/ep_edm/en/contect_698.html SHINI PLASTICS TECHNOLOGIES, INC.

Special Reports

2013 Quarter 1 Issue 14

The Relationship between Heat Conduction and Heat Loss

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In hot runner system, heaters are used to keep thermoplastic resin in both mold debug phase and production phase always in molten state. Heaters must be installed in the system. Heat compensation is necessary because in the production heat may loss because of dissipation. The temperature in the system must be balanced without peak value. However, the unavoidable dissipation of heat makes it too difficult to realize. Within a relevant range, system design and proper choice of materials have deep influence on heat dissipation. To provide simple but effective solutions, the basic knowledge of heat conduction must be taken into consideration.


 

Heat Conduction

Heat conduction means heat transfer between media without macroscopic motion. Heat conduction may happen in solids, liquids as well as gases, but the proper heat conduction only happens in solids. In addition, natural convection can take place because of the density contrast caused by temperature gradient, even the fluids are motionless. Therefore, in fluids, heat conduction and natural convection happen at the same time.

The process that heat transfers from one part of the system to another part or from one system to another is called heat conduction. There are three ways of heat transfer: heat conduction, convection and heat radiation.

Heat transfer can happen in all kinds of media with different performances. The substances which are easy to transfer heat is called good conductor while the substances with bad heat transfer performance are called poor conductor. All metals are good heat conductor.

 

Heat Loss

Heat Loss refers to the heat that human body or constructions dispersed to the outside. Human body heat loss means the heat that human body dissipated to the surrounding environment, among which there are heat loss through evaporation, convection, radiation and a little amount of heat conduction.

Heat loss of hot runner system refers to the heat disperses from hot runner manifold and other components to molds or the surrounding atmosphere, including heat conduction, convection and radiation. Most of the heat loss is determined by the original configuration of runner plates when heat supply and heat loss is balanced in the system. User can avoid this kind of heat loss by reasonable settings and applying proper heat-insulation components.

 

Relationship between heat conduction and heat loss in hot runner system

Firstly, most of the heat transfer in runner system is by heat conduction. Mold system and dimension may change when mold is heated and expanded. System deformation or material failure may occur when taking no account of heat expansion.

Secondly, the reasonable layout of heaters in hot runner system directly affects the utilization of heat energy.

Thirdly, controlled by the temperature controller, heaters can constantly provide heat to the system. Hot runner system in the molds also plays the role of transportation in which heat is the basic factor to keep it smooth. When too much heat is lost, cold melt may occur and in succession affects the resin and products quality.

Heat conduction may lead to heat loss, too. Therefore, too maintain stable and normal operation of hot runner in the mold, heat loss is a very tough problem to deal with. 

  • Heat conduction: to minish the contact area of the support ring and the center pad to reduce heat flow area; adopt material with poor heat conduction performance to produce supporting ring and center pad, such as stainless steel, titanium alloy and sintering ceramic. Use stainless steel to produce set screws.
  • Heat loss through convection: seal off the gaps between the manifolds and plates to stop air circulation; install heat resistance plates to large surfaces of manifolds inwalls and mold structure inside.
  • Heat radiation: to grind and polish the manifolds and the all around side plates to keep the surrounding gaps and spaces cleaning and tidy; install shining aluminum foil plates to the external surfaces of hot runner manifolds; install large areas of heat resistant plates to the external surfaces of hot runner manifolds or internal surfaces of the molds.

The heat transfer of hot runner system in molds is finished here, in the next issue, we will introduce you the temperature control details of hot runner system.

 

Special Reports

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