When selecting hydraulic cylinders for tough operating environments such as in the Aluminium process industry, there are essential factors not to overlook. Aluminium processing presents one of the most arduous of manufacturing environments. Here, applications place unyielding demands on the hydraulic cylinders used to manipulate machinery and equipment. High forces and heavy loads need to be accommodated reliably, around the clock. As a result, design innovation and integral durability are among the prerequisite considerations when purchasing cylinders to meet such important operating criteria.
In this short article we examine the needs of this industry and the key factors to contemplate when specifying hydraulic solutions required for a lifetime exposed to heavy use in hostile environments. After all, getting it wrong can mean inconvenient service failures along with costly downtime, project delays and repairs.
Hydraulic cylinders are an integral part of many heavy engineering operations. In aluminium production processes, for example, hydraulic technology is used throughout the process from smelting to casting into remelt ingots then drying, melting and rolling.
Many think that buying a cylinder in accordance with an ISO standard such as ISO6022 or ISO6020/1 means job done. Wrong – ISO standards define size, mounting and connection requirements to provide commonality on these aspects. They do not define quality, performance or product reliability in any way.
At the top of any priority list should be build quality. Cylinders for tough environments must be of heavy duty, all-steel construction and offer fatigue-free operation at their maximum rated pressure. As a result, smaller bore sizes can often be used, giving reduced component cost. Piston rods are vulnerable to damage in hostile conditions, which is why rods that are precision ground, induction hardened, chrome plated and polished will serve well by providing reduced maintenance, while high force generation capabilities – up to 2000kN, will cover almost all aluminium and steel mill applications.
Why such precise stipulations? Well, failures at heavy engineering plants are not only costly in terms of downtime and repair, but also in terms of hazardous situations leading to potential accidents.
Despite being ruggedly engineered, there should be no underestimating the importance of correct and timely maintenance when it comes to the longevity of hydraulic cylinders. Buyers should look for features such as adjustable, progressive cushioning at the head and cap which reduces shock loads and noise at the end of each stroke, thus extending machine life. What’s more, removable glands and separate bodies with detachable heads and caps will ensure ease of maintenance and low whole-life operating costs, while heavy wall steel tubing honed to a high surface finish helps promote long seal life.
In generic terms, seal system choice should be assessed based on the fluid type deployed, the operating temperature range, the working environment and key performance requirements.
Inside the steel gland, high quality wiper seals, lip seals and rod bearings will provide high levels of low speed and break-out performance, and deliver extended working life in frequent-cycle applications. Where low speed performance and an absence of stick-slip are critical, PTFE seals should be specified for their low friction properties. For arduous use, steel pistons should be fitted with a heavy duty polymer seal. Any piston without broad wear rings to distribute bearing load and to prevent metal-to-metal contact will be an early victim of any misalignment in the cylinder mounting, and may fail to adequately protect the piston seal from contaminants
For extreme duty conditions, where long life and durability are absolutely critical, chevron piston and gland seals are a popular choice. Dedicated seal systems are also available to suit low friction, load holding and high temperature applications.
While it is testament to the durability of hydraulic cylinders that some have been known to remain running adequately after several decades, current technology has improved immeasurably to provide far more efficient and productive solutions.
Parker Hannifin’s 160 bar and 250 bar hydraulic ‘mill’ cylinders, for example, are an established favourite in hostile environments. The latest generation extends the standard fitting of induction hardened piston rods. There is also a new, wider range of mounting accessories, while downloadable CAD models and an online configurator facilitate a faster and cheaper design process. However, if ever in doubt the advice is simple: seek advice.
Andrew Delaney, Cylinder Division Europe, Parker Hannifin