Improvement of key parts of regenerative refrigerator

Due to its unique structure, many parts, and complicated process, the heat recovery refrigerator is only produced by the standard product factory of Hangyang Technology Co., Ltd. in China. However, due to the fast start-up of the equipment (5-7 minutes for liquid discharge), easy operation and high degree of automation, the products are sold all over the country and exported to foreign countries. It has won unanimous praise from users at home and abroad and has become the flagship product of the factory.

There have been thousands of users of regenerative refrigerators, and the product quality has been in a stable state. Some users reported that the cooling capacity of the refrigerator has been significantly reduced after a certain period of operation of the refrigerator. We have made special research in this situation.

1 working principle

The regenerative refrigerator consists of an expansion piston (named extruder in the factory) and a compression piston (named as the main piston in the factory). The working medium (helium or hydrogen) is compressed in the compression chamber and cooled by water. After the heat is released, the cooler and the cold accumulator reach the expansion chamber, where they are expanded by the downward movement of the expansion piston, and the cold is transferred to the outside medium that needs cooling through the condenser. see picture 1. Improvement of key parts of regenerative refrigerator 2 Reason analysis

There are three main reasons for the decline in cooling capacity:

(1) The cold storage device is contaminated.

(2) The heat exchange effect of the water cooler is poor or the inlet water temperature is high, and the water volume

(3) There is leakage between the compression cavity and the expansion cavity.

Pollution of the cold accumulator is mainly caused by the accumulation of water or oil in the working fluid in the cold accumulator, which can be cleaned and dried with petroleum ether and then reloaded; the water cooler is of tubular type, and the fouling between the tubes causes poor heat exchange effect. Dilute hydrochloric acid can be used Clean and remove dirt, or lower the inlet water temperature and increase the cooling water volume. Here we mainly analyze the third situation.

It can be seen from the structure of the refrigerator that the expansion piston acts as a channel to isolate the expansion cavity and the compression cavity, that is, to isolate the channel between the cold cavity (about -200°C) and the hot cavity (about 130°C), and its tightness is aligned. The cooling efficiency of the machine plays a vital role.

The expansion piston adopts a thin-walled stainless steel structure. The lower part is equipped with a piston ring, an elastic ring, and a guide ring, which are matched with the cylinder liner of the water cooler. The guide ring plays a guiding role, and the piston ring and the elastic ring cooperate to act as a seal.

The guide ring is composed of a guide ring body (material is H62) and a guide ring (material is nylon 1010), and the outer circle is φ70g6 (-0.01, -0.029) mm as a whole and then milled; the piston ring is made of nylon 1010 The cylinder liner is made of ductile iron (QT600-3), with an inner diameter of 70H7 (+0.03, 0) mm, with a wall thickness of 1mm and an outer diameter of φ70mm. After roughing, it is normalized and the hardness is HB 229~302.

In use, because the working medium contains impurities such as moisture, the mirror surface of the cylinder liner is corroded during parking, and the mirror surface of the cylinder liner is roughened during operation, resulting in axial scratches on the surfaces of the piston ring and the guide ring, and the surfaces of the piston ring and the guide ring are scratched. The marks further aggravate the abrasion of the mirror surface of the cylinder liner, causing the expansion cavity and the compression cavity to not be completely sealed, reducing the working efficiency of the refrigerator.

3 Test situation

As the cylinder liner is prone to rust, we considered replacing the material of the cylinder liner with a stainless steel material. After the test, it was found that the cylinder liner had a better mirror surface, while the guide ring and piston ring were severely worn, indicating that stainless steel and nylon are not suitable for sealing. Later, the factory manufactured stainless steel cylinder liners, and the guide ring and piston ring were made of self-lubricating PTFE material. The matching size remained unchanged, and the spring ring was not changed. The above parts were installed on the factory’s four-cylinder refrigerator. Two cylinders are made of new parts, and the other two cylinders are installed with original parts for comparison test.

The trial started in 1999 and the situation is as follows:

(1) After the two parts of different materials were made according to the tolerance requirements of the drawings, they were installed on May 19, 1999 and the test started. The four-cylinder refrigerator was equipped with the KL-15 military product's fractionation tower. , It is equipped with an average of two test runs per month, and usually drives alone to prepare liquid when it is needed. By the time the car was dismantled on March 28, 2001, the cumulative driving time was over 800 hours. Before the equipment is installed with new parts, it is necessary to arrange a second overhaul and replacement of parts every year due to the obvious decline in output. The refrigeration capacity of the refrigerator has been normal after the installation of the new parts until the car is dismantled, indicating that the effect of the whole machine after the replacement of the parts has been greatly improved.

(2) After dismantling the vehicle, inspect and measure the piston ring, guide ring and cylinder liner respectively. Observe the wear of the piston ring and guide ring of the new and old materials with naked eyes. There is no obvious difference in the wear of the piston ring and the guide ring. The tolerances are shown in Table 1.

Table 1 Test data of two materials after dismantling Improvement of key parts of regenerative refrigerator

material

Numbering

Piston ring

Guide ring

new material

1

-0.07

-0.09

-0.09

-0.12

2

-0.07

-0.07

-0.12

-0.14

Raw materials

1

-0.01

-0.03

-0.11

-0.07

2

-0.04

-0.10

-0.14

-0.14

From the above data, we can judge that the wear of the new piston ring is relatively uniform,


while the unilateral wear of the old piston ring is serious; the parts of the new guide ring are relatively uniform, while the size of the old guide ring is quite different.

The wear of the cylinder liner is small and can be ignored. However, the use of stainless steel has better wear resistance and corrosion resistance, thus prolonging the service life.

(3) Process comparison: The nylon piston ring needs to cooperate with the spring ring to achieve the sealing effect. However, due to the thin wall thickness and special material of the nylon piston ring, the parts processing must be completed by personnel with rich operating experience. Because the guide ring is a composite material, the process is complicated, and the nylon part is easily separated from the guide ring body. The ductile cast iron cylinder liner is made into blanks by centrifugal casting, and the metallographic structure of the heat treatment often fails to meet the requirements during processing and a large number of scraps are scrapped. With the improved parts, the piston ring material is changed to polytetrafluoroethylene, the size remains unchanged, and the processing difficulty does not increase. The guide ring adopts an integral structure and is directly machined, which greatly simplifies the processing procedure. The cylinder liner is processed with raw materials, and the material has no special requirements, which can guarantee the product quality.

Through the comparison of the above situation, the use of improved parts reduces the processing difficulty of the parts, improves the cooling efficiency of the machine, and prolongs the service life of the equipment.