'Elite' company just keeps on checking
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Graham Montgomerie looks into quality control and product development
WITH SOMETHING so mechanically complex as a clutch and gearbox assembly, the control of quality is vital for the reliability and durability of the system.
Turner-Spicer is one of the elite band of companies which have Ministry of Defence approval — in this case to Defence Standard 05-24, which applies when a design is already established but when conformance to this design can only be determined satisfactorily by inspecting through all the stages of the production process. Thus not only must the product conform to a predetermined standard but the system for checking this conformity must also be checked.
Not only does Turner-Spicer satisfy the MoD requirements, the company also qualifies for the approval by the Civil Air Authority. This is a similar system and runs in parallel to that of the MoD.
Obviously, Turner-Spicer, with a reputation for high quality to maintain, must run its own checks on the quality of its suppliers' products. The first stage is to approve the company.
A superior quality audit (S QA) engineer is sent to vet the systems and procedures of the comany in question, be it a supplier of forgings or, simply, washers. If he is satisfied then the Turner-Spicer purchasing deparment gets the "goahead", but only as far as an initial sample is concerned. These samples are vetted by the goods inventory inspector in order to ensure that they conform both metallurgically and dimensionally.
A supplier who has a sample rejected must resubmit and repeat the procedure.
To put this level of quality assurance into perspective it is worth pointing out that Turner-Spicer has nearly 1,000 outside suppliers, all of whom must have their products checked via the company's SQA engineers.
With experience, it is possible to work on a confidence level with suppliers — Turner-Spicer knows some better than others. The sampling procedure can be relaxed at will. One bad report, however, and the•procedure is tightened up immediately.
The company doesn't grind its gears, it shaves them. This givesthe required level of finish to the teeth without the expense of grinding.
The gear blank is hobbed or shaped to give a rough tooth form, which is then finished off with the shaving cutter. This shaving is done before the heat treatment process so the gear is in effect dimensionally finished before it goes into the furnace. Because it is possible to get a small change in helix angle owing to the heat treatmen1 process, this is allowed for in the design stage by the incorporation of a correction factor.
All gears are checked during the in-house production stages. The first-off gear in a batch is cleared first for the pre-shaved condition and later in the preheat treatment stage. They are also checked after heat treatment to monitor the distortion level.
Turner-Spicer controls all it own heat treatment processeS, including carburising anc induction hardening.
Induction hardening is usual for the selector forks and balancer gears for use in agricultural tractors. These gears are, in fact, the only ones thal Turner-Spicer induction hat dens.
Some gears are also shoi peened (using steel balls rathei than grit) to put a surface ten. sion into the metal — especial at the tooth root — to streng. then it. Nearly all the !owe' gears, for example, first, sec. ond and reverse, are treated ir this way.
The casings for the gear. boxes come from the outside suppliers and when these ars delivered, they come complete with test bars from the same foundry pouring which are ther used for tensile tests and chem ical analysis. Complete box When it comes to assembling the complete gearbox, Turner-Spicer has specific inspection stages where back lash and end-float are checked. Every box is pressure tested for leaks and then tested for correct operation on a rig.
In the case of the SST-10 box used in Roadtrain and the big Bedford TM, the test is doubled up with a dynamic test. This is a "belt and braces" move to ensure a leak free performance in operation.
Same for clutches The overall quality control system for the clutch division is essentially the same as for the gearboxes. This means complying once again with 05-24 although Spicer Clutch Division UK is not yet on the official approved list for the simple reason that the division has moved into a new building which has yet to be vetted and registered by the Ministry.
Costing control is even more critical with clutches because of their relatively high rotational speed. So every batch that is delivered from a foundry is checked metallurgically. This is related to a foundry casting code, which ensures that every cast is checked for metallurgical integrity.
As you would expect with a company having the reputation of Turner-Spicer, a lot of money and man-hours go into product development. Fundamental research into future design is carried out jointly by both the US and UK divisions. There is a continual interchange of ideas and results.
All divisions are linked with the States by telex, and the engineers from both sides of the Atlantic visit each other regularly. So there is no overlap of effort.
On the clutch side, the Product Development Centre at Auburn, Indiana, provides a good example of the extent of the facilities required for a company to stay ahead in technological development. This building houses the latest in sophisticated machinery and testing devices.