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Summary: Winter raises abrasive costs through three channels, not one. Shot toughness falls about 18 percent after 1.5 hours at minus 5 degrees, moisture sneaks into bulk bags, and coating windows shrink from 4 hours to 2. Here is the arithmetic behind a winter shot bill, and the four levers that bring it back down.

Every year between November and February, blast shops in northern China report the same thing: output is steady, but the abrasive line on the cost sheet is up 10 to 20 percent. It rarely comes from one cause. It comes from three at once.

The market backdrop is not the problem

On October 29, rebar across 31 major cities averaged 3,309 yuan per tonne, up 7 yuan. Hot-rolled coil across 24 cities averaged 3,229 yuan, up 5. Plate averaged 3,450 yuan, down 1, and cold-rolled coil held at 3,740. Billet in Tangshan stayed at 2,900 yuan including tax. Three mills lifted construction steel prices by 10 to 50 yuan.

Inventories were still drawing down: 3.6048 million tonnes of hot-rolled coil across 33 cities, down 80,800 tonnes week on week, and 2.3718 million tonnes of cold-rolled across 29 cities, down 21,000 tonnes. Demand is real but cautious, and schedules loosen from November.

Cheaper steel does not make abrasive cheaper. What changes the abrasive bill is physics.

Channel one: toughness drops before anyone notices

Shot is a spherical impact tool. Its life depends on toughness, and toughness is temperature dependent.

At minus 5 degrees Celsius, shot loses roughly 18 percent of its toughness after 1.5 hours of exposure. Carbon steel at minus 20 degrees loses about 60 percent of its impact toughness. Nothing about the machine changed, but the same particle that deformed in October now fractures in December.

The counterintuitive part is the fix. Reducing wheel velocity by 8 to 12 percent lowers impact energy per particle, and breakage falls faster than cleaning rate does. Net consumption drops. Operators resist this because the line looks slower, but the abrasive invoice is the honest scoreboard.

There is also a hard limit. Below minus 15 degrees, Q235 and higher grades should be checked for impact toughness. Below minus 20 degrees, blasting should stop. Brittle fracture in the substrate is a safety issue, not a scheduling one.

Channel two: moisture arrives with the weather

This one is invisible until it stops the line.

Wide day-night swings condense water on the inner surface of bulk bags. The shot does not look wet. Then temperatures drop overnight and the media freezes into lumps that will not discharge. Clearing a feed pipe costs half a shift, and the moisture that does reach the machine corrodes the housing and the wheel from the inside.

Hold moisture below 0.1 percent. Raise bags 15 centimetres off the floor, ventilate the store, keep media away from cement and sand, and never draw from bags stored in the open. A squeeze test before loading separates usable media from media that needs drying.

Channel three: the coating window halves, and rework starts

Blasting is only half the job. What happens in the next two hours determines whether the work is billed once or twice.

Epoxy systems effectively stop reacting below 5 degrees Celsius. At 10 degrees, cure time runs 2 to 3 times longer than at 23 degrees. At 5 degrees, it takes 3 to 4 times as long: 7 days at 23 degrees becomes 28 days at 5. Films that feel dry may not be cured, and adhesion fails weeks later, in the field, at the customer's site.

So the interval from blasting to coating compresses from 4 hours in mild weather to 2 hours in winter. Surface water film above 5 microns ruins adhesion. Steel temperature must sit 3 degrees above dew point. If that margin cannot be held, the correct decision is to stop.

What one shipyard changed

A northern shipyard measured its winter cartridge life at 3 months against 12 months in summer. The cause was condensation blinding the filter media during hot-cold cycling, not dust load.

Their fix was procedural, not capital. After each shutdown, the fan keeps running 30 minutes to purge moisture from the collector housing. Cartridge life returned to 12 months. The same yard now holds 85 percent of summer capacity at minus 25 degrees, with abrasive loss down 22 percent year on year.

That is the pattern across all three channels. The savings come from sequence and settings, not from buying a different grade of shot.

Specifying for cold conditions

Where ambient temperature stays below minus 15 degrees for extended periods, specification matters more than in summer. Under the Q/HX 001-2026 enterprise standard, Mali steel shot must achieve at least 2,200 cycles, hold non-spherical particles under 5 percent, keep sulphur and phosphorus below 0.03 percent, and maintain density at 7.4 g/cm³ or higher. Fewer irregular particles means fewer crack initiation sites when the metal is cold.

The range covers alloy steel shot S230 to S780, stainless cut wire shot 0.3mm to 2.5mm, high-carbon and high-manganese cut wire shot, and angular steel grit G12 to G120. Stock is held at 28 warehouses across China with 72-hour delivery, every batch ships with a test report, and free samples are available for trial.

Website: http://www.sisball.com/ Hotline: +86 400-038-8928 (alternate +86 27-84841595)

FAQ

Q: Is a 10 to 20 percent winter increase in shot consumption normal?

A: It is common but not unavoidable. Roughly half comes from lower toughness at low temperature and half from moisture-related feed problems and rework. Shops that cut wheel velocity by 8 to 12 percent and hold media moisture below 0.1 percent typically recover most of the difference within one season.

Q: Does higher shot hardness help in cold weather?

A: No. Harder particles fracture more easily at low temperature, which raises consumption rather than lowering it. The useful levers are wheel velocity, replenishment rhythm and media quality: cycle life of at least 2,200 cycles and no more than 5 percent non-spherical particles under Q/HX 001-2026.

Q: How do we know whether caked media is still usable?

A: Test by hand and by number. Media that crumbles when squeezed and passes a screen after drying is usable. Hard lumps that will not break should be rejected. The formal criterion is moisture content below 0.1 percent, because media above that threshold carries water into the machine and blocks the feed system.

Q: What temperature stops coating work entirely?

A: Two thresholds govern it. Epoxy systems essentially stop reacting below 5 degrees Celsius, and steel temperature must exceed dew point by at least 3 degrees. If both cannot be satisfied with heating or dehumidification on site, coating should be postponed rather than forced, since failed adhesion usually surfaces after delivery.