When we talk about dilution water in the metallurgical process of high pressure die casting, we are referring to the water used for the formation of water based release agents at the stage of demolding.
Demolding is a key step for obtaining the casting. To carry out properly and with maximum efficiency, it is necessary to make an accurate mold design and choose the right mold release agent.
There are different types of release agents, among which we can mention water-based, oil-based, powder-based or pastes. Each has a determined functionality or application, a working temperature range, and is used for a particular type of piece, alloy, finish, or final use.
Dilution water is the major component of water-based release agents (CASTFLOW), so it is a very important resource, as we will discuss in the following points.
Water-based release agents
Water-based release agents are an emulsion of a set of raw materials with specific compositions, proportions and lubricating nature (which are the active components) in water. The homogeneous mixture of the two phases, which are immiscible in nature, is achieved through the addition of an emulsifying agent and vigorous stirring with temperature control. The final result is an emulsion in which the oil forms the dispersed phase and the water, the continuous phase.
Although the active component of the release agent is the lubricant, the importance of water in this preparation phase of the release agent is crucial because it is the major component, in a proportion that can exceed 99%.
Release agents are deposited on the mold, which receives molten metal covering the whole surface. This deposition is usually done by means of a spraying technique that achieves the formation of very small droplets to cover the entire surface. When the emulsion is in contact with the hot walls of the mold, the water instantly evaporates and a homogeneous lubricant film is formed over the mold, which will facilitate the demolding of the casting.
It is in this process of water contact with the mold and of subsequent evaporation, where we can clearly see the importance of the quality of dilution water, but also in the previous application phase of the dilution over the mold.
The dilution process of the release agent and quality of the dilution water
During the dilution process of the release agent, we must ensure the percentage of dilution by using the appropriate equipment and above all, ensure that the water quality is correct.
To avoid the negative consequences that could result from the use of poor quality water, we need to control the following parameters:
- Conductivity: The electrical conductivity is the capability of an object or product to let electric current pass through it. A value of conductivity less than 400μS / cm is recommended to avoid corrosion in molds and production machinery.
- Hardness: The hardness measures the concentration of mineral salts, particularly calcium and magnesium. A value lower than 125 ppm for the concentration of calcium carbonate is recommended to avoid either possible build up problems in the molds or possible clogging problems with nozzles / pipes.
- Chlorides: Chlorides measure the concentration of chloride anion in a solution. It is recommended to be less than 100 ppm to avoid corrosion problems in molds and production machinery.
- Bacterial Contamination: Bacterial contamination is measured with a bacterial test, and the results must be negative.
When we have dilution water within the previously indicated conditions, we will be working under optimal conditions and ensure the long-term stability of production.
Consequences of the use of a dilution water of poor quality
In the event that the dilution water that we use does not meet the required quality requirements, depending on how far away it is from the above parameters, there is risk of encountering the following problems:
Appearance of residues in the mold, clogging of filters and nozzles which deposit the diluted product, separation of the components of the emulsion, appearance of corrosion problems in molds or machinery, manifestation of bacterial contamination in the dilution tanks.
Of course, our products are formulated to minimize the problems caused by the use of water outside the above specifications, but the farther the actual values are from the recommended values, the more at risk we will be of having any of the problems cited.
We recommend paying special attention to control water hardness, in order to avoid the formation of hard deposits on the mold (build up) and the obstruction of filters, valves, and water pipes. Certainly, this is not the only parameter, but it is one that has most relevance.
On the other hand, it is essential to maintain clean conditions of the dilution tank to reduce the problems derived from bacterial contamination. When the diluted product is dirty, it can cause all sorts of problems with deposits of a different nature, foam formation, or saturation of filters and / or nozzles because of the presence of biofilms; these factors can very negatively affect the release process. For this reason, it is highly recommended to ensure the use of water free of bacteria and to perform regular bacterial analyses to verify the absence of bacteria in the dilution water.
The composition of water-based release agents
Once it is clear which problems can be caused by improper use of dilution water, it is essential to focus on the role of the formulation of the release agent in minimizing these negative effects.
The difference between some release agents and others is the composition of the active component. The most advanced manufacturers are able to design release agents that adapt to the special needs of each process and the users’ requirements.
From the standpoint of dilution water, additives that are included in the active part of the release agent are of particular relevance as previously mentioned. Among them can be included corrosion inhibitors, defoamers, preservatives, and biocides. With this, a custom formulation of the release agent can totally or partially correct the consequences of using dilution water that was not of adequate quality.
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