5 Ways to Improve Your HDPE Water Pipe Processing Quality

Date:2022-11-24 Author:hcscrew

HDPE water pipes are made by extrusion. PE80 and PE100 are the main raw materials for HDPE water pipes. The most common extruders are single-screw, but twin-screw ones are also available. HDPE water pipes are widely used in urban and rural drinking water, industrial water, and agricultural irrigation. They’re strong, age-resistant, lightweight, and easy to install.

The process of producing high-density polyethylene pipe material (PE80, PE100) involves preparing raw materials, formulas, processes, equipment, moulds, and other elements, which always result in issues and defects. What can you do to improve the quality of HDPE water pipes? Here’s what the HUACHEN screw tells you.

high-density polyethylene (PE80, PE100) water supply pipes figure 1

1. The quality requirements for high-density polyethylene (PE80, PE100) water supply pipes

The quality requirements for HDPE (PE80, PE100) water supply pipes include appearance quality, specifications, and tolerances.

Pipe appearance: The pipe’s internal and external surfaces should be clean, smooth, and free of defects like bubbles, scratches, dents, and impurities.

Physical and mechanical properties, specifications, and tolerances: HDPE pipe should comply with the GB/T13663-2000 standard for outer diameter, inner diameter wall thickness, out-of-roundness, hydrostatic strength, elongation, and longitudinal shrinkage.

2. What affects HDPE (PE80, PE100) water pipe production quality?

2.1 Raw materials and formulations

It is important to choose the right raw material and design a suitable formula for high-density polyethylene pipes based on the type and performance of the product.

2.1.1 Resin raw material selection

HDPE pipes are made with resins that have high LCL and MRS values. The right resin should be chosen based on the performance of the product and the forming process.

2.1.2 Colourants

It’s important to pick a colourant that works with resin and has a low water extraction rate. It’s also important to think about the impact it will have on molds and machinery. During the melting and moulding process of the resin, the colourant will be deposited on the mould surface. It will cause surface defects.

3.2 Production equipment

There are several machines used to make high density polyethylene water pipes (PE80, PE100): extruders, heads, vacuum sizing devices, cooling devices, haul-off machines.

3.2.1 Extruders

Extruders determine the plasticizing effect of materials by transmitting materials and providing molding pressure. Material mixing degree, temperature uniformity, and extrusion pressure stability, etc., all affect the plasticizing process. HDPE pipes have a significant impact on their intrinsic quality and glossy appearance thanks to the plasticizing process. Mixing affects how uniform HDPE pipes are at all points. Uneven extrusion temperatures can cause uneven dimensions and deformation, reducing performance. Extrusion pressure fluctuations can cause dimensional changes in the product, unstable production, and even stuck or pulled products.

At present, HDPE water supply pipe processing equipment is basically a single screw extruder. It is a barrier screw with pins on the screw head. The length to diameter ratio (L/D ratio) is 33:1 or 34:1. In the barrel feed section, there is a grooved feed barrel design, which increases the forced feed function. The purpose is to increase the feed volume. It’s possible to get a more effective plasticizing effect. As well as stabilizing production pressure, and improving discharge stability.

China also uses a conical twin-screw extruder to make HDPE double-walled corrugated pipes. It’s a specially designed conical twin screw for HDPE corrugated pipe. Commonly models are 80/156 and 92/188. It has an upgraded hardsurfacing material SKD sleeve fitted barrel to increase service life. With the conical twin screw barrel, you get more feeding capacity and better plasticizing performance.

3.2.2 Die head or mould

With the die head, molten plasticised resin is molded into the cross-sectional shape you need under pressure, which determines how big, how tolerable, how well it looks, how efficient the production process is, and how stable it is. Spiral head feed slots can cause fusion marks and affect the strength of the fusion joint if they’re not designed right. There’s a problem with the flow channel in the head, which causes uneven discharge. Wall thickness uniformity depends on the gap and concentricity of the core and mouth moulds. Currently, machine die heads are available in bracket, spiral, and sieve basket types. High density polyethylene water supply pipes primarily use spiral, sieve basket type die heads.

3.2.3 Vacuum sizing device

The vacuum sizing device makes the pipe billet into a certain roundness, determining the pipe outer diameter size and the size of the roundness. Sizing too small, bad sizing, outer diameter decreases. When the sizing set is long, the friction between the pipe and the sizing set increases, thus increasing traction power.

3.2.4 Auxiliary equipment

Cooling devices improve the appearance and mechanical properties of pipes by fixing their outer diameters. Stable traction devices conform the pipe to a specified thickness and size tolerance.

3.3 Process control

Designing and controlling extrusion parameters directly affects product quality and production efficiency. The extrusion temperature, screw speed, head pressure, vacuum, and traction speed are all important parameters for high density polyethylene (PE80, PE100) water pipes.

3.3.1 Preparation of raw materials

Ensure you get resin and the right amount of each additive. Mix everything evenly. Using drying devices to remove moisture from raw materials. Make sure that the inner and outer walls of the pipe are free of air bubbles.

3.3.2 Extrusion temperature

Extrusion temperature directly influences pipe moulding and quality. If the temperature is too low, the material will not plasticise well and the surface of the formed product will be rough. If the temperature is too high, the plastic will easily adhere to the surface of the die and sizing sleeves. This will cause scratches on the surface of the product. Therefore, it is imperative to select a suitable processing temperature.

3.3.3 Screw rotating speed

One of the most important parameters is the screw rotating speed. As the screw speed increases, the output increases, the shear rate increases, and the viscosity of the material decreases, which facilitates the plasticisation process. While increasing the speed, it is also necessary to consider the plasticization capacity of the extruder and the melt pressure range. Otherwise, the material flow rate is too fast, resulting in the material being pressed into the head before it has fully plasticized. It seriously affects the product’s quality. Therefore, the screw speed should be set low at first and gradually increased.

3.3.4 Die head pressure

In general, when the die head pressure is increased, the melt volume will be compressed. There will be a compacting of the molecular chain. Material viscosity will increase and fluidity will decrease. As a result, extrusion output will decrease. The extruded product will, however, be dense and of better quality. Too little pressure on the die head causes the billet to break easily and lose its mechanical properties.

3.3.5 Vacuum degree

Usually the larger the vacuum degree, the better the pipe billet sizing; if the vacuum degree is small, the pipe billet sizing is not good, the outer diameter of the pipe is small, and the deviation of roundness is large.

3.3.6 Traction speed

Extrusion speed and traction speed need to match. If you run the pipes too fast, the wall thickness will increase or local accumulation will occur in the tube; if you run them too slowly, the wall thickness will increase or local accumulation will occur.

Summary

A clear understanding of the quality of HDPE water pipe (PE80, PE100) will help manufacturers improve production. The selection of raw materials, the selection of forming equipment, the control of individual processes, and the timely, effective, and accurate correction of any temporary defects. We will then update the common production defects and countermeasures of HDPE pipes.

You can contact us for the latest upgrade options and the most competitive quotation for HDPE water pipe extrusion screw barrel.

About us: HUACHEN-Screw Barrel Factory

HUACHEN Screw has been an outstanding HDPE water pipe extrusion screw barrel manufacturer in Zhoushan Jintang since 1993. With many years of experience designing and processing plastic machinery replacement parts, HUACHEN Screw can provide its customers with a wide range of services, including drawing rebuilding, design, modification, and customized screw barrel. Our company has also successfully exported and supplied screw barrels to customers worldwide. >>Learn more about our company

TAGS

extrusion screw barrel, pe screw barrel, plastic pipe processing, single screw barrel

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