28mm injection moulding caps

In addition, our company has established cooperative relationships with plastic raw material suppliers, printing manufacturers, etc. to ensure the supply of raw materials and printing quality. Through our rich experience and perfect supply chain, our company can provide customers with high-quality customized 28mm injection moulding caps  moulding products to meet their specific needs. At the same time, we have 10 years of professional foreign trade service experience, understand the foreign trade process, and better serve our customers. For 28mm injection moulding caps  moulding products, we can make corresponding plastic parts, which is mainly done through injection molds.

The molding process for a 28mm injection-molded cap is a sophisticated system involving molds, equipment, materials, and processes:

Step-by-step Analysis of the Injection Molding Process

Raw Material Preparation and Pretreatment:

Common Materials: 28mm injection-molded caps primarily use PP (polypropylene) or PE (polyethylene). These materials are cost-effective and meet food contact standards.

Drying: If the material has a high moisture content (such as some PE materials), it is typically dried at 55°C for approximately two hours to prevent bubbles or silver streaks after molding.

Core Steps of Injection Molding:

Plasticization and Injection: The pretreated plastic granules are melted in the injection molding machine barrel through heating (PP barrel temperature is approximately 180-280°C) and screw shearing (screw speed range is 1-150 rpm). The granules are then injected into the mold cavity at high speed. The injection molding machine can achieve an injection rate of up to 484 g/s.

Holding Pressure and Cooling: After the melt fills the mold cavity, holding pressure (typically 60-80% of the injection pressure) is applied to compensate for the material's shrinkage due to cooling and prevent product shrinkage. 7 The mold is then cooled and shaped using cooling channels within the mold (usually warm water1). The mold temperature is typically controlled between 60-90°C7, which is crucial for product quality.

Mold Opening and Ejection: After cooling is complete, the mold opens, and the injection molding machine's ejector system (with an ejection force of approximately 70.6 kN2) pushes the ejector pin or plate to eject the formed bottle cap from the mold.

Post-Processing and Quality Control:

Post-Processing: After demolding, the bottle cap requires gate trimming7 and undergoes necessary post-processing (e.g., annealing of PE parts by soaking them in hot water for 2-4 hours7).

Quality Inspection: This is a critical step in ensuring product quality. Bottle cap dimensions (for example, the mouth dimensions of a 28mm bottle cap must meet the drawing requirements), sealing performance (e.g., no leakage after a 0.2MPa internal pressure test for 30 minutes), and the opening force of the anti-theft ring (e.g., a pulling force of 25-30N is required for initial opening) must be rigorously inspected.

The Critical Role of the Mold

The mold is the heart of injection molding, and its design and construction directly impact the quality and production efficiency of the cap.

Number of Cavities and Layout: To improve efficiency, a mold with multiple cavities is often used (e.g., one cavity, two cavities, one cavity, four cavities, or even higher). Due to its smaller size, the 28mm bottle cap is well-suited for a multi-cavity layout.

Gating System: Common gate types include:

Point gate: Suitable for caps with high aesthetic requirements and automatic separation, but with a more complex mold structure (requiring a three-plate mold).

Latent gate: Automatically shuts off the gate upon mold opening and is a common option. Hot runner systems: Widely used in high-speed production, they can reduce runner agglomeration, improve material utilization, and shorten molding cycles (supporting rapid molding cycles as short as <2 seconds6).

Cooling systems: An efficient cooling circuit1 (such as a wraparound cooling system3) is crucial for improving production efficiency and product uniformity.

Mold release and thread processing: For bottle caps with threads, in addition to forced demolding5 (suitable for soft materials such as PP) and slider core pulling7 (for side holes or undercuts), a spin-off mechanism (using a gear rack or motor to drive the core rotation to achieve thread demolding) can also be used.

Process Parameter Overview

The following are some typical process parameters for 28mm injection molding of caps.

Process Parameters:

Barrel Temperature: 180-280°C (9), with a maximum limit of 250°C for flame-retardant materials.

Mold Temperature: 40-50°C (PS) (9) / 60-90°C (7), depending on the material.

Injection Pressure: 200-600 bar (PS), typically 70 MPa-100 MPa (PE).

Holding Pressure: 60-80% of the injection pressure to prevent shrinkage and internal bore deformation.

Screw Speed: 1-150 rpm.

Cooling Time: Over half of the entire molding cycle.

Pay Close Attention to Common Defects

During production, pay close attention to the following common defects:

Flash (burr): Caused by insufficient clamping force, mold wear, or poor venting.

Shrinkage: Caused by uneven cooling due to insufficient holding pressure or time.

Bubble: Insufficient raw material drying, with moisture or volatiles in the melt.

Glue deficiency: Caused by insufficient injection volume, low injection pressure, or low material temperature.

Weld marks: Failure of the melt to fully fuse when it converges within the mold cavity affects strength and appearance.

Core Advantages and Applications

The core advantages of the 28mm injection molding process lie in its high efficiency, high precision, and high quality. Through precise mold design, stable injection molding technology, and automated production, we can produce a variety of bottle caps that meet the requirements of food, beverage, and industrial applications. We can also integrate features such as anti-theft rings, vents, and cutters to meet diverse needs.

We are a 28mm injection moulding caps moulding manufacturer, providing high-quality 28mm injection moulding caps moulding manufacturing. As long as you want to customize/develop 28mm injection moulding caps moulding products, you can find us. We have professional injection mold design and mature manufacturing technology, providing you with one-stop service, from product design-mold making-product production-product packaging-product transportation, we can help you in every link. As long as you come to us, we will provide you with the ultimate service and satisfy you in terms of product quality, production time, information dialogue, etc.

Plastic Injection Mould making

Plastic molding specifications

Mold design:

Transaction process:

Mold testing:

Product packaging

Factory

We are Custom Plastic Mold factory. Our factory is plastic injection mold maker. we has 17 years of experience in professional custom plastic mold and 10 years of foreign trade experience. We are custom Plastic Mold supplier. We can provide custom Plastic Mold service. Our factory can make the Injection molded plastic parts, and the quality of the products will satisfy you.

We have more than 50 high-end machines and hundreds of engineers and designers. We can provide one-stop service, from product design - mold making - product production - product packaging - transportation. We have a complete production chain. We can meet all your requirements.

Services we provide:

Professional custom mold service, Plastic mold design and manufacturing .plastic product production, product design, mold design, blow mold customization, rotational mold customization, die-casting mold customization. 3D printing services, CNC manufacturing services, product packaging, customized packaging, shipping services.

We always adhere to the principles of quality first and time first. While providing customers with the highest quality products, try to maximize the production efficiency and shorten production time. We are proud to tell every customer that our company has not lost any customer since its establishment.If there is a problem with the product, we will seek a solution actively and take responsibility to the end.

FAQ

Q1: Are you trading company or manufacturer ?

A: We are manufacturers.

Q2. When can I get the quotation?

A: We usually quote within 2 days after we get your inquiry.

If you are very urgent, please call us or tell us in your email so that we can quote for you first.

Q3. How long is the lead-time for mold?

A: It all depends on the products' size and complexity. Normally, the lead time is 25 days.

Q4. I have no 3D drawing, how should I start the new project?

A: You can supply us a molding sample, we will help you finish the 3D drawing design.

Q5. Before shipment, how to make sure the products quality?

A: If you don't come to our factory and also don't have the third party for inspection, we will be as your inspection worker.

We will supply you a video for production process detail include process report, products size structure and surface detail, packing detail and so on.

Q6. What is your payment terms?

A: Mold Payment: 40% deposit by T/T in advance, 30% second mold payment before sending out the first trial samples, 30% mold balance after you agree the final samples.

B:Production Payment: 50% deposit in advance, 50% before sending out the final goods.

Q7: How do you make our business long-term and good relationship?

A:1. We keep good quality and competitive price to ensure our customers benefit for best quality products.

2. We respect every customer as our friend and we sincerely do business and make friends with them, no matter where they come from.