Casting paint performance indicators are really many, how to judge the advantages and disadvantages?

First, the main technical indicators of casting
the density of casting coating reflects the amount of solid particle content in the coating. If the casting coating density is too small, then each brush on the mould and core surface of the formation of the coating layer thickness is not enough, difficult to play a protective role, therefore, in general, casting coating density is good, but the density of the paint is not the larger the better, if the density is too large, paint brushing difficulties, will cause uneven coating surface, local accumulation and other problems, will also cause adverse effects on casting quality. There is a certain relationship between the density and concentration of

. The density of the casting coating can be measured by the gauge weighing method or by the Pome meter, but the reading of the pormometer is greatly affected by the viscosity of the casting coating.
condition viscosity
the condition viscosity of the coating is commonly used in the casting production of the 4th and 1st viscosity cups. The purpose of the viscosity determination is to control the brushing of the coating, the depth of the mould and core surface and the thickness of the coating. General casting paint manufacturers have recommended brush conditions viscosity.
suspension
s levitation is an important working performance of casting coatings, and the general measurement methods are relatively high setering method (measure barrel method), seboding instrument method and sedation rate method. Among them, the measure barrel method is one of the simplest and most practical methods.
brushing
generally determined by the experience of operators, a more objective method is to determine the surface viscosity of casting coatings at different shear rates. The ratio of the surface viscosity of the coating at low speed (6r/min) and high speed (60r/min) is both brush index M.
flowing
When painting or flow coating on a mould or core surface, a coating is established after brushing or flowing, often with grooves and brush marks on the surface that may disappear within a short period of time or may remain. The performance of automatically disappearing brush marks or grooves from the surface of a wet coating layer is called leveling.
flowability
Due to the influence of gravity, casting coating in the casting (core) vertical surface has a downward trend, and resulting in the thickness of the lower coating is greater than the thickness of the upper coating, and even the formation of a build-up at the bottom of the cast (core), this nature is called fluidity.
permeability
permeability of casting coatings refers to the ability of coatings to penetrate into mould pores. Casting coating penetration is large, can enhance the adhesion of the coating to the mould, at the same time can strengthen the mould, improve the anti-stick sand resistance of the mould. The depth of coating penetration can be detected by dipping standard sand blocks.
pH of the coating
usually the pH of the casting coating changes within 4 to 11, but alkaline casting coating is more commonly used, usually in the range of 8 to 10. PH is not only used as an indicator of the performance of casting coatings, but also as a method of monitoring the performance of coatings during use and storage, and as a process monitoring indicator for the production and use of coatings. Usually coatings can be measured by color ratio and position metering.
coating breathability
coating forms an isolation layer between the metal and the mould (core) surface, requiring the coating to be dense, except for the vanishing mold coating, the breathability should be low. Breathability can be measured by a standard cylindrical sample at a certain pressure using a certain amount of air.
Coating anti-scratch strength
moulding, core coating, to go through the handling, drying, removal of surface floating ash and distribution box and other processes without damage, therefore, after drying and curing the coating must have a certain surface strength - anti-scratch strength. The more accurate methods to determine the anti-scratch strength of the coating are scratching method, pressure method, mechanical brush method, sand falling method, vibration method and so on. Paint application manufacturers determine the coating anti-scratch strength, can take the hand-scratch method, this method can be the paint anti-scratch strength is divided into four levels:
1, good: with fingernails with force to scratch the coating layer does not drop powder;
2, better: with fingernails on the paint layer drop powder;
3, can: with the finger force coating layer on the drop powder;
4, poor: with the touch of the paint layer drop powder.
the surface strength of the coating measured by the hand-to-hand method is related to the type and dosage of the attachment and binder, and the surface strength of the coating is increased with the increase of the amount of adhesive. This indicates that the main factors affecting the surface strength of the coating are the amount and type of binder. When considering surface strength, the effects of binders are mainly considered.
Coating moisture absorption
painted water-based paint moulds, cores after drying will absorb moisture from the air, so that its performance deteriorates, the strength is reduced, the amount of gas increased sharply, in severe cases can lead to casting sand, loose tissue and pores and other defects. The moisture absorption of the coating is mainly related to the binder, and the water-soluble adhesive has a strong moisture absorption. The moisture absorption of the coating must be detected for long-term storage of coated moulds and cores before casting.
basic method of measuring the moisture absorption of the coating is to keep the coating sample in a constant humidity tank for a certain period of time, and then weigh the sample before and after it is maintained.
thermal conductivity of
the insulation and cooling properties of cast coatings are particularly important for the selection of metallic coatings. The casting thick wall uses a cold paint to accelerate the cooling of the casting, and the thin wall uses a insulation coating to allow the casting to cool slowly. The thermal conductivity of the coating can be determined by dipping into the melt method to determine the amount of gas in the coating.
so-called gas emission is the volume of gas produced by the coating at high temperature per unit mass fraction, expressed in mL/g, with a special gas meter for determination.
burn reduction
burning reduction is a dry paint sample under 105 to 110 degrees C, and the reduced mass of the sample after burning 1h in a non-oxidizing atmosphere gradually heated to 950 to 1000 degrees C accounts for the percentage of the original weight reduction.
sintering point
cast paint sintering point indicates the temperature at which the paint refracing filler particle surface or particle-to-particle mix begins to melt. The method of measuring the less contact of coating is SJY image sintering point tester method and tube furnace sintering method. The evaluation is carried out by five-level evaluation method.
refracing resistance
refers to the melting or softening point of refragent powder in casting coatings, i.e. its ability to withstand high temperatures.
coating heat resistance
casting coating heat resistance refers to the coating layer resistance to high temperature heat to produce cracks and peeling. It is measured by four-level evaluation method.
1: smooth surface without cracks, or only very fine cracks, no peeling between the coating and the substitut;
2: the surface has branches or mesh fine cracks, crack width is less than 0.5mm, no peeling between the coating and the substitut; level
3: the surface of the coating has branches or mesh cracks, crack width is less than
1mm, cracks are deeper, along the horizontal or vertical are not through the rough cracks, the coating and the substitut between no obvious peeling;
From the above performance indicators can be seen, casting coatings as a special category of coatings, its basic requirements and commonly used coatings are not much different, no more than from the paint, coating, use effect three aspects to consider. If high temperature performance is not taken into account, the average civilian coating researcher can fully understand and intervene in the study of this type of coating. China's existing level of casting coatings, including Shen casting and other more powerful, but also with foreign products there is a large gap. The author believes that, if willing, the vast number of casting paint researchers will certainly be able to contribute to the development of China in this field, and thus contribute to the development of China's foundry industry.
II, casting paint indicators of the test method
1, viscosity
from the production of good products to extract 120mL to add viscosity cup ready timing, open the viscosity cup opening, to be oars left to the cylinder 100mL, write down the time
2, density
with a balance will be equipped with 100mL of the weight of the barrel weighing out, and then subtract the quality of the empty barrel, then get the proportion.
3, suspension
from the time of the slurry added to the cylinder calculation, every 8h, 12h, 24h, observe the precipitation of the slurry once, the corresponding scale of the drum is how much, that is, to obtain the suspended value.
4, solid content
according to the amount of dry material added wet material volatility, by reference to the formula to calculate the solid content.
5, leveling
the slurry with immersion, brushing, spraying, flow coating method attached to the casting mould, observe the mould surface of the droplets, there is no accumulation of brush marks, flow marks, generally leveling good non-flow marks less.
6, strength
to coat the mould drying, touch with the finger, scrape, look at the coating off the situation, break the mould, observe the thickness of the coating, as well as the thickness of penetration into the mould.
7, the amount of
and the amount of gas test should be carried out GB/T 2684 "casting sand and mixture test method."
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