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A gripper entering an opening and clamping from the inside outwards – into sleeves, cores, tubes and bores. It holds without touching the outer surface and is therefore the right choice for delicate or coated barrels. Sizing follows the permissible internal surface pressure: cardboard cores and thin-walled plastic centres take far less than steel.
An expanding gripper enters an opening and presses segments, jaws or a bladder outwards against the inner wall. The outer surface of the part stays free – that is the reason for choosing it: for film, paper and label reels whose winding must not be touched, for coated tubes, for rings and bushes.
Expansion is mechanical by wedge or cone, pneumatic by cylinder, or by an inflatable bladder that makes contact over a large area and is gentle on delicate cores.
If the reel hangs on the gripper with its axis vertical, friction between expanding element and core carries alone: holding force is friction coefficient times expanding force. That is a friction grip with all its consequences – safety factor, dependence on the surface, safeguarding against pressure loss.
If the axis is horizontal, the reel rests on the gripper as on a mandrel; the expansion only secures it against sliding off. If the expanding element reaches behind the end of a short core or into a groove, true positive locking results.
The expanding force is spread over the contact area in the core. The smaller that area, the higher the contact pressure. Steel tubes tolerate a lot, cardboard cores and thin-walled plastic cores little; they are dented, crack or are permanently widened.
Sizing is therefore based on the permissible pressure of the weakest core that occurs – with a contact area as large as possible and matched to the inside diameter. Common core diameters for reel goods are 76 and 152 mm, i.e. 3 and 6 inches; the gripper has to absorb the tolerance of the cores.
The gripper holds the core, not the reel. With loosely wound reels or slippery films, the winding can shift on the core and telescope out. This shows up mainly when lifting with the axis vertical. Whether a reel may be lifted that way is a property of the reel and has to be checked on the real item.
Pneumatically expanded grippers need protection against pressure loss: a check valve that holds the pressure in the expanding element, or a mechanism that tightens itself under load. With wedge and cone grippers the weight of the load can be used – the heavier the reel, the stronger the expansion.
What Entracon offers here is on the matching page.
See what we offer| Core | Tolerates | What matters |
|---|---|---|
| Steel tube, steel sleeve | high pressure | friction coefficient on an oily bore |
| Cardboard core | low pressure | large contact area; moisture weakens the core |
| Thin-walled plastic core | low pressure | avoid permanent widening |
| Coreless reel | very little | bladder gripper or a different principle |
When the reel is lifted with its axis vertical or turned between horizontal and vertical. A plain mandrel carries only with a horizontal axis; the expanding gripper holds in any orientation, provided the core takes the force.
Not if the contact area is large enough and the expanding force is matched to the core. Bladder grippers and segments with a large wrap angle keep the pressure low. Dented or damp cores should be sorted out before lifting.
Within its expansion stroke, yes. For clearly different diameters – such as 3 and 6 inches – interchangeable segments or adapters are used so that the contact area matches the core.
One short conversation usually settles more than three quotations. Call or write — you will reach an engineer directly.
Start typing – for example “balancer”, “SAP” or “pipe stress”.
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