What should I do if the thimble of the injection molding machine is not returned?

In the process of injection molding production, the thimble system of the injection molding machine plays a vital role, which is responsible for ejecting the molded plastic products from the mold.However, sometimes the operator will encounter the tricky situation of the thimble not returning, which will not only delay the production progress, but improper handling may also damage the mold and equipment.Don't worry, let's analyze the causes and solutions of this problem in depth.
1. Check the hydraulic and pneumatic systems
For injection molding machines that rely on hydraulic pressure to drive the thimble, it is first necessary to check whether the level of the hydraulic oil is normal.If the hydraulic oil is insufficient, the thimble cylinder may not be able to obtain sufficient power and cannot be returned.It can be observed through the liquid level gauge on the hydraulic fuel tank. If the liquid level is lower than the minimum scale, the hydraulic oil that meets the requirements of the equipment should be replenished in time.
The hydraulic pump is also a key component, it is like a heart to deliver power to the entire hydraulic system.If the hydraulic pump fails, such as wear and tear of the pump body, internal leakage, etc., it will cause insufficient output pressure and cause the thimble to move abnormally.At this time, professional maintenance personnel need to use professional tools, such as pressure testers, to test the output pressure of the hydraulic pump. If the pressure is lower than the standard value, the hydraulic pump should be repaired or replaced.
Some injection molding machines use air pressure to assist the thimble action. At this time, it is necessary to check whether the air source is supplied normally and whether the trachea is ruptured or leaking.You can carefully check along the trachea line and apply soapy water to the suspected air leakage area. If there are air bubbles, it indicates that there is air leakage here. The trachea needs to be replaced or the joint repaired in time.At the same time, check the air pressure regulating valve to ensure that the air pressure setting value meets the requirements for the return of the thimble.
2. Troubleshooting the electrical control system
The action of the thimble is instructed by the electrical control system. First, check whether the relay that controls the thimble is working properly.The relay is equivalent to a “switch”. If it fails, it may not be able to pass the return command to the thimble cylinder.The normally open and normally closed contacts of the relay can be measured by a multimeter to see if its on-off condition is logical in the state of power-on and power-off. If it is abnormal, the relay needs to be replaced.
The limit switch is used to control the stroke of the thimble. If it fails, misjudging the position of the thimble will cause the system to believe that the thimble has not yet reached the return condition, so as to continue to power the thimble cylinder.Carefully check whether the installation position of the limit switch is loose, and whether the sensing head is covered by debris such as oil, plastic debris, etc., which affects the sensing accuracy.If there is a problem, clean or re-fix the limit switch, and replace it with a new one if necessary.
Aging, short-circuiting or disconnection of electrical circuits may also cause problems.Check step by step along the thimble control line to see if the outer skin of the wire is damaged and the joint is loose.For damaged wires, insulating tape should be used to bandage and repair them; loose joints should be re-fastened to ensure stable transmission of electrical signals.
3. Check the mechanical structure
The connection between the thimble and the thimble plate may be loose or stuck.Frequent reciprocating movement for a long time may loose the screws in the connecting parts, causing the thimble to fail to follow the thimble plate back.After stopping, open the mold guard plate, check one by one with a wrench and tighten the connecting screws.If the thimble is found to be bent and deformed, this will increase the resistance to movement and even get stuck in the mold hole. At this time, the curved thimble needs to be removed and straightened or replaced.
Wear or strain on the thimble hole inside the mold will cause the thimble to be subjected to additional friction during movement.This kind of wear may be caused by long-term use, poor mold material, or improper injection molding process (such as excessive ejection force).Minor wear can be repaired by sanding and polishing the thimble hole; if the wear is serious, you need to consider reprocessing the thimble hole or replacing the mold insert to ensure smooth movement of the thimble.
Fourth, consider the factors of injection molding process
The cooling time of the injection molded product in the mold is too long, which will cause the plastic product to shrink and hold the thimble tightly, making it difficult to return the thimble.The cooling time can be appropriately shortened, but care should be taken to ensure product quality and avoid deformation due to insufficient cooling.Through the trial production of different batches of products, combined with the size, thickness and other factors of the product, the cooling time parameters are gradually optimized.
The setting of the thimble output is too large, which may not only damage the product, but also make the thimble face greater resistance when it is returned.Check the process parameter settings of the injection molding machine and adjust the ejector output to a reasonable range. You can usually refer to the successful process cases of similar products and fine-tune them in combination with your own molds and product characteristics.
In short, when the thimble of the injection molding machine does not return, the operator should calmly deal with it, investigate in accordance with the order of hydraulic and pneumatic pressure, electrical control, mechanical structure, and injection molding process, and identify the root cause of the problem and solve it in time.In daily production, we must also do a good job of equipment maintenance, regularly inspect various system components, prevent the occurrence of such problems, and ensure the efficient and stable operation of injection molding production.