Ejection rubber does more than push a cut part out of the die. It controls how the material approaches the rule and how it releases after the cut. When rubber tires, the symptom is often mistaken for blunt cutting rule; separating the two is the first step of any cutting die repair and refurbishment assessment.

Permanent compression and hardening

If rubber does not return to its original height after pressure is removed, ejection force has fallen. A hardened surface can mark board, while a soft or missing zone allows the part to stay on the rule. Comparing zones on the same die makes imbalance visible.

The check is simple: rubber pressed with a finger should spring back at once. Rubber that returns slowly or holds the mark has lost its ejection job. On the same die the sponge on open areas and the profile rubber along narrow channels age differently, so the comparison is made zone by zone.

  • Finger test: rubber that does not spring back has lost its job.
  • A hardened surface marks thin board; a softened zone holds the part.
  • Sponge and profile rubber are checked separately, zone by zone.

Parts remaining in the die

Check rubbering when parts stick at certain corners, operators must pull them free or waste collects between rules. Simply adding harder rubber is not a complete fix; placement and clearance around the cutting rule matter.

A part that always stays at the same corner shows that the rubber or the window fill at that corner is insufficient; inner windows must be filled with rubber completely. Adding harder rubber is rarely the answer; height, distance from the rule and clearance are rebuilt together.

  • The corner where the part stays is marked on the die and photographed.
  • Inner windows are filled with rubber completely.
  • Height and placement, not hardness, are the first things corrected.

Marks and waviness around the cut

Rubber that is too high or too close to the rule can mark thin board. Uneven rubber can produce waviness over broad panels or unwanted pressure near a crease. Replacement should account for the current material and press condition.

Rubber standing far above the rule edge or glued tight against the rule leaves a wavy mark on thin board and crushes the fold line near a crease. Rubber is glued with a small expansion gap at the base of the rule; when material or machine changes the height is reviewed again.

  • A small gap for rubber expansion is left at the base of the rule.
  • Rubber around a crease is placed so it does not crush the fold line.
  • Rubber height is rechecked when material or machine changes.

Localized replacement or a complete reset?

One torn corner may justify a localized replacement. If most rubber has aged, hardness varies or previous patches are inconsistent, rebuilding the full rubber pattern provides a more predictable result.

On a local renewal the new rubber is chosen at the same height and hardness as the old; otherwise two different ejection forces appear on one die. The renewal date and zone are entered on the die card; after several patches, renewing the whole rubber pattern in one go gives the more consistent result.

  • On local renewal, height and hardness are matched to the existing rubber.
  • Renewal date and zone are written on the die card.
  • Once patches accumulate, the whole pattern is renewed at once.

Application note

Photograph the rubber surface and the retained cut part so rule wear can be separated from a rubbering problem.

  • Use the current material and dimensions.
  • Compare a clean sample with the defective sample.
  • Record the decision with photographs and drawings.