Play around with the camera angle to get the best contrast on the monitor. Comments:Īs already mentioned, it can be difficult to see the water levels in the capillaries because of the thin optical depth. Use a CCD camera with close-up lens looking as horizontally as possible the watch glass should sit on a lab jack so a suitable view can be obtained. Be generous with the ink (black, blue or red) the setup needs to be illuminated from behind with a light box, and the level in the thinnest tube is especially difficult to see. It is best to mix the ink and water before setting down the tubes. Capillary action draws the ink/water up the tubes to varying heights.Ĭlamp the tubes to a lab stand and lower them into a petri dish. The tubes, with bores 3, 2, 1 and 0.5mm respectively, are held together by tubing clamps and sat vertically in a watch glass containing ink and water (see figure 1). The setup shows the direct comparison between four capillary tubes of different bores. For information on brazing products or services, click here or contact us.Due to surface tension effects water rises up a narrow bored tube the rise in height being inversely proportional to the bore's radius. When you bring two pieces of metal together, these imperfections and irregularities create channels along which a liquid can move. Questions? Lucas-Milhaupt experts can help you navigate the challenges of joining metals. The example for capillarity: blotting paper absorbing ink/water. For more information from Lucas-Milhaupt on proper brazing procedures, click here. Capillary depend upon density of liquid, surface tension of liquid and the diameter of the tube. Successful capillary action-the process that allows alloys to flow into the joint between two metal parts-is crucial to successful brazing. Parts that are not properly cleaned may carry grease or other debris which will impede the process of capillarity. Variation in spacing will affect the success of your brazing operation because capillarity will be compromised. However, it leaves voids where the oily surfaces interfere with capillarity. If this were a braze joint, it would not be a sound one.įrom these illustrations, we can understand several principles relating to capillarity and brazing.įirst, joint gaps must be of correct, uniform size for capillary action to occur. When we insert these plates into the tray, the liquid rises to fill the gap. But the inside surfaces of the glass have been marked with greasy fingerprints. Test 3: For our next experiment, we have glass plates separated by shims representing an ideal, uniform clearance of 0.0015" or 0.038mm. Remember, in our first test, the liquid filled the gap between the plates completely because the space was uniform, so capillarity could operate. Then the gap becomes too large, and capillarity Only to the point where the clearance is 0.005 - 0.006" or 0.127 Now, when we insert the plates into the tray, we see the liquidĬan only rise part way. These plates are separated by a 0.0015" or 0.038mm shim at the bottom, and a heavier shim of 0.015" or 0.381mm at the top. Test 2: Next, we will demonstrate what happens when we don't have a proper, uniform clearance. This illustrates the value of a close and uniform clearance for successful capillarity during brazing. Let's see what happens when we dip the bottom into a tray of liquid.Īs you can see, the liquid has been drawn up smoothly by capillarity to fill the entire clearance between the plates. This gives us an ideal spacing for capillary action to occur. Test 1: Here, we have two glass plates, with shims of equal size, 0.0015" or 0.381mm, inserted at the top and bottom. Let's head to the lab, where we will conduct several experiment depicting successful capillary action, then capillarity which is inhibited by several factors. Capillarity is defined as movement of a liquid along the surface of a solid caused by the attraction of molecules in the liquid to the molecules of the solid.
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