Conclusions on torque and grease 1

Alexander Dierlamm, Michael Eppard

(CERN)

Measurements of thermal contact

between TOB module and rod

May 2004

Conclusions on torque and grease 2

Introduction

The purpose of the study is to evaluate the effect of the torque applied on the module fixing screws on the cooling performance, and to measure the possible benefit of applying thermal grease in the module mounting points.

The study is carried out using the hybrid temperature measured by the DCU.

For each case, a cycle cooling off – cooling on – cooling off is performed. The temperature difference observed between the cooling off and the cooling on states shows the sensitivity of the measurement to the cooling performance.

The DCUs on the modules used in the test were not calibrated, therefore differences observed between different modules in the same conditions are not necessarily significant.

The measurements were performed at room temperature using C6F14 as coolant.

Conclusions on torque and grease 3

Setup for SS rod

Setup for torque and grease measurement on SS rod

• SS rod in XY table

• modules 1, 3, 5 (on the upper side of the rod) screwed with different torque

• modules 2, 4, 6 not touched (torque not known)

Conclusions on torque and grease 4

No torque (loose screws), no grease, SS rod

SS rod

Conclusions on torque and grease 5

Torque = 150 gcm, no grease, SS rod

SS rod

Conclusions on torque and grease 6

Torque = 325 gcm, no grease, SS rod

SS rod

Conclusions on torque and grease 7

Torque = 500 gcm, no grease, SS rod

SS rod

Conclusions on torque and grease 8

Torque = 1000 gcm, no grease, SS rod

SS rod

Conclusions on torque and grease 9

Grease at SS rod

Grease applied between module support and module.

Conclusions on torque and grease 10

No torque (loose screws), grease, SS rod

SS rod

Conclusions on torque and grease 11

Torque = 150 gcm, grease, SS rod

SS rod

Conclusions on torque and grease 12

Torque = 500 gcm, grease, SS rod

SS rod

Conclusions on torque and grease 13

Setup for DS rod

Setup for torque and grease measurement on DS rod

• DS rod at TOB system test

• modules 1/7, 3/9, 5/11 (on the upper side of the rod) screwed with different torque

• modules 2/8, 4/10, 6/12 fixed with 1000 gcm

• consistent temperatures are measured on the two modules of each pair

the average of the two temperatures is read out

Conclusions on torque and grease 14

No torque (loose screws), no grease, DS rod

DS rod

Conclusions on torque and grease 15

Torque = 150 gcm, no grease, DS rod

DS rod

Conclusions on torque and grease 16

Torque = 325 gcm, no grease, DS rod

DS rod

Conclusions on torque and grease 17

Torque = 500 gcm, no grease, DS rod

DS rod

Conclusions on torque and grease 18

Torque = 1000 gcm, no grease, DS rod

DS rod

Conclusions on torque and grease 19

Grease at DS rod

Grease applied between module support and module.

Conclusions on torque and grease 20

Torque = 150 gcm, grease, DS rod

DS rod

Conclusions on torque and grease 21

Torque = 325 gcm, grease, DS rod

DS rod

Conclusions on torque and grease 22

Torque = 500 gcm, grease, DS rod

DS rod

Conclusions on torque and grease 23

Torque = 1000 gcm, grease, DS rod

DS rod

Conclusions on torque and grease 24

Summary plots

All modules show consistent behaviour both on the SS rod and the DS rod.

The offset of the probes was not calibrated, therefore the differences between modules are not significant. Only variations of measurements taken with the same probe are significant.

We take as a reference one module with no grease and high torque (1000 gcm) that is never touched (reference module), we choose one other module that is measured in different conditions (test module) and we calculate the temperature difference between the two – in this way we reduce the effect of possible ambient variations. When the test module is in the same conditions as the reference module (no grease, 1000 gcm torque), we impose that the temperature difference be zero, thus deriving an effective relative calibration constant. The variation of this recalibrated difference should give a quantitative measurement of the effect of torque and grease on the cooling performance, with little residual systematic effects.

The results obtained using different test modules are compatible. Two examples, one from the SS rod and one from the DS rod, are shown in the following transparencies.

Conclusions on torque and grease 25

Summary of results for SS rod

SS rod no grease

grease

Conclusions on torque and grease 26

Summary of results for DS rod

DS rod no grease

grease

Conclusions on torque and grease 27

Conclusions

The dependence of the cooling performance on the torque applied on the module fixing screws has been measured on final structures, using the hybrid temperature measurement provided by the DCU.

The measurements were performed on a SS rod and on a DS rod, and repeated after applying grease between the module frame heat spreaders and the rod module supports.

For a torque larger than 325 gcm the cooling performance as measured on the hybrid varies by less than 1°C as a function of torque and/or if grease is added in the module mounting points.

If modules need to be dismounted, grease residues are left on the module frame, on the rod inserts and on the screws ( + on the gloves of the operator). Such residues are difficult to be removed completely.

Side remark: with cooling off the hybrid temperature in a DS rod reaches (possibly exceeds) 50 degrees

Conclusions on torque and grease 28

Pictures from dismounted modules

dismounted DS module

with grease residues

module support with grease residues

Conclusions on torque and grease 29

Recommendations

The applied torque can be lower than the former recommended value of 1000 gcm.

Grease does not improve significantly the performance – that is not critical anyway. In addition to possible remaining concerns on its long term stability and radiation tolerance, grease adds complications and risks in case of possible maintenance operations (module replacements) on rods. As it appears to be not needed, we prefer to avoid having grease in the module mounting points.

Even if it is not a stringent requirement for cooling performance, having a high torque is desirable for mechanical stability (reduce risks of screw loosening during transports, thermal cycles etc.). We would suggest to choose a value of the torque that is as high as possible, while still being easy to be applied. According to our experience values around 700-800 gcm should be comfortable and free of risk.