Roll Cover Two-Stage Curing Process for Wear Resistance
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Solution Overview
Problem
Existing roll covers in high-load applications, such as paper or tissue machines, experience high wear rates and short grinding intervals due to insufficient wear resistance and stress crack issues, particularly under high press loads and chemical exposure.
Innovation Solution
A roll cover with a modulus of elasticity ranging from 500 to 1500 N/mm² is achieved through a two-stage curing process using a resin-hardener mixture of reactive and less reactive diisocyanates, allowing for stronger crosslinking and enhanced hardness, which is produced using a two-component casting method and thermal post-treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a single-stage curing process is used with conventional polyurethane elastomers, then the production process is simple and fast, but the wear resistance is insufficient and service life is short
Solution Approach 1:
The curing process is divided into two distinct stages: a first curing stage that forms a polyurethane elastomer layer with initial mechanical properties, and a second curing stage that creates a heavily crosslinked surface layer with enhanced wear resistance. This segmentation allows each stage to optimize different properties, resolving the contradiction between simple processing and improved service life.
Solution Approach 2:
The invention changes the crosslinking density parameter through the two-stage curing process. The first stage produces a layer with lower crosslinking density for ease of processing, while the second stage increases crosslinking density to achieve the heavily crosslinked surface layer with modulus of elasticity between 500-1500 N/mm² and significantly improved wear resistance.
2Strength
If the modulus of elasticity is increased to improve wear resistance, then hardness and wear resistance improve, but residual stresses and cracking risk increase
Solution Approach 1:
The first curing stage acts as a preliminary action that creates a base layer with adequate mechanical strength and flexibility before the second curing stage is applied. This preliminary structure can accommodate the residual stresses that will develop during the second heavy crosslinking stage, preventing crack formation while still achieving the desired high wear resistance.
Solution Approach 2:
The roll cover consists of a composite structure with two distinct polyurethane layers: a first layer with moderate crosslinking density providing flexibility and stress accommodation, and a second layer with heavy crosslinking density providing wear resistance. This composite approach allows the material to exhibit both high strength and high reliability.
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 resulting roll cover exhibits improved service life and wear resistance, reducing deformation and extending grinding intervals even under maximum loads, while minimizing residual stresses and avoiding cracks during manufacturing.
Implementation Method 1
The resulting roll cover is heavily crosslinked and thus has a high modulus of elasticity and high hardness
Implementation Method 2
a resin-hardener mixture... The resin is a reaction product of a first, more reactive diisocyanate and a diol in a molar ratio of at least 2:1, mixed with a second, less reactive diisocyanate
Implementation Method 3
in a second process step a second curing reaction achieves a modulus of elasticity of 500 to 1500 N/mm 2 , the second process step taking place by means of a thermal post-treatment for at least 48 hours at 120°
Data Source
AI summary
A roll covering is particularly suited for use in the press section of a machine for the production of a web of fiber-based material, for example a papermaking machine, a paperboard machine, or a tissue machine. The roll covering is arranged on a roll core which, in particular, is composed of metal or of a fiber-composite material. The modulus of elasticity of the roll covering is from 500 to 1500 N/mm2.