What the Hell is Coil Expansion?

For those of you not down in the weeds, in expanding coils, the tubes inside a coil of fins are made bigger so that they press hard against the fins. We’re talking about an interference fit here – where the tube is hair’s width larger than the hole in the fin. In fact, when you force that tube to grow, it forms a super solid bond.

• Think of it this way: You have a puzzle piece that’s just a bit too big. You sort of have to force it in, don’t you? Once it’s in, it’s not coming out. That’s the concept behind coil expanding.
• This tight fit is important, because it increases the area of contact between the metal of the tube and the metal of the fin. And more contact is better heat transfer. It’s simple physics, people!

Why Should You Even Care About Coil Expanding?

Fine, so we make the tubes a bit larger. Big deal, right? Wrong. This is one of those small things that makes a world of difference in both the equipment’s life and performance. Here’s why you should be paying attention to coil expanding:

• Best Heat Transfer: The snugger the fit, the more the heat moves. Air pockets are insulation between any gaps you may have, and an efficiency killer. You do want that intimate metal-to-metal contact. It’s like a handshake — a strong grip passes along more than a weak one.
• Strength & Durability: A well expanded coil is a strong coil. That secure fit locks everything in place, preventing leaks and ensuring the entire system remains intact over time. Less tear downs equals less down time, and more money in your pocket.
• Averting Blame in Thermal Resistance: Air space between this tube and fin is the enemy. They work by opposing the flow of heat, which means that your system has to work harder and less efficiently. The gaps disappear with good coil expansion.
• End Sizing Advantages: Some methods of coil expansion even allow you to form the ends of the tubes – examples include belling and flaring. It makes it easy to plug in other wires for other components down the line, saving time and frustration.

The Nitty-Gritty: How on Earth Do We Expand These Coils, Anyway?

It can be accomplished in one of two general ways, each with its own sets of pluses and minuses.

The Mechanical Expander: The Old Faithful

This is the classical and most commonly used procedure. Use the force Like you are physically pushing the tubes out. The typical method is to use a “bullet” — a circular or slightly conical piece of metal that is larger than the inside of the tube.

• The Process: A rod forces this bullet out the tube. The bullet, as it travels, causes the tube to expand out against the fin collars.
• Vertical Mechanical Expanders: Enormous, extremely high-volume high-quality heat exchangers are what companies like Burr Oak Tool are able to produce with massive vertical expander machines. These things can also be huge – I mean we’re talking footprints the size of a small apartment, weighing as much as 40 tons! But they are designed for speed and reliability, with quick cycle times.
• Cons: This process can cause the tube to shorten in length. There is also the friction between the bullet and the tube that can cause buckling if you are not careful. And for very small tubes, you can have higher scrap rates from damaged tubes.

Pressure Expansion: The Modern Marvel

This is a newer method that’s gaining popularity, primarily for smaller diameter tubes. High pressure pops them out instead of bullets.

• Increase Air Pressure: This includes plugging the tubes at both ends and pushing high pressure air through the tube. It happens fast and it’s tidy. It also allows for more uniform expansion and less risk of damaging the tube than the bullet method. You’ll have more tube-fin contact like this.
• Tubular Hydro-Expansion: In this method, you fill the tube with water and apply pressure to make the pipe expand. This generates an extremely strong mechanical bond and is commonly used in baseboard heater coils. But that water may not be friends with refrigerants in applications like air conditioning.
• Servo Control: Advanced pressure expansion systems are servo-driven to regulate the pressure, timing, and settings. This provides you tremendous control over what the final expanded diameter will be.

Here’s a quick rundown:

Where Do They Expand Coil In Practice?

If you work in one of these fields, coil expanding may already be taking place on the ground behind History Books_CLOSED up there.

• HVAC Systems: Consider your air-cooling evaporator coils, and your heat-releasing condenser coils. Coil stretching is critical to their performance.
• Heat Exchangers: Whether for industrial applications or cooling tubes, heat exchangers depend on a secure tube-fin bond that coil expanding helps to create.
• Baseboard Heaters: Coils in baseboard heaters tend to be hydro-expanded for snugness.

YOU HAVE TO CONSIDER EXPANDING COILS.

This is not just shoving something through a tube or pumping air in. There are things you need to think about:

• Tube Material: Copper, aluminum, stainless steel, plain steel, and Cu-Ni alloys are typical. The properties of the material that make up the mass will effect the way it expands.
• Tube Geometry: It’s not just straight tubes compared to hairpin configurations that matter. Standard modern machines will accommodate up to 60 inch coil width, and larger in special instances.
• End Finishing: Once you expand, you frequently prepare the tube ends for joining. It might be sizing belling or flaring. There’s special equipment for this as well.

The Future is Tight (in more ways than one):

The design trend for heat exchangers is small diameter tubes to increase efficiency. In other words, expansion techniques that minimize harm and preserve that all important tube-to-fin interface of the cooling coil are only going to become more vital. And in this respect, pressure expansion is a very promising avenue. The game is all about precision and control – focusing on manufacturability and performance.

So, sure, coil expanding may not be the sexiest subject at the water cooler, but it’s a basic process that informs the effectiveness and dependability of a wide range of systems. Get it right and you’re on your way to success. Get it wrong and you’re just leaving performance — and profits — on the table. Now, get out there and make those connections matter! That presentation? It’s got potential. But your knowledge 0f coil expanding? That’s what’s going to make empires, for real.”

FAQs

What is the purpose of opening a coil? The objective is to tight and secure connection ( interference fit ) between the tubes and fins of a heat exchanger or similar equipment to get good heat transfer.

Why is a good contact with the tube a must? The more contact the better, because that means more heat being conducted between the tube and the fin. Air spaces provide insulation and reduce efficiency.

What is the primary modes of expansion of the coil? There are two principal methods: expansion by mechanical means through use of a bullet, and expansion by pressure application through air or hydraulic pressure.

Pros of pressure to expand vice mechanical expansion? Pressure expansion usually results in more uniform expanded diameter, greater retention of internal tube enhancements, less risk of tube damage, and possibly higher production efficiencies.

In which industries is coil expanding very often used? The sectors of the industry focused in coil expanding are HVAC as well as heat exchanger production.

What should I take into account when choosing a coil expansion? Items such as tube size & type, process type and production volume will help narrow down the options for the optimal heat exchanger.

Are there any special processing requirements for the wires after the coils have been expanded? Sure, most of time you’re going to have to sized, belled, or flared the ends of the tube to make some joint to something else in the system.

Is expansion of the coil an important issue in the operation of a heat exchanger? Absolutely. In the development of efficient thermal contact, it is indispensable and important to focus on the thermal performance, durability, and thermal efficiency of heat exchange systems.