Setting Spherically Seated Platens: Quick Tips for Testing

00:10: When running compression tests, even small misalignment between platens can cause uneven loading, inaccurate results, or premature specimen failure.

00:19: Spherically seated platens solve this problem by incorporating a convex, spherical surface nested into a matching concave housing, allowing the platen to self-align up to 4 degrees.

00:29: In this video, we'll show you how to set up spherically seated compression platens, and how to use them to achieve either precise platen parallelism or uniform load distribution on non-parallel specimens.

00:42: Typically, a spherically seated compression platen is paired with a rigid fixed platen. It's recommended to use the spherically seated platen as the upper platen and the rigid platen on the bottom.

00:52: This setup is commonly used when testing materials such as concrete, metals, plastics, composites, and structural components — especially in applications where strict alignment requirements apply, such as Nadcap-controlled testing environments.

01:13: To establish precise parallelism between platens, begin by installing the rigid compression platen on the bottom of the test frame.

01:21: Once it's in position, tighten the checknut securely.

01:25: Before installing the spherically seated platen, ensure the four locking screws are loose to allow free self-alignment.

01:34: Once installed in the upper connection, tighten the checknut.

01:38: To align the platens, use the frame handset to jog the crosshead downward while closely monitoring movement.

01:45: If your system has a micro-jog function, use it to continue lowering the crosshead until the platens just make contact and a small compressive load is detected.

01:55: As a working guideline, apply a seating load of approximately 1/1000 of the load cell capacity — for example, 50 N on a 50 kN load cell.

02:04: Do not exceed 5% of load cell capacity during this step, as overloading can cause damage.

02:11: Once the target load is reached, tighten the four locking screws on the spherical seat.

02:16: The upper platen is now locked into the precise parallel alignment with the lower platen and ready for testing.

02:27: If your specimen surfaces are not perfectly parallel, such as concrete cylinders or irregular components, you'll want to leave the four locking screws loose during the test.

02:37: Install both platens the same way as before, then place the specimen between them.

02:42: In this method, the spherically seated platen remains unlocked throughout the test, allowing it to self-align onto the specimen surface.

02:50: As the platens are driven onto the specimen, the upper platen adjusts naturally, conforming to the specimen surface and distributing the load uniformly.

02:59: In the Bluehill^® method, apply a small preload — no more than 10% of your expected peak load — to confirm the upper platen is making contact with the specimen before the test begins.

03:10: The spherical seat is engineered so this adjustment occurs without lateral movement, ensuring consistent axial loading and accurate results.

03:19: That covers the two primary setup methods for spherically seated compression platens, whether you need precise platen parallelism or uniform loading on non-parallel specimens.

03:30: For more setup guidance and application tips, subscribe to our YouTube channel, and visit instron.com. Thanks for watching.