Plants with mixed SKUs ask the same question early: can one machine wrap everything? For shrink film, the honest answer is that an L-bar sealer comes close, but only inside its size envelope. Outside that envelope you are not buying a machine, you are buying a problem.
This article covers what a flat type sealing machine actually does, the one dimension rule that decides whether it fits your product, and how to read the specification sheet before you order.
What a Flat Type Sealing Machine Actually Does
The names overlap in this category. Flat type sealing machine, L-bar sealer, and L type sealer all describe the same idea: a sealing frame shaped like an L that closes on the film, seals two sides, and cuts at the same time.
The process has two stages, and they are usually two separate machines:
1. Seal and cut. The product sits on the infeed, film folds over it, and the L-shaped blade seals the two open sides while trimming the waste. What comes out is a loose bag around the product.
2. Shrink. The bagged product passes through a hot air tunnel, the film tightens, and you get the finished pack.
The SD-BL450 is the first stage. It seals and cuts; it does not shrink. If you buy the sealer without a tunnel, you get bagged products, not packed ones.
Where It Sits on the Line
Upstream, products arrive either manually or from a conveyor. Downstream, the shrink tunnel does the shrinking, then packs cool and go to boxing or palletizing. The sealer is the middle step and usually the one that sets the pace for the whole line, so its speed rating deserves a careful read.
The One Rule That Decides Everything: W + H
Read the size specification in this order:
- Product width: 30 to 300 mm
- Product height: 1 to 150 mm
- Width plus height (W + H): must not exceed 400 mm
- Standard length: 130 to 500 mm. Products between 50 and 120 mm long need an additional sealing attachment.
The W + H limit is the one people miss. A product 300 mm wide and 60 mm high is fine: 360, under the limit. A product 300 mm wide and 150 mm high is 450, over the limit, and no amount of adjustment will fix it. The frame physically cannot close around it.
The limit traces back to the blade. The cross blade is 470 mm long, and the W + H ceiling of 400 mm leaves the margin the seal needs on both ends. When you see a competitor claim a bigger W + H on a similar footprint, check their blade length first.
Do this before any enquiry: take your largest product, write down width, height, and length, and check all three against the numbers above. It takes two minutes and prevents the most common mismatch in this category.
SD-BL450 Specifications
| Parameter | Value |
|---|---|
| Power supply | 220 V, 50–60 Hz, 6 A |
| Power | 1.7 kW |
| Air supply | 0.5–0.7 MPa |
| Packing speed | 10–35 pcs/min (depends on product size) |
| Conveyor speed | 15 m/min |
| Max product width | 300 mm (min 30 mm) |
| Max product height | 150 mm (min 1 mm) |
| W + H limit | ≤ 400 mm |
| Standard product length | 130–500 mm (50–120 mm needs an attachment) |
| Longitudinal blade | 570 mm |
| Cross blade | 470 mm |
| Belt width | 330 mm |
| Table height | 780 mm |
| Film width | 150–450 mm |
| Max film roll diameter | 300 mm |
| Film type | POF |
| Film thickness | 0.015–0.025 mm |
| Sealing temperature | 180–225°C (varies with film and ambient) |
| Machine dimensions | 1,650 × 1,050 × 1,400 mm |
| Working environment | 0–40°C, humidity ≤ 90% |
Two numbers in that table carry more weight than the rest. The 780 mm table height is what you need to match against your existing conveyor, and the 0.5–0.7 MPa air supply is what your compressor has to hold, not occasionally reach. Plants that run the sealer off an already loaded compressor get inconsistent seals and blame the machine.
Film: What the Settings Actually Mean
The machine runs POF. Film thickness between 0.015 and 0.025 mm covers most packs, and the choice is a cost-versus-toughness decision: thinner film costs less per pack and punctures more easily in transit, thicker film costs more and forgives rough handling. If you are shipping export containers, start at the thicker end and step down once you see how the packs arrive.
Sealing temperature sits between 180 and 225°C, and it is not a set-once value. It depends on the film grade and the ambient temperature in your plant. A line that seals correctly at 195°C in winter can produce weak seals at the same setting in a 38°C summer shop, because the film starts warmer. Some operators run two settings by season, and that is a reasonable practice rather than a workaround.
Film width runs 150 to 450 mm, and the roll diameter tops out at 300 mm. A larger roll means fewer changes per shift, which matters more than people expect once you are running continuously.
Reading the Speed Rating
The rating is 10 to 35 packs per minute, and the parenthetical matters more than the range: actual speed depends on product size. Small products hit the top of the range because the frame travels a short distance and the film advances quickly. Large products drop toward the bottom, because the sealing dwell and the film advance both take longer.
The conveyor runs at 15 m/min, which caps throughput regardless of how fast the frame cycles. If a supplier quotes you 35 pcs/min without asking what your largest product is, they are quoting the best case, not your case.
The Operating Sequence
For anyone who has not run one, the sequence per shift start is short:
1. Load the film roll and thread it over the folding plate, checking that it tracks centered.
2. Set the sealing temperature and dwell time for the film you loaded, then run two or three scrap packs and pull the seals apart to check them.
3. Set the product stop and guide to the product width so packs sit square to the blade.
4. Feed product and let the frame cycle. The operator’s job is loading, not timing.
5. Send the bagged packs into the tunnel and check the first finished packs for loose corners before running the batch.
Step 2 is the one that gets skipped, and it is the one that prevents an hour of bad packs.
Where the Sealer Stops and the Tunnel Starts
The sealer draws 1.7 kW, which is modest. The tunnel is where the power goes. Our SD-4522 internal circulation tunnel runs about 6 kW with dual frequency drives and insulation, and the SD-4020 is the economy version at around 9 kW with a single drive and no insulation. On two shifts, that difference shows up on the power bill long before it shows up in the machine price.
Pair the sealer to the tunnel by throughput, not by price. An undersized tunnel throttles a sealer that could run faster, and you end up paying for capacity you cannot use.
When an L-Bar Sealer Is the Wrong Machine
Three cases send buyers elsewhere. Products longer than 500 mm do not fit the standard frame. Products whose width plus height exceeds 400 mm do not fit at all. And very high volume single-product lines are better served by a dedicated wrapper, which is why tape roll packaging usually runs on machines built for rolls, like the SD-60SS, rather than on a general purpose L-bar sealer.
If your product mix is wide and volumes are moderate, the L-bar sealer is usually the right first machine. If volumes are high and the product never changes, it is the wrong one.
Common Questions
Can it handle my smallest product?
Width goes down to 30 mm and height down to 1 mm, so the lower bound is rarely the problem. Length is. Below 130 mm, and specifically between 50 and 120 mm, you need the additional sealing attachment. Tell us your shortest product when you enquire.
Can I use PVC or PE film instead of POF?
This machine is specified for POF. Running a different film changes the sealing temperature and the shrink behaviour, and the tunnel has to match. Ask before you switch, not after.
Do I need an air compressor?
Yes. The seal and cut action is pneumatic and needs 0.5 to 0.7 MPa held steady. If your compressor is already running other equipment near its limit, budget for a dedicated one.
How do I know which tunnel to pair with it?
Match the tunnel throughput to the sealer’s realistic output for your largest product, then check the tunnel aperture against the pack cross-section. If you send us your product dimensions and target packs per shift, we will size the pair for you.
