WRENCH AND SPANNER

Wrench is also known as spanner which is basically used to deliver mechanical advantage in providing required torque for turning object such as nut, fasteners. These wrenches are chrome-plated to avoid the corrosion. 

There is specific process for manufacturing wrench such as Forging, annealing process, rolling, punching process, drawing and polishing process, CNC rough cutting, surface grinding, vibrating, heat treatment, electroplating process, fine cutting via CNC and at last assembly.

There are various types of wrenches, let us consider some typical and frequently used spanners in industrial life.

1. Box-end wrenches, Tap wrenches
2. Combination wrenches, Torque wrenches
3. Open-end wrenches, speed wrenches
4. Hammer wrenches , monkey wrenches
5. Adjustable wrenches or spanner
6. Pipe wrenches , socket wrenches
7. Allen wrenches, chain wrenches

Material selection for Wrench

Material selection is very crucial phase during designing of Wrench or spanner. There are a lot of materials for designing of wrench so it is very difficult task to select the appropriate materials for designing of wrench. 

Material selection for wrench depends on following terms

1. Cost of material & its Availability
2. Environmental condition where product (gear box) is to be used
3. Quality of wrench
4. Type of duty such as heavy duty, light duty ,medium duty, heavy duty & extra heavy duty

On the basis of above terms, we may understand about materials, as described below, suitable for making wrench or spanner.

1. Alloy steel ( hardened and tempered)
2. Chrome vanadium steel DIN-838
3. Highly fractural toughness and good tensile strength materials such as SAE 4340 & SAE4140

Specific properties of material for manufacturing wrench

Mechanical properties of selected material play a very important role in respect of life, productivity, and capability to provide torque of wrenches. Let us consider some specific properties of material for wrenches. 

Tensile strength	Elongation	Reduction of area	Hardness (HRC)	0.2 % of proof stress
689 M Pa	20 %	40 %	18	80

Above mentioned values are provided for special grade of alloy steel used for manufacturing the wrenches, apart from this material should have good resistance against corrosion and should have larger fracture toughness with good tensile strength. 

Manufacturing Process for Wrench

As mentioned in above production line, we may understand the current technique to produce the wrenches are as following

1. Creation of rough cast with the help of thermal forging.
2. Annealing process and removal of carbide materials attached due to previous step.
3. Providing required shape.
4. CNC rough cutting to achieve desired specifications.
5. Heat treatment to increase the toughness of material.
6. Finally material will go for a protective layer to withstand against oxidation and attrition.

Type of loading

During the application of wrench, there are mainly two forces that must be considered and these are as mentioned below

Torsion forces

When wrench is used to provide the torque to open or tighten the nuts, contact portion of nut and wrench, both, will be subjected with torsion forces.

Compression forces

Contact area of wrenches and nut, both, will be subjected with compressive forces

Shear forces

Contact area of wrenches and nut, both, will be subjected with shearing forces also

Bending force

Wrench is also subjected with bending forces as during the application of wrench contact.

We must think that there will be not any tensile force during application of wrenches

Future development

There are various points that must be considered in order to meet the demand easily with good service life.

1. Some alloying elements such as Chromium, Nickel, Vanadium and molybdenum will be useful to meet the desired chemistry of material for wrenches.
2. Hardening and tempering with the help of furnaces (atmospherically controlled) to achieve the demand of a neutral, through hardened structure, consisting of tempered marten site
3. In order to reduce the internal stress and suitable of grain flow, Material used for manufacturing the wrenches should be heat treated to increase the toughness.
4. Thermal treatment increases toughness property of the wrench so that wrench may withstand high stress during the application.

Let us share our technical experience here......... 

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