Silicate Plant Batch QC: Checkpoints Before Packing

Packing is the last gate at Zhongzhi Chemical, not the first test. Plant QA at the Changyi silicate factory walks an industry-typical order — raw material, modulus, crystallization and drying, screening, then the bag — and holds any lot whose batch COA sits outside the purchase-order window. The sequence below is how solid silicate lines are normally released. It is not a disclosure of reactor settings, recipes, or unpublished capacity.

Industry-typical path, then the window

Step	What batch QC is watching	Why the COA has to land in the window
Raw material	Identity and the incoming assay	A wrong feed makes every later number meaningless. Packing cannot repair it.
Modulus	Molar ratio SiO₂ / Na₂O against the buyer’s window	The ratio is fixed before the solid is finished. A miss is a different alkali balance.
Crystallization / drying	Moisture appropriate to the form on the order	A lot that is still outside the moisture line will cake after the liner is closed.
Screening	Mesh: overs and fines versus the named cut	Dust, flow, and dissolve follow the screen, not a visual “it looks like powder.”
Packing	Only a lot already inside all three	The bag seals the result. It is not a fourth assay.

Metasilicate is one line in the Changyi portfolio, near a 1:1 modulus. A buyer’s window is whatever that purchase order locked — not a brochure midpoint. How plant QA compares a specification to the batch COA is already written on spec sheet versus batch COA. This page is where that comparison sits in the plant: before the packer.

Modulus is a hold, not a packing note

Modulus is SiO₂ / Na₂O. Once the ratio is outside the window, drying and screening do not bring it back. Zhongzhi release practice is to write the buyer’s window onto the order, assay the lot, and keep the lot off the packing line if the COA misses. A worked teaching pair already used on this site (modulus 1.15 against a window near 0.95–1.05) lives on the COA article — same figures, not a new case. The reading checklist is on how to read a batch COA.

Moisture is the drying gate

After crystallization and drying, batch QC reads moisture against the form on the order. Crystal water and free moisture are different lines. Anhydrous and pentahydrate are different solids; the Na₂O bands already published on this site, and why a kilogram is not the same dose, are on effective solids. This checkpoint does not add a moisture percentage. If your order names a ceiling, that ceiling is the window. A result outside it is a hold. Packing a wet lot is how a caking complaint gets manufactured. What the liner and the warehouse do after a dry lot is released is on plant packaging and moisture control.

Mesh is the screen, not a look

Screening is the industry-typical step before the bag. The mesh window is the cut the purchase order names — powder, a coarser granular cut, or a screen you already run. Overs and fines are weighed against that cut. This page does not publish a new mesh table. Send the cut you claim; plant QA puts that row on the release COA when it is part of the order. “Powder” on a brochure is not a mesh result.

The batch COA is the release sheet

1. Lock modulus, moisture, and mesh on the order before the lot is scheduled.
2. Assay at the matching step. A miss at modulus, moisture, or mesh holds the lot.
3. Pack only when the batch COA sits inside the window. A previous lot, or a typical, does not clear this one.
4. Ship that COA with the goods. A sample on Downloads shows the format. It is not the shipment certificate.

HG/T 2568-2021 remains the public industry-standard layer for industrial metasilicate, already discussed on this site. It does not replace the three windows on your order, and it is not a new promise of iron, whiteness, or moisture.

What to send so the windows can be locked

• Form, and the modulus window if your formula has one
• The moisture line you already claim, and which water it means
• Mesh or screen cut
• Packing and destination
• Volume as a request for the current supply plan

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