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Product Bulletin - Muffles

SECO/WARWICK began to design and manufacture muffles in-house in 1995 after rejecting poor quality work and long lead times from outside sources. We recognized that we could build a better quality muffle in our plant, providing customers with better value and expedited delivery.   Today, SECO/WARWICK maintains the engineering intelligence for both SECO/WARWICK and Camlaw brand controlled atmosphere brazing furnace muffles.  SECO/WARWICK has the technical expertise and original drawings to provide you with a muffle that will correctly fit your furnace.

Braze Muffle Styles and Advantages

Radiation Muffle Design

Replacement Radiation muffle for Camlaw furnace

Both Camlaw Ltd. and SECO/WARWICK Radiation mesh belt furnaces use a flat plate bottom muffle. The flat plate provides a solid support for the mesh belt. It also allows the belt to drag debris out of the muffle as it travels through the furnace thus keeping the bottom clean. Furnaces utilizing a chain driven belt sometimes use a muffle with a corrugated bottom. This provides longitudinal strength as well as making it possible to include replaceable wear plates under the chain. Not all chain furnaces use corrugated bottoms. Thicker bottom material can be used in lieu of corrugations to improve service life.  The top of SECO/WARWICK's radiation muffles are normally made of thinner gauge material. Temperature uniformity and response time is greatly enhanced due to the thinner section's lighter thermal mass.

Patented Conve Furnace Muffle

Convection Muffles

Convection furnaces use a special muffle with fan towers and air distribution plenums within the muffle. These muffle have their bottom, top and sides corrugated for strength. SECO/WARWICK developed the design and patented the convection muffles used in our CAB furnaces.

Selecting the Right Alloy

Muffles are most commonly fabricated from type 304, 316, 330 and  Inconel 600 depending on the process.  All nickel chrome alloys have trade-offs in service life, strength and cost.  AISI 300 series stainless steels, austenitic, are the most common alloys used in interior construction because they have good corrosion resistance  (except in chlorine), temperature stable microstructures (reduced distortion for quench, less thermal fatigue) and good ductility (can be readily formed).

AISI 300 Series characteristics

• 302 - general purpose, base alloy, used to 1500 degrees F
• 304 - similar to 302 with about half the carbon, better corrosion resistance (has L grades with less carbon), better weldability &H grades that have had high temperature soak to fix carbide locations & slightly higher carbon that helps creep properties, widely used to 1600 degrees F
• 309 - superior scale resistance, good strength at high temperatures, used for retorts, radiant tubes to 1700 degrees F, comparable to cast alloy HH
• 316 - Mo significantly improves corrosion resistance, lower cost than 309, easier to weld, similar temperature use range
• 330 - good corrosion resistance, strength to 2000 degrees F, usedfor muffles, retorts, trays, baskets, comparable to cast alloy HT
• Superalloys are the most expensive material choice for muffles. They tend to be more corrosion resistant, stronger and have better creep properties at high temperature.  Customers need to be cautious about selecting a Superalloy for this application because the investment may not be worth the relatively small gain in performance.
• Inconel 600 is nickel based with excellent resistance to oxidation and strength to 2100 degrees F., used for muffles, fixtures and belts where corrosion is a problem