3. Gasket material and performance evaluation. The weakest link of PHE is the gasket. Over the years, it has been the focus of public attention and exploration, and some progress has been made in temperature resistance and corrosion resistance materials and their performance evaluation.
(1) Nitrile rubber (NBR) is generally suitable for working conditions below 120 ℃.The newly developed high-temperature NBR can reach 145 ℃, and the hydrogenated NBR can reach 160 ℃; EPDM used only 150 ℃, the high temperature EPDM has increased to 160 ℃; Fluoro-propylene rubber (FPM) can be used at 175 ℃; the applicable temperature of graphite laminated gasket can reach 400 ℃, which can well replace compressed asbestos fiber gasket.
(2) Coated gaskets use general rubber or metal blocks as the core, and are wrapped with polytetrafluoroethylene (PTFE) or fluorinated synthetic materials, etc., which can be used for highly corrosive media or increase the temperature limit. HISAKA is the first to use PTFE-coated NBR gaskets, which greatly expands the application fields of PHE than in the past, and the gaskets have a longer service life. ALFA-LAVAL has used this gasket for double-plate welding PHE.
(3) With the development of non-adhesive sealing gaskets, the formulation of materials for non-adhesive sealing gaskets must be slightly changed, requiring more stable performance, more durability and better tear resistance.
(4) To evaluate the temperature resistance of gaskets, there are two main indicators: compression set and hardness at rated temperature. For new gasket materials, generally the ring sample test and the overall test of the plate and the gasket are required, and the test time is 5-40 days. The recommended use temperature limit of gaskets should be lower than the compression set curve after considering a certain safety factor.
The quality and service life of the plate heat exchanger largely depend on the quality and service life of the gasket. For many heat exchangers, the plates are generally not damaged, and the gasket is prone to aging and cause leakage. Therefore, the quality of the gasket determines the quality and service life of the heat exchanger.