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Injection Molding Regrind Blend Cost Calculator

Runners, sprues and start-up scrap can go back into the process as regrind, which cuts the resin you buy. The question is how much saving it really gives, and whether you generate enough regrind to sustain a given percentage. This calculator answers both.

Your numbers

kg
per kg
per kg

Labor, energy and granulator wear.

per kg
20 %
%

Runners, sprues, start-up purge and reusable scrap as a share of total throughput.

Your results

Blended cost per kg
$2
Annual saving versus all virgin
$88,800
Cost of one kg of regrind
$0
Saving per kg of resin processed
$0
Regrind needed per year
40,000
Kilograms.
Regrind generated per year
24,000
Kilograms.
Surplus (+) or shortfall (-)
-16,000
Positive means you generate more regrind than you use.

Savings ignore any property loss, extra scrap or customer limits on regrind. Many specifications cap regrind use and require approval.

Save results:

Annual saving vs regrind percentage

Sweeps Regrind in the blend from 0 to 50, holding your other inputs fixed.

Model regrind and co-products in your ERP

Optional: a short conversation on tracking regrind lots and costs.

Optional. The tool and every export work without this. No spam.

How to use it

Enter the resin you process in a year, the virgin price, your grinding cost and the handling cost for drying and testing regrind. Choose the regrind percentage you want in the blend and the share of throughput that you generate as reusable runner and scrap. The results show blended cost per kilogram, annual saving, regrind needed, regrind generated and whether you have a surplus or a shortfall.

  • Set generation from real runner and purge weights.
  • Count only reusable regrind, not degraded scrap.
  • Check customer and spec limits on regrind.

The math

Regrind has a cost, grinding plus handling, so it is not free. Blended cost is virgin price times the virgin share plus regrind cost times the regrind share. The saving per kilogram is virgin price minus blended cost, and the annual saving multiplies that by the resin processed. Supply matters too: if you generate 12 percent of throughput as reusable regrind, a steady 20 percent regrind blend is not sustainable, because you would need to buy or hold extra regrind. In balance, the regrind share cannot exceed the share generated.

Reading the result

At the defaults, a 20 percent blend cuts the blended cost per kilogram by roughly forty cents and saves a six-figure sum per year on 200 tonnes, but the plant generates only 12 percent regrind, so the tool shows a shortfall. In practice, set the blend at or below the share you generate, and keep a separate allowance for resins where the specification or customer limits regrind to a lower share. The chart makes the linear nature of the saving clear: each added point of regrind gives the same increase.

Quality cautions

Every pass through the barrel can shorten polymer chains, change melt flow and lower impact strength, and hygroscopic resins pick up moisture in regrind. Keep regrind clean, labeled and dried, track by lot and resin grade, and test melt flow and mechanical properties when you raise the percentage. Medical, automotive and aerospace customers often limit or prohibit regrind, so confirm before you plan on it.

Frequently Asked Questions

How much regrind can I use in injection molding?

Many general purpose parts tolerate 10 to 30 percent, but the right limit depends on the resin, the part requirements and customer specifications. Test properties and confirm limits before raising the share.

Is regrind really free?

No. Grinding, handling, drying, testing and storage all cost money, and degraded properties can cost more in scrap. The saving is the virgin price minus those costs.

Why does my regrind run out?

A blend percentage cannot exceed the share of throughput you generate as reusable runners and scrap. If you plan for more, you will run out unless you buy regrind or reduce the blend.

Should regrind be dried?

For hygroscopic resins such as nylon, PET, PC and ABS, yes. Regrind can absorb moisture quickly because of its high surface area, so dry the blend to the supplier's recommended moisture level.

If your ERP does not track regrind as a co-product or recycled input, we can help model it so costs and lot traceability stay correct.

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