I. Raw material formula ratio (core foundation)
Main rubber: Natural rubber NR / Styrene Butadiene Rubber SBR as the main materials
Supporting additives: Sulfur (sulfurization agent), Carbon black/White carbon black (reinforcement), Aging inhibitor, Softening agent, Coloring agent, Wear-resistant additive
Mixing requirements: Mix in accordance with national standards proportion, avoid recycled waste rubber and inferior additives, ensure tensile, aging resistance, and leak-proof performance
II. Plasticizing mixing (first step)
All raw materials are put into the plasticizer machine and mixed at high temperature in a sealed environment
Achieve uniform fusion of the rubber, consistent hardness, and clean filtering of impurities
Function: Enhance rubber elasticity, toughness, and tensile strength, prevent cracking and powder shedding problems from the source
III. Lamination into sheets
The mixed rubber is sent to the lamination machine and pressed into uniform thickness rubber sheets of 1.2–1.8mm
Strictly control the thickness tolerance of the sheet, ensure uniform thickness without thin spots, bubbles, or impurities
Uneven thickness is the main cause of leakage and bag bursting in the later stage
IV. Cutting and punching
According to the standard version of the hot water bag, use molds to punch out upper and lower two sheet bag bodies
At the same time, punch the bottle mouth and hanging ear positions, with regular edges, no loose edges, and no gaps
V. Pre-inlaying of inserts + positioning of sheets
Pre-insert PP/Metal bottle mouth inserts and water-stop sealing parts in advance
The two sheets of rubber are precisely aligned and adhered, with the bottle mouth, sealing edge, and tail completely aligned
There are two types of structures for pre-inlaying assembly: upper water-stop and lower water-stop, with the positioning accuracy of the water-stop parts directly determining the leak-proof effect
VI. Molded hot pressing for shaping
The adhered rubber sheets are placed in a dedicated hot water bag mold and hot-pressed at high temperature and high pressure
Let the two rubber sheets edge hot-melt together to form a complete bag body
The sealing edge is tight, without gaps, and no virtual edges or delamination risks
VII. High-temperature vulcanization (the most critical part of the entire process)
Process parameters: Temperature 140–150℃, duration 20–30 minutes
Vulcanization effect:
Cross-linking of rubber molecules, transforming from soft rubber to strong and durable finished product
Improving tensile, tear resistance, high and low temperature resistance, and aging resistance
Removing rubber odor, stabilizing product quality
Insufficient vulcanization: rubber becomes soft, sticky, prone to aging and cracking, and has an extremely short lifespan
Excessive vulcanization: rubber becomes hard, brittle, loses elasticity, and is prone to bursting
VIII. Edge trimming and shaping
Remove the excess edges and burrs around the bag body
Smooth and regular the bottle mouth threads, sealing edge flaws, and overall appearance
IX. Air tightness water test full inspection (100% factory inspection mandatory)
Inflate, wait for leakage test, check pinholes, hidden cracks, and sealing edge gaps
Add warm water and wait, test the air tightness of the bottle mouth, mold edge, and tail
Non-conforming products are directly scrapped, and must not be included in the finished products
X. Surface treatment + printing LOGO
Clean and deodorize the rubber body surface
Print brand logo, specifications, execution standards, safety warning words
Printing process: Screen printing, hot stamping, embossing, etc. are available for selection
XI. Assembly of accessories
Assemble sealing rubber rings, threaded caps
Check the water-stop structure, tightness of the bottle cap, and sealing tightness to ensure no leakage or slipping
XII. Final inspection + cleaning + packaging and storage
Inspect the appearance, elasticity, sealing performance, and no flaws or odors
Wipe clean, ventilate to disperse odor
Pack in separate dust-proof bags/colorful boxes, box and store, complete shipment
Summary of process core
Plasticizing → Lamination → Cutting and punching → Sheet alignment and embedding → Hot pressing molding → High-temperature vulcanization → Edge trimming → Leak test and quality inspection → Printing → Assembly → Packaging
90% of all quality problems arise from these 5 links: rubber formula, sheet thickness, vulcanization temperature and duration, sealing edge hot pressing, water-stop part assembly.
