Online shopping has become more prominent than ever, so the needs of the packaging industry have expanded significantly. As a result, the types of heat sealers have increased to meet the ever-growing demand. While there are many different types of specialised sealing machines to pick from, there are only two popular methods for heat sealing – direct sealing, impulse sealing. Understanding the advantages and potential disadvantages of each method can help you find the right product and procedure for your specific application.

Impulse Heat Sealer

This sealing method is typically used for joining thermoplastic materials like polyurethane and polyethylene. These materials require moderate temperatures to be effectively sealed. Impulse heat sealers are used for sealing Tyvek, Mylar and many other types of bags, tube and pouch materials. Impulse heat sealing is commonly used to seal metalised, multi-layer and oxygen-barrier pouches and bags. When properly set up, you can join two sheets of heavy thermoplastic materials with ease.

When you’re looking to buy heat sealer, you’ll notice either one or two, flat or round replaceable heating elements made of Nichrome alloy or other specialised materials located at the bottom and/or top of the sealing bars. The Nichrome alloy is between a Teflon fabric and a heat-resistant, resilient rubber pad. Once the materials that need to be sealed are placed in the sealer jaws, the jaws close and are held securely by mechanical or pneumatic pressure. An electric current heats up the Nichrome alloy for a specified amount of time in order for it to reach the needed sealing temperature. The jaws will keep holding the materials even after the heat cycle is done, allowing the welded material to cool, fusing the materials completely. depending on the materials being used, impulse heat sealers require a predetermined combination of pressure, heat and time between each step.

The big advantage of this type of sealing is its safety. The high heat needed to complete the seal is only present when the jaws are closed under pressure and when the Nichrome is energised. As a result, it’s almost impossible to burn yourself when you come in contact with the jaws. While the jaws can keep some of the residual heat for a couple of hours, the temperatures never reach a high enough level to be dangerous.

Another big advantage of impulse sealing is that you have complete control over the temperature of the seal wire, the cooling cycle while the material is still in the jaws and the pressure. You also get a considerable reduction in operating costs, as the sealing element is energised for a short time, resulting in lower power consumption.

Constant Heat Sealer

Unlike impulse sealing, where the temperature goes up and down quickly, constant heat sealing provides a highly controlled temperature at the jaws, making it more adaptable to some poly-coated and thermoplastic materials. This sealing method can join two sheets of materials together, as long as the material doesn’t overheat, causing it to become weak and thin. However, constant heat sealing still uses one or two heated sealing bars, except the sealing bars are held at the same sealing temperature throughout the process. Once a constant heat sealer has reached a suitable temperature, they can maintain it at an extremely accurate level.

Even though the seal bars are hot, most modern machines feature protective barriers in order to reduce the risks of burn injuries. The constant heating and cooling cycles in impulse sealers can deform and stress the sealing element unless you use a temperature controller. Constant heat sealing, on the other hand, reduces the repetitive expansion and shrinking of the material, so it doesn’t deform or stress as much. This makes constant heat sealing a preferred option for sealing some materials.

Joint Strength and Seal Integrity

These are two important considerations in a wide range of industries, such as in medical device manufacturing. The joint strength and seal integrity can be tested in a few different ways. There can be some confusion between what constitutes seal strength and integrity. A strong seal doesn’t necessarily mean strong seal integrity. This is due to the fact that the seal passes a standardised test that doesn’t establish the microbial barrier necessary for sterile barrier device packaging. Heat-sealed pouches and bags can be tested for their ability to sustain a vacuum, pull strength, seal permeability, burst strength and other criteria. So when you buy heat sealer of any kind for medical device manufacturing purposes or any other industry that requires the joint strength and seal integrity to be top-notch, make sure it conforms to industry standards for sterile barrier testing procedures. At the end of the day, the success of your sealing processes will come down to understanding the specifics of your methods, materials and procedures used for your specific industry or application.