An introduction to... Welding & Welding Safety

Transcription

1 An introduction to... Welding & Welding Safety

2 Contents General Introduction... p. 2 Duty Cycle, Power Sources & Welding Considerations... p. 3 ARC welding... p. 4 MIG welding... p. 5 TIG welding... p. 6 PLASMA Cutters... p. 8 INVERTER Welders... p. 8 F.A.Q.... p. 9 WELDING:- Verb [with object]: Join together (metal pieces or parts) by heating the surfaces to the point of melting with a blowpipe, electric arc, or other means. (oxford online dictionary, ) What is welding? Put simply, welding is a fabrication process that joins metals by fusion. This is achieved by melting the work pieces and adding a filler material to form a pool of molten material (more commonly known as The Weld Pool ).This weld pool then cools and becomes a strong joint. Welding has many uses such as production/manufacturing, repair and art. Practice is required to achieve good welding results. Types of welding There are three common types of electric welding and they all have their advantages and disadvantages which we will go into more detail in this guide. In basic terms the three types of welding are; ARC: An electric ARC is formed between a flux coated electrode (welding rod) and the work piece. The welding rod and work piece melt together to from the weld pool. MIG: Utilises a continuously fed wire from a reel and uses a shielding gas to protect the weld pool from the atmosphere. Gasless MIG utilises a continuously fed solid flux cored wire from a reel. The flux cored wire is used to generate the shield in similar principle to that of the ARC welding electrode. TIG: An electric arc is formed between a non-melting electrode made from a very durable metal called tungsten and the work piece. Only the work piece melts to form the welding pool. Health & Safety Welding is a potentially hazardous undertaking, precautions and the correct procedures are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes (plus exposure to intense ultraviolet radiation). A welding helmet, gloves and fire proof overalls are required to be worn as a minimum. For more information on welding safety and best practices when welding please visit FIRE Precautions Never weld near flammable materials or gas cylinders. Do not weld fuel containers until the correct steps have been taken to remove all vapours Where possible always have a fire extinguisher close by, during and after the welding process GENERAL If the unit is used under unusual circumstances e.g. in wet or damp conditions, on boats or in an elevated position, extra thought and consideration must be given to additional hazards associated to these circumstances. If in doubt seek professional advice Only qualified or suitably trained personnel should carry out repairs Do not operate the unit with covers removed Always make sure that all electrical connections (mains supply plugs, cable terminals, earth clamp, electrode holder, torches) are correctly installed and are tight FUMES Toxic gases are given off during the welding process. Where ventilation is poor or in confined spaces, use a fume extractor GLARE The welding arc gives off direct heat and ultra-violet radiation. Always protect the eyes of the operator and any bystanders from the glare during welding. Always use a welding helmet or face shield fitted with the proper shaded lens of protection 2

3 Duty Cycle, Power Sources & Welding Considerations The term Duty Cycle is used commonly throughout the welding industry, but what does it mean? As a welder is used it gets hot. All welders are protected by a thermal overload. The duty cycle relates to the amount of time in which a welder is designed to weld continuously at a pre-determined output (amp) before the thermal overload operates. Duty Cycle is described as a percentage and relates to a period of ten minutes. Therefore a welder rated 40% at 100amp, means the welder can weld for 4 minutes in 10 when set at an output of 100amp. The higher the output (amp) setting the quicker the welder will heat up. When using the welder at a higher output (amp) the Duty Cycle will reduce, and the lower output (amp), the higher the duty cycle. The duty cycle will also reduce the more & more you use the welder and you will only get the full duty cycle from a cold, unused welder. So you may have realised by now that the Duty Cycle is an important factor when choosing your welder. You must also consider the type of material and what thickness you wish to weld. This will determine the current output requirement from the welder. Then consider how much welding will you be doing (consider future requirements) this also will determine the duty cycle. So, if you require 100amp to perform a weld it does not necessarily mean any 100amp welder will do. You may need a 150amp or 200amp welder which can give you 100amp output at the required Duty Cycle. thermal cut-in temperature thermal cut-out Z A Y X time Point A is for when the machine is cold. Point X is the point at which the machine has been welding for a period of time and the thermal overload has activated. Point Y is the point at which the machine has cooled down enough for the thermal overload - the drop out. Period Z is the machines duty cycle. Note: The thermal overload is designed to protect the welder from damage. Repeated operation of the overload indicates use of a welder with a lower a duty cycle than is required and damage may be caused to the welder. As well as the duty cycle there are a few other considerations to take into account when choosing your welder. The type of metal being welded and its application. This will decide the type of welding consumables needed and may limit what type of welding The thickness of the metal. This will determine the current level required The amount of welding to be done and in what time. This gives an indication of duty cycle The electrical supply that s available where the welding will take place With the above, a shortlist of machines can be drawn up and it may be that the job can be under taken with more than one process. There may be cases where the job cannot be done with the preferred type of welding. 3

4 ARC Welding ARC welding or MMA (Manual Metal ARC welding) was first developed in the early part of the 20th century. ARC welding fuses two or more pieces of metal together by an electrical arc formed by current flowing directly across the gap between the metal being welded and an arc welding rod. The weld requires some cleaning after the process is complete and practice is recommended in order to obtain the best results. To produce an ARC weld, the ARC welding rod is struck against the work piece until the arc is created. The electric current is provided by the arc welder which forms the arc between the welding rod and work piece. This causes a portion of the metal work piece to melt and form a molten pool of metal. The flux coating of the ARC welding rod partially burns to generate gas. This prevents the molten metal from reacting with the surrounding atmosphere and to help the stability of the arc. The remaining flux is melted at the same time and flows over and into the molten pool of metal. The flux that flows over the pool then cools and leaves slag which is chipped away to give the final finish. The diagram below is an indication for welding positions and shows the electrode should be placed at 15 for the optimum weld position. The advantages of ARC Inexpensive equipment - due to high operator Input Specialist electrodes are available for hard-facing, high-strength, cast iron and other metal alloys makes the process extremely versatile Uses a flux coated electrode to shield the weld so there s no need to carry gas or a wire feeder making it ideal for portable use The disadvantages of ARC Takes considerable training and practice to master Very difficult on thin metal Weld will need to have flux cleaned off which extends job completion time Rod length is limited so multiple rods maybe needed to complete a job SIP s Top Tips for successful ARC welding Always keep welding rods dry Always practice on scrap work piece first Select the correct size and type of ARC welding rod for the job in-hand. See table below; DIAMETER LENGTH WORKPIECE CURRENT INCHES MM MM THICKNESS AMPS 1/ mm / mm / mm / mm / / mm / mm

5 MIG Welding MIG Welding (which stands for Metal Inert Gas ) method is similar in principle to ARC welding but does not require welding rods making it more refined and suited to the welding of very thin sheet metals such as car body panels. Practice is recommended in order to obtain the best results but the basic principle of MIG welding still remains much the same as when it was first developed over 60 years ago! A MIG welder makes use of a wire feed system inside the machine and a trigger activated welding torch which is where all the action takes place. The welding current is passed to the welding torch with the metal wire fed through it. An arc is generated between the wire and the metal work piece causing the wire to melt simultaneously with the metal work piece. This produces a molten pool which creates the weld similar to that of ARC welding. A shielding gas is also fed to the torch during the entire process to act as the shielding agent. This prevents the molten material from reacting with the surrounding atmosphere leaving little or no residue, giving the benefit of cleaner welds. With MIG welding you will have to take into consideration that the type of metal and the metal s thickness will determine the wire type, wire diameter and what gas to use. The guide below explains what gas to use for different metals and why. Mild Steel: Argon/CO 2 or Pure CO 2 Stainless Steel: Argon/Oxygen or Argon/CO 2 Aluminium: Pure Argon Argon/CO 2: 80% Argon 20% CO 2 (commonly) giving a clean smooth weld Pure CO 2: 100% CO 2 This gas is very cold, therefore cools the weld pool thus requiring more welding power than when using Argon/CO 2 however this gas is much cheaper than Argon CO 2 100% Argon: Used for aluminium. Pure inert gas giving no effect on the arc, acting purely as a shielding agent Gasless welding Gasless wire feed welding is a different process which combines features from both ARC and MIG. Again, practice is recommended in order to obtain reasonably clean results. The welder is more similar to a MIG welder than an ARC welder - they may even be referred to as a MIG welder. Instead of employing a gas as a shielding agent, the wire used is cored with a solid flux. This flux prevents the molten material from reacting with the surrounding atmosphere, similar in principle to an arc welding rod. This combination produces a hybrid that is very simple to use and fairly inexpensive, It s also excellent for use outside in windy conditions. Thin sheet metal can be welded and there is no need to keep a MIG gas supply. The resultant weld does however require some cleaning. The advantages of MIG welding Higher welding speeds Less post welding cleaning - saving you time No stub end losses or wasted man hours caused by changing electrodes Low skill factor required to operate The disadvantages of MIG welding Higher initial setup costatmosphere surrounding the welding process has to be stable (hence the shielding gasses) therefore this process is limited to draught free conditions in gas mode Higher maintenance costs due to extra electronic components SIP s Top Tips for successful MIG welding Always feed the wire with the torch straight Always remove wire after use and store in a dry place to prevent corrosion Use the correct gas and check the gas flow rate is not too high to limit wastage Keep the torch as straight as possible and keep the shroud tip clean 5

6 TIG Welding TIG Welding stands for Tungsten Inert Gas and has been around since TIG welding is similar in principle to both ARC and MIG welding. An arc is formed between an electrode and the work piece as in ARC, and a shielding gas is used as in MIG welding. The TIG welding process is very precise, controllable and capable of giving high quality welds on most types of metal. The process does, however, require much practice and skill to ensure top quality results. The electric current supplied by the TIG welder passes between the electrode made from a very durable metal, called Tungsten, and the metal work piece. This forms the arc which causes a portion of the metal work piece to melt and form a molten pool of metal. If required, a non-fluxed filler rod (compatible with the work piece metal) is added to the molten metal pool to form the weld. When TIG welding the initial arc can be started in three ways; 1. Scratch Starting. The Tungsten is scratched against the work piece until the arc is created. 2. Lift Arc. The Tungsten is touched against the surface then lifted off. The arc starts just as the Tungsten breaks contact with the work piece. 3. HF Start. The Tungsten is held off the surface, by only a few mm s, and the high frequency (HF) trigger pressed. High frequency voltage is applied to the Tungsten and creates a spark across the gap between the tungsten and workpiece this allows the arc to start. The Tungsten is then drawn away sufficiently to avoid contact whilst still maintaining the arc. The distance between the work piece and the Tungsten is governed by the amount of welding current in use and the Tungsten diameter. TIG welders are available as DC or AC/DC. DC welders are suitable for all metals except aluminium, magnesium and their alloys. AC/DC welders are suitable for all metals. The advantages of TIG welding Welds more types of metals and alloys making it extremely versatile Very good control allows a precise and clean weld to be produced No slag, sparks or spatter to clean away Low smoke/fumes Can weld very thin metals The disadvantages of TIG welding The Work piece must be very clean Low filler metal deposition rate Slow process/low productivity Equipment is expensive Highly skilled process. Lots of practice required SIP s Top Tips for successful TIG welding Read up as much as possible & watch tutorial videos on online Make sure you have the correct welder for the job e.g DC or AC/DC Make sure you have the correct tungsten electrode for your work piece The most common are; RED = DC Tig WHITE = AC Tig GREY = AC & DC 6

7 Below is our handy guide to selecting the correct tungsten TIG electrode. Colour Material Description Orange Red 4% Thoriated Tungsten 2% Thoriated Tungsten This is the most commonly used type of tungsten is the standard that is used for comparison to other tungsten. However, since it is a low-level radioactive hazard many users have switched to other alternatives. Notwithstanding this issue, Thoriated tungsten is still the most commonly used tungsten and is good general use tungsten. It has one of the lowest work functions, and it performs well when overloaded with extra amperage. However, it does not hold its point as well as some other non-radioactive tungsten that have been introduced. This tungsten is used primarily for DC welding and may split if used for AC welding Black 1% Lanthanated Tungsten In Europe this has been the most popular alternative to Thoriated tungsten for most applications. It is available as 2%, 1.5%, and 1% Lanthanated tungsten. Lanthanum Trioxide has the lowest work function of any of the materials. Thus, it usually starts easiest and has the lowest temperature at the tip, which resists grain growth and promotes longer service life. Testing of 2%Lanthanated material showed that it offers much longer life than Thoriated if not overloaded and better arc starting in most applications. The Lanthanum in this tungsten is a rare earth material and is not radioactive. This tungsten is primarily used for DC welding, but will give good results for AC welding Grey 2% Ceriated Tungsten Ceriated tungsten was introduced as the first non-radioactive alternative to Thoriated tungsten. 2% Ceriated tungsten is how it is most commonly offered and is readily available. It is known to be especially good for DC welding. Due to its properties, it would generally be good for short welding cycles and also where a specific number of welds are called for (then the electrode is to be replaced). Higher amperage applications are best left to Thoriated or Lanthanated material. This tungsten is used primarily for DC welding and may split if used for AC welding White 1% Zirconiated Tungsten This material is most commonly used for AC welding because it has a more stable arc than pure tungsten. It also resists contamination well in AC welding. Finally, while it has better current carrying and arc starting characteristics than pure tungsten, on the whole it is the worst non-radioactive tungsten from a performance standpoint Green Pure Tungsten This material has a very high work function thus it is more difficult to start and produce a stable arc than other materials. Also, because of the high work function, the temperature at the tip is higher and grain growth occurs. This leads to an unstable arc, starting difficulty, and a shorter service life. This material is only used for AC welding, however, better alternatives are available 7

8 PLASMA CUTTERS Plasma cutters quickly and easily cut sheet metal of various types and thickness. They are used in many areas of industry and home use. The plasma cutting process involves the combination of compressed air and a flow of electric current to form a plasma jet. The plasma jet melts and clears a portion of the work piece. The compressed air is provided by an air compressor that s connected to the plasma cutter, and the electric current used to produce the plasma jet is supplied by the plasma cutter. For a cut to take place, an earth cable must be connected to the work piece to act as a return for the current back to the plasma cutter. When the torch trigger is pressed the compressed air supply is fed through the torch and into the plasma torch head. It s split two ways, one for torch cooling and the other to help form the plasma jet and clear away the molten metal pool generated by the heat of the plasma. At the same time as the air flows an electric current is also passed to the torch. This current forms an arc inside the torch head between the electrode and cutting tip. The compressed air forces the arc through a small hole in the cutting tip forming the arc into a plasma jet. To plasma cut, the torch has to be steadily drawn across the work piece. This steady action allows the plasma and compressed air to work together to melt and clear the molten metal. Should the torch be drawn across the work piece to fast then the plasma will not have sufficient time to penetrate through to the underside of the work. The plasma jet at the torch nozzle is extremely direct and intense typically reaching temperatures in excess of 24,000 ºC. This facilitates a narrow cutting area and a cut with virtually no heat spread or distortion even on thin sheet metal. The cut can be made in any direction. Plasma Cutter Safety Precautions Safety glasses made to BSEN 169:2002 must be worn at all times Long and loose hair must be contained Sturdy footwear with rubber soles must be worn Close fitting/protective clothing to cover arms and legs must be worn Respiratory protection devices may be required for some operations Oil free leather gloves and spats must be worn Hearing protection may be required when cutting thick material INVERTER Welders These hi-tech machines are a fairly new technology and have many advantages over traditional welders. They make use of sophisticated components and electronic circuits to change AC current into DC current with a wide power adjustment range. Inverter Welders produce a smoother arc when welding and their lightweight and easily portable as they use smaller transformers than conventional welders. Some run off a 13amp power supply and Inverter Welders can be bought for all applications - ARC, TIG/ARC (dual purpose) and MIG welding. However Inverter Welders are more expensive than traditional welders. SIP have a new patented range of professional hi-tech inverter welders, inverter plasma cutters, plus multi-functional Inverter machines. These units are highly portable and extremely controllable making use of anti-stick circuitry ensuring a stable ARC and all have exceptionally high duty cycles. They all come with a 2 year warranty and are ideal for a varied range of applications; such as fabrication, general and auto repairs, agricultural repairs and on-site welding. 8

9 F.A.Q. Q. Can I operate my inverter welder from a generator? A. The ARC Inverter welders are generator friendly, the MIG,TIG and PLASMA units are not Q. My machine is 230V so why is it not fitted with a 13amp plug? A. 230v is not always a 13amp power supply. Double check what power supply you have and which type of plug is required Q. Can I fit a 13amp plug to a 16amp supply welder? A. Fitting a 13amp plug to a 16amp welder can damage the machine, the wiring and it will not operate to its full performance. It could also void your product warranty Q. What gas supply do I need for a plasma cutter? A. An air compressor is required to work the plasma cutter Q. Is a Transformer based welder better than an Inverter Welder? A. Both have numerous advantages and disadvantages depending on the job, inverter technology makes machines more compact, lighter, more efficient and more controllable Q. Can I weld aluminium with a DC Tig Machine? A. No, but you can use an ARC welder electrode, to weld aluminium Q. What is Inductance Control? A. Inductance control allows accurate manipulation of the ARC characteristics, tailoring the ARC to the metal type and thickness as well as the type of gas used Q. What Is Pulse? A. Pulse helps when welding thin metals, pulses of high current are added to a low welding current, the high current melts the metal and the low current keeps the arc going, this prevents holes forming Q. What are the common methods used to start the plasma for plasma cutting? A. Manual - you press the torch head down against the work to start the arc A. HF - high frequency/high voltage used to create path for current to flow between the electrode and cutting tip A. Air - air pressure is used to draw an arc either by air pressure moving the cutting tip or electrode A. Pilot Arc - This is a lower current arc that flows before the full cutting current starts, you can have pilot arc with all the starting methods 9

10 An introduction to... This guide is intended for reference only. For specific machines always refer to the manufactures user guide. If you would like more information or explore our full range of welding equipment, please use any of the contact options below. SIP INDUSTRIAL PRODUCTS LIMITED Gelders Hall Road Shepshed Loughborough Leicestershire LE12 9NH UK GENERAL ENQUIRIES Tel: Fax: TECHNICAL / AFTER-SALES SERVICE Tel: Fax: technical@sip-group.com Every reasonable effort is made to present current and accurate information at the time of print. However, SIP do reserve the right to change details or specifications without prior notice. E & OE. Contents and images are copyright SIP Ltd. and cannot be reproduced without express written permission. Job No.: MB /13