INVAR 36 / ALLOY 36 MATERIAL

Large commercial aircraft have been using increasing amounts of advanced composites (primarily carbon fibers in an epoxy resin matrix) for component parts such as aircraft control surfaces, body fairings and structural supports.

lnvar 36 has now become the material of choice for tooling moulds for many commercial airplane manufacturers.

Advanced composite components are manufactured by consolidating and curing multiple layers of resin impregnated carbon fibers against a solid mold surface. Processing them requires applying heat and pressure via the mould.

Aircraft surfaces must be precisely aerodynamic, and the components dimensionally accurate advanced composites. It is therefore essential that the thermal expansion mismatch between the composite material and the mold is minimised during the 177°C cure cycle. If there is a significant difference in coefficient of thermal expansion (CTE), inaccurate part dimensions and warpage of the composite components will occur.

Invar 36 tooling due to its low rate of expansion more successfully produces accurate parts over traditional tooling materials previously used. These traditional materials included soft tooling such as fiberglass, machinable epoxy boards, high density foam, clay or wood/plaster, and hard tooling such as aluminium or mild steel.

Invar 36 combines robustness, durability, accuracy and stable dimensions which make it ideal for mass production tooling moulds.

Aerospace applications impose many challenging conditions on the equipment such as acceleration during launch, effect of gravity as orbit is achieved, vibration, vacuum, and thermal variation. This causes continuous stress on the equipment.

The requirements of material for opto mechanical space applications are low thermal expansion, and to be dimensionally stable. Most solid materials expand when their temperature is increased however in space dimensional stability is essential, that is, how to control it and keep it within specific limits.

Aerospace Optical Mirror Mounts are used to mount optical mirrors in a stable stationary position in laser or optical systems.

To operate effectively the mount has to be ultra stable, exert low stress on the optics to minimize optical surface distortion, have high stiffness to maintain the optic alignment, maintain the specified tolerance in the operational temperature range, maintain the position of the optical element throughout its assigned life time, and have minimum mount size and weight.

Long term dimensional stability is required for support structures in many instruments having optical components like mirror mounts. For example, optical imaging systems on space flights such as the Saturn bound Cassini spacecraft impose very strict requirements on the optical mounts supporting the camera system. Not only must the material meet the dimensional stability requirements, it must also be machinable and have adequate mechanical strength.

Invar 36 is a suitable and widely used material for space applications due to its low coefficient of thermal expansion (CTE), and because its mechanical and dimensional stability properties can be controlled and modified using specific heat treatment and cold working processes.

Some typical applications include lens and mirrors cells, interfacing spacers between optics and other structures, optical measuring equipment, metering rods for telescopes and laser cavity structures.

Invar 36 has been discovered very significant for containers that are utilized to transport liquid natural gas (LNG) on tankers. It reduces the low temperature cryogenic contraction effect and virtually eliminates thermal induced stresses.

Ships and other vessels that carry liquid cargo such as Liquefied Natural Gas (LNG) have to withstand severe conditions externally and internally. During shipment LNG is supercooled to liquid form at -162 degrees C and pumped into container tanks. Traditional steels become brittle at such low temperatures so Invar 36 with its suitable properties and weldability is increasingly being used as a lining material for the containers.

Invar is used for bimetallic strips for controllers which capitalises on the effect of two different metals with different coefficients of linear expansion causing movement at set temperatures. A bimetallic strip metal is made by laminating two metals together which have different rates of expansion. Bimetallic strips are used in many applications including clocks, thermostats, thermometers, circuit breakers, temperature gauges, time delay relays, lamp flashers, fluorescent lamp starters, household devices such as irons, chip fryers, ovens, grills and many more.

For some applications the bimetallic strip is shaped into a coil and when heated or cooled, the metals making up the strip expand and contract at different rates. When this coiled strip is heated, the metal on the inside expands more and the strip unwinds, when cooled the strip re-coils. For a typical switch mechanism a temperature adjustment lever is connected to the center of the coil and a mercury switch is mounted at the end of the coil. When the coil winds or unwinds, it instructs or tips the mercury switch one way or the other, and triggers an electrical circuit.

Bimetallic thermometer gauges use quick reacting bimetal coils. They are manufactured from two cold-welded metal strips with different thermal expansion coefficients and rotate in proportion to temperature. The rotary movement is conveyed to the pointer with low friction. They can be used for numerous industrial applications including; the petroleum industry, heating and ventilation equipment, food processing, water treatment plants, chemical processing, air conditioning, the iron and steel industry.