The Aluminium Age – 21st Century

250px-Aluminium-4

Our Technical Advisor, Mr. R.R. Nair’s report on Aluminium Fire Fighting Equipments in Industrial Safety Review Magazine

Fire fighting appliances made in aluminium alloys are very popular in many advanced countries. However, in India aluminium alloys are used only to a limited extent for manufacturing fire fighting appliances. Probably due to lack of awareness on the subject, both users and manufacturers of fire fighting appliances are not eager to use the products made in aluminium alloys.

1. Introduction:
We use Aluminium every day, even though we don’t pay too much attention to it and often don’t even realize it.  Today, aluminium is the most widely used metal in the world after iron. Global production of aluminium in 2005 was 31.9 million tonnes. Forecast for 2012 is 42-45 million tonnes.  According to a report by the British Geological Survey, in 2005, the Peoples Republic of China was the top producer of aluminium with almost a one-fifth world share, followed by Russia, Canada and the USA.
Aluminium alloy is used in the manufacture of automobiles, bodies of airplanes, ships, electrical equipment, machinery, building construction materials, variety of consumer products including utensils, furniture’s, packaging materials, fire fighting appliances, storing of liquefied natural gas, etc. Fire fighting appliances made in aluminium alloys are very popular in many advanced countries. However, in India aluminium alloys are used only to a limited extent for manufacturing fire fighting appliances. Probably due to lack of awareness on the subject, users of fire fighting appliances are not eager to use the products made in aluminium alloys. There seems to be a misconception that the gunmetal and stainless steel are much superior in strength and corrosion resistance than the aluminium alloys.
In fact the aluminium can also give enough strength and corrosion resistance provided proper alloys are mixed with aluminium. On the contrary, the fire fighting appliances made in aluminium alloy can give many advantages over the gunmetal and stainless steel. This article will give an overview of the subject.

2.Production:
The word Aluminium comes from the term ‘Alumen’. Alumen is the Latin name for Alum, a group of aluminium compounds that occur in nature. The word ‘Aluminum’ is used in America and ‘Aluminium’ in other countries including the UK. Aluminium is the third most abundant element after oxygen and silicon. It is the most abundant metal in the Earth’s crust. It makes about 8.3% by weight of the Earths solid surface. Almost all metallic aluminium is produced from the ore bauxite. Large deposits of bauxite occour in Australia, Brazil, Guinea, Jamaica, and the primary mining areas for the ore are in Australia, Brazil, China, India, Guinea, Indonesia, Jamaica, Russia and Surinam.
Aluminium production is a two-step process. First, aluminium oxide is separated from bauxite by the Bayer process. In this process, bauxite is mixed with sodium hydroxide, which dissolves the aluminium oxide. The other compounds in bauxite are left behind. The aluminium oxide is then treated with a process developed by Hall-Heroult. Although, Hall-Heroult process, consumes a lot of energy, this method is now extensively used throughout the world to isolate aluminium from ores such as bauxite. The Hall-Heroult process produces aluminium with a purity of above 99%. Further purification can be done by the Hoope process. The process involves the electrolysis of molten aluminium with a sodium, barium and aluminium fluoride electrolyte. The resulting aluminium has a purity of about 99.99%.

3. Physical & Chemical Properties:
Aluminium is a soft durable, lightweight, ductile and malleable metal with appearance ranging from silvery to dull gray, depending on the surface roughness. Its CAS number is 7429 – 90-5. It has a melting point of 660.32 deg C and a boiling point of 2519 deg C. Its liquid density is 2.375 grams per cubic centimeter.  It can be formed into almost any shape.  Pure aluminium is soft and has little strength. The strength and durability of aluminium alloys vary widely, not only as a result of the components of the specific alloy, but also as a result of heat treatments and manufacturing processes. When it alloy with small amounts of copper, magnesium, zinc and other elements, to form aluminium alloys, the added elements give aluminium strength and other properties that make it one of the most useful of all metals. Copper and magnesium increase the strength and hardness of aluminium. Magnesium makes aluminium easier to weld. Manganese helps aluminium resist rust and also provides strength. Silicon lowers the melting point of aluminium and makes it easier to cast. Tin makes aluminium easier to shape with metal working tools. Zinc, especially when combined with magnesium, gives added strength. Other elements like Bismuth, Boron, Cadmium, Chromium, Cobalt, Iron, Led, Lithium, Nichol, Sodium, Titanium, Vanadium and Zirconium may also be alloyed with aluminium for special purpose.

Some of the general properties of aluminium and it alloys are given below:

  • Aluminium is one of the lightest metals. It weights about 170 lbs per cu. ft. (2720 kgs/cu.mtr) – about the thirds as much as steel.
  • Certain aluminium alloys are as strong as steel. They get stronger at extremely low temperatures.
  • When aluminium reacts with oxygen, the metal forms an invisible layer of chemical compound, called aluminium-oxide, which protects aluminium from corrosion.
  • Aluminium resists the effects of wind, rain and pollution.
  • Aluminium conducts electricity about 62% as well as copper. Aluminium wire can, therefore, carry the same amount of electric power as copper wire that weights twice as much.
  • Aluminium heats up quickly and evenly. It also cools quickly.
  • Hold the capacity of light and heat reflection. Reflects about 80% of the light that strikes aluminium. It also reflects heat well.
  • Non-magnetic and does not produce sparks when struck
  • Can be shaped by almost any metal working processes.
  • Can be bolted, riveted, welded and joined by most methods used for other metals.
  • Can be recycled.

Aluminium is recyclable. Recycling involves melting the scrap though a significant part is lost as dross (ash like oxide). The dross can undergo a further process to extract aluminium, The recycled aluminium is known as secondary aluminium, but maintains the same physical properties as primary aluminium.

4. Uses:
Aluminium is used as pure metal, in alloys, and in a variety of compounds. Aluminium alloys are classified in numbered series according to the other elements they contain.  The 1000 series is reserved for alloys of nearly pure aluminium metal. They tend to be less strong than other alloys of aluminium. However, these metals are used in the structural parts of buildings, as decorative trim, in chemical equipment, and as heat reflectors.  The 2000 series are alloys of copper and aluminium. They are very strong, are corrosion (rust) resistant. Aluminium alloys are commonly used in everyday kitchen utensils, in truck paneling and structural parts of aircraft.  The 3000 series is made up of alloys of aluminium and manganese. These alloys are not as strong as the 2000 series, but they also have good machinability. They are used for cooking utensils, storage tanks, aluminium furniture, highway signs, and roofing.
Alloys in the 4000 series contain silicon. They have low melting points and are used to make solders and to add gray coloring to metal. Solders are low-melting alloys used to join two metals to each other. The 5000, 6000, and 7000 series include alloys consisting of magnesium, both magnesium and silicon, and zinc, respectively. These are used in ship and boat production, parts for cranes and gun mounts, bridges, structural parts in buildings, automobile parts, and aircraft components.

The largest single use of aluminium (28 percent) is in the transportation industry, mostly used in manufacture of car and truck. About 23 % of all aluminium produced finds its way into packaging, which includes aluminium foil, beer and soft drink cans, paint tubes, and containers for home products such as aerosol sprays. About 14 percent of all aluminium goes into building and construction, which includes  windows, door frames, screens, roofing, siding, construction of mobile homes and structural parts of buildings. The remaining 35 percent of aluminium goes into a staggering range of products, including electrical wires and appliances, automobile engines, heating and cooling systems, bridges, vacuum cleaners, kitchen utensils, garden furniture, heavy machinery, specialized chemical equipment and fire fighting appliances.

5. Health Effects:
Aluminium is remarkably non-toxic. Aluminium is not as toxic as heavy metals, but there is evidence of some toxicity if it consumed in excessive amount. Studies have shown that consumption of acidic foods or liquids with aluminium significantly increase aluminium absorption. Aluminium sulfate has an LD50 of 6207 mg/kg (oral mouse) which corresponds to 500 grams for 80 kg person. Some toxicity can be traced in deposition in bone and the central nervous system, which is particularly increased in patients with reduced renal function. In very high doses, aluminium can cause neurotoxicity, and is associated with altered action of the blood – brain barrier. A small percentage of people are allergic to aluminium and experience contact dermatitis, digestive disorders, vomiting or other symptoms upon contact or ingestion of products containing aluminium, such as deodorants or antacids. In the 1980s, some health scientists became concerned that aluminium might be associated with Alzheimer’s disease. However, it is still not clear whether aluminium plays any part in Alzheimer’s disease. Some authorities believe that breathing aluminium dust may also cause health problems. It may cause a pneumonia-like condition currently called aluminosis. Again, there is not enough evidence to support this view.

6. Aluminium Alloys:
Aluminium alloys are available in various chemical compositions. As per British Standard BS 1490: 1988, they are designated as LM-2, LM-4, LM-5, LM-6, LM-9, LM-10, LM-12, LM-13, LM-16, LM-18, LM-20, LM-21, LM-22, LM-24, LM-25, LM-26, LM-27, LM-28, LM-29 and LM-30. Whereas Indian standard IS 917:1975 (Specifications for Aluminium and Aluminium alloys Ingots and Castings for General Engineering Purposes) has re-designated these alloys the digital systems in accordance with IS 6051: 1970 (Code of Designation of Aluminium and its alloys). As per IS 617: 1975, the entire range of alloys has been classified into two groups namely (i) commonly used alloys and (ii) special application alloys. The commonly used alloys are sub-divided into two groups namely (i) sand and gravity die-casting alloys and (ii) pressure die-casting alloys.

Aluminium alloys used for sand and gravity die-casting are alloy 4223 (LM-4), 4423, 4450 (LM-25), 4600 (LM-6) and 4600A. Aluminium alloys used for pressure die-casting and alloy 4420 (LM-24), 4520 (LM-2), 4600 (LM-6) and 4600A. Aluminium alloys used for special applications are alloy 1950 & 1900 (LM-0), 2280 (LM-11), 2285 (LM-14), 2550 (LM-12), 4223A (LM-22), 4225 (LM-16), 4300 (LM-18), 4323, 4525, 4635 (LM-9), 4685 (LM-13), 5230 (LM-5) and 5500 (LM-10).

Bureau of Indian Standards (BIS) allows the use of Aluminium alloys for the manufacture of various fire fighting appliances and fittings, such as Fire Hose Delivery Couplings, Branch Pipe, and Nozzles. (IS-903:1993) Fire Hydrant Stand-Post Type (IS-908:1976) Fire Hydrant Stand Pipe (IS 5714:1981)) Underground Fire Hydrant – Sluice Valve Type (IS 909:1975) Revolving Branch Pipe (IS 906:1988), First Aid Hose Reel (IS 884: 1985), Branch Pipe Universal (IS 2871:1983), Portable Pump Sets (IS 942:1982), High Capacity Portable Pump Set (IS 12717: 1989). BIS recommends that the aluminium alloys used shall be die-casting only and shall confirm to IS designation 4250, 4450 (LM-25), and 4600 (LM-6) of IS 617:1975. However, alloy 4225 (LM-16) is permitted to use instead of alloy 4250 for the manufacture of Suction Hose Couplings, Underground Fire Hydrants and Branch Pipe.

7. Chemical Composition:
The chemical composition and mechanical properties of aluminium and aluminium alloys vary from alloy to alloy. Majority of castings for common applications are produced from aliuminum-silicon-copper with 0.5 to 4% copper and 8 to 13 % silicon. The chemical composition of alloy 4450 (LM-25), 4600 (LM-6), 4225 (LM-16), and 4420 (LM-24) are compared below:

Chemical Composition of Aluminum Alloys
4450, 4600, 4225, and 4420

Alloying metal
Percentage as per IS 617:1975
4450 (LM-25) 4600 (LM-6) 4225 (LM-16) 4420 (LM-24)
Copper 0.1 max 0.1 max 1.0 – 1.5 3.0 – 4.0
Magnesium 0.20 – 0.45 0.10 max 0.3 – 0.6 03 max
Silicon 6.5 – 7.5 10.0 – 13.0 4.5 – 6.0 7.5 – 9.5
Iron 0.5 max 0.6 max 0.8 max 1.3 max
Manganese 0.3 max 0.5 max 0.5 max 0.5 max
Nickel 0.1 max 0.1 max 0.3 max 0.5 max
Zinc 0.1 max 0.1 max 0.5 max 3.0 max
Lead 0.1 max 0.1 max 0.2 max 0.3 max
Tin 0.05 max 0.05 max 0.1 max 0.2 max
Titanium 0.2 max * 0.2 max 0.2 max * 0.2 max
Others 0.15 max. 0.50 max
Aluminum Remainder Remainder Remainder Remainder

* Titanium, if present, shall be not less than 0.05 %

Aluminium alloy 4450 (LM-25) has high mechanical strength in the fully heat treated condition and high resistance to corrosion and these qualities make it versatile for a wide range of engineering equipment such as cylinder blocks and heads and other castings required in road transport. This is an improved alloy over the old A-8 alloy of BS. The range of application of this alloy is widened as the alloy may be used in “as cast” and partially hardened condition. Higher proof strength, greater hardness, pressure tightness and dimension stability on temperature variation of this alloy are used with advantage in aircraft industry and other castings like valve bodies, pneumatic tools, etc.

Aluminium alloy 4600 (LM-6) has an excellent cast ability and fluidity which permits the alloy to be used of intricate and thin walled castings. Alloy 4600 (LM-6) is also recommended for those die-casting for which the service operating conditions require a resistance to corrosion better than offered by alloys 4520 (LM-2) or alloy 4420 (LM-24). This alloy is most suitable for those requiring highest resistance to corrosive atmosphere and direct contact with chemicals, foodstuffs and seawater. The ideal fluidity and freedom from hot tearing of this alloy facilitates the production of complex castings of large surface area and their walls.

Aluminium alloy 4420 (LM-24) has a highest mechanical strength, greater hardness and better machinability than alloy  4520 (LM-2) and alloy 4600 (LM-6). The casting characteristics of this alloy are very good. Aluminium alloy 4225 (LM-16) has high strength and greater hardness, which is maintained, at temperature up to 200 deg C. It is good for pressure tightness. Amongst alloys 4450(LM-25), 4420 (LM-24), 4600 (LM-6), and 4225 (LM-16), the alloy 4600 (LM-6) is the most suitable aluminium alloy for manufacturing fire-fighting equipment. Alloy 4600 (LM-6) exhibits excellent resistance to corrosion under both ordinary atmosphere and marine conditions. The mechanical properties of aluminium alloy 4600 (LM-6) is given below:

Mechanical Properties of Aluminum Alloy 4600 (LM-6)

Mechanical Properties Sand-cast Chill-cast Die-cast
0.2% Proof Stress (N/mm2)* 60 – 70 70 – 80 120
Tensile stress (N/mm2) 160 – 190 190 – 230 280
Elongation percentage 05-Oct Jul-15 02-May
Impact Resistance – Charpy (Nm) 6 9
Brinell Hardness Number 50 – 55 55 – 60 55 – 60
Endurance Limit (5 X 107 cycles +/-mm2) 51 68 70 – 100
Modulus of Elasticity (x 103 N/mm2) 71 71 71
Shear Strength (N/mm2) 120

* The Value shown is typical for sand and chill cast bars produced to the requirements of BS: 1490 or die – cast 6 mm diameter test bars, minimum specification requirements are in heavy type.

8. Advantages:
Fire fighting appliances and fittings cast out of aluminium alloys hold many valuable properties that make it an exceptionally useful metal.  Some of the advantages of using Fire Fighting Appliances and Fittings made in Aluminium Alloys are listed below:

  • Fireman can easily maneuver the appliances and fittings made of aluminium as they are very light in weight.
  • They are strong as steel and as such they can replace the appliances and fittings cast out of gunmetal or steel.
  • They can be used for a longer period since they are corrosion-free.
  • Since, aluminium has resistance to wind, rain and pollution, the appliances and fittings made of aluminium can be used for outdoor action.
  • Since aluminium is non-magnetic and does not produce sparks when struck, the appliances and fittings made of aluminium can be used near flammable or explosive material.
  • Since aluminium can be recycled, it is more economical to produce fire fighting appliances and fittings in aluminium alloys.
  • Since aluminium has less re-saleable value the chances of pilferage is much less.

9. Conclusion:
In India, Aluminium alloys are not very much popular in producing the fire fighting appliances. Aluminium alloy 4600 is an excellent and the most suitable aluminium alloy for manufacturing a variety of fire fighting appliances. It exhibits the required tensile stress, elongation, impact resistance, brinell hardness, endurance limit, modulus of elasticity, corrosion resistance, shear strength, etc. The manufacturers of fire fighting appliances should make use of the advantages of this alloy and, manufacture more and more fire fighting appliances. The users of fire fighting appliances should encourage the products manufactured in aluminium alloys because of its added advantages over gunmetal and stainless steel.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s