Materials for Invar 36 Components - IMS

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.

Unique Properties of Invar 36

Before diving into the various Invar 36 components, it's crucial to examine some of its outstanding properties.

Low Thermal Coefficient

The coefficient of thermal expansion (CTE) is the rate at which metals expand or contract with temperature changes. Invar 36 has an exceptionally low CTE of about 1ppm/K over a temperature range of 39.2-96.8°F. It showcases a thermal expansion rate roughly one-tenth that of carbon steel at temperatures up to 400°F. Below is the average CTE of Invar 36 at different temperatures:

Corrosion Resistance

Invar 36 boasts excellent corrosion resistance, enabling it to withstand months in an oxidative environment without rusting. While its oxidation affinity is much lower than standard steel, applying grease to Invar 36 components can further enhance their corrosion resistance.

High Dimensional Stability

Thanks to its minimal CTE and low temporal change at room temperature, Invar 36 offers exceptional dimensional stability, making it invaluable for designing precision mechanical systems across different industries.

Popular Applications of Invar 36

Engineers highly regard Invar 36 for its phenomenal thermal expansion characteristics and dimensional stability. Thus, this alloy finds extensive use in applications ranging from watch parts to satellites. Here, we discuss some of the notable applications of Invar 36.

Tapes

Invar 36 is widely used for making tapes because these tapes can measure baselines with greater accuracy than steel tapes. Due to its low thermal expansion and high corrosion resistance, Invar tapes are ideal for devices that must retain constant dimensions under varying climatic conditions.

Boiler Tubes

Invar 36 tubes serve as boiler tubes that require high dimensional stability and low thermal expansion. These tubes exhibit low thermal expansion up to 200°C and maintain strength even at cryogenic temperatures, making them suitable for various industries, including food, oil, gas, and pharmaceuticals.

Pendulum Clocks

The period of a clock pendulum depends on the length of the pendulum rod, which can change with temperature fluctuations. Variations in temperature can impact the actual readings of the clock. Invar 36's low thermal expansion makes it ideal for manufacturing pendulum clocks, ensuring accurate timekeeping.

Bimetallic Strips

Bimetallic strips used in thermometers convert temperature changes into mechanical displacement and are also used for precision instruments. These strips, made of yellow brass and Invar, work well together since brass curves more than Invar when heated, allowing accurate high and low temperature readings.

Machining Challenges With Invar 36 Components

Machining Invar 36 components can be challenging, even for experienced machinists. Although similar to steel, Invar 36 is very soft and ductile in its annealed state. This characteristic makes it difficult to machine, producing gummy chips that can stick to the tool. Furthermore, Invar 36 is prone to work hardening, leading to plastic deformation ahead of the tool and making it harder to cut with each pass. This results in poor surface finishes and potential tool breakage.

Machining Invar 36 requires specialist knowledge and suitable tools, such as chip breakers, to manage these challenges efficiently. Utilizing sharp tools with more teeth and a rigid setup can minimize chatter and work hardening, ensuring a smoother machining process. After machining, Invar products should be annealed to relieve any internal stress for dimensional stability.

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Due to the unique requirements for machining Invar 36 components, transforming Invar into usable parts can be cost-prohibitive for smaller machine shops and fabricators on tight budgets.

Purchase Machine-Ready Invar 36 at a Reasonable Price

For over two decades, Industrial Metal Service has collaborated with fabricators, welders, and machinists in the San Francisco Bay Area and beyond, supplying precision-cut Invar stock at reasonable prices to meet specific project needs.

We supply new metals directly sourced from U.S. mills. For smaller machine shops on tight budgets, we also provide verified metal remnants from larger manufacturers. In addition to Invar 36, we offer other popular metals like steel, aluminum, titanium, and copper.

Contact us today to discuss your metal requirements. We ship nationwide with no minimum order requirements, getting you what you need fast.

A Guide to Controlled Expansion Alloys

Controlled Expansion Alloys: What Are They and Which Is Right for Me?

When searching for alloys for your application, you will likely encounter controlled expansion alloys.

The alloy expansion rate refers to an average coefficient of thermal expansion (CTE). Controlled expansion alloys have been carefully formulated to produce a specific CTE within certain ranges.

Controlled expansion alloys fall into three categories: low thermal expansion, matching expansion, and high thermal expansion. Here are some of the most common controlled expansion alloys and their suitable applications:

Kovar

Kovar, made from nickel, iron, and cobalt, is one of the most commonly used controlled expansion alloys. Kovar's expansion characteristics are closely regulated to match hard or borosilicate glass or ceramic. This makes it ideal for hermetic sealing applications, such as:

• Production of transistors, diodes, and electronic tubes
• Hybrid circuit casings and oscillator housings
• Scientific instruments and vacuum systems in scientific research

Primarily used in electronics and aerospace industries, Kovar comes in a range of forms: plate, round bar, square bar, flat bar, sheet, coil, wire, and tube. Its consistent thermal expansion and shock resistance make it reliable for these applications.

Invar

Invar, composed of nickel and iron, is known for its exceptionally low thermal expansion rate, exhibiting nearly zero CTE. This property makes it suitable for applications requiring constant dimensions in changing temperatures, including:

• Radio and electronic devices, electrical transformers, high voltage transmission lines, and circuit breakers
• Precision equipment elements like lasers, measuring and positioning devices, thermostats, and precision condenser blades
• Shadow masks and frames like those used in cathode ray tubes and OLED
• Mold and lay-up tools for composites

In addition to its dimensional stability between -100°C and 260°C, Invar is durable, flexible, and easy to machine. It is available in various forms, such as plate, round bar, square bar, flat bar, sheet, coil, and wire, making it a top choice for composite manufacturing.

Alloy 42

Alloy 42, composed of iron and 42% nickel, is another controlled expansion alloy with a low and consistent CTE over a range of 20-300°C. Like Kovar, it matches the expansion rates of hard or borosilicate glass and ceramic, as well as silicon, making it suitable for glass-to-metal or ceramic-to-metal sealing applications, such as:

• Electrical components like semiconductor lead frames in integrated circuits
• Bi-metal thermostat strips
• Thermostat rods
• CRT electron guns
• Electrical devices such as electric bulbs, radio valves, television tubes, fluorescent lights, and automotive and industrial lamps

Capable of withstanding extreme temperatures, Alloy 42 is also shock-resistant, preventing seal cracking. Its good workability and weldability make it a versatile option available in forms such as round bar, sheet, and coil.

At City Special Metals, we provide a specialist range of Kovar, Invar, and Alloy 42 in various forms and sizes to meet your specific needs.

If you need more information or wish to discuss your requirements, contact us today.

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