Exhaust and cooling of injection mold

Exhaust and cooling of injection mold

Exhaust understanding

Cause of gas in mould

When the mold is closed, the air in the mold cavity is not completely discharged;

The water vapor produced by the high temperature of the existing water in the plastic raw materials that have not been completely dried;

Corrosive and volatile gases (gas) produced by the decomposition of internal molecules of plastic raw materials after high temperature melting and high-speed filling

Problems caused by poor escaping of mould

Scorch of product surface

When filling, the plastic flows at a high speed, resulting in the compression of air and high temperature;

Poor filling of products

When the plastic is filled, the gas that is not discharged will produce resistance to its flow, so that the part of the product cannot be filled;

Obvious glue line

When the plastic is filled and combined, the gas has resistance to its flow, which slows down its flow, lengthens its combination time and misses the optimal temperature of crystallization;

Poor air escape results in internal defects, surface pits, crepes, bubbles, silver thread and other poor quality of products

Die surface corrosion

In the process of repeated forming, due to the poor escaping gas, the inner part of the die cavity is squeezed by high temperature and high pressure gas to make its surface damaged (gas)

Understand escape routes

1、 Definition of escape route:

The way of gas (gas and air) flowing out of mould cavity when products are forming

2、 Escape function:

1. It is favorable for filling and forming of products, shrinking, lack of materials, air lines, brightening and escaping of products

Related

2. It is advantageous to extend the service life of the mould, and the gas escape is not good, which makes the gas deposit and corrode the mould core

Processing requirements for product escape tank:

Additional escaping parts and principles:

Additional parts of escaping gas:

PL surface, thimble, sliding block, inlet, rib depth, material channel

Principle of additional escape location:

1. Add at the last arrival of materials

2. Added to the right side of the injection port

3. Add to the most difficult part

4. To be added to the joint line of products

Reference value of mold escape depth of common plastic materials

In order to prevent forming overflow (Burr), different plastic materials adopt different air escape groove depths:Setting: mm

2、 Mold cooling

Product cooling: when the product is formed, the injection molding machine will inject the molten plastic into the mold. It needs to cool down in the mold to form the product shape

Principle of cooling: quickly take away the heat of plastic

Mold cooling: use medium to control mold temperature in a certain range

Influence of cooling system on product quality:

a. Product gloss and appearance (gloss, flow mark, binding line)

b. Forming shrinkage (deformation, depression, bending)

c. Product characteristics (residual stress: bending. Crack: PC viscosity is high, material is easy to occur). (better crystallization: higher strength, hardness and heat resistance)

Basic understanding of waterway:

The cooling coal body used for mold temperature regulation includes: water, oil, ethylene, glycol, etc

*The mold temperature shall be controlled by the mold temperature regulator. The mold temperature shall be below 90 ° C. the water shall be used for temperature adjustment. When the temperature is relatively high, the oil, ethylene or glycol shall be used. When the temperature is extremely high, the heating pipe can also be used for heating

*The cooling system is designed to evenly cool the products. During the whole cooling process, more than 70% of the heat of the products is taken away from the male mold side. Therefore, the male mold part must be taken as the key point in the trade-off consideration

*The cold coal should flow into the high temperature area near the runner gate first

*Water storage areas should be avoided

*In addition to cooling effect, the layout of waterways should also pay attention to the balance of mold temperature (try to use multiple groups of circulation)

*If necessary, other forms of cooling besides water can be added to achieve good cooling effect