Fill Factor Explained: How to Calculate Rubber Batch Size

Fill factor is one of the most important numbers in rubber mixing, but it is often misunderstood. In this episode, we explain how fill factor connects the recipe written in kilograms to the internal mixer chamber measured in liters, and how to calculate the correct rubber batch size using chamber volume, fill factor, and compound density. We break down what the manufacturer’s chamber volume really means, why you never fill an internal mixer to 100%, and why batch weight changes from compound to compound even when the mixer and fill factor stay the same. Using a real Banbury-type mixer example, we walk through the calculation step by step: chamber volume × fill factor × specific gravity = batch weight. You’ll also learn what happens when a mixer is underfilled or overfilled, why low fill factor weakens dispersion, how high fill factor can create dead spots and ram seating problems, and why 0.75 is the standard starting point — not the final answer. We also connect fill factor to rotor speed, drop temperature, dispersion quality, and mixing cycle optimization. #RubberMixing #FillFactor #InternalMixer #BanburyMixer #MyRubberHeart ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ABOUT THIS CHANNEL My Rubber Heart is your weekly deep-dive into rubber science, polymer chemistry, and the materials engineering that quietly powers the modern world from tires and seals to medical devices and aerospace components. New video every Monday. PERFECT FOR Materials science & chemical engineering students R&D chemists, compounders & process engineers Rubber & tire industry professionals Polymer & chemistry enthusiasts Anyone curious about how everyday materials really work NEVER MISS AN EPISODE Subscribe and turn on the bell so YouTube tells you when the next one drops: 👉    / @myrubberheart   LET'S TALK RUBBER Drop your questions in the comments I read every one Share your own lab/plant experiences with the community Suggest a topic and it might become next week's video SUPPORT THE SHOW Like the video it genuinely helps the algorithm Share it with one colleague, classmate, or fellow nerd ⚖️ DISCLAIMER I work in the rubber industry, but My Rubber Heart is an independent, personal project. All views are my own and do not represent my employer or any affiliated organization. Content is for informational and educational purposes only and is not professional, engineering, compliance, or regulatory advice. Use at your own risk. #RubberScience #PolymerChemistry #MaterialsEngineering #Vulcanization #Elastomers #ChemicalEngineering #RubberTechnology #STEM #ScienceEducation #MyRubberHeart #Sustainability #TireTechnology