To make a multi-step manufacturing process as efficient as possible, it’s critical to look at the time impact of each component task. One example involving composite materials for automotive applications involves parts made by compacting soft magnetic composite material. Traditional sintering furnaces are often used to remove lubricant from the formed compacts, but this can result in quality discrepancies to the parts, damage the furnace, and slow the entire manufacturing process down.
Here, we’ll examine the problem and a new approach to lubricant removal made possible by redesigning the standard sintering furnace.
The Challenge of Delubing
As Coble et al. note, “although the industry has worked to reduce the amount of lubricant that is mixed into the powder, there is always a need for some. The problem arises when the compact is to be sintered. The lubricant must be removed from the compact or a carbon residue [i.e. soot] will form and detrimentally impact the properties of the final product.” A common lubricant used by many manufacturers is ethylene bis stearamide (EBS).
Conventional sintering furnaces are not able to maintain the necessary temperature range for lubricant removal without also causing it to decompose and create soot. Often, this is because often the radiant heat in these furnaces heats the parts too quickly to temperatures that are too high, which contributes to sooting. If lower temperatures are used; however, it may take
multiple passes through the furnace to remove the lubricant.
Efficient Manufacturing of Soft Magnetic Composite Compacts
Research shows that lubricant removal is best accomplished at lower temperatures and for longer periods of time than those traditionally used in conventional sintering. It is also beneficial to add moisture in a controlled way to prevent soot formation. A conventional sintering furnace can be redesigned into a multi-function furnace capable of
the appropriate range of temperatures, treatments, and processing times for effective lubricant removal.
Abbott Furnace Company’s Vulcan furnace is capable of the specific parameters needed for delubing compacts. It includes convective heat transfer, automated loading, and adjustable
belt speed, all of which allow for greater control over temperature and atmospheric conditions during delubing.
“The Vulcan uses an independent moisture source that provides fine control of the amount of water that is introduced. The injection location and fine moisture control provide moisture to react with any carbon that is being dropped during the lubricant break down. Moisture injection in conventional systems is typically insufficient, difficult to control, or influences the thermal control of the system, all negatively influencing the quality of lubricant removal process,” as Coble and colleagues explain.
Research has shown that the complete removal of the lubricant can have a significant impact on the quality of the product. In some cases, the physical properties of the product may be improved by as much as 18% over those produced via conventional sintering.
Another furnace innovation for the production of soft magnetic composites is the Nautilus. Stephen L. Feldbauer, Ph.D. describes the furnace and the process. “The goal of this technology is to use the vast research that has been conducted in lubricant removal to effectively remove all the lubricant from the compact in a single pass. Without leaving the equipment, the product is then delivered directly to the secondary process step, be it steam, air cure, or 650°C processing in nitrogen. Hence, the multiple passes for lubricant removal, the cost of repetitive heating and cooling, and the extra handling of the product are eliminated. The result is a process that is up to four times more efficient than processing soft magnetic composites with conventional powder metal processing equipment.”
Steps in Continuous Processing of Soft Magnetic Composite Parts
Here’s a simple summary of the process:
- Ferrosilicon particles are mixed with phosphorus and lubricant to form the composite material
- Material is molded into the desired shape
- Compact is ejected from the mold
- Compact is loaded onto a conveyor to run through the Nautilus
- Stage 1: Convection heat treatment chamber to remove lubricant
- Stage 2: Internal track moves the compact further down the chamber for steam/air/nitrogen curing
- Part is unloaded, cooled, and ready for assembly or the next manufacturing step
A more detailed discussion of this process and supporting research is found here.
If you work with soft magnetic composites, this improved sintering application for the delubing process can have a big impact on your manufacturing process. As a leader among sintering furnace suppliers, Abbott Furnace Company has the know-how and equipment you need – please contact us to learn more and discuss your next project!