The forming of reinforced concrete covers primarily involves precast casting and curing. The process begins with mold preparation, typically using steel molds or high-strength composite material molds. A release agent is applied to the inner wall to ensure smooth demolding after forming. Cement, aggregates, and mixing water are measured according to the design mix proportions and thoroughly homogenized using a forced mixer. The concrete is then poured into the mold, and a vibrating table or immersion vibrator is used to remove air bubbles, ensuring the slurry fills the mold cavity and forms a dense structure. For reinforced covers, the reinforcing steel cage must be accurately positioned before the concrete initially sets to avoid displacement and uneven stress. After pouring, the material must be covered with moisture-retaining material for standard curing. Suitable temperature and humidity promote cement hydration, gradually forming a high-strength hardened body. The demolding time depends on the air temperature and cement type; removing the mold too early can lead to edge damage, while removing it too late will disrupt production. This process emphasizes uniform mixing and compaction, which are fundamental to ensuring the integrity and durability of the cover plate.
The forming of cast iron cover plates follows a melting, casting, and cooling process. Raw materials are crushed and screened before being fed into melting equipment, heated above the liquidus line to completely melt, and then processed through slag formation, desulfurization, and spheroidization to adjust the composition and microstructure. The melt maintains good fluidity under heat preservation and is then quantitatively injected into a preheated sand mold or metal cavity, filling with gravity to achieve the designed geometric contour. The casting temperature and cavity preheating temperature must be precisely controlled to prevent cold shuts, shrinkage porosity, or cracks. The liquid metal gradually cools within the cavity and undergoes a eutectic transformation, forming a solid casting. Cooling rate affects grain size and graphite morphology. For ductile iron, slower cooling promotes the precipitation of spheroidal graphite, thereby improving toughness and impact resistance. After molding, it requires sand removal, cleaning, trimming, and surface protection treatment to ensure dimensional accuracy and corrosion resistance meet standards.
The molding of composite material covers often employs a compression molding process. The resin matrix, curing agent, and filler are mixed uniformly according to the formula, and pre-cut fiber reinforcement is laid, with the layering direction matching the expected stress path. After mold closing, high pressure is applied to fully impregnate the fibers with resin and expel residual gas. Simultaneously, a cross-linking reaction is initiated under heating conditions, causing the matrix to change from a viscous flow state to a solid state. The synergistic effect of pressure and temperature not only ensures a dense and defect-free product but also allows for control of fiber volume fraction and interfacial bonding strength. After curing, the product is demolded, trimmed, and surface-treated to obtain a smooth and durable finished product. The advantage of this process is that it can mold complex shapes in one step and achieve performance designability, but it requires strict control over mold precision and process parameters.
The molding of stone covers falls under the category of mechanical cutting and surface finishing. After directional selection, raw blocks are cut into slabs according to design dimensions using diamond circular saws or band saws. The cutting process requires controlled feed speed and cooling lubrication to minimize chipping and micro-cracks. The slabs then undergo coarse grinding, fine grinding, and polishing processes, progressively reducing surface roughness with different grit sizes to achieve both anti-slip properties and aesthetic appeal. For large slabs, splicing and reinforcement are also necessary to ensure overall stability.
In general, the forming process of canal covers is a product of the integration of materials science and manufacturing technology. Each process focuses on eliminating defects, optimizing structure, and improving performance, providing reliable components for various applications. With the development of intelligent manufacturing and precision control technologies, the stability and consistency of the forming process are expected to further improve, driving the industry towards higher quality and efficiency.