Beryllium Copper Plunger Tips
Beryllium Copper Plunger Tips have been the standard of the Die Casting Industry for the past 30 years. They have stood the test of time for several reasons, however, they may not be the standard much longer
Beryllium Copper Plunger Tips wear easily against the hardened and often nitrided H13 steel shot sleeve. When the shot sleeve distorts due to nonuniform heat the bore no longer stays round. This causes areas to be under size thus causing friction and wear on the plunger tip. As we know excessive wear will eventually cause enough clearance for molten metal to bypass the tip.
Beryllium Copper Plunger Tips have acted as a band aid for die casters. Factors that contribute to poor tip life include sleeve distortion, sleeve lamination or soldering, poor plunger lubrication, poor plunger rod alignment, and inadequate plunger tip cooling, If these factors are present a Beryllium Copper Plunger Tip will simply wear down. Beryllium Copper Plunger Tips generally do not last much longer than 5,000 - 10,000 shots under the best conditions and with a relatively small diameter.
Changing a plunger tip can take from several minutes to several hours depending on the size, proximity, and available staff.
What used to be an advantage in the past is now a disadvantage. As cycle times decrease and demand for more efficient production increases the thermodynamics of beryllium copper is no longer an advantage as once thought. Die casters have usually been caught between competing parameters due to biscuit size. As the biscuits become shorter due to faster cycle times too much metal is chilled in the biscuit prior to the shot. Making a biscuit too large wastes metal and energy and could cause the biscuit to explode during ejection. When biscuits solidify prior to intensification the energy previously intended to push the metal in the cavity now has no place to go and impacts the parting line. Keeping this metal semi-solid or liquid prior to intensification is vital.
Generally speaking Beryllium Copper is not cheap. Especially as the size of the plunger tip increases. Often companies offer a reclamation discount which helps bring the cost down as long as the usage and quantity warrants it. Different Beryllium contents usually 10 and 20 will change cost.
Studies have shown that instances of prolonged exposure to atomized Beryllium can cause Berylliosis and other health issues. (see article by USACHPPM - http://chppm-www.apgea.army.mil/documents/FACT/64-003-0302). Sanding a plunger tip on a manual lathe to bring it to size is an example of atomizing this material and should be avoided at all times.
Steel Plunger Tips
Steel Plunger Tips are not new to the die casting industry. However, in years past the technology and understanding of the complex thermodynamics were not where they are today. In order to make the steel plunger tip viable for today's industry the major factors for tip failure must be addressed. Pegasus Industries has developed a shot sleeve that does just that. Eliminating the distortion in the shot sleeve while providing proper cooling and adequate lubrication has opened the door for vast improvements with the plunger tip. For more information about Thermal Control Shot Sleeve go to: http://www.pegasustcs.com/store.asp?pid=22651&catid=19905
Steel Plunger Tips have several advantages over Beryllium Copper. Most importantly they last longer. Steel has a much greater resistance to wear than Beryllium Copper. Average plunger tip life of a Pegasus Steel Plunger Tip is 30,000 shots for a 3-1/2" diameter. Steel Plunger Tips are also generally less expensive. Especially in the diameters of 3" and greater. Steel Plunger Tips are much more durable iin the thread interface with the plunger rod. Often times the softer Beryllium Copper will have weaker threads and more problems with leaking at that juncture. Steel to steel threads are much stronger and will have less tendancy of leaking.
Probably the most significant advantage next to the longevity is the thermal impact on the casting process. Steel has about a 5 to 1 slower conductivity rate than Beryllium Copper. This means that steel plunger tips do not cool the metal in front of the plunger tip prior to the shot. Steel Plunger Tips that are used in conjunction with the Pegasus Thermal Control Shot Sleeve have the advantage of die end sleeve cooling which only cools the biscuit after the shot is made for rapid ejection and solidification. This means die casters can cast with shorter biscuits without any impact on intensification and part quality.
For more information on Steel Plunger Tips visit http://www.pegasustcs.com/store.asp?pid=22652&catid=19905
