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Experience | Who Blocked the Oil Circuit of the Five-Color Offset Press?

If lubricating oil is the blood of the machine, then the oil pump is the heart of the machine. Once the heart encounters a problem, it will inevitably lead to a series of serious consequences.

Our company once encountered a strange incident: the oil pump of a five-color offset press suddenly stopped supplying oil, even with the replacement of a new oil pump. After more than ten days of intense efforts, the fault was finally successfully resolved. Here, I would like to share the maintenance experience of this fault with everyone.

Symptoms of the Fault

One afternoon, our company's Heidelberg five-color offset press suddenly experienced a 'cardiac arrest' phenomenon (the oil pump could not supply oil).

Based on our experience in oil circuit maintenance, we immediately carried out emergency disassembly, repeatedly cleaned various filtration systems, and then reinstalled and debugged. However, the problem persisted.

So, we suspected whether the oil pump's output was insufficient due to excessive wear?

To quickly eliminate the fault, the equipment department decided to purchase a new oil pump to address the urgent production needs. However, as there was no stock domestically, and imported oil pumps required a week to arrive, the production department decided to take advantage of the waiting time to perform the annual overhaul of the machine.

During this period, we thoroughly checked the old oil pump and found it to be in good condition, so we continued to install and use it. After three days of trial operation, everything seemed normal.

But one night half a month later, the oil pump suddenly stopped working again, and the computer displayed a message indicating low circulation lubricating oil flow. If the operation continued, the control system would automatically lock the main motor.

And once the main motor was locked, the consequences would certainly be more serious!

Replacing the New Oil Pump

The next day, we visited the site again, suspecting that the old oil pump might be damaged and unable to work for a long time.

By now, the new oil pump had arrived, so we immediately got to work, dismantling the casing and drilling into the machine. Finally, we replaced the old oil pump with the new one.

Surprisingly, after starting the new oil pump, it still did not supply oil. Upon careful observation, we found that an unloading hole beside the partition valve on the inner wall of the wallboard was constantly spraying oil. This indicated that the oil pump was working normally, but the oil pumped out could not enter the oil pipe.

Clearly, the key issue now was that the oil circuit was blocked.

Thorough Investigation

To quickly solve the problem, we sought advice from some experienced engineers, but unfortunately, there were no ready answers. With no other options, we had to rely on ourselves. Learning the basics of the offset printing workshop, one can also rely on oneself. Click here to learn.

We pondered and suspected whether the two solenoid valves on the partition valve were faulty?

The next day, when we returned to the site and carefully dismantled the valve core, we found that the internal structural parts were undamaged; when we connected a 24V power supply, it still worked flexibly as usual. This indicated that the solenoid valve was good.

We then speculated, could it be that the oil pipe was connected in reverse? Impossible! Were the upper and lower positions of the solenoid valve reversed? Impossible!

Were the solenoid valve wires connected in reverse? Even more unlikely!

With each suspicion, verification, and denial, and then suspicion, verification, and denial again, the hope kindled within us was extinguished time and again. Everyone almost lost their direction.

In this situation, everyone involved in the repair was severely hit, but no one gave up. We decided to try again.

After lunch, we once again crawled into the machine, installed the solenoid valve, and carefully connected the wires.

To verify the function of the solenoid valve, we decided to cut off the power supply to the solenoid valve. Surprisingly, the oil circuit was unblocked, but as soon as power was applied, the oil circuit was completely blocked.

Analysis of the Cause

It turned out that the two solenoid valves of this five-color offset press had different functions. One of them was responsible for switching the oil pressure between 1 bar and 12 bar, and the other was responsible for switching to lubricate the side bearings and paper feeding chain when the oil pressure switched to 12 bar.

According to the computer settings of the five-color offset press, when the machine runs at 15,000 revolutions per hour, the oil circuit needs to perform action switching through the solenoid valve to transmit 12-bar pressure lubricating oil to the side drum bearings, shaft sleeves, and paper feeding chain for timed lubrication. After lubrication, the solenoid valve core operates to switch back to the main circulation.

However, in some cases, the relay, due to frequent power on and off over the years, causes the contacts to generate sparks like arc welding, sticking together.

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When the oil circuit switching is completed and the relay is required to power off, it cannot be disconnected. The solenoid valve controlled by it continues to be powered on, erroneously blocking the main machine oil circuit circulation.

At this point, we suddenly understood why the solenoid valve was so hot when we first removed it—it was because the relay contacts were sticking, causing it to work incorrectly in a continuous powered-on state.

Conclusion

The troubleshooting of this fault has given me a deep understanding: difficulties are like springs; if you are weak, they are strong. As long as we think of more ways and persist a little longer, we can overcome them!

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Here is the translation of the ten dust removal methods in a printing factory:

Tape Wrapped on Paper Feeding Wheel Dust Removal Method: Dust removal is achieved by wrapping double-sided or fiber tape around the paper feeding wheel, using the adhesive property of the tape. This method has the advantage of noticeable initial dust removal effects and relatively easy installation. However, over time, the tape may accumulate paper debris, forming hard blocks that can lead to indentation on the printed surface. Regular cleaning of dust on the wheels is necessary.

Tape Attached to the Paperboard Dust Removal Method: When dust sticks to the printing plate, causing white spots in printing, double-sided tape can be attached to the areas with print defects. This helps remove dust from the printing plate, avoiding the need to wipe the plate. However, there is a risk of the tape sticking to the printing plate or other surfaces.

Vertical Brush Dust Removal Method: Printing machines typically have a row of brushes, and over time, the brushes may wear out and collect dust. Regular cleaning and maintenance are required for these brushes. If the brushes wear out, they lose their dust removal function. The height of the brush installation should also be periodically checked, and using double rows of brushes may improve dust removal efficiency.

Roller Brush Dust Removal Method: This method involves adding a printing unit with two brush rollers. The brush rotation speed is lower than the equipment speed, creating a speed difference for effective dust removal. However, this method requires a relatively high investment.

Water Dust Removal Method: Installing a full-size printing plate for the first color and applying water to clean paperboard dust. This method works well, especially in winter to prevent paperboard from cracking. The drawback is that printing may become prone to ink loss after applying water, and cleaning the ink rollers takes a longer time.

Equipment Cleaning Dust Removal Method: Due to the significant dust in cardboard and paperboard workshops, dust easily falls into the top and machine baffle of the printing machine. Failure to clean the equipment in a timely manner can lead to the accumulation of a considerable amount of dust at the top, causing print defects. Regular equipment cleaning is crucial.

Floor Water Sprinkling Dust Removal Method: Dust on the floor mainly comes from the slotting unit, where paper dust generated during slotting easily flies into the equipment. Sprinkling water on the floor prevents the paper dust from flying up, making it a convenient method.

Dust Pipe Cleaning Dust Removal Method: Installing a row of dust suction devices on the side of the brush, similar to a vacuum cleaner, but the suction port spans the width of the printing machine. Each suction pipe can be individually closed, and dust removal is achieved by adjusting the suction force.

Paperboard Running Empty Dust Removal Method: Directing the paperboard through the printing machine unit while running it empty to remove dust, followed by actual printing. This method is relatively time-consuming, and there is a risk of board crushing. It is not recommended for frequent use.

Manual Brushing Dust Removal Method: The simplest and most time-consuming method with relatively good effectiveness. It involves manually brushing each sheet of paperboard and then organizing them before printing. Suitable for a small quantity of paperboard but becomes highly time-consuming for larger quantities.

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The Green Development Path of Printed Rubber Fabric Manufacturing

Jiangsu Kangpu Company has achieved significant results in green process manufacturing during the "13th Five-Year Plan" period. Through continuous process improvement, efforts to maintain technological advancement, and alignment with the increasing global emphasis on environmental protection, the company has strengthened the environmental attributes of printed rubber fabric manufacturing, leading it towards a green development path. This journey has been challenging and arduous, but we are fortunate to have successfully developed a comprehensive set of green manufacturing processes. Let's now review the green reform and development journey of Jiangsu Kangpu Printing Technology Co., Ltd.

Green Process Reform during the Pulp Making/Coating Period

The pulp making/coating process was once the sole production process for printed rubber fabric manufacturing, dominating the industry's history for a century.

In the traditional process of rubber fabric manufacturing, rubber needs to be dissolved in organic solvents to form a viscous rubber slurry, known as the pulp making process.

The formed rubber slurry contains impurities, requiring filtration. The traditional method involved pouring the slurry into a specially designed nylon filter bag, allowing gravity to facilitate natural filtration, known as gravity pulp filtering. This method is open, and due to the viscosity of the slurry, the filtration time is long, resulting in significant unorganized emissions of organic solvents.

Post-green process reform, pulp filtering was changed to pressure filtration, wherein the rubber slurry is pressurized inside a fully enclosed vessel. Simultaneously, an automatic metering system for organic solvents was introduced, with the solvent automatically injected into the pulp-making equipment in a sealed state. This method reduced unorganized emissions of organic solvents during slurry filtration by over 80% and increased efficiency by 70%.

The coating process is the main procedure, where the filtered slurry needs to be uniformly applied to the base fabric. Prior to technological transformation, workers manually applied the slurry to the scraper using a spoon, known as manual coating. This process resulted in severe unorganized emissions, and operators had to wear gas masks. With the green process reform, a closed-pressure automatic coating system was adopted, using compressed air to pressurize the slurry along pipelines for coating. This not only reduced emissions but also significantly reduced the labor intensity of workers.

After coating, drying is essential, utilizing heat and airflow to evaporate the organic solvents in the slurry on the base fabric, forming a dry rubber film.

In the early stages, organic solvents generated during the drying process were directly emitted into the atmosphere, becoming a major volatile organic compound (VOC) emission in the production of printed rubber fabric, contributing to air pollution. Around 2008, Shanghai Xinxing Company invested again to environmentally upgrade this process. Collaborating with the Institute of Automation, Chinese Academy of Sciences, they successfully developed and installed a "Toluene Recovery Device." Following this, Shanghai Xinxing invested 7 million to install two toluene recovery devices with a 30,000 air volume. After inspection by local environmental authorities, emissions fully complied with national standards. Additionally, toluene recovery rates reached 80%, allowing the recycled toluene to be reused in production.

During the pulp making/coating process, the company achieved a peak of environmental reform.

Green Technological Development in the New Era

From an environmental perspective, although transformations like pressure filtration, automatic coating, and toluene recovery significantly reduced organic solvent emissions, using toluene still led to emissions, even with strict treatment. Statistics show that despite many environmental transformations and control measures in the pulp making/coating process, 20% of toluene is still emitted into the atmosphere each year.

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Is there a production process that achieves completely zero VOC emissions? The answer is yes. Production processes using water as a solvent and solvent-free calendering processes can achieve this goal. However, although the paths are there, walking them is not easy; otherwise, the pulp making/coating process would not have dominated the printed rubber fabric manufacturing field for a century globally.

Regarding solvent-free calendered rubber fabric manufacturing processes, the company initiated basic research a decade ago, achieving certain results. Although calendering technology is a mature process in the rubber manufacturing industry, due to the high precision and performance requirements of rubber fabric production, globally, apart from a few companies using calendering technology, most multinational companies in rubber fabric manufacturing use pulp making/coating processes. Building on the preliminary research results of Shanghai Xinxing, Jiangsu Kangpu Company further conducted technical research, thoroughly solving a series of technical challenges such as rubber refining, calender thickness, and compounding. In 2018, the solvent-free calendered rubber fabric production process of Jiangsu Kangpu Company passed the ministerial-level scientific and technological achievement appraisal organized by the China Petroleum and Chemical Industry Federation, with the appraisal conclusion being "leading domestically and internationally advanced." This marked a significant success in the environmental manufacturing technology of Jiangsu Kangpu Company's printed rubber fabric. The implementation of the calendered rubber fabric manufacturing process completely resolved the problem of the remaining 20% toluene waste gas emissions, achieving zero emissions of toluene solvent waste gas in the printed rubber fabric manufacturing process.

In 2019, Jiangsu Kangpu Company dismantled all pulp making/coating equipment and fully transformed into a solvent-free calendered production process. In the green development journey of printed rubber fabric manufacturing, a revolutionary leap forward was achieved in China. The country stands at the forefront of the world in the green development of printed rubber fabric manufacturing.