1.Properties of flow coating
(1) The rheological properties meet the requirements of flow coating process.
(2) Suitable coating thickness. Generally, the coating thickness difference should be ≤ 0.2mm.
(3) With appropriate permeability. The diameter of sand particles with a surface depth of 1.5-2 times.
Some of the following performance requirements, similar to the requirements for ordinary coatings.
(1) Good suspension stability.
(2) Sufficient resistance to cracking and high temperature stability.
(3) Good sand resistance.
(4) Low gas generation and good air tightness.
(5) Good storage.
(6) Raw materials are cheap and rich in resources.
Viscosity, density, suspension, coating, permeability, fluidity, leveling, coating uniformity, anti over flow, anti accumulation, etc.; working performance, coating surface strength, gas generation, anti shock heat cracking, anti sand adhesion, etc.
2. Test method for process performance of flow coating
2.1 density
The density of paint is composed of the density of various components of paint. In the composition of coating, the density of all solvents is lower than that of refractory powder, suspending agent and binder. Generally, if the coating density is large, the viscosity is large, the coating thickness is thick, and the fluidity is poor; otherwise, the viscosity is small, the coating thickness is thin, and the penetration is deep.
The thixotropy of coating will affect the result of coating density measurement with Baume meter.
The weighing method is simple, easy and accurate. The determination method is: first weigh the weight of the plug measuring cylinder m1g (accurate to 0.01g), then pour the fully mixed coating to be tested to the elevation of 100ml, and then weigh it to m2g, then the coating density ρ is m2-m1 / 100g / cm3.
2.2 viscosity
The rotating viscometer is used to measure, and the current cup method is often used in the production site. The funnel type viscosity cup with diameter of Ф 6 ± 0.1mm, Ф 4 ± 0.1mm and volume of 100 ± 2ml can be selected. Flow cup viscosity is also called conditional viscosity, in S.
2.3 suspension
The determination methods of coating suspension are cylinder method and settling column method. Ф 30mm × 100ml plug measuring cylinder, make it reach the elevation of 100ml, (24h), suspension Ф.
V – volume of clear liquid of upper clarification layer of suspended coating.
2.4 permeability and coating
Thin wall casting 0.15-0.30mm;
Medium casting 0.30-0.75mm;
Thick wall casting 0.75-1.00mm;
Extra thick casting 1.00-2.00mm;
In most production of small and medium-sized steel castings, the coating thickness of 0.5-0.8mm is generally the best.
2.5 leveling
Direct observation method and quantitative coating dispersion leveling method were used to determine the leveling property of brush coating.
Level 1: the coating surface is smooth and flat, RA ＜ 6;
Grade 2: slightly uneven bulge on the coating surface;
Grade 3: the coating surface has lamination, ripple marks and other traces, not obvious;
Grade 4: the coating surface has obvious defects such as lamination, ripple mark, etc;
Grade 5: the coating surface has serious corrugations, laminations and other defects, with accumulation.
2.6 coating uniformity, anti over flow and anti accumulation
The qualified coating shall ensure that the thickness of the upper and lower coating on the sand mold surface is as consistent as possible, which is called coating uniformity. In flow coating, the most difficult to control is the coating thickness and uniformity, which is also the key to control the performance of flow coating. Production length × width × thickness = 200mm × 40mm × 20mm. Measure the coating thickness A1 and A2 at 20 mm and 180 mm from the bottom, △ δ = | a1-a2|, the larger the △ δ is, the worse the coating homogeneity is.
The flowing of coating refers to the ability of coating to flow downward under the action of gravity. First, at the beginning of flow coating, if the fluidity of the coating is poor and the coating is not easy to flow, it is easy to make the coating flow, pile up, the coating is too thick, and low marks are produced; but if the year is too low, it will cause excessive flow, too thin coating, bare type, etc. The other is the flow when the coating structure is restored after the coating is poured down. At this time, the flow is serious, which results in poor uniformity of the coating. In order to make the coating flow well in a short time at the beginning of flow coating, make the coating evenly distributed on the surface of the mold cavity, and then restore the structure quickly, take the coating thickness < 0.2mm as the flow excess, and take the unclear groove and accumulation as the poor stacking resistance.
2.7 liquidity
The flow coating requires good fluidity, grooves and narrow seams can enter into the coating, and the coating is easy to flow out without accumulation, and the coating has good uniformity. It is easy to produce defects such as unclear sand mold outline, ripple mark, lamination, etc. the molding sand is made into a flow groove, inclined at 10 °, 5ml of paint is slowly injected into the funnel, so that it falls into the chute, and the flow length represents the fluidity. The method adopts a long strip sand sample with length × width × thickness = 130mm × 23mm × 6mm. 1g coating is dropped on one end of the sand sample until it stops flowing, and its flow length is measured after drying. The angle between the sand block and the horizontal plane is 80 °. Use a pipette to absorb the paint, pour 3ml on its upper end, and then quickly erect it until the paint stops flowing.
2.8 drop mark resistance
If the flow coating flows to some downward corners of the sand mold and is not lost, it will form a convex suspension, which is a drop mark. Drop mark is one of the most serious defects in flow coating.
Level 1: no drop mark
Grade 2: there is a convex hanging object with an angle of less than 0.5mm;
Grade 3: there are 0.5-1mm convex hanging objects at the edges and corners;
Grade 4: there are 1-2 mm convex hanging objects at the edges and corners;
Grade 5: convex hanging objects with an angle of ＞ 2mm.
