The vortex type powder selector is a key grading equipment in the production
of sheet sand, responsible for screening high-quality fine powder with a mesh
size of 100-200 (requiring a coarse powder carryover rate of ≤ 3%), which
directly affects the fineness and coating effect of the sheet sand. If there is
poor grading accuracy (pass rate of qualified particle size is less than 90%)
and a high amount of coarse powder carryover (>100 mesh coarse powder
accounts for more than 8%), it will cause the surface of the board to be
polished rough and the paint film to pill. Based on the characteristics of high
whiteness and low impurities of board sand (quartz sand/feldspar sand), a
three-step investigation method is summarized to quickly restore the grading
performance.
Step 1: Optimize the structure of the powder selection chamber and the flow
guiding system - the core components determine the separation effect
Improper design of vortex blades and guide plates is the main cause of poor
grading.
Inappropriate angle or speed of vortex blades: blade angle less than 25 °,
insufficient centrifugal force, and ineffective separation of coarse powder;
Greater than 35 °, high airflow resistance, fine powder mixed with coarse
powder; The speed is below 1200r/min, the grading threshold is shifted, and
coarse powder is mixed into the finished product. Adjust the blade angle to 28 °
-32 ° and calibrate the speed to 1400-1600r/min through a frequency converter
(select high speed for fine powder classification and low speed for medium
coarse powder); Replace wear-resistant ceramic blades (hardness HRC ≥ 70) to
avoid angle deviation caused by wear.
Deformation or uneven spacing of the guide plate: bending deformation of the
guide plate disrupts the stability of the eddy current field; The spacing
exceeds 20mm, the airflow is turbulent, and there are graded blind spots.
Correct the verticality of the guide plate (deviation ≤ 1mm), adjust the spacing
to 15-18mm, and fix it according to the "circular uniform distribution"; Install
wear-resistant lining plates on the inner wall of the powder selection chamber
to reduce structural deformation caused by material impact.
Step 2: Calibrate airflow parameters and feed control - parameter matching to
improve accuracy
Improper settings of wind speed, air volume, and feed rate can exacerbate
grading issues.
Low or fluctuating wind speed: If the selected powder wind speed is below
2.5m/s, the fine powder cannot be carried up by the airflow; The fluctuation
exceeds 0.3m/s, and the grading accuracy fluctuates greatly. Use an anemometer
to detect and adjust the frequency of the induced draft fan to stabilize the
wind speed at 3-3.5m/s; Install an air volume balance valve to ensure a stable
pressure difference of ± 50Pa inside and outside the powder selection chamber,
avoiding external airflow interference.
Overloading or uneven feeding rate: exceeding the rated processing capacity
(such as 30t/h, actual 38t/h), material accumulation in the powder chamber, and
inability of airflow to penetrate; The feed is constantly increasing and
decreasing, and the eddy current field is instantly imbalanced. Use an
electronic belt scale to control the measurement and maintain it at 80% -90% of
the rated value; Install a spiral feeder and fabric feeder to evenly disperse
the material into the powder selection chamber, with the material layer
thickness controlled between 5-8mm to avoid local overload.
Step 3: Adapt to the characteristics and pretreatment of the board sand -
avoid faults at the source
Insufficient humidity, impurities, and pre-treatment of materials can affect
the stability of grading.
High moisture content or soft impurities in materials: when the moisture
content exceeds 3%, fine powder binds with coarse powder to form "false
particles" that are difficult to separate; Mixing with soft impurities such as
sawdust and clay can easily block the flow channel. Before classification, a
drying process is added (moisture content is reduced to below 1.5%), and a
magnetic separation+screening combination device is installed to remove soft
impurities and large particles (>2mm); Install an ultrasonic disperser (with
a power of 600W) at the feed inlet to break down the adhesive clumps of easily
bonded board sand.
Poor sealing of the finished product collection system: leakage of the
collection pipeline, infiltration of external air, and damage to the negative
pressure environment; The filter bag of the dust collector is clogged, and fine
powder cannot be effectively collected. Replace the pipeline sealing gasket and
reinforce the connection with sealant; Select PTFE coated filter bags (pore size
3 μ m) and blow back once every 2 hours to ensure that the dust collector
resistance is ≤ 1500Pa and the fine powder recovery rate is ≥ 99%.
Daily maintenance should pay attention to: clean the coarse powder outlet at
the bottom of the powder selection chamber every day, check the status of the
blades and guide plates; Calibrate the speed, wind speed, and feed rate weekly,
and tighten the bearing seat bolts; Monthly inspection of filter bag damage and
replacement of aging seals. By taking the above measures, the classification
accuracy of the board sand can be improved to over 95%, and the coarse powder
carryover rate can be reduced to below 2%, ensuring the polishing and coating
effect of the board. If there are still problems, it is recommended to contact
the manufacturer to optimize the eddy current field design and match the grading
requirements of specific particle size board sand.