The 10-ton/hour production line of an oyster sauce factory in Jiangsu put into operation in 2023 was shut down 5 times a day on average, and a single shutdown took 30 minutes to clean up. The monthly output loss reached 12 tons, and the direct economic loss exceeded 80000 yuan. The technical team initially believed that the plug was caused by the high viscosity of oyster sauce (12000mPa · s). The large-aperture filling head was replaced successively and the viscosity was reduced by heating the material. However, the plug frequency only decreased by 10%, and the problem has not been cured.

1. Case Background: Production Dilemma of High Viscosity Material Plug

the production line of the oyster sauce factory adopts the process of "mixing storage tank-pipeline transportation-piston filling machine", and the main product is gold standard oyster sauce added with 3% oyster meat particles. At the initial stage of production, the filling head needs to be disassembled and cleaned twice a week, and the oyster meat lumps and sauce solidifies 0.5kg each time. The initial response measures taken by the technical team revolved around "reducing material viscosity:

1. the aperture of the filling head was expanded from 8mm to 12mm, but the filling accuracy was reduced from 2g to 5g due to the large aperture, which did not meet the requirements of GB 7718-2011 label identification, and 3 batches of products were returned by the merchant;

2. the temperature of oyster sauce was increased from 25 ℃ to 40 ℃ by pipe heating device, and the viscosity was reduced to 8000mPa · s, but the aroma of oyster meat was lost by 30%, the flavor score of the product was reduced from 92 to 78, and the terminal sales volume decreased by 15%.

After two consecutive months of commissioning, the plug problem has not been solved, the effective operation rate of the production line is only 85%, and the enterprise is facing the risk of customer order delay.

2. Surface Problem Investigation: Misjudgment Mistake of "Material Viscosity"

the initial investigation direction of the technical team is completely focused on the material itself and the single point of the filling head:

1. the rheological properties of the oyster sauce were tested to confirm that it was a non-Newtonian fluid with obvious shear thinning characteristics-a viscosity of 5000mPa-s at a shear rate of 100 s¹ and a viscosity of 12000mPa-s at rest;

2. dismantling the filling head, it was found that the blockage was concentrated in the contraction section of the discharge port, and the blockage was an agglomeration of oyster meat granules and starch;

3. the filling head with different aperture was tested, and it was found that the larger the aperture, the lower the shear rate during filling, the higher the viscosity of the material, and the easier the clogging.

At this time, the technical team realized that simply adjusting the filling head or material viscosity could not solve the problem. The core reason for the plug was not "the material was too sticky", but the continuity of the production process was broken.

3. essence problem mining: material and beat mismatch is the core incentive

through continuous 12-hour tact and material condition monitoring of the whole process of mixing, conveying and filling, the root cause of the problem is finally located:

1. the stirring beat is not synchronized with the filling beat: The fixed rotation speed of the stirring storage tank is 20rpm, and the stirring and discharging beat is 8 times/minute (125kg for each discharge), but the suction beat of the filling machine is 10 times/minute (100kg for each suction), resulting in discontinuous supply of materials in the pipeline. The static time of local materials exceeds 2 minutes, oyster meat particles and starch are rapidly agglomerated under static conditions, and the agglomeration diameter exceeds 10mm, which cannot pass through the filling head;

2. stirring process not adapted to non-Newtonian fluid characteristics: The shear rate produced by the stirring rate of 20rpm is only 20s, which cannot effectively suspend the oyster meat particles. The sedimentation rate of the particles at the bottom of the storage tank reaches 15%, and the settled particles form a blockage when they are transported to the filling head through the pipeline;

3. transmission pipeline without pulsation suppression device: The suction process of the piston filling machine will cause the pressure fluctuation of the material in the pipeline, and the fluctuation range will reach ± 0.2MPa. When the pressure is low, the flow rate of the material will drop sharply, and the particles will aggregate to form agglomerates.

4. solution: matching beat + optimization process, completely solve the plug problem

to address the core problem of mismatch between materials and beats, the technical team implemented three targeted corrective measures:

1. stirring and filling beat synchronous linkage the motor of the stirring tank is changed to frequency conversion control, and the PLC system is linked with the suction beat of the filling machine. The rotating speed of the stirring tank is automatically increased to 40rpm for each suction of the filling machine, and is restored to 20rpm after 10 seconds, so as to ensure that the shear rate of the materials in the pipeline is always maintained above 50 sg¹, the viscosity of the materials is stable at about 6000mPa · s, and the particle sedimentation rate is reduced to below 1%;

2. installation of online homogenizing device: An online homogenizer with a shear rate of 500s is installed in front of the inlet of the filling machine to carry out secondary homogenization on the materials transported to the filling head, and the agglomeration of oyster meat granules and starch is broken to less than 2mm to ensure that the materials can smoothly pass through the filling head with an aperture of 8mm;

3. installation of pipeline pulsation suppressor A pulsation suppressor with a volume of 50L is installed on the pipeline at the inlet of the filling machine to control the pressure fluctuation range in the pipeline within ± 0.05MPa to avoid particle aggregation caused by sudden drop in material flow rate.

After rectification, the frequency of filling head plugging was reduced from 5 times per day to 0, the effective operation rate of the production line was increased to 99%, the filling accuracy was stable at +/-1.5g, the product flavor score was restored to above 90 points, the terminal sales volume rose by 12%, the monthly output loss was reduced by 12 tons, and the annual economic loss was recovered by more than 960000 yuan.

5. practical operation warning: high viscosity material production needs to pay attention to process continuity matching

the core value of this case is to provide 3 practical warnings for high-sticky food manufacturers:

1. avoid single-point adjustment errors: The plug of high-viscosity material is not a simple material viscosity problem, which cannot be solved only by replacing the filling head, heating the material and other single-point measures, but needs to be investigated from the rhythm coordination angle of the whole process;

2. adapting non-Newtonian fluid properties: High-viscosity foods are mostly non-Newtonian fluids. The beats of stirring, conveying and filling should be adjusted according to their shear thinning characteristics to ensure that the materials are always in a dynamic shear state in the whole process and prevent particles from settling and caking;

3. establish beat linkage mechanism the rhythm synchronization of stirring, conveying and filling equipment is realized through PLC system to avoid local static agglomeration caused by discontinuous material supply, which is the core means to solve the problem of high-viscosity material plug.

Conclusion

the plug problem of high-viscosity food is essentially a collaborative failure of the production process, rather than the "viscosity" of the material itself. Enterprises need to jump out of the inertial thinking of single point adjustment, pay attention to the matching of material characteristics and equipment beat, through the system optimization process and equipment linkage, in order to completely solve the problem of plug downtime, to ensure production efficiency and product quality.