U-Bolt Application and Design

 
 
U-bolts are single piece cold or hot formed fasteners. U-bolts are manufactured from wire and round stock by cold or hot forming methods. U-bolts are sold throughout industry, are available with saddle clamps and can be custom manufactured to design specifications. With all custom manufactured hardware, there will be setup costs in terms of tooling.

Common u-bolt installation and applications include the following:

  • Antenna Section secured
  • Wire cable
  • Automotive Leaf Spring
  • PIping supports

Applicable ASTM Specifications:

  • A153 - Hot dip galvanizing specification.
  • A193 - Alloy steel and stainless steel bolting materials for high temperature service.
  • A194 - Carbon and alloy nuts for bolts for high pressure and high temperature service.
  • A307 - Carbon steel bolts and studs ranging from 1/4" through 4" diameter.
  • A320 - Alloy steel and stainless steel bolting materials for low temperature service.
  • A325 - Structural bolts, steel, heat treated, 120/105 ksi minimum tensile strength.
  • A354 - Quenched and tempered alloy bolts, studs, and other externally threaded fasteners.
  • A449 - Quenched and tempered steel bolts and studs.
  • A490 - Structural bolts, alloy steel, heat treated, 150 ksi tensile strength.
  • A563 - Standard specification for carbon and alloy steel nuts.
  • F1554 - Anchor bolts designed to anchor structural supports to concrete foundations.
  • F2329 - New specification covering hot dip galvanizing.
ASTM - American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services.

U-Bolt Types

General U-bolt design Consideration:

Bend Radius

Round formed u-bolts, square or rectangular formed U or v-bolt the minimum bend radius is the driving design limitation The minimum ben radius achievable is governed by material characteristics, size and end-item strength requirements. During the bending or forming operation, deformation occurs at the radii as the material is stretched and compressed over the forming mandrel or tooling. During the forming operation, the material is yielded and plastic deformation in the form of diameter loss or necking at the bend area.

In general, the larger the radii per unit of material thickness, the less the necking or deformation of the material at the bend area. In general, one should design their u-bolt with the largest possible bend radius. The minimum radius should not be less than 1/2 X (0.5 X) the wire or rod diameter for low tensile materials and 11/16 (.69 X) the wire diameter for high tensile materials.

Steels with low toughness and ductility should have the radii larger than 11/16 X (.69 X) round diameter. Radii less than these are manufacture-able, however do tend to have excessive residual stresses in the bend area and cracking, excessive necking may occur during forming.

Be aware that a reduction in initial rod or wire diameter will occur in the bending area regardless of material characteristics.

Thread and Bend radius:

In general, thread are manufactured on the round stick before forming operations. The minimum distance between the last thread and the bend radius is not less than 1.5 X diameter of the round stock, however 2 X the u-bolt diameter is preferred.

Bend radius Flattening:

The inside area of a u-bolt radius can be manufactured with a flat contact area for better mating as assembly. Depending on material thickness, ductility one should design the thickness or the width of the flat area to be not less than +/- .025 ". Additionally, the flat contact area can be manufactured by post machining operations, however there will be a significant costing increase depending of volume os parts.
 
Dimensioning and Tolerancing:
 
Engineering drawings for custom U-Bolts and saddles should have the minimum required mechanical dimensions and tolerances required to manufacture the components. For example, when designing to industry standard wire or rod sizes, the engineering drawing should indicate the relative size (wire diameter) as a reference on the drawing face. Also, one can indicate the industry standard diameter within a materials specification note.
 
When dimensioning and tolerancing the U-Bolt radius, spread of other features, the design dimensions are placed on the geometry requiring the relative precision or mating requirements when using industry standard diameter stock.
 
More extensive and complete engineering dimensions and tolerances may be required in precision applications.

U-bolt Saddles, Saddle Clamp Plates:

Saddle clamps are design or supplied and a matched set to the u-bolt. Saddle clamps are used to apply the clamping forces, distribute the assembly loading and properly secure to piping, antenna, etc. In the mage shown, the saddle clamp in manufactured by forming operations from flat sheet metal stock. The thru hole features where likely punched or pierced prior to the forming operations.

 

 

U-Bolt with Saddle Clamp

Size
Thread Length
Fits
1/4-20 "D" (Thread Major Diameter and Pitch)
P
L
T
(Thread Length)
Pipe/Tube
9/16
1-3/8
3/4
1/4
3/4
1-1/4
3/4
3/8
3/4
1-3/4
1
3/8
3/4
2-3/4
2
3/8
3/4
4-3/4
4
3/8
1
1-3/4
1
1/2
1-1/8
2-1/4
1-1/4
3/4
1-1/8
3-1/2
2-3/4
3/4
1-3/8
2-3/4
1-3/4
1
1-3/4
2-3/4
1-1/4
1-1/4
2
3-1/2
1-3/4
1-1/2
5/16-18 --> (T)
1-3/8
2-1/2
1-1/4
1
1-3/8
3-3/4
2-1/8
1
1-3/4
3
1-1/2
1-1/4
1-3/4
4-1/4
2-1/2
1-1/4
2
3-1/4
1-1/2
1-1/2
2
3-11/16
2
1-1/2
2
4-11/16
2-3/4
1-1/2
2-1/2
3-1/2
1-1/2
2
2-1/2
4-3/16
2-1/4
2
2-1/2
5-3/16
3
2
3/8-16 --> (T)
2
3-1/8
1-1/2
1-1/2
2-1/2
3-5/8
1-3/4
2
3
4-1/8
1-3/4
2-1/2
3-1/2
4-5/8
2
3
3-1/2
6-1/2
3
3
1/2-13 --> (T)
3
5
2-1/2
2-1/2
3-1/2
5-1/2
2-1/2
3
4
6
2-1/2
3-1/2
4-1/2
6-1/2
2-1/2
4
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