Project 1

INTRODUCTION:

Crutches help people who have injuries or illnesses that affect their legs walk. They can be used short term, such as during recovery from an accident or surgery, or long term, such as for a lifelong disability.

Crutches have evolved significantly throughout the past decades.

On a general basis, we are more habituated to the crutch that patients use to shift their weight to their forearms.

Sketch and design of crutch\

So basically thre are four types of crutches:

1.Axillary Crutches:

These are the most commonly seen crutches around, also known as underarm crutches.

They are mainly made of either wood or aluminum. This model can be adjusted easily with a patient’s overall height and hand height.

While operating on an axillary crutch, you need to be able to flex your elbow roughly about 30 degrees.

In any normal condition, the top of the crutch and armpit (axilla) should have a distance of about two to three fingers and on the ground 6 to 8 inches from your foot.

In any case of inability to stand up straight, you just need to shave 16 inches from your actual height to determine the height of your axillary crutch.

Forearm Crutches

Forearm crutches or less popularly known as Lofstrand crutch and elbow crutch.

The cuff of the crutch has to be at a distance of 1 to 1.5 inches from the elbow. The forearm crutch enables the patient to flex from 15 to 30 degrees.

The bottom tip of the crutch should stay 2 to 4 inches from the foot sideways and 6 inches in front of your foot.

European countries commonly use these types of crutches.

IN the US, patients with cases of Polio or other lifelong disabilities have suggested these designs for their overall ergonomics and ease of use.\

Gutter Crutches

With a simple modification in forearm crutches, we can call gutter crutches. Rheumatoid patients are mostly known for using gutter crutches.

A gutter crutch will enable patients or older people to maintain balance and distribute their weight if they need to rely on tools to accomplish such a goal.

Comfortable and soft padded forearms are a gutter crutch’s specialty.

One adjustable handgrip and strap are connected to the highly durable metal tube. For the overall comfort of the hand, rubber ferrule is used.

A gutter crutch is usually prescribed to rheumatoid arthritis patients because of their weak grip due to joint pain.

Hands-free Crutch

Hands-free crutches came into being from the adverse side effects of underarm crutches.

We’ve described underarm or axillary crutches before, and they are not friendly at all.

They are known to hurt your hands, underarms, and wrists from continuous and non-conventional uses.

So, to resolve these hands-free crutches were born. These are most commonly known as knee crutches.

These are designed for slightly less sensitive patients, but if they can use them they are almost as mobile as the next person.

These crutches don’t have any function for hands or wrists rather they can be strapped to the thigh and knee to provide support.

The base of the crutch is designed to sustain weight in one leg so this crutch is rather useful than underarm crutches.

PARTS OR COMPONENTS OF DIFFERENT TYPE OF CRUTCHES:

1)Foot Rubber

2)End CAP,aluminium

3)Main Tube,composite

4)Union fitting aluminium

5)Handle Tube,Composite 

6)Grip,EVA Foam

7)Handle end CAP,aluminium

8)Arm Support Tube,Composite

9)Arm Support Pivot ,rivets

10)Arm support fitting,aluminium

11)Arm Support clip,plastic

SHAPING OR MANUFACTURING PROCCESS:

ALLUMINIUM:Alluminium was shaped through the extrusion method.

Aluminum extrusion is a process by which aluminum alloy material is forced through a die with a specific cross-sectional profile.

At a fundamental level, the process of aluminum extrusion is relatively simple to understand.

The force applied can be likened to the force you apply when squeezing a tube of toothpaste with your fingers.

As you squeeze, the toothpaste emerges in the shape of the tube’s opening.

The opening of the toothpaste tube essentially serves the same function as an extrusion die. Since the opening is a solid circle, the toothpaste will come out as a long solid extrusion.

Below, you can see examples of some of the most commonly extruded shapes: angles, channels, and round tubes.

Rubber Extrusion

Extrusion is a continuous manufacturing process in which rubber is squeezed through a die and then vulcanized (industry terminology for cured). The die gives the extrudate its shape. The required pressure is produced via a conveying screw, in which the material is mixed, compressed and extruded through the die form to produce the final shape.

Extrusion Process Steps

• The extrusion process begins with the unvulcanized (uncured) rubber compound being fed into the extruder.
• Next, the flutes of the revolving screw will carry the rubber forward into the die, with an increase in pressure and temperature occurring as the material gets closer to the die itself.
• Once it reaches the die, the built up pressure forces the material through the openings, where it will consequently swell in various degrees based on the material compound and hardness.
• Because rubber has this tendency to swelling, many extruded parts require compensation on the cross sections of the die.
• During the vulcanization (curing period), the extruded rubber will swell or shrink in both its cross section and its length depending on the type of rubber compound used.

2. Rubber Compression Molding

Compression molding is a process that involves taking a rubber compound or mixed raw material and creating “preforms” in the basic shape of the end product. The preforms provide a surplus of material to be placed in the cavity, thus ensuring a total cavity fill. Once in place, the mold is then closed, applying both heat and pressure to the preform and allowing it to fill the cavity. When the cavity is filled, excess preform material spills out into overflow grooves. Following this step the rubber is then demolded, usually by hand, leaving us with the molded rubber product.

Compression Molding Process Steps

• Uncured rubber is preformed into a control weight, shape and specification.
• Rubber preform is then placed into the mold cavity.
• Rubber mold is then closed compressing the rubber to fill the molds cavities.
• The mold remains closed under pressure and held at a temperature to allow the rubber to reach optimal cure.
• Compressed rubber parts are then removed from the mold and the process is ready to begin again.

TESTING:

Alluminium :Alluminium Rods  are tested on three basic parameters:

1)Rigidity

2)Hardness

3)Brittleness

4)Temper

Not only are some materials more rigid than others, but by alloying metals of low rigidity a compound may be produced which shall have a high rigidity. Rigidity is a structural property of matter and is not due to hardness.

With the sample of tool-steel from which our diagrams were made, the rigidity is the same whatever be the temper or the hardness.

When given a dark-blue spring-temper it withstood various applications of stress both by weight and impact up to 800 pounds and up to a 5-inch fall without any effect upon the strength or shape of the bar. The bar was then hardened as much as possible and tested by weight to 400 pounds when it broke. The rigidity of the hardened steel was exactly the same as when blue. In both states the steel had the same bend and therefore the same elasticity up to 400 pounds, and yet the hard steel was brittle compared with the blue steel. We may properly say, then, that a metal need not be rigid to be brittle, nor does varying brittleness involve necessarily varying rigidity. Rigidity is not an element of strength or weakness, but it is a very important element in a structural material. It cannot be determined by the ultimate strength or by the total deflection, but only by making a spring-line and measuring the angle of rigidity.

Stress is measured on the ordinate or base-line from the zero-point in pounds avoirdupois for the weight-machine, and for the impact-machine by the number of the blows or by the value of each blow in inch-pounds.

Deflection is the distance (at right angles from the base-line) traversed by the center of the bar under any given stress. It is measured in hundredths of an inch from the base-line, the scale being laid off on the abscissa passing through the zero-point.

The stress diagram may be a straight line if the deflections are proportional to the stresses (Hook’s law), or a curve if the deflections increase more rapidly than the stresses. The diagram may conform to Hook’s law for a certain distance and afterwards become a curve. The point where proportionality ceases is usually called the limit of elasticity. It is the limit of perfect elasticity, but a better term for it is the limit of proportionality.

Aluminium Elasticity

Elasticity is the property by virtue of which a body tends to regain its original volume or shape after it has been distorted. Elasticity is perfect or imperfect according as volume or shape is wholly or only partially regained. Elasticity of shape is the only elasticity considered in the testing of materials of construction, and in our tests only so far as it relates to the recovery of the central point in a test-bar one-half inch square and 12 inches long, supported at the ends and subjected to stress applied at the center in a direction at right angles to the length.

The measure of elasticity is the distance that the center of the test-bar moves towards regaining its original position on the base-line when the stress is removed.

The length of this line is given in hundredths of an inch, and is measured on the zero (or a parallel) abscissa. If the center of the bar returns to the base-line, the bar is perfectly elastic, and the diagram will generally be a straight line. In such a case the measures of elasticity and deflection are the same.

We can call the measure of elasticity elastic deflection.

For convenience we shall call the straight line conforming to Hook’s law a spring-line, as we denote the rigidity by the angle this line makes with the zero abscissa.

When the deflection is not proportional to the stresses, the additional deflection will not be recovered when the stress is removed. Such part of the deflection as is recovered is the elastic deflection, and the portion not recovered we may call set deflection or permanent set, or simply set.

To divide the total deflection, as produced by the weight-machine, into elastic and set deflection, we proceed as already described, viz.:

When we think that we have applied nearly as much stress as the bar will stand, we run the machine back to zero. If the bar has received any set the pencil will not come back to the zero of deflection, although it rests on the abscissa marking the zero of stress at a distance from the ordinate equal to the total permanent set.

If we now run the machine forward we shall describe a new stress- diagram, in which the deflections are proportional to the stresses, and it is therefore a spring-line, and its angle is the angle of rigidity. If now we lay off a line parallel to this spring-line and tangent to the original diagram at its zero-point we can see that between the base-line and this plotted spring-line all deflections are elastic deflections, and that between this spring-line and the original diagram all deflections are set deflections.

Aluminium Resilience

The definitions of this term, as given by various writers on the strength of materials, cover the idea of the work that can be done by a body, which has not taken set, in recovering its original form after stress has been removed ; in other words, the work done in producing elastic deflection.

Some writers say that the area of the diagram bounded by the base-line, the spring-line and the abscissa, measuring elastic deflection at the point of greatest stress (i.e., one-half total stress multiplied by elastic deflection), represents the total resilience. Some even multiply one-half stress by the total deflection in cases where set has been taken, as for example, in tests of cast-iron. All these writers seem to consider that the length of the line measuring elastic deflection depends upon the stress exerted to produce this deflection. For this reason we have endeavored to give a definition of elasticity that shall be entirely independent of the stress that produces the elastic deflection.

We doubt the advisability of using the term resilience in a general way, for, although elastic deflection is proportional to the stress in each given material, yet the elastic deflection for different materials is not the same for equal stresses.

 RUBBER TESTING:

The resilience strength of the rubbers can be tested with the help of high quality of  Rebound Resilience Tester, which is used to measure the strength of elastomers, rubbers and other products that can bear the impact forces and shocks. The resilience or elasticity of the materials is determined by the efficiency of the products to bear shock and to measure its strength that cab reduces the effect of these shocks and forces by its own. Assessing the elasticity of a rubber material is a major property that measures the durability of the product. The testing machine works on the procedure to compute the maximum height of rebound of the standard needle.

Resilience Tester by Presto – For Measurement of Elasticity

Presto Stantest offers a wide assortment of rubber testing instruments out of which rebound resilience tester is used to measure the quality of elasticity and resilience of rubber and elastomers to shocks and forces. The device is assembled as per the standards that are introduced by national and international standardization authorities. For more information on the testing machine