Views: 4577 Author: Site Editor Publish Time: 2020-03-09 Origin: Site
Temperature control machine was initially used in the temperature control industry of injection moulds. Later, with the development and application of machinery industry more and more widely. So how to choose the appropriate mold temperature machine?
1. Heat balance control of injection moulds and heat conduction of injection moulds is the key to the production of injection moulds. Inside the mold, heat from plastic is transferred to the material of the mold by thermal radiation, and to the heat conducting fluid by convection. In addition, heat is transferred to the atmosphere and the mold base through thermal radiation. The heat absorbed by the heated fluid is taken away by the mold temperature control machine. The thermal balance of the die can be described as P=Pm-Ps. P is the heat taken away by the mold temperature control machine; Pm is the heat introduced by the plastic; Ps is the heat that the mold emits to the atmosphere.
2. The main purpose of controlling the mold temperature is to heat the mold to the working temperature, and the second is to keep the mold temperature constant at the working temperature. If the above two points are successful, the cycle time can be optimized to ensure the high quality of the injection molded parts. Mold temperature affects surface quality, fluidity, shrinkage, injection cycle and deformation. The different mold temperature can have different effects on different materials. For thermoplastics, a higher mold temperature generally will improve surface quality and flow, but will extend cooling time and injection cycle times; a lower mold temperature will reduce the shrinkage in the mold, but will increase the shrinkage of the molded part after demolding. For thermoset plastics, a higher mold temperature typically will reduce cycle time, which is determined by the time required to cool the part. In addition, in the processing of plastics, a higher mold temperature will also reduce the plasticizing time and reduce the number of cycles.
3. The temperature control system consists of three parts: mold, temperature control machine and heat transfer fluid. In order to ensure that heat can be transfered to the mold, the various parts of the system must meet the following conditions:
(1) Inside the mold, the surface area of the cooling passage must be large enough, and the diameter of the flow path should match the pump capacity. The temperature distribution in the cavity has a large influence on the deformation and internal pressure of the part. Properly setting the cooling channel not only reduces the internal pressure and improves the quality of the molded part, but also reduces cycle times and reduces product costs.
(2) The mold temperature machine must be able to keep the temperature of the heat transfer fluid constant within the range of 1℃- 3℃.
(3) The heat transfer fluid must have good thermal conductivity. Most importantly, it must be able to transfer a large amount of heat in a short period of time. From a thermodynamic point of view, water is significantly better than oil.
4. The mold temperature machine is composed of a water tank, a heating and cooling system, a power transmission system, a liquid level control system, a temperature sensor, an injection port and so on. Typically, the pump in the power transmission system causes the hot fluid to reach the mold from the water tank with the built-in heater and cooler, and then return from the mold to the water tank; the temperature sensor measures the temperature of the hot fluid and transmits the data to the control system. The controller regulates the temperature of the hot fluid to indirectly adjust the temperature of the mold. If the temperature of the mold exceeds the set value of the controller in production, the controller will open the solenoid valve and connect to the intake pipe until the temperature of the hot fluid, that is, the temperature of the mould returns to the set value. If the mold temperature is below the set value, the controller will turn on the heater.
5. Temperature moulding machines are classified according to the heat conducting fluid (water or oil). Usually the maximum outlet temperature of a water-conveying thermostat is 95℃. Oil-transporting thermostat is used in the case of working temperature (≥ 150℃). Usually, the mold temperature machine with open water tank heating is suitable for water temperature or oil temperature machine, and the maximum outlet temperature is 90℃ to 150℃. The main feature of this mold temperature machine is simple design and economical price. On the basis of this kind of machine, a kind of high temperature water temperature machine has been developed. Its permissible outlet temperature is 160℃ or higher. Because the heat conductivity of water is much better than that of oil at the same temperature when the temperature is higher than 90℃, this machine has outstanding high temperature working ability. In addition, there is a mandatory flow temperature control machine. For safety reasons, this temperature control machine is designed to operate at temperatures above 150℃ and use heat conducting oil. In order to prevent the oil from overheating in the heater of the model temperature machine, the forced flow pumping system is used in this machine. The heater consists of a certain number of tubes stacked together, in which there are heating elements with fins.
6. Controlling the temperature in the mold is not uniform, and it is also related to the time point in the injection cycle. After injection, the temperature of the die cavity rises to the highest level, the hot melt touches the cold wall of the die cavity. When the parts are removed, the temperature drops to the lowest level. The function of the thermostat is to keep the temperature constant between θ2 min and θ2 max, that is to say, to prevent the temperature difference (Δθw) from fluctuating up and down in the production process.
The above tips are expected to be helpful to you.