Keramicalia

Tel: +27 (0)11 412 3261 or +27 074 587 2728 Fax: +27 (0)11 692 1232
We manufacture specialised refractories and ceramics.

Dump Mix

Dump mixes were developed in response to an enquiry for a material to repair the impact areas of ladle floors. They had to be capable of being installed fairly hot, must be self-levelling and self de-airing and develop strength immediately and retain it to high temperatures. They also need good thermal shock resistance.

These criteria are difficult to meet. Keratab Dump Mix was eventually perfected to display all of these properties. It turned out to be ideal for certain applications in furnace roofs. The biggest application is in feed chutes for submerged arc furnaces. These are subjected to extreme abrasion, mechanical abuse during installation and thermal shock. They are water cooled, and therefore exposed to extreme thermal gradients. Maintaining high strength over the whole temperature range is therefore critical. Vibration casting through the spiral of water pipes is impossible, and only a self-flowing, self-deairing castable can be used. The same applies to water-cooled roof sections. Electrode seals are another major application. The formers are a bit tricky, but have been made. Another application is delta sections. The castings have to be flat on top.

Dump mixes can be used with stainless steel fibres. The piece protruding from the shell of feed chutes and the first 50mm inside the shell is normally reinforced with 3% stainless steel fibres.

Reducing Dump Mix must be discharged directly from the mixer into the mould, and mixes must be made in rapid succession. Dump mixes are fast setting and highly exothermic. Where circumstances require it, slow setting Dump Mixes can be made.

 

Keratab Dump Mix

Description; A dumping mix is a self-levelling castable for discharge directly into the installation. It flows rapidly without any assistance,and de-airs itself. It is based on tabular alumina. It can handle severe thermal shock.

Chemical analysis;

Al2 O3

90.0%

Fe2 O3

0.2%

SiO2

0.2%

CaO

9.6%



Cold Crushing Strength:

 

C.C.S. MPa

Density g/cm³

Air dried

40g/cm³

2,78

110ºC

38g/cm³

2,74

400ºC

94g/cm³

2,64

1200ºC

54g/cm³

2,50

Mixing; Mix with +9% water. It flows for about 20 minutes. It should be discharged directly into the mould, since its flow properties do not allow handling in buckets or wheelbarrows. No vibration is needed. Heat of hydration is high, but delayed. (About 7 hours) Drying should be slow and careful, as the material has very low permeability and a very fine pore size distribution.

Packaging; 25kg plastic bags.

Shelf life; 12 months in unpunctured bags.

Test results are based on single cubes.

Reducing Dump Mix

Description; A dumping mix is a self-levelling castable for discharge directly into the installation. It flows rapidly without any assistance,and de-airs itself. It has very high mechanical strength at all temperatures. It can handle severe thermal shock.

Al2 O3 83.3%
Fe2O3 0.09%
Na2O 0.5%
K2O 0.07%
SiO2 24%
CaO 5.3%

Density: 2,79g/cm³ = Use 2,79 tons per m³.

Cold Crushing Strength:

Air Dried 42 MPa      
 110°C      68 MPa
 
400°C

99 MPa 

 
800oC oxidising 98 MPa
800oC reducing 139 MPa
1000oC 84 MPa
 
1200°C   72 MPa  

 Mixing; Mix with +6% water. Can be mixed in 2 minutes in an ordinary concrete mixer. It flows for about 20 minutes. It should be discharged directly into the mould, since its flow properties do not allow handling in buckets or wheelbarrows. No vibration is needed. Heat of hydration is high, but delayed. (About 7 hours) Drying should be slow and careful, as the material has very low permeability and a very fine pore size distribution.

Packaging; 25kg plastic bags.

Shelf life; 12 months in unpunctured bags.

Test results are based on single cubes.

Repair of dump mix castings

Dump mixes rely on their vast specific surface area for their bond strength and rheological properties. This also results in several other significant properties; Good thermal shock resistance Very strong capillary suction. High surface tension, which makes them stick to buckets rather than falling out. They are not sucked dry by conventional materials if cast against them. Hydraulic bonded materials cast up against them are sucked dry. Therefore Dump mixes cannot be used to repair dump mixes. Interrupted castings will not bond at the joints.

A viscous phosphate bonded mix, Phospatch can be used to repair dump mixes. It is very fast setting and will bond to almost any surface. It can even bond to a surface vertically above it. It has been used to repair the inside of arc furnace roofs by pouring through electrode holes into shuttering under the roof.