The Working Principle of The Hauler in An Extruder

In an extruder production line, the hauler is a key piece of equipment connecting the extruder to subsequent devices (such as cooling water tanks, cutting units, and winders). Its core function is to stably pull the continuous products (e.g., pipes, profiles, sheets, cables, etc.) extruded from the extruder die, and to impart a certain traction tension and speed to the products, ensuring stable dimensions and regular shapes of the products.

Working Principle of the Hauler

Power Transmission and Speed Control

A hauler usually consists of a drive motor (mostly a variable-frequency motor or servo motor), a reduction mechanism, and traction wheels (or traction rollers). The motor drives the traction wheels to rotate through the reduction mechanism, and its rotational speed can be precisely adjusted via a frequency converter or servo system to match the extrusion speed of the extruder — the traction speed must maintain a dynamic balance with the extrusion speed:

If the traction speed is slightly faster than the extrusion speed, it can apply appropriate tension to the product, preventing the product from sagging or deforming due to its own weight (especially applicable to pipes, cables, etc.).

If the speeds do not match (either too fast or too slow), it will cause dimensional deviations in the product (such as uneven wall thickness of pipes, dimensional over-tolerance of profiles) or surface defects (such as wrinkles, over-stretching).

Clamping and Traction Action

Traction wheels are usually arranged in upper and lower pairs (or in combinations of multiple roller sets). The product passes between the traction wheels, and traction is achieved through the friction between the wheel surfaces and the product surface. Some haulers can adjust the clamping force of the traction wheels via air cylinders or mechanical structures:

For rigid products (such as PVC profiles), the clamping force must be moderate to avoid damaging the surface.

For flexible products (such as plastic hoses, films), the clamping force needs to be precisely controlled to prevent deformation or over-stretching.

Coordinated Control with the Extruder

In modern extruder production lines, the hauler and the extruder achieve linkage control through a PLC or host computer:

The screw speed of the extruder determines the basic extrusion volume, and the hauler speed is adjusted in real-time according to the extrusion volume (the speed ratio can be preset) to ensure the stable linear speed of the product.

Some high-end systems combine feedback from product dimension detection sensors (such as laser diameter gauges) to automatically fine-tune the traction speed, compensating for fluctuations in the extrusion process (such as changes in extrusion volume caused by uneven melting of raw materials), and ultimately ensuring product dimension accuracy.

Summary of Core Functions

The hauler is the "speed and tension regulator" of the extruder production line. Through stable traction action and speed matching with the extruder, it "smoothly draws out" the extruded continuous products from the die and provides stable conveying power for subsequent processes such as cooling, shaping, and cutting. It is key equipment to ensure the quality of extruded products (dimensional accuracy, surface flatness).