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Annealed wires are commonly used for applications where good strength and long life are desirable.
These wires are extremely ductile and can withstand high winding stress without cracking or failure.
But what exactly is an annealed wire? And what is the process of wire annealing?
Wire annealing is a heat-treatment process that reduces the internal stresses and reorients the grain structure, reducing the strain hardening effects in a metal wire. This aspect, in turn, increases the wire's formability, reducing its brittleness and making it more durable.
This article discusses annealed wires in detail by going through the process of wire annealing and the types of annealed wires available.
In the end, the article also compares galvanized wire and annealed wire.
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Annealed wire is a wire that has been heat-treated to enhance its mechanical properties such as ductility and durability to make it suitable for metal forming applications.
Generally, low-carbon steel wires are annealed to produce annealed wires, but it also applies to wires of different metals, such as copper, aluminum, brass, etc.
Annealed steel wires are used for winding and tying applications, whereas copper and aluminum wires are suitable for ornamental purposes, such as making artifacts.
Wire annealing involves heating the wire above its recrystallization point, followed by controlled cooling to avoid cracks in the wire.
Cold working of metal to draw into wires results in the development of internal stress in the wire, rendering it brittle, which makes it unsuitable for further processes.
Wire annealing reorients the grain structure of the wire to eliminate any internal stresses, reducing the possibility of any void formation or propagation that might lead to fracture.
Therefore, annealed wire is suitable for applications where high flexibility with excellent durability and strength is desirable in the wire.
There are two significant ways to anneal a low-carbon steel wire: batch annealing and strand annealing.
Batch annealing involves placing a batch of steel wires inside a furnace to heat them.
The furnace is generally filled with hydrogen gas to avoid oxidation of steel wires.
An external covering is placed on the wires to prevent them from burning or changing colors.
The batch is heated above the recrystallization temperature of steel and then allowed to cool down slowly to attain high ductility.
Strand annealing involves integrating the process of annealing with the drawing of wires.
In strand annealing, the steel wires are pulled through tubings filled with hydrogen gas and heated up to 1260 °C.
After passing through the hot tubings, the wire is then pulled through water-filled tubes to cool them down.
The slower the rate of this operation, the lesser will be the thermal shock experienced by the wire and the better the ductility.
The complete annealing process takes about 5 to 7 hours. After the heating stage, the temperature of the steel wire ranges from 700 to 800 °C.
Lastly, the annealed wire can also be lubricated with oil to prevent rusting and give a more shiny appearance.
Annealing eliminates strain-hardening effects by reducing internal stresses and preventing crack formation.
Annealing a copper wire is a simple and quick process.
The equipment required for this operation includes a blow torch, a heat-resistant surface, and metal tongs.
For safety purposes, the user must wear safety goggles and gloves and keep a fire extinguisher nearby to avoid accidental fire.
Firstly roll the copper wire into a spool and place it on a suitable heat-resistant surface, like a block of concrete or a brick.
The wire is rolled because heating a single strand of wire makes it difficult to uniformly distribute the heat throughout the workpiece.
Then use a blow torch to heat the wire. Maintain a constant back-and-forth movement of the torch to ensure uniform heating.
Constantly monitor the texture and color of the wire. Stop the torch when the wires turn bright red, indicating the transition into the melting phase.
After this color disappears, heat the wire slowly until this color reappears. Repeat this process 2 to 3 times.
Another technique to identify that annealing temperature has been achieved is to apply paste flux on the wire and heat the wire until the paste flux turns charred black.
Once complete, remove the wires from the fire-resistant surface using tongs and quench them in cold water to cool the wires.
Generally, copper wires tend to attain a black color after annealing, due to the soot that forms on their surface.
Wipe off the wires with a cloth and polish them with oil for lubrication and visual purposes.
You can use this method to anneal wires of different materials, but require some trial and error to find the appropriate annealing temperature of that material.
Annealed wires differ mainly based on the technique employed in their manufacture.
Black annealed wires have an anti-corrosive surface coating that leads to a black color of wire.
The protective coating is generally applied after annealing the wire and provides a slippery texture to the wire.
These wires have excellent ductility and can elongate by about 10% of their length without fracture, making them suitable for tying/baling products that are prone to expansion.
This wire is usually composed of low-carbon steel and possesses a tensile strength of up to 540 N/mm2, and is available in diameters varying from 0.17mm to 4.5mm.
Although these wires provide good corrosion resistance, the coating has poor abrasion resistance, rendering the wire prone to rusting in abrasive conditions.
As a result, hot-dip galvanization of wires is preferable for applications where corrosion resistance is of utmost importance.
Black annealed wires are used in several applications, such as., baling haystacks in the agricultural sector, handcrafting, etc.
Bright annealed wire has a smoother and shinier external surface, making it preferable for decorative purposes.
It is usually composed of low-carbon steel and can have a tensile strength of up to 500 N/mm2, and is available in diameters varying from 0.2 mm to 0.4 mm.
This wire is also employed in binding and tying applications; however, its most commonly used for weaving applications.
Due to the absence of an external protective coating, it is highly vulnerable to rusting.
Based on the difference in wire gauge, wire form, and packaging, there are other types of annealed wires, with merchant wire, box wire, and tie wire being the most common ones.
Merchant wire is generally a spool of annealed wire rolled on a stand.
Box wire comprises more compact and tightly wound annealed wire coils packed into small boxes.
Tie wire can be packaged either like a box wire or merchant wire.
Due to its ductility, durability, and low cost, wire annealing has various applications in different industries.
The agriculture industry uses annealed wire for baling branches and hay in stacks.
Moreover, the construction sector utilizes annealed wire for setting up fencing or used as rebar tie wires.
The manufacturing industry employs them in binding and tying applications. These wires are also used as safety locks for nuts and bolts to prevent accidental removal of nuts.
Barbed wires often comprise annealed wires.
Binding and tying applications also extend into the mining sector for holding raw materials together.
Annealed wire is also used as wire mesh for packaging molds.
Different artworks also use annealed wires due to their ductility and smooth surface finish.
Galvanized and annealed wire differ in several aspects.
Galvanized WireAnnealed WireMore resistant against rust and corrosion due to an external protective surface.More prone to rust and corrosion compared to galvanized wire.Less flexibility and more stiffnessMore flexible and ductile.Better durability in outdoor conditionsLesser durability in outdoor conditionsUndergoes galvanization i.e. addition of external zinc protective layer.Undergoes the annealing processPossesses a more visually aesthetic surfacePossesses a relatively plain appearanceUsed in applications demanding stiffness, like packaging and wire meshUsed in applications demanding flexibility, like ropes, wire mesh, and filtersGalvanized wire vs annealed wireThe galvanized wire can also be annealed, which can impart beneficial material properties, like increased flexibility and ductility; however, that will cost more and be more time-consuming.
For outdoor applications involving tying, binding, or netting, galvanized wires are preferable due to their more favorable material properties, making them more durable.
However, for indoor and small-scale applications, annealed wire is cheaper and better suited for use due to better flexibility and ductility.
Moreover, galvanized wires are preferable for different types of ornaments and artworks as they are visually more appealing.
Annealed wire is easier to tie around or bind, so DIY users can easily use it for their relevant purpose.
Contrarily, the galvanized wire being stiffer, is more difficult to handle manually, due to which it is more common in commercial usage where machines or rope braiders perform the function of tying and binding.
Annealed wire is generally used for tying and baling applications where good ductility is desirable.
Although wire annealing is suitable for industrial applications, you can perform DIY wire annealing by using a blow torch to heat the workpiece, followed by controlled cooling.
You can also purchase annealed wires and use them for your applications, eliminating the need for annealing them by yourself.
Generally, black annealed wires are suitable for applications that demand corrosion-resistant properties over aesthetic value, whereas bright annealed wires are comparatively less resistant to corrosion.
Annealed steel is stronger than untreated steel as it is more ductile, making it softer and machinable.
Yes, the annealed wire will rust over time as the surface will be more vulnerable and exposed to corrosion and contact with air after the heat treatment it undergoes. Its surface needs to be coated for enhanced protection.
The grain structure of annealed wire is the molecular orientation within the annealed wire. A uniformly arranged grain structure indicates that the material can more easily undergo forming operations.
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