By elaborating on the key indicators of pipeline powder, such as setting time, particle size distribution, magnetic material content, and heat generation, this document discusses how to control powder quality during the production process and analyzes the various factors that influence these indicators.
1、Factors affecting the time required for powder dispersion.
The definition of setting time is: the time required for a specified volume of powder coating to become a non-deformable material under specified conditions after melting. Longer setting times result in better film smoothness, while shorter setting times result in poorer film smoothness. This effect is more pronounced in rapidly curing powder coatings.
For the production of high-performance anti-corrosion powder, the ratio of length (D) to diameter (L) of the screws should be between 12:1 and 14:1. The mixing time of the material inside the machine should be kept below 20 seconds. This ensures that the agglomeration time of the powder remains relatively consistent, resulting in good film gloss and smoothness.
If longer-to-diameter ratio screws are selected, especially when the material is mixed within the screw for 30 seconds or more, the powder's cohesion time is significantly reduced, leading to uneven coating, reduced gloss.
2、Factors affecting particle size distribution
Numerous factors can influence the particle size distribution: the thickness of the raw material flakes, the feed rate, the rotational speed of the primary and secondary grinders, the airflow volume, and the wear of the impactor and gear.
Powder for pipelines, when applied in thick layers, typically has an average particle size controlled between 45 and 55 μm. If the powder is used as anti-corrosion coating inside the pipeline, the average particle size can be adjusted to improve leveling, and can be controlled at around 40 μm. Typically, the mesh size of the pipeline powder screen is 100.
3、Factors affecting the content of magnetic materials
1、According to the standard SY/T 0315-2013 "Technical Specifications for External Coating of Steel Pipe Welding with Epoxy Powder," the requirement for magnetic material content is ≤0.002%.
Factors that affect the content of magnetic materials include: the inherent magnetic material content in the raw materials (especially magnetic fillers) and magnetic materials generated from equipment wear. When establishing a formula and selecting raw materials, it is essential to carefully control and match the materials, and to choose raw materials with low magnetic material content.
Methods to reduce the content of magnetic materials:
Firstly, improve the formulation to reduce filler content and lower powder hardness.
Two: Appropriately increase the extrusion temperature to accelerate the melting speed of the materials, reducing wear and tear on the screws and screw sleeves.
Three: Replace with more durable materials to reduce wear and tear on screws, screw sleeves, and impact pins and gear teeth.
Four: Implement a magnetic device system to attract and remove magnetic materials from the material, thereby reducing the content of magnetic materials.
Considering factors such as overall production cost and performance, it is recommended to use materials that are more resistant to wear, reducing wear and tear on screws, sleeves, and impact pins and gears. Experiments have shown that ceramic materials have a higher production cost, but almost no wear, and their magnetic content is: 0.0010%, which allows for long-term use and reduces the need for replacement, thus reducing the overall production cost of the powder.
4、Factors affecting the heat release amount (ΔH)
In the case of powder coatings, the heat released during the chemical reaction under heat conditions is referred to as the reaction heat, also known as the heat of reaction. This is represented by ΔH.
In the industry standard SY/T 0315-2013 "Technical Specifications for the External Powder Coating of Steel Pipelines," the requirement for the ΔH index is ≥45J/g. Some project specifications require ΔH ≥ 55J/g.
The amount of heat generated is significantly related to the design of the curing system. Different curing systems exhibit vastly different heat generation rates. Furthermore, during the production of the same powder formulation, certain stages can also influence the heat generation.
① The melt extrusion process has a significant impact on heat dissipation. The longer the material mixes in the screw, the lower the heat dissipation. Therefore, when producing powders for pipelines, it is necessary to select a screw with the appropriate length-to-diameter ratio. While ensuring that the mixing effect is not compromised, the goal is to minimize the time the material spends mixing in the screw.
② During the cooling and crushing process, ensure the smooth flow of cooling water in the pressing roll. Aim to reduce the temperature of the crushed material to below 35°C, and ideally below 30°C.
③ During the grinding process, it is crucial to control the grinding chamber temperature. When the air temperature is high, the cooling fan should be turned on to ensure that the grinding chamber temperature remains at a low level.
④ Storage temperature: Ideally, store the powdered finished product in a warehouse with a temperature below 35°C.
Source: Fangyuan Anti-Corrosion Materials Co., Ltd. (Victory Oilfield)