Abstract: This paper introduces the design and debugging of soft and hard co-extruded PVC profile moulds and the production process of the product.
Key words: PVC profile, soft and hard coextrusion, mold, process
I. Introduction
With the vigorous development of chemical building materials, more and more co-extruded PVC profile products. Two-color co-extruded PVC profile, co-extruded PVC profile with new material and recycled material, soft and hard co-extruded PVC profile directly extruded on the profile, core steel lining and PVC micro-foamed outer layer coextrusion PVC profiles, these co-extruded products have recently emerged in the chemical building materials family and become a very popular product in the market. The development of these co-extruded products is strong, especially in North China, the co-extruded products are very popular. Last year and the first half of this year, the company produced nearly 30 sets of co-extrusion molds for several customers in North China, which fully met the requirements and was delivered for production.
This paper gives an example to introduce the design and commissioning of soft and hard co-extruded PVC profile moulds and the production process of profiled materials in domestic production.

Second, PVC soft and hard coextrusion profile product legend
Soft and hard co-extrusion sash products are shown in Figure 1:

Figure 1 Co-extruded profile product map

Third, the mold design

1. Introduction to coextrusion
The soft part of the soft and hard coextruded PVC (the material is modified polyvinyl chloride, the elasticity is very good) is that the SPVC hot melt is bonded to the HPVC through the die. There are two ways of soft and hard coextrusion: one is pre-coextrusion, that is, both come out from the profile mold, and have been co-extruded together, and then cooled and shaped into profiled products through the sizing die; the other is Extrusion, that is, PVC profiled material is produced in the same way as ordinary profiled material, except that the profiled exit die is cooled and formed by the sizing die, and the SPVC is co-extruded to the desired part of the profile before being pulled into the profile.
This article describes the former coextrusion.
2, co-extrusion mold design
The soft and hard co-extrusion profile mould can be regarded as the co-extrusion runner or the shaped cavity of the ordinary profile mould reprocessing soft material, so the design of the soft-hard co-extrusion profile mould is not very complicated, because ordinary We have seen a lot of profile molds, and there are quite a few articles in the newspapers. We will not repeat them here.

Figure 2 is a schematic diagram of the ST80 fan co-extrusion die, and Figure 3 is a schematic diagram of the ST80 fan co-extrusion die.

Figure 2 ST80 fan co-extrusion die

3, the design of the co-extrusion joint
The co-extrusion joint is a tie between the main machine and the co-extrusion machine, referred to as a co-extrusion head, one end of which is coupled with the co-extrusion and the other end of which is coupled with the die. Generally, the angle α is less than 60 ° C, and the length of L is not suitable, and is generally selected between 40 and 100 mm. If L is too long, the melt resistance of SPVC will be too large, and the material stagnation time will be too long to decompose. If L is too short, it will cause poor plasticization of SPVC melt and affect production and product quality. Figure 4 is a simplified diagram of a co-extrusion joint head.

ST80 fan co-extrusion die shaping die

Figure 4 co-extrusion joint

Fourth, mold debugging
Firstly, the soft and hard co-extruded PVC profile moulds are debugged according to the usual debugging method of ordinary PVC profile moulds without considering the soft co-extrusion. When the shape and dimensions of ordinary PVC profiles are close to the drawings and standards, Then open the co-extrusion machine to see the soft part of the head discharge and the passing mode, because the SPVC melt is very good in the head, the flow path size of the head during the mold making, including the flow path, split, split design The length of the flow channel, the geometry and size of the interface between the plates are slightly different from the design, so that the SPVC discharge may have two (the bead is four strands). The length of the SPVC blank is proportional to the size ratio of the product map. Large, at this time, the length and length of the SPVC blank becomes the basis for correcting the die.
The length of the soft and hard co-fluid channel in the head has a direct relationship with the tear strength of the soft and hard co-extruded products. I think this relationship is more closely related to the joint surface area and tear strength of the soft and hard parts, but The length of the soft and hard co-fluidic flow channel is limited by the fact that the two melts are not clamped in the machine head. Therefore, it is necessary to carefully grasp the mold according to experience, otherwise it will lose weight.

In the sizing die, the soft PVC parison is not suitable for vacuum setting. Because the soft and hard hot melt is easy to tear or block the mold from the joint surface, what is the shape of the SPVC blank? This is to add a watering device at the entrance of the sizing die, so that the cooling water can be continuously and evenly deposited on the surface of the SPVC parison, and a hardened layer is formed on the surface, and then enters the sizing die to cool and shape the cavity in the sizing cavity. Of course, if you do not want the water spray device, you must do some treatment in the inlet part of the mold, so that the SPVC blank does not block the mold, does not tear and can be cooled and shaped.
The shape of the SPVC part of the model cavity is not suitable, otherwise the SPVC blank can not pass, even if it is temporarily passed, if the whole production line fluctuates slightly, it is easy to cause the mold block. At this time, it is necessary to enlarge the part of the SPVC blank in the fixed mold. The cavity size can be solved.
5. Production of co-extruded products
To be honest, the production of soft and hard co-extruded PVC profiles is more troublesome than the production of ordinary PVC profiles. The production of ordinary PVC profiled products is very strong. The normal production has strict requirements on the continuous stability of the entire production line and process. After the SPVC co-extrusion, the coordination between the main machine and the co-extrusion machine is stable. The continuous stability of the traction and the main machine must be strict. Ensure that fluctuations in which factors in the system will affect the normal production. From another perspective, this also puts higher demands on the quality of the operators.
Taking the ST60 fan production process as an example
Raw materials:
Hybrid powder for HPVC profiles with composite stabilization system.
The SPVC co-extruded part is purchased with rubber modified pellets.
Equipment:
The main machine is the SJSZ-60 twin-screw extrusion line.
The coextrusion machine is a SJ45×20 single screw extruder.
The host process temperature is shown in Table 1.
Main screw speed: 28 rpm.
Feeding speed: 26 rpm
Table 1 Unit: °C
Body joint body die head screw core
Zone 1 District 2 Zone 3 District 4
170 164 163 161 160 180 182 185 91
The coextrusion machine temperature is shown in Table 2.
Table 2 Unit: °C
Body coextrusion machine
Zone 1 District 2 Zone 3 District 4
138 155 156 150 140
Co-extrusion machine screw speed: 12 rev / min
Production line traction speed: 1.8 m / min
Six, several key issues besides the mold
1. The raw material formula of PVC profile has a significant influence on the tear strength of the soft and hard coextrusion part. The influence of the variety and dosage of the external lubricant on the soft and hard coextrusion part must be taken seriously. Because the national standard GB/T8814-1998 "hard polyvinyl chloride (PVC) profiles for doors and windows frame" does not mention the problem of soft and hard co-extruded PVC profiles. Therefore, according to the co-extruded profile products of the brother manufacturers and their own test results and user opinions, the enterprise standard is established to ensure and control the tear strength and appearance quality of the co-extruded products.
2. The formulation of the co-extruded SPVC pellets can not be ignored. Such as the temperature resistance of the stable system in SPVC. The proper amount and balance of the lubrication system should ensure that the SPVC melt plasticization is good, the tearing strength of the less adhesive die and the co-extruded product meets the requirements.
3, the production of soft and hard co-extruded PVC profiles on the production line process temperature requirements are more demanding, especially the head temperature.

The temperature of the machine head is too low, the plasticization is insufficient, the strength and surface gloss of the hard PVC profile are not good, the soft and hard coextrusion part is wrinkled, the continuous stability of the machine head discharge is poor; the head temperature is too high, and the SPVC melt viscosity is low. It is easy to decompose and foam, the adhesive die is more serious, and the tear strength of the soft and hard co-extruded profile is significantly reduced (this may be inconsistent with some people's ideas). Therefore, in the production process of soft and hard co-extruded PVC profiles, it must be carefully observed. Patiently adjust the appropriate host, co-extrusion machine speed and process temperature to ensure qualified product production.


Wuxi Jiahong Plastic Technology Co., Ltd. has nearly 30 years of experience in research and development and granulation of modified PVC pellets. The professional technical service team can provide one-stop system solutions for customers. For more information about the product, please visit our official website: www.yfztp.cn, consult online customer service or call the hotline. Fixed line: 0510-68755207 Mobile: 15190220696, we will be happy to help you.

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