How does an oily release agent form a stable release film between high-strength concrete and the steel mold?
Publish Time: 2026-01-15
In the production of precast concrete components, especially products like pipe piles, square piles, or hydraulic sheet piles that require extremely high geometric precision and surface quality, the demolding process is often a crucial step that determines success or failure. High-strength concrete, due to its low water-cement ratio and dense cementitious materials, easily adheres strongly to the smooth surface of the steel mold during the hardening process. Improper demolding can result in scratches and pitting, or even chipped edges or the entire pile becoming stuck in the mold, causing multiple losses in time, materials, and mold. A high-quality oily release agent achieves clean and efficient one-time demolding by constructing an "invisible yet indestructible" barrier between the concrete and the steel mold.This release film is not simply formed by applying a layer of oil to the mold surface; it relies on a precise chemical formula and film-forming mechanism. Oily release agents typically use high-purity mineral oil or synthetic oil as a base, supplemented with film-forming aids, lubricating components, and surfactants. After being evenly sprayed or rolled onto the clean, dry inner wall of the steel mold, the solvent evaporates rapidly, leaving a very thin yet continuous oil film. This film possesses excellent hydrophobicity and low surface energy, preventing moisture and cement paste from the fresh concrete from wetting the steel mold surface, thus physically blocking the chemical bonding and mechanical interlocking between hydration products and the metal.More importantly, this film must possess sufficient cohesive strength and thermal stability. During the high-frequency vibration process after concrete pouring, the paste exerts a violent impact on the inner wall of the mold; in the subsequent steam curing stage, the temperature can rise to tens of degrees Celsius or higher. Inferior release agents are easily washed away or decomposed at high temperatures under such conditions, leading to localized failure. High-performance oily release agents, through molecular structure design, possess excellent heat resistance and shear strength after film formation, maintaining complete coverage even under harsh process conditions, without cracking, migrating, or emulsifying.Furthermore, a skillful balance of lubrication properties is also crucial for successful demolding. The release film needs to be sufficiently "slippery" to reduce frictional resistance during demolding and prevent tearing of the pile surface due to concentrated tensile stress; however, it cannot be too "slippery" to avoid affecting the early support stability of the concrete or causing segregation. High-quality release agents achieve a delicate balance between smooth demolding and stable molding by controlling the film thickness and adhesion characteristics. At the moment of demolding, the pile and mold separate naturally, like "the moon emerging from the clouds," leaving a smooth, mirror-like surface with sharp, distinct edges.It is worth noting that this isolation effect also extends to improved long-term production efficiency. A single coat can support multiple uses, reducing downtime for touch-ups; minimal steel mold residue after demolding facilitates quick cleaning and extends mold life; more importantly, the increased yield directly reduces waste disposal costs and rework risks. For precast plants with large daily output, this small "drop of effort" accumulates into significant benefits.Of course, truly high-quality release agents must also consider environmental friendliness and compatibility—they must be free of harmful aromatics, have a low odor, not affect the bond strength with reinforcing bars, and not interfere with the adhesion of subsequent pile splicing or anti-corrosion coatings. It's not just a process aid, but also an integral part of green and intelligent manufacturing.In summary, the reason why the oily release agent can ensure the one-time molding of high-strength concrete components without sticking to the mold is not through crude isolation, but through a dynamic protection system built with molecular-level intelligence. Silently resting on the steel mold, it quietly dissolves the strongest adhesive force at the critical moment of initial concrete setting. When straight, smooth piles are successfully extracted, the flawless surface is the most powerful silent declaration of this "invisible film"—in the precise world of industrial manufacturing, sometimes the most powerful force comes precisely from the gentlest separation.
