Solvent cementing

How solvent cementing works

A solvent (or solvent-based cement) is applied to the joint surfaces. The solvent dissolves the top layer of the plastic, and when the parts are pressed together, the dissolved polymer chains intermingle. As the solvent evaporates, the chains re-entangle, forming a molecular bond that is essentially a weld — the joint becomes part of the material itself.

Solvents and cements by material

Material Solvent/Cement Working time Full cure Joint clarity
PMMA Acrifix 1S 0116 (solvent)
Acrifix 1R 0192 (reactive)		 30–90 s (solvent)
3–5 min (reactive)		 24–48 h Excellent (near-invisible with 1R 0192)
Polycarbonate Methylene chloride
Scigrip 16 (thickened)		 30–60 s 24–48 h Good (slight haze possible)
PET-G Methylene chloride
Cyclohexanone mix		 30–90 s 24–48 h Good
HIPS / ABS MEK (methyl ethyl ketone)
Acetone (ABS)		 15–45 s 12–24 h N/A (opaque materials)
PVC (rigid) THF (tetrahydrofuran)
Tangit PVC cement		 15–30 s 24 h N/A

Safety: Solvent handling

Methylene chloride, MEK, and THF are volatile organic compounds (VOCs) with significant health hazards. Work in well-ventilated areas or under fume extraction. Wear nitrile gloves (not latex — solvents pass through latex) and safety glasses. Refer to the Safety Data Sheet (SDS) for each solvent. Some jurisdictions restrict methylene chloride use — check local regulations.

Achieving optically clear joints in PMMA

For display cases and premium products, joint visibility must be minimized. The key factors for clear PMMA joints are:

  • Edge preparation: joint surfaces must be flat, smooth, and free of machining marks. Diamond-polished or flame-polished edges produce the best results.
  • Cement selection: Acrifix 1R 0192 (two-component reactive cement) produces the clearest joints. For water-thin solvent application, use Acrifix 1S 0116 via capillary action.
  • Gap control: surfaces must make intimate contact. Gaps wider than 0.1 mm will be visible even with reactive cement.
  • Dust and moisture: work in a clean, dry environment. Particles trapped in the joint are visible and permanent.
  • Cure time: do not stress the joint for at least 24 hours. Full strength develops over 48–72 hours.

Adhesive bonding

When joining dissimilar materials (plastic to metal, plastic to wood, or different plastics that are not solvent-compatible), adhesives provide a versatile solution.

Common adhesive types

Adhesive type Best for Bond strength Working time Limitations
Cyanoacrylate (CA) Small parts, quick assembly Medium–High 5–30 s Brittle, blooming (white haze), stress cracking on PC
Two-part epoxy Structural joints, dissimilar materials Very high 5–60 min Not optically clear, mixing required
UV-curable acrylic Glass-to-plastic, transparent joints High UV exposure: 10–60 s Requires UV transparency of at least one substrate
Double-sided tape (VHB) Mounting, signage, panels Medium Instant Not structural, temperature-dependent
Silicone sealant Flexible joints, sealing Low–Medium Skin: 15 min, cure: 24 h Low strength, flexible
Hot melt Packaging, temporary assembly Low 5–30 s Low temperature resistance, visible

Stress cracking warning

Cyanoacrylate adhesives (super glue) cause stress cracking in polycarbonate. Never use CA on PC parts. For PMMA, CA can also cause micro-cracks around the joint zone, especially if the acrylic has internal stress from machining. If CA must be used on PMMA, choose a flexible formulation and test on scrap first.

Welding (thermal and ultrasonic)

Ultrasonic welding

Ultrasonic welding uses high-frequency vibrations (20–40 kHz) to generate frictional heat at the joint interface. The plastic melts locally, and when vibration stops, the molten material solidifies into a molecular bond. The process is fast (0.5–3 seconds), repeatable, and requires no consumables.

  • Best materials: ABS, HIPS, polycarbonate, acrylic (with care)
  • Joint design: requires an energy director (triangular ridge) at the joint interface to concentrate vibrational energy
  • Applications: high-volume assembly, hermetic seals, internal fixtures

Hot-plate welding

A heated plate (matched to the material’s melting temperature) is placed between the two surfaces. Both surfaces are pressed against the plate until molten, the plate is withdrawn, and the parts are pressed together. Used for large, flat joints in PMMA, PP, and PE.

Hot-air welding

A hot air gun softens a plastic welding rod and the joint surfaces simultaneously. The rod material fills the joint, similar to metal welding. Common for PVC fabrication (tanks, ducts) and repair work.

Mechanical fastening

Mechanical joints allow disassembly and do not require curing time. They are often the best choice for products that need maintenance access, field assembly, or when joining thick sections where adhesive cure-through is impractical.

Common methods

  • Machine screws + threaded inserts: brass heat-set or ultrasonic inserts pressed into pre-drilled holes. Provides durable metal threads in plastic. Torque limits must be observed to prevent cracking.
  • Self-tapping screws: thread-forming screws for softer plastics (HIPS, ABS, foamed PVC). Not recommended for brittle materials (PMMA, PS).
  • Snap fits: integral clips designed into the part geometry. No additional hardware needed. Requires careful design of cantilever beam dimensions and material strain limits.
  • Rivets: aluminum or plastic rivets for permanent mechanical joints. Good for joining plastic to metal frames.
  • Magnets: neodymium magnets bonded into recesses for tool-free assembly/disassembly. Popular for display case lids and removable panels.

Drilling holes in PMMA

Standard metal drill bits can cause PMMA to crack, especially near edges. Use special plastics drill bits (60° point angle with polished flutes) or step drills. Always drill a pilot hole first, keep speeds moderate (1000–3000 RPM), and avoid excessive feed pressure. Maintain a minimum distance of 1.5 × material thickness from any edge.

Joining method comparison

Method Strength Optical clarity Disassembly Speed Cost
Solvent cement Very high Excellent No Medium Low
Reactive cement Very high Excellent No Medium Medium
Epoxy adhesive High Poor No Slow Medium
UV adhesive High Good No Fast High
Ultrasonic weld High N/A No Very fast High (equipment)
Screws + inserts Medium N/A Yes Fast Low
VHB tape Medium N/A Difficult Very fast Low

See also

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