Analysis of the causes of bubbles in rubber products vulcanization and solutions

When rubber products are vulcanized, bubbles are a quality defect that often occurs when rubber products are vulcanized, which not only affects the appearance quality of the product, but even the internal quality of the product. Through on-site observation and analysis of the causes of bubbles generated by vulcanization, measures were formulated to solve the problem, which minimized the occurrence of bubbles and improved the appearance quality of the product. 

There are many factors for the bubbles of rubber products in vulcanized products. The key reasons are raw materials, rubber mixing and processing, process operations, vulcanization equipment and molds.

First:Raw material factors   

1. 1. Reason analysis (1) The moisture and volatile content of natural rubber exceed the standard (2) The moisture content of chemical raw materials and auxiliaries, ingredients and other links increases. (3) The steel cord is damp, and the steel wire glue is not dry. (4) The moisture regain of fiber cord is high, the original yarn is higher than 2%, and it is higher than 1% before calendering. 

 2.Solution  (1) After cutting the natural rubber, take bake measures to control the moisture and volatile content according to the standard, strictly prohibit exceeding the standard, and reduce the moisture content in the raw rubber. (2) Add moisture-proof measures when storing chemical raw materials and auxiliaries. In rainy season, rainy season, and foggy weather, it is especially necessary to help transportation, storage, processing and other links to prevent raw materials from getting damp and getting wet. The prepared raw materials are filled with plastics. (3) Unpack the steel cord 1 hour before use to keep the indoor humidity not exceeding the standard, avoid the steel cord from being damp, and drying the steel wire after coating with glue. (4) The fiber cord is heated and dried before calendering, and the moisture regain of the cord is less than 1% before entering the calender.  

Second, semi-finished parts factors 1, cause analysis 

(1) The additives in the rubber compound are not uniformly dispersed during mixing. (2) The mixing temperature is low, and the moisture is not volatile. When the temperature is high, the sulfur is easy to melt or scorch when the sulfur is added to the open mill when the temperature is high. (3) The rubber material is parked for insufficient time or is not parked for production use. (4) The rubber material is not evenly smelted, and the surface is not smooth when it is molded.  (5) When the rubber material is smelted on the open mill, the surface is wrapped with air, and the discharged rubber material has the phenomenon of trapping air. 

2. Solution measures (1) Optimize the production formula, use easily dispersible additives to replace the currently used additives, increase the application of dispersants, homogenizers and other processing aids, and improve the dispersion performance of various additives. (2) The rubber compound is produced by the two-stage process of an internal mixer. During the first stage of mixing, the temperature is increased to fully volatilize the moisture and volatile matter in the raw materials. The rubber material is parked and then mixed in the second stage. Within the temperature range of the accelerator, avoid short scorch time or scorch. (3) The processes of plasticizing, one-stage mixing, two-stage mixing, and molding process strictly control the parking time of semi-finished products. Allow various additives to fully diffuse, improve the uniformity of the rubber compound, and at the same time facilitate the recovery of stress and strain under mechanical action. (4) The rubber material should be evenly heated, and the rubber material should be mixed evenly through operations such as cutting knife, dropping plate, and tamping. It adopts a separate operation method of hot refining rubber supply and output to improve the smoothness of the surface of the output rubber. (5) Adopt the extrusion process to extrude the rubber material, and the surface of the extruded rubber material no longer has the phenomenon of trapping air.

 Third. Production operation 1. Reason analysis (1) The control of the roller temperature of the open mill, the temperature of hot-melting rubber supply, and the temperature of extruding and discharging are not strict, and there are bubbles on the surface of the semi-finished parts. (2) There is a lot of air in the rubber and thread of the pressure tube, and it is difficult to drain during molding and vulcanization. (3) The thickness and width tolerances of the semi-finished parts are too large, and the weight tolerance is large, which affects the flow of rubber in the mold. (4) When preforming, multiple layers of rubber material are easy to trap air and cause blistering in the rubber. (5) The steel cord is only hung on the surface during dipping. The air content in the steel wire is high, and the space between the steel wires is large. It is easy to trap air when the film is attached. (6) The pressure during vulcanization is low, and the rubber material has poor compactness and easy to produce bubbles.  (7) The temperature and time during vulcanization cannot meet the process requirements, which will also cause low-sulfur bubbles. 

2. Solution  (1) Control the temperature of the mill roll , Capacity, to prevent the overheating of the rubber material from producing air bubbles that are difficult to remove when wrapped in the rubber. (2) The calendered rubber cord is arranged with multiple sets of cotton threads along the warp to increase the exhaust effect between the rubber cord layers. The calendered rubber cord is equipped with a bubble-piercing device before winding to increase the air exhaust effect between the rubber cords. (3) Modify the design of the extrusion die plate to make the shape of the rubber material conducive to the die, strictly control the construction dimensions and tolerances of the rubber semi-finished product, and prevent the product from trapping air. (4) When multiple layers of rubber need to be stacked during pre-forming, press the vent valve on the rubber to reduce air trapping between the rubber layers, or use a bubble needle to pierce the air bubbles on the surface of the rubber. (5) The steel cord is modified from dipping paste and film to extrusion coating to reduce the air content in the steel wire in the rubber and reduce the air trapping phenomenon when the film is applied. (6) Set the cavity pressure reasonably to ensure that the vulcanization should reach the pressure, so that the rubber can flow and fill the cavity. (7) Strictly control the production operation according to the specified vulcanization temperature and time, and change the manual control operation to the microcomputer group control production operation. 

Forth. Equipment and Mould 1. Reason analysis (1) The temperature control system of the plate vulcanizing machine has a large deviation. When the temperature control is high, the temperature of the mold is high, which reduces the flow time of the rubber material. (2) The mold surface is damaged and uneven, which affects the fluidity of the rubber compound. (3) Dirt is easy to accumulate on the surface of the mold, which affects the fluidity of the rubber material and easily causes bright scars on the body. (4) The mold exhaust line and the exhaust line hole distribution is unreasonable, the exhaust line is too thin, and the diameter of the exhaust hole is too small, which affects the exhaust effect. (5) The unreasonable design of the grooves and lead angles on the side iron teeth of the mold will cause layers to be generated when the rubber enters, and the gas cannot be drained after the inclusion. The rubber compound is prone to turbulence, turbulence, and overlap when the mold is closed and exhausted.

 2. Solution  (1) Improve the temperature measurement point and temperature control sensor system of the plate vulcanizing agent, so that the temperature in the mold cavity is consistent with the temperature displayed by the instrument. (2) Repair the damaged parts of the mold surface in time, and the manufacturer shall take measures to protect and prevent damage to the mold surface to avoid damage to the mold surface. (3) The surface of the mold shall be cleaned and polished quantitatively and regularly to ensure the desired smoothness of the mold surface. (4) Improve the layout of mold exhaust lines and exhaust holes, which are connected vertically and horizontally, and the distribution tends to be reasonable. The exhaust lines are appropriately thickened, and the diameter of the exhaust holes is enlarged to enhance the exhaust effect. (5) Optimize the design of the side grooves and corners of the mold to reduce the eddy current and overlap of the rubber products. Through the analysis of the causes of bubbles in the vulcanization of rubber products, formulate rectification plans to solve the problems, strengthen the use and management of raw materials, standardize rubber mixing processing, improve process operations, optimize mold design and other measures, and implement measures such as the surface of rubber products. , The quality defects of bubbles and bright scars between the glue layer, the pattern and the middle of the steel cord are significantly reduced, which improves the appearance quality of the product .