How do you calculate the gunning defect rate?

Divide the defective gunned area by the total area gunned. Here 8 units defective out of 250 gunned is a 3.2% defect rate on that lining.

What does the gap-to-target number mean?

It's the distance between your result and the reference target you entered. In the example the calculator reports a 91.8-point gap against a 95% target, flagging how far the raw ratio sits from the benchmark.

What is a good gunning defect rate for refractory repairs?

Well-controlled gunning on accessible surfaces often stays under 3-5% defective area. The 3.2% in this example is respectable; climbing past 8-10% points to nozzle distance, water ratio or mix flow-rate problems.

What causes high gunning defect rates?

Wrong nozzle-to-surface distance, too much or too little water at the nozzle, cold shell, uneven material feed and excessive rebound are the usual culprits. Each shows up as delamination, sag or low-density patches at inspection.

How do I reduce my gunning defect rate?

Standardize nozzle distance and angle, control water addition tightly, pre-heat cold shells and slow the pass rate on overhead work. Re-measure defective area after each change to confirm the rate is dropping.

Gunning rate vs anchor count — how do they relate?

Anchor count sizes how many anchors hold the lining; gunning rate grades how well the sprayed material bonded over them. Poor anchoring often shows up later as a rising gunning defect rate.

Refractories, Furnace Linings & Foundry Consumables calculator

Gunning Rate Calculator

Gunning rate here measures the share of a gunned refractory surface that comes out defective — delaminations, sags, low density or rebound-scarred zones — against the total area shot. Refractory QA leads and foundry maintenance engineers use it to judge whether a gunning crew and mix are holding quality before the furnace goes back to heat. A high defect rate on a gunned repair means early spalling and an unplanned reline, so catching it at inspection is far cheaper than at the tap hole. This calculator returns the defect rate and, against a target acceptance benchmark, the gap you need to close.

What this calculator does

Gunning rate here measures the share of a gunned refractory surface that comes out defective — delaminations, sags, low density or rebound-scarred zones — against the total area shot.
Use it when gunning rate in refractories, furnace linings and foundry consumables needs a clean rate and gap-to-target you can put on a tier board.
Computes the gunning defect rate as defective area divided by total gunned area, and the gap between that rate and your quality target.

Formula used

Gunning Rate rate = affected amount ÷ total amount
Gap to target = target rate - calculated rate

Inputs explained

Rejected or defective gunning area:
Total gunned lining area inspected:
Target gunning acceptance rate:

How to use the result

Use it right after a gunning repair or new gunned lining, when inspection results are in, to grade the crew and mix.
It is an area-based ratio and doesn't weight by defect severity — a small critical hot-face flaw counts the same as a large cosmetic one.

Current U.S. benchmarks

The producer price index for steel mill products stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. Quotes priced off last quarter's material cost miss this move.
Industrial electricity averages 8.66 cents per kWh across the U.S. (EIA, Apr 2026), up 5.5% from a year earlier. Energy-intensive steps carry this directly into unit cost.
The U.S. has 3,569 primary metal manufacturing establishments employing about 354,911 workers (Census County Business Patterns, 2023).

Common questions

How do you calculate the gunning defect rate? Divide the defective gunned area by the total area gunned. Here 8 units defective out of 250 gunned is a 3.2% defect rate on that lining.
What does the gap-to-target number mean? It's the distance between your result and the reference target you entered. In the example the calculator reports a 91.8-point gap against a 95% target, flagging how far the raw ratio sits from the benchmark.
What is a good gunning defect rate for refractory repairs? Well-controlled gunning on accessible surfaces often stays under 3-5% defective area. The 3.2% in this example is respectable; climbing past 8-10% points to nozzle distance, water ratio or mix flow-rate problems.
What causes high gunning defect rates? Wrong nozzle-to-surface distance, too much or too little water at the nozzle, cold shell, uneven material feed and excessive rebound are the usual culprits. Each shows up as delamination, sag or low-density patches at inspection.
How do I reduce my gunning defect rate? Standardize nozzle distance and angle, control water addition tightly, pre-heat cold shells and slow the pass rate on overhead work. Re-measure defective area after each change to confirm the rate is dropping.

Last reviewed 2026-05-12.