As a precision instrument frequently used in the medical field, the molding process of syringes directly determines the dimensional accuracy, mechanical properties, and biosafety of the product. With the diversification of materials and the refinement of application requirements, the molding process not only carries the task of transforming raw materials into usable devices, but also needs to achieve high-quality, high-consistency mass production in a clean and controlled production environment to meet stringent medical regulatory requirements.
The molding of glass syringes, typically using borosilicate glass, mainly employs a combination of drawing and blow molding methods. First, a glass preform with uniform wall thickness is drawn by high-temperature melting. Then, after softening by heating in a mold, it is blown to form the tube shape and scale markings in one step. This process requires precise control of the temperature profile and blowing pressure to ensure the syringe is transparent and bubble-free, with uniform wall thickness and an inner diameter that meets the volume calibration requirements. After molding, annealing is required to eliminate internal stress and prevent the risk of breakage due to temperature differences or mechanical impact during use.
The mainstream process for disposable plastic syringes is injection molding, suitable for medical polymer materials such as polypropylene, polyethylene, and polycarbonate. The process flow includes stages such as raw material drying, melting and plasticizing, high-pressure injection into the mold cavity, pressure holding and cooling, and demolding. Mold design must consider the syringe shape, scale clarity, and piston fit tolerances. Mirror polishing and micro-texturing are commonly used to improve inner wall smoothness and reduce drug residue. For pre-filled syringes or dual-cavity syringes with complex structures, multi-component injection molding or insert injection molding techniques are employed to combine different materials or functional areas in a single molding process. During molding, melt temperature, injection speed, and cooling rate must be strictly controlled to avoid defects such as shrinkage marks, warpage, and internal stress concentration.
The molding of the needle tip and needle seat is equally critical. The needle tip is often made of stainless steel tubing, precision broached and ground, and then electrolytically polished to reduce surface roughness. The needle seat can be directly injection molded or machined, and then welded or bonded to the needle tip. Precision control in this stage affects puncture smoothness and connection sealing; it is usually completed in a cleanroom, supplemented by online visual inspection to remove defective products.
Post-molding processing includes printing graduations, applying silicone oil, sterilization, and aseptic packaging. The silicone oil coating must be uniform and thin to reduce piston sliding resistance and prevent contamination of the medication. Sterilization processes, depending on the material, can be ethylene oxide, radiation, or steam sterilization, and must be performed within validated parameter ranges to ensure adequate sterility.
Overall, syringe molding is a systematic technology integrating materials science, mold engineering, and precision manufacturing, with each step revolving around precision, cleanliness, and safety. With the introduction of intelligent manufacturing and process analysis technologies, the molding process is moving towards digital monitoring and closed-loop control, providing a more robust guarantee for improving product quality and production efficiency.