Optimal Hot Runner Design for Recycled Material Pallets

Recycled plastic, new perspectives. The plastic pallet manufacturer, Ribawood, and the hot runner company, Oerlikon HRSflow worked together to develop a hot runner solution that produces reusable and 100% recyclable pallets.

Transporting and storing products on modern plastic pallets is becoming popular in a sector traditionally dominated by wooden solutions. Plastic pallets are safer, very durable and recyclable. A quality in full compliance with future needs which are progressively connected to Circular Economy. As sustainability remains a priority, challenges for the injection molding industry are increasing.

Ribawood, the plastic pallet manufacturer, partnered with Oerlikon HRSflow to develop a hot runner solution able to produce lightweight pallets. The product is composed of fully recycled material. Quality issues swayed from surface defects to more serious issues that could affect the safety and function of the finished product, as well as the performance of the hot runner system. The main challenge was primarily connected with clog problems of the hot runner channels due to the foreign particles usually present in the recycled material.

Application field: Logistics & Environmental

Part name: Pallet

Nominal weight: 6900 g

Nominal thickness: 3 mm

Molding material: HDPE regrinding

Hot runner system: 8 drop system: Wa Series Oerlikon HRSflow

Injection type: Conical Valve Gate

Rheological Analysis

The first step was understanding the behaviour of the polymer within the mold cavity.

The complexity of processing recycled material is usually related to foreign particles, leading to obstructions in the hot runner channels. The use of software to conduct a rheological analysis helped to define optimal injection pressure and speed based on the special material features.  

Hot Runner System

The technological solution was a hydraulic 8-drop hot runner system equipped with conical valve gate (Wa nozzle series) from Oerlikon HRSflow. Special attention was given to the gate configuration, due to a 14 mm diameter and a hot runner bore diameter of 32 mm. Any issues related to channel clogs would be avoided. In addition, the gentle injection pressure combined with low speed allowed for better control of the melt flow. This prevents any streaking or flow marks that could jeopardize the cosmetic and functional result. Continuing, the lower injection pressure allowed for the use of LPIM (low pressure injection molding) technology, maximizing production efficiency. With this design approach, system maintenance can be significantly reduced, avoiding long and costly downtime.

Oerlikon HRSflow: José Moreno, General Manager of Spain states, “developing and producing high-performance hot runner systems for plastic injection molding is a complex process. It requires high expertise and continuous desire to face new challenges. The project carried out together with Ribawood is a clear example of great collaboration. Both parties put into play their own knowledge to get the best result: a 100% reusable and recyclable pallet which combines a strong attention to sustainability with a high structural result”.

The Finished Product

Ribawood is an international company located in Zaragoza, that began operations in 1975. Business focuses on the transformation of plastics and extrusion of Woodstock® sheets, a plastic designed for the automotive sector that contains a derivative of wood. In the early 2000s, it became to diversify the production in the packaging sector by injecting pallets, boxes and containers of recycled plastic.

Pioneers in the recycling of their own waste products, with a production capacity of 2.5 million pallets per year, Ribawood can recycle their own pallets at end of their life. The growing demand for this product in the world of logistics is due to high durability and minimal impact to the environment, enabling companies to comply with their zero-waste commitments.

Ribawood needed a business partner that could operate within their versatile manufacturing process. Several tests revealed that the balanced hot runner solution from Oerlikon HRSflow would guarantee the high structural result of the entire part. There would also be no internal stress, despite working with 100% recycled material.