MPIM Valve Stem Surface Finish and Leakage Control
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Solution Overview
Problem
Conventional methods for manufacturing metal valve stems for pressurized metered dose dispensers face challenges such as distortion, material failure, leachables from plastic materials, and rough surface finishes, which can lead to drug deposition and occlusion, especially in complex shapes and configurations.
Innovation Solution
Metal powder injection molding (MPIM) is used to manufacture valve stems with desirable surface finishes and resistance to pressurized propellants, allowing for complex shapes and configurations with tight tolerances without the need for post-machining, using stainless steel grades with high corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal valve stems are manufactured by deep drawing or machining, then material strength and corrosion resistance are improved, but surface finish becomes rough leading to drug deposition and occlusion
Solution Approach 1:
The invention changes the manufacturing process parameters by using metal powder injection molding instead of traditional deep drawing or machining. This process allows for the formation of smooth internal surfaces with appropriate roughness parameters (Ra values) that prevent drug deposition while maintaining the required mechanical strength and corrosion resistance of the metal valve stem
Solution Approach 2:
The invention replaces the mechanical machining process with a powder metallurgy process. Instead of using cutting tools that create rough surfaces, the valve stem is formed by injecting metal powder into a mold and sintering it, which inherently produces smoother internal passages and surfaces that do not seed drug accumulation
2Manufacturing precision
If metal valve stems are manufactured by machining, then dimensional accuracy can be achieved, but production cost increases and internal surfaces remain rough
Solution Approach 1:
The invention performs the shaping action during the molding process itself rather than requiring subsequent machining operations. The metal powder is injected into the final shape with tight tolerances directly in the mold, and the sintering process consolidates the powder into the precise dimensional configuration, eliminating the need for expensive post-machining operations
3Ease of manufacture
If plastic materials are used for valve stems, then manufacturing cost is reduced, but leachables are introduced into the pharmaceutical formulation
Solution Approach 1:
The invention uses metal powder as the base material with controlled surface characteristics, creating a composite structure that combines the chemical inertness of metal (preventing leachables) with optimized surface roughness properties. The metal powder injection molding process creates a unique microstructure that maintains metal purity while achieving the desired surface finish for pharmaceutical compatibility
4Strength
If conventional manufacturing methods are used for complex valve stem configurations, then material strength is maintained, but distortion and material failure occur
Solution Approach 1:
The invention changes the fundamental manufacturing parameters by using powder injection molding with controlled sintering conditions. This process allows complex configurations to be formed without the mechanical stresses and distortion associated with traditional machining, while the controlled atmosphere and temperature profiles during sintering prevent material failure and maintain structural integrity
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
MPIM provides valve components with smooth surface finishes, low porosity, and reliable operation with low actuation forces, minimizing propellant leakage and ensuring accurate dosing, as demonstrated by the use of 316 or 316L-grade stainless steel valve stems in metered dose dispensers.
Implementation Method 1
individual particles of a metal or a metal precursor are sintered to yield a metal component
Data Source
Figure 1~2
Figure 3
AI summary
Use of metal powder injection molding for the manufacture of a metal valve component, such as a valve stem or a valve body, of a metered dose dispensing valve for use in a medicinal pressurized metered dose dispenser, such as an inhaler.