Cracks after flame cleaning

Crack Formation after Thermal Cleaning

Introduction

Heat cleaning is a process in which, thermal energy is used to clean components or substrates. Thermal cleaners use a combination of high temperature, oxygen, and pressure. The process is useful for removing oil, grease, flux, and other contaminants usually found in manufacturing and industrial processes. Despite its usefulness and non-invasive nature, thermal cleaning can produce fractures and cracks in certain substrates, components, and materials. This paper will examine the crack formation after thermal cleaning.

Process of Heat Cleaning

Thermal cleaning is a process in which temperatures in excess of 800⁰C (1472F) are used to remove organic material from components without any direct contact. This process is often used as an alternative to chemical cleaning in cases when the substrate is not able to withstand the harsh chemicals used in chemical cleaning processes.

The process often involves the use of industrial ovens, heated in a recirculating air flow environment. Recirculation reduces the amount of air released, preventing the release of dangerous volatile organic compounds. Heat is usually applied to the substrate while recirculating oxygen to burn off the contaminants. Pressurized oxygen or oxygen enriched air is typically used to increase temperatures, reduce process time, and dissolve organic oils and grease. The components are exposed to the thermal energy and oxidization process until the unwanted organic material has been removed. This is usually followed by a cooling cycle to return the components to their original temperatures. The entire process usually takes 15 minutes to an hour.

Causes of Crack Formation

After heat cleaning, it is possible for cracks or fractures to form in certain components and substrates. This is due to the rapid thermal cycling, rapid heating and cooling, and sudden temperature changes. When a substrate is rapidly heated and cooled, it undergoes thermal stresses. These thermal stresses can cause the substrate to expand and contract, leading to cracking.

In addition, when high temperatures are used and the substrate is exposed to oxygen, oxidation can occur. Oxidation involves the release of electrons by burning off contaminants. As the substrate is cooled, this new layer of oxidized material can also cause cracking. This type of crack is referred to as thermal fatigue.

Other Causes of Cracking

Other than thermal cycling and oxidation, cracks can form in substrates due to a variety of other causes. These include corrosion, contamination, and the material properties of the substrate itself. For example, if the substrate is unstable at high temperatures or is prone to warping, it can cause cracks to form as the substrate cools. Similarly, if the substrate is contaminated with oils and greases, it can also provide stress points, leading to cracking. Lastly, if the substrate is exposed to too much oxygen during the thermal cleaning process, it can cause oxidation, which can also lead to cracking.

Conclusion

Cracking is a common issue caused by thermal cleaning. This is due to the rapid heating and cooling process, as well as exposure to oxygen, which can cause oxidation of the substrate. In addition, other causes such as corrosion, contamination, and material properties can also lead to cracking. It is important to be aware of these potential causes in order to prevent cracking during thermal cleaning processes.

Cracks often form after a flame cleaning process. Flame cleaning is a process used to remove material such as oxide layers on metal surfaces. It is an effective method of metal preparation and the flame itself actually has no direct effect on the underlying surface of the metal. However, cracks have been known to form due to the highly localized heating caused by the flame. As the metal expands and contracts during the process, it strains the metal which can ultimately cause cracks to form.

The severity of the cracking is often proportional to the size of the affected area. Areas that are subjected to higher temperatures due to the flame will also be more likely to crack. If the metal is heated too rapidly, thermal shock can occur which can cause larger and deeper cracks that might not have occurred if the heating process was slower. Extremely large areas can sometimes crack even without the application of heat.

Inherent issues with the metal due to a manufacturing defect can also cause cracking. These defects could be anything from air bubbles in the metal existing prior to flame cleaning, or impurities. The metal might also be too brittle to be subjected to the heat of flame cleaning and will inevitably crack because of it.

The best way to avoid cracks while flame cleaning is to select the proper size of tip and flame intensity to prevent large areas from being subjected to too much heat. Operators should also use moderate flame speeds to reduce thermal shock and should perform pre-heating and post-cooling where applicable. It is also important to perform regular maintenance on the equipment to ensure that all components are in good working order. Lastly, using a metal that is of high quality and low porosity can minimize stress concentrations, minimize distortions and maximize the chances of success.