatment line uses a 600 to 900 mm wide belt furnace with 7 to 9 zones. The springs are typically made from spring steel grades 51CrV4, 60Si2Mn, or 55Cr3. The austenitizing temperature is 850 to 880 degrees Celsius, the quench is oil, and the temper is 400 to 500 degrees Celsius. Throughput is 200 to 500 kg per hour depending on the spring size and the belt loading density.
The atmosphere is endothermic gas with tight carbon potential control. The springs must have less than 1 percent decarburization on the surface, and the carbon potential is typically set at 0.05 percent above the steel's nominal carbon content to maintain the surface carbon during austenitizing.
Powder Metallurgy Sintering
Powder metallurgy parts are sintered in mesh belt furnaces at 1100 to 1280 degrees Celsius. The sintering process bonds the metal powder particles together to form a solid part, and the atmosphere is typically a hydrogen-nitrogen mixture or pure hydrogen to prevent oxidation.
The sintering furnace has 5 to 7 zones: burn-off zone (to remove the pressing lubricant), pre-heat zone, high-heat sintering zone, slow cool, and final cool. The high-heat zone is gas-fired with radiant tubes, and the maximum temperature is limited by the radiant tube material (typically 1280 degrees Celsius for silicon carbide tubes).
Throughput on a 600 mm wide belt sintering furnace is 100 to 300 kg per hour. The largest sintering furnaces in the world are 900 to 1200 mm wide and run 500 to 800 kg per hour. MONTE INTELLIGENCE supplies sintering furnaces for iron-based PM parts, stainless steel PM parts, and soft magnetic composites.
Bright Annealing of Stainless Steel
Stainless steel stampings, wire forms, and tubes are bright annealed in mesh belt furnaces at 1050 to 1150 degrees Celsius in a hydrogen-bearing atmosphere. The process produces a bright, oxide-free surface that is suitable for subsequent fabrication without pickling.
The bright annealing furnace has 5 to 7 zones with gas-fired radiant tubes or electric heating elements. The atmosphere is typically 25 to 75 percent hydrogen in nitrogen, with a dew point below -40 degrees Celsius. The cooling zone uses a recirculating fan to cool the parts under the protective atmosphere to prevent re-oxidation.
Throughput on a 600 mm wide bright annealing furnace is 50 to 200 kg per hour. The parts must be clean and dry before entering the furnace to prevent contamination and water spotting.
Brazing Applications
Copper brazing of steel assemblies, aluminum brazing of heat exchangers, and silver brazing of tool joints are all done in mesh belt furnaces. The brazing temperature is typically 600 to 700 degrees Celsius for copper brazing and 580 to 620 degrees Celsius for aluminum brazing. The atmosphere is nitrogen-hydrogen or pure nitrogen with a small fluorine-bearing addition for aluminum brazing.
The brazing furnace has 5 to 7 zones with electric heating elements. The parts are loaded on the belt with the brazing filler metal pre-placed in the joint, and the furnace melts the filler and wets the joint surfaces. The parts exit the furnace and are cooled under atmosphere to prevent oxidation.
Stress Relieving of Small Parts
Small machined parts, welded assemblies, and spring wire are stress relieved in mesh belt furnaces at 400 to 700 degrees Celsius. The stress relieving cycle is shorter than the hardening cycle, typically 20 to 40 minutes, and the throughput is higher.
A standard stress relieving furnace has 3 to 4 zones and runs 500 to 1500 kg per hour. The atmosphere is typically air (for carbon steel) or nitrogen (for alloy steel). The temperature uniformity is plus or minus 10 degrees Celsius, which is looser than the hardening furnace specification.
Selection by Industry
For buyers specifying a mesh belt furnace, the choice is driven by the part geometry, the process recipe, the throughput target, and the available energy source. The MONTE INTELLIGENCE engineering team reviews these parameters with the buyer and recommends a furnace configuration with the appropriate belt width, heating length, zone count, and atmosphere system.
Visit www.cnlymonte.com/products-mesh-belt-furnace.html for product specifications and industry case studies. For a project discussion, email helenxu@cnlymonte.com with subject line mesh belt application and details on your part geometry, process recipe, and throughput target.
