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Fully Automatic Wet-Spray Trolley Pipeline Pre-Lubrication Method
Release time:
2026-10-12
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Summary:
Pre‑lubricating the delivery pipeline before concrete spraying is an essential step in wet‑spraying operations. The purpose of pre‑lubrication is to form a lubricating film on the dry inner walls of the pipeline, ensuring that the concrete being pumped during the actual spraying process flows smoothly, reducing frictional resistance and effectively preventing pipe blockages. If concrete is pumped directly into an un‑lubricated, dry pipeline, the pipe walls will rapidly absorb moisture from the concrete, causing its workability to decline sharply and frictional resistance to increase dramatically—conditions that can easily lead to pipe blockages or even pipe bursts.
I. Basic Principles of Pre-Lubrication
The inner wall of the pumping pipeline is a dry metal surface with a relatively high coefficient of friction. If concrete is pumped directly into the pipeline, the initial pumping pressure will increase significantly. Pre‑lubrication reduces the initial pumping resistance substantially by creating a lubricating buffer layer between the pipe wall and the concrete, enabling the concrete to flow as a stable plug‑flow within the pipeline. Pre‑lubrication typically involves two steps: first, pumping clean water to wet the pipeline, followed by pumping a lubricant to form a lubricating film.
II. Traditional Mortar Lubrication Method
The conventional pre-lubrication method employs a two-step process: “wetting with clean water followed by lubrication with cement mortar.”
Step 1: Prime with water. Before starting the actual pumping operation, add an adequate amount of clean water to the hopper and activate the pumping system to flush water through the pipeline, ensuring that the inner walls of the pipe are thoroughly wetted. This priming action helps minimize water absorption by the concrete on the pipe walls, thereby reducing the risk of reduced workability due to water loss. Once priming is complete, open the discharge port to drain any remaining water from the hopper.
Step 2: Pump lubricating mortar. After wetting with clean water, pump lubricating mortar into the hopper. The lubricating mortar may be a cement‑sand mortar mixed at a ratio of 1:2, or a cement‑sand mortar with the same composition as the concrete mix. The amount of mortar should be sufficient to lubricate the entire pipeline, typically ranging from 0.5 to 1.0 cubic meters. When the delivery pipeline is particularly long, first pump a measured quantity of clean water, then follow with the mortar, to ensure adequate lubrication.
During operation, first fill the hopper with a 1:1 cement‑water slurry or clean water. After pumping this material to lubricate the pipeline, discharge any remaining material from the hopper, then add the standard shotcrete mix and begin work. It should be noted that the cement slurry or cement mortar used for lubrication must be evenly distributed; it must not be poured in concentrated patches onto the structural elements.
III. Polymer-Based Pipe-Lubrication Method
Polymeric pipe‑lubricating agents are a new type of lubricant that has been gradually introduced in recent years. They are formulated from a variety of polymeric materials and can be rapidly dissolved by stirring at room temperature, yielding a viscous, lubricating, transparent liquid that enables pipeline lubrication without the use of mortar.
Instructions for use: Add an appropriate amount of clean water (typically 20 to 30 kg) to the hopper, start the mixing system, and slowly pour the pipe‑lubricating agent into the water. Mix thoroughly until fully dissolved, then let the solution stand for a short time to develop a viscous consistency. Pump the prepared lubricant solution into the pipeline to form a uniform lubricating film on the pipe walls. For pipelines up to 50 meters in length, use one bag of lubricant per application, diluted with 20 to 25 kg of water. A small admixture of the lubricant solution in the concrete has no significant effect on strength; however, the used solution must still be drained away from the structure.
Compared with traditional mortar, pipe‑lubricating agents eliminate the need for dedicated vehicles and associated costs for mortar transportation, streamline construction procedures, and reduce job‑preparation time.
IV. Precautions for Pre-Lubrication Operations
Displacement control. During the pumping of lubricant, the displacement should be kept at a low level—typically no more than 15 cubic meters per hour—to ensure that the lubricant adheres uniformly to all sections of the pipe wall.
Seamless transition between pre‑lubrication and formal spraying. Once the lubricant has been pumped through, formal spraying should commence promptly to prevent the lubricant layer from remaining in the pipeline for too long, which could result in a loss of fluidity. Before introducing the formal spray material, any residual clean water or slurry in the hopper must be completely drained.
Sequence for starting the air supply and pumping. During pipeline lubrication, first activate the forward pump to deliver the lubricant, then open the air line. Do not perform reverse pumping while the air is on. After completing pipeline lubrication, shut down the equipment, drain any excess water from the hopper, and then load the spray material to begin operations.
It is strictly prohibited to pour lubricating materials into the structure. Neither cement mortar nor pipe‑lubricant solutions shall be discharged into the structural elements; they must be dispersed and treated in accordance with applicable regulations.
Maintenance during prolonged shutdowns. When equipment is out of service for an extended period, apply lubricating oil to the inner walls of the pipelines to prevent rusting and the solidification of concrete residues.
V. Quality Verification of Pre-Lubrication
After pipeline lubrication is complete, the effectiveness of the lubrication can be assessed by observing the condition of the lubricant discharged from the nozzle. When the lubricant exiting the nozzle exhibits a uniform, viscous consistency with no visible particulates, it indicates that a continuous lubricating film has formed on the inner wall of the pipeline, and formal injection operations may commence. If the lubricant flow is intermittent or contains obvious foreign matter, the pipeline should be inspected for blockages or poorly sealed joints.
Pre‑lubrication is the initial step in wet‑spraying operations for shotcrete rigs and serves as the first line of defense against pipe blockages. Whether using the traditional mortar method or a pipe‑conditioning agent, the core objective is to establish a continuous, uniform lubricating film on the inner wall of the pipeline, thereby ensuring smooth concrete delivery downstream.
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