Nimble Fingers SPLIT HAIRS
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Girls in the Leyland Injectormanufacturing Department Work Enthusiastically to Limits of Which Men Might Weil be Proud
Accuracy Means Efficiency An injector is orie of the most Vital components of a ystern by Whieh extremely minitteTaiia• calibrated quantities of fuel: -are -stipplied to "aii: oil engine. Any ‘deviatiOn betWeen one injector and-another will eause rough running, andany leakage at the nozzle, rapid carbonizing!
The body of a Leyland ifijector
of high-quality cast-ircin, and: every part of an injector, except.the spring, is made in the factory, which also carries out all the heat treatment necessary.
After rough machining, the casting is stabilized by heat treatment. The needle bore is machined to in.
less 0.00125 in. :and .honed to in. less 0.0008 in. The 5/64 in. diameter oil passage. is drilled at .2,000 •r,p.m., and it can be as deep as 4k. ins.. in some Models'. A secend,bEat' treatMent is then given. The second honing Of th.e needle bore is to size
less 0 0001 to 0.0002 in., then it is finish lapped, using a tiny split castiron sleeve on a fine taper in conjunction with carborundum paste of 700 grade.
For the sake of accuracy and to avoid any risk of lack of alignment of the nozzle locknut, the thread for this ort the body is milled. The hexagon nuts are milled six at a time, using three pairs of cutters.
Machining the Nozzle
The nozzle itself is turned to fine limits on a Brown and Sharpe automatic, and is drilled to a time cycle of 22 secs. If this be exceeded it is found that the holes become: rough or out of position. They require a tiny twist drill of 0.25 mm. diameter.
Drilling is followed by a microscopic inspection of. the.inside of the nozzle to see that the holes are evenly spaced. After heat treatment, the face of the fitting flange is lapped on a rotating plate, this being carried on until • if two nozzles be pressed together with the flanges in contact they will stick, because air cannot enter between them.
The nozzle holes are checked for size by allowing petrol to flow through them, and a certain amount most be passed in a given time. A check on the quantity is easily effected. The petrol is contained in glass tubes marked off at various heights, and the error mast • not exceed plus or minultwo seconds in 40.
The pip end is ground in relation to the nozzle seating, as, of course, the needle does not tit closely into the bore of the nozzle, for the fuel must travel between the two,. and it is most important that thepip-should be concentric with the seating.
Catching theShadow
The nozzle must be accurate in every way, and it is checked by a Carl Zeiss Shadowgraph (which gives a magnification of 30), when it must coincide with a permanent marking already imposed on the screen. The nozzle is also rotated while being screened, to test its concentricity Tungsten 'carbide laps are employed for finishing the nozzle seats. The interior of the nozzle end is, of course, coned to take the needle valve, and both the finish and angle of this are tested in the Shadowgraph.
The lapping machine for this work has eight spindles, four being loaded to 20 lb., the other four being under a load of about 10 lb for finishing. These spindles lift automatically and periodically to allow the fine carborundum paste to have access to the
.seatings. The time taken is two minutes for each operation.
After finishing, each nozzle is tested for its spray form, and is put under a pressure of 150 atmospheres to make certain that oil does not seep between needle and nozzle.
Special case-hardening steel is employed for the needle valve; after roughing out, this receives a first heat treatment.
For centring purposes a small hole is machined and tapped in the upper end, and following this the needle is straightened between centres, then
case-hardened. Rough grinding is carried out with three machines for the three diarneters, and a fourth grinds for length. The point is then rough-ground to act as a centre.
Fine Needlework The next operation is to grind 0 006 in. from the t-in. diameter. This is done in three stages of 21, 21 and 1 thousandth, as it would not be possible to obtain the necessary accuracy if the whole amount were ground off at one operation. This grinding maintains the size, roundness and parallelism at 0.0001 in. Lapping follows. It is carried out between two castiron plates to an accuracy of 0.00006 in._ this being checked on a Taylor Hobson Electro-limit, the whole scale of which represents only half a thousandth One reason for the need for great accuracy is that in operation the needle valve gradually revolves, and to make certain of cone concentricity the needle bears on its own exterior while turning for the cone to be ground. The needle is finally tested in the nozzle bore by building up oil pressure in the lower part to 150 atmospheres, and it must fall to 100 atmospheres in not less than 12 secs. and not more than 28.
High-Frequency Hardening Above the needle valve is the injector end plug, surrounding the spindle of which is the valve spring. This plug limits the lift of the needle valve to between 0.016 and 0.018 in. To give a long wearing life, the spindle end is hardened for about in. This is effected rapidly and uniformly by dropping each plug into a high-frequency hardening machine, where it is heated for a few seconds and automatically sprayed with cooling water.
Cleanliness of the incoming fuel is ensured by a clever device known as an edgewise filter This forms part of the inlet adaptor. It consists of a round plug, the major portion of which is milled off to form a square. The fuel, entering a small hole at one end has to pass between the edges of the square and the bore of the adaptor before it reaches a hole at the other end. As the plug
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is 0.002 in. smaller in diameter than the body of the adaptor, this means that any particle greater than 0.001 in. is arrested. The tolerance for the adaptor bore is 0.0003 in.
Testing of the bore, which is drilled, reamed and bored, is carried out in a novel way by ascertaining the rate of escape of compressed air between it and a hollow spindle over which it is thrust. The escape rate is shown by a column of liquid in a
glass tube. The operator can, by rotating the adaptor and sliding it along the test spindle, check the bore for both size and parallelism. Any
wear on the spindle can be corrected from time to time by adjusting the machine. This measuring instrument is of Solex make.
At this point mention may be made of another particularly accurate instrument made by the Sigma Instrument Co., Ltd., of Letchworth, Herti, and known as the Sigma Electric-Pneumatic Comparator. The Leyland Company possesses the first one made, which can measure differences of 0.00001 in, in bores.
Assembly and Test
Reverting to the injector, when all the parts have been finished and thoroughly cleaned, they are loosely, assembled. Then one girl at a time takes charge of the job for final assembly and testing. During this period she changes the parts around as required and reassembles until she is satisfied that the whole component is correct.
It is interesting to note that final inspection is not under the control of the production foreman, so that there can be no possibility of coercion or temptation to pass the slightest fault, even when production is urgent.
Each injector is sprayed with rust preventive before packing.
An important side line of this department is a service section for reconditioning injectors.
It had not been our intention when paying this visit to the Leyland Works to spend so much time in this particular section; in fact, it was not our object to do more than have a rapid glance over the whole works. However, our excuse for upsetting the schedule drawn up for our benefit was our enthusiasm for something ,rather out of the ordinary—not that the rest of the works was in any way uninteresting.