Materials for Invar 36 Components

Invar 36 is a nickel-steel alloy containing 36% nickel and 64% steel, coupled with 0.5% each of carbon and manganese, with metallurgically negligible quantities of sulfur, phosphorus, and other elements. It has a low thermal expansion, which makes it highly sought-after for applications requiring dimensional stability for a wide range of temperatures.

Below, we detail some of the most notable properties and applications for Invar 36 components and explain why purchasing Invar from a reputable metal supplier can save you time and money when it comes to machining.

Unique Properties of Invar 36

Before discussing various Invar 36 components, let’s have a look at some of its unique properties.

Low Thermal Coefficient

The rate at which metals expand or contract with a subsequent rise or decrease in temperature is known as their coefficient of thermal expansion (CTE). Invar 36 has a very low CTE of about 1ppm/K over a limited temperature range of 39.2-96.8°F, and the rate of thermal expansion is roughly one-tenth that of carbon steel at temperatures up to 400°F. It has the lowest thermal expansion rate of any metal. The following table shows the average CTE of Invar 36 for different temperatures.

Corrosion Resistance

Invar 36 offers high resistance to corrosion, as it can be left for months in an oxidative environment without showing any rust spots. Though its affinity to oxidation is much less than that of ordinary steel, it is imperative to grease the Invar 36 component for the highest corrosion resistance.

High Dimensional Stability

The remarkably low CTE of Invar 36 at room temperature, coupled with low temporal change, offers superior dimensional stability to Invar components. Therefore, Invar 36 is extensively used for designing precision mechanical systems in different industries.

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Popular Applications of Invar 36

Invar 36 is prized by engineers for its phenomenal CTE and dimensional stability. Thus, the alloy finds a wide range of applications ranging from watch parts to satellites. However, we will discuss some of the more notable applications of the Invar 36 alloy below.

Tapes

Invar 36 is extensively used for building tapes, as Invar tapes can quickly measure a baseline with higher accuracy rather than steel tapes. Because of Invar’s low thermal expansion and high corrosion resistance, it can withstand the outdoors with no oxidation. Thus, Invar 36 tapes are good for parts of devices required to produce a constant dimension under varying climatic conditions.

Boiler Tubes

Invar 36 tubes are useful as boiler tubes requiring high dimensional stability and low thermal expansions. Invar 36 tubes display low thermal expansion up to 200°C and retain strength even at cryogenic temperatures. The tubes are available in various sizes and forms for various industries such as food, oil, gas, and pharmaceuticals.

Pendulum Clocks

The period of a clock pendulum depends on the length of the pendulum rod, which can vary with temperature. Any temperature change can manipulate the actual readings of the clock—for example, an increase in temperature will cause the rod to expand and will make the pendulum longer. This causes the clock to lose time, thus making it inaccurate. Because of its low thermal expansion, Invar 36 is often used to manufacture pendulum clocks to maintain time accuracy.

Bimetallic Strips

Bimetallic strips are used in thermometers to convert a change in temperature into mechanical displacement. They’re also used to build precision instruments. The bimetallic strip is made up of yellow brass and Invar. As brass tends to curve more than Invar when heated beyond room temperature, incorporating a combination of both works perfectly to measure high and low temperatures.

Machining Challenges With Invar 36 Components

Machining Invar 36 components can be a challenging process for even expert machinists. Invar 36 may seem very similar to steel, but it is very soft and ductile under an annealed condition, making it hard to machine. Machining produces gummy chips that stick around the tool. Also, Invar 36 is prone to work hardening. That said, the surface goes through plastic deformation ahead of the tool and gets harder to cut through with each pass, leading to a poor surface finish and broken tools.

Machining Invar 36 requires the relevant expertise and the right tools, such as chip breakers, to overcome challenges with ease. Using a chip breaker can help avoid too much accumulation of gummy chips around the tool. Using other sharp tools with more teeth also helps.

The machining setup may change with the type of tools selected for the job. For instance, a rigid setup is imperative to minimize chatter and avoid work hardening while using carbide tools. However, no such arrangements are necessary while working with helical tools. Post-machining, Invar products must be annealed to release any internal stress present to ensure dimensional stability.

Considering the number of unique requirements for machining Invar 36 components, transforming Invar into usable parts can be a costly process for smaller machine shops and fabricators on tight budgets.

Purchase Machine-Ready Invar 36 at a Reasonable Price

For more than two decades, Industrial Metal Service has worked with fabricators, welders, and machinists from the San Francisco Bay Area and beyond supplying precision-cut Invar stock at a reasonable price to meet unique project requirements.

We supply new metals sourced straight from U.S. mills—however, for smaller machine shops on a tight budget, we can also provide verified metal remnants obtained from larger manufacturers that no longer require the scrap. Aside from Invar 36, we also supply other popular metals such as steel, aluminum, titanium, and copper.