Ambrell Induction Heating
Ambrell Induction Heating
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PRO Skills Webinar Q&A

We are always pleased by the depth and thoughtfulness of the questions asked during our PRO Skills webinars. Dr. Dahake has matched his answers with the questions put to us in our last webinar.

For example:

Q: How portable is the unit?

A: Ambrell makes small portable units that are similar in size to an over-sized VCR. As the power delivery increased the units transition to table top devices. Even higher powers are housed in floor standing units.

Q: Does parallel coil arrangement require a higher amount of current ?

A: Parallel coil arrangement ensures that each section has the same operating voltage, which is being delivered by the induction generator. The current is then divided based on the inductance of each section. Lower inductance sections have more current flowing through them, than higher inductance sections.

 Q: Is possible to heat an electrically non-conductive material ? example glass

A: Electrically non-conductive materials do not heat directly with induction. However, these materials can be heated by conduction, convection or radiation using a conductive material between the induction coil and the non-conductive material.

 Q: How does the heating effect a anodizing or powder coated parts?

A: Usually induction heating does not affect anodized aluminum parts or thin metallized coatings. Some metallic coatings, if thicker may sometimes get affected by induction.

Q: What's the difference between Frequency and Amperage? You mentioned Frequency equates to amplitude or strength of the magnetic field into the part. What effect does controlling amperage have?

A: Frequency of operation determines how deep the induced electric currents will penetrate the metal part. Higher the operating frequency the higher is the amount of heat produced and shallower is the depth its produced in. Amperage of the coil determine the strength of the magnetic field. The higher the amperage, the higher is the magnetic field. Amperage does not affect the depth of the induced eddy currents in the metal part.

Q: What is a Faraday ring?

A: A Faraday ring or shield is a device that absorbs magnetic fields radiated by induction coils. Local sections can be insulated with shorted loops or rings, however for general shielding a Faraday cage is recommended around the induction coil to block magnetic field radiation in all directions.

Q: How to set the SH value of a metal alloy?

A: Any metals handbook will be able to provide the specific heat for various metals.

Q: What is the influence of frequency (kHz) in power calculation?

A: Frequency of operation determines how deep the induced electric currents will penetrate the metal part. Higher the operating frequency the higher is the amount of heat produced and shallower is the depth its produced in.

Q: Can a painted steel part be heated or is there any limitations in Induction heating?

A: Usually induction heating is not affected by painted steel parts, anodized aluminum parts or thin metallized coatings. Some metallic coatings, if thicker may sometimes get affected by induction.

Q: If I know the distance between the coil diameter and part diameter, can I calculate the frequency required to penetrate JUST the outer skin layer of the part?

A: The parameters required to determine the depth of the induction heat requires resistivity of the metal being heated, magnetic permeability (if any, else u = 1) and the frequency of operation. The coil diameter and the part diameter do not factor in this calculation.

Q: I generally forge steel parts. You mentioned for the deep heat using a low frequency; What is that frequency range?

A: Forging applications typically require a combination of low frequency and adequate soak time for optimal performance. Frequencies in the 1-10kHz range are typically used for forging applications.

Q: What is a good rule of thumb between the size of the part and the depth of power to produce efficient heating of the whole part.

A: Usual rule of thumb is to have a time cycle that is 25 times the square of the diameter of the part for efficient heating. So if a part is 2 inches in diameter, the heat time should be 25 times 4 which is equal to 100 seconds. If faster times are required then more than one part should be heated at the same time.

Q: Can you explain the levitation phenomenon observed during vacuum induction melting of metals?

A: Induction heating coils create a magnetic field. This magnetic field interacts with the molten metal to create eddy currents. There is magnetic levitation due the magnetic field in the molten metal. Since the magnetic field drops in intensity with distance from the coil, the molten metal jumps in and out of the magnetic field.

Q: How can induction heating be more efficient in energy consumption. What parameters relation has to be take care?

A: Induction heating efficiency is derived from the following: selective heating, energy produced directly inside the metal without the aid of a transfer medium, and the ability to insulate the hot part from losing its heat to the environment.

Q: Is centering the part in the coil critical?

A: The position of the part in the coil determines the magnetic field interaction between the coil and the part. Centering of the part inside the coil is always recommended, however there are certain metals and heating application where centering is not too critical.

Q: What is the material of turbine blades?

A: The material used for land-based turbines is Inconel or an alloy similar to Inconel. Aircraft turbine blades are made of titanium.

Q: How is the induction process affected by environment, humidity,? how can we measure or control the quantity of tin in our processes?

A: Environmental factors like humidity, ambient temperature etc play an important role in sensitive soldering applications by changing the amount of heat required from the induction heating system. The amount of tin in a soldering application can be controlled by the use of preformed rings of solder that guarantee the same amount of the tin solder per joint.

Q: I am interested in induction brazing small parts (OD less than .25 ") and I was wondering how the coil design, ( ID of coil, number of turns) affect the heated zone and what is the best way to control the heated zone. Is there a rule of thumb to get the best consistency out of the heated joint?

A: Proper coil design operating at the correct frequency should easily control the heat to your small part brazing application. It is recommended that you seek application consulting advice to set the process up correctly.

Q: Is there a formula to illustrate the effect of coupling distance or is it just inverse square law? I have seen illustrations, but never a mathematical example on the effect.

A: Inverse square law is a good approximation of the coupling efficiency in round coils.

Q: We are interested in heating various types of samples in a mechanical testing environment. We want a very uniform temperature on both long round samples and sheet samples. As good as +/- 3 C at 1200 C. We are Interested in ways to assure minimum thermal gradient on edge to center and end to end.

A: Proper coil design operating at the correct frequency should easily control the heat to your heating application. It is recommended that you seek application consulting advice to set the process up correctly.

Q: What calculations are needed to determinate the temperature that a coil that the heated material doesn't go thorough its center, it passes just above the coil ?

A: Proper coil design operating at the correct frequency should easily control the heat to your heating application. It is recommended that you seek application consulting advice to set the process up correctly.

Q: What is typical frequency for graphite susceptor for heating to 1500C and above

A: The frequency required to heat a graphite susceptor is determined by the wall thickness of the graphite susceptor. It is recommended that you seek application consulting advice to set the process up correctly.

Q: Is there any health hazard if the operator is being exposed to Induction heating environment ?

A: Yes, there are various health concerns as the safety of the operator working on an induction setup can never be under valued. It depends on the time of exposure to the magnetic fields and the intensity of the magnetic fields.

Q: Can a shop worker with a pacemaker operate any induction equipment?

A: It is generally advisable to not have shop workers with pace makers operate the induction equipment. Proper clearances from appropriate authorities need to be obtained before an area can be declared safe for such operation.

Q: Is there a safety problem if you have a pace maker for your heart?

A: It is generally advisable to not have shop workers with pace makers operate the induction equipment. Proper clearances from appropriate authorities need to be obtained before an area can be declared safe for such operation.

Q: What precautions would an operator need to take while using a bare coil...like PPE or is there a hazard in touching the coil?

A: Operators using a bare copper coil should wear gloves with appropriate voltage ratings. Non-metallic shields can also be placed between the coil and the operator to avoid accidental contact.

Q: How do you ensure your induction installation doesn't display magnetic field outside the coil ? Do you provide a certificate proving there are no magnetic leaks...

A: Ambrell recommends outside agencies that can plot the magnetic fields radiated from the induction coil. A typical Faraday cage would then need to be installed to eliminate any magnetic fields around the induction coil. Once the cage is installed, one would need to run the tests again to prove that the stray magnetic fields have been controlled. The testing agency will then provide a certificate for your particular application.

Q: We have painted steel cylindrical part, is there any limitation using induction heat for the painted parts?

A: As long as the paint is not electrically conductive, there should be no issue using a painted cylindrical part.

Q: Can you employ induction based heating towards heating powdered metals directly.

A: Yes, induction heating can be used to heat powdered metals directly. However, the rate and efficiency of heating depends on a number of factors like packing density, type of metal, size of the individual particle and the temperature required.

Q: For shafts such as SAE 1045 and SAE 4140, is a post oven tempering or draw back operation required?

A: Induction heat treating will typically deliver an as quenched hardness close to RC(Rockwell) 60. Depending on the final use of the shaft a post oven tempering may be required to increase the ductility and other properties.

Q: I heard that induction heating can be used for cancer treatment? is that right?

A: Yes, induction heating is used to heat injected nanoparticles in tumors and cancer cells. The local heat produced destroys these cells.

Q: Temperature measurement: some infrared temperature devices are affected by induction and so shouldn't be put too close to magnetic field. is there a way of estimating the magnetic field range? to be able to determine at what distance to place the infrared temperature measurement devices.

A: General rule of thumb for induction is that metallic objects should be placed 2-2.5 times the internal opening of the induction coil. This opening is the internal diameter for round coils. There are some instances where the intensity of the magnetic field is strong enough that larger separation is required. If this is not practical then a Faraday cage or shield may be used to block the magnetic field from reaching the temperature measuring device.

Q: How to avoid or reduce the oxidation problem? Maybe use of vacuum is a good idea that also lowers the consumption of insulation.

A: Any oxygen-free environment can be used to reduce the oxidation of metal parts. This can be created using a vacuum setup or evacuated chambers that are back-filled with inert gasses like Argon, Nitrogen or Helium.

Q: In induction brazing steel to carbide is the steel the only metal actually heated by induction? If so how much hotter must the steel be heated generally to acheive the proper brazing temperature?

A: Both Steel and Tungsten carbides couple to the induction heating field. However since steels are typically magnetic they couple to induction field and produce heat due to eddy current heating as well as hysteresis heating. Tungsten carbide only heats due to eddy current heating. Therefore steel typically heats at a faster rate than the carbide.

Q: How can ramping up heat and tapering off heat during a cycle help the processes or cycle time?

A: In certain applications the energy delivered by the induction coil on the surface of the parts is greater than the ability of the metal to conduct it away. This results in skin heating only. However if uniform thru heating is required, then a controlled ramp and taper of the heat can be used to avoid high temperature differences between the surface and the core of these parts.

Q: What would be basic power, frequency, time parameters for optical fiber applications (sealing glass fiber in metal tube with glass preform)?

A: Optical fiber applications typically require precision in the delivery of the heat. Since the parts are small, power required is typically less than 1-2 kW. However frequency required is higher, usually in the 100-300kHz rage.

Q: Any recommendations on how to control scale build-up on billets during Induction heating? We are using Induction Heating for billets to be forged into crankshafts.

A: Scale buildup during induction heating can be reduced by introducing an inert atmosphere around the part being heated. This can be a Nitrogen, Argon or similar gas air purge.

Q: Is there an equation for temperature soaking time? My procedure requires a uniform temperature thru the whole wall thickness.

A: There is certainly an equation for soaking time for a particular metal at a particular temperature. A detailed numerical simulation would be needed to determine this time.

Q: What would happen if a brazing operation suddenly stops and the part is reheated?

A: In most cases a part can be reheated if the original brazing cycle did not complete. The time to heat the same part a second time may be shorter if the part is already warm or if the braze alloy was partially flowed during the first heat.

Q: For semi-automation, would a customer prefer to move the part through the coil or can the coil be moved through a stationary part?

A: Either option is possible with Ambrell power supplies. The actual setup will depend on the ease of doing one vs the other. Usually the cheaper option is chosen.

Q: This applies to thin shell annealing and trying to manage heat to avoid melting.

A: For thin shell annealing increasing the length of the coil should be increased to increase the heating time and lower power densities. This is typical for channel coil setups. For helical setups multiple position coils can be used to produce parts without melting while preserving production rates.

Q: We have noticed that the closer the metal piece to the coil during induction, the higher the temperature reached. Is is ok to put the metal piece as close to the coil as possible? or its better to keep the metal a few mm away from the coil although we will loose in temperature rise.

A: Theoretically the closer the metal part to the coil, the faster is the heating rate in the part. However, in production environments reasonable air gaps are used to overcome the design tolerances in parts, coils and the handling fixtures used to hold the parts.

Q: What needs to be considered with hermetic soldering with gold nickel plated Kovar with Metal and glass solder?

A: Hermetic soldering applications require the joint to be designed correctly for induction. Cleanliness of the joint area, proper design and placement of the glass solder and the control of the heat from the induction coil all play an important role in a successful soldering application.

Q: Are induction heating systems used in cobotic automation? Can you describe how that is typically installed?

A: Induction heating can be readily used in cobotic applications. Usually the coil and/or the Ambrell remote workhead can be manouvered to the heating location for such applications.

Q: After induction hardening 1045 or 4140 do you have to perform an oven draw back or tempering process?

A: Induction heat treating will typically deliver an as-quenched hardness close to RC(Rockwell) 60. Depending on the final use of the shaft a post-oven tempering may be required to increase the ductility and other properties.

Q: Do you have applications for heating liquid flows in tubes?

A: Yes, induction heating is routinely used to heat fluids flowing through metal tubes. Ambrell has provided solutions to numerous such applications.

Q: We are a little new to low frequency induction heating and we are wondering how to design a coil to focus on heating a slug for friction spin welding. We want to heat the part (1.46inches diameter by 2.4inches long) to about 400degrees. we want to heat the hole part including the end flat edge that is friction welded.

A: Proper coil design operating at the correct frequency should easily control the heat to your heating application. It is recommended that you seek application consulting advice to set the process up correctly.

Q: Any advice on a material for a rail for the part to pass through our coil horizontal coil. Currently we have tried tungsten carbide which is working but the repeated heating is wearing it. We also have an Alumina ceramic from Mc MasterCarr we will try. Thank you.

A: The forging industry typically used water cooled rails that are coated with a hard facing material to wear. Ceramics will typically not be able to withstand the tough environment.

Q: What should we consider for brazing Nitinol tube to 304 S/S fitting?

A: First step would be to determine the correct brazing alloy that wets well to both the Nitinol and the SS fitting. Proper coil design operating at the correct frequency should easily control the heat for your brazing application. It is recommended that you seek application consulting advice to set the process up correctly.

Q: We use close contact. What options are there to run larger gaps, say 1 inch, without coupling loss?

A: Unfortunately without increasing the size of the induction generator, it will be difficult to increase the air gap between the part and the coil.

Q: Can you address ceramic processing where temperatures are 1200 to 1500C and above.

A: Applications with ceramics at high temperatures typically require an inert atmosphere of hydrogen to enable proper flow of the braze alloy on the ceramic. The hydrogen acts as a reducing gas and actively removes any free oxygen from the area. Proper safety precautions need to be taken when running such applications.

Q: Why are some coils coated and some not?

A: Induction coils are basically coated for two reasons. First is safety from accidental contact by operators and machinery. Second is to prevent the loss of heat from the hot part due to radiation, and convection. These types of coating are typically of the form of epoxy coatings, ceramic coatings, or any non-metallic coatings like silica sleeves or higher temperature alumina sleeves.

Q: We saw some coils having a loop in the middle causing a reverse coiling direction on both side, What is the goal of making such loop?

A: Some research setups require distinct zones of heat with dead zones of heat between these zones. Induction coils from Ambrell can then be customized with reversed windings to obtain such heat patterns.

Q: What sort of precision is needed locating the part within the coil?

A: The precision required in the final temperature of the parts determines how precisely it needs to be placed inside the induction coil. For typical brazing processes, the parts can be placed within 1-2 mm tolerance.

Q: Do coils need to be custom fitted to parts or can you use the same coil for a 30" part that you would use for a 10" part for instance?

A: A coil used to heat a 30in part can certainly be used to heat a 10 in part given the following two criteria. First there should be enough spare capability in the power supply to overcome the coupling loss to the 10 in part in the larger coil. Second, the time to heat the smaller part may be much longer given the poor coupling to the part.

Q: What is the material used for flexible coils? And what is the temperature limit of a flexible coil?

A: The flexible coil (EasyCoil) is made with copper braid on the inside of a rubber or non conductive flexible hose. Water flows inside the rubber hose so there is no temperature produced inside. However the temperature limit of the exterior of the hose determines the temperature of the application. Occasionally a ceramic sleeve is wrapped around the rubber hose for high temperature applications. We recommend you share your application details with Ambrell applications consultants for correct evaluation of your project.

Q: Why are some coils coated and some not?

A: Induction coils are basically coated for two reasons. First is safety from accidental contact by operators and machinery. Second is to prevent the loss of heat from the hot part due to radiation, and convection. These types of coating are typically of the form of epoxy coatings, ceramic coatings, or any non-metallic coatings like silica sleeves or higher temperature alumina sleeves.

Q: Channel-type coils, what are the problems or advantages for heat treatment (hardening)

A: Handling of long, difficult parts is easier when hardening using channel coils. However, channel coils are not as efficient as regular helical coils and therefore require longer heating times of larger induction power supplies.

Q: What Software do you recommend for canalize process and how

A: There are a number of different software programs available for analysis. Magnetic modelling software provides visualization of magnetic fields, thermal programs show the pattern of heat flow through the part. Coupled magnetic and thermal modelling software are the best to evaluate the induction heating process. Examples of such programs are ANSYS, COMSOL and many others.

Q: If a thermocouple is placed on the heated surface which we want to know the temperature, is there some interaction between thermocouple and the magnetic field ? and what is the accuracy we can have with a thermocouple near the magnetic field ?

A: If a thermocouple is used to measure the temperature of the surface of a metal part, the thermocouple should be well anchored to that surface, either by welding it to the surface or attaching with high temperature glue. Smaller wire diameter should be used for the thermocouple to reduce the coupling to the magnetic field. Also the wire should be placed so that there is minimal interaction with the induction magnetic field.

Q: What variables might the induction controller adjust in a system using feedback from a pyrometer to control heating in a process? Frequency?, Voltage?, Current? and can the authority or range of allowed adjustment can be set?

A: A feedback loop can typically adjust the voltage, current or the power of the induction power supply. This depends on the make and model of the induction generator. Frequency is typically not a variable adjusted with the feedback loop. Ambrell power supplies always scan for the resonant frequency of the electrical setup and operate at resonance at all times to deliver energy at optimal efficiency.

Q: Approximately what is the price difference among the 3 different types of coolers?

A: The price of the coolers vary based on the kW of cooling. Usually the cost of cooling per kW reduces for all three at higher cooling capacities. Since there are numerous manufacturers of the cooling devices globally, it is not practical to quote a price here.

Q: For the water used for cooling, is there specific characteristics requirements like resistivity for example ?

A: Yes, Ambrell has a standard water specification that is recommended for trouble free operation.