Innovative Plunger Lubricants to Reduce Operational Costs and Increase Efficiency

In high-pressure die-casting the molten metal is injected into the die cavity through a cylindrical sleeve by a piston (or plunger) that forces the molten metal through a narrow orifice at high speed and pressure. Proper lubrication of the plunger is essential to provide smooth filling of the cavity, reduce energy consumption during the shot and extend the life of the plunger tip and sleeve.

Plunger lubricants are used to minimize the wear to the plunger tip, thus increasing its lifetime and reducing the downtime for replacement. They also help provide a seal around the tip to prevent molten metal from leaking past the tip and causing mechanical problems in advancing and retracting the plunger. The temperatures inside the shot sleeve are typically about 100 degrees C (210°F) less than those in the die. Chem-Trend makes a wide range of products to protect the shot-end components and assist in the production of high quality castings, while minimizing any adverse environmental effects.

Porosity is one of the biggest problems in die casting. The die casting process is very often used to make lightweight components out of light metals to replace steel or iron parts. Since the intrinsic strength of these lighter metals is less than that of steel, anything that can adversely affect the strength of the component is undesirable. The presence of small pores within the cross section of the casting can have a big impact on the tensile strength. Gas porosity is a consequence of the very high velocities at which the metal is injected into the mold. However, it can also be aggravated by the presence of water on the die and the decomposition of any organic compounds within the die and the shot sleeve. Since plunger lubricants tend to contain water, organics or both, they can contribute to this problem. Chem-Trend’s well-designed efficient products facilitate accurate dosing into the sleeve and produce small amounts of decomposition products, thus having a negligible effect on the porosity in the casting.

Pellet plunger lube porosity defects Oil-based plunger lube porosity defects Water-based plunger lube porosity defects
Pellet plunger lube Oil-based plunger lube Water-based plunger lube

The presence of dark or discolored areas on the surface of the castings can invariably be traced to the application of plunger lubricants. In most cases either too much lubricant or the wrong kind of lubricant has been applied.

Over application of plunger lubricants example "A"Over application of plunger lubricants example "B"
Over application of plunger lubricants

While this can be due to a lack of care or variation between operators, it may be symptomatic of deeper problems. Using too much plunger lubricant is usually a sign that the plunger life is being stretched or there is some misalignment. Chem-Trend’s high efficiency and high performance products allow the correct amount of lubricant to be applied consistently.

High-efficiency plunger lubricant
High-efficiency plunger lubricant

Chem-Trend products are available in a variety of forms for convenience. Solid plunger lubes are most frequently supplied as small pellets that are introduced by an automated device through the pour hole into the shot sleeve. The carrier is designed to melt and then assist in the distribution of additives over the surface of the tip and shot sleeve.

Oil-borne plunger lubricants are similar in function but, as they are liquids, they may be applied with or without atomization to enhance surface coverage. Chem-Trend is a world leader in clean engineered products that can provide exceptional wear performance even in large plunger systems. Our high efficiency products typically can be used at about half the feed rates of conventional plunger lubricants.

Graphite is a key functional material in many plunger lubricants. It can be supplied in a variety of carriers including oil, water and waxes. The carrier serves not only as a lubricant itself, but also to help distribute the additives over the surface of the shot sleeve, and, depending on the method of application, to hold the additives in place once applied. Chem-Trend technology has focused on liquid graphite formulations that provide extremely stable suspensions and slurries that improve the accuracy of feeding, and reduce waste in the plant.

Stability comparison of filled plunger lubes
Notice the uniform stability of the graphite lubricant in the carrier for the Chem-Trend product (right) as compared to a competitor (left).

A common concern in the shot-end of the die-casting machine is the formation of smoke and flames when molten metal is added into the shot sleeve. The heat of the melt can cause the organics in the lubricant to catch fire and, as this is a low oxygen environment, the incomplete combustion results in the formation of smoke. Chem-Trend has addressed this through water-based lubricants and special formulations that reduce the smoke and flammability of oil-based materials.

Smoke comparison test of plunger lubes
While heating Chem-Trend lubricants to production temperatures alongside the competitors (left), you will notice the lower smoke formation by the Chem-Trend product (right).

 

Flammability comparison of "filled" and "unfilled" plunger lubricants
Flammability comparison of "filled" and "unfilled" plunger lubricants

We are continually innovating new plunger lubricant technologies to support the die cast industry. Why not contact us to see how our knowledge, experience and products can help improve your operation’s bottom line?

Want to find out what Chem-Trend can do to help you? Contact us and give us a chance to improve your molding, casting and forming operations.

Resources

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