Green sand moulding additives
Introduction
The main product produced is graded coal for use as a moulding sand additive to foundry greensand plants in the manufacture of iron castings. This product can be supplied in various gradings to suit the casting type and weight of casting and generally two types of coal have dominated the foundry industry.
These are both low in ash and high in volatile with one coal classed as a swelling coal and other with no swell. High total carbon and low sulphur complete the product suitability and both are excellent in performance.
Graded coal in the form of a “superfine” grading (240#) is used as a fuel in boilers and still in use at our Brancepeth Works to dry products, prior to grinding materials such as metallurgical coke.
Other products and operations include
- Anthracite
- Activated carbon
- Lustrous carbon formers
- Bentonite
- Gilsonite
- Commission grinding
- Pulverised fuel
Coal analysis
| Typical particle distribution % retained Graded coal | 1.00 mm 16 # BSS | 0.50 mm 30 # BSS | 0.21 mm 72 # BSS | 0.15 mm 100 # BSS | 0.075 mm 200 # BSS | <0.075 mm 200 # BSS |
|---|---|---|---|---|---|---|
| 30 | 0 | 23 | 47 | 12 | 13 | 5 |
| 75 | 0 | 13 | 37 | 15 | 22 | 13 |
| 100 | 0 | 10 | 28 | 12 | 22 | 28 |
| 145 | 0 | 2 | 18 | 15 | 25 | 40 |
| 190 | 0 | 0 | 5 | 8 | 30 | 57 |
| 240 | 0 | 0 | 0 | 2 | 8 | 90 |
Graded coal is used mainly as an additive to greensand systems to create a reducing atmosphere in the mould and prevent metal penetrating into the sand leaving a smooth, clean iron casting surface. Depending on the metal type and the size of the casting normally determines the grading of coal to be used. Coarse grades are used in high pressure vertical moulding systems such as Disa units and medium and finer grades are used in horizontal plants but this varies depending on other factors such as performance, Bentonite type and sand quality.
We specialise in two main coals which have been selected for their all round properties and in particular in their low ash content and high volatile evolution. High total carbon and low sulphur complete the product suitability and both are excellent in performance.
One coal has a high swell index and many foundrymen value this property whilst others prefer the slightly higher volatile coal with no swell.
| Element | Value |
|---|---|
| Ash | 2 – 3.5 % |
| Volatile | 34 – 42 % |
| Moisture | 4 – 7 % |
| Lustrous | 8 – 12 % |
| Sulphur | 0.6 – 0.8 % |
Coal / Bentonite / Lustrous Carbon products
Ideally these products should not be mixed for efficiency reasons but for customers with limited storage or safety issues our Pulverbond range can overcome these limitations. By using air to mix these products we keep the critical coal grading while blending in standard foundry grade Bentonite and if required, Lustrous Carbon products to enhance the blends. Please find here our latest bentonite formulations.
Safety considerations are important when dealing with coal and allied products and the practice as been to blend graded coal with Bentonite to ensure safer handling and no ADR transport regulations.
We can blend any percentage of graded coal, Bentonite and lustrous carbon formers such as Gilsonite and Pitch based products to suit the customer needs. A typical blend is 50:50 coal:Bentonite. If lustrous carbon products are added, this is normally 40:10:50 coal:lustrous carbon:Bentonite.
Application of graded coal
The main application for graded coal and coal/Bentonite blends is in foundry use for greensand systems. graded coal is added in conjunction with Bentonite and the purpose is to help strip clean the casting from the sand. A clean strip results from the layer of carbon deposited and the resultant castings have a clean surface free of sand related defects.