Cover Image
close this book Boiling Point No. 31 - August 1993
View the document Clays for Stoves
View the document Effects of the Clay/Non Clay (C/NC) Ratio on Stove Behaviour
View the document Clay/Non Clay Test Procedure
Open this folder and view contents Clay Testing - 5 Country Reports
View the document Clay Preparation Techniques
View the document The Sudanese "Muddy" Stove
View the document Cement Stoves from India
View the document The Chencottai Chulah
View the document Zambian Double Wall Clay Stove
View the document GTZ News
View the document Kenya Downdraught Kiln for Stove Liners
View the document The KCJ - from Artisan to Factory
View the document Working with Village Women in NWFP, Pakistan
View the document Smoked Maasai
View the document Kachel Ovens
View the document Metal Stoves for Developing Countries
View the document News
View the document Research & Development
View the document Publications
View the document Letters to the Editor

Cement Stoves from India

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

45,000 liners/annum

45.000 liners/annum

Installed

(150pcs/day)

(150 pcs/day)

Capacity

   

B. Total

Rs813,300

Rs296.700

Capital Investment

   

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 1450C 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.


Fig 1 - Cross-section of the Portable Janta Chulha, a typical stove which could be made with castable refractories

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.