CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent Application No. PCT/CN2020/119392 with a filing date of Sep. 30, 2020, designating the United States, now pending, and further claims priority to Chinese Patent Application No. 202010510277.4 with a filing date of Jun. 8, 2020. The content of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure belongs to the technical field of high-temperature thermal structures, and particularly relates to a method for sealing a high-temperature heat pipe.

BACKGROUND

Heat pipes can be divided into the low-temperature heat pipes (operating at −270° C. to 0° C.), the normal-temperature heat pipes (operating at 200° C. to 600° C.) and the high-temperature heat pipes (operating at 600° C. or above) according to their use temperatures. Since the high-temperature heat pipes operate at extremely high temperatures, a passive heat transfer mode is applied extensively in the fields of aerospace, nuclear electric power generation and military industry. With liquid metal or molten salt as a working medium, the high-temperature heat pipes have good thermal stability and low saturated vapor pressure at high temperatures. The high-temperature heat pipes are made of stainless steel, high-temperature alloys or refractory metal.

When the high-temperature heat pipes made of refractory alloys are sealed, tube bodies and end caps are combined, and valves need to be added at the end caps for subsequent pouring and vacuum degassing, which is complicated. Part of the refractory metal has high hardness and high brittleness, and thus is difficult to machine. In addition, it is difficult and costly to manufacture valves with end caps, thereby limiting the manufacturing efficiency of the high-temperature heat pipes.

SUMMARY

The technical problem to be solved by the present disclosure is to overcome the defect of a complicated process for manufacturing a high-temperature heat pipe in the prior art. The present disclosure provides a method for sealing a high-temperature heat pipe, which may reduce cost and improve manufacturing efficiency.

In order to solve the above technical problem, the present disclosure employs the technical solution: the method for sealing a high-temperature heat pipe includes:

(1) necking and reducing two ends of the heat pipe separately, so as to obtain a necked end and a reduced end;

(2) sealing the necked end by laser welding or electron beam welding;

(3) placing the heat pipe in an inert gas glove box, and pouring a working medium without impurities into the heat pipe;

(4) heating the heat pipe, connecting the reduced end to a vacuum pump, pumping gas inside the heat pipe by the vacuum pump to vacuumize the heat pipe, such that pressure in an inner cavity of the heat pipe reaches a target pressure, and flattening the reduced end; and

(5) sealing an opening of the flattened reduced end by electron beam welding or laser welding, so as to obtain the high-temperature heat pipe.

Preferably, step (1) of reducing one end of the heat pipe includes:

(1-1-1) fixing the heat pipe to a fixture of a lathe, and mounting a spinning reducing die in the lathe; and

(1-1-2) driving the spinning reducing die to rotate, and simultaneously driving the heat pipe to move toward the die axially so as to insert the heat pipe into the spinning reducing die, so as to reduce one end of the heat pipe.

Preferably, the spinning reducing die includes a retainer and a plurality of steel balls, where the steel balls are fixed in the retainer, so as to form a reducing hole.

Preferably, step (1) of necking the other end of the heat pipe includes:

(1-2-1) fixing the heat pipe to a fixture of a lathe, and mounting a spinning necking die in a lathe chuck; and

(1-2-2) driving the spinning necking die to rotate, and simultaneously driving the heat pipe to move toward the die axially so as to insert the heat pipe into the spinning necking die, so as to neck the other end of the heat pipe.

Preferably, the spinning necking die in step (1) includes an upper pressing die and a lower pressing die, where a first groove is provided in one side of the upper pressing die, a second groove is provided in one side of the lower pressing die, the upper pressing die and the lower pressing die are spliced, and the first groove and the second groove are spliced to form a necking groove.

Preferably, in step (4), after vacuumizing, the pressure of the inner cavity of the heat pipe is lower than 1×10−3Pa.

Preferably, in step (1), after reducing, an outer diameter of the heat pipe is 6-8 mm.

Preferably, the method further includes: cleaning to remove surface oxide skin and lubricating oil of the heat pipe subjected to necking and reducing between step (1) and step (2).

Preferably, in step (3), a water content and an oxygen content of the inert gas glove box are both lower than 0.5 ppm.

Preferably, after step (5), the method further includes: placing the high-temperature heat pipe in a pressure maintaining container with high-pressure helium for at least 2 hours, then vacuumizing the pressure maintaining container, and checking the quantity of the helium left in the pressure maintaining container, where when partial pressure of the helium in the pressure maintaining container is less than 1×10−3Pa, the high-temperature heat pipe is qualified.

The present invention has the beneficial effects:

1. by necking and reducing the two ends of the heat pipe separately, and sealing the necked end of the heat pipe by laser welding or electron beam welding, the working procedures for manufacturing the high-temperature heat pipe are simplified and the cost is reduced; and

2. by flattening the reduced end of the vacuumized heat pipe, the opening is rapidly and temporarily sealed; and by sealing the opening of the flattened reduced end by electron beam welding or laser welding, non-condensable gas in the high-temperature heat pipe is effectively reduced, and the working medium is prevented from being oxidized, so as to obtain the high-temperature heat pipe with good gas tightness.

