Trouble Shooting-Shot Sleeve and Plunger Tip Failure
Probably the number one cause of shot sleeve failure is erosion opposite the pour hole. Erosion can be retarded by designing with heavy walls, nitriding the sleeve, using funnels, lowering metal temperatures and by the use of water cooling. Holes can be drilled into the wall of the sleeve and connected so that there is a continuous flow of water or hot oil in the area opposite the pour hole.
Another cause of failure is soldering or buildup on the wall of the sleeve. It restricts the tip and causes uneven wear leading the tip to become out of round. Soldering can be caused by misalignment, less than 50% fill or a less than .80% Fe content of the molten aluminum. Nitriding, good alignment and periodic honing can help prevent soldering.
The plunger tip can also be restricted by uneven thermal expansion. Uneven temperatures at different places of the shot sleeve cause stress and distortion. Hot metal in a cold sleeve can cause stress exceeding the strength of the sleeve. When the die is closed the shot sleeve becomes longer and bends upward, becoming longer on the bottom. Preheating the sleeve to 500-600 degrees F., will help east thermal shock and lessen distortion. Machine platens must also be checked to make sure they are not out of flat. Uneven platens will cause strain when the die is clamped and possibly break the collar of the shot sleeve.
Misalignment is a major cause of shot sleeve failure. It causes excessive and uneven wear to the tip and sleeve from drag due to the the lack of clearance. This restricts the space required for lubrication on one side and on the opposite side too much clearance is allowing metal to enter and solidify. Here again we have soldering which acts as a wedge and can cause severe scoring or splitting.
Next: Trouble Shooting-Proper Alignment