On Thursday February 11 participated in Desenfranquiciados 6 held in AC.
Here attached the press releases of El Comercio and El Peruano.
It was a very interesting and productive.
Tuesday, February 16, 2010
Saturday, February 6, 2010
Pink Poofy Short Dress
HOW TO HANDLE THE TORQUE? THE SUNDIAL
HOW TO HANDLE THE TORQUE? There
today a tightening method reliable and economical. Of all the systems used perhaps the most uncertain of all is the one that uses torque control as a process of adjustment of a screw, the causes of the inaccuracy of the torque control method are many. Among the causes are mechanical manufacturing tolerances, surface finish, diameter the hole, the seat material, the presence of a washer and even the coefficient of friction between the screw and nut, for which discrepancies had been reported 300% for screws made of the same material. To save a little situation many companies have developed their own tables with the values \u200b\u200bof torque or torque adjustment from field trials and when a manufacturer provides torque values \u200b\u200bfor screw their teams they should be used preferably on general tables available to the public.
Despite uncertain exactly how little of this adjustment method by measuring the torque, paradoxically is the most used by mechanics, technicians and maintenance engineers.
In this issue we will give the necessary guidelines for proper use of tables of torque for the screws.
In the technical literature, manuals, catalogs, etc.., There is a huge variety of tables to determine the torque or torque of a screw thread diameter function and quality of them, but few technicians who use it correctly.
is a common misconception among maintenance personnel to adjust the torque wrench to torque values \u200b\u200bshown in the tables for adjusting screws, not taking into account the uncertainty of the instrument and tighten the physical conditions in which the screw is the property of the hole and if normal or fine thread, if you wear washer, etc.
What usually happens is an over-torqued the screws because of ignorance or disregard the restrictions required for the use of these tables.
The tables usually torque the torque placed on the diameter of the screw thread, thread type, quality (material) of the screw and the coefficient of friction. They also tend to accompany the values \u200b\u200bof torque, the preload generated by the torque screw deajuste function.
The tables are set for new screws, surfaces bonding steel-steel, seamless soft tissues between the bonded, tolerance 6g/7H rocks, holes and half-finished seats, depending on the type of screw head and the friction coefficient values \u200b\u200bglobal. On the other hand, the tightening torques specified in most metric tables are based on 90% of the yield point gives (Rp0.2) of screw material and a temperature of 20 º C. This is the main reason why you should not directly use the values \u200b\u200blisted in the tables for the torque wrench setting. By not considering the uncertainty of the tool tighten the screws may be under strain over 90% of Rp0.2, which together the effects of workload on the screw the stresses generated in it can easily exceed the material yield strength of the screw causing relaxation, a phenomenon that manifests as spontaneous loosening of the screws.
When using a table of torque should be taken into account all this information and be cautious in their use according to the particular application of the screw.
For proper use of torque tables have to deal with the following information:
1. Temperature of the screw: The tables are usually referred to 20 º C this, there are tables for temperatures of 100 ° C and for temperatures older.
2. Friction coefficient depends on the type of surface treatment of the screw (galvanized surface finish) if lubricated or not. (See table at end of article).
3. Type of screw and screw: The tables are based on the type of screw (hex or allen) and thread pitch (coarse thread boards and tables for fine thread).
4. Screw Material: The information gives the screw, either by brand or by numbers or letters and numbers, normally recorded in the head of twang.
5. Diameter of screw thread: The tables give the values \u200b\u200bof torque depending on the diameter of the thread.
6. Torque meter uncertainty: The uncertainty of the tool is given by the manufacturer.
With this information by hand, we proceed to seek the maximum bolt torque as a function of thread diameter and the above parameters in the table of proper torque.
7. Determine the average value of torque as a function of the uncertainty of the torque meter.
THIS IS THE VALUE OF ADJUSTMENT TOOL .
8. If we know the bolt preload values \u200b\u200bor the values \u200b\u200bof load on it, we can verify whether the burden of adjustment (preload) resulting from specific torque is sufficient to prevent separation of parts together. Otherwise must use another screw top quality material or using larger diameter screws.
EXAMPLE:
is to be set hex screw thread M12 with normal, grade 10.9, without lubrication (μ = 0.14) non-galvanized and operating temperature around 20 º C. The torque wrench to use is to gauge needle with ± 17% uncertainty.
know:
1. Room temperature.
2. Global friction coefficient: 0.14.
3. Regular screw and hex head.
4. Material: 10.9.
5. Screw diameter: M12.
6. Uncertainty of the torque wrench: ± 17%.
According to the table of torques according VDI 2230, the tightening torque for this screw is 137 Nm and preload caused by the adjustment is 61.5 kN. See table.
today a tightening method reliable and economical. Of all the systems used perhaps the most uncertain of all is the one that uses torque control as a process of adjustment of a screw, the causes of the inaccuracy of the torque control method are many. Among the causes are mechanical manufacturing tolerances, surface finish, diameter the hole, the seat material, the presence of a washer and even the coefficient of friction between the screw and nut, for which discrepancies had been reported 300% for screws made of the same material. To save a little situation many companies have developed their own tables with the values \u200b\u200bof torque or torque adjustment from field trials and when a manufacturer provides torque values \u200b\u200bfor screw their teams they should be used preferably on general tables available to the public.
Despite uncertain exactly how little of this adjustment method by measuring the torque, paradoxically is the most used by mechanics, technicians and maintenance engineers.
In this issue we will give the necessary guidelines for proper use of tables of torque for the screws.
In the technical literature, manuals, catalogs, etc.., There is a huge variety of tables to determine the torque or torque of a screw thread diameter function and quality of them, but few technicians who use it correctly.
is a common misconception among maintenance personnel to adjust the torque wrench to torque values \u200b\u200bshown in the tables for adjusting screws, not taking into account the uncertainty of the instrument and tighten the physical conditions in which the screw is the property of the hole and if normal or fine thread, if you wear washer, etc.
What usually happens is an over-torqued the screws because of ignorance or disregard the restrictions required for the use of these tables.
The tables usually torque the torque placed on the diameter of the screw thread, thread type, quality (material) of the screw and the coefficient of friction. They also tend to accompany the values \u200b\u200bof torque, the preload generated by the torque screw deajuste function.
The tables are set for new screws, surfaces bonding steel-steel, seamless soft tissues between the bonded, tolerance 6g/7H rocks, holes and half-finished seats, depending on the type of screw head and the friction coefficient values \u200b\u200bglobal. On the other hand, the tightening torques specified in most metric tables are based on 90% of the yield point gives (Rp0.2) of screw material and a temperature of 20 º C. This is the main reason why you should not directly use the values \u200b\u200blisted in the tables for the torque wrench setting. By not considering the uncertainty of the tool tighten the screws may be under strain over 90% of Rp0.2, which together the effects of workload on the screw the stresses generated in it can easily exceed the material yield strength of the screw causing relaxation, a phenomenon that manifests as spontaneous loosening of the screws.
When using a table of torque should be taken into account all this information and be cautious in their use according to the particular application of the screw.
For proper use of torque tables have to deal with the following information:
1. Temperature of the screw: The tables are usually referred to 20 º C this, there are tables for temperatures of 100 ° C and for temperatures older.
2. Friction coefficient depends on the type of surface treatment of the screw (galvanized surface finish) if lubricated or not. (See table at end of article).
3. Type of screw and screw: The tables are based on the type of screw (hex or allen) and thread pitch (coarse thread boards and tables for fine thread).
4. Screw Material: The information gives the screw, either by brand or by numbers or letters and numbers, normally recorded in the head of twang.
5. Diameter of screw thread: The tables give the values \u200b\u200bof torque depending on the diameter of the thread.
6. Torque meter uncertainty: The uncertainty of the tool is given by the manufacturer.
With this information by hand, we proceed to seek the maximum bolt torque as a function of thread diameter and the above parameters in the table of proper torque.
7. Determine the average value of torque as a function of the uncertainty of the torque meter.
THIS IS THE VALUE OF ADJUSTMENT TOOL .
8. If we know the bolt preload values \u200b\u200bor the values \u200b\u200bof load on it, we can verify whether the burden of adjustment (preload) resulting from specific torque is sufficient to prevent separation of parts together. Otherwise must use another screw top quality material or using larger diameter screws.
EXAMPLE:
is to be set hex screw thread M12 with normal, grade 10.9, without lubrication (μ = 0.14) non-galvanized and operating temperature around 20 º C. The torque wrench to use is to gauge needle with ± 17% uncertainty.
know:
1. Room temperature.
2. Global friction coefficient: 0.14.
3. Regular screw and hex head.
4. Material: 10.9.
5. Screw diameter: M12.
6. Uncertainty of the torque wrench: ± 17%.
According to the table of torques according VDI 2230, the tightening torque for this screw is 137 Nm and preload caused by the adjustment is 61.5 kN. See table.
With this information we calculate the value for the torque wrench setting.
7. Average value:
Because the torque wrench may be tightening the screws with that +17% is considered that the value given in the table corresponds to 117% of the tool, hence we deduce that the mean torque is:
137 ÷ 1.17 = 117.09 Nm
value adjustment tool torque: 117 Nm .
8. Pre-load: The minimum bolt preload due alignment on the torque wrench is de-fined by the minimum value of torque which corresponds to -17% of the tightening tool.
117.09 x [(100-17) / 100] = 117.09 x 0.83 = 97.18 Nm
The minimum preload is determined by applying a simple rule of three between the values \u200b\u200bof torque and preload res table and tighten the two previously calculated minimum:
137 Nm 61.5 kN
--------------- --------- X kN 97.18 Nm
------- X = 43.63 kN
minimum preload screw: 43.63 kN
If we were "designing" a system and knowing bolting preload value required by screw the board does not slip or separate, we can compare and see if the screw selected is appropriate, if not, you can repeat the calculations for different quality of material or take the decision to use a larger screw diameter. Finally, that experience will dictate the final value of tightening the screws
I should clarify that the tables millimeter screw torques can not be extrapolated to the imperial screws as the "degrees" of the screws to differ " quality "metric screw, as tolerances and manufacturing steps.
This example is clear in what way is safe use a table of torque with the assurance that we tend not over-torqued a screw.
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