Batch sheet and mixing

Sizing a batch

The Batch Sheet page turns the recipe into the weights for one mix. Size it either way:

• By the propellant mass you want.
• By the grains you plan to cast. The volume of the grains times the recipe’s density gives the mass.

The waste allowance covers what stays on the bowl and tools. 10 percent is a common starting point for small batches.

The running total column is the scale reading after each addition when everything goes into one bowl. Print the sheet and tick off each ingredient as you weigh it. The sheet can also be copied or saved as CSV.

Grades and particle sizes

Grades and particle sizes splits one ingredient into lots that are weighed separately, for example ammonium perchlorate as 70% 200 micron and 30% 90 micron. Choose the ingredient, add a grade for each lot, and give each a name and a share. The shares must total 100%.

The sheet, its CSV, the cost column and the batch log then show one line per grade. The performance calculation is unaffected, because the grades are the same chemical. Burn rate is not: a finer oxidizer burns faster. To measure that, see Comparing burn rates.

Curative

The Curative card appears when the recipe has a binder.

1. Pick the binder and the curative.
2. Enter the binder’s hydroxyl value.
3. Choose the NCO:OH cure ratio. A ratio of 1 is stoichiometric; lower gives a softer grain.

Curative product lists common commercial curatives, including IPDI, PAPI 27 and 94, Mondur MR, Isonate 143L and Desmodur N100, and fills in the equivalent weight from the NCO content the maker publishes. Type over it with the figure from your own lot if you have one.

The card shows the curative the batch needs and the ratio the recipe has now.

Action	What it does
Set recipe to this ratio	Changes the binder and curative weights in the recipe, keeping their combined weight and every other ingredient the same.
Add to the recipe	For a recipe with no curative yet, adds the right amount of the library ingredient for the chosen product.
Keep the recipe’s curative at this ratio automatically	The curative’s weight follows the binder’s whenever you change the recipe, the hydroxyl value, the equivalent weight or the ratio. Its weight box on the Formulation page is locked while this is on.

Cost

Set Cost to Show to price the batch. Type what you pay for each ingredient, per kilogram or per pound. Prices are remembered for every recipe that uses the ingredient.

The sheet then shows the cost of each ingredient, the batch total, and the cost per kilogram and per pound of propellant. The total covers the whole mix including the waste allowance, and counts only the ingredients you have priced.

Batch log

Log this batch records a mix you actually made: the planned weights, the weights you measured, the batch number, date and notes. The Batch log card lists them, for this recipe or for all, and each can be saved as CSV.

Hazard flags

Flags appear under the recipe, and print on the batch sheet, when it contains a combination or ingredient with a well-known hazard:

• Chlorates with sulfur, ammonium salts, phosphorus or metal powders.
• Perchlorate and metal powder with no binder (flash powder).
• Metals that react with an oxidizer when damp.
• Primary and high explosives.
• Beryllium, heavy metals, chromates and fluorine compounds.
• Flames hot enough to be hard on hardware.

Red flags are combinations that can ignite or explode on their own or are acutely toxic. Amber flags need a specific precaution.

The flags cover a short list of textbook cases matched by ingredient name and formula. A recipe with no flag has not been shown to be safe. Read the safety data sheet for every ingredient and follow your rocketry organization’s safety code.