DIE TEMPERATURE CONTROL
Die temperature has considerable influence role on the quality of die cast parts and on the production cycle.
Working with a die at excessively low temperature, you can encounter the following problems:
• Rapid die wear;
• Difficult ejection;
• Piece contraction around pins;
• Bonding between metal and die;
• Reduced efficiency of die releasing lubricants;
• Unreliable casting dimensions;
• Incomplete filling.
On the other hand, if die temperature is too high there will be:
•Difficult casting expulsion (warping, gripping);
• Fast release lube degradation
• Longer cycle time
• Unreliable casting dimensions
• Formation of bubbles
• Presence of porosities and cavities during expulsion
• Increased die wear
As a result, the correct die temperature is crucial to obtain a smooth and high level of productivity and to optimize the production cycle.
Thermal regulators are electrical-mechanical devices designed to regulate dies temperature used during die casting production.
Thermal regulation takes place by heating and/or cooling a fluid (diathermic oil or pressurized water), which is pushed through an electric-driven pump inside cavities within the die. Heat transfer is obtained by convection between fluid and cavity surface and by conduction within the die body itself.
Our thermal regulators provide for the following main advantages:
1) IMPROVEMENT IN THE MECHANICAL AND STRENGTH CHARACTERISTICS OF CASTINGS.
2) POTENTIAL BOOST IN CASTING PRODUCTIVITY BY REDUCING CYCLE TIME.
3) EXTENDED DIE LIFE.
4) REDUCTION OF INITIAL REJECTS.
HEAT REGULATORS TO IMPROVE DIE CASTING QUALITY
The mechanical characteristics of a casting are strictly connected to the alloy structural and granular content. When the number of granules increases per unit volume, i.e. with a fine crystal structure, the following improvements are observed:
- stretching %;
- tensile strength;
- hardness;
Crystal dimensions in a casting are undoubtedly connected to local cooling time:
When using temperature regulators, you will get a very fast cooling rate, thus improving the mechanical and strength specifications of each piece.
When components have different thickness, their mechanical and strength properties are made consistent with a constant solidifying time around all the component areas: heating excessively cold areas (thin areas) and cooling excessively hot areas (thick areas).
HEAT REGULATORS TO BOOST PRODUCTIVITY
Temperature regulators can boost company productivity.
Increasing the number of casts per hour will also increase the quantity of heat transferred from the casting to the die (for UNI 5076 alloy Q = 798 Kj/Kg). As a result, die temperature will increase and this will in turn increase the casting cooling time.
With the aid of heat regulators, you can maintain a high number of casts, because this temperature rise is dissipated through increased cooling.
HEAT REGULATORS TO INCREASE DIE LIFE
Dies normally used in casting have variable physical and mechanical properties that change with temperature, as shown in the page alongside.
When using a thermal regulator it is possible to pre-heat dies to:
• Overcome steel ductility/fragility temperature (about 150°C), below which structural failures are very likely to occur, due to thermal fatigue.
• Reduction in thermal gradient between die and casting both on the initial phase and during down times, so as considerably to reduce thermal stresses within the steel die.
Die life can be extended by as much as 27 – 30 %.
HEAT REGULATORS TO REDUCE INITIAL REJECTS
When preheating a die at the start of a cycle or during down time, die life is increased and thermal shocks are reduced, thus decreasing the number of casts necessary to bring the temperature to the required level.
As a result, it has been shown that the potential for reduction in rejected casting has reached 65%.