𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞 : 𝐆𝐞𝐥 𝐭𝐢𝐦𝐞: 𝟏𝟎𝟎 𝐬𝐞𝐜𝐨𝐧𝐝𝐬 ✓ 𝐑𝐢𝐬𝐞 𝐭𝐢𝐦𝐞: 𝟏𝟏𝟎 𝐬𝐞𝐜𝐨𝐧𝐝𝐬 ✓ 𝐁𝐨𝐭𝐡 𝐰𝐞𝐫𝐞 𝐰𝐢𝐭𝐡𝐢𝐧 𝐭𝐡𝐞 𝐞𝐱𝐩𝐞𝐜𝐭𝐞𝐝 𝐫𝐚𝐧𝐠𝐞. 𝐁𝐮𝐭 𝐭𝐡𝐞 𝐟𝐨𝐚𝐦 𝐬𝐭𝐢𝐥𝐥 𝐜𝐨𝐥𝐥𝐚𝐩𝐬𝐞𝐝.

𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞

𝐆𝐞𝐥 𝐭𝐢𝐦𝐞: 𝟏𝟎𝟎 𝐬𝐞𝐜𝐨𝐧𝐝𝐬 ✓

𝐑𝐢𝐬𝐞 𝐭𝐢𝐦𝐞: 𝟏𝟏𝟎 𝐬𝐞𝐜𝐨𝐧𝐝𝐬 ✓

𝐁𝐨𝐭𝐡 𝐰𝐞𝐫𝐞 𝐰𝐢𝐭𝐡𝐢𝐧 𝐭𝐡𝐞 𝐞𝐱𝐩𝐞𝐜𝐭𝐞𝐝 𝐫𝐚𝐧𝐠𝐞.

𝐁𝐮𝐭 𝐭𝐡𝐞 𝐟𝐨𝐚𝐦 𝐬𝐭𝐢𝐥𝐥 𝐜𝐨𝐥𝐥𝐚𝐩𝐬𝐞𝐝.

Why?

Because gel time and rise time were being checked as two separate numbers.

They are not two separate checks.

They are one reaction-balance diagnostic.

And the diagnostic is the gap between them.

In a balanced polyurethane foam system, gel time should occur slightly before rise time like typically by 0–20 seconds.

That means the polymer network reaches critical viscosity just as the foam finishes expanding. The structure has enough strength to hold the final rise height, lock the cells, and maintain stable volume.

But when the gap moves in the wrong direction, the defect tells the story.

If rise leads gel by more than 20 seconds😊 :

The blowing reaction is ahead of the gelling reaction.

Foam expands before the polymer network has enough strength to hold it.

Result: collapse, subsidence, large cells, voids, weak top skin, and density variation.

That is a gelling deficit.

If gel leads rise by more than 40 seconds:

The gelling reaction is ahead of the blowing reaction.

The network locks too early while CO₂ generation is still trying to expand the foam.

Result: tight cells, under-rise, splits, harsh feel, and higher-than-target density.

That is gelling excess.

So the question is not only:

“Is gel time within range?”

or

“Is rise time within range?”

The better question is:

“Which reaction is winning?”

The gel/rise gap answers that.

But before changing any catalyst, one step is critical:

Verify stoichiometry first.

Do not adjust catalyst based only on timing instinct.

Check the actual running index from current CoA values — not only from the formula sheet ( they must have to be verified before starting the production).

Confirm %NCO from the current isocyanate drum.

Confirm OHV from the current polyol batch.

Confirm water EW as 9, not 18.

This point is important:

Using water EW = 18 under-counts water’s reactive hydrogen contribution by half. That silently shifts the real index and changes how you read the reaction balance.

A new isocyanate drum with a different CoA %NCO changes NCO availability to both the blowing and gelling reactions at the same time.

That can shift the gel/rise gap.

On the production floor, it may look like a catalyst problem.

But sometimes it is not a catalyst problem.

It is a raw material data problem.

So the correct sequence is:

Read the gap.

Verify stoichiometry.

Identify whether the system is gelling-deficient or gelling-excessive.

Then adjust the correct catalyst side.

Not the side that feels intuitive.

👇

source : #PolymersIQ

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