If you’ve ever torn apart an older internal combustion engine—say, a 1990s pickup truck, or a small outboard motor you’ve used on fishing trips—you might have noticed those curved, porous half-moon rings tucked between the crankshaft and the engine block. Those are powder metallurgy half bearings, and for anyone in the heavy equipment, automotive, or small engine industry, they’re more than just a component: they’re the quiet workhorse that keeps crankshafts spinning smoothly through thousands of hours of torque, vibration, and extreme heat. Powder Metallurgy Half Bearing
I’ve been in the powder metallurgy (PM) half bearing supply business for 12 years now, and I’ve heard every question in the book from engineers and plant managers: “Why did my bearings fail on that high-torque assembly line?” “Why do some batches hold up for 5 years, and others wear out in 12 months?” The answers almost never boil down to a single mistake. The performance of a PM half bearing is the sum of tiny, interconnected choices we make at every step of the process—from the metal powder we source to the way we finish the final part. Let’s break down the key factors I see time and again, both in my factory and in the field tests our clients run.
First, let’s start with the foundation: the metal powder itself. You can’t make a good PM part without good raw material, and half bearings are no exception. Most of our half bearings are made from pre-alloyed iron powder mixed with small amounts of copper, graphite, and sometimes tin—each ingredient serves a specific purpose, but getting the balance right is non-negotiable. Copper, for example, adds hardness and fatigue resistance, which is critical for bearings that endure repeated crankshaft flex. Graphite acts as a solid lubricant, reducing friction right out of the gate before the engine’s oil pump can build up pressure. Too much graphite, though, and the part becomes brittle—one of our clients in agricultural equipment learned this the hard way a few years back. They switched to a cheaper powder blend that bumped graphite content by 2% to cut costs, and within 3 months, half their bearing inventory was cracking under the heavy cyclic loading of a farm tractor’s crankshaft.
Particle size and shape matter just as much as composition. Fine, spherical particles pack more evenly during compaction, leading to a more uniform pore structure, while irregular, flaky particles create interlocking that can boost strength—if you get it right. We test every batch of incoming powder using a laser particle sizer, and we reject any powder that has a mix of sizes that’s too wide. If there are too many large particles, they create gaps in the green (un-sintered) part that can become stress risers, where cracks start to form as soon as the bearing is put under load. Too many ultra-fine particles, and the powder compacts too tightly, trapping gases during sintering that cause porosity defects deep in the bearing wall.
Next up: the compaction process. Compaction is when we press the powder into the half bearing shape using a die, and the pressure and speed of that press directly shape the part’s density and consistency. Density is everything for PM bearings—higher density means better strength, wear resistance, and load capacity, but too high a density can eliminate the tiny, interconnected pores that hold oil. Most of our half bearings run at a density of 6.2 to 6.8 g/cm³, a sweet spot where there’s enough porosity for oil retention to lubricate the crankshaft, but enough solid metal to handle the load.
One common mistake I see with new compaction operators is uneven pressure across the bearing surface. A half bearing isn’t a simple block of metal; it has a curved inner surface, and the ends where it meets the other half of the bearing have sharp corners. If the press doesn’t apply even pressure around the entire part, some areas will be less dense than others. Those low-density spots wear faster, and over time, they can cause the bearing to seize or score the crankshaft. We’ve fixed this for clients in the automotive racing industry, who were seeing uneven wear on high-performance engines: we adjusted our compaction press’s pressure profile to match the curvature of the half bearing, and wear rates dropped by 35% in their field tests.
Then comes sintering, the step where we heat the compacted part in a controlled atmosphere furnace to bond the metal particles together. The temperature, hold time, and atmosphere all affect how strong and porous the final bearing is. Sintering iron-based bearings usually happens between 1100°C and 1250°C, but even a 25°C difference can make a huge impact. If we heat too quickly, the surface of the part sinteres before the inner pores can clear out, trapping contaminants that cause defects. If we hold at temperature too long, the metal grains grow too large, reducing fatigue resistance. The atmosphere is equally critical: we use a mixture of nitrogen and hydrogen to prevent oxidation during sintering. Oxidized particles don’t bond well, leading to weak spots that break down under load. A few years ago, a power outage in our furnace caused a brief dip in the nitrogen flow, and a batch of bearings came out with a thin oxide layer on the inner surface. Even though we only lost 5% of the batch, that oxide layer acted like sandpaper on crankshafts, leading to a wave of returns from one of our construction equipment clients. We now have a redundant atmosphere control system, so that mistake never happens again.
After sintering, there’s a whole set of secondary processes that affect performance, starting with sizing and finishing. Sizing is when we press the sintered bearing into its final dimensions, closing up a small percentage of pores and adjusting the inner curvature to fit the crankshaft perfectly. Too much sizing, though, can crush the pore structure, reducing oil retention. We limit sizing to a 0.02 to 0.05 mm tolerance, just enough to eliminate any irregularities from compaction. The inner surface finish is another big one: bearings that are too rough will wear the crankshaft, while bearings that are too smooth won’t hold oil properly. We usually finish our half bearings to a Ra of 0.8 to 1.6 micrometers—soft enough to ride on a thin oil film, but textured enough to trap it. We’ve had clients who tried to save money by skipping the precision grinding step, and their bearings would leak oil at low engine speeds, leading to dry starts and early failure.
Porosity control is a factor that’s easy to overlook, but it’s tied to almost every step of production. Half bearings rely on connected, open pores to store oil, which is released under pressure as the crankshaft spins. If the pores are too small or closed off, the bearing can’t hold enough lubricant, leading to metal-to-metal contact. If they’re too large, the bearing is weaker and can’t handle high loads. We measure pore size distribution using a mercury porosimeter, and we target an average pore size of 10 to 20 micrometers. That’s the perfect size: large enough to hold plenty of oil, but small enough to keep the bearing’s strength up. We also test oil retention capacity by weighing the bearing before and after soaking it in oil, and we require a minimum of 15% oil content by weight for all our half bearings. That might sound like a lot, but it’s the difference between a bearing that runs for 10,000 hours and one that seizes after 1,000.
Of course, the application itself matters just as much as the manufacturing process. A half bearing that works perfectly in a small lawn mower engine will fail miserably in a heavy-duty diesel truck, and vice versa. The load on the bearing, the speed of the crankshaft, the type of oil used, and even the operating environment all play a role. For example, in agricultural tractors, bearings are exposed to heavy shock loads when plowing or hauling, so we adjust our powder blend to add a bit more nickel, which boosts impact resistance. In outboard motors, which run at high speeds and require immediate lubrication even when the engine is cold, we increase graphite content a little to improve boundary lubrication during start-up. I always tell clients that a bearing is only as good as how it’s matched to its application—we don’t use a one-size-fits-all formula, and we never hesitate to tweak our process when a client has unique operating conditions.
Another often-underestimated factor is surface treatment. We offer two main options for our half bearings: oil impregnation, which we’ve already mentioned, and sometimes a thin layer of lead or tin plating for high-load applications. Lead plating was common for many years, because it’s an excellent solid lubricant, but environmental regulations have pushed us to use tin alternatives for most new clients. A few years back, a client in the marine industry wanted to switch back to lead plating to reduce wear on their high-load crankshafts, but we worked with a plating supplier to develop a tin-nickel alloy that performs almost as well, with zero environmental impact. That’s the kind of adjustment that comes from listening to our clients and staying on top of industry changes.
We also test every lot of bearings before they leave our factory, not just for dimensions and oil content, but for performance too. We run a bearing fatigue test on a custom dynamometer, spinning the bearings at 3,000 RPM and applying a 1,500 N load to simulate real engine conditions. If a bearing fails that test, we trace it back to the root cause—was it a bad powder batch, uneven compaction, or a furnace temperature spike? Last year, we had a batch that passed all dimensional checks but failed the fatigue test, and we found that a small group of particles in the powder were slightly too large, creating a weak spot that only showed up under cyclic loading. That’s why we don’t rely on just lab tests—we run real-world simulations to catch issues before they get to our clients.
I’ve seen too many suppliers cut corners to lower costs: using cheap powder, skipping precision finishing, or not controlling their furnace atmosphere. The problem is, those shortcuts don’t just lead to product failures—they damage relationships. A client might save a few cents per bearing, but if their production line stops because of a bearing failure, that’s thousands of dollars in lost revenue for them, and a bad reputation for us. That’s why we invest in quality control at every step: we test powder in three different ways before it goes into production, we have operators check every compaction die for wear, and we run 10% of every batch through our dynamometer test. For us, a bearing isn’t just a part—it’s a promise that our client’s equipment will run when they need it.
If you’re in the market for powder metallurgy half bearings, whether for automotive, construction, agriculture, or marine applications, don’t just go for the lowest price. Ask about the powder composition, density, porosity control, and testing processes the supplier uses. The right half bearing is one that’s matched to your specific application, with a consistent manufacturing process that eliminates the defects that cause early failure. We work closely with every client to tailor our bearings to their needs, whether that’s adjusting the alloy blend, tweaking surface finishes, or adding special treatments for extreme operating conditions.
If you’re looking to source powder metallurgy half bearings with reliable performance, consistent quality, and a supplier that will stand behind their product, reach out to our team to discuss your specific requirements. We’re here to help you find the right bearing solution for your equipment, no matter the application or operating conditions.
Rack Style Slack Adjuster Sintered Parts AA1 References
- German, R. M. (2015). Powder Metallurgy Science and Applications. Metal Powder Industries Federation.
- ASM International. (2018). Powder Metallurgy Materials and Processes. ASM Handbook, Vol. 7.
- Childs, T. H. C. (2006). Wear of Materials. Butterworth-Heinemann.
- Danninger, H., & Gierl, C. (2008). Sintering of Powder Metallurgy Parts. Powder Metallurgy, 51(1), 35-40.
- Tong, K., & Lu, J. (2019). Performance Optimization of Iron-Based Powder Metallurgy Bearings. Journal of Manufacturing Processes, 45, 782-789.
Taizhou Hualian Powder Metallurgy Products Co., Ltd
Taizhou Hualian Powder Metallurgy Products Co., Ltd. is one of the most professional manufacturers and suppliers of powder metallurgy half bearing in China for over 20 years, supplying the best products and service. Feel free to buy high quality powder metallurgy half bearing from our factory.
Address: No.53 Changshun Road, Bingang Industry Zone, Shamen Town, Yuhuan County, Zhejiang Province.
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