Story
RecyclingMust climate protection impair quality?
PTFE and upcyclingDoes that sound too good to be true?
PTFE
For what?
PTFE or polytetrafluorethylene is often used in industrial areas such as sealing technology, electrotechnology or in chemical plants.
Character profile
The polymer has a sensational profile: high temperature and weather resistance, very good resistance to chemicals and a low friction coefficient are just some of the properties to be emphasized. This makes PTFE a material with extremely versatile use, in particular when subjected to high temperatures or heavy friction.
Problematic properties
However, the material also has its drawbacks. As a result of low intermolecular interaction between the polymer chains, pure PTFE demonstrates low modulus of elasticity, a high cold flow as well as a high wear rate.
Tailor-made filling material mix
In order to compensate these properties and to improve the mechanical properties on the other hand, a tailor-made filling material mix is needed. In particular in the area of sealing materials as used in reciprocating compressors, this optimization is highly relevant. The thermal load and the dynamic pressure stress are particularly high there. Depending on the process gas to be compressed, individual filling material combinations are required here.
PTFE recycling – a great challenge
The special and individual processing make the recycling of PTFE a really demanding challenge. Finally, all filling material mixes consist of highly individual materials in accordance with the respective requirements.
STASSKOL
Experts for tailor-made plastics
Recycling
The recycling challengeHow do you recycle a highly filled material mix?
A very work-intense process is necessary for the sustainable handling of PTFE because PTFE is extremely difficult to recycle. These work-intense process flows finally crush the plastic so that the particle size is as small as possible. The amazing result shows that the recycled material not only meets the quality of the new goods, but even exceeds the quality of the original material.
In order to ensure successful implementation of the process, the so-called Press Sinter Method is applied. This can either be implemented as Cold Compression Molding (CCM) or as Hot Compression Molding (HCM). When using the press and sinter method for PTFE, the material or the mix must again be crushed to the original particle size of some 20 to 40 µm. Primarily, small particle sizes are required.
Manufacturing semi-finished products under standard processing conditions
Mono-fraction collection
of chips and remnants of the corresponding material
Coarse crushing
of all the PTFE waste collected with a customary cutting mill
Fine grinding
the crushed particles with a special jet impact classifier mill
Mixing in
the ground material into the new goods in different proportions using a powder mixer
Manufacturing semi-finished products under standard processing conditions
Production of semi-finished products
of semi-finished products
Checking the properties of the materials
Using hardness and density measurement, tension tests and tribological characterization
Process engineering
Trial and errorSelection of the experiment materials
Whilst SK202 is a CCM-PTFE with glass fiber, carbon and graphite, SK801 is an HCM-PTFE with carbon fiber and thermoplastic filling material.
These two materials were selected in order to enable application of both the cold and hot compression processes. The cold pressing process is a greater challenge because the size of the pulverulent particles plays a special role. A mixture with a significant proportion of carbon and glass fibers was selected because here the danger of reduction of the fiber length ratio and consequently a direct effect on the material’s properties exists.
From coarse to fineBut how?
Here, the professionals for fine and finest grinding are involved in the project: the NEUMAN & ESSER Process Technology experts.
NEUMAN & ESSER Process TechnologyMore than 90 years’ experience in mechanical process technology
The right technologyICM 15 for fine particle sizes
For impact grinding, the grinding material is filled into the grinding zone via a constant air flow. During grinding, the grinding tools throw the feed material into the liner and crush it. The constantly present purge air flow carries the ground material out of the grinding zone. This material discharge is blocked by a fast-rotating classifier wheel. The grinding fineness can be set flexibly using the jet impact classifier’s rotary speed. The classifier wheel can only be passed by particles which are small enough to find a route through a gap in the classifier wheel at a high speed. The variation of the parameters grinding speed (m/sec), mass flow (kg/h) and the classifier wheel speed (m/sec), the process can be regulated to achieve the desired particle size. The extent of filling of the grinding chamber also influences the result decisively.
The advantages of the ICM are in its narrow grain distribution with precise upper grain restrictions of 20 μm to 2,000 μm and the low particulate matter shares.
Grinding
The grinding experimentSK202 and SK801 in the ICM 15
At a throughput of 6.9 kg/h for the SK202, a particle size of 47.7 µm resulted and at a throughput of 2.5 kg/h a particle size of 44.6 µm.
For the SK801, the particle size was 56.7 µm at 9.7 kg/h throughput and 47.5 µm at 2.7 kg/h throughput.
Marc Giersemehl
Technical Managing Director NEUMAN & ESSER Process Technology
A wordon the subject of process engineering and the grinding test procedure
The first result SK202 and SK801 in the ICM 15
The first result SK202 and SK801 in the ICM 15
Analysis procedure
CharacterizationMeasurement of the mechanical and tribological properties
Wear resistance Measurement of the tribological properties
Wear resistance Measurement of the tribological properties
Large particles reduce the mechanical rigidity
Large particles reduce the mechanical rigidity
The maximum recyclate share of SK202 Recyclate mix options
The maximum recyclate share of SK202 Recyclate mix options
The maximum recyclate share of SK801 Recyclate mix options
The maximum recyclate share of SK801 Recyclate mix options
Knowledge
The resultPTFE is recyclable!
That is different for hot compressed PTFE materials. Here, despite the increased particle size, a semi-finished product can be won from pure recyclate whose properties can compete with those of new goods. That also has to do with the molding process during which the material is impinged with pressure whilst it is in a thermoelastic state above the glass transition temperature. As a result, air trapped in the green pellet can escape, providing a considerably denser material structure as opposed to cold compression materials.
The results show that waste from well-filled sealing materials can be recycled based on PTFE and then reintroduced into the production process. This is not only interesting with regard to strengthened environmental protection, but can also provide processing companies with a financial advantage. Moreover, properties such as the resistance to wear are influenced positively due to use of the recycled material.
Process integration
Process integrationImplementation into the production
The Dressler Group combines the technology of the NEA PT with competent expertise and years of experience in the in the grinding of plastics.
Thus, recycling can be realized in 3 steps:
1. collection and pre-grinding of the chips by STASSKOL.
2. refining by means of ultra-fine grinding by the Dressler Group
3. introduction of the ground powder into the STASSKOL mixing process.
The realization of the project not only protects the environment, but also improves the durability of the materials and reduces the company's dependence on the current raw material situation.
A triple win due to the cooperation within NEA GROUP, as well as with Dressler Group as a strong partner.
Conclusion
Marc Langela
Central Division of Technology STASSKOL
A Wrap-Upto the recycling possibilities of PTFE.
See you again
STASSKOL
STASSKOL Profil Sealing technology for more than 100 years
STASSKOL Profil Sealing technology for more than 100 years
Translated with www.DeepL.com/Translator (free version)
Founded in 1920
as “Deventer Werke”[works]
Locations
in Germany, USA, China.
114 employees
worldwide
Sealing experts
for compressors and rotating equipment
High-performance plastics
up to 1,200 mm diameter
In-house material production
Own research & development
State-of-the-art test bench
Patent forge
Tribometer
Endurance test for sealing elements under realistic conditions and functional testing and wear behavior
STASSKOL locationsCan be found worldwide
STASSKOL products must meet the most stringent requirements and are constantly developed further. Experience and manufacturing know-how are passed on from generation to generation and are very valuable for the company.
STASSKOL productsHigh-performance plastics with outstanding properties for demanding applications
High-performance plastics
ESKAFLON – PTFE-based
PTFE is a highly fluorinated high-performance plastic which is characterized by high temperature resistance, excellent chemical stability as well as by low friction coefficients.
ESKAPEEK – PEEK-based
PEEK is a thermoplastic, partially crystalline high-performance plastic and belongs to the group of polyaryletherketones. This high-performance plastic was originally developed for use in Aerospace.
ESKIASINT – PI-based
The group of the polyimides belongs to the absolute pinnacle of high-performance plastics. Dependent on their chemical structure, polyimides belong to the group of fusible or non-fusible materials.
Compressor seals
Piston rings and rider bands
Piston rings and rider bands are used in horizontal, vertical and v-shaped cylinders
Gastight piston rings
The piston rings of reciprocating compressors need to be constantly pressed against the cylinder wall. This guarantees optimum sealing efficiency.
Hyper-Products
Hyper compressors are a key element in the production of low-density polyethylene (LDPE).
Piston rod packings
Piston rod packings (short form PRP) are used in double-acting reciprocating compressors to seal the crank-side cylinder. Because the packing rings seal on the reciprocating piston rod, they wear out over a period of time.
CNGS Piston rod packing
STASSKOL manufactures piston rod packings for a wide variety of applications. For CNG (LPG) filling station compressors, a new gas-tight piston rod packing “Compressed Natural Gas Solution” has been developed, which has significantly lower leakages than the standard piston rod packing.
AIRS Piston rod packing
A special packing was developed for air applications, the AIRS – Air Solution, which differs optically clearly from the standard.
Single Sealing Ring
The patented STASSKOL Single Sealing Ring combines the main sealing ring and cover ring to one unique unit.
LESS Static pack
A compressor relieves pressure via the piston rod packing after shutdown. The installation of a static pa (a Zero Emmision Sealing Solution) prevents the escape of process gas into the atmosphere during machine downtime, therefore avoiding any leakages, and resulting in a zero emission system.
Oil wiper packing
The oil wiper packing can be used in compressors of a horizontal, vertical or angled design. The packing are exclusively applied in crosshead machines.
SOSS – Standard Oil Sealing Solution
The SOSS – Standard Oil Sealing Solution – can be used in compressors of a horizontal, vertical or angled design. The packing are exclusively applied in crosshead machines.
BOSS – Balanced Oil Sealing Solution
The BOSS – Balanced Oil Sealing Solution – is an innovative scraper design. These oil wiper packing is characterized by a high scraping efficiency and tightness that avoids direct oil passage and overflowing process gas from the intermediate distance piece.
Intermediate packing
In reciprocating compressors the compression chamber is sealed against the distance piece by means of a piston rod packing. 100% sealing efficiency is technical not possible even in case of piston rod packings with a buffer gas system there is a possibility that process gas is able to enter the first distance piece.
Valves
The valves of a compressor belong next to piston rings, rider rings and piston rod packings to those parts which require frequent replacement due to wear. STASSKOL offers to OEM the reconditioning of these valves.
Seals for rotating shafts
Shaft seals
Roots, cell, screw, liquid ring or turbo compressors require sealing elements in a wide variety of shapes to seal the compressed medium from the atmosphere. STASSKOL products for these applications go under the name DynamicSeal.
Shaft sleeves
Shaft sleeves are excellent applicable as wear protection for shaft of all types of shaft seals.
Labyrinth seals
Labyrinth seals are non-contact and therefore also wear-free shaft seals.
Mechanical seals
STASSKOL offers mechanical seals for a wide range of applications. Our team of experts can help you find your individual sealing solution.
Mixer seals
STASSKOL offer in addition to standard shaft seals and sliding ring seals a range of mixers seals. The mixer seals are used for sealing against suspensions and powders in fast-running and slow-running applications.
Thomas Borchardt
Managing Director STASSKOL GmbH
A wordabout STASSKOL topics and content
Exkurs
Digression: Sintering
When sintering, three stations are passed through, where the volume and porosity of the preform are reduced. Initially, the preform is compressed, before its porosity is reduced during the second phase. During the third step, powder particle sinter necks are formed via surface diffusion between the powder particles, providing the sintered body its rigidity.
The difference: cold compression vs. hot compression
The difference: cold compression vs. hot compression
Cold compression
In particular, cold compression is used for processing thermoplastics which do not soften when heated, e.g. fluoroplastics. Here, the material is pressed into cold molds and subjected to heat treatment after extrusion from the mold by sintering.
Hot compression
For hot compression, pulverulent recipes are pressed under high pressure (≥ 700 bar) to preforms in a mold and the tool then heated to a temperature higher than the melting point. After the softening temperature is exceeded, molding pressure is again exerted on the material structure. Therefore, also in case of very well-filled recipes, it is also possible to achieve an excellent bond between the filler components and the plastic matrix.
Exkurs
Digression: Sintering
When sintering, three stations are passed through, where the volume and porosity of the preform are reduced. Initially, the preform is compressed, before its porosity is reduced during the second phase. During the third step, powder particle sinter necks are formed via surface diffusion between the powder particles, providing the sintered body its rigidity.
The difference: cold compression vs. hot compression
The difference: cold compression vs. hot compression
Cold compression
In particular, cold compression is used for processing thermoplastics which do not soften when heated, e.g. fluoroplastics. Here, the material is pressed into cold molds and subjected to heat treatment after extrusion from the mold by sintering.
Hot compression
For hot compression, pulverulent recipes are pressed under high pressure (≥ 700 bar) to preforms in a mold and the tool then heated to a temperature higher than the melting point. After the softening temperature is exceeded, molding pressure is again exerted on the material structure. Therefore, also in case of very well-filled recipes, it is also possible to achieve an excellent bond between the filler components and the plastic matrix.
PT
Functionality of the ICM
Test CenterIndividual practice trials
Image VideoGrinding and Classifying Systems
Manfred Salgert
Managing Director NEUMAN & ESSER Process Technology
A wordabout the topics and tasks of NEUMAN & ESSER Process Technology
Leading provider
for sustainable process solutions for solids
71 employees
worldwide
Headquarters in Germany
Further locations in the USA and Brazil as well as offices in Egypt, China and Malaysia
Almost 100 years’ experience
in mechanical manufacturing
Generously dimensioned Test Center
for scaling-up and dimensioning tailored production and crushing systems for the customer
Solution provider for grinding and classifying systems
including downstream and upstream system components
Portfolio
with mills, rounding machines, air classifiers, cyclone separators and filters for dry particle processing
Traditional applications
in the ceramics, pigment, preparation and fertilizer industries and also for powder coating production
Sustainable solutions
for electromobility and energy storage batteries, recovered carbon black as well as protein enrichment
After Sales Service
for modernization of and revamping existing grinding systems, also third-party devices
Product portfolio
Pendulum mill PM
For fine grinding and drying
Jet impact classifier mill ICM
For dry fine grinding brittle materials
Jet impact classifier mill eXtra ICX
For energy-efficient, dry finest grinding
HM hammer mill
For grinding, crushing and processing soft to medium-hard grinding material
GRC guide ring classifier
Top yields with precise separation limits and minimum energy requirements
DC deflector classifier
Highly efficient air classifier
Deflector classifier eXtra DCX
Highly efficient air classifier which, in particular, has its strengths in the classification of finest products.
Cyclone classifier CSF
Extra precise separating cuts in the fineness range between 5 µm and 250 μm.
Improved properties through recycling
Recycling
PTFE and upcycling
PTFE – what’s that?
Experts for tailor-made plastics
The recycling challenge
Recycling – step-by-step
Trial and error
From coarse to fine
NEUMAN & ESSER Process Technology
The right technology
The grinding experiment
A word
The first result
Characterization
Wear resistance
Large particles reduce the mechanical rigidity
The maximum recyclate share of SK202
The maximum recyclate share of SK801
The result
A Wrap-Up
Outlook
See you again
STASSKOL Image Film
STASSKOL Profil
STASSKOL at a glance
STASSKOL locations
STASSKOL products
High-performance plastics
Seals for rotating shafts
A word
Digression: Sintering
The difference: cold compression vs. hot compression
Functionality of the ICM
Test Center
Image Video
A word
At a glance
Product portfolio