What a KPO Fastening Set Contains
A crane runway rail is not held in place by the bolts alone. The KPO fastening system works as an assembly in which a shaped clamp presses the rail foot down onto a base plate, screw spikes or bolts provide the clamping force, a spring washer maintains that force against vibration, and an insulating component separates the rail from the grounded structure. Each element has a defined material and specification, and substituting one part without checking the others is the most common cause of a runway going out of gauge.
| Component | Qty per set | Material / grade | Reference standard |
|---|---|---|---|
| KPO clamp | 4 | Q235 | GB/T 700 |
| Screw spike | 8 | Class 4.6 Q235 / class 5.6 35# steel / class 8.8 45# steel | ISO 898-1 |
| HS bolt | 4 | Class 4.6 Q235 / class 5.6 35# steel / class 8.8 45# steel | ISO 898-1 |
| Hexagon nut | 4 | Class 5 35# steel / class 8 45# steel | Prevailing-torque type, DIN 985 |
| Spring washer | 8 | 65Mn spring steel | GB/T 1222 |
| Base plate | 2 | Ductile iron QT500-7 / QT450-10, or cast carbon steel | GB/T 1348 |
| Insulator | As required | Glass-fibre reinforced nylon PA66 | Project electrical requirement |
Clamp sizes in common use are KPO3, KPO6 and KPO9. Screw spikes are normally supplied at M24 in 150 mm, 160 mm and 180 mm lengths, and HS bolts at HS26 and HS32, so the assembly can be matched to the available installation depth and to the rail section. Base plates are made for UIC54, UIC60, 50 kg/m, 60 kg/m and S49 rails in ordered sizes, which is what allows one fastening family to cover a workshop crane and an outdoor gantry crane of very different capacity.
Matching the Clamp Type to the Crane Duty
Selection starts with the load the runway actually sees, not with the rail size. Three factors decide the clamp: the crane's lifting capacity and therefore the wheel load, the operating frequency and duty class, and the operating environment - an indoor light-duty workshop crane, a semi-portable crane in a storage yard, or an outdoor gantry crane exposed to wind load and temperature change.
A KPO3 clamp is used on smaller rails and light indoor cranes, where lateral and longitudinal forces are modest and the fastening mainly has to keep the rail in gauge. A KPO6 clamp is the general-purpose choice for medium-duty installation on workshop and yard runways with regular operation. A KPO9 clamp is intended for heavy-duty service, on large gantry cranes and on runways carrying high wheel loads or frequent travel cycles, where the higher clamping force and heavier section are needed to resist the rail creeping along the runway and the lateral thrust produced when the crane skews. In all three cases the clamp works with the same family of components, which simplifies spares holding: the clamp and the screw spike length are normally the only parts that change between duties.
Materials, Property Classes and Standards Compliance
The material specification is what determines the service life of the assembly. Clamps are produced from Q235 structural steel to GB/T 700, with a minimum yield strength of 235 MPa and a tensile range of roughly 370-500 MPa, which gives the clamp the ductility it needs to deform slightly and continue to hold rather than cracking under repeated wheel impact. Bolts and screw spikes are specified by property class under ISO 898-1: class 4.6 material has a nominal tensile strength of 400 MPa and a yield strength of 240 MPa, class 5.6 has 500 MPa and 300 MPa, and class 8.8 has 800 MPa and 640 MPa. Quality carbon steel grades such as 35# (GB/T 699) are used for the higher classes, and the class must be selected on the required clamping force rather than on the bolt diameter alone.
Nuts of the prevailing-torque type with a nylon insert, specified under DIN 985, are used so that vibration cannot progressively release the clamping force - a plain nut will loosen on a runway far faster than on a static structure. Spring washers are produced from 65Mn spring steel to GB/T 1222 and are replaced, not re-used, whenever the assembly is opened. Base plates are cast from ductile iron grades QT500-7 or QT450-10 to GB/T 1348, giving a minimum tensile strength of 500 MPa with 7% elongation or 450 MPa with 10% elongation respectively, or forged from low-carbon or high-carbon steel where the design calls for it. The insulator is a glass-fibre reinforced nylon PA66 component, chosen for mechanical toughness together with electrical insulation so that the crane structure remains safely isolated under damp and dusty conditions.
Installation and Torque Control
Installation follows a fixed order. The base plate is positioned and seated flat on the runway structure, and the rail is laid onto it; where the structure is irregular, the plate is bedded rather than pulled down by over-tightening the bolts. The insulator is fitted before the clamp, since forcing the insulator into position after the clamp is tightened damages the component and reduces its insulation. The clamp is then placed so that it bears evenly on the rail foot, and the screw spikes and HS bolts are tightened in a sequence that loads the plate evenly, working from the middle of the assembly outwards and finishing with a second pass at the specified torque.
Bolts should be tightened with a calibrated torque wrench to the value on the drawing. Under-tightening leaves the rail free to move and produces wear on the base plate and the clamp; over-tightening crushes the washer, cracks the insulator and can yield the clamp so that it never regains its grip. Expansion gaps at rail ends must be set at the ambient temperature recorded during installation, and the alignment and gauge of both runways checked after the fastening work is complete, because a runway fastened in a curved or misaligned condition is difficult to correct later.
Maintenance and Component Renewal
Once installed, the assembly needs a simple, regular routine: check every clamp for movement or a gap opening under the clamp face, verify torque on a sample of bolts, look for cracked or discoloured insulators, and inspect the base plates for cracking or corrosion. Spring washers and nyloc nuts should be treated as single-use items on a runway, because both rely on a deformation that is lost the first time they are tightened. Any clamp that has been deformed by impact should be replaced rather than straightened. Where a rail has to be renewed, the fastenings are normally renewed at the same time, since the cost of the assembly is small compared with the cost of a second access to the same position. Keeping a small stock of clamps, spikes, washers and insulators in the three duty sizes allows a defective position to be corrected during a normal maintenance window instead of waiting for a delivery.
Frequently Asked Questions
Q: What is the difference between KPO3, KPO6 and KPO9 clamps?
A: They cover different duty levels: KPO3 is used on smaller rails and light indoor cranes, KPO6 is the general-purpose clamp for medium-duty workshop and yard runways, and KPO9 is intended for heavy-duty service on large gantry cranes and high-load runways.
Q: Which bolt property classes are used in a KPO system?
A: Classes to ISO 898-1: class 4.6 with 400 MPa nominal tensile and 240 MPa yield strength, class 5.6 with 500 MPa and 300 MPa, and class 8.8 with 800 MPa and 640 MPa, in materials such as Q235 to GB/T 700 or 35# and 45# quality carbon steels.
Q: Why use a nylon-insert prevailing-torque nut?
A: Because a runway is a vibrating structure; the insert holds the preload that a plain nut would lose, so the clamping force on the rail foot stays stable over time.
Q: What material is used for the base plate and the insulator?
A: Base plates are commonly cast from ductile iron QT500-7 or QT450-10 to GB/T 1348, or forged from carbon steel, while insulators are made from glass-fibre reinforced nylon PA66 for combined mechanical strength and electrical insulation.
Q: Can a spring washer or a nut be re-used when a rail is replaced?
A: No. Spring washers and prevailing-torque nuts rely on a one-time deformation, so they are replaced whenever the fastening is opened; the clamp itself is re-used unless it has been deformed.
Q: What rail sections can a KPO system fasten?
A: Base plates are produced for UIC54, UIC60, 50 kg/m, 60 kg/m and S49 crane and railway rails in ordered sizes, with screw spike lengths of M24 in 150 mm, 160 mm and 180 mm to suit the installation depth.