Monometer was approached by West Country Tiling to comment upon and try to resolve reoccurring failures in their furnace crucible, and a variable melting performance. The furnace in question was a 1-tonne lead capacity crucible supplied by another company.

A very interesting and complimentary video was also included from the client showing their production and manufacture of lead-roof sheeting.  http://www.youtube.com/watch?v=YxywudfRvTE

Monometer assessed the furnace design including burner system, together with the process requirements.

Following investigation, several problem areas were identified including:

• Localized spot heating of a restricted area of the crucible that was causing damage to the crucible fabrication,

• Natural vulnerability of the fabrication to thermal stress was exacerbating premature crucible failure,

• The air gap between furnace brickwork and crucible was insufficient to allow necessary flame circulation for distribution of heating around the crucible.

• The effect of the burner angular position combined with proximity to the exhaust resulted in hot combustion gases traveling mainly straight from burner to exhaust without proper circulation around the crucible.

Furnace modifications were therefore advised as follows:

• Angular re-positioning of the burner with respect to the crucible for the purpose of promoting circulation of flame around the crucible and eliminating as far as possible localized spot heating.

• Burner repositioning with respect to the exhaust, so to promote circulation to the longest possible path prior to exhaustion.  

• Reduced firing rate

• Replacement of the fabricated crucible with a smaller redesigned cast iron crucible for the purpose of improved melting performance and crucible life. The smaller crucible was to allow an increased gap between the furnace brickwork and crucible to allow hot gas circulation around the crucible; the cast iron construction was to promote heat transfer both around and through the crucible to the charge materials within and to eliminate vulnerability to thermal stresses.

All recommendations were implemented by the client, and ultimately the melt time was considerably reduced, fuel efficiency increased in proportion to the reduced melt cycle time and following a reduced normal firing rate, and issues concerning crucible longevity and reliability were entirely eliminated.

Attractive economy of the work required to implement the proposed solutions was achieved by the client carrying out fabrication work locally and since the majority of the existing burner fabrication was reused and constituent parts retained. Additionally, Monometer was able to supply a competitively priced made-to-measure bottom-pouring cast iron crucible.

After the furnace modifications at West Country Tiling had been completed, and the new pot had been fitted, Toby Pitt commented “Despite my unnecessary worrying the outcome is perfect.  Thank you”.

Monometer welcomes enquires for new furnace equipment as well as for assisting with updating or problem-solving performance issues whether process or furnace related.