The sealing performance of the positive and negative pressure pipes in positive and negative pressure molding machines is a key factor affecting molding quality. Its role spans core processes such as pressure transmission, material flow, and molding stability. Inadequate pipe sealing can lead to pressure decay, gas leakage, or material penetration, which in turn can cause molding defects, dimensional deviations, and even equipment failure, directly impacting final product yield and production efficiency.
During the positive pressure stage, pipe sealing is crucial for accurate pressure transmission. During positive pressure molding, compressed air is delivered to the mold cavity through pipes, promoting material filling and solidification. If there are leaks in the pipes, compressed air can escape during transmission, causing the actual pressure in the cavity to fall below the set value. This insufficient pressure impairs material flowability, preventing it from fully filling mold details, resulting in surface depressions, edge burrs, or internal voids. For example, in the molding of precision electronic component housings, poor sealing of the positive pressure pipes can lead to localized uneven wall thickness, compromising the product's electromagnetic shielding performance.
During the negative pressure stage, pipe sealing directly affects material retention and molding stability. Negative pressure molding extracts air from the mold cavity to create a vacuum, forcing the material to adhere to the mold surface under atmospheric pressure. If the negative pressure piping is poorly sealed, outside air can penetrate the mold cavity through leaks, disrupting the vacuum environment. This loss of vacuum can weaken material adhesion, leading to defects such as delamination, warping, or surface ripples. For example, in automotive interior molding, leaky negative pressure piping can cause leather or fabric to lose contact with the substrate, leading to bulging or peeling after long-term use.
In the process of alternating positive and negative pressure molding, piping sealing places higher demands on the response speed of pressure switching. The molding of some complex structures, such as those in the manufacture of special-shaped pipes or hollow components, requires rapid switching between positive and negative pressures to achieve directional material flow. If the positive and negative pressure piping is not properly sealed, pressure switching can be delayed or fluctuating, leading to erratic material flow, internal stress concentration, or structural deformation. This problem is particularly prominent in the molding of high-strength composite materials in the aerospace industry, where poor sealing can cause delamination between layers and reduce overall strength.
Pipeline sealing also indirectly affects the molding process by affecting equipment energy consumption and operating costs. Leaky positive and negative pressure piping causes compressed air or vacuum pumps to continuously run to compensate for pressure loss, significantly increasing energy consumption. Frequent pressure fluctuations also accelerate wear on components such as seals and valves, shortening equipment lifespan and increasing maintenance frequency and downtime. For example, in a food packaging molding line, a pipe leak can increase a single piece of equipment's annual electricity consumption by thousands of kilowatt-hours, while production losses due to maintenance can exceed 5% of total output.
Furthermore, pipe sealing plays a crucial role in the adaptability of the molding process. Different materials (such as plastics, rubber, and metal powders) have varying sensitivities to positive and negative pressure parameters. Inadequate sealing can impair the equipment's ability to control these parameters. For example, in powder metallurgy molding, a leak in a positive-pressure pipe can cause powder to fly, contaminating the mold and equipment. A leak in a negative-pressure pipe can lead to uneven powder adsorption, creating density gradients and affecting the product's mechanical properties.
To ensure molding quality, the piping system of both positive and negative pressure molding machines requires a highly leak-tight design, including specialized sealing rings, welding processes, and pressure detection devices. Regular maintenance and leak detection are also crucial. Pressure decay testing or helium mass spectrometry leak detectors can promptly detect and repair sealing defects. Only by ensuring the tightness of the pipeline can we give full play to the advantages of positive and negative pressure molding machines in terms of precision, efficiency and stability, and meet the demand for high-quality molding in the high-end manufacturing field.
