GREFEE -Thread Case

Created by: Felix    Position: Project Director

With the product diversity increasing, the threads of plastic products is also changing. While, the thread is basically the functional feature, mainly plays as role of connecting all parts. In the meantime, it also has a function of adjusting the tightness of assembly according to the length of thread. We will share some skills in thread products designing, manufacturing and production through our multiple successful thread cases.

Thread function:

1.Connection: in mechanical products, the plastic parts with threads can be connected easily with other products with threads. Most plastic parts need to be connected with metal or bracket products by threads. This makes the whole assembly process easier and more stable. At the same time, it also guarantees the accuracy. What’s more, this connecting method also can bear a certain degree of stretch and twisting. Also, it can ensure the reliability of connection.

The most common case is the threaded accessories on cars, which can effectively prevent the possibility of parts falling off due to vibration during vehicle operation.

2. Good sealing performance: Threads can provide good sealing performance. Common bottle caps use the principle of thread sealing. When the cap is tightened by threads, the tight fit between the threads and the squeezing effect between the cap and the bottle mouth can effectively prevent liquid or gas leakage.

3. Precise adjustment function: The most common products that embody the adjustment function of threads are also the most commonly used in our lives, such as faucets, which can accurately control the flow of water by adjusting the thread position. Another example is cameras, which can achieve fine adjustment of the lens position by rotating the threads, thereby achieving the desired photo quality.

4. Easy to repair: if any parts need to be changed, the injection parts with threads can complete removal and reinstallation easily, such as the drain valve of the washing machine, the corner joint of the water pipe, etc.

Thread type:

External thread: the processing method of external thread is relatively easy. Most plastic products with external threads can be completed with mold without many structions. Simply make the tooth shape on the front and rear mold cores of the mold. The thread on mold cores can be processed by CNC, EDM, etc. when the shapes of product need structure to produce, like the threads on from old, Haff row can be made in the front mold. When the threads is at the rear mold, The demolding of the thread can be achieved through the positioning of both sides.

Internal thread:compared to external threads, the manufacturing of the internal threads is more difficult as it is required to design complex structure on the mold. The driven method of demolding structure include hydraulic cylinder drive and hydraulic motor drive. Although these two demolding methods are relatively complex in designing and manufacturing. At the same time, corresponding power devices and control systems need to be equipped. Thus, the cost and maintenance both will increase. However, these two structures also have non-replaceable advantages. For internal threads requiring high demolding and high accuracy, this way can accurately contraol the whole demolding process.

Below are multiple threads structure products produced by GREFEE, including external and internal threads. At the same time, it also includes injection molding and threaded products using blow molding technology.

External thread demolding: This center fixed shaft has external threads and no special structure or requirements. Therefore, only the threads need to be designed on the front and rear mold cores of the mold, processed by EDM, and polished to SPI-B2 level.

product information:

Part Name：Spool Holder.Spindle

Project Name：M11202

Part Number：NXAN-01-P002

Part Size：347.7X35.5X30.1mm

Mold Size：400.0X600.0X341.0mm

Part Weight：173g

Mold Weight：525KG

Cavity/Core Material：NAK80

Cavity Number：1X2

Gate Type：Cold runner，Side gate

Design Cycle：2 days

Manufacture Cycle：25 days

Molding Cycle：65 S

Production Machine：250T（HAI TIAN）

Manufacture Date：Aug 2023

Internal thread demolding: this thread product is functional part, which is used to fix the centered fixed shaft as the screw. Therefore, it is internal thread. The internal thread works by cylinder drives the racks to move. Use a rack to drive the central gear to rotate, and then drive the central gear back to complete demolding.

product information:

Part Name：Spool Holder.Nut

Project Name：M11203

Part Number：NXAN-01-P005

Part Material：HDPE

Part Size：39.4X39.4X15.0mm

Mold Size：400.0X350.0X436.0mm

Part Weight：9g

Mold Weight：430KG

Cavity/Core Material：NAK80

Cavity Number：1X4

Gate Type：Cold runner，Sub gate

Design Cycle：3 days

Manufacture Cycle：25 days

Molding Cycle：45 S

Production Machine：160T（HAI TIAN）

Manufacture Date：Aug 2023

Internal extraction and demolding process: Firstly, the braces and the tooth spacing of the braces must be kept the same as the tooth spacing of the production line, and the main function of the braces is guidance. The oil cylinder drives the rack to move, and at the same time, the rack drives the central shaft gear 2 to rotate, and then drives the gear 3, thereby driving the main screw to achieve integrated rotation and demolding.

Processing consistency: The tooth pitch of the product must be consistent with the tooth pitch at the bottom of the gear center axis, otherwise it will damage the tooth shape of the product. Meanwhile, as each component is located between different sections of the mold, the holes between the templates must maintain concentricity.

Material selection: the rack and accessories need to use good material. The rack needs to use 45# or more higher grade material. The fixation and adjustment of rack can be bronze to reduce the friction and friction heat and prevent the rack from overheating and getting stuck.

Precise adjustment: there are totally 20 adjustment detents at the bottom of the center axis guided braces. Rotate 3 degrees to adjust once, and adjust the tooth height position to 0.02mm, which can achieve precise adjustment.

Core Area Cooling: Although the center shaft sleeve is made of bronze, which effectively reduces heat generated by friction in the main shaft, the primary heat source originates from the threaded shape at the top of the center shaft. This area is in direct contact with the plastic material, making it the focal point of heat generation. Therefore, to ensure dimensional stability of the product, reduce cooling time, and improve production efficiency, cooling the core area is essential. In our design, we utilize a spray tube system to direct cooling water to the heat-concentrated core area, enabling rapid cooling of the core region.

Details of the internal structure of the thread mold

Grefee has customers that are R&D companies. Our suggestion is that if the product market is niche market or the product have not received good feedback, or the mold manufacturing cost is not enough to cover the complex mold structure. It is better to adopt manual insert method to achieve the batch production of products with threads.

Manual insert, thread demoulding case 1: Quantity 1000 sets. Compared with mechanical drive, manual thread stripping has a simple and clear structure, low manufacturing cost, high maintainability, and is also suitable for small batch production.

Thread details, smooth inside and clear tooth shape

Manual insert, thread demolding case 2: Quantity 500 pieces, compared with cylinder drive, mold cost is reduced by 40%, and manufacturing cycle is shortened by 10 days.

Thread product: below molding

The most common thread product produced in below molding is the beverage bottle. The bottle mold design is similar as the injection molding products with external structure. No extra structure design with only requiring threads on the front and read molds.

GREFEE Below molding mold

GREFEE blow molding products, environmentally friendly, biodegradable materials

GREFEE produced multiple thread products. Our engineer have rich experience in this type of product. Our team can provide valuable advice in processing and production method according to the shape, material, structure and requirement of product, as well as the accuracy requirement of threads. Grefee always strive for the best quality regardless of how complex and different the process and production methods.