Injection molding machines come with several components and features that play an important function in plastic part manufacturing. The valve gates make up one of the important parts of this machine. Moreover, the valve gate injection molding technique is a unique and effective one and well-suited for large-volume manufacturing.
Also, these are hot runner gates that feature a special gate pin or valve. The value gate’s main function is to ensure the proper plastic flow inside the mold. Here, we’ll be explaining everything that relates to valve gating for injection molding. These include their types, key design considerations, pros and cons.
Why is Injection Molding Gate Design Necessary?
Injection mold designs have a direct effect on the plastic mold’s outcome. When these gates are well designed, they manage the direction and volume of melted plastic flowing inside the mold. This function ensures that the plastic doesn’t flow towards the nozzle rather than into the mold.
Furthermore, the gate design allows the melted plastic to touch all areas of the mold before it cools. Therefore, it ensures that the plastic doesn’t harden untimely and unevenly. It also protects the plastic parts from deformations like stress fractures or breaks.
In addition, injection molding gates generate heat through dissipation. Appropriate gate designs help increase the temperature of the polymer, thereby preventing the development of weld lines and flow marks. With a more comprehensive injection molding process, product designers and manufacturers can eliminate runners, thereby ensuring an easy post-processing treatment.
What are Valve Gates for Injection Molding?
Valve gates are mainly useful for hot runner systems. Its main objective is to manage the plastic’s melt flow into the mold. It achieves this by controlling the shut-off time, preventing the two flow fronts from colliding at the center.
To lock the gate, the nozzle makes use of a valve stem. Through mechanical force, it slides itself forward, sealing the gate in the process. Also, utilizing mechanical shut-off pins, valve gate systems regulate the plastic flow inside the cavity of the heated mold, thereby ensuring the opening and closing of the hot runner nozzles at the tip.
Furthermore, the valve-controlled system stays closed in the course of mold opening and part ejection, which gets rid of melt decompression of the thermal gated systems. It is so because the gate seal remains robust when the hot runner system’s manifold is under pressure.
Modifying valve gates is a difficult task; this makes them more effective compared to other gate types. For this system, valve gates block the exit, ensuring that the plastic does not flow out. This makes the molding process very reliable. Note that the stem may create a little depression at the center of the gate as it protrudes through it.
What are the Types of Valve Gates for Injection Molding?
In this section, we will be considering the different types of valve gates as well as their applications.
- Solid Wedge Valves
- Parallel Slide Valves
- Flexible Wedge Valves
- Bellow Seal Valves
- Split Wedge Valves
- Non-rising Stem Valves
- Rising Stem Valve Gate with Outside Screw
Solid Wedge Valves
This valve gate features a solid disk that attaches to the stem and opens and closes the value through an up-and-down movement. Because they are very durable, they play a significant role in high-pressure applications.
Furthermore, these gates are very efficient and hardly leak compared to other types. Moreover, operating them is very difficult compared to other types of gates because to close and open, they need more torque.
Parallel Slide Valves
The parallel slide valve gate includes a disk that can slide in an upward and downward movement, thereby ensuring that opening and closing the valve is easy. This is only suitable for low-pressure applications because it can resist high pressures.
Flexible Wedge Valves
Flexible wedge valve gates have two hinges that connect the disk to the step. This allows it to move from one side to the other, up and down, as well as ensuring that it opens and closes easily. Furthermore, these valve gating for injection molding has higher pressures compared to other valve types. This is why they are useful in high-pressure applications.
Bellow Seal Valves
This valve gating mold has a quick response to low-pressure variations. Furthermore, it has a flexible construction, which permits greater temperature and pressure variations. The bellow seal valve gate provides effective solutions because you can implement it with advanced technologies to ensure that users can determine the rates of leakage.
Split Wedge Valves
A split wedge valve gate is used when there is a need to regulate the flow of particles and fluids. This is possible by using a system with a wedge shape and having two bolts that guide the sides of the valve’s body, allowing it free passage via the seat ring.
Furthermore, with consistent pressure, it can split through tough materials like metals, molten resin, and oils. With their great mechanical design, split wedges provide more safety towards immediate changes in the flow rate. This valve gating solution is best used in construction sites and petrochemical plants.
Non-rising Stem Valves
The non-rising stem valve gate is also called the insider screw valve, which is usually threaded inside the gate. Here, both the stem and hand wheel move together. Also, its stem doesn’t rise and fall, with the flow medium staying in line with the stem
Rising Stem Valve Gate with Outside Screw
This type of valve gate is also called the Outside steam and York type. Its stem rises whenever you open the valve and it closes whenever it lowers. This reveals the valve gate’s position. Also, the stem threads and the flow media aren’t in contact.
What’s Sequential Valve Gate (SVG) Controllers?
The sequential valve gate controllers play a vital role in the valve gate system. Let’s discuss how this technology works.
The valve gate system requires the use of multiple distinct gates. Each of these distinct gates needs to be opened independently. This is where the sequential controller comes into play. It works by opening each group of gates independently.
There are two different methods of achieving this. The first method requires one valve gate controller for all the gates. Here, all gates open and close at the same time. On the other hand, the second method requires the use of a sequential valve gate controller which opens each gate or group of gates independently.
Furthermore, each gate or group of gates needs a separate controller. For instance, a machine could have twelve valve gates which are grouped into four groups of three of them each. To open three gates at a time, you will need four independent controllers. Sequential gating requires more controllers.
A sequential valve gate is a much better method of filling a mold as it is efficient and quick. Also, this technique prevents the formation of gas bubbles, thereby improving dimensional stability. In addition, this technology has a shorter molding cycle time which results in increased production and better flexibility.
A sequential gating valve gate system fills up the mold’s fill valves from the center. This technique allows uniform distribution of material in the cavity, making it a much better option.
The sequential fill valve-controlled system doesn’t only lower costs and cycle time. Consequently, it also prevents blemishes from forming on injection molded parts. This system also improves the efficiency of the valve gate injection molding process.
Key Design Considerations for Valve Gate in Injection Molding
There are various types of injection molding valve gates, with each having different techniques for molding various components. Therefore, you need to consider some important factors when choosing the best method to use.
Valve Gate Placement
Gates are usually placed in different ways. Therefore, it could be harder to separate as gates due to their placement method. Also, their order can cause deformities and lines to form in molded section parts. Therefore, you need to be careful of how you place gates on the design of the mold.
Valve Gate Size
You must ensure the size of the valve gate, which allows proper shearing anytime the mold goes through the machine. This is because the gate dimensions must enable proper filling of the mold. Gates with smaller sizes have high shear heating rates. If the size is too big or too large, they can increase flow pressure. Therefore, it is important to choose gates with the perfect size for the best outcome.
Part Shape and Finish
The design of each valve gate injection molding is created in such a way that it can mold parts with various shapes. In the end, these gates achieve a particular finish. For example, the design of a cashew gate can work in smaller parts and provide an even and smooth surface finish.
This is why you must first determine the ideal gate that works with your parts and the desired surface finish. Also, you may need to check out for certain factors like undercuts. Undercuts can be a major hindrance to the ejection of finished plastic parts.
How Gate Location Impacts the Quality of Injection Molding
An Injection molding gate region is a tiny opening, usually found between the cavity and the runner. Although the gate design deals with details like sizing the injection molding gate, the location determines if the process will be successful and the quality of the completed parts.
In addition, the location of the gate helps to reduce or avert possible problems relating to errors in gate size. Placing the gates wrongly could result in molding defects like weak spots, uneven thickness, fractures, etc. Choosing the best possible location for the gate ensures that you utilize the right gate quality and size.
What are the Pros and Cons of Valve Gates?
Pros of Valve Gates
Low material waste
Material waste increases the cost of production, particularly in large production runs that require the use of more materials. Therefore, Valve gates are one of the best approaches to lowering material waste.
There is less leakage of material during production. This is because valve gate systems employ an open-and-close technique during injection. A hot runner mold lacks a gate shutoff. On the other hand, cold runners have both a runner system and a large sprue.
Better regulation
With the valve gating systems you can have better control over the whole valve-gated process involved in injection molding. These systems allow you to regulate the amount of material you put into the mold. Therefore, this gives you better control over certain parameters like time and amount of material needed for making a part.
Reduced injection molding defects
The valve gating system can help to reduce injection molding defects since it enables you to have control over factors like material flow and temperature. These factors have a great impact on the injection molding process. A valve gate ensures parts are created without issues like sinking.
Cons of Valve Gates
Up-front costs
If your desired project requires the creation of small parts, valve gates aren’t a good approach as they will end up incurring a substantial cost. The single-valve gate system is very pricey. Therefore, it isn’t a cost-effective approach for simpler projects.
High maintenance and costly repairs
Since valve gate systems cost a fortune, their maintenance and repair cost a lot too. They have complex structures and parts like heating elements and many moving parts. Therefore, they require care and a good maintenance system which could be costly.
Considerations for the Best Valve Gate
Valve gate systems are more expensive compared to other gate systems. Therefore, it is advisable to integrate them for applications that require to maintain their desired performances. Also, you get better control and versatility. Therefore it is crucial you consider certain factors before choosing the best valve gate for your injection molding project. These factors include
- The gate’s position and placement in the injection molding machine
- The gate’s ability to secure the molten plastic within the mold.
- The expected production capacity
- The valve gate’s compatibility with your nozzle
Conclusion
We hope that the article has given you vast knowledge regarding the valve gate injection molding process. Are you interested in injection molding and gated molds? You wish to get custom plastic prototypes as well as end-use production parts? RapidDirect is an expert in providing low-volume, cost-effective, and high-quality injection molding solutions utilizing valve gate technology. Please request a free injection molding quote with us today and we will reach out to you to discuss your project needs.
Frequently Asked Questions
Open gate systems describe a system that deals with the injection of melted plastic directly into the cavity. This gives a molded item some tiny marks. However, for valve gate systems, the valve pins control the opening and closing of the hot runner nozzle ensuring that the melted plastic doesn’t drool or string at the tip.
Most times, all you need to do is turn the valve gate in an anticlockwise direction to open it, then to close it, turn it in the clockwise direction. Normally, these directions are marked somewhere on the valve’s outer body or the handwheel.
Valve gates may not close completely if there are sediments built into the body of the valve. Also, it could be caused by a damaged stem. All you have to do is check if the stem area of the valve is damaged. Most times, this damage comes from corrosion and wear.
To inspect a valve gate, open its gate plate and allow the valve’s pressure to rise to the required test value. Next, close the plate and then take out the valve gate to see if there is a leakage coming from the gate plate sealing.
