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mica band ceramic heaters

What Is the Difference Between Mica Band Heaters and Ceramic Band Heaters?

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Thermal Corporation infographic explaining the differences between mica band heaters and ceramic band heaters

Home > Blog Archive > Category: Industrial Heating Technology > What Is the Difference Between Mica Band Heaters and Ceramic Band Heaters?

 

The Differences Between Band Heaters: Mica Bands vs Ceramic Bands

 

There are two types of band heaters that Thermal Corporation manufactures: mica band heaters and ceramic band heaters. There are strong points with each type, and the general differences are laid out below:

Temperatures

Ceramic band heaters can withstand a higher temperature than mica band heaters. Ceramic band heaters have a maximum operating temperature of 1200⁰F vs a maximum operating temperature of 800⁰F for a mica band heater.

Heater Life

Ceramic band heaters typically (but not always) have a longer life expectancy. This is due to the coiled resistance wire that is fed through ceramic blocks (called knuckles) vs. the thin resistance ribbon that is used in mica band heaters. The coiled resistance wire has a smaller ratio of surface area to internal cross-sectional area and thus doesn’t really oxidize and burn through as fast as the ribbon.

Watt Density

Mica band heaters can have a higher watt density than ceramic band heaters. Because the resistance ribbon in a mica band heater is tightly clamped between pieces of mica, there is better heat transfer from the ribbon to the exterior surfaces of the heater. Also, in general, mica band heaters will have less unheated area than a ceramic band heater, especially in smaller band heaters.

Customizability

Mica sheets can be cut into custom shapes and sizes, whereas ceramic band heaters are limited by the size of the knuckles. Because of this, mica band heaters are also much more customizable when it comes to dimensions. Ceramic band heaters are limited to 1/2″ width increments, whereas mica band heaters can be any width within the upper and lower limits of at least 1″ by 1″, depending on the specific mica band configuration.

Pricing

Ceramic band heaters are more expensive than mica bands. The ceramic knuckles are quite expensive when compared to the thin sheets of mica that mica bands are constructed from. However, this difference may be compensated for by the increased efficiency of the ceramic band heater.

Insulation Options

Standard ceramic band heaters have one layer of 3/8″ thick ceramic paper insulation over the knuckles, and then a stainless-steel outer sheath that reflects heat back into the process. The “Heat Saver” ceramic band insulation option has one layer of 1/8″ thick ceramic paper topped with a reflective stainless-steel sheath, and then an additional 2 layers of 3/8″ thick paper, topped by an additional sheath. All of this insulation yields a higher efficiency heater vs. a mica band heater. Ceramic band heaters also offer a “Vented Outer Sheath” option, seen in the image below. This allows heat to escape from the process, if needed for your application.

Closing Remarks

In conclusion, you just need to examine your heating process and specific needs for a band heater and decide between a mica band heater or a ceramic band heater. If we can be of any assistance, please let us know. Mica bands are cheaper, can have higher watt density, and are more easily customizable. Ceramic bands are more efficient, can withstand higher temperature, and generally last longer.

 

Have Questions?

Contact our engineers at (800) 633-2962 x152, or by email at engineering@thermalcorp.com.

 

Written by Kyle Otte
Edited by Shelby Reece
Date Published: 01.14.2020
Last Updated: 01.14.2020

 

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cooker band

Case Study #167: Heating Too Slow? Check Your Process Set-Up

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Home > Blog Archive > Category: Case Studies > Case Study #167: Heating Too Slow? Check Your Process Set-Up

Case Study #167

I once worked with a customer that manufactured flexible fishing lures. They had two set-ups for creating the lures- an old system and a new system. The two systems were virtually identical except for the fact that the newer system, for which they purchased a band heater, heated up too slowly.

diagram of Thermal Corporation one-piece mica band heater next to cooker

Initially, I was led to believe that they were using a two-piece mica band heater. If they had been using a two-piece heater, I would have suspected that the heater was wired incorrectly. There are two ways to verify this.

Two Ways to Determine if a Two-Piece Heater is Wired Incorrectly

  1. Measure the voltage across each heater half. The voltage on each half should match the stamp on the heater. This particular heater was a 120V heater. So for this case, they should both have read 120V. If 60V was read, then the heaters were wired in series rather than in parallel. This is a common issue we see. (See our blog post on “Should Your Heaters Be Wired in Parallel or in Series?” for more information on this topic.) If the voltage is half of the correct voltage, the wattage output will be 25% of the stamped wattage.
  2. Visually inspect the wiring. One terminal, or lead, of each heater half should be tied to the black 120V wiring. The other end of the heater half should be connected to the “white” neutral wiring.

If the heaters measured the correct voltage, what would you check next?

Turn off the power and disconnect the power leads going to one end and measure the resistance of each heater half. The resistance should be approximately: R = V2 / W

In this case, the voltage (V) was 120V, and the wattage (W) was 1500W as stamped on the heater.

HOWEVER, I found out that this was a one-piece heater and not a two-piece heater. Therefore, what should I check first? If you said, the heater resistance, then you are correct. Before I made this measurement, I asked the following question: Was the LED light on the controller ON all the time?

Why did I ask this question?

The light was ON all the time. If the light was not ON all the time, then the heater was not turned on the entire time as the process heated. This would indicate a possible programming error with the temperature controller.
When I talked to a technician at the customer’s plant, it was mentioned that the temperature controller indicated that the temperature quickly went to 380°F, but the actual process took about 20 to 30 minutes to get hot. I asked the customer to describe the process in more detail. What would I see if I was at the plant looking at the process?

The Heating Process

The heating process was described to me as such: the heater and thermocouples were covered in fiberglass. On the older system, a thermocouple probe is slipped under the edge of the heater. On the new system, a shimstock thermocouple is slipped under the edge of the heater.
The thermocouple probe only has one line contact with the heater and the cooker, like this diagram:

diagram showing thermocouple probe with one line contact with a Thermal Corporation mica band heater and a cooker

Who knows for sure what was being measured?

Now that the customer is using a shimstock thermocouple, it might look like this:

diagram showing a shimstock thermocouple in contact with Thermal Corporation mica band heater and a cooker

It may very well be that the shimstock thermocouple is primarily measuring the heater temperature. In any case, both of these configurations are very poor setups.

The Thermal Corporation Recommendation

We recommended that they place the shimstock thermocouple in the heater gap, up against the cooker. Then, place some high-temperature insulation on top of the thermocouple so when the band is tightened, the strap screw would push the thermocouple up against the cooker securely. This ensures the temperature sensor is measuring the cooker temperature, not just the temperature of the heater.

After these changes were applied to the customer’s process, it corrected their problem, and looked something like this:

diagram of improved heating process with shimstock thermocouple and Thermal Corporation mica band heater

Written by Jim Dixon and Shelby Reece
Edited by Kyle Otte
Date Published: 11.05.2019
Last Updated: 11.05.2019

ceramic heater differences

Differences Between Ceramic Band Heater Insulations

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Home > Blog Archive > Category: Thermal Corp Vlog > Differences Between Ceramic Band Heater Insulations

Thermal Corporation offers 3 types of insulations for our ceramic band heaters. In this video, Kyle Otte explains the differences between them.

Click here to view our ceramic band heater configurations.

Contact us now to Request a Quote!

 

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Written by Kyle Otte
Filmed and Edited by Shelby Reece
Date Published: 10.18.2019
Last Updated: 10.21.2019

Dual Voltage Heaters

Why Users Should Almost Never Use Dual Voltage Heaters

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Home > Blog Archive > Category: Industrial Heating Technology > Why Users Should Almost Never Use Dual Voltage Heaters

What are Dual Voltage Heaters?

diagram of Thermal Corporation dual voltage mica band heater

Some heaters are designed to operate from more than one voltage. These are referred to as Dual Voltage heaters. One of the voltages is always twice the other voltage, such as 240 volt/480 volts. These heaters have three terminals or wires. The terminals are connected one way for 240 volts and another way for 480 volts. (Inside are two separate heaters. For the smaller voltage, the heaters are connected in parallel. For the larger voltage, the heaters are connected in series.)

What are the advantages?

These heaters offer an advantage to OEM manufacturers when building equipment. By using these heaters, the OEM can put Dual Voltage heaters on the equipment without knowing which voltage their customer will use. If they did not use Dual Voltage heaters, they would end up building the equipment for one voltage and then if their customer wants the other voltage and they would have to change all the heaters. With these heaters, the OEM just provides documentation on how to connect up the heaters for each voltage. Thus, many heaters shipped on OEM equipment are dual voltage heaters. Dual voltage heaters are more complex and cost more than single voltage heaters, but still make sense for OEM manufacturers.

Failed Heaters

When the equipment is installed at the customer’s facility, it is connected to the appropriate voltage. Eventually one of these heaters fails. Now, what should the replacement heater look like? Should it be a dual voltage heater? Usually, when then equipment is installed, the voltage very rarely changes. Now, in this case, a heater of similar configuration but operating only from a single voltage should be used. Many times, the failed heater is taken to the purchasing agent and the agent is requested to buy a heater just like this heater.

Conclusion

If a user purchases a dual voltage heater rather than a single voltage heater, the dual voltage heater will be more expensive, more non-standard, more complex and because of the complexity, have a shorter life. So for a lower cost and a more reliable heater, order a single voltage heater rather than a dual voltage heater.

Looking for a specific heater? Click one of the links below to browse our product line.

Cartridge Heaters

Mica Band Heaters

Strip Heaters

Rectangular Band Heaters

Ceramic Band Heaters

Thermocouples & RTDs

Custom Heaters

Written by Jim Dixon
Edited by Shelby Reece
Date Published: 05.09.2018
Last Updated: 09.06.2019

case study

Case Study #075: How to Improve the Life of a Mica Band Heater

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Home > Blog Archive > Category: Case Studies > Case Study #075: How to Improve the Life of a Mica Band Heater

Case Study #075

A customer phoned our engineering department here at Thermal Corporation complaining that he was experiencing very poor life with a mica band heater– a life of only one week! He explained that the application was to heat a flange that was attached to a gate at the end of an extruder. The extruder was adding a layer of nylon to wire-in cross-head die. The flange sat between the gate and the cross-head die. (The cross-head die had its own separate heater.) The flange also had a thermocouple, extending radially, out of it. The application looked something like the image you see below.

diagram of the heater, flange, gate, cross-head die, and thermocouple application

The flange had a width of 1″ or so and a diameter of 5″. The mica band heater was our configuration 514 with a hose at 90° from the gap. This gap measured 1/2″ to accommodate the thermocouple. The heater the customer had been using had 675 watts at 240 volts. The watt density of this heater was 66.5 watt/in2 and the operating temperature was 520°F.

What questions should we ask? What could we recommend?

Based on the diameter and operating temperature, the maximum watt density for this heater should be in the mid-30’s. The watt density the customer was getting was twice that (at 66.5 watts/in2). Earlier, Thermal had supplied the heater with 500 watts (49.3 watts/in2), but this heater did not last either.
By looking carefully at the flange width, we noticed that the width of the flange was about 11/4“. The mica band heater we had been supplying had only a 1” width. Next, we looked at the configuration of the mica band. A configuration 500, while not providing much more heated area, did provide a lower ribbon, or wire watt density. Then, we examined how much heat was required to control the process. Looking at the ammeter (a meter which displays the current being drawn by the heater), we saw that the heater was staying on for a total of 8 seconds. Then, it was turning off for only 6 seconds before turning on again. This means that the heater was on for 8/(6+8)%, or 57%, of the time. Thus, the heat required to control the process was 57% of the 675 watts, or 385 watts. To provide a safety margin, we would want to add 15% or so more heat to this minimum in the heater.

Therefore, with the wider width and the change in configuration from 514 to configuration 500, we could get 450 watts in the heater with a watt density of 33.25 watts/in2. We made a sample of this configuration for the customer to try.

Additional Notes

We also noticed that in the process, following the cross-head die, was a laser sensor used to measure the diameter of the nylon coating. Because the smoke from the extrusion process got on the laser sensor lens, the customer had installed a fan. The purpose of this fan was to blow the smoke away from the lens. As it turns out, the fan was blowing directly on the heater and the gate it was attempting to heat. This increased the heat loss and the heat required from the heater. The customer agreed to place a shield, if needed, between the fan, and the heater and gate. This would most likely permit the wattage and watt density to be further reduced.

Written by Jim Dixon and Shelby Reece
Edited by Kyle Otte
Date Published: 07.19.19
Last Updated: 09.03.19

temp vs heat loss in heater

Temperature vs Heat Loss In a Heater

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Home > Blog Archive > Category: Industrial Heating Technology > Temperature vs Heat Loss In a Heater

We often get questions regarding how much power (or wattage) is needed to maintain a process at a certain temperature. That is a complex question. In this article, we will discuss the general concepts that are used to determine wattage needs.

Energy Balance

First, we start with a simple energy balance: Ein = Eout

Ein is the rate of energy coming into the system. This is the wattage that is generated by the heater when an electrical current is passed through a resistance element inside the heater. Every heater is stamped with a wattage and a voltage. So, energy coming into the system is a variable that can be controlled.
Eout is the rate at which energy leaves the system. Eout is often what we want to determine because we can control Ein (the rate of energy coming in) and set it equal to this value. This consists of energy that is input into the process and leaves the system, e.g., plastic is melted, formed into a part, and then ejected from a machine. The heat that is absorbed by that plastic leaves the system. Eout also consists of power that is lost to the surroundings and is not used by the process. We call this waste heat. So, we need to determine both of those components. Power lost to the atmosphere can be approximated using heat loss graphs that are readily available online. In most cases, a wide variety of surface conditions, temperatures, and insulation thicknesses are plotted on these graphs. The end result of this calculation should yield a rate of energy loss (typically in watts per square inch) that is lost to the surroundings.

Rate of Energy Consumption

Next, we’ll look at the rate of energy consumption of the process. This is often much more complicated to determine.

For Example…

Let’s look at a process where we heat a chunk of polypropylene plastic from a temperature of 100°C to melting temperature (175°C). We are going to process one of these blocks of plastic every 15 minutes. The correct equation is:

where, E = power required in watts m = mass(kg) (25 in our example) cp = specific heat (Joules/kg°C) (1,920 in our example) = change in temperature (°C) (75 in our example) t = time in seconds (900 in our example)

Using the numbers above, we calculate that E = 4,000 which means we need 4,000 watts for this process. We can now add this 4,000W to the heat lost to the surroundings that we found on the approximate heat loss curve. That will give us a total steady-state wattage that we need to keep our process functioning.

Some Important Notes

  • Start up time is often an important consideration for selecting heaters.
    • Using the simple example above, if we wanted to heat the same mass of polypropylene from room temperature to melting temperature in the same amount of time, we would need more wattage.
  • No matter what the calculations say, it is a good idea to add 20% to this power requirement as a “safety factor” when sizing heaters. Why?
    • It is always good to allow for some error in the calculations.
    • Heater lifetime is improved if the heater does not run 100% of the time. The ideal run time, using a short cycle time, is 75% – 80%.

Written by Kyle Otte
Edited by Shelby Reece
Date Published: 04.17.2019
Last Updated: 01.29.2020

electrical drawing

Case Study #204: How to Determine Amperage for Heaters

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Home > Blog Archive > Category: Case Studies > Case Study #204: How to Determine Amperage for Heaters

Case Study #204

A customer called in and wanted to know what amperage he would be using on a machine with six heaters. The power supply was 460V, 3 phase power, and the heaters were wired in a delta configuration with two heaters on each branch. (See image below)

diagram of heaters wired in delta configuration with two heaters on each branch

To Determine the Amperage:

6 heaters (R1 – R6) each at 230V, 1,000W

The resistance of each heater is calculated using the following formula:

R = V2 / P

So, the resistance of each heater equals 2302 / 1,000 = 52.9Ω

R1 = R2 = R3 = R4 = R5 = R6 = 52.9Ω

Now, we wire two of these heaters in series between two legs of 460V, 3 phase power. Each leg looks like:

diagram of one leg of 460V, 3 phase power

In series, we can add resistances and simplify the circuit to look like this:

diagram of a simplified circuit of 460V, 3 phase power

Now, finding the current is easy.

I = V / R
I = 460V / 105.8Ω
I = 4.35A

So, the amperage is 4.35A for each leg.


Have a technical question about a heating application? Shoot our engineering department an email today at engineering@thermalcorp.com.


Written by Jim Dixon and Shelby Reece
Edited by Kyle Otte
Date Published: 07.11.2019
Last Updated: 09.03.2019

heater drawing

Case Study #013: The Current In a 3-Phase Band Heater

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Home > Blog Archive > Category: Case Studies > Case Study #013: The Current In a 3-Phase Band Heater

The Current In a 3-Phase Band Heater

We had a call from a customer questioning how to calculate what the current would be for each wire in 3-phase band heater. Here is the band heater breakdown: 480V, 3,000W, 3-phase. The heater looked something like the diagram you see below.

Diagram of Thermal Corporation 3-phase band heater

Inside this heater, it was wired in a “wye” configuration. The wye configuration wiring diagram would look like:

diagram of a wye wire configuration inside the 3-phase band heater

The resistance of each winding card inside the heater is equal, giving us a balanced load. Therefore, each phase will handle 1/3 of the load. 1/3 of 3,000W is 1,000W.
480V is the voltage between the 3 phases (line to line). The voltage between any phase and the ground (line to ground) is:

480V divided by square root of 3 equals 277V

Now that we know the wattage and voltage in each leg of the 3-phase power, we can calculate the current.

Current = Watts / Volts = 1,000W / 277V = 3.6 Amps in each leg

Was This Case Study Helpful?

Let us know! We will continue to post more case studies offering solutions to your questions on different industrial heating applications.

Have a different question?

Did this post not answer your question? Contact our engineers and we will be happy to answer any questions you have regarding industrial heaters, applications, or industrial heating technology! Shoot us an email, phone call, or instant chat message now!


Written by Jim Dixon
Edited by Shelby Reece and Kyle Otte
Date Published: 10.07.2019
Last Updated: 10.08.2019

watt density on heater

What is Watt Density and How is it Related to Heater Life?

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Home > Blog Archive > Category: Industrial Heating Technology > What Is Watt Density and How Is It Related to Heater Life?

Watt Density: Basic Definition

Watt density is a measure of the rate of heat being transferred through the surface of the heater.

For example, if you were to draw a 1″ x 1″ square on the surface of the heater, how much power (or heat) would pass through that area? The answer is the heat per unit area, so basically the watts per square inch.

So, How Is it Related to Heater Life?

Basically, the higher the watt density, the higher the temperature is inside the heater (assuming all other variables are constant). As the temperature inside the heater increases, the materials inside the heater are operating closer to their breaking point. This results in shorter heater life.

Mica Band Heaters

For satisfactory heater life of mica band heaters, the following density should be maintained:

Heater DiameterWatt Density
Less than 3"Less than 50 watts/square inch
Between 3" and 6"Less than 40 watt/square inch
Between 6" and 10"Less than 35 watts/square inch

Cartridge Heaters

For satisfactory heater life of cartridge heaters, the density should be less than 200 watts/square inch.

Ceramic Band Heaters

For satisfactory heater life of ceramic band heaters, the density should be less than 35 watts/square inch.

Higher operating temperatures require a lower density for equivalent temperatures inside the heater and equivalent heater life.

watt density of a Thermal Corporation ceramic band heater is less than 35 watts per square inch


Written by Jennifer Taylor
Edited by Shelby Reece
Date Published: 09.25.2018
Last Updated: 09.06.2019

Ceramic Band Heater

What Are Vented Band Heaters?

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Home > Blog Archive > Category: Industrial Heating Technology > What Are Vented Band Heaters?

What are Vented Band Heaters?

image of a Thermal Corporation vented band heater

Vented band heaters are used for high temperature heating and cooling extrusion processes.

Standard Ceramic Band Heaters

Typical ceramic bands contain an extra layer of insulating ceramic paper laid on top of the ceramic knuckles with the intention of focusing heat into the extrusion barrel or process. In fact, Thermal Corporation offers a “Heat Saver” option on ceramic bands which is an additional layer of thicker ceramic paper that increases efficiency and heat retention. Typical ceramic bands have a polished stainless steel outer sheath that reflects heat back into the process and slows radiation losses. In short, most ceramic band heaters are designed to keep heat in and minimize heat losses to the atmosphere.

Vented Band Heaters

diagram of a Thermal Corporation vented band heater

Vented bands reverse this equation. The goal is no longer to solely focus heat back into the process, but rather to maintain heating capability while also allowing heat to easily escape when cooling is needed. In pursuit of this goal, vented band heaters have no ceramic paper insulation. There are no added layers to trap heat. Additionally, the outer sheath has holes cut in it to allow maximum air flow for heat removal.

How Do We Achieve This?

Thermal Corporation uses a unique triangle type pattern for the vented outer sheath. This allows for a large percentage of open area across the heater, which speeds cooling, while also maintaining a rigid construction. Additionally, holes can be built into the heater itself allowing air to reach the barrel directly. Note that adding holes to the heater will limit the total wattage available.

Click here to contact Thermal Corporation regarding your specific application requirements.

Written by Kyle Otte
Edited by Shelby Reece
Date Published: 03.18.2019
Last Updated: 09.03.2019

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