Just as some human beings have good DNA that predisposes them to good health, high performance and great longevity, so it is with some engineering thermoplastics that are supplanting metals in many applications.
One of the thermoplastic family favourites from an engineering point of view is polyethylene, represented in the Dotmar EPP family by the Polystone range of ultra high molecular weight polyethylenes (UHMW-PE).
Ultra high molecular weight polyethylene (UHMWPE) is an all rounder in thermoplastics. It has long molecular chains, with a molecular weight numbering in the millions, usually between 2 and 6 million.
The properties of PE are closely related to the length of the molecular chain (molecular weight) and the crystallinity. The longer the chain, the higher the molecular weight, the better the desired characteristics of Polystone from HD (P300) to UHMWPE (P7000).
Rochling Polystone UHMWPE exhibits a molecular weight of over 7 million, which is significantly more than other commercial grades of UHMWPE available.
This results in an extremely tough material that exhibits an array of characteristics. A higher molecular weight of Polyethylene has a significant influence on important technical properties.
These versatile thermoplastics feature long molecular chains that serve to transfer load more effectively to the polymer’s backbone by strengthening intermolecular interactions.
This results in one of the durable thermoplastic polyethylenes on the market – and one that is odourless, non-toxic, tasteless and can offer considerable weight and cost savings compared with metal alternatives.
Its uses cover a diverse spectrum of applications, including bulk material handling; food processing and beverage machinery; mining and mineral processing equipment; manufacturing equipment; civil engineering and earthmoving equipment; and transport-related applications, including truck trays, bins and hoppers.
Advantages of Polystone UHMWPE include:
- High impact strength, even at low temperatures. This translates into good resistance to stress and high resistance to cracking
- High resistance to corrosive chemicals - It is highly resistant to most alkalis and acid, organic solvents, degreasing agents and electrolytic attack. Non-toxic
- Weatherproof - Extremely low moisture absorption
- Low coefficient of friction
- High dielectric resistance better than Teflon (PTFE)
- Lightweight and easy to handle
- Self lubricating - No need for lubricating agents that could cause contamination
- Highly resistant to abrasion - 15 times more resistant to abrasion than carbon steel
- Coefficient of friction comparable to that of Teflon, but with better abrasion resistance
- Physiologically inert - Odourless, tasteless and non-toxic
- Low cost per kg when compared to metal
- Pressed and planed for optimum flatness
- Wide operational temperatures (-260 to +90°C)
- Easy to produce, assemble and an economic material
When compared with traditional polymers, Polystone UHMWPE has high resistance to abrasion and chemical erosion, while at the same time eliminating cracking under higher impact situations.
Additionally, the range’s self-lubricating character yields a non-stick surface comparable with PTFE. Put all these benefits together with low moisture absorption character and low coefficient of friction and have the most durable plastic available anywhere - and ready to go into service just about anywhere.
However, it is important for the engineer and designer to appreciate that no single product in the Polystone UHMW-PE family exhibits all of the desirable characteristics that a customer looks for in a polymer.
In selecting the suitable Polystone for particular applications, it pays to know the difference between the major categories.
These include the following:
Polystone 7000
Polystone 7000 is the general purpose UHMWPE. It is suitable to engineered applications, where its properties of high impact strength, wear and abrasion resistance are required.
Polystone Ultra
Polystone Ultra is specifically formulated for improved sliding characteristics, enhancing its resistance to wear, abrasion, and environmental stress cracking.
This material is ideally suited to flow promotion and mechanical transmission support products. Sharing the key advantages of general purpose UHMW-PE, this material is engineered to deliver high performance in applications such as:
- Bulk storage flow promotion
- Bulk storage wear liners
- Mechanical chain guides
- Mechanical wear strips
Polystone Ultra not only reduces friction, wear, clogging and noise compared with metal, but also never needs lubrication.
Polystone 7000SR
Polystone 7000SR is specifically formulated to suit applications where reduced static is required in handling of bulk materials and other high speed sliding applications. These include lining of storage systems and change parts for the beverage industry.
It is particularly suited to:
- Bulk storage flow promotion
- Bulk storage wear liners
- Grain industry
- Coal handling
Polystone M Flametec
This is the first flame retardant and anti static (FRAS) UHMWPE that has the following features:
- Halogen free
- Antimony free
- No strong smoke emission
- Non-toxic smokes/gases
- Technical properties of UHMWPE are not reduced
- Fire Rating - achieved UL94 class V0
Applications for which it is designed include underground mining, scraper blades, hopper liners, liner beds, wear profiles, impact slider blades and chain guides
Polystone Matrox
Polystone Matrox is a specially formulated premium grade UHMWPE. Its combination of properties includes high abrasion resistance, good non-stick properties and corrosion resistance.
Polystone Matrox is ideally suited for the lining of hoppers, bins and earth moving equipment to promote flow, reduce hang-up and carry-back.
This new premium grade polymer alloy liner is specifically designed for lining hoppers, chutes, bins, dump truck bodies, dozer blades and many other applications requiring solutions to sliding, abrasion and release of sticky, hard-to-move materials. MATROX delivers high production flow rates at optimum wall angle.
Its formulation achieves a low co-efficient of friction. Strict measurement of results during its development ensure an extremely high quality product for use in many demanding bulk solids handling industries, including mining, minerals and concentrate handling, quarrying, chemical, filtration, packaging, timber and marine engineering.
Engineers should consult appropriate technical guidance for which engineering plastics suits particular applications. One advanced resource to determine particular products for particular properties is provided by the Dotmar website.