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How to Design a Spreader Bar
Sparta’s approach to optimizing the spreader bar design (otherwise known as lifting bar or lifting beam) is an iterative process. Variations in the design of the multi-lift spreader bar evolve over a period of time as requirements and technology change and the demand for a more efficient product is desired. In the following article I discuss the design process for optimizing the spreader bar design used for hoisting and lifting.
In the past, we have been asked by several customers to design variations of a multi-lift spreader bar. These spreader bars generally have one structural member down the center with hooks off the bottom to suspend a load. They also include either one or two hooks off the top to attach to a spreader bar. The idea is to distribute the load over the beam so you can pick up large items with vertical slings and only one crane.
I want to take this opportunity to walk through the spreader bar design process and discuss some design optimization techniques that occur during the engineering phase of this product. The Sparta spreader bar has been through three design iterations described below. This process demonstrates how design engineers at Sparta optimize for manufacturing.
Design #1 – Typical Spreader Bar Design
The typical approach to a spreader bar design looks like this:
This example has an I-beam down the center and a series of lugs welded on the top for attaching to the crane. This spreader beam also has a series of lugs on the bottom to attach to the product. The double lugs on each end allow for pinning the unit directly to the hook of a crane to maximize hook height. This is especially a concern on indoor overhead cranes. This design has roughly 206” of weld, weights 450lbs and when running the assembly expert from Solid Works you get the following results:
This is usually the spreader bar lifting product that customer asks for. It gets the job done, it meets all the functional requirements of the design, but it isn’t exactly “optimized.” At Sparta, we design products that are optimized for manufacturing in order to save on resources and manufacturing time and to create a more efficient design overall.
Design #2 – One Part and Zero Welds – Optimizing the design of the spreader bar
Achieving Cost Savings
As the design engineer is alternating between producing rough concepts for the design and calculating the approximate material size, they should also be questioning what can be done to optimize the product for manufacturing?
Generally, when designing products for industrial & oilfield applications optimization generally means reducing the price. The following factors are a good indication of a product’s price:
2. Inches of weld
3. Number of parts.
Reducing any of these factors without substantially increasing complexity will net an overall savings.
One of my favorite ways to optimize a design is to take multiple parts and try and combine them into one part. In the case of the spreader bar design, this approach can be taken to the extreme and the spreader bar design can be manufactured as one piece (with no additional welded parts). This would look something like this:
Evaluating A One Part, No-Welding-Required Spreader Bar Design
The main advantage to a one part / zero-weld spreader bar design: The main advantage of reaching a zero welding state is that because this is a below the hook lifting device, the welds need to get magnetic particle inspection done. If you can design your product to have no welds this will circumvent needing an annual weld inspection (done by a somewhat specialized non-destructive tester).
The main disadvantage to a one part / zero-weld spreader bar design: The problem with this particular design system is that they are heavy and a susceptible to out of plain bending. You also need some fairly specialized machinery to cut this design (tend to be >1.5” thick).
Design #3 – A Zero Weld and Scalable Design – Optimizing the design of the spreader bar
Another iteration in the spreader bar design process also yielded a no welding system. This time, we added some resistance to out-of-plane bending as well as reducing the technology required to build the unit. The third iteration looks like this:
This design utilizes two structural channels which are great for out of plain bending and also very scalable to any required size. The plate steel lugs are simple and easy to manufacture and can essentially be made to any strength. The same lug is repeated throughout the design regardless of whether a lifting point is needed above or below the beam. This gives the user plenty of places to attach to and has the added advantage of being configurable and adjustable to whichever width is required. This spreader bar design also very efficient and transfers forces between the suspended load and the cranes holding it. The whole system requires no welding and can be manufactured using a band saw and a drill press (if necessary). This design uses 9 parts but most of them are repeated and in total there is only 2 unique parts.
Related Content: Sparta has several spreader bar designs available for purchase
A Design Engineer’s Process for Creating a Spreader Bar Design
No product is ever finalized. Constant improvements to design elements and overall design solutions should be evaluated as customer requirements change and technology improves. The three spreader bar design iterations discussed above demonstrates some of the improvements made during the concept phase. Our design engineers continually evolve one design idea over time. After the design phase is complete and we are happy with the improvements, the design engineer can be move on to the analysis phase and detailed design drawings.
If you are interested in purchasing spreader bar design drawings for any of our spreader bars, please contact us for more information.
- Spreader Bars & Manbaskets
- Rating Plates and B30.20 Below the Hook Lifting Devices
- Heavy Tand-Tri Crane Dolly
- Spreader Bar 101 – Why do I need a spreader bar?
- Spreader Bars vs. Lifting Beams