Flexible Heaters: Mounting Method Matters
Designed to conform to the operating environment and deliver heat where needed, flexible heaters are fitted into applications where other heaters would falter. When selecting a flexible heater for process heating, also think about how the heater will be mounted in the application.
Industries around the world will experience cold interior operations or outdoor environmental temperatures that can impact the performance of equipment. For example, airline foodservice operations must keep finished meals at a food-safe temperature in all weather conditions until the meals are served once the planes are in the air. In other applications, the equipment, components and products must be maintained within a specific temperature range to prevent equipment malfunctions, device failure or spoiled products.
Flexible heaters provide heat directly to the necessary components, no matter their shape and size. They can be flexed and wrapped around surfaces to provide heat to specific components. Also, flexible heaters are lightweight, so they do not affect moving parts in applications where the component’s weight would factor into how it functions. Offered in many styles such as silicone rubber heaters, polyimide or Kapton film heaters, and transparent materials, flexible heaters are rugged enough to withstand moisture and chemical exposure.
Secure attachment of the flexible heater is paramount. Some applications may require the flexible heater to be detachable on demand. Other equipment requires a permanent bond and superior heat transfer capabilities so that the component stays at a constant temperature. This article will explore mounting methods, their benefits and the types of applications where a specific mounting will be used.
Types of Flexible Heater Mountings
Manufacturers use four mounting methods for flexible heaters:
- Pressure-sensitive adhesives (PSA).
- Factory vulcanized mounting.
- Silicone room-temperature vulcanizing (RTV) bonding.
- Removable mounting attachments.
Some mounting methods are dependent on the level of heat generated while others must provide heat transfer capabilities.
1. Pressure-Sensitive Adhesives
Using a pressure-sensitive adhesive involves having a flexible heater with an adhesive surface that is preattached. The protective backing is removed just before the flexible heater is placed on the component. It may have a single side of adhesive or a double-sided coating.
PSA mountings for flexible heaters are suitable for smooth, clean surfaces or for slightly curved surfaces. It is the most economical and fastest mounting method available.
If PSA is used with a silicone rubber heater, a rubber roller should be applied to avoid trapping air bubbles underneath the adhesive. Such air pockets can cause the flexible heater to experience hot spots or undergo premature failure. High temperature PSAs should be requested for applications that exceed 300 to 400°F (149 to 204°C) for heaters made from Kapton or other polyimide films, or 400 to 500°F (204 to 260°C) for silicone rubber heaters.
To control the viscosity level of the product, a flexible heater can be used. Lower viscosity can allow the liquid and product to flow better in processing pipes or liquid-dispensing machines.
2. Factory Vulcanized Mountings
Factory vulcanized mountings involve taking the flexible heater and mounting it to the component using a vacuum oven. The flexible heater becomes adhered permanently to the component.
Factory vulcanized mounting is suitable for metal surfaces such as stainless steel, anodized aluminum or black anodized aluminum. During mounting, the flexible heater (silicone rubber type, for example) fills in the microstructure of the metal material. Most often, the component mounting will be performed in-house before the finished product is sent to the user for further component installation into equipment.
Factory vulcanized methods are appropriate when good heat transfer capabilities are needed. Because the flexible heater itself is fastened to the component — without anything obstructing the contact point — good heat transfer results. Also, the bond is strong and permanent.
This method can be used for applications where the temperature will reach a maximum of 500°F (260°C) when using a silicone rubber flexible heater. It also is suitable for a heater made from Kapton or other polyimide film that reaches a maximum temperature of 300°F (149°C).
3. Silicone Room-Temperature Vulcanizing
Silicone RTV involves adhering the flexible heater to the surface of the component by using a silicone adhesive that is both room temperature and ambient humidity cured. Both one-part adhesives and two-part adhesives (consisting of a resin and a catalyst that are mixed together) can be used. The adhesive is applied to the silicone rubber heater, and then the heater is positioned onto the part. A small roller is run across the heater to remove air pockets and securely adhere the heater.
Silicone RTV is suitable for components used in field applications where high temperatures will be produced during operations. This mounting method can be used for heaters that will provide up to 5 W/in2 and temperatures of 500°F (260°C). It offers superior flexibility, and it is resistant to harsh weather, mildew, mold and humidity. When using the silicone RTV that is a two-part adhesive system, this mounting type is suitable for large flexible heater applications.
4. Removable Heater Mounting Attachments
One of the last things that a manufacturer wants to do is attach a flexible heater with a permanent mounting to a component where a detachable mounting is more suitable. Knowing which are permanent and which are detachable will allow a user to select the right mounting for the appropriate length of time. Removable mounting attachments allow a flexible heater to be taken off easily when a permanent attachment is not viable or desired. These mountings may consist of:
- Hook-and-loop fasteners.
- Snap grommets.
- Nylon straps.
- Silicone straps.
Removable mounting attachments often are preferred for flexible heaters that will be attached to components that may have sharp cutouts or rough edges. These attachments prevent the heater from chafing against the component’s surface, so the heater does not become damaged or slip off. Removable mounting attachments are suited for applications where the flexible heater can be attached quickly because they are easy to use. One thing to keep in mind is that some removable mounting attachments with straps may become elongated after repeated use. In addition, foreign dirt and debris such as hair, clothing fibers or dust can become attached to hook-and-loop fasteners.
A silicone flexible heater can be placed on flat surfaces as well as for applications where a large heater is needed that offers multiple watt densities. It also can handle higher temperatures while in humid and outdoor environments.
Benefits of Using the Right Mounting Method
Using a mounting method that best suits the application can prevent a failure in working components and operations. A user also must take into account the working environment where the flexible heater will be used. Sudden temperature changes, rain, snow and extreme sun can impact how well the flexible heater will remain attached and whether the mounting method will give the suitable lasting bond. The following scenarios suggest the mounting types that would be best suited for the given application.
Heat Transfer Capabilities. There may be applications where a company requires the maximum amount of heat to be transferred from the flexible heater to the component. In these instances, the flexible heater must have as much contact as possible with the surface area. The mounting method selected should offer unlimited heat transfer capabilities based on the desired temperature that is required.
For these applications, factory vulcanized mountings have the best maximum heat temperatures of up to 500°F. They also do not rely on any bonding adhesives or mounting attachments to be put into place. Another method that offers good heat transfer capabilities is a PSA mounting.
High Temperature Capacity in Outdoor Applications. Outdoor applications will experience moisture conditions that can cause mold or mildew. The user also may desire a mounting method that is not negatively impacted by the ultraviolet sunlight, and one that can withstand temperature fluctuations or humidity. In some uses, the mounting may need to offer more thermal stability during high temperatures as well as flexibility.
A silicone RTV is suited for outdoor applications with fluctuating temperatures and high generated heat. This mounting method also is suitable when the component will be stored for long periods of time. The room temperature bonding adhesive has a lifespan of up to 40 years.
Rough and Sharp Surface Edges. Certain flexible heaters will need to be attached to edges that are irregular in shape and have sharp margins. When looking at mountings, the user should consider a mounting that will not adversely affect the flexible heater when attached to the rough surface. They also must consider the amount of space available for the mounting to be successfully attached.
Mounting attachments such as hook-and-loop fasteners, grommets and straps can help a user attach the heater at the right location. Using such mounting materials, the heater will not chafe against the rough surface that could damage the heater components. In addition, certain attachments such as nylon straps can withstand pushback pressure of up to 35 lb.
Uniform Surfaces and Lightweight Applications. There will be applications where the weight of the flexible heater can impact how a component works in operations. Even the slightest added weight from a separate mounting attachment could significantly hamper the part. In these instances, PSA mountings offer ease of use where a lightweight and flexible attachment is desired. The adhesive is placed on the heater with a uniform thinness. (By contrast, a silicone RTV is applied using a brush, and the curing bond adhesive may have thick and thin spots.)
The one thing to keep in mind is that PSA mountings must be applied to smooth, clean surfaces. If the environment generates a lot of dirt, oil, grease or grime that cannot be removed, then the pressure-sensitive adhesive may not attach fully.
Industry for Flexible Heater Mountings
Among others, the aerospace, medical-device production and foodservice markets use flexible heaters on products and equipment of varying shapes, sizes and operations. The type of mounting method is important to ensure a tight bond to the heater while not preventing the full use of the product or component. Here are some of the common types of mounting methods seen in these industries.
Medical-Device Manufacturing. Flexible heaters with sensors are used extensively in the medical industry in a range of devices. Surgical tools, small catheters, blood analyzers, incubators and hemostasis equipment contain silicone rubber heaters, transparent heaters and heaters made from Kapton or other polyimide films. Mountings often used in the medical device industry include pressure-sensitive adhesives as well as factory vulcanization.
Aerospace Industry. The aerospace industry relies on flexible heaters to prevent electronics and probes from becoming damaged due to moisture, humidity and environmental temperatures. Commonly, these heaters are used for instrument panels to dry out the electronics, de-ice probes or defog infrared and security devices. PSA heater mountings and removable mounting attachments typically are used based on the specific application.
Foodservice Industry. When it comes to the foodservice industry, keeping food at an optimal temperature to provide hot meals is desired. Flexible heaters will be used in places that require constant, low-to-medium temperatures during the work period while offering chemical and moisture resistance. PSA mounting often is used for these flexible heaters to ensure a tight seal.