Learn proper techniques for applying and drying sealing adhesives on can lids. Includes mixing guidelines, equipment setup tips, and drying requirements for durable seals.

Preparing and Handling Sealing Adhesives

Mixing adhesives correctly is the first step for reliable can lid sealing. For water-based adhesives, stir them for 20-30 minutes before use—enough to create surface movement but avoid creating bubbles. Keep storage temperatures above freezing. Solvent-based adhesives need high-speed mixing (30-40 minutes) using foldable blades. Always use anti-static tools and ensure proper ventilation to meet safety standards.

Transportation and Filtration

When moving adhesives to the injection machine, use grounded containers and avoid contact with copper, brass, or zinc. Filter the adhesive before it enters the machine—a 40-mesh screen works best. Install pressure gauges to monitor clogs and clean the filter regularly to prevent blockages.

Adjusting Adhesives for Injection

Solvent-based adhesives: Use a Sealing Adhesive Adjustment Device (CCU) with gear pumps to maintain consistency. Heat the adhesive to 37-43°C—never exceed 49°C to prevent bubbles. Control adhesive volume by adjusting back pressure (30-50 psi).

Water-based adhesives: Transfer them using piston pumps, not gear pumps. Keep injection pressure stable between 15-30 psi. If temperatures vary by over 11°C daily, heated hoses help maintain consistency.

Setting Up the Injection Machine

The machine needs a lid stacker, clamping head, and plate matched to your lid design. Ensure it can achieve 2.1 injection turns and 0.75 reverse turns. Test clamping head speed using this formula:

Clamping Head Speed = Discharge Speed × Gear Ratio

For example, 350 lids/min × 7.5 gear ratio = 2,520 RPM. Check gear ratios manually if unsure by marking rotations during a feeding cycle.

Key Components and Operation Tips

Separation blade: Adjust its height to the lid’s curl height plus 0.001-0.007 mm. Too tight? Damaged lids. Too loose? Double feeds.

Clamping head fit: It must snugly hold lids without shaking. Loose heads cause uneven adhesive; tight fits lead to nozzle contact and blockages.

Upper press head cushion: It keeps lids in place and triggers adhesive flow. Ensure it applies enough pressure to prevent slippage but allows a 0.25-0.76 mm lift for lid movement.

Nozzle Positioning and Drying

Position the nozzle 0.8 mm above the lid surface. Keep it close to the clamping head wall without touching. After injection, dry lids thoroughly—solvent-based adhesives need ventilation, while water-based require heat. Let lids dry for 48+ hours before packaging to ensure full curing.

Safety Reminders

Follow fire safety rules for solvent-based adhesives. Their fumes can create flammable environments—store lids properly and ensure workspace ventilation.