Every worm drive screw, manufactured by a cold forming process, takes up a slightly spherical shape. The height of the thread faces falls off at both ends, with the full thread cross section only in the centre.
Due to the torque applied while tightening the screw, reaction force F times screw radius R, the screw tips out of its horizontal position Ð a . This means that the screw head lowers towards the band (Fig. 1).
To prevent this the TORRO® screw head is fitted with a support bearing (Fig. 2).
Benefits:
1 .The axis of the screw is prevented from tilting. The full cross section of the thread remains engaged.
2.The lift-out force FR1, caused by the thread flank angle of about 10", will be kept small (Fig. 3). No change to the housing and no jumping of the thread.
Without a support bearing on the head of the screw (Fig. 1 and Fig. 4) the tilting of the axis of the screw means that the flank angle (about 10') is added to the screw axis misalignment a, resulting in a large increase in the lift out force FR2. (FR2 > FR1 ).
The screw tightening torque causes the housing to tip in the direction of turning. A high edge pressure occurs. This can cause damage particularly to the fabric ply of the hose (Fig. 5). (F2 > F1 )
Due to the offset extension on the asymmetrical TORRO® housing R2 becomes > R1 and thus the edge pressure becomes smaller (Fig. 6). (F2 > F1) .
The housing joint is on the F1 compression side and is thus relieved. On the tension side there is no weakening due to welding, rivets etc. (Fig. 6).
The asymmetrical pressing on the band reduces the amount by which the band passing through the screw is displaced to the side. (Fig. 7).
The edges of the band are raised, thus gentle on the hose. The screw support bearing both acts as a band-end deflector and prevents the socket spanner from being pushed off. (Fig. 8).
A short saddle means a good snug fit even in the lower clamping size range A < В (Fig. 8 and 9).
The housing to band joint is neither welded nor riveted. The bottom of the housing does not protrude and damage the hose (S2 < S1) (Fig. 8, 10 and 11).
The screw head of the TORRO® (W1, W2) is equipped with a combination screw (hexagonal, slotted and Philips head) so that installation is both simple and easy with a commercially available tool: with a hexagon wrench or a with a slot and Philips head screw driver.
For professional installation we recommend using the TORRO® flexi screw driver. This cap wrench has a flexible shaft and enables secure installation even in places which are hard to get at.
The decisive feature giving a high, even pressure is the flush contact of the housing saddle on the hose, as provided by TORRO® (Fig. A).
The pressed worm drive band of the TORRO® designs prevent any damage to the outer skin and fabric ply of the hose (1). The photograph 2 shows small, undamaged pressure traces on the hose after the use of a TORRO® with a 12 mm band width. Tightening torque: 5 Nm Temperature: + 150°C over 4 hours, -20°C over 4 hours.
The supports on the asymmetrical housing present any tilting in the direction of turning. The unwelded housing connection is decisively relieved since it is only on the pressure side. The table shows the recommended static tightening torques.
|
clamping range |
TORRO®
b = 7,5 + 9 |
TORRO®
b = 12 |
TORRO® S
b = 9 |
TORRO®
b = 12 |
|
8-12 |
1,5 Nm |
- |
1,5 Nm |
- |
|
8-16 |
2,0 Nm |
- |
2,0 Nm |
- |
|
From 12 - 22 |
3,0 Nm |
- |
3,0 Nm |
- |
|
From 16 - 27 |
- |
5,0 Nm |
- |
5,0 Nm |
Subject to technical changes. Prices on request. All orders are subject to our standard terms and conditions of sale.
"As a quality certified company, we guarantee constantly high quality standards. NORMA® products are manufactured using modern production techniques and high value materials. They are safe if used for the purposes specified by us and if our assembly instructions are obeyed. If you have any doubts about possible uses and correct fitting, please contact us for advice."
Abbreviations:
b = band width
B = overall width
h = overall height
L = overall length (screw and housing)
s = band thickness
C = across flats size
|
|
b |
W1 |
W2 |
W3 |
W4 |
W5 |
|
TORRO® and TORRO® with spring |
7,5 |
- |
|
|
- |
- |
|
9 |
- |
|
|
|
|
|
12 |
- |
|
|
|
|
|
TORRO® S |
9 |
|
- |
- |
- |
- |
|
12 |
|
- |
- |
- |
- |
*C6 with slot for band width 9 mm are still available but should not be used for new projects.
Materials
|
|
Materials International Standard Designation
|
|
|
DIN
|
AISI/AS
|
BS
|
AFNOR NF
|
SS
|
SUS
|
|
W1
|
completely zinc platet steel
|
|
band and housing W2 screw
|
1.4016
|
430
|
430 S 17 |
Z8C17
|
2320
|
430
|
|
zinc plated steel and yellow chromated
|
|
W3
|
1.4016
|
430
|
430 S 17
|
Z8C 17
|
2320
|
430
|
|
W4
|
1.4301
|
304
|
304 S 15 |
Z6CN 18-09
|
2332
|
304
|
|
W5
|
1.4401
|
316
|
316 S 31 |
Z3CND 17-11-1
|
2347
|
316
|
|
tension spring
|
1.4310
|
301 |
301 S 22 |
Z12CN 18-09
|
2331
|
301
|
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