Bentonite Testing for Foundries 10 th October 2016 Australian Foundry Conference - Geelong

Transcription

1 Bentonite Testing for Foundries 10 th October 2016 Australian Foundry Conference - Geelong

2 Which Bentonite? The reason for this paper = not much information available comparing bentonites So how do you as a foundryman decide which bentonite you should use? 2

3 Bentonite The mineral of a thousand uses! Crayons Ceramics Washing Powders Cosmetics Lotions Consumer Products Medicines Shampoos Cat Litter 3

4 Bentonite The mineral of a thousand uses! Drilling Fluids Waterproofing Absorbents Metalcasting Animal Feed Commercial Uses Iron Ore Pelletising Geosynthetic Clay Liners Sealants Edible Oil Clarification Wine Clarification 4

5 Bentonite Basics The name Bentonite was originally used by Knight in 1898 Subsequently Geologists confirmed it originates from volcanic ash and is a rock Bentonites are generally classified as either Sodium (swelling) or Calcium (non-swelling) although some others such as Australian or Turkish are closer to a Calcium but are classified as Magnesium Both Ca and Mg can be converted to activated sodium bentonite by treatment with sodium carbonate Generally foundries will use a blend of blend of bentonites to get a blend of the properties (and balance cost) 5

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20 Which Bentonite? THE most important property is.. THERMAL DURABILITY 20

21 What is Thermal Durability? It is a major indicator of how the bentonite will perform at higher temperatures It is a function of the chemistry and cannot be altered by chemical treatment Higher thermal durability can significantly reduce total costs Higher thermal durability can increase greensand consistency There are a few relatively simple but important primary analytical tests that should be used in conjunction when choosing a clay that has the thermal durability that meets the foundry needs the best 21

22 1. Thermogravimetric Analysis (TGA) Heating a sample at a controlled rate and measuring changes in physical and chemical properties 1. Physical moisture is evaporated 2. The workable section of the material during which material can be cycled 3. Crystal structure breaks down and crystal moisture is lost 4. Bentonite is dead and no longer able to operate as required Mass (Weight %) Temperature

23 USA (Wyoming Na) Bentonite 23

24 Chinese (Act-Ca) Bentonite 24

25 Blend of USA (Na) & Chinese (Act-Ca) Bentonite 25

26 Indian (Act-Ca) Bentonite 26

27 Practical Schematic 27

28 Moisture As Received Generally, Bentonite samples have a moisture content of 8 12% as received Consistency is desired requirement. Higher moisture bentonite can lead to clumping, and blocking during transporting Low moisture bentonite will generate more dust particles % Moisture As Received % Above 13% can lead to clumping and blocking Below 6% can lead to higher dust levels A B C D E F G Moisture As Received %

29 Cation Exchange Capacity (CEC) (meq/100g) An indication of purity A higher CEC value leads to higher moisture absorption A higher CEC value can also mean a higher free swell, but not always Higher CEC value after calcine is better material For a foundry, a higher CEC value provides better rehydration of the bentonite for repeated cycles Sample A would be considered a better foundry meq/100g CEC (meq/100g) A B C D E F G CEC (meq/100g) CEC Calcined (meq/100g) material than Sample B 29

30 Total Hardness Bentonite Platlets have Cation Exchange sites consisting of Na+, Ca++, Mg++, K++, NH4++. Total Hardness is a measure of the Ca++ & Mg++ on the surface. Total Hardness target for Activated Bentonite = 20. Less than 10 normally means over activated. Total hardness is a measure of consistency would be a very consistent Bentonite Total Hardness Total Hardness (meq/100g) A B C D E F G Total Hardness (meq/100g)

31 Example of CEC and Total Hardness CEC minus Total Hardness is an indication of how much Na+ are present. Generally if more than 50% of CEC is Na+ - it is considered a Na Bentonite (Activated Ca Bentonites can also be in this range) Examples: o o o Sample A has a CEC of 97, and TH of 25. Na content is 72 Sample B has a CEC of 80, and TH of 60. Na content is 20. This is a Ca Bentonite Sample C has a CEC of 97, and TH of 36. Na content is 61. This is likely a CEC - Total Hardness Example CEC (meq/100g) Total Hardness (meq/100g) Na+ A B C under activated Ca bentonite 31

32 Hot Compression Test Tests the compression strength at 890oC and 1010oC Gives valuable information on how the bentonite will behave after being exposed to elevated temperatures and being dehydrated PSI Hot Compressive Strengths - Bentonite Type Comparison % Sodium (SPV) 67% Sodium/33% Act Calcium 33% Sodium/67% Act Calcium 100% Act Calcium (VF10) Hot Compressive Strength 890 C Hot Compressive Strength 1010 C

33 Free Swell Test Tests the ability of a clay to absorb water A higher swell is not always better for foundry A good sodium bentonite free swell of 20-30mls/2gr of clay is very sufficient for superior foundry performance Free Swell ml/2g Free Swell 0 Volclay SPV CB73 CB37 Probond Bentonite Type 33

34 Greensand Control Recommended Daily/Weekly Tests Active Clay Loss on Ignition Daily/Weekly Control Total Fines Wet Tensile 34

35 Greensand Control Recommended Hourly/Batch Tests Compactability Permeability Hourly/Batch Control Temperature Green Compression Strength Moisture 35

36 Bentonite Properties by Region 36

37 Typical International Property Variations Ventilated Disc Foundry 37

38 Less is Best Additive Consumption 3 Less Is Best - Additive additions Dust Extraction Cost 2 1 Water Demand Refractoriness 3 = Higher 2 = Medium 1=Less 0 Fumes Flowability Low Additives Medium Additives Defects Mould Density High Additives 38

39 Thank you Any Easy Questions? 39

40 Bentonite Testing for Foundries 10 th October 2016 Australian Foundry Conference - Geelong