The airflow classifier is the core equipment for fine processing of
high-purity quartz sand (SiO ₂ ≥ 99.99%), responsible for screening products in
a specific particle size range of 100-500 mesh (with a required particle size
deviation of ≤± 5% and a fine powder carryover rate of ≤ 2% in coarse powder),
directly determining the quality of raw materials in high-end fields such as
quartz glass and semiconductor packaging. If there is a drift in grading
accuracy (particle size deviation exceeding 8% within 1 hour) or excessive fine
powder carryover (>5%), it will lead to product degradation and hinder access
to the high-end market. Based on the characteristics of extremely low impurity
content and high particle dispersion requirements of high-purity quartz sand, a
three-step screening method is summarized to quickly restore classification
stability.
Step 1: Optimize Airfield Control and Pressure Stability - Core Dynamics
Determine Accuracy
The fluctuation of wind pressure and air volume, as well as uneven
distribution of airflow, are the main causes of accuracy drift.
Insufficient wind pressure stability: If the outlet pressure fluctuation of
the Roots blower exceeds 0.03MPa, it will cause a sudden change in the airflow
velocity in the grading zone, and the grading threshold will shift accordingly;
Pipeline leakage causes the actual air volume to be 15% lower than the rated
value, and the fine powder cannot be effectively carried out, resulting in an
increase in fine powder carryover in the coarse powder. Install a high-precision
stabilizing tank (with a volume of ≥ 1m ³) and use a pressure transmitter to
achieve closed-loop control, stabilizing the air pressure at 0.28-0.32MPa;
Perform air tightness testing on pipeline connections, replace aging gaskets,
reinforce interfaces with sealant, and ensure that air loss is ≤ 5%.
Disordered airflow distribution or improper guidance: Deformation and uneven
spacing of the guide plate can lead to the formation of vortices in the airflow,
resulting in locally high or low wind speeds; If the deviation of airflow
velocity in the grading zone exceeds 0.2m/s, it will cause significant
differences in particle size of the same batch of products. Correct the
verticality of the guide plate (deviation ≤ 0.5mm), adjust the spacing to 8-10mm
and distribute it evenly; Install an airflow homogenizer at the inlet of the
classifier to control the fluctuation of airflow velocity within ± 0.1m/s,
ensuring uniform and stable airflow in the classification field.
Step 2: Calibrate the grading wheel structure and speed control - the core
components determine the separation effect
Wear, speed fluctuations, or abnormal clearances of the grading wheel can
exacerbate fine powder entrainment.
Grade wheel wear or dynamic balance imbalance: blade wear exceeding 1/4 of
the original thickness will reduce centrifugal separation force, and fine powder
is easily discharged with coarse powder; The dynamic balance deviation exceeds
0.3g · m, causing vibration during operation and disrupting the stability of the
airflow field. Replace the silicon carbide wear-resistant blade (hardness HRC ≥
75), calibrate it with a dynamic balance instrument after installation, and
ensure that the deviation is ≤ 0.1g · m; Regularly clean the fine powder
attached to the surface of the blades (once a week) to avoid dust accumulation
and change the stress state of the blades.
Speed fluctuation or excessive clearance: Speed fluctuation exceeding 50r/min
(target speed 1800-2200r/min) can lead to unstable centrifugal force and
difficulty in controlling grading accuracy; If the gap between the grading wheel
and the shell exceeds 0.8mm, a "short-circuit airflow" will occur, and fine
powder will mix into coarse powder without effective separation. Select a
high-performance frequency converter with a frequency conversion accuracy of ±
1r/min, and set the speed according to the target granularity (choose high speed
for fine-grained and low speed for coarse-grained); Adjust the position of the
grading wheel to control the gap between 0.3-0.5mm, and install wear-resistant
bushings to reduce the increase in gap after long-term operation.
Step 3: Adapt material characteristics and pre-processing - avoid carryover
risks at the source
Poor material dispersion, impurity contamination, or excessive humidity can
affect the grading effect.
Material agglomeration or high humidity: High purity quartz sand has a
moisture content exceeding 0.3%, and particles are prone to moisture absorption
and agglomeration, forming "false particles" that cannot be effectively
separated during grading; Agglomerated particles with a diameter exceeding twice
the upper limit of classification will be mistakenly classified as coarse powder
and discharged together with fine powder. Add a microwave drying device
(temperature 80-100 ℃) before feeding to reduce the moisture content to ≤ 0.1%;
Install an ultrasonic disperser (power 600W, frequency 25kHz) to eliminate
initial material agglomeration and ensure particle monodispersity.
Fluctuations in feed volume or contamination by impurities: feed volume
exceeds the rated value by 10%, material overload occurs in the grading area,
and the airflow cannot fully carry fine powder; Metal impurities (particle
size>0.5mm) mixed into the raw materials will collide with the grading wheel,
causing instantaneous fluctuations in speed. Use a weight loss feeder to
accurately control the feed rate and maintain it stable at 85% -95% of the rated
value; Install an electromagnetic iron remover (magnetic field strength ≥
12000Gs) and a precision sieve (aperture ≤ 0.3mm) at the feed inlet to double
remove impurities and large agglomerates.
Daily maintenance should pay attention to: detecting wind pressure, speed,
and feed rate every day, and recording parameter changes; Clean up residual
materials in the grading wheel, guide plate, and pipeline every week; Monthly
calibration of pressure transmitters, tachometers, and feeder measurement
accuracy; Perform quarterly dynamic balance checks on graded wheels and replace
worn bushings. By implementing the above measures, the classification accuracy
deviation can be reduced to within ± 3%, and the fine powder carryover rate can
be ≤ 1.5%, meeting the high-end application requirements of high-purity quartz
sand. If there are still problems, it is recommended to contact the manufacturer
to optimize the airflow field simulation design and match the grading parameters
of specific particle size ranges.