Sealed and Stackable Plastic Parts moulding

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 Sealed and Stackable Plastic Parts 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 Sealed and Stackable Plastic Parts moulding products, we can make corresponding plastic parts, which is mainly done through injection molds.

# Key Considerations for Injection Molding of Airtight + Stackable Plastic Products (Primarily kitchen storage; food-contact applications; typically made from food-grade copolymer PP)

Two core, overlapping constraints:

1. **Airtightness**: The dimensions of the sealing lip/groove must be stable with minimal deformation to ensure a leak-proof fit.

2. **Stackability**: The positioning structures (for vertical alignment) must be precisely controlled so that stacked units remain stable—without wobbling, jamming, or compromising the seal.

Additionally, the product must meet food-contact safety standards (e.g., GB 4806.7 / EU 10/2011).

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> Typical products: Airtight storage containers, food preservation boxes, portioning containers, and draining storage sets with lids.

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> The primary challenge: Polypropylene (PP) is a semi-crystalline material prone to post-molding shrinkage. **Airtight features are highly sensitive to dimensional precision, while stacking ribs can alter local shrinkage and stress distribution.** This often leads to a common failure: a container may be perfectly airtight at room temperature, but after being stacked and exposed to hot water, the sealing lip deforms, the seal fails, or the stacking structures become jammed/wedged. ## I. DFM Structural Design (Critical Initial Phase)

### 1. Wall Thickness and Ribs

- Main wall thickness: **1.4–1.8 mm**; maintain uniformity throughout, with a thickness variation of ≤25%.

- Rib thickness: ≤0.6× the main wall thickness; include a radius (R) of 0.3–0.6 mm at the base.

- ✅ Avoid adding reinforcing ribs directly to the outer surface of the sealing lip/flange; this can cause sink marks on the exterior, uneven shrinkage at the sealing interface, and an irregular sealing line.

- ✅ Position stacking ribs and bosses independently—do not integrate them with the sealing lip/flange. This prevents shrinkage-induced pulling, which could deform the sealing ring.

- The sealing area at the container opening is the most precision-critical part of the component; minimize the use of ribs or abrupt structural changes near the sealing ring.

### 2. Two Common Sealing Approaches

#### Option A: Rigid-to-Rigid Sealing (PP-on-PP, no separate gasket)

Unilateral clearance at the mating interface (lip/flange): **0.10–0.18 mm**

- Design a narrow, continuous sealing line (rather than full-surface contact), with a width of 0.8–1.2 mm.

- The surface of the sealing line must be perfectly smooth—free of gate marks, weld lines, or flash.

- Use radii (R) for transitions at the interface; avoid sharp corners (which trap debris and are prone to flash).

#### Option B: Soft Gasket Sealing (PP groove with a TPE ring—most common for kitchenware)

- Determine the depth and width of the sealing groove based on the required compression of the TPE ring (typically 25%–35% compression).

- Apply radii (R) to the bottom and internal corners of the groove; include small overflow recesses at the ends of the groove.

- ❗**Ensure no weld lines occur within the sealing groove**; any height variation caused by a weld line will lead to air or water leakage.

- Avoid making the groove too deep, as this can cause damage during demolding and lead to deformation at the base of the groove. ### 3. Stacking Structure Design (Coordinating with the Sealing System is the Key Challenge)

1. For stacking alignment features (protrusions/recesses), **avoid a continuous, fully closed loop**. Leave gaps for venting and material overflow; a closed loop traps air, causing the parts to push against each other during stacking, which can force the lid open and compromise the seal.

2. Carefully calculate the stacking alignment height: once stacked, the **stacking ribs should make contact with the limit stops first**, ensuring the sealing interface is not subjected to excessive, rigid compression (this is critical!).

- Sequence: Stacking ribs make contact → reach the limit stop → the sealing interface achieves a light, precise fit.

- If the sequence is reversed (i.e., the sealing ring is forcibly compressed during stacking), long-term creep—exacerbated by the thermal expansion of PP when exposed to hot water—will lead to permanent deformation of the seal.

3. Ensure the stacking structure is **concentric and symmetrical** relative to the sealing ring. Asymmetrical stacking ribs can generate lateral forces, pulling the sealing ring out of position.

4. Incorporate chamfers for stacking guidance to facilitate alignment and prevent scratching the sealing surfaces or the TPE gasket during assembly.

### 4. Draft Angles & Undercuts

- PP sealing surfaces: ≥1°. Maintain a consistent draft angle across the sealing interface to ensure uniform width of the sealing surface along its entire circumference.

- Draft angles within the sealing groove: ≥1.2°. Any surface damage (scuffing/tearing) to the inner walls of the TPE groove can trap debris and lead to leaks.

- **Avoid "forced-ejection" undercuts** in the sealing surface area. Any surface damage or internal stress caused by forced ejection will immediately destroy the sealing performance. If undercuts are necessary, place them in non-sealing areas and utilize angled lifters or sliders.

We are a Sealed and Stackable Plastic Parts moulding manufacturer, providing high-quality Sealed and Stackable Plastic Parts moulding manufacturing. As long as you want to customize/develop Sealed and Stackable Plastic Parts 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.

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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.