Technical Guide3 min read

How to Eject Curved Ribs with D-Shaped Ejector Blades

Key Takeaway: D-type blades are ideal for ribs with one flat wall and one curved wall — the flat ejection face contacts the flat wall while the curved back clears the curved wall.

Curved Rib Geometry

Many injection-molded parts have ribs that are not rectangular — one wall is flat (perpendicular to the parting line) and the opposite wall follows a curved contour (e.g., inside a cylindrical housing). Standard rectangular blades contact both walls, but the curved wall contact is a line contact that can cause stress concentration and rib cracking. D-type blades solve this by providing flat contact on the flat wall and clearance on the curved side.

Application Examples

Cylindrical housing ribs: Internal ribs in round housings (motors, pumps, filters)
Fan blade root ribs: Structural ribs at the base of fan blades
Pipe fitting ribs: Internal support ribs in pipe connectors and fittings

Frequently Asked Questions

Can the D-type curve radius be customized?+

Standard D-type blades are cut from round bar stock with fixed radii. Custom radii are available for large orders (MOQ 50+). For one-off requirements, a standard D-type with the closest radius is usually sufficient — the curved back provides clearance rather than contact.

How does ejection force compare to rectangular blades?+

D-type blades provide approximately 60–70% of the contact area of equivalent rectangular blades. For ribs requiring maximum ejection force distribution, rectangular blades are preferred.