PP laboratory fume hoods
Self-supporting hoods and compact bench-top hoods – chemically resistant, with filter on request.
View in the shopProcess · Joining technology
Hot-gas welding
Hot-gas plastic welding for leak-tight tanks, trays and special constructions. Semadeni welds PP, PE, PVC-U and PVDF – also for chemical plants and spill trays.
What is hot-gas welding and how does Semadeni use it?
Hot-gas welding is a joining process for thermoplastics: the joint faces and a filler rod are heated with hot air, plasticised and joined under pressure – similar to welding metal. It creates leak-tight, durable seams and suits tanks, trays and special constructions that bonding or mechanical joints cannot achieve. Semadeni welds PP, PE, PVC-U and PVDF – no other thermoplastics – and builds spill trays, chemical tanks and laboratory fume hoods from them. Which seam and material are suitable depends on the medium, temperature and pressure; the design is clarified per application. Not all plastics are weldable – PMMA, PC and PS, for instance, are bonded or mechanically joined. We test the tightness of every finished construction as standard, with water or a spark tester.
Process
Benefits of Hot-gas welding
Leak-tight, durable seams
Welded joints are material-bonded and tight – decisive for tanks, spill trays and special constructions with medium contact.
Chemically resistant materials
PP, PE, PVC-U and PVDF cover a broad spectrum of acids, alkalis and solvents – checked by material.
In-house production in Ostermundigen
Welding is done in our own plastics machining shop – the same production that builds the series products in the shop.
Tank and plant construction
Trays, tanks and vessels as special construction from your drawing or your dimensions.
Repair & special construction
Single fabrications and small batches as well as repairs to existing plastic constructions.
Tightness test as standard
Every finished construction is tested with water or a spark tester – documented as needed.
Technical possibilities
A framework for pre-clarification. We define material, seam and wall thickness based on medium, temperature and pressure of the specific application.
Possibility
Range
Process
Manual hot-gas welding with filler rod; heated-element welding on request
Weldable materials
PP, PE, PVC-U, PVDF – no other thermoplastics
Not weldable
PMMA, PC, PS – bonded or mechanically joined
Components
Tanks, trays, spill trays, laboratory fume hoods
Testing
Tightness test (water or spark tester), as standard
From drawing to leak-tight construction
01
Design & material choice
Design based on medium, temperature and pressure; choice of the resistant thermoplastic.
02
Cutting & preparation
Cutting of sheets, edge preparation for the seam.
03
Welding
Hot-gas welding with filler rod; heated-tool welding for series parts.
04
Testing & acceptance
Visual inspection and tightness test with water or a spark tester, documentation as needed.
What components & sectors is it for?
- Spill trays and hazardous-substance storage in chemistry and laboratory
- Tanks and vessels with medium contact
- Laboratory fume hoods, extraction units and custom lab furnishings
- Special constructions for plants and process technology
Welding or bonding?
Criterion
Hot-gas welding
Tightness
high (material-bonded)
Materials
weldable thermoplastics
Strength
high, durable
In detail
Leak-tight joints in plastic
Where tanks, trays and special constructions must hold media safely, it comes down to the seam. Hot-gas welding joins thermoplastics material-bonded and tight – a property that bonded or bolted joints do not reliably achieve with medium contact. Semadeni builds special constructions for chemistry, laboratory and industry from it.
Material decides resistance
Not every plastic is weldable
At Semadeni the weldable materials are PP, PE, PVC-U and PVDF; we do not weld other thermoplastics. PMMA, PC and PS cannot be reliably hot-gas welded – they are bonded or mechanically joined. Resistance to a specific medium depends on material, concentration and temperature; we choose the material per application.
Qualified execution and acceptance
Seam quality, evidenced on the component
How leak-tight a plastic seam is shows on the finished construction. Every seam is visually inspected; in addition we test every construction for tightness with water or a spark tester and document the result for your acceptance. The design – material, seam type and wall thickness – is defined beforehand from medium, temperature and pressure.
Made in-house
Welded at Semadeni – in stock in the shop
Full laboratory furnishings categoryThese series products are made in our own plastic-welding shop in Ostermundigen and can be ordered directly from stock – the same fabrication that also builds your special construction.
Sink unit top SPOT 03
Welded PP top for the laboratory sink – base unit made to measure on request.
View in the shopFrom the assortment
Before welding: containers and tubs from stock
All articles in the shopNot every task needs a welded one-off. For containment, storage and transport, Semadeni stocks containers, tubs and large receptacles in polypropylene (PP) and polyethylene (PE); only where size, geometry or volume go beyond that do we weld to size in Ostermundigen.
Spill pallets
View in the shop
Trays, basins and tubs
View in the shop
Tubs, drums, buckets
View in the shop
Pallet boxes and large containers
View in the shopFrequently asked questions about Hot-gas welding
Which plastics can Semadeni weld?
Weldable are PP, PE, PVC-U and PVDF – we do not weld other thermoplastics. Not weldable are PMMA, PC and PS – these we join by bonding or mechanical fastening. Which material suits your medium and temperature is clarified per application.
What is the difference between hot-gas and heated-element welding?
In hot-gas welding (manual), joint faces and filler rod are plasticised with hot air – flexible for tanks and special construction. In heated-element welding, a heated tool melts the joint faces directly, which are then pressed together – for higher seam strength in series.
How does Semadeni evidence seam quality?
On the component, not through a standard number: every seam is visually inspected, and every construction is additionally tested for tightness with water or a spark tester – we document the result for your acceptance. Suitability for a specific medium we additionally check by material and application.
Are welded tanks suitable for aggressive media?
Resistance depends on the material, the medium, concentration and temperature – not on the welding alone. PVC-U and PVDF cover many acids and alkalis, PP is broadly chemically resistant. We choose the material based on your medium and check resistance by product and application.
Does Semadeni test the tightness of the finished construction?
Yes, and as standard on every finished construction – with water or a spark tester, depending on the component. We document the result to your requirement, for example for the acceptance of spill trays or tanks.
References
Hot-gas welding in practice
A Near-Natural Spectacle
A bio pool with a black plastic basin and overflow channel, its water surface mirroring the sky.
On the Green Meadow
A made-to-measure swimming pond, integrated into a Jurassic limestone wall and framed on three sides with thermo-ash decking.
Secret Garden
Two made-to-measure water basins across two levels – the garden took third place at the Taspo Awards.
A Pool for Koi Carp
An L-shaped natural pool for breeding koi carp – the centrepiece of a garden in western Switzerland since 2018.
Custom Plastic Sink Units for School Buildings
Almost 50 recessed washbasin units in plastic, made to precise measure for the cantonal school in Menzingen.
What Custom Laboratory Equipment Has to Do with Climate Protection
Self-supporting laboratory fume hoods in plastic for Climeworks – chemical-resistant and cut precisely to the space.
Your project?
Describe your application – we'll show what a solution can look like.
Discuss your projectContinue in the cluster
- CapabilityView
CNC machining & cutting
Precision plastic cutting to size and CNC machining – for single parts, small batches and standard formats. Semadeni machines acrylic, PP, PE, PVC, PC and all common thermoplastics from batch size one.
- GuideView
Chemical resistance
How resistant is a plastic to a chemical? Semadeni's resistance list rates 26 plastics against individual substances at 20, 40 and 60 °C. This guide explains the classes a, b and c, shows values for common media and says where the list reaches its limits.
- SolutionView
Industry & manufacturing
Plastic solutions for industry, mechanical engineering and trade: spill pallets, containers, cut-to-size semi-finished products and special constructions in PP, PE, PVC-U and other technical thermoplastics – custom manufacturing to drawing from batch size one, from Swiss production in Ostermundigen.
Looking for a leak-tight plastic construction?
Send a drawing or your dimensions with medium, temperature and requirements. We choose the resistant material, weld the construction and test the tightness – personally from Switzerland.
