Leveling and filling compounds are used to level surfaces, fill cavities, and shim or set machinery. They often have filling and sealing properties. There are several basic types of leveling and filling compounds. Floor leveling resins, liquid shims and chocking compounds are used to horizontally align and set machine tools, compressors, engines, pumps, and other machinery. Surface fillers, fairing compounds, mastics, and repair compounds are used to fill large cavities and provide a smooth surface for subsequent operations. For example, mastics are often used to bond tiles to sub-flooring. 

Leveling and filling compounds use many different chemical systems. Some contain acrylics, elastomers, natural or synthetic rubbers, or epoxy resins. Others contain ceramic or inorganic cements, phenolics, formaldehyde resins, vinyl compounds, or reinforced materials with fillers, pigments, or chopped fibers. Commonly used chemical systems for leveling and filling compounds include polypropylene (PP), polysulfide, polyurethane (PUR), polyester, vinyl ester, polyisobutylene, or polybutene. Bismaleimide (BMI) thermoset resins have temperature resistance and processing characteristics similar to epoxy resins. 

There are several curing technologies for leveling and filling compounds. Typically, thermoset materials and hot melt adhesives are cured with heat or heat and pressure. Vulcanization, a thermosetting reaction, uses heat and/or pressure in conjunction with a vulcanizing agent to produce leveling and filling compounds with greatly increased strength, stability, and elasticity. Single component curing systems consist of a resin that hardens through the application of heat or a reaction with surface moisture. Two-component and multi-component curing systems consist of two or more resins and a hardener, crosslinker, activator or catalyst. Specialized leveling and filling compounds are also available.

Selecting leveling and filling compounds requires an analysis of physical, mechanical, and thermal properties. Physical properties include viscosity and gap fill, the space between the material and substrate. Mechanical properties include tensile strength and elongation, the percentage amount of deformation. Thermal properties for leveling and filling compounds include use temperature, thermal conductivity, and coefficient of thermal expansion. Use temperature is the range of temperatures to which materials can be exposed without degradation of structural or other required end-use properties. Thermal conductivity is the linear heat transfer per unit area through a material for a given applied temperature gradient. The coefficient of linear expansion (CTE) is the amount of linear expansion or shrinkage that occurs in a material without a change in temperature.  

Leveling and filling compounds vary in terms of material compatibility and features. Some products adhere to ceramics or glass, concrete or masonry, metal, paper, plastic, rubber, or porous surfaces. Other products are compatible with substrates made from composite materials, textiles, fabrics, or wood. In terms of features, leveling and filling compounds that are designed for electrical and electronics applications often provide protection against electrostatic discharge (ESD), electromagnetic interference (EMI), and radio frequency interference (RFI). Materials that are electrically conductive, resistive, insulating, or suitable for high voltage applications are also available. Flame retardant products reduce the spread of flames or resist ignition when exposed to high temperatures. Thermal compounds and thermal interface materials that use a phase change are able to absorb more heat from electronic devices or electrical components.

Leveling and filling compounds are used in many industries and applications. Some products are used in aerospace, automotive, or marine applications. Others are designed for use with electrical power products and high voltage applications. Materials that are suitable for medical, pharmaceutical and food processing applications meet requirements established by the Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA). Products that meet military specifications (MIL-SPEC) are also available. Original equipment manufacturers (OEMs) and repair, maintenance and overhaul (MRO) organizations also use leveling and filling compounds.


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