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.
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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.
Before discussing various Invar 36 components, let&#;s have a look at some of its unique properties.
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.
Temperature (°F) Average CTE [in/in/°F x 10(-6)] 200 0.72 300 1.17 500 2.32 700 4.22Invar 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.
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.
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.
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.
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.
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 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 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.
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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.
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.
On the search for alloys for your application, there is no doubt that you will come across controlled expansion alloys.
The alloy expansion rate refers to an average coefficient of thermal expansion; controlled expansion alloys have been carefully formulated to produce a specific coefficient of thermal expansion (CTE) within certain ranges.
Falling into three categories, you will find low thermal expansion, matching expansion and high thermal expansion. Here are some of the most common controlled expansion alloys and which applications they are most suited for:
One of the most used alloys is Kovar which is made up of nickel, iron and cobalt. It is classified as a controlled expansion alloy because the expansion characteristics of Kovar are closely controlled in order to match hard / borosilicate glass or ceramic. This means that it will expand and contract at a similar rate to these materials, making it the most popular alloy for hermetic sealing applications (Glass to Metals Sealing). Some of these applications include:
Mainly used in the electronics and aerospace industries, Kovar comes in a range of forms: Plate, Round Bar, Square Bar, Flat Bar, Sheet, Coil, Wire and Tube. The uniformity of thermal expansion characteristics and shock resistance makes it a reliable choice for these applications.
Invar is made up of nickel and iron and is classified as a low expansion alloy. It has one of the lowest thermal expansion rates, exhibiting near zero coefficient, which makes it suited to applications where it is required to maintain constant dimensions in changing temperatures. Applications with these requirements include:
As well as dimensional stability between -100°C & 260°C, Invar is durable, flexible and easy to machine. It comes in a range of forms such as: Plate, Round Bar, Square Bar, Flat Bar, Sheet, Coil, and Wire, and has become a popular choice for composite material manufacturing.
Alloy 42 is made up of iron and nickel (42%) and is classified as a controlled expansion alloy. With a low and consistent CTE over the range of 20-300°C, it matches hard / borosilicate glass or ceramic similarly to Kovar; it also matches silicon and has the capability for glass-to-metal or ceramic-to-metal sealing applications. Some of these applications include:
With the ability to withstand extreme temperatures, Alloy 42 is also shock-resistant so the seal will not experience any cracking. It benefits from good workability and weldability and comes in a range of forms such as: Round Bar, Sheet and Coil.
At City Special Metals, we hold a specialist range of Kovar, Invar and Alloy 42 in unique forms and size so you can find the perfect alloy for your application.
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