Introduction to Z Purlins and Roll Forming
Z purlins are light-weight structural steel members with a Z-shaped cross section. They are most commonly used as roofing and wall materials in metal building systems. Z purlins provide an efficient and cost-effective option for roof and wall framing.
Roll forming is a metal working process used to create long sheets or sections with a uniform cross-section. It works by forcing a strip of metal through a series of roller dies that bend and form the material into the desired shape. Roll forming is an efficient, high volume production method ideal for producing components like Z purlins.
Advantages of Z Purlins
There are several key advantages that make Z purlins a popular choice:
High Strength-to-Weight Ratio
The Z-shape gives Z purlins greater strength and stiffness relative to their light weight. The flanges help stabilize the member against buckling and twisting. This high strength-to-weight ratio allows Z purlins to span greater distances between supports.
Ease of Installation
Z purlins feature lips along the flanges that allow them to interlock with sheeting. This self-aligning capability makes installation quick and simple. Z purlins don’t require welding or bolting in most applications.
Cold-formed Z purlins are an economical option compared to hot rolled steel sections. Minimal material is used to achieve maximum structural performance. The automated roll forming process is also fast and affordable.
Available in Long Lengths
Z purlins can be continuously roll formed to lengths over 60 feet. This reduces splicing and can speed up installation time. It also allows for fewer roof and wall supports.
Roll forming lines can be set up to produce custom Z purlin sizes and gauges for specialized applications. Features like bolted tabs can also be integrated into the profile during forming.
Overview of Z Purlin Roll Forming Machines
Z purlin roll forming lines take a coil of flat sheet metal strip as the raw input material and process it through a series of forming stations to incrementally bend the strip into the final Z shape.
Here are the key components that make up a Z purlin roll forming system:
- Uncoiling Machine – Feeds the flat strip from a coil into the roll forming line. It straightens and flattens the coil material to prepare it for forming.
- Accumulator – Acts as a buffer to allow uninterrupted operation of the roll forming line by taking up any slack in the feed material.
- Guide Roller Assemblies – Position and support the strip to keep it tracking straight through the line.
- Forming Stations – Each station has a pair of shaped rollers that make a series of small incremental bends to gradually form the strip into the Z profile.
- Hydraulic Press – Applies pressure to make the final punching/cutting operation for holes or slots in the web.
- Shearing Device – Cuts the continuously formed Z purlins to specified lengths as they exit the line.
- Conveyor System – Transports the cut Z purlins out of the forming area.
The key advantages of Z purlin roll forming machines include:
- Highly automated process for efficient production
- Capable of producing lengths over 60 feet to minimize splicing
- Adjustable forming rollers allow for custom purlin depths and thicknesses
- Built-in quality control systems help ensure dimensional accuracy
- Safety guards and protective wear strips for reliable operation
- Low maintenance requirements compared to other forming processes
Roll Forming Process Step-by-Step
The roll forming process involves gradually bending and shaping a metal strip through a series of roller stations in a continuous sequence:
The strip (typically galvanized steel) is unwound from a coil by the uncoiling machine and fed into the roll former in a flat, straightened condition.
Accumulators act as buffers that take up the slack between the uncoiling and forming areas to allow both processes to operate continuously at their own pace.
Guide rollers or other positioning devices keep the strip aligned, centered, and supported throughout the line.
As the strip passes through each station, precisely positioned rollers make small bends until the complete profile is formed. The bend radius is controlled to avoid cracking the metal.
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A shearing device cuts the continuously produced Z purlins to specified lengths as they exit the roll former.
Hole Punching or Slotting
Optional secondary processes like punching holes or making slots can be integrated using hydraulic presses and die tools.
Formed Z purlins are automatically conveyed out of the system on a roller table or conveyor for easy bundling and distribution.
Sensors, gauges, and scanning systems are utilized to monitor critical dimensions and immediately flag any out-of-tolerance parts.
Primary Components of a Z Purlin Roll Forming System
Modern high-speed Z purlin roll forming lines integrate a range of components and technologies to maximize productivity and precision. Here is an overview of the key elements that make up a complete system:
The uncoiler or decoiler feeds the flat coiled strip into the roll former. Key features include:
- Powered unwinding of coil
- Expandable mandrel to accommodate different coil widths
- Straightening rollers to remove coil curvature
- Feed roller tables with adjustable speed control
- Protective enclosures and safety devices
The accumulator acts as a buffer zone between the uncoiler and form rollers:
- Allows continuous uninterrupted operation of line
- Looping pits or cartridge-type accumulators
- Dancer rollers maintain optimal strip tension
Sequential stations have counter-rotating rollers that make incremental bends:
- Hardened rollers custom machined to precise profiles
- Hydraulic or servo-electric roller adjustment
- Quick change-out for rapid reconfiguration
- Roll protection from wear or damage
Shears or saws cut the formed purlins to length:
- Pneumatic, servo-electric, or hydraulic actuation
- Fixed or flying ball screw slides
- Precise cut length control and positioning
- Cycle rates matched to roll former speed
Optional hydraulic end punching units create holes or slots:
- Single or multi-punch heads
- Punch and die tool sets for holes or slots
- Programmable punch patterns and sequences
- Stripping mechanisms clear scrap after punch
Belt or roller conveyors transport finished purlins:
- Smooth transfer from the production line
- Adjustable speed control
- Stops or power turns to meter purlin flow
- Offloads bundles for shipping or staging
The control system automates and monitors the roll forming process:
- PLC-based control with HMI operator interface
- Integration of all machine modules and safety devices
- Monitoring of production speed, temperatures, and pressures
- Database storage of job/order recipes and parameters
- Diagnostic capabilities and alarm notifications
Safety guards and devices prevent injury:
- Interlocked barriers around moving parts
- E-stops, pull cords, and safety mats
- Sensors that halt motion if tripped
- Lock-out mechanisms for maintenance
Optional Secondary Processes
In addition to the primary roll forming process, Z purlin lines can integrate secondary processing capabilities:
Hydraulic punching units create holes in the purlin web:
- Enables bolted connections for specialized purlin jobs
- Single or multi-punch heads for different hole patterns
- Quick change-out of punch/die sets
- Scrap stripping mechanisms clear leftover slugs
Narrow slots can be formed in the web for bridging connections:
- Slotting heads cut various slot shapes and lengths
- Slots enable overlapping of purlins atop girts/purins
- No drilling or secondary operations required
Local stiffeners can be formed into the purlin web:
- Rollers indent short stiffening ribs into the web
- Strategically placed for added structural rigidity
- Improves span capacity and strength
Custom profiles can be produced:
- Forming rollers machined for unique shapes
- Special options like tapered purlins available
- Broadens range of applications beyond standard purlins
Quality Control and Measurement
Integrated inspection systems and in-process monitoring ensure the roll formed Z purlins meet stringent quality standards:
- Laser or optical gauges scan critical dimensions
- Monitor web height, flange width, hole placement, etc.
- Probe contact or non-contact measurement
- Real-time detection of any out-of-tolerance parts
- Ultrasonic or radiation gauges measure material thickness
- Verify correct gauge along entire purlin length
- Monitor for thinning or thickening of material
- High resolution cameras provide views of all sections
- Operators examine purlins for defects continuously
- System alerts for any line stoppages or faults
- All measurement data is logged and archived
- Statistical analysis for capability studies
- Traceability for tracking coils or production lots
- Laser or camera scans create digital models
- Compare to CAD models to detect variations
- Advanced QA tool for comprehensive analysis
Practical Applications of Z Purlins
Thanks to their high strength, long span capability, and ease of installation, Z purlins are ideal for large metal buildings with open floor plans:
- High ceilings and widely spaced columns suit Z purlin long spans
- Interlocking purlins quickly cover large roof areas
- Reduced structural steel needs cut costs
- Minimize interior columns to maximize open floor space
- Long spans facilitate flexible layouts and clear sight lines
- Easy to add doors, lights, ventilation as needed
- Long roof spans create open interior layouts
- Ideal for “big box” stores like Walmart or Target
- Can integrate skylights or clerestories
- Unobstructed interiors accommodate seating
- High roofs with long spans suit sanctuaries
- Cost effective for large gathering spaces
- Clear span interiors for fields, tracks, courts
- Allows heights needed for gymnasiums, arenas
- Light-weight, easy to install and reconfigure
Benefits of Using Z Purlins
There are many compelling benefits that make Z purlins a smart choice for metal building projects:
- High strength-to-weight ratio
- Thinner gauge material can span greater distances
- Z-shape provides superior flexural rigidity
- Light-weight composition requires less raw material
- Reduces number of interior columns and rafters
- Smaller foundations result in additional savings
- Speedy installation with interlocking system
- Long sections minimize splicing and connections
- Roll formed standard lengths for quick ordering
- Various depths and gauges readily available
- Easily integrated with other building systems
- Custom options like holes or stiffeners available
- Lower material cost than hot rolled sections
- Highly efficient automated production
- Quick payback compared to other structural options
Cost Analysis of Z Purlins
Z purlins provide excellent value relative to the performance they deliver. Here is a look at the typical cost factors:
- Galvanized steel coil feed material
- Varies based on steel prices and coating
- Heavier gauge yields greater capacity
- Capital investment in roll forming equipment
- Labor, utilities, maintenance, consumables
- Higher automation = lower labor cost
- Z purlins allow longer spans so fewer needed
- Also reduces quantity of rafters, girts, columns
- Less complex connections vs. built-up sections
- Interlocks with sheeting for quick assembly
- Pre-cut lengths speed on-site erection
- Minimal use of bolts, welds, or clips
- Durable galvanized coating for long service life
- 30+ year building lifespan easily achievable
- Low maintenance requirements
Choosing the right Z purlin for an application involves considering factors like:
- Required load capacity
- Roof slope and span between supports
- Building width and purlin run lengths
- Wind and snow load levels
- Exposure and climate considerations
- Budget constraints or cost targets
- Availability of raw material coils
- Existing inventory of certain sizes
Load span tables are used to determine the necessary depth and thickness based on application requirements. A qualified engineer performs final purlin sizing and specification.
Trends and Innovations
Some current trends and innovations in Z purlin roll forming include:
- High-Strength Steel – New Generation 3 steels allow greater spans and load capacity or material savings.
- Inline Punching – In-process hole punching reduces secondary operations.
- Servo-Electric Components – Servo motors provide speed and precision improvements.
- In-Line Gauging – Real-time gauges help detect any forming defects.
- Pre-Curved Purlins – Ability to induce curvature for pre-arched building designs.
- Specialty Coatings – Colored or patterned finishes now available beyond basic galvanizing.
- Sustainable Materials – Use of higher recycled content steel.
- Automated Production – Systems that run lights out with minimal oversight.
What is the typical thickness of Z purlins?
Z purlins are commonly available in thicknesses ranging from 16 gauge to 12 gauge. The most popular size is 16 gauge which provides adequate strength for many typical purlin applications. 14 gauge and 12 gauge offer greater load capacity for longer spans or heavy loading.
What depth Z purlins are generally used?
Common Z purlin depths include 8″, 10″, 12″ and 16″. Deeper sections like 10″, 12″, or 16″ are used when longer roof spans are required. Shallower 8″ purlins are suitable for shorter spans and less loading.
How long can Z purlins span?
With 16 gauge material, typical Z purlin spans range from 15-30 feet depending on the load, purlin depth, and other factors. Longer spans are possible with larger Z sections, heavier gauge material, or higher strength steel grades.
How are Z purlins connected to rafters or joists?
Z purlins feature integral self-aligning lips that enable them to be directly attached to metal roof deck or sheeting using simple through-fastener screws. This creates a stable, fixed roof diaphragm.
Do Z purlins require any welding or bolting?
Most Z purlin roof systems do not require welding or bolting. The self-interlocking purlin and roof panel design allows quick installation using just screws into the supporting structure. Some applications do use bolts for specialized connections.
What is the typical spacing between Z purlins?
For roof framing, Z purlins are commonly spaced 4-6 feet apart. This spacing may vary based on roof loads, the purlin depth and gauge, and the roof panel specifications. Purlins are typically spaced closer together near eave lines.
Should Z purlins be installed with the flange up or down?
Orienting the purlins with flanges up helps prevent water from pooling at the purlin joints. It also provides a flat surface for consistent contact with the roof panels. Some designers prefer flange down configurations but additional panel clips may be required.