Method of stabilizing springs

In a method of treating a coil spring to improve its performance and reliability when operating at elevated temperatures, the spring is first stressed by applying a load of preselected magnitude and then, while the load is maintained, the spring is heated until it relaxes or collapses to a predetermined extent at which stage the heating is automatically discontinued and the applied load is afterwards removed. Apparatus for carrying out the method in relation to compression springs includes a spring supporting base, an overhead operating head with a vertically movable ram or plunger for applying the predetermined load, means for passing an electric heating current through each spring while beneath the operating head, and limit switch means which responds to the position of the ram or plunger and terminates the supply of heating current when the loaded spring has reached the required predetermined value of relaxation or collapse. The apparatus may also include means for carrying out a preliminary cold pressing of the springs before the hot pressing operation.

FIELD OF THE INVENTION 
This invention relates to a method of treating springs for improving their 
performance or reliability when operating at elevated temperatures, and to 
apparatus or equipment for carrying out the method of treatment. 
BACKGROUND OF THE INVENTION 
It is well known that springs operating under stress tend progressively to 
acquire some degree of permanent set and this tendency increases with 
increase of operating temperature. This effect can thus present a serious 
problem in some cases. For example, helical coil compression springs used 
in internal combustion engines as valve springs operate at elevated 
temperatures as high as 160.degree. C. 
To overcome this problem, attempts have been made to stabilize springs 
intended for operation under stress at elevated temperatures by subjecting 
them to a "hot scragging" or heat stabilizing treatment. In this prior art 
treatment, the springs are deliberately heated and loaded, while hot, so 
as to cause them to relax or collapse. This procedure has been effective 
in reducing somewhat the tendency toward changes in physical properties 
during subsequent operation under stress at elevated temperatures. But, 
the manner in which such heat treatment process is carried out is 
important, and methods or techniques previously proposed have not been 
generally as satisfactory as may be desired. 
SUMMARY OF THE INVENTION 
According to the present invention, a method of treating a spring for 
improving its performance or reliability when operating at elevated 
temperatures comprises first, stressing the spring by applying thereto a 
load of preselected magnitude. Then, while application of said load is 
maintained, the spring is heated sufficiently to cause it to commence to 
relax or collapse. The heating step is maintained until the relaxation or 
collapse of the spring has reached a predetermined value at hich point the 
heating is discontinued automatically. Finally, the load is removed when 
the spring has cooled toward ambient temperature. 
In carrying out the method of treatment as defined above, a cooling medium 
is applied to the spring, while still subjected to said load, immediately 
after the heating is discontinued. This rapid quenching can be 
advantageous. Thus, with helical coil compression springs, rapid quenching 
has been beneficial in producing batches of springs with an unusually 
accurate or uniform loaded length, as well as having enhanced stability of 
physical characteristics when subsequently operating under stress at 
elevated temperatures. 
Conveniently, the heating step is carried out electrically by passing a 
high current through the spring while under load. A switch operates 
automatically to switch off the heating current as soon as the spring 
reaches the aforesaid predetermined value of relaxation or collapse. For a 
helical coil spring, such as a helical coil compression spring, this will 
be represented by a predetermined length. The same switch may also control 
operation of a valve, through an associated electrical circuit, for the 
supply of a coolant liquid to quench the spring on termination of the 
heating. 
In general, the temperature to which the spring is heated during the 
treatment process is not critical so long as it is above the operating 
temperature of the spring during subsequent service and below a 
temperature which would cause adverse permanent changes in the physical 
characteristics of the material of which the spring is composed. For a 
helical coil compression spring for use as an internal combustion engine 
valve spring, it may for example be in the range 100.degree.-400.degree. 
C. Usually, both the heating current, which determines the temperature, 
and the pre-selected load applied will be selected on the basis of 
providing a convenient time factor for carrying out the method of 
treatment. 
For helical coil compression springs in particular, the method of treatment 
may advantageously be further developed to include an additional 
preliminary operation. The spring is temporarily fully compressed at 
ambient temperature by temporarily applying thereto a prestressing load 
without heating. The prestressing load will in general be greater than the 
pre-selected load to which the spring is subjected during the subsequent 
heating process. The preliminary operation results in the spring aquiring 
a certain degree of initial permanent set which can be helpful in reducing 
the time for which the subsequent heating treatment has to be applied. 
Apparatus or equipment for carrying out the method of the invention 
generally includes means for supporting a spring to be treated so that it 
is free to change in dimensional characteristics, means for applying a 
pre-selected load to the spring while it is so supported, and means for 
heating said spring while under load. Limit switch means is effective to 
automatically terminate the heating of the spring when dimensional 
characteristics thereof have changed, under the influence of said load and 
heating, and reached a limit which can be correlated with a predetermined 
value of relaxation or collapse. 
The invention is particularly suitable for treatment of helical coil 
springs, especially helical coil compression springs.

DETAILED DESCRIPTION 
Referring to the drawings, the apparatus comprises a fixed base plate or 
bed 10 providing a horizontal supporting surface 11. An operating head 12 
is disposed above surface 11 and includes a vertically movable ram or 
plunger 14 adapted to be loaded by one or more weights 15 and to rest upon 
the upper end of a spring 16 placed upright on the supporting surface 11 
beneath. The head 12 is carried by an overhead frame plate 18 supported by 
pillars 19 (not shown in FIG. 1). Head 12 includes a mounting block 20 
having a vertical bore 21 providing a slideway for the ram or plunger 14. 
Pneumatic control cylinder means 22 raises the ram or plunger 14 before 
and after each treatment cycle of operations. 
This pneumatic control cylinder means 22 comprises a vertically disposed 
air cylinder 24 having piston head 25 which operates within a cylindrical 
cavity 26 of a casing 27 rigidly fixed to the upper end of ram or plunger 
14. Three spaced cylindrical pins 30 are secured to piston head 25 and 
pass through holes in bottom end plate 29 of casing 27. Pins 30 project 
downwardly to form legs adapted to contact the upper surface of mounting 
block 20. When piston head 25 is towards the lower end of cavity 26 pins 
30 are fully extended through bottom end plate 29, causing casing 27, and 
ram or plunger 14, to be raised to the maximum extent (as shown in full 
lines in FIG. 1). When air cylinder 24 is operated to move piston head 25 
toward the upper end of cavity 26, pins 30 are in effect retracted, 
relative to casing 27 which, together with ram or plunger 14, then moves 
vertically downwardly. 
Electrical lines 32 and 33 are connected at one end to a low voltage, high 
current supply (e.g. in a range of 1 to 6 volts sufficiently low to avoid 
sparking at several hundred amps). As shown, lines 32 and 33 are 
connected, respectively, to a copper insert contact plate portion 34 of 
supporting surface 11 and to an insulated copper insert contact plate 
portion 35 on the bottom end of the ram or plunger 14. This electrical 
connection establishes good electrical contact with the opposite ends of 
the coil spring 16 and permits passage of the electric heating current 
during operation. A limit switch 38 operates when ram or plunger 14 has 
descended to reach a predetermined level above supporting surface 11 to 
thereby break the supply circuit of the heating current. 
Limit switch 38 is shown schematically in FIG. 1 as a micro-switch disposed 
on mounting block 20. Switch 38 is adapted to be actuated by a projecting 
finger 39 located on casing 27. Alternatively, switch 38 may be a 
proximity switch. An adjustable mounting (not shown) enables limit switch 
38 to be set to operate at the required level of descent of ram or plunger 
14. The associated electrical circuitry (not shown) is arranged so that 
limit switch 38 acts also to cause, simultaneously with the opening of the 
heating current supply circuit, closing of a coolant supply circuit. A 
coolant fluid, conveniently water with a corrosion inhibitor additive, is 
supplied to a coolant discharge outlet 40 in the base plate or bed 10 
beneath the spring 16 via a valve (not shown). Closing of the coolant 
supply circuit opens this valve. Thus, spring 16 is rapidly cooled or 
quenched at the end of the heating stage, while still under load. 
The apparatus illustrated also includes means for applying a pre-stressing 
load to each spring 16 while cold in a preliminary operation. The 
pre-stressing means comprises a vertically disposed air cylinder 45 which 
is also carried by overhead frame plate 18 in spaced relationship to head 
12. Each spring for treatment is first placed on supporting surface 11 
beneath ram 46 of air cylinder 45 which causes ram 46 to descend and apply 
a compressive load sufficient substantially to fully compress the spring 
in this state. Ram 46 is then withdrawn, and the pre-treated spring is 
then brought beneath head 20 for the heat treatment already described. 
An appropriate conveyor or automatic feed means is used for handling and 
passing a plurality of springs successively through the treatment 
locations. In this embodiment, the conveyor or feed means comprises a 
carriage 50 slidably mounted on a pair of guide rods 51 fixed above base 
plate or bed 10. Carriage 50 carries three pivotally mounted feed fingers 
53 which are linked together by a coupling rod 54. In their operative feed 
position, feed fingers 53 extend at right angles to direction of movement 
of the carriage 50, as shown in full lines in FIG. 2. Fingers 53 are 
retained in this position by a friction retaining catch such as a 
spring-pressed ball catch. Under pressure, however, feed fingers 53 can be 
swung into an inoperative position as shown in broken lines in FIG. 2. 
Movement of carriage 50 is controlled by a feed air cylinder 55. The 
springs are discharged through a chute 57 to a delivery station X, on the 
surface 11 of the base plate or bed 10. Delivery station X is in alignment 
with "cold pressing" station Y beneath air cylinder 45 and with a "hot 
pressing" station Z beneath head 12. The spacing between these stations X, 
Y and Z is equal and corresponds to the spacing between feed fingers 53. 
To understand the operation through one complete cycle on a spring, start 
from the right hand side, as viewed in the Figures. On the first feed 
stroke of the feed air cylinder 55, a spring is caught up by the righthand 
feed finger 53 at delivery station X and is transferred to station Y. At 
this stage, the lefthand feed finger 53 reaches a fixed cam 60 so that all 
the feed fingers 53 are swung into their inoperative positions through the 
interaction with coupling rod 54 as the feed stroke is completed. The feed 
air cylinder 55 then makes a return stroke at the end of which, the 
righthand feed finger 53 contacts a fixed cam 61 at the righthand end so 
that all the feed fingers 53 are moved back into their operative feed 
positions. The preliminary "cold pressing" operation is then carried out. 
Then, the feed air cylinder 55 makes its next feed stroke during which the 
spring, pre-treated at station Y, is moved to station Z by the middle feed 
finger 53 and the righthand feed finger 53 moves another spring from the 
delivery station X to station Y. After the following return stroke of the 
feed air cylinder 55 and re-setting again of the feed fingers 53, the 
first spring is subjected to the "hot pressing" operation at station Z. 
Simultaneously, the preliminary "cold pressing" operation is carried out 
on the second spring at station Y. 
When these operations are completed, on the next feed stroke of the feed 
air cylinder 55, the lefthand feed finger catches the treated spring at 
station Z and moves it along to a discharge station W, defined by 
discharge opening 70 in the base plate or bed 10. Discharge station W is 
reached just before the end of the feed stroke, and the following springs 
are each moved one station ahead. 
Thereafter, the cycles of operations can continue repetitively with three 
springs being moved stepwise between successive stations at each feed 
stroke. Suitable trip valves or switches (such as switch 68) and timing 
means are provided to sense each stage in the operational cycles and to 
initiate the following stage. 
If desired, a plurality of arrangements as described may be combined in a 
single machine having a common spring feed supply station and multiple 
heads for treating a multiplicity of springs simultaneously. Furthermore, 
it will of course be understood that many variations and modifications in 
the constructional details can be made within the scope of the invention 
as defined in the appended claims.