What are the advantages and disadvantages of silicone heating pads, heating pads, and electric heating pads?

Manufacturers that require localized heating for their applications turn to the benefits of flexible heaters mounted on components and equipment. These heaters can provide low or high levels of heat at varying temperatures to provide the appropriate heat transfer depending on the application.
Heater materials are configurable and customizable to fit a wide range of applications. Manufacturers will need to select a heating element that provides the appropriate amount of heat, balanced heat distribution, and the ability to place multiple watt densities in the flexible heater. Two common heating elements include wire wound and etched foil.
Wirewound Elements
Wirewound elements consist of a resistance wire of a specified diameter. This wire can have a single strand or consist of several strands that are braided together and placed on a fiberglass core. This wire is then vulcanized onto a neoprene substrate or nylon reinforced silicone rubber as the material can range in thickness from 0.032 inches. The resistance wires are wound into a specific pattern so that they are evenly spaced throughout the substrate layer.

Example of manufacturing a wirewound element flexible heater.

Wirewound elements have many benefits. These elements can provide a higher level of physical strength, making them ideal for heating applications where there may be frictional forces on the flexible heater. Flexibility is another major advantage of wirewound flexible heaters. They can easily handle tight radius bends because the wire can be wound and placed in long strips for applications that require larger heaters.
Wirewound elements are the original element of flexible heaters and are a suitable choice for manufacturers seeking larger silicone heaters. Today, manufacturers still use this type of element for a variety of applications, including food heating equipment as well as heating pipes.
Etched Foil Elements
Etched foil is a newer technology compared to the wirewound elements that have been used for the past 40 years. The main difference of etched foil is that it is not composed of a metal wire. Instead, much like a circuit board, it is a thin alloy metal with resistive properties that is acid-etched into the substrate material. The foil can be as thin as 0.005 inches and looks similar to aluminum foil. Manufacturers of flexible heaters will form the metal foil into rectangular flat shapes that are placed in a pattern with a width of at least 0.10 inches.

Example of a manufactured etched foil element flexible heater.

Etched foil elements can offer particular advantages to manufacturers seeking thinner flexible heaters in applications where size and weight are serious issues. They can be used for both short and long run production runs because these elements allow for higher power density and the ability to heat quickly.
Although etched foils require a wider width to provide the same wattage and resistance as wound elements, these elements can be placed closer together without contact and shorting. Therefore, etched foils can be in tighter spaces on the substrate. Finally, manufacturers can achieve more precise temperature control with complex heat distribution characteristics.
Alloys for Heating Elements
Certain metal alloys have both thermal conductivity and resistivity, making them suitable for use as heating elements. Alloys consist of a base metal and other trace metal elements that are added during a specific process to change the mechanical, structural, electrical, thermal, and conductive properties of the base metal. The inherent properties of the alloy may be increased, such as greater corrosion resistance or electrical conductivity, or impurities may be reduced. Common alloys used in heating elements include stainless steel, nickel-chromium, copper-nickel, or Inconel 600.
304 Stainless Steel
Stainless steel 304 is a metal alloy composed of chromium and nickel as it is also combined with carbon. It can be formed using a variety of techniques including hydroforming. The main benefits of stainless steel are excellent heat transfer capabilities, corrosion resistance, and ease of fabrication. It has a heat capacity of 20°C and a maximum mechanical temperature of 420°C.
Nickel-Chromium
Nickel-Chromium contains a percentage of nickel and chromium. The addition of chromium increases resistance as well as corrosion resistance to high temperatures, making this alloy suitable for wire wound elements due to its ductility and strength. This alloy has a maximum operating temperature of 1100°C and a heat capacity of about 20°C.
Copper-Nickel
Copper-Nickel has incredible corrosion resistance as well as electrical resistance. This alloy is often sought after due to its good machinability. Although it is more suitable for 400°C heating elements, it has a maximum mechanical temperature of 600°C. It also offers a heat capacity of 20°C.
Inconel 600
Inconel 600 alloy is best suited for applications that require high corrosion and electrical resistance, and it is also non-magnetic, which makes this alloy ideal for flexible heater elements used with products susceptible to magnetism, outdoors, and in wet environments. It contains a combination of nickel, chromium, and some iron. It also has high chemical resistance. The alloy has a heat capacity of 20°C and a mechanical temperature of 1100°C.
Use the Correct Heating Element for Your Application
The best way to select the right heating element for the application is to determine the required watt density, desired heat transfer and preheat, the operating environment, and the size of the heater required. If a manufacturer needs a large, solid heater with a tight bend radius and multiple watt densities throughout, a wirewound heater can do the job. For applications that require a thin, flexible heater with fast heating and good overall heat transfer capabilities, an etched foil element can be used.