Although the manual metal arc (MMA) process has relatively basic equipment requirements, it is important that the welder has a knowledge of operating features and performance to comply with welding procedures for the job and, of course, for safety reasons.
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The main components of the equipment required for welding are:
Tools required include: a wire brush to clean the joint area adjacent to the weld (and the weld itself after slag removal); a chipping hammer to remove slag from the weld deposit; and, when removing slag, a pair of clear lens goggles or a face shield to protect the eyes (lenses should be shatter-proof and noninflammable).
The primary function of a welding power source is to provide sufficient power to melt the joint. However with MMA the power source must also provide current for melting the end of the electrode to produce weld metal, and it must have a sufficiently high voltage to maintain the arc. A constant current (drooping) characteristic is used.
MMA electrodes are designed to be operated with alternating current (AC) and direct current (DC) power sources. Although AC electrodes can be used on DC, not all DC electrodes can be used with AC power sources.
As MMA requires a high current (50-300A) but a relatively low voltage (10-50V), high voltage mains supply (240 or 440V) must be reduced by a transformer. To produce DC, the output from the transformer must be further rectified. To reduce the hazard of electrical shock, the power source must function with a maximum no-load voltage, that is, when the external (output) circuit is open (power leads connected and live) but no arc is present. The no-load voltage rating of the power source is as defined in IEC -1 and IEC -6 and must be in accordance with the type of welding environment or hazard of electrical shock. The power source may have an internal or external hazard reducing device to reduce the no-load voltage; the main welding current is delivered as soon as the electrode touches the workpiece. For welding in confined spaces, you should use DC or AC with a low voltage safety device to limit the voltage available at the holder to less than 48V rms.
There are four basic types of power source:
AC electrodes are frequently operated with the simple, single phase transformer with current adjusted by means of tappings or sliding core control. DC rectifiers and AC/DC transformer-rectifiers are controlled electronically, for example by thyristors. Modern power sources called inverters use transistors to convert mains AC (50Hz) to a high frequency AC (typically 50 kHz) before transforming down to a voltage suitable for welding and then rectifying to DC. Because high frequency transformers can be relatively small, principal advantages of inverter power sources are undoubtedly their size and weight when the source must be portable.
The electrode holder clamps the end of the electrode with copper contact shoes built into its head. The shoes are actuated by either a twist grip or spring-loaded mechanism. The clamping mechanism allows for quick release of the stub end. For efficiency the electrode has to be firmly clamped into the holder, otherwise poor electrical contact may cause arc instability through voltage fluctuations. Welding cable connecting the holder to the power source is mechanically crimped or soldered. Electrode holders should conform to IEC -11.
It is essential that good electrical connections are maintained between electrode, holder and cable. With poor connections, resistance heating and, in severe cases, minor arcing with the torch body will cause the holder to overheat. Two cables are connected to the output of the power source, the welding lead goes to the electrode holder and the current return lead is clamped to the workpiece. The latter is often wrongly referred to as the earth lead. A separate earth lead may be required to provide protection from faults in the power source. The earth cable should therefore be capable of carrying the maximum output current of the power source. For guidance see DD CLC/TS .
Cables are covered in a smooth and hard-wearing protective rubberised flexible sheath. This oil and water resistant coating provides electrical insulation at voltages to earth not exceeding 100V DC and AC (rms value). Cable diameter is generally selected on the basis of welding current level. The higher the current and duty cycle, the larger the diameter of the cable to ensure that it does not overheat (see BS 638 Pt 4). If welding is carried out some distance from the power source, it may be necessary to increase cable diameter to reduce voltage drop.
The quality of weld relies upon consistent performance of the electrode. The flux coating should not be chipped, cracked or, more importantly, allowed to become damp.
Storage
Electrodes should always be kept in a dry and well-ventilated store. It is good practice to stack packets of electrodes on wooden pallets or racks well clear of the floor. Also, all unused electrodes which are to be returned should be stored so they are not exposed to damp conditions to regain moisture. Good storage conditions are 10 degrees C above external air temperature. As the storage conditions are to prevent moisture from condensing on the electrodes, the electrode stores should be dry rather that warm. Under these conditions and in original packaging, electrode storage time is practically unlimited. It should be noted that electrodes are now available in hermetically sealed packs which obviate the need for drying. However, if necessary, any unused electrodes must be redried according to manufacturer's instructions.
Drying of electrodes
Drying is usually carried out following the manufacturer's recommendations and requirements will be determined by the type of electrode.
Cellulosic coatings
As these electrode coatings are designed to operate with a definite amount of moisture in the coating, they are less sensitive to moisture pick-up and do not generally require a drying operation. However, in cases where ambient relative humidity has been very high, drying may be necessary.
Rutile coatings
These can tolerate a limited amount of moisture and coatings may deteriorate if they are overdried. Particular brands may need to be dried before use.
Basic and basic/rutile coatings
Because of the greater need for hydrogen control, moisture pick-up is rapid on exposure to air. These electrodes should be thoroughly dried in a controlled temperature drying oven. Typical drying time is one hour at a temperature of approximately 150 to 300 degrees C but instructions should be adhered to.
After controlled drying, basic and basic/rutile electrodes must be held at a temperature between 100 and 150 degrees C to help protect them from re-absorbing moisture into the coating. These conditions can be obtained by transferring the electrodes from the main drying oven to a holding oven or a heated quiver at the workplace.
When welding, the welder must be protected from heat and light radiation emitted from the arc, spatter ejected from the weld pool, and from welding fume.
Hand and head shield
For most operations a hand-held or head shield constructed of lightweight insulating and non-reflecting material is used which conforms to EN175. The shield is fitted with a protective filter glass, sufficiently dark in colour and capable of absorbing the harmful infrared and ultraviolet rays. The filter glasses conform to the strict requirements of EN 169 and are graded according to a shade number which specifies the amount of visible light allowed to pass through - the lower the number, the lighter the filter. The correct shade number for MMA welding must be used according to the welding current level, for example:
Note: The current ranges are different for other processes.
Clothing
For protection against sparks, hot spatter, slag and burns, leather gloves should be worn. Various types of leather gloves are available, such as short or elbow length, full fingered or part mitten. Other protection such as leather aprons may be required depending on the application.
Fume extraction
When welding within a welding shop, ventilation must dispose harmlessly of the welding fume. Particular attention should be paid to ventilation when welding in a confined space such as inside a boiler, tank or compartment of a ship.
Fume removal should be by some form of mechanical ventilation which will produce a current of fresh air in the immediate area. Direction of the air movement should be from the welder's face towards the work. This is best achieved by localised exhaust ventilation using a suitably designed hood near to the welding area.
Further information
Please refer to:
IEC -1: Arc Welding Equipment - Part 1 Welding Power Sources
IEC -6: Arc Welding Equipment - Part 6 Limited Duty Arc Welding Power Sources
EN 169: Personal eye protection. Fillers for welding and related techniques. Transmittance requirements and recommended use.
EN 175: Personal protection : Equipment for eye and face protection during welding and allied processes.
IEC -11: Arc Welding Equipment - Part 11. Electrode holders.
This Job Knowledge article was originally published in Connect, January . It has been updated so the web page no longer reflects exactly the printed version.
As the welding machine brands and welders types are various, and there are wide variations in prices, nearly all novice welders and experienced welders are bothered by welding equipment selection. Hence, we will share the most completed welding machine selection guide to help you buy an ideal welding power source.
Content:
I. Know the Application Scenarios. (Amperage, Voltage, and Portable)
II. Make Clear the Welding Material. (Welding Process)
III. Know Welding Machine Brands. (Reputable, Reliable, and Efficient)
IV. Budget for your Welding Machine. (Balance between Price and Quality)
V. Seek Help from Expert Welding. (Professional guidance)
I. Know the Application Scenarios.
First of all, before you buy a welder, you need to know whether your welding device will be used at home, in a factory, in a complex outdoor production environment, or in a variety of locations.
The standard voltage of residential and commercial properties is 110/120 volts AC, and welders with a rated voltage of 110V are entry-level welders suitable for the most basic welding projects. The rated voltage of most welding machines is 220/240 volts, which can handle easy and simple welding projects. For outdoor welding operations, an engine-powered welding machine is needed.
In addition, if the welder is used in a fixed place, then you may have no requirement for weight and mobility, otherwise, the welding equipment must be lightweight and portable.
II. Make Clear the Welding Material/Process.
Do you know what material you will weld? The welding material plays a decisive role in your selection of a welding machine and welding process. Welding is usually done on three elements: carbon steel, stainless steel, and aluminum. If you weld mild steel, MIG, TIG, and MMA welding are all supported only if the correct consumables are used. If your welding material is aluminum, AC/DC TIG welding machine, and MIG welding machine will be used.
As different welding materials have different features, you'd better make clear your welding material before you choose welding equipment. The table below shows you the welding process selection of different welding materials.
Are you interested in learning more about mma 500 welding machine? Contact us today to secure an expert consultation!
Metal
MIG welding
Stick Welding
TIG
Flux-cored welding
Steel
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Stainless steel
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Aluminum
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'
Brass
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Iron
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'
Titanium
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Chromyl
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Steel
'
'
'
Copper
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Cast Iron
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Magnesium
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Note: for more details on the MAG/MIG/TIG/MMA welding equipment selection, you can contact us.
III. Know Welding Machine Brand.
To choose the right welding machine, you should recognize some reputable welding equipment brands in a particular field. Seldom welding machine manufacturers are good at manufacturing submerged arc welding machines, gas-shielded arc welding machines and stick welding machines at the same time.
For example, Megmeet Welding Technology, a leading designer and manufacturer of GMAW welding equipment (MAG/MIG/TIG) for manual, robotic, and automatic welding, supplies high-end digital welding equipment and dedicated technical support to our partners and customers. To get a quote, you can contact us at: https://www.megmeet-welding.com/en/contacts
IV. Budget for your Welding Machine.
Welding machines are a kind of high-value equipment, and generally the higher the amperage & voltage, the higher the price, so you must make a reasonable budget based on your requests. Remember, you can never buy ideal automated welding equipment for $20, but it's possible after increasing the budget.
In addition, it's not wise to compromise the welding device quality for budgetary reasons. If you buy a low-quality welding machine at a low price, you will run the risk of increasing costs due to low welding efficiency and bad welding results.
V. Seek Help from an Expert Welding.
If you are still unknown which welding machine to choose in the final part, you can consult experts in the welding industry or professional customer managers of a particular welding machine company. Normally, you can get the quote and the spec sheet from the customer manager, and all your questions will be solved with their patient guidance. If you want to buy a GMAW welding machine, you can contact megmeet welding technology to get the quote and spec sheet.
The above 5 tips are enough to help you make the right decision. In one word, to choose the right welding machine, you should start with your realistic needs, make a realistic budget, and make a balance between the quality and the price.
To grasp more welding machine selection tips and welding tips and tricks, you can collect the Megmeet News Center Page to read the articles published from time to time.
Contact us to discuss your requirements of china welding equipment. Our experienced sales team can help you identify the options that best suit your needs.