Kitabı oku: «Welding For Dummies», sayfa 3

Mig welding

You can mig weld steel in any position, and that’s one of the reasons mig is the most popular choice for steel welding projects. Another reason: You can get a very smooth steel weld with mig, and you can also avoid a lot of the spatter and waste that you may get with stick welding. You’ll have a hard time finding a piece of steel you can’t weld with mig; very thick pieces of steel work out fine as long you have a powerful mig machine, and you can even weld extremely thin pieces of steel with mig welding.

Tig welding

Like mig welding, tig allows you to join all different thicknesses of steel. Tig also affords the advantage of a very clear view of your welding area, because tig produces very little smoke or slag (waste).

If you choose tig for your steel welding jobs, make sure you have your equipment set up correctly. Ask your welding supply shop for the charts that help you determine the correct amperage, shielding gas flow rate, and polarity for tig welding steel. You also need to be sure that you use the right filler rod (a metal rod that melts and becomes part of your welding puddle to add strength to your weld), or the quality of your weld may suffer greatly.

Don’t use oxyacetylene filler rods when you’re tig welding. The copper coating creates impurities in the finished weld.

Going with Stainless Steel

Stainless steel is pretty incredible stuff. It’s remarkably durable and strong, and as a result it’s used in countless applications all over the world. I doubt you’ll be able to practice welding for long before some stainless steel object catches your eye as a possible project component (if it hasn’t already).

Understanding the differences between steel and stainless steel

Stainless steel is different from regular steel because it contains 10 to 30 percent chromium. Chromium is added to the steel to create the resistance to corrosion that makes stainless steel so famous (and useful!). Stainless steel can contain a few other substances that make it perform at an even higher level; nickel is the most common.

Stainless steel today is classified into two general series:

❯❯ The 200 to 300 series includes stainless steels made with chromium, nickel, and sometimes manganese. They’re more resistant to corrosion than the 400 series, and they generally have better qualities for welding.

❯❯ The 400 series includes stainless steels that don’t contain nickel. They can’t be hardened as much as the 200 to 300 series.

Stainless steel’s most notable (and desirable) quality is its resistance to corrosion. The combination of steel and chromium creates an outer surface that’s terrific at resisting rust. Because of that quality alone, stainless steel is used in a huge variety of applications, from beer kegs to hypodermic needles to the St. Louis Gateway Arch.

Deciding when to use stainless steel

Why would you want to use stainless steel in one of your welding projects? Here are a few examples.

❯❯ You need part or all of the project to be rust-proof. This goal is pretty self-explanatory, but if your project is going to be located outside – especially in an area that gets a lot of precipitation or salt abuse – and you can’t let it get rusty, stainless steel is one option to consider.

❯❯ You don’t mind spending some extra money. Compared to other metals (carbon steel, for example), stainless steel is expensive! It can cost as much as five times more than steel.

❯❯ You need part or all of the project to be hygienic. The strong, consistent surface of stainless steel means that it doesn’t have tiny irregularities in the surface that bacteria and other critters can cling to. It also means that you can clean the surface with some pretty powerful cleaners without damaging the material. For those reasons, stainless steel is a popular choice for food preparation and storage equipment, and also for medical purposes.

Looking at stainless steel welding methods

If you want to weld stainless steel, your three best options (by a mile) are stick welding, tig welding, and mig welding. Generally speaking, stainless steels are slightly more difficult to weld than carbon steels. That’s because stainless steels have lower melting temperatures, and more thermal expansion (they expand more than steel when heat is applied).

❯❯ To stick weld stainless steel, you have to use a flux-coated electrode, which protects the metal from the air while you’re welding and helps make the weld even more corrosion resistant. Keep in mind that stick welding is the messiest of the arc welding methods, and that can be a drawback when you’re welding stainless steel. The random arc marks and spatter caused by stick welding can compromise stainless steel’s pristine surface and appearance.

When selecting stick welding electrodes for stainless steel welding projects, make sure you pick electrodes that have a -15 or -16 suffix. For example, a commonly used electrode for stick welding stainless steel is E-308-16. For more information on picking out stick welding electrodes, take a look at Chapters 5 and 6.

❯❯ Tig welding stainless steel is a great option when you’re looking to weld thin pieces. I recommend using argon as your shielding gas. You can read more about shielding gases for tig welding in Chapters 7 and 8.

❯❯ Mig welding is nice and fast, so it’s the ticket if you want to weld thicker pieces of stainless steel. In those cases, tig welding can just take too long.

Working with Aluminum

If you’re looking for a strong, lightweight metal, chances are your search can stop at aluminum. It’s a remarkably versatile material that’s usually at or near the top of the list of most-welded metals. If you stick with welding for very long, you’re probably going to want to weld some aluminum, and I can’t blame you. Read on to find out more about welding this wonderfully dynamic metal.

Perusing the properties of aluminum

So what makes aluminum so special? For starters, it reacts with oxygen in the air and produces a very tough oxide film on the surface. This aluminum oxide is extremely durable, and it effectively protects the metal underneath it. (That’s why aluminum is so resistant to corrosion.)

The aluminum oxide film that covers pieces of aluminum that have been exposed to the air for long periods of time has a higher melting point (3,600 degrees Fahrenheit) than the pure aluminum underneath it (1,200 degrees Fahrenheit). For this reason, you have to remove the film before you can weld aluminum.

Aluminum conducts heat about five times better than steel, and interestingly, it doesn’t change color when you heat it up. (Steel, of course, turns all kinds of different colors as you heat it up to different temperatures.) It weighs about one-third as much as steel.

Pure aluminum is a popular choice for welders, but many different aluminum alloys have also been developed. A classification system of four-digit numbers has been created to identify the various aluminum alloys. The first digit is the really critical one because it tells you what is included (other than aluminum, of course) in the alloy. Here are the details:

❯❯ 1XXX: Unalloyed aluminums made up of at least 99 percent pure aluminum

❯❯ 2XXX: Copper

❯❯ 3XXX: Manganese

❯❯ 4XXX: Silicon

❯❯ 5XXX: Magnesium

❯❯ 6XXX: Silicon and magnesium

❯❯ 7XXX: Zinc

❯❯ 8XXX: Other materials (tin is one example)

The two types of aluminum you’ll probably weld most often are pure aluminum and aluminum alloy 3003.

Recycle your old aluminum! Almost two-thirds of the aluminum used today has been recycled, and that’s the environmentally responsible thing to do.

Eyeing aluminum welding techniques

If you ask me, welding aluminum isn’t any more difficult or problematic than welding steel. It can take some getting used to, but after you have the hang of it, you can weld aluminum quickly and efficiently by using any one of the three major arc welding methods: stick, tig, and mig.

❯❯ My first choice for welding aluminum is always tig welding. You need to use alternating current (AC) with continuous high frequency to get the best results. (If those terms don’t make any sense, flip over to Chapters 7 and 8 for more information on tig welding.) And as with all other tig welding endeavors, make sure you select the right tungsten electrode and shielding gas for the job.

❯❯ If you’re going to be welding thicker pieces of aluminum, consider going with mig welding. As with stainless steel (see “Going with Stainless Steel” earlier in the chapter), aluminum can take a long time to weld if you’re working with thick pieces, and mig welding makes the process go faster. Be sure to keep your electrode wire clean, use a 30-degree leading travel angle, and go with pure argon for your shielding gas. (If those details are Greek to you, check out Chapters 9 and 10.)

❯❯ So what about using stick welding for aluminum? Well, it can be done, but I wouldn’t recommend it if you can go with tig or mig instead. Not many stick welding electrodes are available for working with aluminum, and maintaining good arc stability is tough. On top of that, you have to fight a constant battle to make completely sure that you keep the covering on the electrode extremely clean and dry, or you’re sunk. Bottom line: Avoid stick welding aluminum unless you simply have to do it.

Considering Other Metals

You can do a whole lot of welding with only steel, stainless steel, and aluminum, but you’ll inevitably want to branch out a little and work on some less commonly welded metals. Here’s a quick rundown of some of those metals, and you can find more information on them sprinkled throughout the other chapters of the book.

❯❯ Copper and copper-based alloys

Used for: Plumbing, electrical products, roofing, and as an additive to gold and silver to increase the strength of jewelry.

Welding process: You can use mig or tig welding for copper and copper-based alloys. Mig welding works in all positions and it’s especially useful for thicker pieces of copper. If you use mig for welding copper, be sure you use direct current electrode positive (DC+). Go with tig if you want to weld thinner pieces of copper – I recommend using direct current electrode negative (DC–).

❯❯ Magnesium

Used for: An alloy in steel. Makes steel resistant to abrasion, so it’s perfect for rock crushers, grinding tools, grinding mills, and so on.

Welding process: Use tig for welding thin pieces of magnesium-based alloys; use mig if the pieces are thicker.

Some magnesium-based alloys have high levels of zinc in them. Avoid welding those alloys if at all possible because it’s extremely hard to keep them from cracking.

❯❯ Nickel-based alloys

Used for: An alloy in stainless steel. Nickel in the 200 and 300 series stainless steels is the most resistant to corrosion.

Welding process: You can use any of the big three arc welding methods for welding nickel-based alloys. Stick welding gives you a weld that’s stronger than the base metal. (That’s good!) Tig welding a nickel-based alloy involves using a 2 percent thoriated tungsten electrode and argon as your shielding gas. You can tig weld a nickel-based alloy in any position. (If some of those terms look a little wacky to you, flip over to Chapter 7 for some gory tig welding details.) Finally, if you’re going to be mig welding a nickel-based alloy, plan to use a 50/50 mix of argon and helium for your shielding gas. Like tig, you can mig weld these alloys in any position.

PRECIOUS METALS

You may think it sounds crazy, but you can definitely weld precious metals like gold, silver, and platinum. Gold can be soldered (welded at a temperature below 840 degrees Fahrenheit) or brazed (welded at a temperature above 840 degrees Fahrenheit), and I recommend doing so with a gas torch – check out Chapter 13 for more on brazing and soldering. The same goes for silver. Platinum is a little different; oxyfuel (see Chapter 11) and tig are your best bets when welding platinum. Oh, and you may want to be sure you have a good lock on your welding shop before you start welding metals that cost thousands of dollars per ounce!

Chapter 3
Setting Your Sights on Welding Safety

IN THIS CHAPTER

❯❯ Making sure you have the right safety gear

❯❯ Understanding basic safety rules for welding

❯❯ Knowing how to prepare for and handle accidents and injuries

What’s the most important aspect of welding? The answer is simple: safety. What good does a beautiful weld and a job well done do you if you’ve hurt yourself (or others) in the process?

Many dangerous elements make up any welding operation. You use massive amounts of electricity to join metals (which are often sharp and heavy) through melting. You’re constantly at risk for electric shock, serious eye injuries, and burns. It’s not exactly a pillow fight, is it?

You can’t change the basic elements that make welding dangerous, but you can (and should, without fail) take every precaution to make sure your welding projects are as safe as possible. Your approach to welding safety should be complete and relentless; just one careless move or lack of safety preparation can result in serious injury or death.

In this chapter, I cover all the aspects of welding safety that you need to understand and remember when you get started as a welder. As I mention many times throughout this book, this chapter is really the most important one, and I hope you read it carefully and take its information to heart.

Welding safety is no accident! Be sure to take the precautions necessary to ensure your safety and the safety of those around you. You also need to make sure anyone who comes near your welding projects is aware of proper welding safety practices so that they can help keep themselves safe as well.

Gearing Up to Protect Yourself

A big part of welding safety is making sure you have the right safety equipment on hand for every job, and that’s what I discuss in the following sections. Figure 3-1 shows a welder in full protective gear; make sure you have all these items available before you get going on any welding project.

FIGURE 3-1: A welder wearing recommended safety gear, including ample eye protection.

Choosing eye protection

To protect your eyes from flying debris (usually metal), which you encounter plenty of if you weld regularly, make sure you wear safety glasses in your shop at all times. Make a habit of putting them on as soon as you walk in the door – that way, you’re always protected.

To fully protect your eyes from the damaging effects of ultraviolet welding rays, you need a welding helmet. These helmets protect your eyes (and the rest of your face) from damaging rays, and they include special lenses that allow you to see your work clearly without suffering eye injuries, which I discuss in “Shielding yourself from burns” later in the chapter. (Check out Figure 3-1 for a look at what a welder with a welding helmet looks like.)

You need to get a helmet appropriate for your particular welding work. New welders often buy helmets that don’t cover all their needs, or purchase ones that are far too heavy duty (and therefore expensive) for the projects they want to do. The following list explains the features of welding helmets that can help you figure out which helmet is right for you:

❯❯ Shade number: The lenses in welding helmets are rated according to shade number. Shade numbers for welding range from #8 to #14. The higher the shade number, the higher the amperage (the amount of electrical energy flowing through a circuit) you can use when welding without damaging your eyes. Most welding operations are carried out at shade #10, but if you get above 140 amps you must get a darker lens with a shade in the #12 to #14 range.

❯❯ Auto-darkening or passive lens: Many welding helmets now offer an auto-darkening lens that automatically increases the shade number to account for more-intense welding rays. The alternative is a passive lens, which is the older style of helmet that has a fixed shade number. Auto-darkening helmets are nice because you can see through the lens when you don’t have a live welding arc, so you don’t have to constantly take your helmet off and put it back on when you’re working on a project. However, auto-darkening helmets are much more expensive. Passive lens helmets are cheaper, but you’ll likely have to remove them and put them back on over and over while you’re welding.

❯❯ Comfort: Make sure you get a helmet with an adjustable headband that feels comfortable on your head and neck. The helmet should stay in place and shouldn’t pinch your head.

Welding helmets take a lot of abuse, but you don’t have to replace your helmet if it gets nasty or dinged up. You can always repair or replace parts of the helmet (lenses, shields, and headbands for example) instead of emptying your wallet on a new one.

Sunglasses don’t protect the eyes from welding rays. Don’t even think about using them as eye protection.

Make sure you do whatever you can to protect the eyes of others who may be near your welding projects. Ultraviolet welding rays are so powerful that they can penetrate through closed eyelids. If you have bystanders, make sure you say “Cover!” loudly before you strike an arc and get started welding. (You need to let your audience know beforehand what to expect when you say “Cover!”, of course.)

Keeping the right fire extinguisher on hand

With all the extreme heat and sparks created during a welding job, you shouldn’t be surprised if something catches fire at some point. Because fires are a very real threat, keep a fire extinguisher on hand at all times.

Four main types of fire extinguishers (shown in Figure 3-2) work on four different kinds of fires:

❯❯ Class A: Class A extinguishers take care of any fires that produce ash. These fires usually involve wood, cloth, or paper.

❯❯ Class B: Class B fire extinguishers are for fighting fires caused by flammable liquids, such as gasoline, oils, and paints.

❯❯ Class C: Electrical fires call for Class C fire extinguishers. Don’t use any water- or foam-based extinguishers on an electric fire, or you put yourself at risk of serious shock.

❯❯ Class D: Use Class D extinguishers on metal fires. Combustible metals like magnesium, potassium, and sodium are extremely flammable, and fires based on these materials are very dangerous. Class D extinguishers are best for these fires because the other classes often disperse a metal fire instead of putting it out, and that makes the situation worse.

You should keep a Class C extinguisher nearby when you’re welding, in case an electrical fire breaks out. I recommend also keeping a Class B on hand for oil fires.

In addition to fire extinguishers, keep a water source (a hose, for example) and a bucket of sand nearby when you’re welding. They can come in handy when you need to control ash and metal fires, respectively, without the need for special extinguishers.

The best way to avoid needing an extinguisher is to cut down on the flammability of your project in the first place. For example, you may find the need to weld a metal 55-gallon drum. (It’s a common welding task.) If so, take care to ensure that the drum doesn’t have residual flammable materials on the interior. Before welding, be sure to clean the interior with steam or a chemical cleaner.

FIGURE 3-2: Four classes of fire extinguishers.

Wearing protective clothing

If you’ve ever thought of yourself getting started on your first welding project wearing a pair of shorts, an old t-shirt, and a pair of flip-flops, think again. If you want to keep your body safe from the hazards of welding – especially burns – you have to always wear appropriate protective clothing.

Welding produces a huge amount of hot metal sparks and flying slag (molten metal). To keep your skin from being burned, choose clothing made from the right material. One of the best options is 100-percent wool, but it can be difficult to find and is extremely hot. (Some people are also allergic to wool.) I prefer 100-percent cotton, and it’s the most popular material used for welding clothing. The fabric should be thick (because welding rays can penetrate thin fabric and burn your skin like a sunburn) and dark-colored; black and dark blue are good options.

Sorry, but you can’t use that old polyester leisure suit from the ’70s when you’re welding. Synthetic fabrics like polyester, nylon, and rayon are unsafe for welding because they can melt and adhere to your skin when they get hot. And that definitely does not promote leisure.

Before welding, check to see that your clothes are free from oil and anything else flammable. They should also be tight fitting and free from holes and frayed or torn edges. Here are a few more clothing-related details to bear in mind.

❯❯ Shirts: Wear long-sleeved shirts only, and tuck your shirttail into your pants. If you wear a shirt with front pockets, make sure they have flaps covering them so that sparks can’t fall down inside. Keep your shirt sleeves rolled down at all times.

❯❯ Pants: Make sure your pants cover the tops of your shoes or boots so that sparks can’t get in.

❯❯ Gloves: Protect your hands with leather gauntlet gloves. Don’t wear cotton gloves at any time.

❯❯ Boots or shoes: Go with leather boots or shoes, and make sure they come up high on your ankle. Leather is the best option because it protects you from the hazards and heat created by the welding process. The tops of the shoes should be smooth so sparks don’t get trapped.

❯❯ Hats or beanies: You can buy a welder’s beanie to keep your hair from catching fire – not a bad idea.

❯❯ Leather jackets: A full leather jacket protects you from sparks and slag when you’re doing work in unusual positions, but many such jackets are very hot and heavy to wear. If a leather jacket is too hot and uncomfortable, you can buy leather sleeves and bibs only. These items are cooler and more comfortable, but they do leave your back unprotected.

❯❯ Leather aprons: These items protect your lap, and I highly recommend wearing one if you plan to sit down while welding.

❯❯ Spats: If you’re going to have a large amount of sparks and slag (the waste products that come from the flux) falling at your feet, you may consider getting some spats (shoe covers). Leather spats greatly reduce the risk of burns on your feet and damage to your shoes or boots.

Be careful what you have in your pockets when you weld. If you have a cigarette lighter or matches in your pocket during a welding project and a spark gets close enough, it can cause a fire in your pocket.

Watching health hazards: Using a respirator and Material Safety Data Sheets

Keep the Material Safety Data Sheets (MSDS) for every chemical and other potentially hazardous material in your welding shop on hand. These sheets describe all the properties of a given substance and include details on potential health hazards. Make certain that you and anyone who enters your welding area know the dangers of the materials on hand.

If you’re going to be working with metals or other materials that can produce toxic fumes – check your MSDS to be sure – you should wear a respirator. Simply welding or cutting certain materials can cause a welding plume, which is a mixture of dangerous gases, fumes, and smoke, and that’s definitely not the kind of thing you want to inhale if you’re interested in avoiding respiratory problems.

Figure 3-3 shows four types of respirators:

❯❯ On the top left, you can see a welder’s mask, which works to keep fumes out of your lungs.

❯❯ The mask on the top right has canisters that filter fumes and other hazardous materials while you’re welding. You can get different types of canisters to match the kinds of hazards specific to various welding projects.

❯❯ The basic dust mask on the bottom left offers the least amount of protection.

❯❯ The mask on the bottom right filters out particulate matter, so it’s a step up from the basic dust mask but doesn’t do much to protect you from harmful chemical fumes.

FIGURE 3-3: Four different respirator masks.

The metals you weld aren’t the only items that can cause harmful fumes – the substances that may coat those metals can also be hazardous. If you suspect that a piece of metal may be coated with paint or another kind of chemical that may generate dangerous fumes when heated up, be sure you remove that substance (with a chemical cleaner or grinder) before you weld.

In order for a respirator to be completely effective, you need to fit it with the right filter. Check your MSDS to find out which filter you need to protect your respiratory system from a given substance. You can also ask for help at your welding supply store.