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A Comparison of Aluminum Alloys AL850 and AL6061 for Manufacturing Labyrinth Seals and Bearings

AL850 is a specialized alloy used for labyrinth seals, engine bearings, connecting rods, hydraulic pumps, and a variety of other industrial applications. AL6061 is a more general purpose alloy used in architectural extrusions, aircraft parts, bicycle frames, and automotive parts. The key difference between the two is the relative strength and the chemistries of each aluminum alloy.

AL850 contains approximately 6% Tin (Sn), which gives this alloy better lubricity than AL6061 and small amounts of copper and nickel which adds to its strength. With the additions of other metals such as copper, nickel, titanium, and silicon, aluminum-tin bearing alloys such as AL850 can be used where bearings are required to withstand high speeds, heavy loads, and extreme temperatures. Engineers carefully consider and compare these characteristics in order to choose which aluminum alloy has the required properties to make a particular product.

Why AL850 over AL6061?

To understand why the use of AL850 in aluminum alloy castings for labyrinth seals and bearings is important, it’s helpful to further understand the differences between AL850 and AL6061. As previously discussed, there are three main components that make AL850 superior to AL6061 for manufacturing labyrinth seals and bearings:

  • AL850 has a better machinability than AL6061
  • AL850 has improved lubricity over AL6061
  • AL850 has a higher tensile and yield strength than AL6061

Machinability

Machinability is the ease at which material can be cut or machined. Aluminum AL850 can be machined to tighter tolerances and adhere to more precise specifications than castings made from AL6061. The superiority of the machinability of AL850 is also shown in the chip form; AL6061 results in a chip form that is long, stringy, and continuous in contrast to the discontinuous chip of AL850, which is more desirable, making the chip break of AL850 superior to that of AL6061. The discontinuous chip break of AL850 allows for a heavier depth of cut resulting in improved machining cycles- a potential cost benefit to the customer. The typical depth cut for AL850 is twice as deep to that of AL6061.

Machinists and engineers looking at machinability ratings when determining the best aluminum alloy to use for their application. On a machinability scale ranging from 0-100, AL6061 has a rating of 50, whereas AL850 has a rating of 90. According to machinists experienced in working with both alloys, because of this higher machinability rating, an operator can push AL850 faster with greater depth of cuts than with AL6061.

Lubricity

Erie Bronze & Aluminum suggests using AL850 castings because of their lubricity properties. However, the lubricity of a substance is not a mechanical property and cannot be measured directly. To determine lubricity, manufacturers observe the amount of wear that is caused to a surface during a set timeframe. Other factors such as surface size, temperature, and pressure are also taken into consideration. Improved lubricity decreases the friction and wear of labyrinth seals and bearings.

Tensile Strength and Yield

The tensile strength, or the ability of a metal to withstand tensile loads without failure, is another important factor when choosing an alloy for your applications. Yield stress, characterized as the point of stress level where the material begins to have permanent deformation and the material will no longer return to its original shape and size after the applied stress, is also a key factor to consider when choosing which aluminum alloy would best suit the requirements of the project.

The units of measure for tensile and yield strength is the Megapascal (Mpa). The Mpa is used for measuring internal pressures and stress on material. AL6061 has a tensile strength of 115 MPa whereas AL850 has a tensile strength of 160 MPa. As for yield strength, AL6061 has a limit of 48 MPa and AL850 has a limit of 75 MPa. Having strong tensile and yield strength is an important factor to consider when selecting the best aluminum alloy for the production of labyrinth seals and bearings since brittle metals are more likely to rupture.

When looking at the areas of machinability, lubricity, and tensile strength, AL850 has been shown to be superior to AL6061. Better machinability, improved lubricity, and high tensile and yield strengths are all long-term benefits to consider when shopping for the right aluminum alloy. Additionally, when factoring in machining cost, wear-life and production cycle time, AL850 is a superior alloy that can be used in place of AL6061 for many applications.

Types of Products Produced using AL850 Aluminum Castings

AL850 is just one of the three specialized aluminum alloys Erie Bronze & Aluminum produces in tube and ring form, customized to each customers exact OD, ID, and length requirements. . Typically, these AL850 castings are used by customers to manufacture labyrinth seals, bearings, and bearing housing units used for large motors and compressors. One of the most common uses for AL850 is labyrinth seals. Labyrinth seals, a non-contact type of mechanical seal, are critical components in compressors. They are used on the impellers of a rotating shaft to seal a high-pressure area from a low-pressure area to minimize gas leakage.

Aluminum alloy castings, specifically castings made from AL850, are also a great choice for the production of bearings. Bearings made from AL850 produce highly engineered components that enable machinery to move at high speeds and carry remarkable loads with ease and efficiency. Aluminum alloy bearings offer precision, durability, and the ability to rotate at high speeds with minimal vibration. If a product twists, turns or moves, it probably has a bearing on it.

Bearing housing units are the supporting piece of the bearing. Imagine the housing unit as a pedestal used to provide support for a rotating shaft. Bearing housing units made from AL850 aluminum castings help control other bearings and various accessories needed for a motor or compressor.

If you’re in search of a premium manufacturer of aluminum castings for labyrinth seals or bearings, click here to contact Erie Bronze & Aluminum and speak with a highly trained sales expert.

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