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Common scrap reasons of vacuum brazing furnace

First, the breakdown of thermocouple breakdown products.

1 phenomena and causes

When soldering is heated, the thermocouple shell is broken at high temperature. The conduction temperature display of thermocouple is obviously inaccurate. As the air enters the furnace, the vacuum of the vacuum furnace decreases rapidly. Products are oxidized and scrapped. General thermocouple shell breakdown, in the last furnace near the thermocouple near the obvious fog or blackening.

2 solutions

During brazing, the recording temperature is unstable, sometimes exceeding the temperature or lower than the actual temperature in the furnace. It is necessary to replace the thermocouple or shell when the above two points are found. When the thermocouple breakdown, the trace air enters the furnace chamber, the product is blackened, and it can be rejected or re brazed. At high temperature, the shell breakdown time is short, the section is small, must be re-brazed, brazing furnace temperature must be higher than the furnace temperature 5 degrees before whitening. If the breakdown time is more than half an hour, the breakdown section is large, and the products in the furnace are basically scrapped.

Two, return to oil scrap

1 phenomena and causes

Oil return refers to the improper operation of vacuum furnace, mechanical pump oil into the tube or furnace gallbladder to make the product blackening point or product oxidation if the oxidation of serious product scrap and other phenomena called oil return.

2 solutions

In the course of daily operation, targeted methods may be adopted for the following 3 situations. First, the vacuum pressure in the vacuum furnace is above 8.5E2, and the mechanical pumping force is less than the vacuum pressure. When the valves are opened, the pump oil enters the furnace with the draft tube. So the furnace has a furnace temperature below 800. Nitrogen can be poured into the vacuum furnace to make the vacuum pressure less than 8.5E2 after starting the mechanical pump to open the valves for pumping, according to the specified order of operation. Second, when the product temperature in the furnace is higher than that in the process of strong cold and high temperature, the vacuum furnace is restarted. The partial pressure must be opened so that the furnace pressure at 2.5E2, can simultaneously open two mechanical pumps to make mechanical pumps smooth operation for 3 minutes, open the valve to pump. Operate in prescribed sequence. Third, check whether the pressure in the furnace is atmospheric balance when the product is released or the furnace is opened. Whether positive pressure or negative pressure should be inflated, the vent valve should be opened and the pressure in the furnace will be balanced. Then close the bleed valve and start the mechanical pump to open the valves and open the locking ring. There are two kinds of oil returning: (1) oil returning before high temperature, according to the amount of oil returning, the convex table after the product is less than usual, the appearance color is the same as the normal product, but the product will be scrapped when the static pressure is about 5p. So the operator pays special attention. (2) Low temperature oil return, refers to the oil return in the strong cold or out of the furnace, the product surface has black spots, can be wiped with green sand belt, but the inherent quality of the product remains unchanged.

Three. Quenching of product materials

1 phenomena and causes

When the product is quenched and cracked, under the condition of strong cooling, the process card stipulates that 304 material is below 930 degrees. 403 materials below 850 degrees. When the temperature of the strong cooling is higher than that of the process card, the surface of the product can be quenched or cracked without obvious difference, and the whole furnace has been scrapped.

2 solutions

Employees should operate strictly according to regulations when they operate normally. Especially the strong cooling switch, at the end of high temperature insulation, nitrogen automatically flushing, fan automatically start rapid strong cooling, resulting in the whole furnace product scrap. Another situation is that we are more tired in the second half of the night operation, it is easy to see the wrong furnace temperature, misoperation caused by the whole furnace scrap.

Four, knock and scrap

1 phenomena and causes

Collision scrap refers to the operation of the product after clamping or discharging when it encounters other items resulting in product scrap called Collision scrap.

2 solutions

We can't touch other objects while we are running. Check whether the clamping is bumped before entering the furnace. Put into the furnace to be serious, pay attention to light. When the product is released, the product can not touch the mold. When the product is oiled, it must be placed in balance when it is turned over. The bottom plate can not touch the vacuum furnace parts when it is turned into oil after being turned on.

Five, parts shift scrap

1 phenomena and causes

The displacement of parts of vacuum furnace products refers to the brazing worker pushing the clamped products to the designated furnace inlet area by trolley and putting them on the furnace inlet vehicle after clamping. Improper force in the process of pushing furnace or other objects, so that a part of the product displacement, not found brazing out of the furnace after the product scrap called product displacement scrap.

2 solutions

We should pay special attention to the whole process, so that we can solve the problem in a slow light way.

Six, product injury and scrap

1 phenomena and causes

In the process of clamping, when used on the plate, because of poor quality in the clamping, high temperature brazing ceramics after compression form very few blocks. Dip in the base plate or film during the oiling process. When stack is running.

2 solutions

People pay attention or correct ceramic or correction process without ceramic chips.

Seven, claw claw scrap

1 phenomena and causes

It refers to the clamping ring loose in the brazing process to meet the product sheet or flange, resulting in product scrap, called claw scrap.

2 solutions

In addition, the clamping ring position and method should be considered in the design.

Eight, product perpendicularity scrap

1 phenomenon

In high temperature brazing, the product inclines in different directions, resulting in the scrapping of the product and the scrapping of the product perpendicularity.

2 main reasons for scrapping

1, the furnace support fracture, so that the 8 beams are not level.  2, when the furnace is placed, the stove orchid and the grate are not straight.  3, the mainstay of the furnace orchid is uneven due to the deformation of the stainless steel.  4. The thickness of the welding die is not uniform.  5, the placement structure is unreasonable.  6, the deformation of the furnace strip is large.

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