14 November 2018
Life Cycle Paper
MasterLock Combination Lock Materials
For decades, the most effective and commonly used method for locking and securing is owed to the combination lock. These locks are used to fasten a physical object in place usually to prevent use or theft. The combination lock has changed throughout time and multiple different design patterns have emerged within the past decade. Between the many versions of the combination lock, only several models have stood out and have made lasting impressions on users. One such model which I shall acknowledge here as an example above all is the appearance of MasterLock’s combination locks and its success in the lock industry. Its simple and sleek model has allowed it to be one of the very few prosperous combination lock designs in the world. Perhaps this is because MasterLock’s lock composition is made up of sturdy and reliable parts that are strong and most efficient for its job. We all know that combination locks are made out of hard metals, but no one really views the lock holistically, taking into account the other various raw materials that have an effect on its durability. MasterLock’s products are made out of many raw materials that are each crucial for the mechanism to function.
Although MasterLock’s combination locks come in different classes defined by quality (depending on security level), the recipes are generally the same: die-casted zinc, Nylon 6, Zamak, and stainless steel. To understand why Masterlock’s design has thrived in the lock industry for so long, we must dig deeper and further question the significance of these materials. Why steel over aluminum or brass? Why Nylon 6 over the other Nylon types?
Zinc die-cast is used in locks to galvanize the steel base of the lock. Because zinc is corrosion resistant, the die-cast faultlessly protects the lock’s metal, outer casing. Today, the main zinc mining territories are located in Canada, Peru, Russia, Australia, and the United States. Zinc ore mining can occur through different processes, but the leading mining method is by the way of cut and fill stoping. Cut and fill stoping is practiced underground in which the mine is cleared by blasting and drilling. Once the zinc is supplied, it undergoes extracting and refining processes such as electrolysis in order to remove sulfur from the captured zinc ore.
MasterLock prefers to use zinc die-cast because zinc is one of the most fluid alloys. Due to its thinness and lightness, zinc is more readily castable and takes less material to be cast, saving money and energy. Compared to aluminum and magnesium dies, zinc has a significantly low melting point, meaning that the alloy has a longer life cycle than the other two metals. As well, zinc produces a faster and greater die yield when being manufactured, in comparison to aluminum.
To separate the internal discs in a combination lock in order for them to turn separately, spacers called nylon washers are inserted in between them. Nylon is a silky, plastic polymer made of many molecule branches comprised of acid and amine atoms. Because nylon does not exist in nature, suppliers have to engineer it from petroleum. Petroleum bubbles found in porous rock are drilled from the surface of the Earth and are transferred to a refinery for processing. Nylon washers are typically made out of Nylon 6, Nylon MDS, and Nylon 6/6 which are all different forms of Nylon polymers with different additives.
MasterLock’s combination locks are comprised of Nylon 6 washers (see fig.1).
This type of washer in particular exhibits excellent elasticity, has high strength, and is abrasion resistant. This means that as the discs in the combination lock turn, the spacers in between them readily resist wear and tear, easily protecting the surface of the gears. Compared to any other Nylon form, Nylon 6 has the highest moisture absorption. Thus, MasterLock uses Nylon 6 because of its higher impact strength and fatigue resistance.
Many lock brands use brass, aluminum, or other steel alloys as their combination lock’s outer shell casing. MasterLock, on the other hand, uses stainless steel because its properties are most suitable for the function of a combination lock. Stainless steels are made out of an abundance of primary components found on earth: nickel, carbon, iron ore, nitrogen, chromium, etc. The process of steelmaking starts with the extraction of iron ore. Magnetic rollers are used to extract the ores, which are then processed into bundles to be put into a blast furnace. To reduce the iron oxides in the ores, coke – heated coal in the absence of oxygen – is added to the blast furnace. Flux agents are also added to clean any impurities in the ore. Hot air is blasted into the furnace and causes the coke to burn and react with the iron ore, yielding molten iron. To produce stainless steel, the iron is put through varying processes such as the oxygen furnace, the electric arc furnace, or pulverized coal injection. The product, steel, is melted with chromium, nickel, silicon, carbon, and other basic elements to form the finished product: stainless steel.
What properties of stainless steel caught MasterLock’s eye? Compared to brass, stainless steel does not rust or erode quickly under moisture or extreme weather conditions. This is because steel forms a protective oxide layer on its surface. This layer allows steel to be anti-rust and weather resistant, making it ideal for outdoor applications. Due to its hardness, steel can also resist high temperatures, unlike aluminum. Although stainless steel is heavier than brass and aluminum, it is much stronger than the two, which is essential for the durability of a combination lock. As well, stainless steel has a sleek, clean, and fresh finish that does not fade, making it more appealing to consumers. These varying qualities make stainless steel versatile and fit for MasterLock’s combination lock design.
No one really ever stops to consider the raw materials that go into the production of an object. As for the combination lock, MasterLock uses raw materials that provide the best service for locking and securing. As we unveil these raw materials used for the internal and external parts of MasterLock’s combination locks, it is clear that the mechanism is comprised of substances that are fit to be durable and long lasting. MasterLock uses Nylon 6 instead of Nylon 6/6 for its washers because Nylon 6 has better elasticity, is stronger, and is abrasion resistant. MasterLock uses die casted zinc instead of aluminum or magnesium because zinc is more energy efficient and its material is fluid and therefore more easily processed. It is also has a longer life cycle which is an ideal characteristic for a combination lock. Another major combination lock raw material is steel. The combination of die-cast zinc and plated steel in a combination lock makes it exceedingly resistant to bolt cutters and other heavy-duty, hindering tools. Although many lock producers use brass or aluminum for their design, MasterLock chooses steel for several reasons. Steel is more physically appealing, is stronger than most hard metals, and its oxide coat protects it from the elements.
All of the raw materials used in MasterLock’s recipe prove to be crucial to serving durability, longevity, and strength. The little contraption unlocks a symphony of many raw materials that all play an important role in the function of the combination lock.
Fig. 1. Marshall Brain, "Inside a Combination Lock", 1 April 2000, HowStuffWorks.com. <https://home.howstuffworks.com/home-improvement/household-safety/inside-lock.htm>
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Brain, Marshall. “Inside a Combination Lock.” HowStuffWorks, HowStuffWorks, 1 Apr. 2000, home.howstuffworks.com/home-improvement/household-safety/inside-lock.htm.
Life Cycle of Master Locks: Energy
Combination locks are removable locks made of varying metal parts that help secure items in place and can only be opened with a key. They can only be opened “by the alignment of its interior parts in a definite position” (“Combination Lock”). Combination locks are usually mass produced in a factory setting. One of the most popular lock making companies is Master Lock. The company used to have a plant in China, but brought the plant back to Milwaukee, Wisconsin in 2011 (Schmid). The process involves an assembly line that requires machinery such as punch presses, steel cutters and form presses. Different kinds of combination locks use different kinds of materials. Combination locks are made of different metals, primarily steel. For example, some locks use brass for the body of the lock while others use a stainless steel cast. There are different types of steel that can be used in the creation of locks: cold-rolled steel and stainless steel. The other parts that are not steel are usually made of aluminum or zinc and are created through the die casting process. Master Lock makes various kinds of combination locks, but the stainless steel combination lock uses the best kind of metal for the body.
In order to simplify the combination lock making process, it would be best to first discuss stainless steel. Depending on the what kind of process is used to make stainless steel, either hot rolling or cold-rolling, it can take up to about 2000 megajoule per tonne (Fruehan, et al). After it is made, the next thing to do is transport metal to the factory. It is unclear where Master Lock gets its steel from, but there are two steel big steel manufacturers near Wisconsin. One in Illinois, which is south of Wisconsin and one across Lake Michigan in Michigan (“Top USA”). Once the steel arrives at the manufacturing plant, it is then made into all the individual pieces needed to make a combination lock. Master lock uses stainless steel over regular steel that is cold-rolled for the case of the lock. The term cold-rolled defines a process that finishes steel. The key difference between cold-rolled steel and stainless steel is that cold-rolled is made of carbon and iron and stainless steel is an iron alloy that uses a mixture of metals (Anderson). Stainless steel consists of iron, chromium, nickel, silicon, manganese, nitrogen and carbon (“How is Stainless Steel Made?”). The ratios of the elements influence the properties of the stainless steel. Some companies choose to use cold-rolled steel because it is cheaper but has low corrosion resistance compared to stainless steel (Anderson). Another difference between the two is that stainless steel is often lighter. The energy cost of producing stainless steel is 54 MJ/kg, while the energy cost of creating cold-rolled steel is about 35 MJ/kg. Even though the energy cost of creating stainless steel is greater than creating cold-rolled steel, it is less susceptible to harsh situations. The internal parts usually made up of cold-rolled steel include the inner case and the combination disc (“Combination Lock”). The parts made up of stainless steel include the internal disc spring, the back cover and, most importantly, the case. After the steel parts are produced in Milwaukee, they are sent to the next location.
The next process that is important to the lock making process is die casting; the life cycle of this process is studied in depth by Stephanie Dalquist and Timothy Gutowski and will be summarized in this section. Die casting is one of the processes used to make two important parts of a combination lock: the bar and the shaft. The molds (or dies) to create these parts are made of steel and have an embodied energy of 84 MJ. The lifespan of a die depends on the casting metal. For aluminum, the average amount of castings that can be made with one die is 100,000. In America, aluminum is the most common metal used in the die-casting process, followed by zinc. These metals are then melted using reverberatory furnaces, which can be powered by electricity or natural gas. Even though the efficiency of natural gas furnaces is not as good as electric furnaces, it is the most popular choice due to the lower costs. Next, the melted metal is cast using high pressure hot chamber machines. There are two different kinds and the one used depends on the metal. For metals with high melting points, like aluminum and magnesium alloys, it is best to use a cold chamber machine. Metals with lower melting points, such as zinc, use hot chambers machines. These machines are estimated to use about 2.5 MJ/kg per year. After the metal part is allowed to solidify, it undergoes the finishing touches (Dalquist and Gutowski). Overall the die casting process uses 9 MJ/kg and about 15 MJ/kg if losses are included.
The die casting process happens at the Milwaukee Master Lock plant. The source they use for die-casting is unknown. Most companies use aluminum for die casting because of its abundance. However, even though aluminum is more abundant than zinc, there are advantages to using zinc during the die-casting process. Zinc has great fluidity which allows for “Zamak, an alloy of zinc, would allow for “thinner, more intricate, and more complex” casts (“Benefits of Zinc Die Casting”). Another important fact about zinc is that it allows dies to last longer. Because of its low melting point, “dies for zinc parts can last up to 10 times longer than dies used for aluminum” (“Benefits of Zinc Die Casting”). The lower melting point means that there is less energy that goes into melting zinc than aluminum. Therefore, zinc is a great contender for metals used in die casting. However, zinc is not as abundant on earth as aluminum and should be used wisely.
After all the parts are made, they are sent out to Master Lock’s location in Mexico. This is the final step of the processes involving the creation of locks. In Mexico, the pieces are put together by hand. Master Lock produces millions of locks for schools across the US each year (Schmid) They also send locks to places like China, for example (Schmid). At one point in Master Lock’s history, a majority of production occurred in China, but production was recently moved back to its original location in Milwaukee (Schmid). The process of making locks includes a variety of subprocesses, including steel making and die casting. These processes ensure that all the required parts for a combination are made. Different types of material have impact on how much energy it takes to make a lock, however the most effective material for the body of the lock is stainless steel due to its durability and ability to withstand corrosion. In die casting, the process usually involves aluminum because of its abundance. However, it is not the most effective metal for die casting. Zinc allows more casts to be made from one die by having a lower melting point and strength. Even though the type of metal Master Lock uses for die casting is unknown,they do use stainless steel to create durable and reliable locks.
Anderson, Mark. “What Are the Differences Between Stainless Steel and Cold Rolled Steel?” Mead Metals, Inc., www.meadmetals.com/blog/what-are-the-differences-between-stainless-steel-and-cold-rolled-steel.
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Dalquist, Stephanie, and Timothy Gutowski. “Life Cycle Analysis of Conventional Manufacturing Techniques: Die Casting.” Manufacturing Engineering and Materials Handling Engineering, 2004.
Fruehan, R.j., et al. “Theoretical Minimum Energies to Produce Steel for Selected Conditions.” Jan. 2000, doi:10.2172/769470.
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