The planetary mixer is the core equipment for the production of quartz
crucibles, responsible for mixing high-purity quartz powder, binders,
dispersants and other raw materials into a uniform slurry (requiring a mixing
uniformity of ≥ 99% and no obvious layering after 24 hours of standing), which
directly affects the density, strength and high temperature resistance of the
crucible. If there is uneven mixing (local quartz powder agglomeration) and
slurry layering (upper clear liquid accounts for more than 10%), it will cause
pores and cracks to appear after the crucible is formed, and the qualified rate
of the finished product will drop sharply. Based on the high purity and precise
ratio of quartz crucible raw materials, a three-step investigation method is
summarized to quickly restore the mixing performance.
Step 1: Optimize the mixing structure and blade configuration - the core
components determine the mixing effect
Improper blade type, speed ratio, and mixing chamber design are the main
causes of poor mixing and stratification.
Poor compatibility or wear of propeller blades: Choosing ordinary anchor type
propeller blades may result in insufficient shear force on high viscosity quartz
slurry, leading to aggregation; The blade wear exceeds 1/4 of the original
thickness, the mixing force decreases, and there are more dead corners in local
mixing; The planetary carrier runs eccentrically (with a deviation of over
0.5mm), the clearance between the blades and the mixing chamber is uneven, and
the mixing strength fluctuates. Replace the "double screw belt+dispersing disk"
combination blade, with the screw belt responsible for overall flipping and the
dispersing disk cracking local agglomeration; Choose stainless steel
wear-resistant blades, calibrate the concentricity of the planetary carrier
during installation, and control the gap between the blades and the cavity wall
at 2-3mm to avoid residual raw materials.
Imbalance in the ratio of revolution/rotation speed: When the revolution
speed is below 15r/min, the overall flow of the material is slow and the mixing
period is prolonged; When the rotational speed is higher than 300r/min, the
local shear force is too strong, which damages the stability of the adhesive; If
the ratio of the two exceeds 5:1, it is easy to generate eddy currents, which
can cause the slurry to layer. Adjust parameters through a frequency converter,
with a revolution speed of 20-25r/min and a rotation speed of 200-250r/min, and
control the ratio between 1:8-1:10; Adopting the "gradient speed regulation"
mode, mixing at low speeds in the early stage and dispersing at medium speeds in
the later stage to avoid excessive shearing.
Step 2: Calibrate the material ratio and feeding process - Raw material
adaptation and stability improvement
Improper moisture content of raw materials, dosage of additives, and feeding
sequence can exacerbate mixing problems.
Insufficient moisture content or dispersant in quartz powder: If the moisture
content exceeds 0.5%, quartz powder is prone to moisture absorption and
aggregation, making it difficult to disperse; When the dosage of dispersant is
less than 0.3%, the settling speed of the slurry particles is fast, and they
separate into layers after standing; If the dosage exceeds 0.8%, it will reduce
the viscosity of the slurry and affect subsequent molding. Select high-purity
quartz powder with a moisture content of ≤ 0.3%, and accurately add dispersants
according to the "quartz powder mass of 0.4% -0.6%"; Pre dry the quartz powder
(temperature 120 ℃, time 2 hours) before adding, to eliminate initial
agglomeration.
Chaotic feeding sequence or insufficient mixing time: adding adhesive first
and then quartz powder can easily lead to excessive local bonding; Mixing time
is less than 40 minutes, and the raw materials are not fully fused; Over 80
minutes, energy consumption increases and the slurry heats up and deteriorates.
Follow the feeding sequence of "quartz powder → dispersant → small amount of
water → binder → supplementary water", with a 5-minute interval between each
feeding to ensure gradual fusion of the raw materials; The total mixing time
should be controlled at 50-60 minutes, with one stop in the middle (5 minutes)
to clean the residual material on the mixing chamber wall.
Step 3: Adapt slurry characteristics and equipment protection - avoid
layering risks at the source
Improper cleanliness, temperature control, and discharge method of the mixing
chamber can affect mixing stability.
Residual or abnormal temperature in the mixing chamber: Residual old slurry
(thickness exceeding 1mm) on the chamber wall can contaminate the new material
and cause uneven mixing; During the mixing process, if the temperature of the
slurry exceeds 40 ℃, it will accelerate the aging of the binder and reduce the
stability of the slurry. Clean the mixing chamber with pure water after each
use, air dry before putting it back into use; Install a cooling jacket on the
outer wall of the mixing chamber, introduce circulating cooling water, and
control the temperature of the slurry at 25-35 ℃ to avoid heating and
deterioration.
Improper discharge method or static environment: direct gravity discharge,
the slurry is prone to stratification due to uneven flow rate; Temperature
fluctuations exceeding 5 ℃ or humidity exceeding 60% in a static environment can
affect the stability of the slurry. Adopting the method of "spiral
pushing+uniform discharge" to avoid sudden changes in flow rate; After the
slurry is discharged, it should be stored in a constant temperature and humidity
environment (temperature 25 ± 2 ℃, humidity 50 ± 5%), and gently stirred for 1
minute before settling to reduce settling and layering.
Daily maintenance should pay attention to: checking blade wear and planetary
carrier operation status every week, and tightening connecting bolts; Calibrate
the tachometer and feeding measuring device monthly, and clean the dead corners
of the mixing chamber; Replace worn blades every quarter and test the sealing of
the mixing chamber. By taking the above measures, the uniformity of the slurry
mixture can be improved to over 99.5%, and the layering rate should be ≤ 3%
after 24 hours of standing, ensuring stable quality of the quartz crucible
molding. If there are still problems, it is recommended to contact the
manufacturer to optimize the blade structure and match the mixing requirements
of high-purity quartz slurry.