A Detailed Explanation of the Manufacturing Process and Seamless Technology for Rubber Coated Timing Belts

Plasticizing Process: Raw rubber must possess a certain degree of plasticity to meet the requirements of subsequent processes. For raw rubber with a Mooney viscosity of 60 or higher (theoretical) or 90 or higher (actual)—such as NR, hard NBR, and hard rubber—plasticizing is necessary. This can be performed using an open mill or a closed mill. Although open mills involve high labor intensity and low production efficiency, they offer flexibility and require minimal investment, making them suitable for situations with frequent changes. The speed ratio between the front and rear rollers is 1:1.15–1.27. Operating methods include thin-pass plasticizing, roller-wrapping plasticizing, frame-climbing, and chemical plasticizing agents. The plasticizing time does not exceed 20 minutes, followed by a rest period of 4–8 hours. In contrast, the internal mixer offers high production efficiency, convenient operation, low labor intensity, and uniform plasticity. However, high temperatures may cause a slight decline in the physical and mechanical properties of the compound. The operational process is as follows: weighing → feeding → plasticizing → discharging → blending → calendering → cooling and demolding → storage. The operation takes 10–15 minutes, followed by a resting period of 4–6 hours.

Rubber Coating for Timing Belts | Timing Belt Rubber Coating | Rubber Coating for Toothed Timing Belts

Mixing Process: This process involves adding various compounding agents to rubber to produce a compound. When mixing in an open mill, first wrap the raw rubber around the front roller for a brief 3–5-minute preheating period. followed by the addition of raw rubber → activators and processing aids → sulfur → fillers, plasticizers, and dispersants → processing aids → accelerators in that order, paying attention to the volume of the rubber pile. Subsequently, the mixture is homogenized through kneading techniques, which include the diagonal cutting method (eight-knife method), triangular wrapping method, twisting method, and pounding method (walking knife method). The formula for calculating the rubber loading capacity of an open mill is v = 0.0065 * d * l (where v is volume, d is the roller diameter, and l is the roller length). The roller temperature should be maintained between 50–60°C. Mixing in a banbury mixer is divided into primary and secondary mixing stages. Single-stage mixing is completed in one pass, following the sequence: raw rubber → small additives → reinforcing agents → plasticizers → discharge → sheet press with sulfur and accelerators → sheet removal → cooling and storage; two-stage mixing is divided into two stages: the first stage involves raw rubber → small additives → reinforcing agents → plasticizers → discharge → sheet pressing → cooling; the second stage involves masterbatch → sulfur and accelerators → sheet pressing → cooling. During the mixing process, strict control must be maintained to prevent quality defects such as agglomeration of additives, abnormal specific gravity, blooming, uneven hardness (too high or too low), and scorching.

Vulcanization Stage: Vulcanization is the key process that imparts the final physical and mechanical properties to rubber products. During vulcanization, close attention must be paid to potential issues, such as material shortfall (caused by trapped air between the mold and rubber, insufficient weighing, insufficient pressure, poor compound flow, excessive mold temperature leading to scorching, premature scorching, or insufficient thickness resulting in inadequate flow), bubbles and voids (caused by insufficient vulcanization, insufficient pressure, impurities or oil contamination in the mold or compound, excessively high mold temperature during vulcanization, or too little vulcanizing agent resulting in slow vulcanization), surface cracking (caused by excessive vulcanization speed, dirty molds or rubber residue, excessive use of release agents, or insufficient rubber thickness), product breakage during demolding (caused by excessive mold temperature or prolonged vulcanization time, excessive use of vulcanizing agents, or improper demolding methods), and processing difficulties (caused by excessive or insufficient tear strength of the product), and ensure vulcanization quality by optimizing process parameters and operational procedures.

Rubber-Coated Synchronous Belts | Synchronous Belt Rubber Coating | Rubber Coating for Toothed Synchronous Belts

Utilizing a mature one-piece mold vulcanization process, we have achieved seamless, joint-free rubber-coated synchronous belts. This seamless technology significantly extends the product’s service life, prevents delamination and breakage, ensures more stable performance during high-speed operation, and delivers a comprehensive upgrade in quality. Compared to seamed timing belts, seamless timing belts reduce the risk of damage caused by stress concentration at the joints. They are better suited for high-load, high-speed operating environments, providing users with more reliable and durable transmission solutions.