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Thermal cleaning of plastic contaminations  #10(116), 2012

Juris RADUS,
Uman Ltd.

The development of polymer processing technologies along with optimization of production processes make the problem of cleaning draw holes, melt pumps, hot runner components, blown film die heads, heat exchangers, nozzles, filters, etc. especially acute, because only clean and undamaged parts of equipment can guarantee the highest quality of the final product of plastics. And this is just the reason why the more and more processors choose the thermal cleaning systems of the German company SCHWING Fluid Technik GmbH (, ensuring qualitative, safety, ecological, rapid and cost-effective cleaning of tools

What is a thermal cleaning?
The cleaning process of contaminated equipment parts from the polymers is being held in an oven of special type and at temperature of 300 to 500°C. In the oven’s cleaning chamber the so-called pyrolysis takes place – thermal decomposition of polymers into components while converting plastics from the solid state to gaseous one.

SCHWING Fluid Technik GmbH produces four types of furnaces for heat treatment, which implement pyrolysis at different process conditions: in vacuum, in a fluidized (boiling) layer (with oxygen), hydrolytic (without oxygen), via burning-out ((with a small amount of oxygen). Operation of all systems is based on the common principle: cleaning process is carried out under low level of oxygen or without it (i.e. at zero level). The lack of oxygen prevents arbitrary inflammation of the polymer on the parts, which results in irreversible corruption of metal structure. During pyrolysis carbon black and gases are produced, that are either burned in thermal afterburner or cleaned in a catalytic converter.

The pyrolysis is followed by the second stage of thermal cleaning - oxidation. That’s the only way to completely remove the residues of carbon, particularly for not disassembled parts. Very often just the lack or insufficiency of oxidation stage determines the cleaning quality. After pyrolysis and oxidation that remove organic contaminations, the parts’ surface might be fouled only by organic residues originally contained in the polymer – say, pigments. Removal of inorganic can be fulfilled via quite simple procedures – air blowing with compressed air, flushing with water under pressure, wiping with a soft cloth. In case of micron openings the treatment in an ultrasonic bath is required.

Thermal cleaning ensures the main objective – it retains the structure and geometry of the metal parts, as they are not subjected to chemicals or open flame, there’s no risk of the point material overheating. Besides, mechanical impact, human factor and environmental pollution are also excluded. Thermal cleaning can be applied both to assembled blocks and separate parts. Safety of the parts and the cleaning process itself becomes a priority task, as soon as requirements on safety production increase along with development of technologies; it is also worth noting that the prices on equipment and spare parts have also a stable tendency to growth. Hence nowadays there can be hardly found a company that is ready to subject its high-value equipment to a risky, low-quality or hazardous cleaning process. Therefore the interest in SCHWING Fluid Technik technologies is constantly growing, and the range of companies that use the equipment of SCHWING for the heat treatment, is continually expanding.

Equipment for thermal cleaning
Each product line - CompactClean, VacuClean, InnovaClean and MaxiClean – comprises several modifications of the base line model, differing in sizes of the working chamber. Chambers of the MaxiClean series can be manufactured according to customer requirements – say, in 2011 SCHWING Fluid Technik has installed at the plant in Shanghai (China) MaxiClean system having length of 9 meters.

CompactClean is a compact system for thermal cleaning of small-size parts (the base of so-called loading basket starts with 210x300 mm size). Several models can be connected to a standard balloon of propane-butane, thus allowing to install the system at any workshop. CompactClean is widely used by laboratories and small enterprises to clean such parts and tools as nozzles, valves, small filters.

The systems of vacuum pyrolysis VacuClean are also available in several implementations. They are commonly used for cleaning “sensitive” equipment, like blow die heads for multilayer films, spinnerets, large screws, hot runners. VacuClean 0810T and 1212T models are specially designed for cleaning candle filter bundles or breaker plate columns. Global manufacturers of polymer fibers, polymers and various polymer products are gradually replacing the expensive, complex chemical (TEG bath) and mechanical cleaning concepts, as well as prohibitive treatment by an open flame, by the technologies of SCHWING Fluid Technik. Such world famous companies as Windmoeller & Hoelscher and Hosokawa Alpine use the cleaning equipment of SCHWING Fluid Technik.

MaxiClean systems are designed for cleaning large or heavily contaminated parts. They are often used to clean manifolds, heat exchangers, hot runners, blown film die heads.

InnovaClean systems fundamentally differ from all others in that the retort is filled with the heat transfer ThermClean sand, which is fluidized by compressed air thus providing a boiling bed without abrasive impact on the parts’ surfaces – they are not get damaged because of the low velocity of the ThermClean, which serves only for heating uniformity. In this scheme the pyrolysis and oxidation are carried out simultaneously, which speeds up the cleaning process and makes it more efficient. InnovaClean systems are of particular demand in production of polymer fibers. Moreover, InnovaClean is the sole system of thermal cleaning capable to clean parts of halogenated polymers (PVC, PTFE, PEEK, polymer-sand blends) and plastics containing bromine, fluorine, iodine.

Thermal cleaning is designed for all types of polymers without exception – usually it’s just the matter of proper cleaning system, as well as optimal temperature and time operating modes.

The company SCHWING Fluid Technik was founded in 1969; in 1990 the company started to take orders on the parts cleaning from polymers. To date SCHWING Fluid Technik has thermal cleaning centers in 6 countries on the 3 continents. The company, operating under the brand name SCHWING Technologies since the end of 2012, annually cleans at its enterprises over a quarter of million of parts of various kinds from all types of polymers. 20 years of experience made the company’s specialists the high standing experts in the cleaning technologies for equipment and parts. SCHWING systems successfully work at the plants in Russia and Belarus. Since 2011, the company’s representative in Russia is Uman Ltd. (Saint-Petersburg).

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