PTFE Components for Aluminium Smelter Pneumatic Potline Cylinders

Pneumatic cylinders used in aluminium smelting operate in one of the most demanding environments for engineering components. Positioned directly above molten aluminium, these cylinders are exposed to elevated temperatures while being required to provide reliable, repeatable movement in a harsh industrial environment.

Dotmar Engineering Plastics supplies and machines specialised PTFE compounds for components used in crust breaker and feeder cylinders within aluminium electrolytic cells.

Through its Fluoro Pacific PTFE division, Dotmar can formulate specialised PTFE compounds, manufacture the material into stock shapes and machine the material into finished components through its network of manufacturing workshops across Australia and New Zealand.

Pneumatic cylinders in aluminium reduction cells

Aluminium is produced in electrolytic cells, commonly referred to as "Pots", which are arranged in long rows known as Potlines or Pot Rooms.

Each cell incorporates pneumatic cylinders used for functions including crust breaking and alumina feeding. Multiple cylinders are typically installed on each Pot, with four crust breaker cylinders and four feeder cylinders being a common configuration, although this can vary between installations. 

The cylinders are positioned directly above the molten aluminium. Although a crust forms on the surface of the molten aluminium and provides some shielding from radiant heat, the pneumatic cylinders can experience temperatures in the order of 200°C. 

This combination of elevated temperature, mechanical loading, friction and wear creates demanding requirements for the materials used within the cylinders.

PTFE components for high-temperature pneumatic cylinders

PTFE is naturally well suited to elevated-temperature applications and offers low friction. However, virgin PTFE alone may not provide the mechanical strength and wear resistance required for loaded components, particularly when operating at elevated temperatures.

For this reason, compounded PTFE grades are used for critical wear and sealing components.

Dotmar's Fluoro Pacific PTFE division formulates a range of compounds designed to modify the properties of PTFE to suit specific operating requirements. Standard compounds such as Tetron G, Tetron LG and Tetron HG, together with specially formulated grades such as Tetron BL, can provide the balance of temperature capability, mechanical performance and wear resistance required for demanding pneumatic cylinder applications. 

Critical cylinder components

PTFE compounds are used in several critical components within the pneumatic cylinders.

Cartridge bushes and rod seals

Located at the nose of the pneumatic cylinder where the rod exits the cylinder, the cartridge bush and associated seals are among the components closest to the molten aluminium and therefore experience some of the highest temperatures.

The PTFE material provides low-friction operation and sealing while maintaining the required performance at elevated temperatures.

Piston seals

Piston seals provide the sealing interface within the pneumatic cylinder and are exposed to mechanical movement, pressure and elevated temperatures.

Wear bands

Wear bands support and  guide the piston within the cylinder, helping to control movement and eliminate metal-to-metal contact.

The piston is positioned further from the molten aluminium than the rod end of the cylinder, but temperatures remain significant because of the proximity to the cell. 

Compounded PTFE for performance at elevated temperatures

Material selection is particularly important when PTFE components are required to withstand both elevated temperature and mechanical loading.

While virgin PTFE can withstand the temperatures encountered in these applications, its mechanical properties and wear resistance can limit its suitability. Compounding PTFE with selected fillers and additives allows the material to be engineered for improved performance under load and wear conditions.

Dotmar's Tetron range provides several options for these applications, including:

• Tetron G – a standard 25% glass-filled PTFE grade providing improved creep resistance, mechanical properties and wear resistance. 
• Tetron LG and Tetron HG – a variation on Tetron G developed for applications balancing mechanical and wear performance, together with friction and counter-face wear. 
• Tetron BL – a specially formulated PTFE compound developed for specific application requirements. 
• Tetco V – a modified PTFE compound that can provide reduced permeation of high-pressure gases compared with standard PTFE. 

The objective is not simply to select the highest-performing material, but to identify the material that provides the appropriate combination of performance, service life and cost for the application.

Where more demanding operating conditions justify a higher-performance material, Dotmar's engineering and commercial teams can evaluate alternative PTFE compounds and other advanced engineering plastics.

Tetco V for high-pressure pneumatic applications

In addition to wear and sealing components, Dotmar has experience applying modified PTFE compounds to pneumatic systems where gas permeation can be an issue.

Tetco V provides lower permeation of high-pressure gases compared with standard PTFE, making it suitable for applications such as pneumatic manifold blocks. Dotmar has direct experience addressing pressure loss associated with gas permeation when standard PTFE has been used in these applications. 

Tetco V can also be formulated with additional additives where improved mechanical and wear performance is required.

From PTFE compound to finished component

A key advantage of Dotmar's offering is the ability to support the complete material-to-component process.

The Fluoro Pacific PTFE division develops and manufactures PTFE compounds, which can then be produced into stock shapes such as:

• Cylinders 
• Billets 
• Sheets 

These stock shapes can subsequently be machined into finished components to customer drawings or specifications.

This provides customers with access to material formulation, stock-shape manufacturing, engineering support and precision machining through a single supplier.

Dotmar's machining capability allows PTFE components to be manufactured for both replacement parts and ongoing production requirements, with machining performed within Dotmar's network of workshops.

Engineering support for demanding applications

Selecting a PTFE compound for a high-temperature pneumatic application requires consideration of more than temperature resistance alone.

Load, temperature, friction, wear, sealing requirements, dimensional stability, counterface material and operating conditions all influence material selection.

Dotmar's engineers and technical sales team can work with customers to understand the application requirements and identify an appropriate PTFE compound and component design.

From compound formulation and stock-shape manufacture through to finished machined components, Dotmar can provide an integrated engineering plastics solution for demanding aluminium smelting applications.

Talk to our engineering team about your application and requirements.