Automotive Radiator Coolant Hose Extrusion Process Analysis

Basic Principles and Equipment of Extrusion
Extrusion is to use the rotation of the screw of the extruder to push the rubber compound forward in the barrel, and use the heating device to heat and soften the rubber compound to obtain good plasticity and fluidity. When the rubber compound reaches the end of the screw and is extruded through a die of a specific shape, due to the limitation of the die and the extrusion pressure, the rubber compound is given a shape consistent with the die outlet, thus forming a hose blank with a certain cross-sectional shape and size. ​
The core equipment of extrusion is the extruder, which is mainly composed of a hopper, a barrel, a screw, a heating system and a transmission device. The hopper is used to store the raw materials of the rubber compound and continuously feed the material for the extrusion process; the barrel is the place where the rubber compound is heated and plasticized, and there is a heating device inside to heat the rubber compound to the appropriate processing temperature; the screw rotates in the barrel, and the screw is used to transport, compact, melt and homogenize the rubber compound through the thread structure. The screw speed, aspect ratio and other parameters have an important impact on the extrusion process and product quality; the heating system accurately controls the temperature of each section of the barrel to ensure that the rubber compound reaches the ideal processing state at different stages; the transmission device provides power for the screw to ensure its stable rotation. ​
In addition to the extruder, a traction device and a cooling device are also required. After the Automotive Radiator Coolant Hose billet is extruded, the traction device pulls it out of the mold at an appropriate speed to prevent the hose billet from sagging and deforming due to its own weight, and at the same time controls the extrusion speed and length of the hose; the cooling device generally uses air cooling or water cooling to quickly reduce the temperature of the hose billet after extrusion, so that it can be quickly shaped to prevent the shape change or surface quality degradation due to excessive temperature.​
Key operating points in the extrusion molding process​
During the extrusion molding process, temperature, pressure and extrusion speed are three key parameters that need to be strictly controlled. They are interrelated and affect each other, and directly determine the quality of the hose blank. ​
Temperature control is the primary task of extrusion molding. Different sections of the barrel need to be set at different temperatures to achieve gradual heating and plasticization of the rubber compound. The temperature of the initial section is low, and its main function is to compact and convey the rubber compound; the temperature of the middle section is high, which promotes the melting of the rubber compound; and the temperature of the section close to the mold needs to be appropriately reduced to avoid excessive softening of the rubber compound in the mold, which affects the accuracy of the extruded shape. In addition, the mold temperature is also very important. The appropriate mold temperature helps the rubber compound to be extruded smoothly and reduce surface defects such as bubbles and dents. If the temperature is too high, the rubber compound will become too viscous and too fluid, resulting in unstable dimensions and rough surface of the extruded hose blank; if the temperature is too low, the rubber compound is not fully plasticized, which is prone to problems such as extrusion difficulties and surface cracks. ​
Pressure is also indispensable for extrusion molding. The pressure generated by the rotation of the screw pushes the rubber compound forward, so that the rubber compound is fully compacted and plasticized in the barrel, and is smoothly extruded through the mold. The extrusion pressure must be kept stable and moderate. If the pressure is insufficient, the rubber compound cannot fully fill the mold cavity, which will cause defects such as uneven wall thickness and internal gaps in the hose blank; if the pressure is too high, it may cause damage to the mold, increase the energy consumption of the equipment, and may also cause the rubber compound to degrade under high temperature and high pressure, affecting the physical properties of the hose. ​
The control of the extrusion speed should not be ignored. The reasonable extrusion speed should match the screw speed and the traction speed. If the extrusion speed is too fast, the rubber compound stays in the barrel for too short a time, the plasticization is not sufficient, and the traction device may not be able to pull the hose blank out in time, resulting in hose accumulation and deformation; if the extrusion speed is too slow, it will reduce production efficiency, and the rubber compound may stay in the barrel for too long, causing over-vulcanization and other phenomena, affecting product quality. The operator needs to determine the optimal extrusion speed through repeated debugging based on the characteristics of the rubber compound, mold specifications and equipment performance.​
The influence of extrusion molding on the quality of coolant hoses ​
The quality of the extrusion molding process is directly related to the quality and performance of the coolant hose. If the wall thickness uniformity of the hose blank after molding is poor, the thin parts are prone to rupture due to the inability to withstand the coolant pressure during subsequent use, causing coolant leakage and affecting the cooling effect of the engine; the rough surface will increase the coolant flow resistance, reduce the cooling efficiency, and may also cause premature damage to the hose due to stress concentration. ​
Improper control of temperature, pressure and extrusion speed during the extrusion molding process may also cause defects such as pores and cracks inside the hose blank, seriously weakening the strength and sealing performance of the hose. These defects will gradually expand under the influence of long-term scouring of coolant and the complex environment of the engine compartment, eventually leading to hose failure and threatening the normal operation of the automobile engine. Therefore, strictly controlling the extrusion molding process and ensuring the quality of the hose blank are the key to producing high-quality coolant hoses. ​
Synergy between extrusion molding and other process links ​
Extrusion molding is not an isolated production link. It is closely connected and coordinated with other process links in the manufacture of coolant hoses. Before extrusion molding, the preparation quality of the rubber compound directly affects the smooth progress of the extrusion process and the quality of the product. High-quality compound rubber should be evenly mixed and have good plasticity, otherwise problems such as extrusion difficulties and rough product surface will occur. After extrusion molding, the hose blank needs to undergo reinforcement layer processing (such as winding fiber braid or wire braid layer), vulcanization treatment and other processes to further improve its strength, temperature resistance and corrosion resistance. The reinforcement layer processing needs to be carried out when the hose blank has a suitable softness and shape to ensure that the reinforcement material fits tightly with the hose blank; the vulcanization treatment needs to accurately control the temperature and time according to the state of the hose blank after extrusion molding, so that the rubber molecules are fully cross-linked and achieve ideal physical properties. Each process link is closely linked, and only by coordinated cooperation can an excellent performance automotive radiator coolant hose be produced. ​