The automatic sampling machine is a key equipment for quality control in
quartz sand production lines, responsible for proportionally sampling finished
or semi-finished sand samples (with a sampling representativeness error of ≤
3%), providing accurate samples for quality testing. If the sampling
representativeness is poor (the deviation between the test data and the actual
data exceeds 5%) and the material is stuck frequently (more than 3 times per
shift), it will lead to quality misjudgment and production line shutdown. Based
on practical experience, summarize the three-step troubleshooting method to
quickly restore accurate sampling.
Step 1: Optimize sampling structure and location - Sampling rationality is
the foundation of precision
The improper design and installation position of the sampling head is the
core reason for poor representativeness.
Inappropriate diameter or shape of sampling head: If the diameter is less
than 3 times the maximum particle size (such as quartz sand with a maximum
particle size of 5mm and a sampling head diameter of only 10mm), large particles
will be intercepted; The sampling head is designed with a flat mouth, which is
prone to material accumulation. The sampling is for surface sand samples, which
cannot reflect the overall quality. Replace the "horn shaped sampling head" with
a diameter set to 5 times the maximum particle size (e.g. 5mm particles with
25mm diameter) to ensure uniform entry of coarse and fine particles; Adopting a
"slanted opening" at a 45 ° angle to the direction of material flow to avoid
concentrated sampling of surface materials.
Improper installation position or depth: Installed at the edge of the
conveyor belt, only taking material from one side; Insufficient insertion depth
(<1/2 of material thickness), did not retrieve the underlying material.
Install the sampling machine in the middle of the belt, ensuring that the
sampling head covers more than 80% of the belt width; Adjust the insertion depth
to 2/3 of the material thickness, install a limit device to fix it, and avoid
displacement during operation.
Step 2: Calibrate control logic and operating parameters - Program adaptation
for anti jamming materials
Abnormal sampling frequency, duration, and driving system can lead to
material jamming and sampling deviation.
Unreasonable sampling parameter settings: low frequency (sampling once per
hour), incomplete sample coverage; The duration is too short (<5 seconds),
and the sampling volume is insufficient (less than half of the detection
requirement); Excessive frequency (once every 10 minutes) can easily cause
material accumulation and jamming. According to the production line capacity
adjustment: when the capacity is 50t/h, a sample is taken every 20-30 minutes
for 8-10 seconds to ensure that the single sampling amount is ≥ 500g; through
the PLC controller preset program, "timed and quantitative" sampling is achieved
to avoid human intervention deviation.
Drive motor or transmission mechanism failure: Insufficient motor power
(0.75kW motor required for sampling 1kg/time, actual use 0.55kW), unable to
drive when stuck; The gearbox is worn out (with a mesh clearance exceeding
0.3mm), and the sampling head is stuck during operation. Replace the matching
power motor and install overload protection device (automatic shutdown alarm
when stuck); Inspect the gearbox, replace worn gears, add industrial gear oil to
ensure smooth transmission.
Step 3: Adapt material characteristics and anti blocking design - avoid
faults at the source
The lack of material status and equipment anti blocking structure will
exacerbate the sampling problem.
High moisture content or large impurities in the material: moisture content
exceeding 8%, fine powder adhering to the sampling channel (wall thickness
exceeding 5mm), resulting in blockage; Mixing oversized impurities (>10mm)
can block the sampling head. Ensure that the moisture content of the material is
≤ 5%, install a sieve (with an aperture of 8mm) upstream of the sampling machine
to remove large impurities; Install a polyurethane wear-resistant lining plate
on the inner wall of the sampling channel, and blow the channel with a
high-pressure air gun (0.5MPa) every week to avoid bonding and material
accumulation.
Improper sample transport method: using vertical transport tubes, fine powder
is prone to settling and accumulating; The conveying speed is too slow
(<0.5m/s), and the material is stuck in the channel. Tilt the conveying pipe
at a 30 ° angle to shorten the length of the vertical conveying section; Install
a vibrator (frequency 20-25Hz) to prevent material settling; Adjust the screw
speed of the conveyor to 60-80r/min to ensure that the sample is quickly
transported to the detection device.
Daily maintenance should pay attention to: cleaning the sampling head and
residual materials in the conveying channel every day, and checking the
operating temperature of the motor (≤ 65 ℃); Calibrate the sampling frequency
and duration every week, and tighten the bolts of the transmission mechanism;
Monthly inspection of PLC control program accuracy and replacement of aging
sensors. By taking the above measures, the representative error of sampling can
be reduced to within 2%, and the number of jamming times can be reduced to less
than once a week, providing reliable guarantee for the quality control of quartz
sand. If there are still problems, it is recommended to contact the manufacturer
to optimize the design of the sampling head and match the material
characteristics of the production line.