Oil Impregnation Process in Sintered BearingsMay 29, 2018
In sintering factories, self-lubricating bearings are manufactured by powder metallurgy (PM) equipment. The machines use a mixing process, not solid component mouldings. Thanks to that difference, manufacturing engineers gain mastery over the subject metal. That’s a powerful manufacturing advantage, one that introduces a lubricating medium to sintered bearings. Technically speaking, we’re in oil impregnation territory, an area that abides in the mixing chamber.
Talking About Oil Impregnation
Before the material compression stage but after powder atomization, the fine grains enter a mixing chamber. The mixing stage has been mentioned in an earlier post, but that post didn’t focus exclusively on the lubricating medium. Let’s fix this bias by shifting attention over to the oil vessel. In here, the viscosity and circulation characteristics of the liquid matter more than the flow of the powder. In here, the lubricant runs evenly so that the materials blend when they finally meet.
Filling the Porous Structure
More important than any other feature, at least until the product reaches the sintering stage, is a matching degree of oil flow and pore formation. An overly lubricated bearing isn’t the goal, nor is a bearing that lacks self-lubricating potency. For this to happen, the equipment should automatically deliver the correct quantity of oil. In order to accomplish this objective, the oil supply mechanism regulates the lubricant feed. Furthermore, a supply of graphite is usually added to the oil. More defined and dense than the lubricant, the carbon-rich graphite aids in the formation of a capillary network.
Matching the Processing Variables
The powder metallurgy equipment uses dies and thermal elements to sinter the bearing. In the meantime, back at the mixing vessel, the speed of rotation is held steady. Powder atomization and grain supply feed also maintain a steady supply rate. As for the oil and graphite supply system, the conduits and containment enclosures here rely on a feedback system as a flow regulating device. On the one hand, the powder is occupying the mixing vessel. Then, on the other hand of things, lubricant viscosity and graphite geometry regulate the oily flow. There are also additives and binders in the lubricant stream, and these extra ingredients cannot be allowed to impact that all-important viscosity factor.
The porosity and interconnecting capillary channels occupy a small percentage of the bearing structure, with product strength providing the upper porosity limit. To gain this porous structure and fill it with lubricating oil, the flow rate must regulate the fluid. Factors that affect this equipment-supply feature include the porosity and temperature of the lubricant, its form as a fluid or wax, and the presence of any fluid thickening additives.
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