Vacuum-type glass-plastic—Metal transition elements for operation in the temperature range 77-4.2 K

Abstract

In cryogenic technology, structural members with low thermal conductivity are produced from pipes made from laminated plastics. These elements include the necks of vessels and containers for storage of cryogenic liquids.The main requirements imposed on the neck (loading-carrying elements) are high strength, low thermal conductivity and gas permeability, and also leak tightness at working temperatures of the elements and sections of their joints with the metal.The literature contains the results of a relatively large number of investigations concerned with the strength and thermal characteristics of composite materials. Therefore, it is not difficult to determine the thermal conductivity coefficient of the glassplastic. However, it is difficult to produce leak-tight glass-plastic pipes from composite materials and sections of their joints with the metal for equipment operating in the temperature range 77-4.2 K because according to the conclusions of a number of authors the adhesion bond between glass fibers and the binder is disrupted at temperatures below 20 K.In this article, the results are presented of the tests of the strength and leak-tightness of glass-plastic necks with metallic tips of AMTs alloy and 12Klil8N10T steel. Tests were carried out at temperatures of 295, 77, and 4.2 K.The technology developed at the Stekloplastik Scientific and Production Association was used to produced necks using winding and pressing processes of shaping glass plastics. The main procedure was the method of the so-called "dry n filament winding the prepreg on the basis of the equal strength glass filament with the cloth weaving with a thickness of 0.1 mm made of alkali-free alumoborosilicate glass and a modified 4,4'-isopropylidenedipbenol oligomer. The filler content of the glass plastic was 0.55-0.6, with the porosity of the composite lower than 1.5%. The described technology of producing the shells of the necks was used in developing nonmetallic cryostats for liquid helium with a capacity of 1.2 liters [1].The methods of joining glass plastic necks with the metallic tips are based on depositing BEN-50 adhesive on the end grooves of the glass plastic followed by combined cold deformation of the joint component at the selected value of deformation of the aluminum component, and also on constraining the glass plastic between the aluminum and steel components of the transition section by cold-welding dissimilar materials [2][3][4]. The BEN-50 adhesive is 61~18N-60-1 block polymer, modified with polyvinyl butyl (PVB) of PSh grade [5].The produced batch of glass-plastic necks with an internal diameter of 60 mm and a wall thickness of 1-2 mm with 2-3 mm aluminum (AMTs) and steel (12Kh18NIOT) tips was tested for leak tightness using a helium leak tester. Vacuum density was not less than 1.3-10 -t3 m3"Pa after 500 test cycles with a pneumatic pressure from 0 to 1.1 MPa, and also after 200 cycles of the effect of thermal impacts with a sharp temperature change (295 ---77 --395 K).Some of the verified necks were tested by tensile loa...