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Welding is one type of manufacturing process by which two or more similar or dissimilar materials can be joined permanently by weld bead formation with or without the application of external pressure, heat or filler material. There exist different types of welding processes, each of them follows unique procedure to weld two or more components. Welding processes can be broadly classified as arc welding, gas welding, resistance welding, solid state welding and intense energy beam welding. Each of these class once again consists of several welding processes. Irrespective of the welding process, a weld bead formation is always desired to join the components by welding. This weld bead forms at the intersection of two components that are welded. It is also worth mentioning that fusion of the faying surfaces of the parent components is not necessary for weld bead formation. In some welding processes, the faying surfaces are fused with the application of heat to get the weld bead, while in other processes, weld bead can be obtained without melting the faying surfaces. On the basis of whether base materials are fused or not, welding processes can be broadly classified into two groups—solid state welding and fusion welding.
In all such welding processes where the faying surfaces of parent components along with the filler material are fused to form the weld bead are called fusion welding. Sufficient heat must be applied by external means for properly fusing the faying surfaces of base metals as well as the filler metal. Thus phase change (solid to liquid and once again liquid to solid) occurs in fusion welding. All arc welding, gas welding, resistance welding and intense energy beam welding processes are fusion welding. On the other hand, if no such melting takes place during welding, then it is termed as solid state welding. Here the joining takes place in solid state and no phase change occurs. However, in solid state welding, parent components may be heated to an elevated temperature but substantially below the melting point of the concerned material (and thus no melting occurs). Instead of external heat, application of pressure is usually necessary for this type of welding. Roll welding, diffusion welding, friction welding, etc. are considered as solid state welding processes. Following passages elaborate similarities and differences between fusion welding and solid state welding.
Induction Heating Equipment & Power Supplies
Induction Heating offers a controllable and localized method of heat without contact to the parts (components) being heated. The heat is generated by inducing an alternating magnetic field into electrically conductive materials. Induction Heating technology is very low cost to run and normally creates significant costs savings versus other traditional process heating technologies. RDO offers Induction Heating equipment, power supplies & metal heating furnaces from 1kW to 500kW in output power and frequency ranges from 1kHz to 1 MHz. We also offer induction heating coils to go along with our induction heating machines.
The capabilities of these induction systems allow us to offer solutions for a wide array of applications, including soldering, brazing, heat treating, bonding, melting, crystal growing, hardening, annealing, and shrink fitting.
We also offer induction heating equipment and high frequency induction heaters for curing adhesives. We are able to provide turn-key solutions from our standard product line and equipped with a complete induction heating laboratory for testing and developing solutions for our customer’s important processes. RDO also has the ability to design and develop custom power supplies & industrial heating machines based on requirements specific to the customer’s application, which can be stand-alone or embedded systems.
What is a thyristor? Types of thyristors and their uses
Thyristors are an interesting class of semiconductor devices. They share similar characteristics with other solid-state components made from silicon, like diodes and transistors. Therefore, distinguishing thyristors from diodes and transistors could be difficult. To add to the difficulty, there are different types of thyristors available on the market.
In some instances, what sets thyristors apart from one another could be just a tiny detail.
Also, depending on the manufacturer, a given thyristor may be known by another name.
To apply thyristors successfully when designing circuits, it is important to know their unique characteristics, limitations, and their relationship with the circuit. That’s why we’re taking some time to sort it all out so that you can have a better understanding of what thyristor is most suitable for your application.
A thyristor is a four-layer device with alternating P-type and N-type semiconductors (P-N-P-N).
In its most basic form, a thyristor has three terminals: anode (positive terminal), cathode (negative terminal), and gate (control terminal). The gate controls the flow of current between the anode and cathode.
The primary function of a thyristor is to control electric power and current by acting as a switch. For such a small and lightweight component, it offers adequate protection to circuits with large voltages and currents (up to 6000 V, 4500 A).
It is attractive as a rectifier because it can switch rapidly from a state of conducting current to a state of non-conduction.
In addition, its cost of maintenance is low and, operating under the right conditions, remains functional in the long term without developing a fault.
Thyristors are used in a wide range of electric circuits, from simple burglar alarms to power transmission lines.
A thyristor with a P-N-P-N structure has three junctions: PN, NP, and PN. If the anode is a positive terminal with respect to the cathode, the outer junctions, PN and PN are forward-biased, while the center NP junction is reverse-biased. Therefore, the NP junction blocks the flow of a positive current from the anode to cathode. The thyristor is said to be in a forward blocking state. Similarly, the flow of a negative current is blocked by the outer PN junctions. The thyristor is in a reverse blocking state.
Another state a thyristor can exist in is the forward conducting state, whereby it receives a sufficient signal to switch on, and it starts conducting.
Let’s take a minute to highlight the unique properties thyristors bring to a circuit by going further into the nature of the signal and the thyristor’s response.
Electron (or Vacuum) Tubes
An electron tube (also known as a 'Vacuum tube', or a 'Valve' ) is a glass or metal enclosure in which electrons move through the vacuum or gas from one metal electrode to another. The vacuum tube is often used to amplify weak currents or act as a one-way valve (rectifier) for electric current.
Before the 1947 invention of the transistor the electron tube was the basis of virtually all electronic devices. The simplest kind of electron tube is the diode, which was invented in 1904 by John A. Fleming. In Greek, “di” means “two,” and it was called a diode since it only had two electrodes inside—the negative electrode or “cathode” and the positive electrode or “anode.” Fleming’s diodes were modified light bulbs, so like light bulbs they consisted of a glass bulb with a filament inside. The filament acted as the cathode, emitting large numbers of electrons, while the anode consisted of a small metal plate mounted near the filament and connected to the outside of the tube by a thin wire.
A diode regulates the flow of electric current and acts like a one-way valve turning current on and off. When a battery is connected to the metal cathode, it heats up and electrons “boil off” from its surface. They fly around inside the glass tube and form an invisible cloud around the cathode. When the diode is placed in a circuit so that the anode is connected to the other terminal of the battery, the cloud of electrons rush toward the anode, as do the new electrons streaming off the cathode. This flow of electrons completes the electric circuit. It is extremely difficult for electrons to flow the other way, so the diode acts as a one-way valve.
Fleming invented the diode for use in radio. One of the most difficult things about receiving radio ways was “detecting” the signal. Mechanical devices had been used to detect the presence of incoming radio waves, but the waves are so weak that they don’t have enough energy to move even a very lightweight mechanical detector. With a Fleming diode and a carefully designed tuning device, radio waves could be detected when they acted on the diode, causing it to turn on or off. The diode was a very sensitive, “electronic” type of radio wave detector.
Controlling the risks from welding
If welding is part of your work activity, you must carry out a risk assessment to identify what measures are required to control the risks from exposure to welding fume.
Regular welders will weld for most of their shift and carry out different types of welding and other associated activities in the same day, depending on the requirements of their job. Their exposure to welding fume will be regular and of a significant duration or high intensity. They will require adequate controls to protect them from the risk of developing occupational lung diseases.
Sporadic welders will carry out welding infrequently when it is incidental to their main manufacturing operation. Engineered fume controls will not normally be expected for occasional welding carried out less than once each week and lasting less than 1 hour. In these situations, ensure that respiratory protective equipment (RPE) and good general ventilation is provided to control exposure to welding fume. But, you must also consider the protection of others nearby and ensure the general ventilation is effective at removing and dispersing the welding fume.
For example, a car mechanic wearing RPE with good general ventilation in the workplace, carrying out an occasional short welding job on a car with a broken exhaust support bracket, would meet the minimum requirement for compliance.
Without controls in place, workers will be exposed to welding fume. This video shows typical fume emissions arising from MIG welding.
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