Each cylinder moves slowly through a paint spray booth where paint, in powder form, is sprayed on, then passes through an oven for 20 minutes, then onto a cooling conveyor for the paint to cure (harden)

A human operator checks the exterior paint to make sure it has fully covered the metal (checks thickness) and has no visible defects

Chubb Fire Extinguishers

Chubb Fire Extinguishers undergo internal and external coating to protect the metal from the effects of water.

The extinguisher body is made from carbon steel, pressed and drawn and passed through a wash and thinly coated with Iron phosphate to reduce the risk of corrosion. Once the robot welder has shaped it into a recognisable cylinder, it is pressure tested for leak integrity, then thoroughly dried inside by passing over a hot pipe. If the extinguisher needs lining (due to the fact it will contain water and therefore rust the metal) it is passed onto lining area. Powder filled extinguishers do not need lining as there is no danger of rusting.

The lining machine, known to its operators as the nodding donkey because of its movement, rocks the cylinder forward and back. Gas burners heat each extinguisher through a cycle time dependent on size of cylinder. The plastic lining material is in powder form, placed in a hopper above the cylinder. The rocking motion causes powder to fall into the extinguisher a little at a time, while the heat causes it to melt and stick to the inside of the extinguisher, and start to harden. In this way the extinguisher is coated internally with a thin, solid plastic lining attached to the metal.

An operator checks each cylinder for temperature and adhesion and makes sure that excess plastic is removed from the screw threads (where the valve will later be screwed in), and that the lining has covered the bottom of the extinguisher.

A plug is screwed into the top to prevent shot from getting into the cylinder and damaging the lining, then the cylinder is shot blasted externally to prepare the outer surface for painting. (Shot blasting - a machine contains hundreds of pellets which are fired at any metal placed inside it, to clean the surface.)

Each cylinder is hooked onto an overhead track which moves it slowly through a paint spray booth where paint, in powder form, is sprayed on, then passes through an oven for 20 minutes, then onto a cooling conveyor for over an hour, while the paint cures (hardens). The track moves slowly and continuously.

After this operation a human operator checks the exterior paint to make sure it has fully covered the metal (checks thickness) and has no visible defects.

The cylinder then goes for its electrical continuity test. A probe resembling a chimney-sweeps brush (one central pole with long metal bristles all the way round) is pushed into the cylinder body. The probe produces 10KV, and if it touches metal anywhere inside the extinguisher it bleeps. If no bare metal is found, the extinguisher is fully and correctly lined with an internal plastic coat which will prevent the wet contents from corroding the metal body. The extinguisher can then be filled with water or any of the water-based media used to extinguish fires.

Summary: Each extinguisher designed to contain water will be coated inside with a plastic lining attached to the inside wall. This lining is tested by using an electrical circuit to make sure there is no bare metal showing after the process. Note the plastic lining acts as an electrical insulator to protect it from the atmosphere.

Note: there is an alternative method we used for some small extinguishers until recently. The extinguishers were aluminium, not steel, and were coated inside with a protective lacquer. Other manufacturers may use this, or perhaps other, methods to protect their product from rust.