Posted tagged ‘amp’

August 24, 2011

Problem: you have 100 doors in a row that are all initially closed. you make 100 passes by the doors starting with the first door every time. the first time through you visit every door and toggle the door (if the door is closed, you open it, if its open, you close it). the second time you only visit every 2nd door (door #2, #4, #6). the third time, every 3rd door (door #3, #6, #9), etc, until you only visit the 100th door.

question: what state are the doors in after the last pass? which are open which are closed?

Solution

For example, after the first pass every door is open. on the second pass you only visit the even doors (2,4,6,8…) so now the even doors are closed and the odd ones are opened. the third time through you will close door 3 (opened from the first pass), open door 6 (closed from the second pass), etc..

question: what state are the doors in after the last pass? which are open which are closed?

solution: you can figure out that for any given door, say door #42, you will visit it for every divisor it has. so 42 has 1 & 42, 2 & 21, 3 & 14, 6 & 7. so on pass 1 i will open the door, pass 2 i will close it, pass 3 open, pass 6 close, pass 7 open, pass 14 close, pass 21 open, pass 42 close. for every pair of divisors the door will just end up back in its initial state. so you might think that every door will end up closed? well what about door #9. 9 has the divisors 1 & 9, 3 & 3. but 3 is repeated because 9 is a perfect square, so you will only visit door #9, on pass 1, 3, and 9… leaving it open at the end. only perfect square doors will be open at the end.

SINTERING

August 23, 2011

The operation of heating the green compact at high temperature in a controlled atmosphere (Reducing atmosphere which protects oxidation of metal powders). The Sintering increases the bond between the particles and therefore strengthens a powder metal compact. Sintering temperature and time of sintering depends on the type of powders and the strength required in a final product. The Sintering temperatures usually 0.6 to 0.8 times the melting point of powders.

Type of powder                                   Sintering Temperature                 Time

Aluminium & Alloys                                   370 – 520 C                                  24 hrs

Copper, Brass, Bronze                                700 – 900 C                                  30 Mins

Iron                                                           1025 – 1200 C                              30 Mins

Stainless Steel                                           1180 C                                       20 – 40 Mins

Tungsten Carbide                                      1480 C                                      20 – 40 Mins

Spark Sintering:

The process of simultaneous pressing & Sintering of metal powders by high energy electric spark. This spark is discharged from capacitor bank & removes the surface contaminants from powder particles. This cause the particles to form a solid cohesive mass. Immediately after spark, the current is continued for about 10 Seconds, with high temperature which further strengthens the bond used for sintering Aluminium, Copper, Iron and Stainless Steel.

SINTERING

August 23, 2011

The operation of heating the green compact at high temperature in a controlled atmosphere (Reducing atmosphere which protects oxidation of metal powders). The Sintering increases the bond between the particles and therefore strengthens a powder metal compact. Sintering temperature and time of sintering depends on the type of powders and the strength required in a final product. The Sintering temperatures usually 0.6 to 0.8 times the melting point of powders.

Type of powder                                   Sintering Temperature                 Time

Aluminium & Alloys                                   370 – 520 C                                  24 hrs

Copper, Brass, Bronze                                700 – 900 C                                  30 Mins

Iron                                                           1025 – 1200 C                              30 Mins

Stainless Steel                                           1180 C                                       20 – 40 Mins

Tungsten Carbide                                      1480 C                                      20 – 40 Mins

Spark Sintering:

The process of simultaneous pressing & Sintering of metal powders by high energy electric spark. This spark is discharged from capacitor bank & removes the surface contaminants from powder particles. This cause the particles to form a solid cohesive mass. Immediately after spark, the current is continued for about 10 Seconds, with high temperature which further strengthens the bond used for sintering Aluminium, Copper, Iron and Stainless Steel.