Rotational Moulding Insert Holder with Pneumatic Pressure Equalization
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Solution Overview
Problem
Rotational moulding technologies face issues with blowholes formation and uneven heating, leading to cracking and material waste, due to pressure differences and inefficient heat distribution around inserts in the moulding process.
Innovation Solution
A mould with a temperature control system and pneumatic circuit that allows for independent heating areas and pressure equalization, using insert-holding devices connected to a secondary pneumatic circuit to maintain internal pressure balance and ensure uniform heating around inserts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional insert-holding device with spring and bush is used to allow insert movement during shrinkage, then the insert can move with the manufactured article preventing it from slipping out, but blowholes form around the insert due to pressure differences and trapped air expansion
Solution Approach 1:
The patent removes the bush component from the insert-holding device, eliminating the trapped air volume that causes blowholes. The insert-holder directly engages with the mould wall through a threaded connection, extracting the problematic intermediate bush element that created the air trap and pressure differential issue.
Solution Approach 2:
The insert-holder is designed as a separate removable component that can be independently adjusted and replaced. The device segments the insert anchoring function from the mould structure itself, allowing precise control of insert positioning while maintaining mould integrity and enabling easy modification of the anchoring mechanism.
2Temperature
If the mould is heated uniformly in a hot air oven, then the entire mould reaches melting temperature, but the insert area with greater mass and reduced contact surface receives insufficient heat irradiation resulting in poor polymer coating
Solution Approach 1:
The patent applies localized heating elements directly to the insert-holder or insert area, providing concentrated thermal energy where needed. This creates a temperature gradient with higher heat flux at the insert location, ensuring adequate polymer coating quality in the critical insert region while maintaining overall mould temperature control.
Solution Approach 2:
The insert-holder is pre-heated before insert installation, or the localized heating area is activated first to prepare the surface for optimal polymer coating. This preliminary thermal preparation ensures that when polymer is applied, the insert area is already at the appropriate temperature for proper adhesion and coating formation.
3Manufacturing precision
If pressure is applied inside the mould during rotational moulding to compact polymeric material, then air bubbles are eliminated, but pressure differences cause cracking in the manufactured article at communication points between inside and outside of the mould
Solution Approach 1:
The patent removes communication channels or holes between the mould interior and exterior that allow pressure differentials to cause cracking. By eliminating these weak communication points, the mould structure can withstand higher compaction pressures without creating stress concentrations that lead to article cracking, while still achieving effective air bubble elimination.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution prevents blowhole formation, ensures uniform heating, and reduces material waste by maintaining internal pressure balance and optimizing heat distribution, thereby enhancing the quality and efficiency of the rotational moulding process.
Implementation Method 1
comprising one or more heating elements (16) arranged in at least one predefined area of the mould (10)
Implementation Method 2
a temperature control system configured for adjusting the temperature in said heated area
Implementation Method 3
it is however necessary to introduce technical solutions that avoid the possible defects that the pressure and/or vacuum can create
Data Source
AI summary
The invention describes a mould (10) for the rotational moulding of manufactured articles of plastic material comprising two half-moulds (12, 14), at least one of which is provided, on its surface, with at least one insert-holding device (18) comprising a rod (20) provided with a first end (46) that passes through the wall of the half-mould (12, 14) at a respective passage channel (24) and that is axially movable for projecting inside the mould (10), so that on the first end (46) an insert (22), to be embedded in the moulded manufactured article, can be mounted. The mould (10) also comprises a first pneumatic circuit (32A) able to apply a predetermined pressure, positive or negative, inside the mould (10). At least one insert-holding device (18) is operatively connected to a second pneumatic circuit (32B) able to apply a predetermined pressure, positive or negative, and is internally provided with a plurality of means (34, 36, 38) configured to apply the predetermined pressure at the passage channel (24), so that at the insert-holding device (18) the same predetermined pressure value which generates inside the mould (10) by the first pneumatic circuit (32A) is applied.