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Unstable aggregate gradation is a common technical defect in crushing, screening and sand making lines. Fluctuating particle proportion will lead to unqualified finished products and poor concrete workability. All gradation problems occur in equipment processing links, and the technical causes and targeted solutions are summarized as follows:
1. Crushing Link Gradation Instability Causes
Unstable feed size: Mixed large and small raw materials cause uneven crushing force, resulting in random proportion of coarse and fine particles.
Improper crusher gap setting: Too large discharge gap leads to excessive coarse particles; too small gap produces excess fine powder, breaking standard gradation.
Worn crushing wear parts: Uneven wear of jaw plates, cone liners or VSI rotors changes the crushing cavity shape, causing inconsistent particle output.
Unstable feeding volume: Overloading causes incomplete crushing, while intermittent feeding leads to fluctuating particle fineness.
2. Screening Link Gradation Deviation Causes
Damaged or blocked screen mesh: Partial blockage of screen holes reduces effective screening area, making qualified fine particles remain in coarse aggregate.
Unreasonable screen angle and amplitude: Excessive or insufficient vibration amplitude affects particle screening speed and stratification, resulting in mixed specifications.
Uneven material distribution on the screen: Material accumulation on one side leads to incomplete grading and cross-mixing of different particle sizes.
3. Sand Making Link Gradation Fluctuation Causes
VSI rotor speed deviation: High speed produces more fine sand and powder; low speed increases coarse sand proportion, changing fineness modulus directly.
Abnormal material moisture: Wet materials stick to the rotor and cavity, reducing crushing efficiency and causing uneven sand grading.
Unbalanced material ratio: Unreasonable collocation of coarse stone and fine stone entering the sand maker leads to irregular finished sand gradation.
4. Technical Solutions to Stabilize Gradation
Optimize crushing parameters: Set fixed discharge gap according to material hardness; replace worn liner parts regularly to keep the crushing cavity standard.
Standardize screening operation: Clean screen mesh daily, adjust vibration amplitude and screen inclination, and ensure uniform material spreading on the screen surface.
Calibrate sand making parameters: Fix VSI rotor speed based on target fineness modulus; install pre-drying or pre-screening devices for wet materials.
Adopt graded feeding: Use vibrating feeders with grizzlies to pre-separate fine materials, ensuring uniform feed particle size and stable crushing effect.
5. Production Operation Standards
Keep continuous and uniform feeding to avoid instantaneous overload or material shortage.
Inspect equipment parameters every shift to ensure consistent crushing and screening status.
Sample and test finished aggregate gradation regularly, and adjust equipment parameters dynamically.
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The user purchased two sets of sand production line, each set of equipment includes ZSW490*110 vibrating feeder, PE750*1060 jaw crusher, HST250 single-cylinder cone crusher, JYS1238 sand making machine, YK2460 vibrating screen, 3016 sand washer and so on.
The designed capacity of this sand making project is 200t/h, and the equipment used includes 490*110 vibrating feeder, PE750*1060 jaw crusher, PF1315 impact crusher, 9928 sand making machine, two sets of 2460 vibrating screen, two sets of 920 single screw sand washer, two sets of XSD2816 sand washer, two sets of dewatering screen, and several belt conveyors.
Project configuration: Jaw Crusher PE900*1200, Cone Crusher HST315T, Vertical Shaft Impact Crusher VSI6X1263, Heavy Duty Vibrating Screen 2YKZ3080/3YKZ3080, Vibrating Feeder ZG1220Z/ZSW1360, Twin Screw Sand Washer 2XL1120, Bar Vibrating Feeder ZSW1360B, Bucket Wheel Sand Washing Machine DS4024, dewatering screen TS2450 many types of equipment. They will work together with the whole production line to crush and process the sand trap cobbles and mountain ores into natural sand, mechanism sand, and uniform material.
The finished products of the project are used for high-speed railway construction and neighbouring construction materials, which will strongly promote the local economic development. In the future, Jianye Heavy Industry Company will continue to give full play to its years of practical experience in the sand and gravel aggregate, construction waste resource reuse, industrial powder making, silica sand and other industries, as well as EPC one-stop turnkey services, to cooperate with customers and jointly promote the high-quality, healthy and sustainable development of the sand and gravel industry.
Jiangsu Rugao Calcium Powder Factory purchased two sets of Jianye 4121 high-pressure mills for the production of heavy calcium powder, which is mainly used in the filler industry and coating industry, and now it also maintains a close cooperation relationship with Jianye, and every year Jianye sends technicians or sales managers to visit the user.
The user uses calcined petroleum coke to grind and make powder, and the finished coke powder is mainly used for processing graphite electrodes. In recent years, the price of coke powder rises, the user spends tens of millions of dollars to build a production line with an annual output of 60,000-100,000 tonnes of high-quality coke powder, which is the first phase of the project, using two sets of 6R4528 high-pressure grinding mills of Jianye Company.
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