SPECIFIER NEWSLETTER – ISSUE 18 – JULY 2022
This month we’re giving you an insight into the making of extruded polystyrene insulation.
Have you ever wondered what the ‘extruded’ part of XPS actually is? Or how much recycled polystyrene can be used to make XPS boards?
Read on to find out, and don’t forget to contact us if you have any comments or questions.
Focus on responsible sourcing
How is extruded polystyrene insulation made?
The manufacture of XPS insulation involves a two-stage extrusion process. Following that, the extruded polystyrene foam is calibrated and profiled to create finished insulation boards for use on construction sites.
An XPS manufacturer’s production facility has four bulk storage tanks, each containing a different raw material.
Two are for polystyrene, with one containing virgin polystyrene material and another containing the recycled material amassed from elsewhere in the production process. Because offcuts can be recycled in this way, with up to 30% of the polystyrene used in the process being recycled, demand for raw polystyrene is kept to a minimum.
Another storage tank contains additives used in the foam mix, and the final one contains the gas blowing agent. For every production run, raw materials are measured and combined in a blender to give the correct ‘recipe’ for the product being made.
From the blender, the mix feeds into the extruder – effectively a giant screw that breaks down and mixes the raw materials.
Understanding the ‘extrusion’ of extruded polystyrene
The first of the two stages of extruding XPS insulation involves heating, mixing and gas injection. The virgin and recycled polystyrene included in the initial ‘recipe’ is in crystal form, and must be melted.
Initially, heat is applied from an electrical heating source. Further heat is generated by the shearing action of the extruding screw against the polystyrene crystal. The blowing agent is then injected into the melted polystyrene at high pressure, and it is this action that creates the closed cell structure of the end product.
Without its closed cell structure, XPS insulation would not have the thermal performance, compressive strength and moisture resistance that makes it such a versatile product.
Polystyrene foam now enters the extrusion die head. Different die heads are used to create different products. This is the second stage of extrusion, where the ‘melt’ is cooled using chilled water, ready to exit the die. Careful control ensures it is cooled to the correct temperature and pressure.
Turning extruded foam into finished XPS insulation boards
Polystyrene foam comes out of the die lips into the vacuum chamber, which is a reinforced concrete tube sealed at the top end by a mechanical seal, and at the bottom end by a water seal created by a water pond/reservoir.
The foam begins to expand, not unlike hair mousse or shaving gel coming out of an aerosol can. Calibrating bars control the spread of the foam to give the required thickness and width. A conveyor carries the product down the vacuum chamber, through the water reservoir and into the profiling station.
Here the foam is cut and shaping into insulation boards, including giving the board edges a lap joint or square edge as required. The size of the machinery determines the maximum dimensions of the product, and will be different for each production line.
Continue reading to finish learning about the manufacturing process. Click here.
Polyfoam resource
How does XPS insulation perform compared to other common insulation types? What makes it the ideal choice for below ground, ground floor, and inverted flat roof applications? Our CPD presentation, accredited by the CPD Certification Service, answers all of these questions.
View the seminar online or contact us to arrange online delivery to your team.
What’s caught our eye this month
The future of the built environment according to Mace – via bimplus
We can’t tackle embodied carbon if we don’t measure it properly – via building.co.uk
Approved Documents digitalised to make compliance process simpler – via bimplus
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