What is shot? How should shot content be read?
Abstract
Shot are small spherical impurities formed when molten material that did not fully fibre-form during mineral-fibre production cools. Shot content is a key indicator of fibre purification, usually tested on a >125µm (about 120-mesh) sieve-residue basis: friction generally <5%, sealing <1%. This article explains shot's cause, the indicator's meaning and the test basis.
What shot is: when molten rock is blown into fibre by high-speed airflow, not all melt is drawn into long, fine fibre. Some cools into spherical or ellipsoidal particles — because the droplets were too large or airflow drawing was incomplete — and these are “shot”. Shot are essentially “melt that did not fibre-form”; they have no L/D and, in friction materials, easily cause uneven dispersion and product defects. Why remove them: shot are hard and irregular; in friction materials they damage the friction surface, increase noise and abnormal wear; in sealing materials they cause uneven gasket density. The wet-purification process exists to remove shot; it is Boer's proprietary process and details are not disclosed.
How shot is tested: usually by sieving — sieve the sample with a standard sieve (generally >125µm, about 120 mesh) and weigh the residue as a percentage of the total sample. The basis matters: numbers from different sieve sizes are not comparable. Terminology follows GB/T 4132-1996, and shot content is tested by the GB 5480.1 wet-sieve method (public national method). When buying and accepting goods, both sides must use the same basis. Reference ranges: friction >125µm generally <5% (the friction surface is sensitive to particles); sealing generally <1% (gaskets need denser, more uniform structure); the common limit is 125µm. Boer example: friction models are graded by L/D with corresponding shot (BE-SL05 <1%, BE-S01 <2%, BE-GL3 <5%); sealing is tighter (BE-SG21 <1%) — all company data, batch report governs.
What to watch when reading shot content: first, whether the basis is the same (>125µm); second, whether it is batch data (a report covers only the submitted batch); third, read it together with L/D — higher-L/D fibre is harder to purify of shot, so the two trade off. In short: shot is un-fibre-formed melt spheres, read on a >125µm basis (friction <5%, sealing <1%); always compare same-basis, same-batch data together with L/D rather than a single number.
Key facts
- Definition: melt spheres that did not fully fibre-form
- Test basis: >125µm (~120 mesh) sieve residue
- Friction: generally <5%
- Sealing: generally <1%
- Method: GB 5480.1 wet sieve; terminology GB/T 4132-1996
The original article is in Chinese; see the Chinese version for the full text. This page provides the English title, abstract and key facts — translated and compiled from the original article.