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Cement Stoves from India by Peter Young

Boiling Point
Front cover of Boiling Point issue 31
Issue 31 (1993) Clays for Stoves
ArticleCement Stoves from India
AuthorPeter Young
Extract by Peter Young from paper by Dr K N Maiti, April 1993

The Central Glass and Ceramic Research Institute at Khurja in Uttar Pradesh is the leading research institution for pottery stoves in India. It has recently experimented with castable fireproof cement stoves that can overcome many of the weaknesses often associated with pottery stoves. Although clay has many benefits as a stove material it also has many limitations that are often ignored.

  • the raw clay and additives are of variable compositions which can make planning production difficult and unpredictable
  • commercial production is often labour intensive and can also be capital intensive where kilns and sheds are required
  • the fabrication process is lengthy and highly dependent upon the weather
  • shrinkage on drying and firing not only introduces residual stresses, it also means the stove must be made over size to compensate if it is to be used with a metal cladding
  • pottery needs to be fired, which consumes fuelwood in large quantities
  • ceramic stoves are perceived as being weak and fragile and need careful handling
Table I Stove Production Costs - Ceramic v Castable Refractories :

Techno Economic Data
Ceramic Rouse Castable
Refractory Route

A. Viable Installed Capacity
45,000 liners/annum
(150pcs/day)
45,000 liners/annum
(150 pcs/day)

B. Total Capital Investment
Rs813,300
Rs296,700

C. Cost of Production per Liner


raw materials
Rs8.45
Rs20.30

labour& supervision
Rs2.56
Rs1.92

utilities:
Rs3.13
Rs1.43

overheard expenses :
Rs4.66
Rs3.54

TOTAL
Rs 18.80
Rs. 27.19

D. Profit
Rs3.74
Rs5.59

E. Capital Investment


1) Pay-back period:
4years 9mths
1yr 2 mths

2) Space requirement
1800 sq ft
4500 sq ft

3) Raw materials & additives
4 to 5 materials
Only one material is required

4)Quality control
control of several materials
standard material

5) Production technique
several steps required no firing & production& production cycle is about 10-15 days
cycle is about 4 days

6) Expected life
Unpredictable but on average about 60 heats
May be about 300 heatings

7) Flexibility of the complete production unit
Pottery workshop
Production unit can be set up in a van

In India refractory castables are widely used in the iron and steel making industries to make monolithic linings and appear to be a suitable material to make liners for stoves. Refractory castables are a dry mix of refractory aggregates and bonding materials. When mixed with water, a type of wet concrete mass is formed which can be cast into a mould and left to dry. Ceramic bonding is developed in the casting by heating to high temperatures but this is not essential for stove liners. The refractory aggregates consist of fire clay grog, bauxite, sillimanite and other alumina materials or chromite etc. which do not undergo structural changes on heating.

Refractory castable materials are found to have the following properties and features:
  • they are marketed in polythene lined gunny bags like Portland Cement and are readily available
  • they are expensive at 4000-5000 its/tonne
  • liners can be cast in steel moulds
  • casting is a cold process and saves fuelwood
  • the alumina content in the fire clay in the refractory castable materials normally ranges between 35 and 45%
  • the water requirement to make the mixture workable is in the range 13-16%
  • the bulk density after drying ranges between 1.8 - 2.1 g/cc
  • the cold crushing strength at 110° and at the maximum service temperature 1450°C varies between 100- l SO and 150-250 kg/ cm2 respectively
  • they have a high mechanical strength and resistance and resist both impacts and abrasion
  • they resist thermal shock and spelling
Two production units are planned in India with a production cycle around 3-5 days compared to 10-15 days for pottery liners. The equipment and accessories will consist of rotating mixer, curing tank, vibrator, hand tools, steel moulds, wooden planks for drying racks.

A feasibility study has been carried out on refractory castable liners and the results have been compared to those of a comparable factory making ceramic liners.
Figure 1: Cross-section of the Portable Janta Chulha, a typical stove which could be made with castable refractories
Figure 1: Cross-section of the Portable Janta Chulha, a typical stove which could be made with castable refractories

[top] [end]Conclusion

The cost of the refractory material is high, nearly 3 times the cost of clay. This means the production cost of the castable is nearly 1.5 times more than the ceramic liner. However, when account is taken of the improved durability of the castable which may last 5 times longer than the ceramic liner, the castable stove may prove to be better value.

[top] [end]Contents: Boiling Point 31: Clays for Stoves

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Effects of the Clay-Non Clay Ratio on Stove Behaviour - Clay-Non Clay Test Procedure - Clay Testing - 5 Country Reports - Clay Preparation Techniques - The Sudanese Muddy Stove - Cement Stoves from India - The Chencottai Chulah - Zambian Double Wall Clay Stove - Kenya Downdraught Kiln for Stove Liners - The KCJ - from Artisan to Factory - Working with Village Women in NWFP Pakistan - Smoked Maasai - Kachel Ovens - Metal Stoves for Developing Countries - Chimney Design

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Page created: 29 August 2007; Last edited: 27 November 2008; Version: 1
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Pagename: CementStovesFromIndia @HEDON: RCHA