Hot Melt Glue
Hot melt glue is a thermoplastic adhesive that is supplied in solid cylindrical sticks designed to be melted in an electric hot melt glue gun. The gun uses a heating element to melt the plastic glue which may be pushed through the gun by a trigger or directly by the user applying force to the back of the glue stick. The glue squeezed out of the nozzle is initially hot enough to burn and blister skin. The glue is tacky when it is hot and hardens over time in about a minute.
Hot melt glue sticks are manufactured in several diameters for different glue guns. The most-used size has a diameter of 12 millimetres. Sticks are available in various lengths, from about 10 centimetres up but glue guns will take sticks of any length. Hot-melt and low temperature glue sticks are available for the different types of gun, and some dual-use sticks melt at low temperatures but can be used at high temperatures without degradation.
For domestic use only a few types of stick are available and they are mostly interchangeable. For industrial use there are lots of types of sticks available for special purposes, with the most common diameters being 12mm, 15mm and 45mm. Hot melt glue sticks have different open times (the working time to make a bond), varying from a second or two to several minutes. A range of values of viscosity and heat resistance are available.
Glue guns come in a low-temperature and a high-temperature version. In addition to bonding surfaces together, hot-melt glue can be used to fill gaps, but the properties that allow gap-filling, high viscosity, high toughness etc, keep it from forming an adhesive film as thin and smooth as is possible with other adhesives. Bonds must be made quickly before the glue has time to cool and harden. The glue must usually be applied accurately with the glue gun as it can not easily be spread, but it is always possible to melt and spread the glue later with a heat gun or a household iron.
Hot melt glue can surprisingly be used to assemble and repair foam models as an alternative to foam safe Cyano or UHU POR adhesive. Due to the insulating properties of the foam the hot-melt glue stays sticky for much longer than when used on wood, metal or plastics.
