The Most Comprehensive Guide To Rebar Threading

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Mechanical splices for reinforcing bars are becoming increasingly common in building construction, with rebar thread splicing being the most prevalent. This type of mechanical splice requires pre-fabricating threads on the steel bars before connecting them to a rebar connector.

This article will comprehensively explain rebar threading from multiple perspectives, including its importance, types, specific methods, and precautions.

What is rebar threading?

Rebar threading is the process of machining standard straight or tapered threads onto the ends of rebars using a specialized rebar threading machine- thread rolling machine or a chaser-type threading machine. This allows two rebars to be easily "twisted" together using a Cheeron threaded sleeve, forming a reliable mechanical rebar splicing.

Why are threads added to reinforcing bars?

Mechanical splices increasingly replacing traditional lap splicing and welding due to their superior mechanical properties.

Threaded splices, as a primary type of mechanical reinforcing bar splice, utilize the interlocking force between the internal threads of the coupler and the external threads of the reinforcing bar to achieve a joint strength comparable to that of continuous reinforcing bars.

cheeron-rebar-coupler-thread-connection

Types of rebar threading

I. Right-hand Thread and Left-hand Thread

According to the rotation order of the threads, they are divided into right-hand threads and reverse threads.

Differences between right-hand and reverse threads

1. Right-hand thread

Clockwise rotation is the tightening direction; counterclockwise rotation is the loosening direction. Most standard threads are right-hand threads.

2. left-hand thread (Reverse thread)

Counterclockwise rotation is the tightening direction; clockwise rotation is the loosening direction. The thread is usually marked with "LH" (Left Hand) to distinguish them.

How to choose between right-hand and reverse threads?

Depends on the construction conditions and machinery requirements.

Right-hand threads are generally used.

When the rebar cannot be rotated or needs to be prevented from loosening, reverse threads can simplify operation and improve reliability.

For example, using the CHEERON rebar positioning connector allows connecting two rebars by rotating in the same direction, but the two ends of the rebars have right-hand and reverse threads, respectively.

Therefore, it is essential to confirm the thread direction before machining the rebar threads to avoid connection failure.

II. Straight Thread and Tapered Thread

According to the shape of the thread, there are two types: straight threads and tapered threads.

The difference between straight threads and tapered threads

Tapered threads have an inherent taper, and the thread profile is tapered. The major diameter of the thread gradually changes along the axial direction, exhibiting a "tightening as you tighten" characteristic.

Straight threads have no taper, and the thread profile is cylindrical. The major diameter of the thread remains consistent along the axial direction, making it easy to tighten directly to the end.

The choice between straight threads and tapered threads

Depends on the rebar connector used

The main question is whether to use a tapered thread rebar connector or a straight thread rebar connector.

III. Cutting Threads and Rolling Threads

There are two types: cutting and rib rolling by the thread machining process.

The difference between cutting threads and rolling threads

Cutting threads:

Using cutting tools -chasers to remove excess material to form threads.

Rolling threads:

Removing the ribs on the surface of the rebar using blades, and then using thread rolling wheels to plastically flow the rebar to form threads.

Two Types of Rebar Threading Machines

Different rebar threading processes result in two types of rebar threading machines:

1. Cheeron Chaser-type Rebar Threading Machine

2. Cheeron Rebar Thread Rolling Machine

Learn about the differences between chaser-type rebar threading machines and rebar thread rolling machines.

Which is better, cutting threads or rolling threads?

Cutting threads removes a lot of material, similar to a lathe, resulting in a smaller rebar cross-section and reduced strength.

Thread rolling involves plastic deformation: the strong pressure of the rolling wheel causes the rebar metal to "flow" into a thread shape, with almost no material cutting.

The hardness of the rebar increases during the rolling process, and the strength of the threaded portion is often no less than that of the base material.

Therefore, thread rolling is the choice for the vast majority of steel bar threading.

How to process rebar threads?

Processing rebar threads using Cheeron rebar thread rolling machine

Preparation stage: The rebar should be cut flat with vertical ends. Only qualified rebar can be used on the CHEERON rebar threading machine.
Rib removal: The blades on the thread rolling machine first remove a portion of the transverse and longitudinal ribs from the rebar ends, making the ends smooth cylinders (uniform diameter is key).
Thread rolling: Rollers (usually 3) rotate at high speed, simultaneously applying pressure to the rebar to form standard straight threads.
Cooling and cleaning: Use water-soluble coolant for cooling and lubrication to prevent overheating. After processing, clean the burrs and inspect the threads.

The Cheeron thread rolling machine operation process is shown in the following video:

Precautions for using the CHEERON rebar thread rolling machine

1. Before using the rebar thread rolling machine, the rib stripping length needs to be adjusted.

Otherwise, the rebar thread length will be too long.

2. The rib stripping blade and thread rolling wheel of the rebar thread rolling machine need to be replaced in a timely manner.

Otherwise, the rebar thread rolling effect will be poor, and the thread profile will be incomplete.

3. During the use of the thread rolling machine, when not in use or when changing the blades, the power should be turned off, or the stop button should be pressed to prevent accidents.

What are the inspection standards for rebar threading?

1.Appearance - Thread Length Inspection

Quality inspection should check the appearance and thread size of each thread end. The thread surface should not be damaged or corroded.

The effective thread length should not be less than 1/2 of the length of the rebar coupler, with a deviation of 0~2 pitches.

2. Use of Go/No-Go Gauges - Thread Accuracy Inspection

The rebar thread ends should meet the accuracy requirements and should be inspected using a special thread gauge.

The go gauge should be able to be screwed into the entire effective length smoothly, and the no-go gauge should be screwed into a depth not exceeding three pitches.

Frequently Asked Questions:

1. Is it necessary to install a protective cap after rebar threading?

Failure to promptly install a protective cap after threading can lead to exposed corrosion, affecting the quality of the rebar joint.

2. What if there is a problem with the rebar thread?

There is no choice but to cut off the threaded portion of the rebar using a rebar cutter. Ensure the cut surface is smooth and flat, then re-thread it using a thread rolling machine.

3. How to connect the rebar connector to the threaded rebar?

First, unscrew the protective cap from the rebar thread. Use a wrench to securely connect the rebar to the sleeve and tighten it appropriately. One side of the sleeve should be exposed, and the effective thread length should not exceed two thread pitches (ideally one thread pitch).

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