Cartridge, sausage or barrel: pack economics

Pack format is a production decision disguised as a purchasing one. The same sealant costs different amounts per metre depending on how it is supplied, and the difference is mostly labour and waste.

The three formats

Format	Typical use	Advantage	Cost driver
310 ml cartridge	Repair, low volume	Cheap gun, precise	Highest cost per litre, most packaging waste
400/600 ml sausage	Body shop production	Less changeover, lower waste	Needs a sausage gun
200 L barrel	Line production	Lowest cost per litre	Pump system, minimum volume, cleaning

Where the money goes

A cartridge leaves 5–8% of product behind and needs a new nozzle per tube. A sausage leaves less, and a barrel with a follower plate leaves least — but a barrel that sits half-used between shifts can skin over and cost more than it saved.

The break-even is roughly: below 20 cartridges a week, cartridges are fine; above that, sausages pay for the gun in a few months; above a barrel a week, a pump system starts to make sense.

A changeover calculation

Take a line that runs 40 cartridges a week of one sealer. Each cartridge change costs roughly a minute of gun time plus a nozzle; a sausage change costs the same minute but covers 400–600 ml instead of 310. Over a week that is 40 interruptions versus roughly 25, before counting the 5–8% left in each cartridge.

The saving is not the adhesive price — it is the interruptions and the waste. The same logic explains why barrels win on high-volume lines and lose in a workshop that cannot finish one inside its working life.

Waste arithmetic

The residual product in a cartridge is not a rounding error when a shop uses forty a week.

310 ml cartridge, 7% residual      ≈ 22 ml lost per cartridge
40 cartridges per week             ≈ 880 ml lost per week
600 ml sausage, 3% residual        ≈ 18 ml per sausage
25 sausages per week               ≈ 450 ml lost per week

At a product cost of USD 6 per 310 ml, the cartridge waste is about USD 17 a week — small. The interruptions are not: forty cartridge changes a week is forty chances for an air pocket, a dropped nozzle or a bead that starts thin.

The barrel case is different again. A 200 L barrel with a follower plate wastes almost nothing, but a barrel opened and left between shifts can skin over; the loss is then measured in litres, not millilitres.

Choosing by throughput, not by price list

Weekly volume	Format	Reason
Under 10 cartridges	Cartridge	No gun investment, no shelf-life risk
10–40 cartridges	Sausage	One gun, fewer changes, less waste
40+ cartridges or a line	Barrel + pump	Lowest cost per litre, needs cleaning discipline
Repair and touch-up	Cartridge	Always keep a box, whatever the line uses

The mistake is buying the format that has the lowest price per litre rather than the lowest cost per finished metre. A barrel in a shop that uses ten cartridges a week is the most expensive option on the list.

What this means for buyers

1. Calculate cost per metre at your bead, not price per unit.
2. Buy the sausage gun before the sausage, not after.
3. Do not buy a barrel without the throughput to finish it inside its working life.
4. Keep cartridges for repair and touch-up regardless of line volume.