Cold runner refers to the part between the mold inlet and the product gate. The plastic is kept flowing by injection pressure and its own heat in the runner, which is part of the molding material but not the product. Therefore, when we design the mold, we should consider both the filling effect and how to save materials by shortening and narrowing the flow path. This is ideal, but it is difficult to achieve the best of both worlds in practical application.
Hot runner, also known as no runner, refers to the plastic in the runner after each injection is not solidified, plastic products when the mold will not have to flow out of the mouth. Because the plastic in the flow channel does not solidify, the flow channel is still free at the time of the next injection.
In brief, the hot runner is the extension of an injection molding machine nozzle.
Hot runner mould is widely used in the developed countries and regions of the world. This is mainly because the hot runner mold has the following remarkable characteristics:
Shorten the molding cycle
Due to no cooling time limit of the runner system, the parts can be timely ejection after molding and curing. Many thin-walled parts produced in hot runner molds take less than 5 seconds to complete.
Save plastic materials
In the mold of a pure hot runner, there is no cold runner, so there is no production cost. This is especially important for applications where plastics are expensive. In fact, the major international hot runner manufacturers have developed rapidly during the world's expensive oil and plastic raw materials. Because hot runner technology is an effective way to reduce material cost and material cost.
Reduce waste and improve product quality
In the process of hot runner mold forming, the melt temperature of plastic is precisely controlled in the runner system.
The plastic can flow into the cavity in a more uniform state, and the result is parts of uniform quality. The quality of the hot runner is good, the residual stress is low and the deformation is small. So many high-quality products on the market are produced by hot runner mold.
Elimination of subsequent processes, conducive to production automation
After the hot runner mould is formed, the parts are finished products, no need to trim the gate and recycle the cold runner. Facilitate production automation. Many foreign manufacturers combine hot runner with automation to greatly improve production efficiency.
Expand the application of injection molding process
Many advanced plastic molding processes are developed on the basis of hot runner technology. For example, PET pre-molding, multi-color co-injection in the mold, multi-material co-injection process.
Although hot runner molds have many significant advantages over cold runner molds, mold users need to be aware of the disadvantages of hot runner molds. In summary, there are the following points:
Mold cost rise
Hot runner component price is more expensive, hot runner mold cost may be greatly increased. If the production of the parts is small, the mold tool cost ratio is high, economically not cost-effective. For mold users in many developing countries, the high price of the hot runner system is one of the main problems affecting the widespread use of hot runner molds.
Hot runner mold production process equipment requirements are high
Hot runner mold requires precision machining machinery for assurance. Hot runner system and mold integration and cooperation requirements are very strict, or the mold in the production process will appear many serious problems. If the plastic seal is not good, the plastic overflow damage to the hot runner component interrupted production, the nozzle insert and the gate relative position is not good, resulting in a serious decline in product quality.
Complex operation and maintenance
Compared with cold runner mold, hot runner mold operation and maintenance are complex. If the use of improper operation is very easy to damage the hot runner parts so that the production cannot be carried out, resulting in huge economic losses. For new users of hot runner mold, it takes a long time to accumulate experience.