Overview
At 42 C ambient and 85 percent relative humidity, two things go wrong that do not happen in a temperate plant. HDPE compound takes up moisture between the dryer and the hopper, and the foam cream time shortens until the material skins before it has filled the annulus. Neither problem is solved by running the same line harder; both are solved by changing the utility side of the machine. This buyer has usually already run a line bought from a temperate supplier and is replacing it, or has been warned by a neighbouring plant that bought one.
Process Flow
Casing is extruded with the hopper fed from a dehumidified dryer and the calibration circuit on chilled water, so the wall sets at the same rate it would in a temperate plant. Steel is inserted, the ends are plugged, and foam is injected from temperature conditioned day tanks before the pipe goes to a shaded curing rack.
Key Configuration
The HDPE hopper is fed from a dehumidified dryer sized for the ambient rather than for the resin, and the calibration and cooling circuit runs on chilled water with a closed loop and an air-cooled chiller sized for 45 C ambient. Across DN125-450 mm the spray cooling length is set by the heaviest wall in the band, so the line does not slow down for one thick section. The foam machine is fitted with temperature-conditioned day tanks and insulated lines, because a polyol at 40 C reacts differently from one at 22 C and the shot weight no longer predicts the density.
Applications
District heating is rare in these markets, so the pipe is usually for district cooling, oilfield gathering, industrial hot water or export to a temperate project. The line is therefore often specified with a wider diameter mix and a lower sustained output than a European plant of the same size.
Standards
GB/T 29047 or ASTM C591 depending on the destination, with EN 253 where the end client is European. Whatever the standard, the acceptance test is run at site ambient, and we state the density and closed cell figures the line will hold at 40 C rather than quoting the temperate figure. On the DN125-450 mm line the acceptance standard is agreed in writing before manufacture, and the test schedule follows from it.
Service & Support
The DN125-450 mm line is commissioned over 15 to 25 days by two engineers, with handover tied to a production batch rather than to a signature. Operators on the DN125-450 mm line learn calibration and wall control before foam density and bond, since a casing fault cannot be corrected downstream.
Why Huashida
We have supplied lines that operate in Central Asia, the Middle East and Africa, and we size the utility package for the site rather than for Qingdao. The chiller, the dryer and the day tank conditioning are quoted as part of the line, not left to the buyer to discover.
| Item |
Specification |
| Model / Type |
Vacuum sizing and pipe-in-pipe foaming pre-insulated pipe production line, complete line |
| Pipe Diameter Range |
DN125-450 mm |
| Process |
Casing extrusion, polyurethane foaming, end finishing and testing in one continuous flow |
| Insulation Layer |
Rigid polyurethane foam, density 60 to 80 kg/m³, closed cell content 88% or above |
| Thermal Conductivity |
0.033 W/m·K or lower at 50 °C mean temperature |
| Service Temperature |
up to 120 °C continuous, 140 °C peak |
| Line Output |
260 m² of insulated surface per hour at nominal wall |
| Annual Capacity |
sized against the buyer's kilometre target, not a catalogue figure |
| Casing Extruder |
single screw 120 mm, 33:1 L/D |
| Extruder Output |
500 kg/h of HDPE compound |
| Casing Wall Thickness |
4.0 to 6.0 mm, set by diameter and burial load |
| Vacuum Calibration |
stainless calibration sleeve, vacuum held at -0.04 to -0.06 MPa, water ring pump |
| Cooling |
9 m vacuum tank plus spray cooling, water recirculated |
| Haul Off Speed |
1.5 to 2.5 m/min, set by casing wall and diameter |
| Foam Injection |
high pressure machine, 60 kg/min, impingement mixing at 150 to 200 bar |
| Centring |
steel pipe centred inside the casing before injection, spacer set per diameter |
| Curing |
rack curing 24 hours minimum before end finishing |
| Control System |
Industrial PLC and HMI, recipe per diameter, batch record per shift |
| Operators per Shift |
4 to 6 |
| Installed Power |
calculated per configuration, typically 380 to 620 kW |
| Workshop Requirement |
layout drawing issued with the quotation |
| Commissioning |
site supervision by 2 engineers, 15 to 25 days |
| Documentation |
English layout, foundation, electrical, PID and operation manuals |
| Warranty |
12 months machine, 24 months drive train |
| Certification |
ISO 9001 quality system; CE option for EU delivery |
Technical Prameters:
| |
PE-365/760 |
PE-420/960 |
PE-850/1372 |
PE-960/1680 |
| Main extruder |
SJ-90/33 |
SJ-90/33 |
SJ-120/33 |
SJ-150/33 |
| Pipe diameter (mm) |
Φ365-960 |
Φ420-960 |
Φ850-1372 |
Φ960-1680 |
| capacity (kg/h) |
550-700 |
550-700 |
700-900 |
800-1200 |
| Installed power (kw) |
360 |
380 |
440 |
580 |
| Length (m) |
35 |
36 |
40 |
48 |
Features
The HDPE dryer is sized for ambient humidity rather than resin grade, because at 85 percent RH a standard dryer cannot hold the dew point the extrusion needs.
Chilled water on the calibration circuit with an air-cooled chiller rated for 45 C ambient, so the casing sets at the same rate it would in a temperate plant.
Foam day tanks and transfer lines are temperature conditioned, because polyol at 40 C changes cream time and shot weight stops predicting density.
Density and closed cell figures are quoted at site ambient, not at 23 C, so the acceptance test matches the number in the offer.
Across DN125-450 mm the casing is calibrated under vacuum rather than sized by draw down, so the outside diameter holds along the full length.
HDPE Jacket Process Flow:
- Vacuum Feeding of PE Granules: The raw PE granules are automatically fed into the system via vacuum suction.
- Hot Air Drying: The granules are dried using hot air to remove moisture, ensuring optimal extrusion quality.
- Extrusion Plasticizing: The dried granules are plasticized through the extruder, heated and mixed to form a molten plastic mass.
- Mold Shaping: The molten plastic is shaped into the desired pipe profile by passing through the extrusion die.
- Vacuum Sizing: The pipe is then subjected to vacuum sizing, adjusting its dimensions to precise specifications.
- Water Cooling: The pipe is cooled rapidly by immersion in a water tank to solidify its shape and structure.
- Pulling Out: The solidified pipe is pulled out of the cooling tank at a controlled speed.
- Cutting: The pipe is cut to the desired length using a precision cutting machine.
- Carrier Laying-off: The cut pipes are then neatly laid off onto a carrier for further handling or packaging
Composition of Equipments:
- Hopper Dryer
- Single Screw Extruder
- Extrusion Mould Die
- Head Bracket
- Vacuum Calibration Device
- Water Cooling Tank
- Haul-off Unit
- Planetary Cutting Machine
- Pipe Bracket
- Loader
- PLC (Programmable Logic Controller)
The production steps of the insulation layer for a pre-insulated pipe, specifically focusing on the polyurethane (PU) foam insulation, are outlined below in detail:
- Formation of the Casing Structure:
- The steel pipe is first inserted into the high-density polyethylene (HDPE) outer protection pipe, creating a casing structure.
- Supports are evenly arranged in the annular space between the steel pipe and the HDPE outer pipe to maintain a uniform distance and prevent the two pipes from touching directly.
- The two ends of the casing are sealed with flanges to ensure that the polyurethane foaming material will be contained within the space during the injection process.
- Preparation of the Steel Pipe Surface:
- Prior to the injection of the insulation material, the surface of the steel pipe undergoes pre-treatment such as shot blasting or blast cleaning. This step removes any impurities, rust, or scale, providing a clean and suitable surface for optimal adhesion of the polyurethane insulation.
- Additionally, corona treatment of the polyethylene pipe shell's surface may also be performed to enhance its adhesion properties.
- Injection of Polyurethane Foaming Material:
- The casing structure is hoisted onto a foaming platform specifically designed for this purpose.
- A high-pressure foaming machine is used to inject the polyurethane foaming material into the casing. The material expands and fills the entire annular space between the steel pipe and the HDPE outer pipe.
---FAQ---
Q: Can a standard line be installed in a hot climate?
A: It can be installed, but it will not hold density or dimension without a chilled water circuit and a properly sized dryer. Those two items are the difference, and they are cheaper to specify at order than to retrofit.
Q: Does the foam formulation change?
A: The supplier's formulation window shifts, and we ask for the foam system's temperature sensitivity before we set the day tank temperature. We do not formulate foam ourselves and we do not pretend to.
Q: What decides the casing outside diameter tolerance?
A: On the DN125-450 mm line the sleeve bore carries the shrinkage allowance and the vacuum keeps the tube pressed to it until the wall is rigid.
Q: How is the steel pipe kept concentric inside the casing?
A: At the DN125-450 mm size the spacers are cut to the annulus and fitted at both ends and along the length before the plug goes on.
Q: Why is rack curing specified rather than immediate trimming?
A: On the DN125-450 mm line foam is rack cured because a torn end face is where water enters, and 24 hours is the minimum.
Q: What foam density does the line hold?
A: The DN125-450 mm line controls density through shot weight because the annulus volume is fixed by the casing and the pipe.
Q: What is the delivery time for a complete line?
A: Across DN125-450 mm the manufacturing window is 90 to 120 days from deposit, with transit added afterwards.
Q: How many containers does the line need?
A: Across DN125-450 mm the line travels in six to eight 40HQ containers, depending on curing equipment size.
Your message must be between 20-3,000 characters!
