Rotational Moulding Conference Workshop - Question 1
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Material specifications for rotomoulding powders are important because they provide information about properties that affect the molding process. These specifications include the melt flow index, dry flow rate, bulk density, and particle size distribution which influence how easily the powder will flow into all areas of the mold. Variations in these properties between batches of powder supplied can negatively impact the quality of molded parts by causing uneven wall thicknesses, gaps, and voids if not monitored. It is recommended to request and review certificates of analysis which specify these material properties for each batch received.
![For those who do not have a
microscope handy…
measure quality with Dry Flow funnel
Which powder is better quality?
A
• Dry Flow
22sec
www.ianhansenconsult.com
In most cases standard powder with
faster dry flow is usually better ‘quality’
than slower dry flow
If you receive a Certificate of Analysis [COA] with
each powder batch delivered, you can quickly &
easily compare ‘quality’ by reviewing the Dry
Flow time on the COA](https://image.slidesharecdn.com/workshopproblem1-160627111523/85/Rotational-Moulding-Conference-Workshop-Question-1-13-320.jpg)
Rotational Moulding Conference Workshop - Question 1
- 1. Rotomould Workshop Problem 1 Why are material specifications important to the rotomoulder Materials, by Ian Hansen, Rotoconsult
- 2. Do you have specifications from your powder supplier? Dry Flow Is it the ARMO funnel? Particle Size Bulk Density If you don’t have copy, why not?
- 3. MATERIAL Melt Flow Index (MFI) POWDER Dry Flow Bulk Density Particle Size Do you receive a COA for each different batch of powder delivered ? ianhansenconsult.com
- 4. Do you review the variation in material properties? Can this affect you? 2.4 2.6 2.8 3 3.2 3.4 3.6 13226 13233 13240 13246 13253 13255 13258 13262 13270 13271 13273 13274 13319 13430 13438 13454 13462 13466 13478 13489 13490 13491 13492 13493 13499 14001 14002 14005 14006 14008 14009 14009 14010 14022 14031 14032 14033 14035 Melt Flow Index -10% +10% MFI www.ianhansenconsult.com
- 5. Melt Flow Rate ASTM D1238 or ISO 1133 As MFI increases, polymer flow properties increase As MFI decreases, polymer flow properties decrease Melt Flow Increase Melt Flow Rate, sometimes referred to as Melt Flow Index, is a measure of the viscosity or flowability of the plastic once melted. This provides a value – the Melt Flow Index (MFI) – which gives a relative indication of the ease of flow of a polymer melt. Melt Flow Decrease www.ianhansenconsult.com Source : ARMA Materials Properties Guide
- 6. 20 22 24 26 28 30 13226 13233 13240 13246 13253 13255 13258 13262 13270 13271 13273 13274 13319 13430 13438 13454 13462 13466 13478 13489 13490 13491 13492 13493 13499 14001 14002 14005 14006 14008 14009 14009 14010 14022 14031 14032 14033 14035 Dry Flow Do you review the variation in material properties? Can this affect you? www.ianhansenconsult.com
- 7. Powder Quality important to fill tight corners and threads Dry flow is the measure of how a powder will tumble and flow in the mould during the rotational moulding process. The dry flow affects the heat transfer in the powder pool and how the powder distributes itself over the mould surface. Dry flow depends mostly on the Particle Shape, and to a lesser extent Particle Size. Particles that have been ground poorly will have ‘tails’ and tend to be ‘fluffy’. These two characteristics will give the powder poor flow properties - possible leading to uneven wall thickness, bridging across narrow recesses and a high void content within the moulded product www.ianhansenconsult.com
- 8. Powder Quality important to fill tight corners and threads www.ianhansenconsult.com Image Source: www.aptis.be/ Examples of different flow characteristics
- 9. 9www.ianhansenconsult.com Particle 1 Ideal Particle 2 Very good Particle 3 Poor ImageSource:TPPicture® The most desirable particle is thought to be cubic in shape with generously rounded corners, without tails. WHY? The rate at which powder melts is a function of the shape of powder particles.
- 10. Powder with tails Powder without tails Which powder is better quality? www.ianhansenconsult.com
- 11. Powder without tails Which powder is better quality? www.ianhansenconsult.com
- 12. For those who do not have a microscope handy… measure quality with Dry Flow funnel Which powder is better quality? A • Dry Flow 22sec B • Dry Flow 25sec C • Dry Flow 29sec www.ianhansenconsult.com
- 13. For those who do not have a microscope handy… measure quality with Dry Flow funnel Which powder is better quality? A • Dry Flow 22sec www.ianhansenconsult.com In most cases standard powder with faster dry flow is usually better ‘quality’ than slower dry flow If you receive a Certificate of Analysis [COA] with each powder batch delivered, you can quickly & easily compare ‘quality’ by reviewing the Dry Flow time on the COA