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February 16, 2018 / apexprecitech

WHAT IS THE WORKING PRINCIPLE OF THE P 3-1 TOP ARM ? WHAT ARE THE SECRETS OF ITS SIMPLICITY ?


In the Ring Spinning Industry , more than 75 % of the Ring Frames are fitted with the P 3-1 Top Arm. Two of the world’s biggest manufacturers of Ring Spinning frames employ these top arms in their frames. This top arm was introduced more than 25 years ago and is still being produced in the same form without any modifications. This is a great distinction for an accessory to survive so long in this era of great change and advancement.

While analyzing its success, what strikes us is its simplicity. To explain this , one has to compare this pneumatically powered top arm to a conventional spring loaded top arm. In a typical 1000 spindle ring spinning frame, for 500 spring loaded top arm, there will be minimum of 1500 helical springs, and as much numbers of fasteners to secure them will be needed not to mention the loose spares like spacers, washers etc. In total contrast, this top arm, named P 3-1 , has NONE of the above. Its body is just a hollow  structural element shaped like a rectangular channel fitted with holders for the top rollers. See fig 1. The series of arm bars, running through from end to end serve as the pressurizing elements. The arm bar is essentially a hollow hexagonal pipe with a simple rubber hose running through. These hoses are pressurized with compressed air usually upto 2.2 Kg/sq.cm.

Now you understand that this top arm is saving the manufacturers and spinners crores of rupees every year in springs and accessories alone.

p3-1-top-arm revised

You might want me to go into the working principle in detail. The figure above shows the cross section of the arm bar. the inner rubber tube is pressurizing a small channel like metal section. This is the ledge. The ledge has a length of 13.5 cm and a width of 1.8 cm. The area of this ledge is 13.5 x 1.8 = 24.3 sq.cm. It is this area that is subject to pressurization by the hose. Taking the air pressure in the hose to be 2.2 Kg/sq.cm,

the load exerted on the ledge =   area of the ledge  x air pressure in the hose

                                          = 24.3 x 2.2

                                         =  53,46 Kg.

In a typical spinning situation, the front roller load is about 16 kg, middle roller load is 12 kg and third roller is 16 kilograms. Cumulatively 46 kilograms are need for  one single top arm. The load generated is well within that value.

This is the load exerted on ONE ledge only. There are typically 12 ledges in one arm bar corresponding to twelve top arms. Totally one arm bar is responsible for 636 kilogram of load. This is a phenomenal amount of load considering the size of equipment. Totally for 42 arm bars in a 1008 spindle ring frame, the load generated in the arm bar is 42 x 636= 26,712 kilograms. Achieving twenty six tons of load using static pneumatic pressure is a major achievement and is ONE of the primary reasons for the superiority and simplicity of this top arm.

A lever transmits the load on the ledge to the top arm. The lever is supported on a pivot and while one end sits on the groove side of the ledge the other side is pressed down. The top pressing arm engages with the curvature of the lever and as a result, the load is transmitted to the top arm. This load is further transmitted to the three top rollers. The distribution of the load to the individual top rollers is effected by an ingenious pivot mechanism.

Look at this picture. There are three holes in in a line. The saddle holder at the bottom also has three corresponding holes. A pin runs through these two components once they are aligned. While aligning they can be variably aligned such as  1-1, 1-2, 1-3 etc. The pin also can be inserted in any of the holes for varying the distribution ratio of loads. If the total load of the top arm is 48 kilograms, the first distribution divides the loads such that the front and second rollers together get 64 % rd of the total load i.e  28 kilos while the back roller gets the remaining 36 %  i.e 48x 1/3 = 16 kilo.

The front and second roller   saddle further divide the load in the ratio of 57 : 43. The load value will be 16 kilo for the first roller and 12 kilo for the second roller. In this manner , the final load values of 16, 12 , 16 for the respective rollers is achieved. When different holes and positions are chosen this ratio will vary. A general rule to remember is that the more one hole is towards the operator, the front portion will get more load and vice versa.

The advantages of this Top Arm:

1. The loads of top arms can be adjusted centrally.
2. The increase or decrease of the top roller diameters does not affect the load values since the air pressure and the acting area inside the hose remains constant. This is a super useful feature and such a relief to the spinning technician.

3. The only changeable settings for this top arm is the saddle distances and the pin positions, once these are standardized, there is no more maintenance in these arms.

What should a Spinner Do to maintain these Top Arms Well ?

1. Ensure the hose is in good condition. Change of the hose after its life span is a good practice. The hose loses its elasticity after prolonged use and the ledge no more engages with the hose properly and load drops will occur.
2. Also , the ledge should be checked while changing the hose, if they are distorted , they also need to be changed.
3. Ruptured hoses are a big nuisance and they are undetectable in the noisy shopfloor.. Only a good Top Arm Load Gauge will detect drop in loads. Have our Apex Top Roller Load Gauges handy and keep it in top condition with periodic recalibrations.

4. For top arms converted with Compact Spinning kits, the load requirement in the front roller will be in the range of 20-21 kilograms. Even with increase of air pressure, the average top arm CAN NOT supply that load. Apex has developed a small external spacer which when fitted to the pressing arm of the top arm, instantly increases loads by  4 kilograms thus proving ideal for compact spinning conversions. see picture

20180212_161834

 

What one should not do

1. Never, Never , Never convert the top arm to mechanical spring loads. This drafting structure is only suitable for pneumatic force where the force acts on all sides of the arm bar. That is why P 3-1 drafting has four top arms per stand instead of three as in the case of other top arms. In the case of the mechanically converted systems, the springs act downwards alone thereby creating a upward reaction of the arm bar pipe. This phenomenon will mimic like an increase in top arm load but actually it is killing your whole drafting system. The roller stand can break anytime and your operator will struggle enormously to lift and press the arms. The reconversion to original setting will be again financially straining. We know of many mills who have thought it best to dispose off these Ring Frames itself instead of further spending on the drafting. Please use extreme discretion when tempted to go in these routes. Use our counsel if possible by emailing or telephoning.

2. The cylindrical bush which engages with the pressing arm, is replaced with some extra sized rollers for the purpose of extracting extra load. This is a questionable practice since the removal of the pins and re assembling makes them loose and unfit for further use. Plus, when new hose is replaced, the operator will find it hard to press arm. Apex Precitech has developed a simple externally mountable spacer which instantly increases load.

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