Induction heaters: Brushing away the scale of confustion

Contributing smith and Forged In Fire champion, Derek Melton, writes to clear some of the confusion around the Chinese-made 15kw machines and to provide some guidance for those looking to add one to their shop.

My first exposure to an induction forge was at the shop of Clay Spencer in 2019. I took a power hammer tooling class in which we used the induction machine to do some of the forging. I was unable to stop thinking about these incredible machines for months afterwards.

I don’t pretend to know all there is about the science and technology behind an induction machine, but I can cover the basics.

As I understand it, an induction heater uses electromagnetic induction to create friction in the molecules of a conductive material, such as steel. The heater is built with an electronic oscillator that sends high-frequency AC power through the magnet creating a magnetic field into which a steel can be passed. The resistance of the molecules of the steel causes it to heat from inside.

Growing Use

These machines have found a spot in some blacksmiths’ shops now because they can quickly and cleanly heat steel to forging (even welding) temperatures without using an externally applied heat source such as coal, propane, natural gas, etc.

When I began shopping for an induction heater for forging purposes, I found the process to be a bit confusing. A quick search on eBay showed all kinds of different machines, many with varying numbers of water ports, different paint schemes, and prices that varied to a wide degree.

After many questions and a good bit of research, I believe I can say with confidence that the Chinese company LiHua is the primary manufacturer of most of the machines found online. The different colors, number of water ports and the front panels seem to change based on the model year in which they’re made.

From what I could gather, it seems that there are many vendors who buy these machines in bulk for resale. Therefore, an online vendor in 2021 could be selling machines made years ago, which may look different but have the same performance statistics. I also found that the popular U.S. Solid brand of induction heater, is in fact a re-branded, re-painted LiHua LH-15 unit. Based on my experience and the experience of others who have followed my web guide, I think that most of the machines sold online appear to be of similar quality. Prices in 2020 ranged from $600 to $1,100 for what I believe to be the same machine.

After doing my initial research I decided to purchase a 15kw 220-volt machine. I watched the sub-$700 models on eBay for a year before I bought mine and during that time, I noticed they would occasionally be unavailable for a time but then later re-stocked with certain vendors. If you’re okay not having local, U.S.-based support, keep watching eBay or AliExpress for a 15kw induction heater until you see one that you like that fits your budget.

My experience buying the machine was painless, it arrived in a wooden shipping crate, well packed with cardboard and foam and with two pre-made (albeit too large) coils. After unpacking, I made slight modifications to my induction heater to meet my own quality and safety standards.

Needed Modifications

Many of these units come with dangerously exposed wiring terminals on the back of the machine. On mine, the ground was at the bottom on the outside in the rear, just below the water out ports while the 220-volt terminals were located near the top under an open, hinged lid. I did not like having these wires and terminals carrying 220 volts so exposed and vulnerable, so I added a small junction box with strain relief for the main wire. I then re-routed the ground inside the case and used some good, shrink-fit ring terminals to attach the wires inside the case.

I added a digital aquarium thermometer to monitor the water temperatures in the cooler. I mounted it to the induction heater and can see the water temperature easily while forging. The goal is keeping water temperatures below 130 F in use and to see when the water temp is nearing freezing in winter.

Tubing and Coils

If you’re living in a country that does not use metric fittings, you will need to make adapters to change from the 8 MM tubing to ¼-inch tubing and corresponding nuts. This will be the case if you want to make your own coils. I simply made an adapter using short sections of the original 8 MM tubing soldered to ¼-inch adapters. This allows me to use standard, off-the-shelf parts from a local hardware store to make my own coils.

These induction heaters require a water-cooling system. Whether that be a turn-key cooling system you buy or one that you build, they absolutely will not function without it. The internals of the induction heater can get very hot, cooling them properly is key to longevity with these machines. A water chiller circulates cooled water through the machine and through the coil to manage the temperature. There are two primary requirements for the water-cooling system: sufficient pressure and a correct temperature range of the coolant. Without adequate water pressure or sufficient cooling, the machine will sound an alarm and shut down. This is a fail-safe to prevent you from damaging your machine. I decided to go the turn-key route and purchased the 110-volt WS-25L water chiller which is a 25-liter TIG welding cooler.

An induction machine is only as effective as the coils you make for it. The coils should be appropriately sized for the material you are planning to heat. Just as a blacksmith may have dozens of types of tongs for various material, you will soon discover that you will have dozens of types of coils. A general rule of thumb is to make the coils with approximately 5 MM of space between the material being heated and the inside of the coil. Initially, I had trouble getting the material hot enough when trying to heat ½-inch square mild steel bar with the oversized 2½ -3-inch coil that came with my machine. I made my first couple of custom coils by

Melton’s induction heater setup, front and back, showing modifications with hose and wire arrangements and the 25 liter cooler.

winding ¼ inch copper refrigeration tubing around different sizes of pipe. After making the appropriately sized smaller coil, I was able to get a ½-inch bar to a spark-throwing welding heat in less than 30 seconds at full current.

Copper coils will last longer with a bit of care. I coat them with Meeco Gasketing Cement and Furnace Sealant. It’s a somewhat sticky substance that dries to a hard, rubber like coating and resists temperatures up to 2,000 F. Having the coil coated with this sealant or a ceramic flexible tubing does not affect the heating capabilities at all and keeps you from making contact with the copper and causing a short, which almost always results in a startling shower of sparks and if done enough, can burn a hole in your copper tubing and allow water to suddenly spray out of the coils. I’ve found that I need to re-coat the coils occasionally as I wear through the coating from being careless with material in the coil.

Coils will vary in their effectiveness based on the number of turns and the width between them. I have found that with these 15kw machines, too many turns can cause the machine to fault and not function correctly. For ‘standard’ coils I have found that 3-5 turns appears to work well. There are various other types of coils that can be made to allow the user to not have to pass material through a loop, sometimes these are referred to as “taco” coils, “pancake” coils, etc.

Cost Savings

One of the most common concerns that people have when they see these machines is that they believe that they will greatly increase the cost of their electric bill. These machines are only drawing about 35 amps when the machine is engaged to heat material. Since it does that task so quickly, that engagement period is typically very short. I have not found that my electric consumption has increased to a noticeable degree since moving primarily to induction heating for my work. In a nutshell, I have compared my electric bills over a six-month period between this year and last year and I can see no significant increase in my monthly payments. There may be a $10 or so difference but nothing extreme. I have however, seen a drastic decrease in the amount of propane I have had to buy, so I call that a win.

I have found these machines to be extremely effective for forging and after using one for an extended period. I feel safe in saying that, if possible, I will always try to have one in my workshop. It has become a daily use tool and has changed my forging process for many of the products that I make in the shop.