How to quickly test the peeling performance, breathability, and high temperature strength of the coating for gray cast iron lost foam?

A self-made testing method for the three properties of gray cast iron lost foam coating (molting ability, high temperature strength, breathability), combined with low-cost equipment and simple operation steps:

1. Purpose of shell peeling test: To test the difficulty of coating peeling off from the surface of castings after pouring.  

Method: Sample preparation:

1. Use EPS to make 50 × 50 × 10mm test block, dip the coating to be tested, and dry it for standby.  

2. Embed the test block in dry quartz sand and simulate casting in a high-temperature furnace (heated to a casting temperature of about 1400 ° C for gray cast iron and kept for 5 minutes).  

Testing steps: After cooling, lightly tap the surface of the casting with a metal rod and observe the peeling of the coating layer. Rating standard: Excellent: Automatic coating peeling>90%;  

Good:>80% detachment after light tapping;  

Poor: It needs to be scraped off with force.  

Key point: If the coating contains bentonite or fibers, attention should be paid to high-temperature sintering properties, which can be improved by adjusting the ratio of aggregates (such as quartz powder) to binders.

2. High temperature strength

Purpose of testing: To evaluate the anti cracking or peeling ability of coatings at high temperatures.  

Method: Sample preparation: Apply the coating onto a metal mesh (such as wire mesh) to form a 2-3mm thick coating. After drying, cut into 50 × 10mm strip samples.  

Testing steps:

1. Place the sample in a high-temperature furnace, raise the temperature to 1000 ° C (simulating the instantaneous temperature of molten iron contact), and hold for 10 minutes.  

2. Observation after removal: no cracks: excellent high-temperature strength; Minor cracks: acceptable; Powder shedding: High temperature binders (such as silica sol or aluminate cement) need to be added. Alternative solution: Use refractory bricks as the substrate to apply paint, and conduct scratch testing after high-temperature firing (hardness ≥ 3H is qualified).

3. Purpose of breathability testing: To measure the ability of the coating to allow gas to pass through and avoid porosity in the casting. Simple method: Device: Glass tube (inner diameter 20mm, length 300mm), with a metal mesh supporting the coating layer at the bottom (to make a 1-2mm thick sample). Place the fixed glass tube vertically and connect a U-shaped water pressure gauge below.  

Steps:

1. Introduce a constant air pressure from the top of the glass tube (using an air pump or balloon, with a pressure of 0.1MPa).  

2. Measure the volume of gas passing through the coating per unit time (using underwater gas collection method to measure bubble velocity).  

Calculation: Breathability=Gas flow rate (mL/min)/(Coating area x Pressure difference). Reference value: The permeability of gray cast iron coating generally needs to be greater than 50 (unit: cm ³ · cm/(cm ² · min · Pa)).  

Attention: If the bubble rate is too fast, it is necessary to increase the fiber or sheet material (such as mica) in the coating to reduce the breathability.

Summary of self-made key points and suggestions for material adjustment:

Poor molting ability? Reduce high-temperature binders and increase graphite powder or talc powder. Low heat intensity? Add silica sol (3-5%) or aluminate cement.  

Insufficient breathability? Add 0.1-0.3% wood fiber or adjust the particle size of the aggregate (coarse particles to improve breathability).  

Safety reminder: Wear protective gloves and a face mask during high-temperature experiments to avoid burns.  

Through the above methods, the performance of coatings can be evaluated at low cost, which is suitable for small casting workshops or laboratories. For more accurate data, further calibration can be carried out in conjunction with industry standards such as JB/T 9226-2008.