A catalog shows you a product. A factory visit shows you whether the product you were shown is the product you will actually receive. For a sliding door — a large, heavy, weather-exposed moving assembly built from extruded aluminium, a thermal-break strip, glass, rollers and named hardware — the gap between a brochure and a building site is wide enough to sink a project. This guide is written for buyers, specifiers and distributors who are preparing to walk a sliding door factory and want a checklist that survives contact with reality.
Video calls are useful for first contact, but they are edited. The camera shows the corner the host wants you to see. A physical walk lets you pull a sample off the line, run your thumb along a cut corner, and watch whether the roller path is machined or improvised. The single most valuable thing a visit buys you is the right to be unhurried and skeptical in the same room as the people who build the door.
A visit without your project data is a tour, not an audit. Before you book the flight, prepare a one-page data block and bring it printed. The factory can only verify claims against the thing you are actually buying, so the more specific your inputs, the more real the answers become.
| Bring to the visit | Why it changes the answers |
|---|---|
| Your opening sizes in millimetres (width and height per leaf) | Lets the factory confirm the leaf fits a real series instead of a generic promise. |
| Your glass build (cavity, coating, gas fill, laminate) | Thermal and acoustic results are a function of glass, not just the frame. |
| Climate and exposure loads (wind, salt, sand, temperature swing) | Drives which hardware rating and which coating grade you actually need. |
| Your local code references and the certifying body you answer to | Separates what the factory can evidence from what your jurisdiction requires. |
Ask to see the aluminium itself. ALPES works with 6060-T66 alloy at 1.8–2.5 mm wall thickness. The meaningful question is not "do you use aluminium" but "do you extrude, or do you buy cut lengths from someone who does?" A plant that extrudes controls the dimensional consistency of every chamber; a plant that only cuts cannot. Look for the billet source and the extrusion press, and ask whether wall thickness is measured per batch.
The polyamide strip is what actually interrupts heat flow through the metal frame. Look for PA66GF25 — glass-fibre-reinforced polyamide 66 — formed into a multi-chamber section. Ask where the strip is sourced and whether it is a continuous, properly knurled insertion rather than a thin tape. The width of that strip matters: on the casement side of the range, multi-chamber strips run 34–44 mm, which is part of why those systems reach their published K values.
Ask for a cut corner sample you can handle. A full glue-injection process with injection-moulded structural adhesive and complete corner sealing is a different animal from a mechanically crimped corner with a loose gasket. The corner is where water and air decide whether to enter, so it deserves more than a glance.
Watch how a sash is squared and how the roller carriage is set. Squareness is not a feature you can see in a photo; it is the difference between a door that glides and one that drags from day one. Ask whether squaring is jig-controlled and whether rollers are set to a spec rather than adjusted by feel.
The insulated glass unit is most of the door's area and most of its thermal and acoustic behaviour. Ask about the IGU build: cavity width (24A on SL112/167, 27A on SL126/182(75)), gas fill, warm-edge spacer, and whether the cavity is verified per batch. Glass weighs roughly 2.5 kg per square metre per millimetre of thickness, so the glass choice also sets how much load the rollers must carry — which loops straight back to the roller rating.
These are the parts that decide whether a sliding door still works ten years from now.
A sliding sash is carried by rollers, not hinges. ALPES publishes per-sash ratings of 220 kg driving capacity (SL112/167) and a 400 kg, 20-wheel self-balancing pulley system (SL155). Ask to see the rating on the actual carriage, not in a brochure. One honesty point worth repeating on the floor: the rating is per sash and is dominated by glass weight, so a heavier glass build lowers the usable size even if the carriage rating stays the same.
Water will reach the track; the only real question is where it goes. Look for a genuine drainage path rather than a sealed channel: a 45 mm high-ｄｒｏｐ bottom track with an 85 mm water barrier (SL112/167), or an 8 mm low track / 43 mm high track with eave-style waterproofing (SL126/182), or passive check-valve drainage (SL155). The red flag is a track with no visible weep path — water that cannot leave will eventually find the room.
Sliding doors seal by contact, not by full-perimeter compression the way a casement does. Look for continuous four-side sealing and a gasket at the frame-sash joint (butyl rubber on SL126/182(75)). Ask to see the gasket run unbroken at the corner — a cut-and-butt joint there is where drafts start.
Frame wall width is a property of the series, not of the number of tracks. Four-track SL155 is 155 mm deep; three-track SL126/182 is 182 mm deep. The deeper frame is not automatically "better" — it defines how much structure and glass the section can carry. Ask which series your opening actually maps to instead of assuming more tracks mean more door.
When a sliding glass door manufacturer sources named hardware, ask to see the branded parts on the shelf, not a label that says "German hardware." ALPES works with ROTO and Winkhaus (Germany), CMECH (Red Dot design award, 30,000-cycle tested) and Wehag (Germany). One honesty point to keep in view: a 30,000-cycle figure is a bench test of the hardware, not a promise of door lifespan, and it is measured on the component, not on your assembled leaf.
A trading company can show you samples and prices. It cannot show you the extrusion press, the corner-injection bench, or in-house QC samples carrying your project number. None of that makes a trader dishonest — but it changes who answers the hard question when something is wrong six weeks before shipping. Know which one you are standing in front of.
| Signal | System factory | Trading desk |
|---|---|---|
| Extrusion press on site | Yes, you can walk to it | No — profile is bought cut |
| Named hardware in stock | ROTO / Winkhaus / CMECH / Wehag visible | Often generic or substituted |
| Cut-corner samples on request | Readily available | Rare or refused |
| Who re-answers after a spec change | The builder | A middle layer |
| Ask | A good answer | A red-flag answer |
|---|---|---|
| Where is the profile extruded? | Names the plant and the alloy (6060-T66) | "We have many suppliers" |
| What is the thermal-break strip? | PA66GF25, multi-chamber, named width | "Insulation strip" with no material |
| What is the roller rating per sash? | States kg and which series (220 kg / 400 kg) | "Heavy duty" with no number |
| How is the corner sealed? | Glue-injection, shows a cut sample | Points to a screw or crimp only |
| Can I see the roller drainage path? | Opens a track and shows the weep route | "It is waterproof" with no detail |
Buyers who source from china sliding door manufacturers should know exactly which claims are verified and which are project-specific. The table below separates the two so you can write the right items into the purchase order.
| Published and verifiable | Must be requested per project | Why the gap exists |
|---|---|---|
| 6060-T66 alloy, 1.8–2.5 mm wall | Sliding-door thermal value (K / U) | Not published for sliding series; it is a function of your glass build |
| PA66GF25 multi-chamber thermal break | Max leaf size for your glass weight | Rating is per sash, dominated by glass mass |
| ROTO / Winkhaus / CMECH / Wehag hardware | Project certification for your jurisdiction | Factory evidences; it does not act as your certifying body |
| 100,000 m² Foshan + Zhaoqing base | Warranty terms in writing | Not stated here; request the document before ordering |
| K 1.3 / 1.6 / 1.7 on AW90 / C120 / C116 | Sliding-door performance claims | Those K values belong to casement / tilt-turn, not the sliding family |
Do I need to visit in person, or is a live video walk enough? A live video walk is a good first filter, but only an in-person visit lets you handle cut samples and watch the line unedited. Use video to shortlist, visit to confirm.
What is the most common thing factories try to avoid showing? The corner joint and the track drainage path. Both are where long-term failures begin, so reluctance there is worth noting.
Is a larger manufacturing base always better? Scale helps with consistency and lead time, but the deciding factors are vertical integration (extrusion, corner process, QC) and named hardware — not square metres alone. ALPES operates a 100,000 m² base across Foshan and Zhaoqing.
Why does my glass choice affect the roller rating? Glass is most of the sash weight. A heavier build means the same carriage carries less safety margin, so the maximum leaf size drops even if the roller rating is unchanged.
Can the factory supply my local certification? A factory can provide test reports, drawings and declarations. It does not stand in as your local certifying body — that relationship is yours to establish with your jurisdiction.
What should I put in the purchase order after the visit? The exact series, leaf sizes in millimetres, glass build, hardware brand, drainage type, and every performance figure you were promised — written, not assumed.
