CS213743B1 - Diatomaceous earth for the spray mixture - Google Patents

Abstract

In the production of foundry castings, the correct selection of injection materials for the internal insulation of the mold is important, which is especially important for castings requiring hydraulic impermeability. According to the invention, diatomaceous earth in a mixture of 1 to 2.5% bentonite and 72.5 to 84% water has a loss on drying of no more than 0.9% and a loss on annealing of 0.4%, a granulometry of 0.001 to 0.05 mm. The content of particles of size 0.04 to 0.05 naa is 5 to 15% of the volume of diatomaceous earth. The morphology formed by particles of a needle-like nature is no more than 10%. The diatomaceous earth according to the invention is suitable for foundry castings such as centrifugal cast iron pressure pipes, various fittings, sewer pipes or wheels for rolling mills

Description

The invention relates to injection molding using diatomaceous earth for internal insulation of molds during the casting of cast iron castings, not subject to hydraulic permeability.

Diatomaceous earth is commonly used in the food and brewing industries as filtration media and smoke absorbers, while lower quality diatomaceous earth is used in the beverage industry for its high insulating properties.

The considerable insulating properties of diatomaceous earth are used, after certain treatment and appropriate selection, in foundries for insulating the castings when casting cast iron, heavy and non-ferrous metals. However, these are mainly less demanding smaller castings, for which pressure testing of the impermeability of castings is not performed.

In exceptional cases, diatomaceous earth was also used as the main component of insulating coatings for more demanding castings, e.g. in centrifugal casting of cast iron pressure pipes. However, pipes produced in this way had, among other defects, a high rate of rejection of pipes that showed leaks during pressure testing.

The cause of this high reject rate was primarily the use of unsuitable types of diatomaceous earth.

The above-mentioned shortcomings are eliminated by diatomaceous earth for the injection mixture according to the invention, for the internal insulation of molds when casting foundry castings, especially requiring hydraulic impermeability, consisting of 15 to 25% diatomaceous earth with a content of over 85% silicon dioxide, 1.0 to 2.5% bentonite and 72.5 to 84% water, in weight ratios. The essence of the invention is that the dry diatomaceous earth mass has the following properties: loss on drying max. 0.9%, loss on annealing max. 0.4%, granulometry in the range of 0.001 to 0.05 mm, while the content of particles with a size of 0.04 to 0.05 mm is 5 to 15% of the volume of diatomaceous earth and its morphology is such that particles with a needle-like character are at most 10%.

By using diatomaceous earth according to the invention, the injection is of higher quality, i.e. smoother, adheres better to the mold, does not clog the nozzles, which affects the smooth operation of the line and thus the performance of the equipment and a longer service life of the individual aggregates on the line. However, the main progress lies in reducing the reject rate due to leakage of castings. When using diatomaceous earth according to the invention, this reject rate can be reduced to the order of 1 to 2 56. Another progress is that the precise definition of the quality of diatomaceous earth allows the use of domestic diatomaceous earth.

The spray mixture in the exemplary embodiment according to the invention was used for internal insulation.

or a mold for casting pipes with this composition: 1. 230 1 HgO i.e. 82.7% HgO 5 kg bentonite 1.8% bentonite 43 kg of diatomaceous earth 15.5 36 diatomaceous earth 100.0 56 2. 230 1 HgO i.e. 78 56 _H20 4.5 kg of bentonite 1.5 56 bentonite 60 kg of burnt diatomaceous earth 20.5 56 burnt diatomaceous earth

100.0%

The diatomaceous earth used contained 90% silicon dioxide, loss on drying was 0.8%, loss on ignition was 0.3%, granulometry was 0.006 to 0.05 mm, while the content of particles with a size of 0.04 to 0.05 mm did not exceed 10% of the volume of the diatomaceous earth and its morphology was such that part

213,743 β-type needles made up 5%.

The content of particles with a needle-like character should be zero or very low, or in the form of fragments. It also depends on the quality of the bentonite used. It is most appropriate to use very finely ground bentonite.

The widest application of diatomaceous earth according to the invention is in centrifugal casting of cast iron pressure pipes and grey cast iron by the method of protective spraying of molds. However, it can also be used with advantage in casting cast iron fittings and other castings into molds, in centrifugal casting of sewer pipes, in casting of rolls for rolling mills to insulate the molds before pouring metal for rolls, both centrifugally and stationary cast, etc.

Claims (1)

Diatomaceous earth for the injection molding of the ingot molds in the casting of foundry castings demanding in particular hydraulic impermeability, having a composition of 15 to 25% diatomaceous earth containing more than 85% silica, 1 to 2,5% bentonite and 72,5 to 84% water, characterized in that the diatomaceous earth mass has a drying loss of not more than 0.9% and an annealing loss of 0.4%, a particle size of 0.001 to 0.05 mm, the particle size of which is 0.04 to 0.05 mm, which is 5 to 15% the volume of diatomaceous earth and its morphology formed by needles are not more than 10%.