In this instructable, I will show you how to make an induction heating machine and 7 different applications for it. Induction heating has many practical applications and making one is incredibly simple. First, I will go over the applications and then you can decide if you want to make one of these awesomely useful machines.
Step 1: Induction Case Hardening Steel
In this video I show you how to cryogenically case harden your low carbon steel parts with the induction heater. What you end up with is a material that has a ductile inner core with a hard outer shell. Parts that require impact resistance as well as abrasion resistance are great candidates for case hardening. Low carbon steel does not harden well on its own. When heating the part up and submerging it in a carbon compound, carbon gets impregnated into the surface of the material. This results in a hard outer surface.
Gears, Firing pins, Engine Camshafts, Lock Shackles, Security Fasteners, and Self Drilling Screws are all commonly case hardened. The method of case hardening used in the video is also known as carburizing with a cryogenic treatment. Liquid nitrogen is usually used but I used a isopropyl alcohol dry ice bath. Liquid nitrogen would provide even more benefits by converting even more retained austenite to martensite. Also, if you don't mind the darkness of the part after the hardening process, it's best not to polish it for even more rust protection. The method used in the video can be repeated multiple times until the desired hardness is achieved.
Induction is particularly good at case hardening. This is because of the skin effect discussed in the next step. The same high frequency skin depth that is seen in the working coil is also seen in the part being heated. The higher the frequency, the more the current is flowing on the outside of the material. For steel in this case, the current is only flowing about 6 thousandths of an inch deep. This is perfect for case hardening.
This process should only be used with low carbon steel so I'll show you a way to determine what type of steel you have.
In this video, I'll show you an easy way to determine the carbon content of your steel parts by observing the spark profiles. You can use this technique to find which of your parts would benefit from the case hardening method used in my last video. This is not the most accurate way of determining the composition of the steel, but many welders use this technique when welding unknown materials and is a good test for most non-critical jobs. This technique is known as spark testing.
Step 2: Induction Cooktop
In this video, I make a pancake coil attachment and boil water in about 10 seconds. It works by pulsing the DC at a high frequency(about 160kHz). This creates a constantly changing magnetic field that induces eddy currents in the cast iron skillet. Induction heating is more efficient than many other methods because there is less wasted heat. For example, induction cooktops are more efficient than electric and gas stoves.
The use of my wire choice is quite important here. I used what is known as Litz wire. Litz wire consists of many individually insulated wires. It is the preferred wire for use in high frequency application due to the skin effect.
The skin effect is the tendency of current to flow on the outside of a conductor at high frequencies. The higher the frequency, the shallower the skin depth will be. Using Litz wire will result in much more efficient working coils for your system. Not only does it transfer the energy more efficiently, it also generates less heat of its own. If you have 10amps flowing through 260 strand Litz wire, that's only 38mA of current in each wire. 10amps through a single conductor will generate substantial heat depending on the size.
If you do not want to use Litz wire, the next best thing is copper tubing. It has more surface area for the current to flow so it is more efficient than an equivalently sized solid core wire.
Step 3: Induction Kiln for Melting Metals
In this video, I melt the first pieces of aluminum in my 1000W inductive furnace attachment with my graphite crucible. It works by pulsing the DC at a high frequency. This creates a constantly changing magnetic field that induces eddy currents in the graphite crucible. Graphite makes for a great susceptor because of it's ability to absorb electromagnetic fields and convert them to heat. That's why it's used in many crisper sleeve for microwavable foods. A susceptor is a material that is used for its ability to absorb electromagnetic energy and convert it to heat.
Step 4: Induction Solder Pot
In this video, I explain the material choices I made for my 1000W induction solder pot. I used a steel conduit coupler with a steel plug wrapped with aerogel infused fiberglass exhaust wrap. I made the working coil with litz wire and secured it in place with kapton tape. For an even better solder pot, you could use a graphite crucible like in the last step. In this next video, I show you how to use the solder pot. I feel it really demonstrates the usefulness of the solder pot.
Step 5: Loosening Seized Bolts and Hardware
A torch is commonly used when you can't loosen a seized nut or bolt. By heating the nut with the induction heater, the metal will expand and you can free the seized hardware. Using a torch is dangerous in confined areas and using flameless heat prevents damage to the surrounding parts such as, wire harnesses, fuel lines, anything plastic, anything volatile and flammable. Induction heaters are often used by aircraft mechanics when using a flame would be a bad idea.
Step 6: Induction Levitation
In this video, you can see that the coil is levitating the aluminum. The works because of Lenz's law. This means that when it is introduced to a constantly changing magnetic field, the induced currents in the aluminum create an opposing field to that of the coil. This is the same thing that is happening when you drop a strong magnet down a copper pipe. The magnet is slowed down due to the opposing field that the copper is producing.
Step 7: Battery Powered!
In this video, I test a 16.8V, 33.6V and 50V battery pack for the induction heater. This could be used as a portable induction machine for use with any of the above applications.
Step 8: How to Make One
Minimum Materials You Will Need:
1. Adjustable Power supply or battery pack.
2. ZVS Driver with coil
You can get by with just those parts but I recommend using Litz wire and a power meter as well as some protective equipment. Here are some links to recommended equipment for this project:
Meanwell RSP-1000-48 Power Supply http://amzn.to/1NqHOYz
4S Quadcopter Batterieshttp://amzn.to/1PqNWSz
Litz Wire for Custom Induction Coils http://amzn.to/1kIG6IA
Graphite Crucible http://amzn.to/1Mdj34M
Temperature Meter 2000F(1300C) http://amzn.to/1NqHV6j
Power Meter 100V 50A http://amzn.to/1XnFMNv
Cast Iron Mini Skillet http://amzn.to/1MfaT5y
Aerosol Fire Extinguisher http://amzn.to/1NwFLlx
Bullet Connectors http://amzn.to/1MfaYX7
Fiberglass Exhaust Wrap http://amzn.to/1kIxt0K
XT-60 Battery Connectors http://amzn.to/1Hvb23H
Battery Cell Monitor http://amzn.to/1kxxi81
Heat Resistant Gloves http://amzn.to/20K3xBP
Assembly is as simple as connecting the +terminal of your power supply to the +terminal of the ZVS driver and the -terminal of your power supply to the -terminal of the ZVS driver. The polarity of the working coil does not matter. I recommend an adjustable power supply and using a power meter to give you better control on your heat output.
Step 9: How Does It Work?
This induction heater works by pulsing the DC at a high frequency(about 160kHz). This creates a constantly changing magnetic field that induces eddy currents in conductive materials near the coil. Ferromagnetic materials will also heat up due to hysteresis. This is the heat produced from rapidly changing magnetic fields in the material. Induction heating is more efficient than many other methods because there is less wasted heat. For example, induction cooktops are more efficient than electric and gas stoves. I'll be making more attachments and demonstrating more practical uses for inductive heat.
It's a common misconception that induction heaters don't work for aluminum and other non-ferrous metals. This is not true. This induction heater will heat up aluminum and copper just fine, but not as fast as ferrous metals. This is mainly due to their lower resistivity. The higher the resistivity of the conductive material, the more it generates heat when current is passed through it. The higher resistivity of most ferrous metals coupled with the heating due to hysteresis makes them ideal for induction heating, but they are not the only metals affected by induction.
The three main components of the machine are the power supply, the ZVS driver, and the working coil. The ZVS driver,(Zero Voltage Switching) was invented by Vladmiro Mazilli. It uses resonant zero voltage switching (also know as ZVS) to pulse the power supply very rapidly. This means the MOSFET's are designed to switch (on or off) when the voltage across them becomes zero. Since the MOSFET's switch when there is no voltage across them, they generate very little heat. The main source of heat is caused by the MOSFET's internal resistance and the capacitors constantly charging and discharging. The circuit is fairly simple consists of just two MOSFETs, 6 capacitors, and a few resistors and diodes. You can build the circuit yourself, but it is cheaper to buy a premade board.
Step 10: Thank You
Another great application would be to use it in a tankless water heater. A coil could be placed around the pipe and heat up the water as it passes through. This machine could also be used for wireless charging and powering applications.
Thank you for reading my instructable. I spent a great deal of time on this inductive heating series so I would really appreciate you sharing this with your friends as well as voting for me in the Epilog contest above. I if had a laser cutter it would help me create more educational content for you guys.
Anthony - Proto G