Gas Heated Vacuum Furnace Designs Lower Operating Costs for Vacuum Heat Treatment
The advantages of vacuum heat treating are numerous and well documented. These advantages have traditionally been opposed by a few negatives such as furnace cost, overall operating cost, and in most cases, the cost of electricity as a utility. Typically, these negatives have been countered by the heat treater’s desire to provide vacuum processing to their customers or the requirement of certain materials to be vacuum processed. Over the history of this type of equipment, electric heating has been the primary heating source offered by manufacturers. This scenario has resulted in a well-established vacuum furnace installed base that uses electricity as the heating source.
A Longer History Than You May Think
Surface® Combustion initially investigated the use of natural gas heating in vacuum equipment as early as 1946 when a U.S. Patent was received for a fuel-fired vacuum furnace for the reduction of magnesium oxide in magnesium briquettes. It wasn’t until 1971 that a full-production, gas heated vacuum furnace for coil annealing was manufactured, though. Surface believes that this represents the first gas heated vacuum furnace installed on a full production basis.
Over the past three decades, Surface has devoted extensive research and development efforts to further advance gas heated vacuum furnaces. These furnaces demonstrate the ability to provide metallurgical results equal to the electrically heated designs, as well as reduce overall operating costs. From this extensive development effort, Surface has designed, manufactured, and installed more gas-fired vacuum furnaces over the last thirty years than all other major furnace manufacturers combined.
Various Models Available
Leading the way is the gas heated VacuDraw® single-chamber vacuum tempering furnace with a proven record as a rugged, low-cost heat treating system that has been supplied for a wide variety of ferrous and non-ferrous material process applications. VacuDraw advantages include ±10°F temperature uniformity achieved without moving dampers resulting from a patented circular wind-flow pattern and accelerated cooling using Surface’s external cooler design. The design also provides lower operating costs via gas heating and a unique “hot wall” design that requires no cooling water usage in the casing wall which results in only a 50°F above ambient external furnace casing temperature during furnace operation.
Surface has also developed a single-chamber, high-temperature gas fired vacuum furnace design with a maximum operating temperature of 1700°F. The furnace is heated by metallic, single-ended radiant tubes with ceramic inner tube assemblies. Load cooling is accomplished by an externally mounted blower system which recirculates inert cooling gas though a water-to-gas heat exchanger system and back into the furnace.
A hybrid vacuum design available in Surface’s diverse product offering is a gas heated 1950°F vacuum hardening furnace utilizing silicon carbide radiant tubes with an integral oil quench tank. This furnace design, installed into a Surface Combustion Allcase® Batch Integral Quench Furnace line in the 1990s and, is loaded by a standard charge car assembly. Additional furnace advantages include ±10°F temperature uniformity throughout the 1500°F to 1950°F temperature range, full vacuum processing up to 1950°F, and quick furnace recovery time when charging a cold load into a hot heating chamber. This furnace can also be operated at atmospheric pressure if desired.
Vacuum (Low Pressure) Carburizing is a process that benefits from gas heating. Low pressure carburizing (LPC) temperatures are perfect to utilize Surface Combustion’s patented gas heated radiant tubes. One example is our Cloverleaf™ multi-chamber vacuum furnace with three (3) vacuum carburizing cells equipped with silicon carbide recuperated radiant tubes. Each cell has a dedicated vacuum pump, and all share a 20-bar high pressure gas quench (HPGQ) chamber and oil quench vestibule. This Cloverleaf multi-chamber gas-heated vacuum carburizer offers operating cost savings compared to electrically heated vacuum carburizing tunnel furnace designs.
Surface Combustion is a leading manufacturer of heat treating equipment and has one of the most diverse product offerings for the industry. Contact Surface for the most unique and advantageous vacuum furnace innovations.Read More >