Wood plastic mold is used to manufacture all kinds of wood plastic products. In modern industrial production, mold forming is a common method for products, and the production of wood plastic products is no exception. According to the current process characteristics, the overall requirements of wood plastic products for molds are: first, it can produce high-quality wood plastic products that can meet the use needs in terms of appearance, dimensional accuracy and physical properties; From the perspective of mold use, the requirements are: high efficiency, automation, simple operation and easy maintenance; From the perspective of mold manufacturing, the requirements are: reasonable mold structure, easy fabrication, low cost, and can be accepted by the majority of users. In the daily application of wood plastic products and industrial wood plastic products, wood plastic molds can be divided into the following categories according to the production process of products:

1. Press molding molds: the well-known automobile interior trim panels, ship partitions, vehicle cabin panels, etc. are products produced with press molds.

2. Injection mold: seats, home appliance shells and children's toys in public venues are all molded by injection mold.

3. Hollow blow molding mold: products such as trays and packing boxes are hollow blow molding molds.

4. Extrusion mold: floor, profiles, doors and windows, plates, sheets and other products are formed through extrusion mold. Such products account for more than 60% of domestic wood plastic products.

As a new type of composite material, wood plastic materials are usually made by blending natural plant fiber materials, such as straw, rice husk, wood flour and hemp fiber with different polymer substrates. Therefore, extrusion plays an important role in the processing and production of wood plastic materials. Now the wood plastic extrusion die is specially introduced.

Design of extrusion die for wood plastics

Using modern CAE / CAD design software, we can simulate all the forming conditions of the products we want in the actual production process in the ratio of different natural fiber materials and different polymer substrates. With the deepening of the research on the principle of wood plastic processing technology, the simulation design has gradually approached the actual working condition. Die design is gradually developing from empirical design stage to theoretical calculation design. This is especially true in the design of wood plastic extrusion die, which greatly improves the output and quality of wood plastic extrusion products. At the same time, due to the different polymer substrates used in wood plastic materials and the diversity of natural materials, the design of wood plastic die is several times more difficult than that of other materials. At present, the achievements shown by the wood plastic mold industry are also the crystallization of the success of engineers and technicians in the industry through hundreds of times of hardships and repeated and unremitting tests.

Extrusion wood plastic die structure

Wood plastic extrusion molding is to make the raw materials of wood plastic materials flow during processing by heating or other methods. Under the action of pressure, the required profiles are made through wood plastic molds. Most common wood plastic materials are made by this method. The structure of wood plastic die is mainly composed of extrusion die head and setting die.

1. Extrusion die is the key to determine whether the product can be formed normally. Whether the physical performance index of the product can meet the standard is directly related to the die structure design and manufacturing accuracy.

Generally, the extrusion die structure shall meet the following functions:

A. Make the extruded wood plastic flowing material change from spiral motion to linear motion, so that the uniformity of the material in the extrusion process can be guaranteed.

B. Sufficient extrusion pressure shall be formed on the die to make the product density reach the specified index. If the product density is insufficient, the finished product will be loose, resulting in large dimensional change rate of the product after heating, increase of water absorption, easy aging and mildew, and all indexes will be affected.

C. The die structure shall further homogenize the material. The natural fiber and polymer substrate shall be further fused at the die until they are dispersed and extruded evenly, so as to complete the transformation of wood plastic materials from viscous flow state to solid state.

2. Setting die is a part of the die to ensure that the initial shape of the extruded material comes out of the extrusion die head and becomes the final finished product after cooling and setting. It also plays an important role in the extrusion process.

When wood plastic products are extruded from the extrusion die head into the die, they also have a very high temperature. Generally, the extrusion temperature of polyolefin wood plastic materials is between 110 ℃ ~ 140 ℃, while the extrusion temperature of PVC wood plastic or other wood plastic materials can be as high as 180 ℃ ~ 190 ℃. In order to obtain good finish, accurate size and standard geometry of finished products, the extrusion setting die must meet the following requirements:

A. The size of the shaped mold cavity must meet the accuracy requirements of the overall dimension of the product.

B. The setting die shall have good and uniform thermal conductivity. The shapes of wood plastic products vary greatly. Good thermal conductivity can improve the cooling efficiency of setting mold, so as to improve the production speed of wood plastic products. More importantly, uniform heat conduction is the key factor to ensure the release of stress, avoid bending and improve the internal quality of products.

Extrusion wood plastic mold manufacturing

The extrusion wood plastic mold is generally made of high-quality stainless steel, which is processed by electric processing after calcination and heat treatment. The selected materials generally include 2Cr13, 3cr17, 38CrMoAl, H13 or imported din1 2316 and other materials. The hardness of heat treatment after material processing must reach above HRC55. The processing method of wood plastic mold is similar to that of other material molds. Special attention should be paid to:

1. Wood plastic materials have strong wear resistance to equipment and molds during processing, which is a major feature of wood plastic processing. The service life of general extrusion equipment and die is 3 ~ 5 years, while the wear-resistant life of wood plastic extrusion equipment is usually only about 1 year, and the die life may be shorter. In order to improve the service life of the die, many attempts have been made at home and abroad, such as improving the surface hardness of the die and reducing the surface friction coefficient of the extrusion die channel.

2. For hollow wood plastic mold manufacturing, due to wall thickness, cavity design and other factors, how to solve the problem of uniform internal and external cooling of finished products is the key to mold manufacturing.

Differences of wood plastic molds at home and abroad

China's wood plastic mold processing has been industrialized since 2000, but there is a big gap with foreign advanced technology in concept, technology and equipment. It is embodied in several aspects.

1. Mold material. In addition to the price difference between domestic mold materials and foreign high-quality mold materials (foreign materials are about 5 times higher than domestic ones), foreign materials still have advantages in material refining degree, uniformity of heat treatment and precision control in the processing process.

2. Service life. The service life of foreign advanced extrusion wood plastic molds is significantly higher than that of domestic extrusion wood plastic molds. The main difference is that the mold structure design is reasonable and the material hardness is large, so it is relatively durable, resulting in the service life difference of wood plastic molds at home and abroad.

3. Extrusion speed. The extrusion speed of foreign advanced polyolefin wood plastic molds is 2 ~ 6m / min, and the domestic wood plastic molds can only approach the foreign level of 70% ~ 80% under the condition of reasonable equipment capacity and material coordination. However, the extrusion speed of PVC wood plastic mould in China is almost the same as that in foreign countries.

To sum up, although the progress of domestic wood plastic industry has driven the development of wood plastic mold industry, there are still many problems to be overcome in wood plastic mold manufacturing due to the weak foundation and the gap of overall level. It is believed that with the development of China's building materials industry, wood plastic composites, a new environmental protection material, will be more widely used. Wood plastic molds will seize the opportunity to catch up and create newer and more beautiful wood plastic products to serve the construction of a resource-saving and environment-friendly society.

While other manufacturers focus on mold hardware and one-step wood plastic extrusion process, we are more optimistic about the future of two-step wood plastic extrusion process. The two-step process of separating mixing and extrusion is more suitable for wood plastic extrusion production. Then our process features are:

A high-quality extrusion process requires stable raw materials

2. The tensile strength of profile products can be improved by adopting separate mixing process

3. The mixture humidity can be reduced to less than 1%

4 extruder can ensure the best extrusion operation

5. Good raw materials ensure high-quality wood plastic extrusion effect

6. The extrusion operation parameters are stable

3 suggestions for industry reference:

1. In addition to ensuring the smooth transition and reasonable flow distribution of channel design, wood plastic composites have higher requirements for pressure building capacity and temperature control accuracy.

2. In order to obtain good fiber orientation and product quality, it is necessary to ensure that the machine head has sufficient pressure building capacity and long setting section, and even adopt double taper structure in compression section and setting section.

3. The thermal conductivity of wood plastic composites is poor, and most of their products are special-shaped materials, so it is difficult to cool and set, so water cooling is often used for setting. The cooling channel is reasonably designed to ensure efficient cooling.