Are you an engineer in the industrial or commercial sector? If you are part of the design team, you must know that selecting the best engineering materials is a critical part of your operations. Incorrect material selection has led to numerous disasters including the Boston Molasses Disaster, De Havilland Comet Plane Crashes and the Eschede Train Disaster of 1998. In mechanical engineering, selecting a material can be a difficult undertaking considering the many factors the engineer must consider before settling on a material. The key to this process is to ensure the material not only supports design integrity, but also guarantees structural integrity in the harsh actual field application. As you select the best material for your design, you should be wary about some options.
What choices does the engineer have?
There are four common mechanical engineering materials. First, there are ferrous metals, which include stainless steels, carbon steels, alloy steels, cast iron and tool steels. The second category is plastics, which comprise of thermosets and thermoplastics. The nonferrous metals category covers titanium, magnesium, copper, aluminium and tungsten. Finally, we have adhesives, whose long list includes silicones, epoxies, anaerobics and hot melts.
Historically, and through research, some of these materials have gone into the bad books with engineers for some reasons. Here is a breakdown of 5 engineering materials you should never use.
5 engineering materials you must never use
Lead: Lead is one of the most interesting non-ferrous engineering materials. It features excellent malleability and a low melting point, making it perfect for casting. The metal can be easily recycled, and probably that is why it is abundant. Considering that lead is also low-priced, one might expect it to be the perfect metal for engineering design applications. As a mechanical design engineer, one of your chief concerns is the strength of your product/component. Lead does not fit the bill on this consideration. The metal is extremely weak, worsened by its fatigue and creep characteristics. Even for designs that require minimal strength, lead may not fit. Unless you are adding alloys to the metal, you should NEVER use it. Lead is also an extremely toxic material, and is extremely harmful to the human body if inhaled or swallowed.
Cadmium: Cadmium is also on our list of 5 engineering materials you should never use. This toxic metal is greyish-white, or blue-white in elemental form. This material may be present in industrial paints.
The metal presents both short term and long-term ill effects. Some short-term effects from acute exposure include muscular pain, headache, weakness and sweating. Within 24 hours, the victim may have developed acute pulmonary oedema.
In the longer-term, one may contract cancer of the prostrate or lungs. Generally, the victim will initially suffer kidney damage. Experts also believe that this metal could cause osteoporosis, pulmonary emphysema, anosmia and anaemia.
Exposure may come from grinding, cutting, brazing and any other activity related to structure demolition/renovation. It is important to assess cadmium exposure in such maintenance or construction activities.
Asbestos: Asbestos was a popular engineering material owing to its heat resistance and strength. Most of its applications were in the 19th century. While companies knew the dangers of this material since the 1930s, it was not until the truth came out in 1970 that this material was banned.
Asbestos was mostly found in the building industry, where it was used for the construction of shingles, cement products and floor tiles.
What are the dangers of using this engineering material? You may have heard about mesothelioma cases in relation to asbestos exposure. Mesothelioma is a type of cancer that affects the lungs, heart or abdomen. Exposure to the material can also lead to these other diseases:
- Ovarian cancer
- Lung cancer
Crystalline Silica: Many minerals, including granite and sand, contain crystalline silica. The most common form of this material is quartz. Exposure to this material is rampant among high risk job workers in sectors such as rock drilling, tunnelling and foundry work.
Exposure to this material occurs mostly in the construction industry. Mixing concrete is one of activities that exposes workers to this dangerous material.
How dangerous is crystalline silica? The material is a serious human lung carcinogen. It can also lead to the sometimes-fatal silicosis condition. This material could also cause scar tissue in the lungs. The incurable silicosis can even lead to tuberculosis because it tampers with lung function.
The solution: avoid crystalline silica at all costs.
Halogenated Flame Retardants: These chemicals have been used together with construction materials at the manufacturing stage. They either inhibit chemical reactions, or form a protective film to stop the spread of fire. The problem is that when these retardants are heated, they change into toxic materials. When the gaseous fumes formed mix with dust, they can be inhaled or ingested. Effects of these toxins include cancer, foetal problems and immunotoxicity.
With so many engineering materials available, how can you distinguish the good from the bad? The solution is to know what to expect from the material in relation to what it offers. Are you using any of the five listed materials? You could be endangering life and property.