Woven wire mesh belts are an ongoing cost associated with the operation of a continuous powdered-metal sintering furnace. The life of a T314 stainless steel belt operating in one of these units is typically measured in months. A belt pretreatment to extend the life of the belt and address one failure mechanism has been developed and tested. Initial results have demonstrated a 25% increase in belt life and an overall reduction in downtime that is typically in excess of 18%. The mechanism associated with this failure, the belt pretreatment and subsequent test results are described and reviewed.
Type 314 stainless steel woven wire belts are widely used to convey products through the final sintering stage in powdered-metal (PM) production lines. Although the life of a wire mesh belt is very dependent on the loading, furnace conditions, furnace atmosphere and temperature, it is not uncommon to measure the life of a belt in months. As a result, facilities that regularly work with the woven wire mesh belts in these applications have become quite proficient at replacing belts with minimal cool-down of the furnace and subsequent lost production time. Unit temperatures are typically reduced to below 1500ºF (815°C), and the new belt is fed into the unit as the old belt is being removed. Once completely installed, the temperature is ramped-up as quickly as possible and the unit is restored to service. This process is repeated as necessary throughout the many production lines of today’s PM production facilities.
Over the years, belt designs have steadily improved to permit higher production rates with less downtime for maintenance and overall longer belt life. Recent belt designs, such as Knuckleback™ by Cambridge Engineered Solutions, have been shown to allow higher product throughput rate by utilizing a flattened spiral wire and a reverse bend knuckled and welded edge. Following extensive tests, we have seen favorable results that show improvements of over 50% increased production. While Knuckleback offers significant improvement in throughput and value in optimal furnace conditions, there is still a need for additional improvements. From the standpoint of the belt, there have been and remain typically two problems associated with the frequent installation and use of new belts in sintering furnace units: absence of a proper break-in period for the belt and lack of sufficient de-lubing of the products. It can be shown that these two problems are closely related.
It is generally accepted that for woven metal mesh belts to perform optimally, they should be subjected to a break-in period that could span up to 1-3 days. During that time, the belt is allowed to “soak” while moving slowly through the conveyor as the temperature within the unit is gradually and incrementally increased. This is thought to be an advantage both from a mechanical and metallurgical standpoint. Dimensionally, the belt can slowly adjust to maintain proper seating of the mesh and crimp wires, which promotes more even loading across the belt width along with improved articulation. Perhaps more importantly, free of any special atmosphere, a slower controlled break-in period can be used to promote the formation and growth of an oxidation layer on the belt surface that can provide an important means of surface protection for the belt. Without the proper belt break-in period for a new belt, conversely, the result can be and often is a reduced service life.