Reasons and solutions for bubbles generated during vulcanization of rubber products
The factors causing bubbles in vulcanized rubber products are multifaceted, with key factors including raw materials, rubber mixing and processing, process operations, vulcanization equipment and molds.
1、 Raw material factors
1. Cause analysis
(1) Natural rubber moisture and volatile matter exceeding standard
(2) Chemical raw materials and additives storage, ingredient and other processes are affected by moisture and increase in moisture content.
(3) The steel wire cord is damp and the coating of steel wire adhesive is not dry.
(4) The moisture regain of fiber cord is high, with the original thread exceeding 2% and before rolling exceeding 1%.
2. Solution measures
(1) After cutting natural rubber, drying measures should be taken to control moisture and volatile matter according to standards. It is strictly prohibited to exceed the standard and reduce the moisture content in the original rubber.
(2) During the storage of chemical raw materials and additives, moisture-proof measures should be added. During the rainy season, rainy season, and foggy weather, it is particularly important to assist in transportation, storage, processing, and other processes to prevent raw materials from getting damp and wet. The prepared raw materials are packaged and fed in plastic.
(3) Open the packaging of the steel wire cord 1 hour before use, keep the indoor humidity not exceeding the standard, and prevent the steel wire cord from getting damp. After the steel wire is coated with adhesive, blow it dry.
(4) Heat and dry the fiber cord before rolling, and the moisture regain of the cord before entering the rolling machine is less than 1%
2、 Factors of semi-finished parts
1. Cause analysis
(1) The additives in the mixed rubber are unevenly dispersed during mixing.
(2) The mixing temperature is low, and the moisture is not completely evaporated. When the temperature is high, the sulfur is easily melted or burnt when the rubber is discharged and sulfur is added to the mixer.
(3) Insufficient parking time for rubber materials or production and use without parking.
(4) Uneven heat refining of rubber material and uneven surface during molding
(5) When the rubber material is heated on the open mill, the surface is wrapped with air, and the formed rubber material has the phenomenon of harboring air.
2. Solution measures
(1) Optimize the production formula, choose easily dispersed additives to replace the current ones, increase the application of dispersants, homogenizers and other processing aids, and improve the dispersion performance of various additives.
(2) The mixed rubber is produced using a two-stage internal mixer process. During the first stage of mixing, the temperature is raised to allow the moisture and volatile matter in the raw materials to fully evaporate. After parking, the rubber material is then mixed in the second stage, and the temperature is controlled within the temperature range of adding sulfur and accelerator to avoid short coking time or occurrence of coking.
(3) Strictly control the parking time of semi-finished products in various processes such as molding, first stage mixing, second stage mixing, and molding. Allowing various additives to fully diffuse, improving the uniformity of the adhesive, while also facilitating the recovery of stress and strain under mechanical action.
(4) The hot mixing of the rubber material should be uniform, and the rubber material should be mixed evenly through operations such as cutting knives, dropping plates, and tamping. Adopting a separate operation method of hot melt feeding and molding to improve the smoothness of the surface of the molding material.
(5) By using the extrusion process to extrude the rubber material, there is no longer any air accumulation on the surface of the molded rubber material.
