One of the best ways to ensure worker safety in industrial environments is by preventing falls. Proper footwear with non-skid soles is a must, but there will still be a risk of slipping on stairs and walkways. A textured surface in these areas will produce more friction while walking, providing better traction to prevent worker falls. One of the most common methods to improve slip resistance is the use of diamond plate in these high-traffic areas.
What is Diamond Plate?
Diamond plate goes by many names, including tread plate, checker plate, and deck plate. Whatever the name, it all refers to the same thing: metal flooring with a raised diamond pattern on one side. It can be made of various types of materials from metals to plastic, but is most often produced from aluminum, hot rolled steel, and stainless steel.
Because aluminum is naturally corrosion resistant, aluminum diamond plate is a favored choice for outdoor areas or other environments where the plate is in contact with water. Industrial kitchens, loading docks, and fire escapes often make use of aluminum diamond plate. The surface is able to withstand corrosion and abrasions, and can be easily cleaned.
Steel has the strength advantage over aluminum, making steel diamond plate even more hard-wearing and strong. For this reason, diamond plate made from steel is often used in structural applications such as stairs and ramps. While it offers less corrosion resistance than aluminum, steel diamond plate’s sturdiness holds up well through regular use and cleaning chemicals. It is ideal for indoor location usage such as shop floors and walkways.
Production of Diamond Plate
Although diamond plate may look intricate with its raised interlocking patterns, the process of making it is fairly straightforward. Using a combination of heat and pressure, metal can be made into diamond plate by stamping or hot rolling.
With the stamping method, the metal (generally aluminum) can be used at room temperature. The aluminum is run through a series of large rollers, with each pair of rollers having one raised side and one smooth. As the metal passes through each roller, the massive pressure of the patterned roller embosses those shapes onto the aluminum’s surface. Once finished, the diamond pattern will be firmly stamped into the raised side while leaving the other side smooth.
For steel diamond plate, hot rolling is the usual method of production. A steel slab is flash heated to just above its recrystallization point, and quickly passed through the rollers to produce the diamond pattern and desired thickness. Afterwards the steel is allowed to cool slowly, which helps prevent any major alternations to its mechanical properties. Once cooled to room temperature, the steel plate will have the raised diamond pattern on its surface.
Why Use Diamond Plate?
Diamond plate is most often found in any area where extra traction is needed to help reduce slips and falls. This safety practice applies most importantly to workers, but benefits their usage of industrial vehicles as well. A warehouse loading dock surface made of diamond plate keeps workers steady on their feet, but also provides better traction for forklifts. Finally, the extra strength and durability of the metal plate allows the dock to withstand the heavy weight of forklifts without damage.
The Differences between Hole Punching, Drilling, and Notching
The forging of metal sheet and plate is often just the first step in its overall processing. Sawing will give you the desired size, but depending on the intended purpose of the metal, further operations will need to be done. Material removal services enable metal producers to create the exact customer specifications for components, using hole punching, drilling, and notching. Each process results in material removal, but the choice of method can depend on the metal’s thickness, the location of where the removal will take place, and other factors.
The Material Removal Process
Hole Punching
This shearing process involves a tool with sharp edges capable of punching through a piece of metal. Think of a cookie cutter: no matter what the shape, if the cutter is pressed quickly and firmly into the dough, you’re left with precise edges once the piece is removed. Hole punching works the same way on metal sheet and plate. Whether done using electrical, hydraulic, or pneumatic power, if sufficient force is applied, any shaped hole can be made in the metal.
Notching
Much like hole punching, notching is a shearing operation using a sharp-edged tool. The difference lies in the removal’s location. While hole punching can take place anywhere on the metal, notching occurs only on its edges. Once those notching cuts are performed on the metal’s perimeter, additional bending or forming can be done.
Drilling
This type of material removal uses a drill bit rather than a shearing tool. As the drill is applied to the metal, it continually removes the material until the bit pierces through. While a hand drill can be used, more often this process involves a machine known as a drill press. The operator uses the machine handles to lower the bit onto the metal, which helps enable more precise drilling.
Advantages and Disadvantages
Hole Punching
Hole punching is an appealing option for several reasons, but especially because of its speed. The presses used for hole punching can be incredibly quick, allowing multiple metal pieces to be processed within a short period of time.
Quick processing means a higher production volume, making this highly cost-effective.
The other advantage is flexibility, since hole punching easily creates shapes other than round. Whatever the shape needed – round, square, triangular – the hole punching press can cut that into the metal.
However, successful hole punching is limited to metal pieces with a thinner diameter. It is also dependent on the sharpness of the press, and punching through metal wears on the tool. If not kept sharp, a worn tool leads to punches that are incomplete or have sloppy, rough edges.
Notching
Since notching is a shearing process like hole punching, they share similar pros and cons. The notching tool is fast, and while the process often involves creating vertical cuts, it can be modified to create different shapes. And like hole punching, this type of material removal is best done on thinner pieces of metal. Greater ease of cutting helps ensure the notches will be clean-edged and precise.
Thicker metal can be processed, but requires greater force which is tough on the notching tool. The tool wear requires more supervision and maintenance to best help keep it sharp for notching.
Drilling
Unlike hole punching and notching, which cut through the metal, drilling gradually pierces through it to remove material. While slower than a shearing method, drilling helps to prevent distortion of the metal part. The force needed for punching or notching tools can sometimes leave the metal bent around the location of the cut. Drilling is much better at keeping the surrounding area unaffected, and can be done successfully even on very thick pieces of metal. In addition, drilling is much more affordable since the necessary equipment is less expensive than the tools needed for other material removal options.
However, the use of a drill bit does have its issues. This process can only create a round hole, unlike notching and punching. There is more friction involved due to drilling being a longer process, and friction produces heat which can negatively affect the metal. The friction also wears away at the drill bit, which may need replacement or sharpening to keep the hole precise.
What is Superfinishing?
The word “metallic”: a term synonymous with adjectives such as bright, gleaming, and reflective. However, newly-produced metal straight from the mill isn’t very shiny; in fact, it looks and feels rather rugged. Its appearance is referred to as “mill finish”, and it has a rough and irregular surface texture. The finish is dull, and its color often patchy due to metal oxidation or contamination from mill oil. While it looks unrefined, depending on its use mill finish can be acceptable. Why spend extra time and money to make unfinished metal look better when appearance is unimportant?
However, the majority of consumers prefer their metal products to be smooth and shiny. Beyond the look of mill finish, other processes such as shearing can leave metal with rough or sharp edges. To improve the overall quality of the metal, polishing is often done to create a smooth and shiny surface. But when a finer degree of finishing is needed for certain applications, additional processing such as superfinishing is done.
Superfinishing
Simply put, superfinishing is a level beyond the typical processing done to metal products. The metal has already gone through some type of finishing such as polishing or another surface modification process. To the naked eye, polishing leaves a gleaming surface and metallic shine, but the process can actually result in microscopic structural irregularities on its surface. These irregularities are referred to as the residual amorphous layer. Unlike the rest of the metal which retains its crystalline structure, the amorphous layer has scattered atoms creating a disordered surface. Superfinishing is necessary for situations where removal of that amorphous layer is critical to the metal component’s use.
The Superfinishing Process
During a primary finishing process like polishing, a great deal of friction is needed to smooth away any pits or bumps marring the metal’s surface. On the other hand, the secondary process of superfinishing is a much more precise operation using lower friction. The best way to create lower friction is by the use of a very fine abrasive agent. The height of a superfinishing abrasive agent may only measure from 5 to 8 micrometers: too small for successful polishing, but effective in wearing away the amorphous layer.
After the selection of stone or sandpaper with an extremely fine grit, the abrasive is applied on the metal’s surface while the item rotates in the opposite direction. This is done one small section at a time, both for precision and to keep friction to a minimum. Additional thermal protection is provided by using a lubricant, which helps reduce any heat produced from friction.
Advantages of Superfinishing
Superfinishing is useful for both functional and aesthetic purposes:
• Appearance: the metal is left with tiny crosshatch marks, creating an attractive brushed-metal finish.
• Low Tolerances: the amorphous layer removal performed during superfinishing means the metal’s measurements are much more precise. Polishing may leave metal looking shiny, but on a microscopic level, the surface is still uneven. Superfinishing ensures that the metal’s surface is uniform, because the crosshatching is the same height on every part of the component. The metal’s dimensional accuracy is improved, creating better seals and more precise assembly when the part is used in applications.
• Prolonged Use: precise assembly allows for less friction created during use, because pieces are less likely to press and slide against each other. This reduces wear on the metal, which then requires less maintenance and enables a longer period of use. Automotive parts like rods and shafts are typically superfinished to help extend the lifetime of the part.
Disadvantages of Superfinishing
• Finish: depending on the consumer’s taste, a polished finish may be considered more appealing than a superfinished one.
• Cost: additional equipment is needed to perform superfinishing, adding to the metal’s overall cost.
• Time: while superfinishing is not a particularly lengthy process, the operation does add to the overall processing period for that part. This prolongs the time before a finished product can be shipped or sold.
What is Rebar?
Introduction: What is Rebar?
It’s likely almost everyone has heard of rebar, and seen pieces of it sticking out of a concrete wall or pillar under construction. However, it’s probably also safe to assume most people are not familiar enough to explain exactly what rebar is. Could they describe how is rebar made, and its intended use? We’ll take a closer look at rebar to help answer these questions.
What is Rebar?
Rebar, short for “reinforcement bar”, is a metal bar used to increase the tensile strength of concrete. Concrete is quite hard and has great compression strength, but it is much weaker when it comes to tensile strength. Simply put, this means concrete is prone to cracking or toppling over from its own weight when used for building. A concrete sidewalk rests on the ground, which provides enough support for concrete to stay whole and strong. But when building up for the walls of a stadium, or building across for lengths such as a freeway overpass, the concrete requires reinforcement. The insertion of rebar within the structure helps the concrete to withstand great amounts of pressure and tension.
Rebar is available in several types of metals, and can even be made of fiberglass, but the most commonly used is produced out of carbon steel. This is because steel possesses thermal properties similar to concrete, which means both the structure and the rebar buried within it will react the same way to temperature changes. As the temperature rises and falls, the concrete and steel will expand or constrict together, which helps to prevent cracking.
How is Rebar Made?
Steel rebar is almost always made of recycled steel, taken from the frames of cars, appliances, and machinery which are too old for continued use. These steel pieces are melted down and cast as billets, the term used for long unfinished steel bars. The billet shape allows the pieces to be easily stacked away in storage until needed.
To make rebar, the billets are heated to a very high temperature just short of the steel’s melting point. The red-hot billets are then fed into extrusion machines, squeezing the steel out like toothpaste from a tube. This process is repeated with a series of smaller and smaller extrusion diameters, until it results in steel rods of the desired size.
From there, tooling machinery is used to create the distinctive corkscrew ribbing found on rebar rods. These ribs help to anchor rebar within the concrete, preventing the rods from slipping or bending. The final step is shearing the rebar rods to cut them down to the desired lengths.
How is Rebar Used?
Concrete is an incredibly resilient material – some ancient concrete structures such as the Roman Colosseum are still standing, thousands of years later. However, most concrete does begin to degrade as it ages and begins to form cracks. Cracks allow moisture and air to seep into the concrete, speeding the process and weakening the material’s structural integrity. If left untreated, the cracks can allow oxidation of the steel rebar, causing rust and weakening the steel.
Compromised rebar can lead to serious consequences, because the steel is no longer providing the strong degree of strength and reinforcement to the structure as intended. Not only does it provide building strength, but rebar can also help to prevent cracks from forming. And if cracks do form, the placement of rebar helps experts to predict where they’re most likely to occur, and those spots can be reinforced.
For best effect, rebar is often laid in a grid pattern. The carbon steel’s strength is maximized in grid formation, allowing it to reinforce the concrete despite tensile forces coming from many different directions. Ordinarily, non-heat treated carbon steel would be considered too brittle for construction use. Heat treatments such as hardening or annealing allow steel to retain much of its hardness while making it less breakable. However, this is not a concern when carbon steel is used for rebar, so the alloy can be left untreated. The steel is extremely hard and brittle, and highly vulnerable to rust, but once embedded within the concrete, these qualities are no longer liabilities. The extreme hardness of untreated carbon steel is a benefit, giving the structure added strength and stability.
The Five Types of Carbon Steel Round Tube
The Five Types of Carbon Steel Round Tube
When it comes to steel manufacturing, one type has the lion’s share of the market: by volume, carbon steel accounts for 90% of the steel produced each year. The increasing growth of the oil and gas industry means carbon steel tube and pipe are in constant demand, with over 50% of all steel tube and pipe being used for petrochemical production. Carbon steel’s ability to withstand corrosion and extreme environmental conditions makes it an excellent choice for parts used in oil and gas processing, from drilling to refining and transport.
Round Tube
While tube may look similar to pipe, the two shapes are used for different purposes. Pipe is used to transport substances such as oil and gas, while tube is used as a structural element. For this reason, tube is generally made to be stronger and more robust than pipe. Tube can also come in a variety of shapes such as round, square, or rectangular. When carbon steel round tube is needed, there are five types available for use:
Electric Resistance Welding (ERW)
Produced from cold-formed coil made of low carbon steel, this method uses electric resistance welding to form it into round tube. The welding itself can be done in several ways, but most often through an automated process. This means high quality ERW tube can be produced at a low manufacturing cost, making it a very popular choice for customers.
ERW tube’s affordability and versatility leads to it being used in many applications including automotive frames, supports and stands, and internal machine components.
Cold Drawn Seamless (CDS)
CDS tube starts with steel billets, heated to an extremely high temperature and pierced with machinery to create the tube’s hole. The steel is then rolled to elongate the tube and shrink its diameter, and cooled once it has been formed to the desired shape. This process results in very sturdy tube with thick walls and a smooth surface.
Because CDS tube is not only strong but aesthetically attractive, it is often used for visible automotive parts such as roll bars and frames. Other common uses include hydraulic cylinders, infrastructure columns, and boiler tubing.
Drawn-Over-Mandrel (DOM)
This type of tubing is produced through machining with the use of mandrels. A mandrel is a taper bar, used to gradually increase the diameter of a part placed on it – such as the small mandrels used by jewelers to resize and widen rings. For round tubing, steel coil is sheared and joined by welding, then finished by using mandrels. This machining creates high-quality tube with excellent levels of hardness, strength, and consistency.
DOM tube is used extensively in the automotive industry, found in parts including shock absorbers, dampeners, and seat frames. It is also regularly used in hydraulic parts such as pumps and cylinders.
Hydraulic
This type is manufactured to meet the necessary requirements of hydraulic lines, including the strength to withstand the stress of containing pressurized fluids. Similar to CDS, hydraulic starts with carbon steel bars which are heated, pierced, and rolled until it results in sturdy tubes. Hydraulic tube has a very shiny and bright finish which makes it appealing for its aesthetic quality as well as its overall strength and utility.
Due to its high degree of strength, hydraulic tube can also be used for applications where tubes will be bent or fitted together.
Hot Finished
Also known as seamless tube, this type is made by piercing and rotating an extremely hot piece of carbon steel. The rotation creates the shape, and it then goes through a series of mills to reduce the tube’s diameter and wall thickness. This fairly low-cost process creates a versatile, easily machinable tube. However, hot finished tube sizing tends to be less precise than other types, and its finish looks rougher. For this reason, hot finished tube is typically found in applications where aesthetics or size variance are unimportant.
Seamless tube can be found in heavy-duty uses such as construction and drilling equipment, pillars, and wind turbine components.
Suitability of Welding Carbon Steel
Carbon steel is just as described: a steel alloy containing added carbon, with the carbon making up 0.05% to 2.0% of its weight. This percentage range means carbon steel is a sprawling category, covering many different types of steels with varying levels of carbon. Steel with any other combination of alloying elements can be included in this category, so long as they contain carbon.
Clearly the many possible chemical compositions of carbon steel make it difficult to make blanket statements about this metal. Carbon increases the hardness and strength of steel, but the percentage of carbon added creates different results with the steel’s mechanical properties. Those properties then affect how the metal reacts to further processing such as welding. It is very important to understand the exact qualities of a selected carbon steel to produce a successful weld; doing otherwise risks metal damage or a weld that may fail later during use.
Carbon Content
The most important decision before beginning a weld will be the type of steel to use. Carbon steels are organized as three basic types:
• Low carbon steels: containing less than 0.30% carbon by weight
• Medium carbon steels: containing 0.30% to 0.60% carbon by weight
• High carbon steels: containing 0.61% to 2% carbon by weight
Each of these groups will weld differently due to their carbon content. The higher the steel’s carbon level, the more prone it will be to weld cracking. Low carbon steels can be much more easily welded, which is why they are the typical choice for this process.. However, high carbon steels can be welded, provided extra care is taken with the more brittle material. Heating high carbon steel prior to the weld, as well as afterwards, will help prevent cracking. Additional filler metals may also be used with high carbon steel to create a better weld.
Carbon Equivalency
Once the type of carbon steel is selected, further determination of its weldability is done using the carbon equivalency formula. This formula examines what effect the other alloying elements besides carbon may have on a weld. The percentages of alloying elements are calculated as an additional degree of carbon – and that boosted carbon level translates into a steel considered more difficult to weld. As an example: using the formula means a medium carbon steel with no added manganese will be judged as easier to weld than the same carbon metal including manganese alloy.
Overall Chemical Composition
Even after selecting a lower carbon steel, and calculating an acceptable carbon equivalency, the overall chemical composition should still be reviewed. Some elements will just not take well to welding, even with a great deal of effort. Any amount of lead in carbon steel, for instance, will significantly raise the probability of weld cracks. Other common alloying elements such as sulfur or phosphorus can have the same effect, resulting in a weak or failed weld. While carbon steel with trace amounts of either sulfur or phosphorus can still be welded, the percentages must remain extremely low (approximately 0.05% or less) to avoid weld cracking.
Cooling Rate
The job is still not complete after creating a weld, because as it cools, cracking may develop. Carbon is again the main culprit here, due to it making the steel more brittle. With higher levels of carbon and equivalent alloys, the metal must be cooled at a slower rate to prevent cracks from occurring.
In addition to the steel’s carbon percentage, other factors must be accounted for during weld cooling. The thickness of the steel being welded will affect the cooling rate, and thinner material has a higher risk of distortion. The temperature where the weld is being performed is also important. In cold temperatures, preheating may be necessary even for lower carbon steels, while it can be performed without prior operations in warmer environments.
Buyers Guide To Carbon Steel
¬¬¬¬Six Questions when Buying Carbon Steel
Carbon steel is a widely used material, found in items from structural steel to kitchen knives. However, these industries do not necessarily use the same grade of steel. At its most basic, this metal group is made up of any steel alloy with added carbon. The carbon percentage will usually be somewhere between 0.05% to 2.0% of the metal’s overall weight.
In any chemical composition, a range of 0.05 to 2.0 is a significant margin. Steel is no different: when it comes to formulating steel alloys, the variance in carbon percentage has a transformational effect on the produced metal. Carbon strengthens and hardens the steel, but decreases its ductility. That means the higher the carbon percentage, the less flexible the steel becomes. A high-carbon steel grade put under high or repeated stress would be more brittle and liable to crack. A grade of steel with lower carbon content will be more ductile, but not nearly as strong.
So before starting a project with carbon steel, you should carefully consider the grade you select. It can make a big difference in the end result’s success. Reviewing these six questions beforehand can help in making your choice:
1. Will the carbon steel be machined?
Machining is a process where the parts and shapes are cut from the metal. Because lower carbon grades are relatively softer steel, they are more easily and efficiently machined. A high carbon grade can be used, provided the alloy’s chemical composition includes sulfur which improves the steel’s machinability. Without sulfur, the hardness of high carbon steel will result in major wear of the cutting tools.
2. Will the carbon steel be welded?
In general, the same grades of lower carbon steel more suited for machining can be more easily welded as well. High carbon steels can be used, but often require additional treatments before and after welding. And in contrast to machining, the steels grades containing sulfur are not recommended for use in welding. The sulfur in these alloys will have a higher risk of developing cracks at the weld join.
3. Does the carbon steel need to be heat-treatable?
When it comes to heat, a good rule of thumb is 0.3. Steels with a carbon content of 0.3% or higher can be heat treated easily. This is due to the carbon itself, which helps the formation of martensite crystallization within the steel, reinforcing its hardness and strength. Grades of lower carbon steels lack the carbon necessary for martensite formation, making heat treatments unsuccessful.
4. Does the carbon steel need good formability?
Due to the wide margin of carbon percentages across grades, it can be difficult to say which grades might be more formable than others. The selected grade is often dependent on the shape: rolled sheet requires a much more ductile type of steel, but forming pieces such as angle and beam can involve a wider grade range. Overall, the more ductile carbon steels – meaning, lower carbon grades – are much easier to form.
5. Does the carbon steel need high corrosion resistance?
Because steel’s main element is iron, it is vulnerable to oxidation leading to corrosion. This is an accepted fact that when using any grade of carbon steel, it will develop a certain amount of rust. In applications where corrosion resistance is a high priority, it may be better to consider using another material such as stainless steel instead. To minimize corrosion of carbon steels, they can be coated to create a barrier between the metal and its environment. This can go from involved processes such as galvanization or plating the metal to simply applying a coat of paint.
6. How strong a carbon steel is needed?
The steel’s application is crucial to deciding the strength needed for your metal. High carbon steel is incredibly strong, but if intended to be used for making small parts such as nuts and bolts, your needs would be better served by low carbon steel’s machinability. But while low carbon steel is more formable, it would be worth the greater effort when making tools to use high carbon steel for its hardness and durability. While it may be tempting to select the hardest and strongest material available, its actual use should be an important factor in selecting the right carbon steel.
Common Uses of Stainless Steel
Since the early 1900s, stainless steel has been a fixture in our everyday lives. This alloy can be found everywhere, from watches to skyscrapers and aircraft. Its strength, corrosion resistance, and affordability make it an appealing choice for many projects. Even better, stainless steel is fully recyclable! The alloying elements used in its chemical composition can be extracted from melted stainless steel, and then reused with no degradation in their performance.
Having learned of its valuable properties, it is little wonder that so many different industries rely upon using stainless steel. With a wide range of grades and alloys available on the market, a manufacturer can be sure to find a type of stainless steel to suit their needs. Here are five of the most common uses of this metal alloy:
Construction
Modern construction is largely dependent on stainless steel due to its strength, flexibility, and resistance to corrosion. Its durability makes it a good choice for both interior and exterior use. Skyscrapers and commercial buildings often have frames and exterior cladding made of stainless steel. Its durability means less time and expense can be spent on maintenance, since the metal remains rust-free.
Energy and Heavy Industry
The oil, gas, and chemical industries present a great challenge to construction. These industries typically operate in environments which involve high temperatures and corrosive, toxic substances. Specialized grades of stainless steel have been developed for these industries, designed for enhanced corrosion resistance and able to handle extreme ranges of temperature. These “super-steel” grades are used for storage tanks, pipework, and valves.
Crude oil is an extremely corrosive substance, so stainless steel is invaluable in the construction of offshore rigs and drilling components. Stainless steel can also be found making up the equipment for renewable energy sources such as wind or hydro power. Its resistance to developing rust allows it to withstand the corrosive effects of seawater and varying temperatures.
Automotive and Transportation
Stainless steel has long been an integral part of automotive manufacturing, although mainly used in the past for exhaust systems and trim. With the rise of environmental concerns, more auto makers are expanding their use of stainless steel in structural components due to its recyclability.
The transportation and shipping industries are highly reliant on stainless steel, from shipping containers to tanker trucks. Transporting chemicals and other substances requires strong, non-reactive metals like stainless steel. Its strength also allows for thinner containers, which saves on fuel costs. Its corrosion resistance then requires less maintenance and easier cleaning of those containers and other transport equipment.
Medical Instruments
The production of medical instruments has involved stainless steel for well over a century. While bacteria can form on its surface, its natural corrosion resistance means a stainless steel tool is unlikely to have cracks or grooves where the bacteria can harbor itself. This makes for easy and thorough sterilization of stainless steel medical tools. The stainless steel instruments can be sterilized and reused for many cycles before they will show enough wear to be discarded.
Food Production and Catering
When it comes to cooking, once again stainless steel’s durability and corrosion resistance play key roles. Many foods such as tomatoes are highly acidic, leading to corrosion and discoloration of aluminum or copper cookware. The more reactive a metal, the more it can potentially affect a food’s flavor, often for the worse. Stainless steel is an ideal material for food production and storage because it has strong corrosion resistance, which means the metal does not react to its environment or the substances stored inside it. This durability means less waste; knives, cutlery, and cookware can be used for many years before showing excessive wear.
Stainless steel is an even more important material in commercial food production. As in the medical industry, equipment sterilization is the utmost priority, and stainless steel can hold up to cleaning cycles involving high temperatures and strong anti-bacterial products. Its non-porous surface means bacteria are unable to hide away during cleaning, and lowers the chances of carrying over any germs between food production batches.
The Basics of Welding Stainless Steel
Cracking, spatter, incomplete fusion: just a few of the many pitfalls you may face when attempting a weld. While no approach is completely foolproof, your chances of a successful weld are much better once you have a good understanding of the basics. It is also important to tailor your methods to your choice of material; what works best for one type of stainless steel may not be as helpful with another. In this case, we’ll examine a few of the most popular methods of stainless steel welding.
The Material
There are many different grades of stainless steel, but they all have at least one alloying element in common: chromium. The addition of chromium is what makes steel ‘stainless’, with its characteristic shine and boosted corrosion resistance. However, adding chromium to the steel’s chemical composition – along with other elements such as molybdenum, silicon, or manganese – affect how the metal will react to heat. These elements lower the thermal conductivity of stainless steel, which means heat will not spread as easily through the material. This lack of efficient conductivity requires a stronger heat input, but higher temperatures or an extended welding time increases the chances of a burn-through or other heat-related faults. Whatever process you use for welding stainless steel, it will be a matter of balancing necessary heat input vs the potential for heat damage.
The Processes
There are several different methods of welding stainless steel, but most welders use one of these three types. There are other factors that can be considered in more detailed, but generally the selection depends upon the material’s thickness:
1. Tungsten Inert Gas (TIG) welding
This process is one of the most commonly used for welding stainless steel. TIG welding, often referred to as tungsten gas arc welding, creates a low heat input which makes it the best choice for thinner materials. The heat is generated using electricity, which powers an electric arc between the tungsten electrode and the base metal. An inert gas such as argon creates a sheathing environment around the electrode, protecting and cooling the tungsten. This dampening effect helps to keep a relatively low heat input, as well as creating less smoke and oxidation.
Low heat input means TIG welding is ideal for thin stainless steels or precision welds on critical joints. Its concentrated heat allows for a narrow fusion zone, which calls for a high degree of control over the welding process. After completion, a TIG-produced join requires little to no post-weld finishing.
2. Metal Inert Gas (MIG) welding
Also known as gas metal arc welding, MIG uses electricity to melt and join metal during a weld. However, unlike TIG welding, MIG requires the use of both an inert shielding gas and a solid wire electrode. This filler metal wire is continuously fed during the welding to create the arc between the electrode and base metal.
Due to the higher heat during the weld, MIG is best selected when welding thicker widths of stainless steel or steel plate. It can be adapted for semi-automatic welding processes, since the continuous wire feed allows for long joins. It also produces little spatter and easy cleanup after processing.
3. Resistance welding (RW)
TIG relies upon a welding operator and MIG can be done manually or through automation, but for manufacturers who require a highly automated process, resistance welding is key. The method involves an electrical current run through weld electrodes, which apply force to the pieces being joined (the “resistance” part of the process). This force is converted to heat, and the resulting heat melts the metal enough to join it together. When completed successfully, the molten metal at the point of contact will form a rounded weld, known as a “nugget”.
Unlike the other two processes, RW has a steep initial cost of equipment setup and requires a high amount of power. This means it has little portability and cannot be used in the field like TIG and MIG welding. However, for manufacturing purposes, resistance welding is ideal. It is fast, reliable, requires no filler metals or other materials, and is excellent for sheet metal applications. Stainless steel can get up to weld temperature very quickly using the RW method, so welding can be completed within a few milliseconds.
Aluminum Alloy Tempering Methods
Newly forged metals are extremely hard – hard to a fault, because such a degree of inflexibility makes the metal very brittle. This applies even to alloys made of naturally ductile metals such as aluminum. However, after some type of tempering treatment is done to ease the tension within the metal’s structure, the aluminum will be left stronger and more resilient than before.
Before beginning, it’s important to determine whether the aluminum being tempered is heat-treatable or not. If the aluminum alloy belongs to one of the following series, it should not be heat treated:
Series 1xxx: pure aluminum
Series 3xxx: alloyed with manganese
Series 4xxx: alloyed with silicon
Series 5xxx: alloyed with magnesium
Pure aluminum and aluminum alloyed primarily with one of the elements in the list above do not respond to heat treatment. In these cases, the material can be toughened through other means such as cold working or work hardening.
For the other aluminum series, their tempering can be done through annealing, homogenizing, solution heat treatment, and aging. Aging can then be further split into two groups: natural aging, and artificial aging (also known as precipitation hardening). Whatever the method chosen, the purpose of tempering is to alter the aluminum’s physical and mechanical properties without changing its shape.
Annealing
For aluminum series not considered heat-treatable, annealing is the method used to temper the metal. Work hardening means the metal is placed under repeated strain during use, which causes the grain structures within it to slide against each other. These stretched areas are called slip planes, and as the aluminum continues to be used, there will be fewer and fewer areas left that are not already slip planes. If the aluminum continues to be used without tempering, eventually the metal will be overworked and break.
The annealing process essentially performs a reset on the aluminum. By exposing it to a relatively low heat of 570 to 770 degrees F, the strain within the metal lessens as the crystalline grain structure returns to its original form. Once cooled, the aluminum can again handle the creation of more slip planes.
Homogenizing
When casting aluminum parts using molds, the edges of the part will cool faster than the interior. This uneven cooling affects the structure of the part since some areas, particularly around the edges, will have grains of pure aluminum. The interior may be more combined with its alloying elements, but have remaining pockets of pure aluminum. Because pure aluminum is quite soft, this means those grainy areas will be weaker.
Homogenizing reduces this issue by heating the aluminum to just shy of its melting point, around 900 to 1000 degrees F, and allowing a gradual cooling. Unlike the heat of the mold, the uniform heat during homogenizing allows the internal structure to develop more uniformly. Once this is done, the cast aluminum part will be much sturdier.
Solution Heat Treatment
Solution heat treating is similar to annealing, but the metal is quenched rather than being allowed to cool on its own. When aluminum cools naturally, a greater degree of precipitation occurs. This means the alloying elements within the metal may drop out of place within the metal’s internal structure, rather than being as fully integrated as when newly forged. The sudden cooling from a quench means the alloying structure will be locked into place.
Depending on the type of alloy, the aluminum is heated to 825 to 980 degrees F, almost near melting point. This heat prompts the aluminum and alloying elements to better combine into solid solution. It is then immediately immersed in water to bring a sudden drop in its temperature. After tempering, the part will be stronger due to its improved homogenization.
Aging
After quenching, there is some precipitation which happens naturally in aluminum alloy. However, this is not a drawback – the alloying precipitation helps to reinforce and lock in place the aluminum’s microstructure. If left at room temperature, natural aging will continue to develop for up to 5 days, with most of the hardening taking place within the first 24 hours. This aging window means aluminum can be shaped after solution heat treating, leaving a much stronger piece after both processes are complete.
With artificial aging, the process of precipitation in some alloys may require a second round of tempering to reach its maximum strength. The metal is exposed to a fairly low temperature of 240 to 460 degrees F, just enough to encourage the alloying elements to begin to precipitate within the metal’s interior. It is then quenched again and allowed to finish cooling at room temperature. While more labor intensive, artificial aging will result in a significantly stronger metal in a shorter time period.