Die Casting Machine Plunger Tip
The quality and life of the plunger tip directly affect the efficiency and cost of die-casting production. How to improve the life of the plunger tip and the precise fit tolerance is of great significance for reducing the cost of die-casting production and saving resources.
1. Plunger Tip Life of Different Materials
Different materials have different plunger tip lives. So let’s have a rundown.
- Ductile iron plunger tip, the general life is about 1000 times, the price is low, and it is widely used.
- Ceramic laser cladding technology plunger tip, the general life is about 13,000 times, the price is higher, and there are many applications.
- Alloy steel plunger tipes generally have a lifespan of about 30,000 times, which is difficult to popularize and apply in large numbers due to factors such as high cost and difficult processing in the later stage.
- Beryllium bronze plunger tip, the general life is about 50,000 times, although beryllium bronze has good high-temperature performance, wear-resistance, and thermal conductivity, the material cost is very high, and the application is not very extensive.
2.The Importance of Improving Plunger Tip Life
Take ordinary cast iron plunger tip as an example:
It takes an average of 5 to 8 hours to replace, and each replacement takes 15 to 20 minutes. In addition, due to the wear of the cast iron plunger tip, 1 scrap per shift is achievable.
Preheating the plunger tip requires a slow shot, producing 2 scraps. The power consumption is about 4 kWh for a 280-ton die-casting machine as an example.
High life plunger tip:
The average service life is more than 160 hours, and it is replaced every 20 shifts, which takes 15 to 20 minutes each time. However, compared with ordinary cast iron plunger tipes, high-life plunger tipes can increase production capacity by at least 8 hours and reduce scrap by at least 60 pieces. Taking a 280-ton die-casting machine as an example, it can save at least 80 kWh of electricity.
The above comparison does not include the loss of the furnace and the labor cost. It can be seen that even if the price of a single high-life plunger tip is relatively high, the high-life plunger tip can save the overall cost.
3.Reasons for Wear of Plunger Tip and Shot Sleeve
After experimental analysis, in the process of molten aluminum entering the barrel, due to the slight oxidation of the surface of molten aluminum, a small slag – α-AI2O3 (also known as corundum) will be formed, with a Mohs hardness of 9, second only to diamond.
The hardness of this kind of slag is shorter than Mohs level 9 due to the short formation time, but it is higher than the hardness of the plunger tip. Because the hardness of the ordinary plunger tip is low, when the piston moves with the barrel, it will embed these fine particles with higher hardness into the surface of the plunger tip. This will cause wear and tear on the barrel, the sprue sleeve, and even the plunger tip itself, and eventually, the plunger tip will fail.
4.Features That A Plunger Tip Should Have
On a standard basis, the plunger tip should have the following features.
- The thermal expansion coefficient is small so as not to cause the plunger tipto be stuck in the melting cylinder due to expansion after being heated.
- It has high strength and avoids the disconnection of the connecting thread with the injection rod.
- Good wear resistance.
- A reasonable friction pair is formed between the barrel and the sprue sleeve, and the barrel will not be worn quickly.
- Low price and abundant sources
- Good processing performance.
According to the above requirements, there is currently no material that can fully meet its requirements. It can only be considered comprehensively, and the cost of the plunger tip consumed by each casting can be reduced to a lower level (under the condition of fully protecting the barrel), which is ideal for the plunger tip material.
5.Measures to Improve plunger tip Life
5.1 Management of operators
The responsibility of the operator is clear, and each die-casting machine plunger tip and pressure chamber have a certain service life. If the life of the plunger tip is greater than the specified life, a reward will be given.
In contrast, if the life of the plunger tip is less than the specified life, the cause needs to be analyzed in time to determine the source of the problem. If corrective measures are not taken in a timely manner, appropriate penalties are required.
What should you do?
Establish a reasonable production system by;
- Preheating the plunger tipbefore production,
- Replace the plunger tipregularly,
- Regularly check the cooling water and lubricating oil, etc.
5.2 Concentricity of plunger tip and pressure chamber
We need to regularly check the coaxiality of the plunger tip and the pressure chamber, which is a critical parameter that directly affects the life of the plunger tip and the pressure chamber, and the quality of the casting.
How to detect
Make a mandrel for inspection and insert it into the pressure chamber. The magnetic base of the dial indicator is adsorbed on the mandrel, the head of the dial indicator is placed on the injection piston rod, the piston rod is rotated, and the beating of the dial indicator is required to be within 0.2mm. That is, the coaxiality between the plunger tip and the pressure chamber must be within 0.2mm.
5.3 Plunger tip lubricating material
Commonly used are lubricating particles and lubricants. Commonly used lubricants are mineral oil-based graphite-containing and graphite-free plunger tip lubricating oils, synthetic-based water-soluble lubricants, and waxy lubricating particles.
Particles are cheap but waste a lot; plunger tip lubricants are expensive but generally used by large companies. The lubricating oil can be added to the plunger tip or to the pressure chamber.
5.4 Cooling water
The plunger tip needs to pass cooling water. When there is no cooling water, the temperature of the plunger tip rises sharply, and it will be stuck in the pressure chamber. And it is better to have the water circuit on-off detection. Then, the alarm can be timely when the water circuit is broken.
5.5 Other factors
- The height of molten aluminum should be as low as possible;
- There should be a chamfer on the top of the plunger tipto control expansion;
- The cooling water rotates and flows out, which can improve the heat exchange capacity, etc.
6.Plunger Tip Issues and Improvements
Problem: The surface of the injection plunger tip is unilaterally worn and evenly worn.
Analysis: If there is serious wear on one side of the injection plunger tip, it is basically judged that the coaxiality of the injection is abnormal or the injection rod is deformed; if there is uniform wear, it is caused by the wear of the barrel and the normal wear of the plunger tip.
If the plunger tip is normal wear:
- By changing the floating connection between the injection rod and the piston rod, the coaxiality requirements of the machine can be reduced
- The internal and external lubrication system is used to lubricate the circumference of the injection chamber hole when the plunger tipis followed out. When the hammer is back, the lubricating oil is evenly distributed in the injection chamber hole by the action of the hammerhead, carry out lubrication
- It is recommended to replace the pressure chamber regularly (the general life of domestic H13 material is about 50,000 mold times, and the life of Japanese SKD61 material is generally about 100,000 mold times);
- Change of plunger tipoil (change principle: less gas generation, good lubrication effect, high-cost performance)
If the plunger tip is worn on one side:
- Detect whether the injection rod is deformed (by rotating the injection rod on the detection platform to observe whether there is obvious deformation; it is recommended to replace 60,000 to 100,000 molds according to the production situation);
- Detect the coaxiality of the injection system and recalibrate.
- Check whether the foundation of the die-casting machine is flat.