Optimization Scheme of Mold Temperature Control for WPC Profile Extrusion Production Line

(Compatible with Yongte WPC profile extrusion lines, featuring "precision temperature control + uniform heat transfer + dynamic adaptation" to resolve issues like uneven flow and surface defects in WPC materials (recycled PP/PE with 60-70% wood powder), while balancing product quality and production efficiency)

I. The Core Significance of Mold Temperature Control

The WPC profile mold is a critical component in material forming, where temperature control directly impacts:

The material flowability of the composite material of wood powder and recycled plastic is poor. The low mold temperature will lead to the material filling insufficiency and the flow channel blockage. The high temperature will cause the carbonization of wood powder, the product surface yellowing and the dimensional shrinkage uneven.

Product forming quality: Temperature unevenness may cause defects such as wall thickness deviation, surface roughness, bubbles, and warping in profiles, particularly affecting the flatness and load-bearing strength of construction profiles (e.g., flooring and wall panels).

Productivity: A reasonable mold temperature can reduce the cooling and setting time of the material, match the extruder and the traction machine's rhythm, and avoid the shutdown and rework caused by poor setting.

The core objective is to maintain mold temperature fluctuations within ±2℃, thereby establishing a closed-loop system that ensures uniform temperature distribution across the flow channel, stable material flow, and rapid, precise material solidification.

II. Optimization scheme of mold temperature according to different scenarios

1. Basic temperature setting: accurately match the characteristics of raw materials and products

The core compatibility temperature of WPC materials should be determined by balancing the melting point of recycled PP/PE (130-170°C) with the maximum heat resistance of wood powder (≤180°C). This requires product structure optimization to prevent wood powder carbonization or insufficient material plasticization.

application scenarios	Optimal temperature range for mold performance	Original default settings	optimization logic	quality / efficiency improvement point
Standard section (simple cross-section, such as flat plate, square tube)	170-175℃	160-170℃	The temperature is slightly higher than that of the rear section of the extruder (175-180℃), which reduces the flow resistance caused by the sudden cooling of the material at the die opening.	The discharge speed increases by 10%, and the surface smoothness improves by 20%.
Complex profiles (multi-cavity, thin-walled, with multiple corners, such as decorative moldings)	175-180℃	165-170℃	Increase the temperature in the cavity to ensure full material filling and prevent material shortages or weld marks	The product pass rate increased by 15%, and the rework rate due to material shortages dropped below 1%.
High wood content (≥65%)	172-178℃	165-170℃	The wood powder has poor fluidity, and the viscosity of the material is reduced by moderate heating, while avoiding excessive temperature leading to carbonization of the wood powder.	The frequency of flow channel blockage is reduced by 80%, and the load fluctuation of extruder is reduced by 10%.
Recycled PP/PE has a low melting point (≤140℃)	165-170℃	160-170℃	Match the raw material's melting point to prevent premature cooling or excessive plasticization.	Reduce the shrinkage rate from 3% to less than 1.5%
high speed production (≥2m/min traction speed)	173-177℃	165-170℃	After acceleration, the residence time of material in the mold is shortened, and the temperature rise compensates for the fluidity.	20% increase in productivity, no surface roughness defects

2. Temperature Uniformity Optimization: Solving the Forming Defects Caused by Local Temperature Difference

Temperature variations (≥5℃) frequently occur in the feeding zone, cavity, outlet, and corners of WPC profile molds. To ensure uniform temperature across the entire mold, a combination of zoned temperature control and structural optimization is required.

(1) Upgrading of heating and temperature control in the zone

Renovation plan: The mold heating ring will be divided into 3-4 independent zones (feed zone, cavity mid-section, cavity end, and discharge port), each equipped with a standalone PID temperature controller (±0.5℃ precision), replacing the conventional integrated heating system.

Temperature gradient configuration: feed zone (175-180℃) → mid-cavity (172-175℃) → cavity end (170-172℃) → discharge port (168-170℃), creating a gentle 'front-high, rear-low' gradient that ensures material flow while accelerating solidification.

Results: The temperature difference of each area of the mold is less than 2℃, the deviation of the wall thickness of the profile is reduced from ±0.3mm to ±0.1mm, and the surface flatness rate is increased by 95%.

(2) Optimization of heating element layout

Replace the traditional single-loop heating ring with a semi-encapsulated ceramic heating tile, which adheres to the mold surface (increasing contact area by 60%) and reduces heat loss.

Add auxiliary heating rods (power 50-100W) at the corners of the mold and narrow flow channels to compensate for the rapid heat dissipation and low temperature in these areas.

High-temperature insulating cotton (5-8mm thick) is placed between the heating element and the mold to prevent heat transfer to the frame, thereby reducing the mold's temperature response to ambient conditions.

(3) Flow channel structure adaptation

If there is a dead zone in the mold runner (material is easy to stay), the inner wall of the runner should be polished (roughness Ra≤0.8μm) and the cross-sectional area of the dead zone should be enlarged. In addition, local heating (+3-5℃) should be applied to avoid material retention and carbonization.

For complex cross-section profiles, a "gradient flow channel" design is implemented to maintain uniform material flow velocity across all cavity branches, with temperature fine-tuning (±2℃) for corresponding zones.

3. Temperature control equipment upgrade: improve temperature stability and response speed

(1) Upgrade of the temperature control system

Replace standard thermostats with PID smart thermostats (±0.1℃ precision) that automatically adjust heating power to prevent temperature overshoot (sudden drops after rapid temperature increases).

A temperature feedback sensor (PT100 platinum resistance, response time ≤0.5s) is installed on the inner wall of the mold cavity (not on the heating ring surface) to collect real-time temperature data from the material contact zone, preventing the misjudgment of 'surface temperature meets the standard but cavity temperature is insufficient'.

(2) The cooling system is precisely matched.

The mold should be equipped with partition cooling water: cooling water channel (diameter 8-10mm) is set at the outlet and the end of the cavity, and the cooling water flow rate (0.5-1.5m/s) is controlled by solenoid valve to achieve the balance of "heating and shaping + local cooling";

The cooling water temperature is strictly controlled at 15-20℃ (consistent with the previous production line cooling system optimization), preventing excessive temperature from slowing mold setting or insufficient temperature from causing excessive mold temperature fluctuations.

For complex profiles with sharp corners or uneven wall thickness, a "point cooling" design (using micro-cooling nozzles) is applied to precisely reduce local temperatures and prevent profile warping.

4. Dynamic adjustment strategy: Adapt to changes in production scenarios

Mold temperature is not a fixed value and must be dynamically adjusted according to variables during production to ensure stability.

Variable scenario	Temperature adjustment direction	adjustment range	Adjustment basis
Recycled PP/PE exhibits a +5℃ increase in melting point	Synchronously increase the temperature of the mold.	+3-5℃	Prevent materials from cooling too quickly in the mold, which increases flow resistance.
Increased production speed (from 1.5m/min→2.5m/min)	moderate temperature increase	+2-3℃	Compensates for reduced material dwell time in the mold to ensure full filling
The content of wood powder increased (from 60% to 70%)	Increase temperature	+5℃	The high proportion of wood powder reduces fluidity, requiring temperature increase to decrease material viscosity.
Product upgrade (simple section to complex section)	Increase temperature	+5-8℃	Complex cavity requires higher fluidity to avoid material shortage and welding marks
The ambient temperature drops to ≤10℃	Increase temperature	+3-4℃	Reducing the Influence of Environmental Heat Transfer on Mold Temperature

5. Maintenance and calibration: Ensure long-term temperature control accuracy

Regular calibration: Monthly calibration of PT100 sensors and PID thermostats using standard thermometers, with immediate adjustment or replacement if the error exceeds ±0.5℃.

Cleaning and maintenance: Clean the heating elements and insulation cotton on the mold surface every 3 days, removing plastic residues and wood dust carbon deposits (which can cause uneven heat conduction); inspect the cooling water circuit weekly and remove scale (which reduces cooling efficiency and causes temperature fluctuations).

Replace heating elements: When the heating coil's power drops by ≥10% (as indicated by the thermostat's power display) or heating becomes uneven, promptly replace the heating pad or heating rod (it's recommended to keep spare parts of the same specifications).

Mold preheating protocol: Before startup, follow the 'segmented preheating' sequence (room temperature → 120°C (maintain 30 minutes) → 150°C (maintain 20 minutes) → target temperature (maintain 15 minutes)) to prevent mold deformation from sudden heating and ensure uniform temperature distribution.

III. Troubleshooting and Solutions for Common Issues

Temperatures related defects in moulds	Possible reason	Optimization measures
The profile surface is rough and granular.	The mold temperature is too low, resulting in insufficient material plasticization or poor material flow due to localized low temperatures.	Increase the temperature by 3-5℃; Check if the heating element is damaged and supplement the local heating
The profile surface is yellow with burnt spots.	The mold temperature is too high, causing carbonization of wood powder; or material retention in the dead zone of the runner leads to carbonization.	Cool down by 5-8℃; polish the dead zone of the flow channel and clean the carbon deposits in the mold
Profile warping and uneven dimensional shrinkage	The temperature difference in each region of the mold is large; or the distribution of the cooling system is uneven	Adjust the zone temperature to reduce the temperature difference to ≤2℃; optimize the cooling water circuit to enhance localized cooling.
The deviation in the wall thickness of the profile is significant.	Temperature inconsistency in the mold cavity branches results in uneven material flow velocity.	The temperature of the branch with slow flow rate was increased by 2-3℃.
The mold is not discharging smoothly and is frequently clogged.	The mold temperature is too low, causing the material to cool and solidify; or the wood powder has too high moisture content (due to mixing temperature issues).	Temperature increase by 5-10℃; meanwhile, the moisture content of wood powder should be controlled at ≤3% (optimization of raw material pretreatment process)

IV. Expected Effects After Optimization

metric	Before optimization	postoptimality	amplitude of rise
Temperature fluctuation range of the mold	±5℃	±2℃	Reduce by 60%
Surface qualification rate of the profiles	85%	98%	Increase by 13 percentage points
temperature induced outage	6%	Less than 1%	Reduce by 83%
upper limit of production speed	1.5-2m/min	2.5-3m/min	Increase by 50%
service life of mould	12-18 months	24-30 months	Extend by 100%

Summary

The core of WPC profile mold temperature control lies in "precision matching + uniform heat transfer + dynamic adaptation". Leveraging the composite properties of recycled PP/PE and wood powder, the system achieves full-area temperature uniformity through "zoned temperature control + PID intelligent temperature control + structural optimization". Parameters are dynamically adjusted according to production scenarios (raw materials, speed, product) to avoid defects caused by fixed values. Regular maintenance and calibration ensure long-term temperature control accuracy. The optimized solution not only resolves common issues like surface roughness, warping, and clogging, but also enhances production efficiency and extends mold service life, providing critical support for stable operation of WPC profile production lines.

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