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It’s impossible to do effective die casting without proper lubricants. What are the proper lubricants for die casting and what are the different die casting lubricant benefits to consider? Here is some basic information to get you started.
Lubricants and the Die Casting Process
Once you’ve poured the liquid metal into the mold and it has hardened, you need a way to remove the completed part from the die safely and without damaging the part. The release agent we use to make this happen is called die spray or die lubricant. Before each shot, we apply the die spray or lubricant to ease the part removal from the mold. It’s important to use a precise amount of die lubricant — not enough, and the part may stick, leading to defects and shutting down production. Too much, and you may end up with die lubricant that fails to evaporate, leading to porosity inside the casting and poor surface finish of the part.
Die lubricant is not the only type of lubricant involved in the die casting process, however. There are two major types of lubricants to consider when it comes to die casting: die lubricants and plunger lubricants.
How Die Lubricants Work
Die lubricants are lubricants designed to increase film formation and wetting on the mold surface at the very high temperatures produced during the die casting process. These lubricants serve as die casting release agents, which benefit the system by producing clean, bright castings with less gas generation and a lower likelihood of corrosion or pitting of the mold surface.
Quality die lubricants also allow for a hotter die surface, making the finished part more paintable and better protected against soldering of the die steel which creates poor surface conditions on the cast part. Some of the other major problems the right lubricant can help resolve include:
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Porosity: Porosity means gas bubbles can become trapped in the metal and produce holes in your part. One of the contributors to porosity is improper air venting and excess die lubricant left on the mold surface prior to metal injection. It’s important to choose a lubricant that minimizes overspray so lubricant does not clog up the vents. There are many different lubricants available and some have better properties than others regarding amount of spray required for the part in question.
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In-Cavity Buildup: In-cavity buildup, or carbon, is a dark, extraneous material that can build up in the die cavity. A soft-water based lubricant can reduce the opportunity for unwanted matter to build up within the die cavity.
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Fish Eye: Fish Eye describes a scenario where tiny little holes appear clustered on the surface of your part when painting. The right lubricant cleans off the surface of the part before painting so you get good adhesion without deformities.
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Cold Shut: Cold shut is a phenomenon where dark lines appear on the surface of the casting, especially with magnesium alloys. This occurs when the casting starts to solidify before the molding completely fills. A good lubricant can create more even heat transfer and circumvent this type of problem.
How Plunger Lubricants Work
Plunger lubricants are used to keep the injection plunger and the shot sleeve of the die casting system running smoothly. Good plunger lubricants can improve metal castability, limit porosity, improve injection and lengthen the lifetime of the plungers and sleeves. Plunger lubricants can be wet or dry. Oil-based lubricants are popular choices for plunger lubrication and can be made from mineral oil, vegetable oil or synthetic oils. They can include graphite and are very effective for greasing pistons.
However, many metal casting companies are concerned about environmentally friendly methods of manufacturing, and wet lubricants can eventually end up diluting local waterways. Some die casting companies are moving toward dry lubricants instead. These are clean, user-friendly beads which may or may not include graphite and which can come in different sizes depending upon the plunger tips they need to lubricate.
Dry bead lubricants are an effective way to lubricate plunger tips without endangering the water supply to the extent that oil-based lubricants do.
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