In the plastic mold design industry, there are many types of mold structures. For general mold designers, ordinary sliders and inclined roof structures are familiar to everyone, and they can be designed. But for some special and typical mold structures , there will be a feeling of nowhere to start. Today I will explain to you the design points of the screw thread mold structure. I hope it will inspire the majority of university mold design enthusiasts.
There are two types of threads for plastic products: external threads and internal threads. For external threads with low precision, Huff blocks are generally used to form them, while internal threads mostly require thread unloading devices. Here is a brief introduction to the demoulding method of internal threads and the introduction of gears:
1. According to the action mode:
①The threaded core rotates, and the push plate pushes the product out;
②The threaded core rotates and retreats at the same time, and the product is naturally separated.
2. According to the driving mode:
There are generally two types of tooth extraction molds: one is that the cylinder drives the rack to move, and the other is the motor drives the chain to move.
The oil cylinder drives the rack to twitch
The motor drives the chain to twitch
3. The twitching principle of the thread mold
The teeth pitch of braces and braces must be the same as that of the product, and the braces play a guiding role. The oil cylinder drives the rack 1 to move—the rack 1 drives the gears 2 and 3 to rotate—the gear 3 drives the gear 4 to rotate—the gear 4 and the screw are positioned as one and rotate together, as shown in the figure below.
picture
4. When designing the thread mold, it is necessary to know the tooth pitch. The definition of the thread pitch is the distance that the thread moves in the vertical direction after one rotation, as shown in the figure below.
picture
5. The tooth pitch at the glue position of the product must be the same as that of the screw, otherwise the product will be easily scratched.
6. How to call gears and racks: Hu Bo plug-in can call gears and racks. According to the product ranking in our mold, we can determine the indexing circle required by our gears. Then the gears have the same modulus, and the gears can be called out. As shown below.
7. The calling method of the rack: the calling rule of using Hu Bo’s external rack is also to follow the formula (modulus × number of teeth = diameter of the pitch circle).
8. If you want to design a thread mold, you must understand the relationship between the rack and the gear. The following figure shows the relationship between the rack and the gear and the relationship between each gear.
9. Calculation of the number of turns required for the product and the length of the rack: if the number of turns of the tooth is 5, then the screw needs at least 5 turns to withdraw. The screw is withdrawn for 6 turns, and then the rack twitching distance can be calculated in reverse according to the previous page.
