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Reliability on all levels

Automatic handling of powders in paint manufacture
Reliability on all levels

At the Langfang works of Nippon Paint, the market leader in the Chinese paints and coatings industry, the plan was to convert powder handling – until then mostly performed manually – to an automatic feeding process. The new concept concentrated on the issue of reliability and this is reflected in many aspects of the completed solution, e. g. in the areas of operator protection, process reliability, consistency of product quality and future sustainability.

Apart from water, emulsion and a wide variety of liquid admixtures, half of the major components for the wall paints manufactured at the Langfang works are in powdered form, e. g. chalk, kaolin and titanium dioxide. The total daily use of these three raw materials amounts to almost 400 t. These major components were originally delivered in big bags and 25 kg sacks. Every day, hundreds of tons of powder used to be unloaded from lorries into storage before being transported to the production shop, unpacked, weighed and fed into the dissolvers. This situation not only placed a great physical burden on operating staff; it also entailed a significant risk of accidents due to frequent transport with forklift trucks. The heavy workload from 24-hour operation 300 days a year, and the constant need to open and empty sacks, put machine operators under a lot of strain and repeatedly exposed them to dust. Another serious problem was caused by manual weighing and feeding of dissolvers. Operators assembled batches using the printout of production jobs. The result was also recorded by hand. This meant it was easy for errors to occur due to mix-ups with materials or mistakes in weighing. It was impossible to trace materials and processes.

In the long term, the only way to improve this situation, stressful for all concerned, was by automating various production steps. A solution for the process engineering was worked out together with specialists from the Nippon Paint Group; it included the acceptance of incoming products and storage in addition to automatic weighing and feeding of dissolvers. AZO’s Kastor process control and instrumentation system takes care of controlling the overall process.
The Nippon paint solution in detail
In order to keep dust production to a minimum during unpacking and discharging, the first step was to change the type of packaging for raw materials. The goal was to avoid small receptacles, thus reducing the frequency of discharge operations. The preferred method of delivery was to be in bulk tankers or big bags; delivery in sacks was only to be allowed as an exception. Over 90 % of the raw materials in powdered form, including chalk, calcinated and washed kaolin and titanium dioxide, will in future arrive at the factory in bulk tankers. Pressure conveyors will be used to store these raw materials in six outdoor silos with a capacity of 200 m3.
The core of each Nippon Paint plant consists of four groups with a total of eight 10,000 l dissolver tanks plus another four groups with twelve 5000 l tanks. Two dissolver tanks each share one agitator. In the first stage, only the raw materials handling step was automated for the 10,000 l dissolvers. However, the space requirements and capacity of the piping system for automating the 5000 l dissolvers were also included by the planners from the outset. The AZO plant initially needed to provide 24 batches within 24 hours for the four groups of 10,000 l dissolvers.
One vacuum conveying system exists for each group of dissolvers, in other words four vacuum conveying scales in total. This means that all the components needed for one batch can be transported successively onto the conveying scales and weighed there in the space of 90 min. Due to the limited height available in the production shop, the four scales are not installed directly above the dissolvers but 50 m away on the floor of the storage area. In order to fill the vacuum conveying scales independently of each other while simultaneously supplying the batch, each scale was equipped with its own underpressure generator. By allocating product groups and at the same time removing products from the storage silos, it is possible to provide all scales with products at once. An intelligent control and component selection program helps to streamline this process and avoids unnecessary waiting times.
As soon as a request for material is sent from the dissolver allocated to the conveying scales, the complete batch is discharged from the scales and fed continuously into the agitator tank by a separate pressure conveying system within 30 min. Since the dissolvers are equipped with two tanks each, one tank can be filled while the ready-mixed product is being discharged from the other. This allows very high throughput and optimum use of dissolver capacity.
Handling of titanium dioxide
Titanium dioxide (TiO2) is an especially fine raw material, which is extremely difficult to discharge and convey. It is very adhesive and tends to stick in the conveying lines. Blockages are prevented by using special discharge systems, such as aeration floors and flexible feeder lines. In order to obtain high throughput rates, the TiO2 is weighed directly under the silo and the preweighed batch transported to the conveying scales by pressure conveying.
Process control and visualisation system
The whole powder handling plant is controlled and operated via the AZO Kastor process control and visualisation system. The operator has a clear view of the entire plant on a PC in the central control room. Various functions are performed by the system in order to avoid errors: when filling silos, for instance, operator terminals are attached to the docking stations of the outdoor silos and shut-off valves installed in the silo fill lines. If, say, a bulk tanker is connected to the wrong silo, the controls detect the error and the pressure blower will be unable to start.
In addition, there are operating terminals in each area of the plant where specific production steps must be carried out and acknowledged. The AZO and dissolver controls communicate with each other to ensure that the powder components are added to the dissolver at exactly the right point for the next production process. An operator terminal is situated next to each dissolver tank to acknowledge the different steps in the dissolver feeding procedure.
Kastor provides comprehensive data management for organising production jobs, formulations and the storage of raw materials. The system works through the production jobs based on the stored formulations. The material consumption is recorded, the yield determination documented and batches logged. End-to-end tracing and long-term data archiving are also implemented.
A happy client
The CEO of Nippon Paint China is delighted with the outcome: “Compared with manual operation, the new automatic feeding process from the AZO Group is very consistent. It allows us to optimise the paint manufacturing process and reduce batch times. The production capacity of our existing plants has been increased by 25 %. Product quality is far more stable than before and meets the highest standards in the world for paint manufacture. This investment represents a reliable foundation for our ever-growing share of the Chinese market. Our resolve has paid off in the shortest possible time.”
Hall 4, Booth E25
www.cpp-net.com search: cpp0217azo

Teng Sun
Sales Manager,AZO Ingredients Automation System
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