Quantification of Swelling in Sealing Materials

Abstract

The objective of this study was to quantify swelling in gasket materials to better predict the gaskets life span in heat exchangers. Alfa Laval produces plate heat exchangers, which are a common unit within the process industry. There are different types of plate heat exchangers, and one type is sealed with gaskets. Two common types of rubber used as gasket materials are EPDM and NBR which are studied in this report. A problem that can occur in gasketed plate heat exchangers is that the gasket swell, due to a lack of resistance from the selected gasket material toward the medium. The swelling increase can cause the gaskets to be nonreusable after opening and cleaning the heat exchanger, as it no longer fits. It can also result in failures with leakages.
Both types of rubber were swelled in 1-octanol and 1-decanol. Additionally, EPDM was also swelled in pentadecane and oleic acid, NBR was also swelled in triethyl citrate. The swelling was examined in two different tests, free swelling, and rubber strands. In the free swelling test, small pieces of rubber were completely immersed in a solvent. The rubber strands had only one end of the strand immersed in a solvent. This allowed solvent to diffuse up through the strand.
From the free swelling test, it was shown that most combinations displayed Fickian diffusion, with some deviations. A linear relationship was found between the diffusivity, temperature, and solvents. Similarly, a linear relationship was also found for the equilibrium swelling level, temperature, and solvent. The diffusion up through rubber strands proved to be slow. Therefore, it was examined whether it was possible to find a relationship between the diffusion distance in the rubber strands and the diffusion constant calculated from free swelling.

Popular Abstract

Rubber bands, bouncing balls, erasers and car tires are some examples of things that you probably have encountered at some point in everyday life that are made of rubber. There is no denying that rubber is of great importance to how we live today, involving everything from the objects we encounter in our everyday life to seals in the process industry. Rubber can absorb liquids and increase in size without dissolving. This phenomenon is called swelling. Swelling is a crucial part of determining the durability and suitability of the rubber in different types of applications. Therefore, the goal of this project was to better understand and predict swelling in rubber.
Rubbers have unique properties that make e.g. a bouncing ball bounces back to you. Other applications that the rubber's unique properties are suitable for are e.g. sealing materials. Common sealing applications are important for underground tunnels, doors, windows, heat exchangers, and many more. Rubber works well as a seal as it can regain its shape after it has been deformed. An example of this is that a rubber band snaps back after you have pulled it out and released it. As mentioned, another unique property is that rubber can absorb solvents without dissolving. When rubber absorbs solvents, the size increases. This is called swelling. Swelling can be both positive and negative depending on the application. In underground tunnels, it is desirable for the gaskets to swell. However, in heat exchangers, swelling is not desired since it can cause failures
Alfa Laval is at the forefront of manufacturing heat exchangers. The field of application for a heat exchanger is large, everything from the food industry to the oil industry. A heat exchanger is used to transfer energy in the form of heat between two liquids without mixing the liquids. In a plate heat exchanger, plates are tightly packed next to each other. The heat transfer then takes place between the plates.
Seals are used to keep the liquids apart and to prevent the heat exchanger from leaking. The seals usually consist of rubber. If the rubber seal swells it can cause problems in a heat exchanger. One of these problems is that gasket becoming too large to fit in the heat exchanger, which can lead to leakage and the gasket needing to be replaced. Therefore, it is of great importance to be able to predict how much and quickly a gasket swells.
This project aimed to create mathematical models that can help Alfa Laval predict not only whether rubber will swell and how much in a given solvent, but also at what temperatures, and how fast. The results of this project show that it is possible to find mathematical models that predict swelling. An approach has also been presented to be able to develop similar models for other combinations of rubber and solvents than those that have been tested in our project. Alfa Laval may use these models in the future to e.g. to find how different rubbers will be affected by a temperature change and how long it will take for rubber to swell in a certain solvent.
In addition to this, other unexpected and interesting results were obtained. For example, the maximum swelling does not always increase with temperature (it is normal for swelling to increase with increasing temperature), which probably depends on the type of interactions between the rubber and the swelling liquid.

• author: Möller, Johanna and Erlandsson, Paula
• supervisor: Baozhong Zhang; Henrik Kockum; Rasmus Arvidsson
• organization: Centre for Analysis and Synthesis
• alternative title: Investigation of models quantifying swelling of rubbers
• course: KASM15 20211
• year: 2021
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: elastomer, rubber, gaskets, NBR, EPDM, swelling, diffusion coefficient, polymer technology
• language: English
• id: 9058382
• date added to LUP: 2021-06-29 15:03:19
• date last changed: 2021-06-29 15:03:19