Possible scrapping of vacuum brazing furnace products and Solutions – 3

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11. white edge
12. The product is not brazed through, the filler metal is not fully melted
13. After vacuum brazing, the product turns black or its appearance fails to meet the customer’s requirements
14. The electrode carbon rod discharge product of the connecting block is scrapped
15. Molybdenum spraying on the surface of the product is scrapped

11. white edge
1. Phenomenon and reason: refers to the irregular occurrence of copper free welding seam after brazing, which is called white edge.

2. Solution: The white edge is generally caused by the unreasonable gap between the wafers. But the white edge can be reduced by controlling the photo gap before vacuum brazing.

12. The product is not melted
1. Phenomenon and reason: it refers to the phenomenon that a small part of products in the furnace are not melted when brazing is carried out in the normal process.

2. Solutions: The main reasons for unmelted products are:
(1) The old vacuum brazing furnace needs to open the door or lower door structure during cooling. Operators should close the door or lower door before vacuum brazing, and the door or lower door should not be closed or in place during operation. The new vacuum brazing furnace does not have this problem.
(2) Lining in the furnace wall aluminum silicate fiber felt flow, nickel sheet damage.
(3) Thermocouple temperature measurement is inaccurate.
(4) Unreasonable vacuum brazing process.
(5) There are too many incoming furnaces. The temperature of the center part of the vacuum brazing furnace does not reach the brazing temperature, and the products are not placed according to the specified requirements.
(6) The thermocouple is not regularly checked as required.

13. The surface of the product becomes gray and black after vacuum brazing
1. Phenomenon and reasons: During vacuum brazing, the product will be gray and black due to vacuum furnace leakage caused by sealing or operation error.
2. The surface of the fixture is vented without drying treatment.
3. Solution: You can go white after blackening. The process is as follows: heat preservation at 1060℃ for 35 minutes, which can be solved. But if the high temperature blackens, depending on the degree of seal leakage. Degree of brazing flux loss, if copper flux loss is serious product scrap other reasons. The product blackens when it comes out of the oven. There are two main types of blackening, high temperature blackening and low temperature blackening. High temperature blackening refers to the temperature rise of 1040 ° C to 1120 ° C insulation end from cold to 1040 ° C called high temperature. From 1040℃ self-cooling to 870℃ strong cooling to 50℃ out of the oven called low temperature.

There are several reasons why products go black:
(1) In the process of brazing, a certain part of the furnace (such as the door, door, electrode sealing ring safety valve, etc.) is not sealed.
(2) When the positive and negative pressures are injected, the nitrogen pressure does not meet the requirements or does not fill up the air normally, resulting in gas emission. However, the vacuum loss time is short and can be rewelded and lave, but the temperature of rewelding process must be 5 degrees higher than last time, and the time curve of rewelding process temperature is specified.
(3) Slow oxidation caused by oil return and water leakage in vacuum brazing furnace.
(4) Volatilization of carbon felt and aluminum silicate fiber felt in vacuum brazing furnace insulation layer.
(5) The product surface pollution caused by the lubricating oil of the cooling motor in the vacuum brazing furnace will turn gray and black.
(6) Gray or black hair caused by parts and parts not cleaned, residues of cleaning solution and copper reaction.
(7) After the product comes out of the oven, the chemical reaction of air, moisture and copper on the brazing seam causes the surface of the product to turn gray and black.
(8) Water content and oxygen content of nitrogen exceed the standard. Cause the surface of the product gray and black.

14. The electrode carbon rod discharge product of the connecting block is scrapped
1. Phenomenon and reason: it refers to that during the heating process, the contact surface of the electrode carbon rod of the connecting block becomes loose and produces a strong arc, and the product is scrapped by electric shock around the arc, which is called discharge scrapped. After discharging, it is not found in time, so that the contact point is disconnected, so that the local temperature in the furnace is higher copper injection serious. The other end of the temperature is too low to melt the product.

2. Solutions:
(1) Check the carbon rod connection block of furnace bile electrode in each furnace. Change in time if 2/3 or severe hair loss is found.
(2) When entering the vacuum brazing furnace, it is necessary to be careful and careful. In the vacuum brazing furnace and the products shall not touch or vibrate to the heating parts.
(3) At the end of each brazing furnace, the sundries in the vacuum brazing furnace must be sorted and cleaned. Vacuum every week. Open the upper and lower doors and turn on the fan every three weeks. It is required to rotate the fan for 3-5 minutes, and open and close the door and lower doors for 3 times within 3-5 minutes. Make sure the furnace is clean.

15. Product copper spraying is scrapped
1. Phenomenon and reason: it refers to that in the high-temperature brazing process, a small part of the copper filler material in the heating workpiece material forms atomization in the melting process, and the vacuum degree is not controlled in place, resulting in the atomization of the copper material sprayed on the product or aggregated at a part of the product, resulting in the scrap of the product called copper spraying scrap.

2. Solutions:
(1) Reasonably reduce the solder copper thickness.
(2) At high temperature, the partial pressure is stable at (2.5E2).
(3) Reasonable product placement.
(4) Selection of brazing process;
(5) Regularly check the vacuum instrument.
(6) Product polishing or chemical treatment.