TechArchive

Original article date: April 1999

The concept of a rigidly locking chain to create both push and pull forces is not new but it is now being taken into a much wider area as BILL GENTLES Managing Director of Drives International explains.

Users have the choice of a number of different systems that are in common use for linear motion applications. These generally involve hydraulic/pneumatic cylinders or electromechanical lead and ballscrew drives. The Framo Push Chain represents the development of a simple principle which has to date been used only for very light duty applications.

Now the concept of a rigidly locking chain to create both push and pull forces is being taken into a much wider area covering applications as diverse as using the small 25mm pitch chain to raise a multi-stage telescopic lighting system to heavy duty 60mm and 90mm pitch chains used in steel works rolling mills. The main applications are seen in effecting push-pull movement of medium-sized and large loads in any direction including vertical movement. The chain sprocket can be driven by a gear motor or if preferred by a hydraulic motor. A recent contract was a plasma-torch robot built by a specialist British manufacturer for a Japanese steel works.

It is a special kind of chain which unlike the conventional mechanism becomes rigid when operated under thrust load but which can still be looped and driven by conventional sprocket wheel. The Framo Push Chain can realise thrust forces between 500 and 130kN.

The classic power transmission system involving a continuous chain with at least two sprocket wheels and a tensioning element is replaced by an open-ended chain with two free ends (Fig 1). The drive can be located wherever it is most convenient. The chains are given their push force characteristics by incorporating specially ahaped side links that engage and support each other with very little axial play (Fig 2).

The load is attached for example to the end of the chain with bolts or by a latching mechanism or trunnion using mounting holes.

The other (free) end of the chain can be guided to individual requirements. To keep the space requirement to a minimum it is generally rolled up in a storage configuration. The ease with which build length can be minimised is one of the main advantages.

Depending on the pushing force length and travel speed required the push chain can be configured to run on a given sliding surface or a special guide channel can be supplied. Standard chain sizes with 25 40 60 and 90mm pitch are kept in stock. Chains with 25mm pitch are also available in a plastic version.

Advantages of the push chain and main application areas

• Drives International
• 01462 423000
• Bill Gentles

April 1999