When selecting ceramic fiber products, users focus on various performance data and their test reports. Among these, shot content is a key indicator that significantly influences the product's practical performance. So, what is shot? What are its content standards? And how does it affect product performance?
I. What is Shot?
During the fiberization process of ceramic fibers (via spinning or blowing), some raw materials fail to fully fiberize, forming crystalline particles known as shot. Typically, particles with a size greater than 0.212 mm and a bulk density of 2800–3200 kg/m³ are classified as shot.
Given current production technologies, a certain amount of shot is inevitably present in ceramic fiber products. As long as the content remains within standard limits, the potential impact on thermal conductivity has already been accounted for in the insulation design of industrial kilns. Therefore, users need not worry excessively about its effect on insulation performance.
II. Standard Specifications for Shot Content
According to national standards:
For ceramic fiber blankets with a temperature rating below 1000°C, the shot content requirement is ≤ 25%.
For ceramic fiber blankets with a temperature rating below 1450°C, the shot content requirement is ≤ 20%.
For ceramic fiber products with a temperature rating below 1700°C, the shot content requirement is ≤ 5%.
In the international market, the content of shot particles larger than 0.25mm is typically controlled at ≤ 5%. Due to limitations in domestic fiber manufacturing technology, the current standard for shot content is set at ≤ 15%, approximately twice the international standard. Therefore, when determining the bulk density of ceramic fiber products, the influence of shot content must be fully considered.
SUNTHERM employs advanced production processes to strictly control the shot content of products rated for 1450°C to below 7%. The product surface is flat and white, with shot content significantly lower than conventional standards.
III. Impact of Shot Content on Product Performance
The quality of ceramic fiber products is comprehensively evaluated based on chemical composition, fiber diameter and length, shot content, heating linear shrinkage, and thermal conductivity. Shot content is one of the critical indicators among these.
Reduces Thermal Insulation Performance
High shot content means an increase in crystalline particles within the product. This leads to a looser fiber structure and larger voids, enhancing convective heat transfer. Consequently, the overall thermal conductivity increases, and insulation performance declines.
Weakens Product Strength
Shot disrupts the uniform arrangement of fibers, increases the gaps between fibers, and reduces the overall strength of the module. It also adversely affects wear resistance and electrical insulation properties.
Affects Energy Efficiency and User Benefits
Excessively high shot content will impair the overall energy-saving performance of ceramic fiber products, leading to increased energy consumption and directly impacting the user's economic benefits.
