Lost foam coatings are generally water-based coatings, which will shrink during the coating baking process, different coatings have different shrinkage rates. When the shrinkage rate is large: (1) the coating is easy to crack; (2) the inner corner of the mold bundle is hollow; (3) when the coating thickness is uneven does dry at the same time, the thinner mold will warp deform; (4) ) The die size becomes smaller due to coating shrinkage, which affects the casting size. The detection of the shrinkage rate of the coating can be quantitatively analyzed, which has an important role. The detection method of the shrinkage rate of the lost foam coating:

1 Material preparation

(1) Take a piece of A4 copy paper, the standard size is 297×210mm, cut in half along the width direction, that is, 297×105mm, use one of them to cut out the "I" shape, take the width of the top horizontal, bottom horizontal vertical 15mm, the length is 297mm unchanged.

(2) Take a 450×250mm foam board with a thickness of 10-15mm as a pallet place it on a flat table.

(3) Take a piece of 400×200mm thick 0.01-0.03mm plastic film place it in the center

450×250mm foam board.

(4) Make a rectangular foam frame, the size is shown in Figure 1, the thickness is 10mm, the center is pressed on the plastic film.

(5) Insert 8 pieces of 8-point iron nails into the foam frame fix them with the foam board.

2 Detection of shrinkage

(1) Take the paint to be tested (taken the production site), pour the paint (thickness 1.5-2.0mm) into the frame, weigh the specific gravity through a measuring cup, calculate the required paint weight by multiplying the area in the frame by the thickness the specific gravity. , Pour in by weight level. After leveling, put "I"-shaped copy paper in the center (for measuring the shrinkage size).

(2) When the paint is circulating (8 hours), use a knife to disconnect the paint film along the edge of the foam frame, pull out the iron nails, remove the foam frame the outer film, then enter the oven to bake Take it out until dry, detect the outer length of the "I"-shaped printing paper (3 points can be taken to detect the average) 

(3) Shrinkage calculation: take the test data information as 293mm (that is, the paint has shrunk 297mm to 293mm), then the shrinkage rate = (297-293)/297=1.35%. 

3 conclusion

(1) Different lost foam coatings have different shrinkage rates in view of the difference in formulation. When the shrinkage rate is large, the coating after baking will cause cracking warping, the size of the die will become shorter due to the shrinkage of the coating, which will seriously affect the product quality.

(2) The method of measuring the shrinkage rate of coatings is simple easy to implement, which can carry out quantitative data analysis of shrinkage rate, which is beneficial to the selection of coatings changing the formulation method, reduces the shrinkage rate of coatings, ensures the quality of coatings.