Kiln shells

There are three main alternatives for kiln shell construction material;

• Thin stainless steel sheet
• Corrosion resistant alloy steels, or
• Mild steel with protective coatings.

Of these, Stainless Steel is far superior to the others.

Stainless Steel

The most effective material for the shell is stainless steel. It is unaffected by elevated temperatures, is highly resistant to corrosion and does not require any protective coating either inside or out.

The ceramic fibre lining is light and does not require a robust support structure.

Fig 86-01

Hoods for top-hat kilns similar to that shown in Fig 1 have been built well over four metres long using 0.9mm thick 304 grade stainless steel.

A 120 cubic foot capacity pottery kiln using that material and construction method for the shell was recently taken out of service after well over 25 years use.

0.9mm 304SS sheet is robust enough to allow the attachment of SS brackets or Insultwist pins by spot welding or MIG welding.

Fig 86-02

The hood shown uses four point lift, so does not need to be rigid; a small amount of flexing can be tolerated.

This allows double folded corner joins to be used, as shown in Fig 2. Mating panels are joined with stainless steel snap or pop rivets at between 100 and 150mm centres; a simple and speedy method. The flexing is due to the slight over sizing of the rivet holes allowing the joined panels to move slightly. A number 30 twist drill is used to make a clearance hole for 3.2mm all stainless rivet.

If greater rigidity is required, then random MIG or stick welds can be made to stop relative movement of the panels after the shell is assembled and riveted.

Fig 86-03

Stiffeners can be attached either by spot welding or rivets.

Fig 86-04.

Large areas of roof can be broken up into smaller sections with support provided by ribs as in fig 4. Typically, the ribs can be spaced at about 500-560mm apart so that roof panels can be cut from half width sheets of steel.

This is the construction method used by Riley Glass Kilns for many years. It lends itself to factory laser cutting and folding with site or home assembly requiring no special equipment.

Corrosion resistant alloy steels

Prominent among these is alloy 253MA. In this application it offers no advantage over 304SS and is often more expensive than that material. It is not anywhere as readily available.

Coated mild steel

Mild steel sheet is available with a number of coatings to protect it against corrosion. They include hot and cold galvanizing, zinc or zinc/aluminium.

Unfortunately, as soon as the coating is broken, either deliberately or by accident, the base metal is immediately susceptible to galvanic corrosion. This is particularly the case where lining anchors are secured to the inside of a shell, or where the sheets are secured to a frame. There have been many cases over the years where fibre linings have collapsed because of the loss of attachment of the anchors to mild steel wall or roof panels.